Production of Sugar From Suugar Beet

PRODUCTION OF SUGAR FROM SUGAR BEETS

A Design Report

Presented to

Department of Chemical & Process Engineering

School of Engineering

Moi University

In partial Fulfillment of Requirements

For the Degree of

Bachelor of Engineering

In

Chemical & Process Engineering

Mose Lameck Ondieki ……………………………………

CPE/41/08

Saleh Taher Mohamed ……………………………………

CPE/20/07

Kimathi Harrison Muthiorah ……………………………………

CPE/16/08

Mrs. Florence Ajiambo ……………………………………

SUPERVISOR

21st May, 2013

©Moi University

Sugar Production from Sugar Beet 2012/2013

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ABSTRACT

This report details the production of sugar from sugar beet. Sucrose is the main sugar extracted

from the fleshy root of the sugar beet. Sugarbeet processing operations comprise several steps,

including diffusion, juice purification, evaporation, crystallization, dried-pulp manufacture, and

sugar recovery from molasses. Descriptions of these operations are presented in this report.

Literature review was done to understand the raw material, the product and the types of

processes that are available for beet sugar production.

The unit operations were described and selected for optimum production of the products as

well as ease of design. From these unit operations, a process flow was formulated and

demonstrated in a block diagram.

The mass and enthalpy balances are also included in the report. These aid in the determination

of the processes’ product yield and quantities of raw materials to be used. The processes’

energy requirements were also determined. The balances were undertaken by considering the

laws of conservation of mass and energy and making relevant assumptions.

Equipment sizing and specifications are also included in the report as well as detailed designs of

a plate heat exchange, a filter press and a rotary drum dryer. Process flow sheet for the plant is

drawn to show equipment arrangement and material flows. Economic analysis of the project is

then done to determine its viability. A safety, health and environmental impact assessment is

done and measures are included to mitigate potential hazards. A suitable location for the plant

is selected as well as a proposed layout of the plant facilities.


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DEDICATION

It is to our dear parents that we humbly dedicate this work. They have spared no effort in

looking after us and encouraging us. This work is also dedicated to the Department of Chemical

and Process Engineering for their invaluable support, for making it a reality and for their

cooperation. We do pray that God will grant them long, healthy and enjoyable life.


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ACKNOWLEDGMENTS

With great humility and profound gratitude we would like to thank everyone.

We would like to express our in-depth acknowledgement and appreciation for the assistance

and support received from many individuals, without whom this work would not have been

possible. We are immensely grateful to our supervisor Mrs. Florence Ajiambo. We are really

honored.

The guidance and support of our lecturers is highly appreciated.

Above all, we thank God for keeping us safe and blessing us with good health and giving us the

strength and ability to successfully complete this project.


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DECLARATION

We declare that this report is our own unaided work. It is being submitted for the Degree of

Bachelor of Engineering in Chemical and Process Engineering at Moi University, Eldoret. It has

not been submitted before for any degree or examination in any other university or institution.

Kimathi Harrison Muthiorah

CPE/16/08

……………………………

Saleh Taher Mohamed

CPE/20/07

………………………….

Mose Lameck Ondieki

CPE/41/08

…………………………..

Mrs. Florence Ajiambo

Supervisor

…………………………….


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TABLE OF CONTENTS

ABSTRACT ....................................................................................................................................i

DEDICATION ...............................................................................................................................ii

ACKNOWLEDGMENTS................................................................................................................ iii

DECLARATION ............................................................................................................................ iv

LIST OF FIGURES ........................................................................................................................ ix

LIST OF TABLES .......................................................................................................................... xi

CHAPTER ONE .............................................................................................................................1

1.1 INTRODUCTION .................................................................................................................1

1.2 OBJECTIVE .........................................................................................................................1

CHAPTER TWO ............................................................................................................................2

2.0 LITERATURE REVIEW ..........................................................................................................2

2.1 INTRODUCTION .................................................................................................................2

2.2 BRIEF HISTORY OF SUGAR PRODUCTION ............................................................................3

2.3 FUNCTIONALITIES OF SUGAR .............................................................................................4

2.4 SUCROSE PROPERTIES ........................................................................................................4

2.5 SUGAR BEET .......................................................................................................................6

2.6 TYPES OF SUGARS ............................................................................................................11

2.7 OVERVIEW OF BEET SUGAR PRODUCTION .......................................................................11

2.8 JUSTIFICATIONS FOR SUGAR BEET USE AS RAW MATERIAL ..............................................14

CHAPTER THREE........................................................................................................................16

3.0 PROCESS DESCRIPTION ....................................................................................................16

3.1 HARVESTING ....................................................................................................................16

3.2 RECEIVING AND STORAGE ................................................................................................17

3.3 BEET DRY-CLEANING ........................................................................................................21

3.4 BEET CONVEYING .............................................................................................................22

3.5 BEET FLUMING .................................................................................................................23

3.6 BEET LIFTING TO BEET WASHER .......................................................................................25

3.7 BEET WASHING AND FLUME-WATER TREATMENT ...........................................................25

3.8 BEET SLICING ...................................................................................................................29

3.9 JUICE DIFFUSION ..............................................................................................................29

3.10 PULP TREATMENT ..........................................................................................................33


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3.11 MILK-OF-LIME AND CARBONATION GAS PRODUCTION ..................................................36

3.12 JUICE PURIFICATION ......................................................................................................38

3.13 SULPHITATION ...............................................................................................................43

3.14 EVAPORATION ...............................................................................................................43

3.15 SYRUP CRYSTALLIZATION ...............................................................................................46

3.16 SUGAR DRYING AND COOLING .......................................................................................51

3.17 PACKAGING AND STORAGE ............................................................................................53

CHAPTER FOUR .........................................................................................................................55

4.0 MASS AND MATERIAL BALANCES .....................................................................................55

4.1 STORE ..............................................................................................................................55

4.2 DRY SCREENING ...............................................................................................................56

4.3FLUME ..............................................................................................................................57

4.4 STONE SEPARATOR ..........................................................................................................57

4.5 TRASH SEPARATOR ..........................................................................................................58

4.6 WASHER ..........................................................................................................................58

4.7 DEWATERING SCREEN......................................................................................................59

4.8 CHIP SEPARATOR .............................................................................................................61

4.9 SLICER ..............................................................................................................................62

4.10 DIFFUSER .......................................................................................................................63

4.11PULP PROCESSING ..........................................................................................................65

4.12 JUICE PURIFIER...............................................................................................................65

4.13 FILTRATION ....................................................................................................................67

4.14 EVAPORATOR .................................................................................................................68

4.15 CRYSTALLIZER ................................................................................................................69

4.16 DRYER ............................................................................................................................72

5.0 ENTHALPY BALANCES .........................................................................................................73

5.1 ASSUMPTIONS .................................................................................................................73

5.2 DIFFUSER .........................................................................................................................73

5.3 HEAT EXCHANGER 1 .........................................................................................................74

5.4 HEAT EXCHANGER 2 .........................................................................................................74

5.5 EVAPORATOR...................................................................................................................75

5.6 HEAT EXCHANGER 3 .........................................................................................................76


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5.7 HEAT EXCHANGER 4 .........................................................................................................77

5.8 CRYSTALLIZATION ............................................................................................................78

5.9 DRYER ..............................................................................................................................80

CHAPTER SIX .............................................................................................................................81

6.0 EQUIPMENT SIZING AND SPECIFICATION .........................................................................81

CHAPTER SEVEN .......................................................................................................................90

7.0 EQUIPMENT DESIGN ........................................................................................................90

7.1 DESIGN OF A ROTARY DRUM DRYER BY MOSE O. LAMECK- CPE/41/08 ............................90

7.2 DESIGN OF A PLATE HEAT EXCHANGER BY KIMATHI H. MUTHIORAH - CPE/16/08 .......... 116

7.3 DESIGN OF A PLATE AND FRAME FILTER BY TAHER M. SALEH- CPE/20/07 ...................... 138

CHAPTER EIGHT ...................................................................................................................... 162

8.0 PROCESS CONTROL AND INSTRUMENTATION ................................................................ 162

8.1 INTRODUCTION ............................................................................................................. 162

8.2 INSTRUMENTATION AND CONTROL OBJECTIVES............................................................ 162

8.3 THE FEEDBACK CONTROL LOOP ..................................................................................... 163

8.4 TYPICAL CONTROL SYSTEMS .......................................................................................... 164

CHAPTER NINE ........................................................................................................................ 167

9.0 ECONOMIC AND PROFITABILITY ANALYSIS ..................................................................... 167

9.1 INTRODUCTION ............................................................................................................. 167

9.2 PLANT DEVELOPMENT TIMELINE ................................................................................... 168

9.3 CAPITAL INVESTMENT .................................................................................................... 168

9.4 ANNUAL CASH FLOW ANALYSIS ..................................................................................... 180

9.5 PROFITABILITY ANALYSIS................................................................................................ 182

CHAPTER TEN ......................................................................................................................... 189

10.0 SAFETY, HEALTH AND ENVIRONMENTAL IMPACT ASSESSMENT ................................... 189

10.1 INTRODUCTION............................................................................................................ 189

10.2 SAFETY ......................................................................................................................... 190

10.3 ENVIRONMENTAL IMPACT ASSESSMENT (EIA) ............................................................. 196

CHAPTER ELEVEN .................................................................................................................... 200

11.0 HAZARD AND OPERABILITY ANALYSIS (HAZOP) ............................................................ 200

11.1 INTRODUCTION............................................................................................................ 200

11.2 PURPOSE OF HAZOP..................................................................................................... 200


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11.3 HAZOP PROCESS .......................................................................................................... 201

11.4 HAZOP CONCEPTS ........................................................................................................ 201

11.5 SAMPLE HAZOP ANALYSIS ............................................................................................ 202

CHAPTER TWELVE ................................................................................................................... 206

12.0 PLANT LOCATION AND LAYOUT ................................................................................... 206

CHAPTER THIRTEEN ................................................................................................................ 212

13.0 REFERENCES ................................................................................................................ 212

APPENDICES ........................................................................................................................... 214

APPENDIX A: DATA .............................................................................................................. 214

APPENDIX B: FORMULAE ..................................................................................................... 215

APPENDIX C: DETAILED SAMPLE MASS BALANCE CALCULATIONS ........................................ 216

APPENDIX D: DETAILED SAMPLE ENTHALPY BALANCE CALCULATIONS ................................. 222

APPENDIX E: EQUIPMENT SIZING CALCULATIONS ................................................................ 225


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LIST OF FIGURES

Figure 2. 1 Molecular structure of sucrose molecule ...................................................................5

Figure 2. 2 Solubility of sugar at different temperatures (Mosen Asadi, 2007).............................6

Figure 2. 3 Sugar beet (Beta vulgaris L): the root, leaf and flowering patterns (Wikipedia.com) ..6

Figure 2. 4 Sugar Beet Compositions ...........................................................................................9

Figure 2. 5 Purity profile during Sugar production .....................................................................12

Figure 2. 6 Flow diagram for beet sugar production ..................................................................15

Figure 3. 1 Topped beet (Wikipedia.com) ..................................................................................16

Figure 3. 2 Effects of temperature on sugar loss in beets (van der Poel 1998) ...........................21

Figure 3. 3 Beet conveying operation (Mosen Asadi, 2007) .......................................................23

Figure 3. 4 Beet flume (Mosen Asadi, 2007) ..............................................................................24

Figure 3. 5 Rake trash separator (Mosen Asadi, 2007) ...............................................................25

Figure 3. 6 Beet washing operations (Mosen Asadi, 2007) .........................................................26

Figure 3. 7 Juice diffusion process (Mosen Asadi, 2007) ............................................................30

Figure 3. 8 Counter-current diffusion (Mosen Asadi, 2007) .......................................................30

Figure 3. 9 Pulp treatment operations .......................................................................................34

Figure 3. 10 Carbonation gas production (Mosen Asadi, 2007) ..................................................36

Figure 3. 11 Flow diagram for juice purification operation(Mosen Asadi, 2007) ........................ 44

Figure 3. 12 Multi-effect evaporator system (Mosen Asadi, 2007) .............................................45

Figure 3. 13 Three-stage crystallization .....................................................................................48

Figure 7. 1 Schematic picture of a direct-heat counter current rotary dryer ..............................92

Figure 7. 2 Countercurrent rotary drum dryer assembly ............................................................93

Figure 7. 3 Gasketed plate heat exchanger .............................................................................. 117

Figure 7. 4 Nature of fluid flow through the plate heat exchanger .......................................... 119

Figure 7. 5 Log mean temperature correction factor for plate heat exchangers ...................... 122

Figure 7. 6 Gasketed plate heat exchanger components (www.graham-mfg.com) .................. 134

Figure 7. 7 The chevron plate used in the gasketed plate heat exchanger ............................... 135

Figure 7. 8 Clip-on gasket used in the plate heat exchanger .................................................... 136

Figure 7. 9 Schematic diagram of a filtration system ............................................................... 138


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Figure 7. 10 Mechanism of cake filtration (Ladislav Svarovsky, 2000) ...................................... 139

Figure 7. 11 Mechanism of deep bed filtration (Ladislav Svarovsky, 2000)............................... 139

Figure 7. 12 Scheme to show the principle of plate-and-frame presses (Svarovsky, 2000) ....... 146

Figure 7. 13 A typical filter press (Mosen Asadi, 2007) ............................................................ 146

Figure 7. 14 Caulked and gasketed frame (www.durcofilters.com) .......................................... 159

Figure 7. 15 Steel welding neck flanges, 6 bar ......................................................................... 160

Figure 8. 1 Block diagram of a control loop.............................................................................. 163

Figure 8. 2 Flow controller for the flowrate of CaCl2 and anti-foaming agent to the diffuser ... 165

Figure 8. 3 Figure showing a pressure controller used to maintain .......................................... 165

Figure 8. 4 Teperature controller for the flow of steam to heat exchanger thus controlling the

temperature of exit stream flowing to carbonation tank 1 ...................................................... 166

Figure 8. 5 A level controller used to maintain thin juice level inside the carbonation ............. 166

Figure 9. 1 Cumulative Cash Flow Curve .................................................................................. 182

Figure 9. 2 Break-even Point Chart .......................................................................................... 188


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LIST OF TABLES

Table 2. 1 Stations for beet sugar production ............................................................................13

Table 4. 1 Mass balance for storage section ..............................................................................56

Table 4. 2 Mass balance around dry screener ............................................................................56

Table 4. 3 Mass balance around flume ......................................................................................57

Table 4. 4 Mass balance around stone separator.......................................................................58

Table 4. 5 Mass balance around trash separator .......................................................................58

Table 4. 6 Mass balance around washer ....................................................................................59

Table 4. 7 Mass balance around dewatering screen ..................................................................60

Table 4. 8 Mass balance around chip separator .........................................................................62

Table 4. 9 Mass balance around slicer .......................................................................................63

Table 4. 10 Mass balance around diffuser .................................................................................64

Table 4. 11 Mass balance for pulp processing ............................................................................65

Table 4. 12 Mass balance for liming...........................................................................................66

Table 4. 13 Mass balance for carbonator ...................................................................................67

Table 4. 14 Mass balance for filter system .................................................................................68

Table 4. 15 Mass balance on evaporator ...................................................................................69

Table 4. 16 Mass balance around boiling pan ............................................................................70

Table 4. 17 Mass balance around centrifuge .............................................................................71

Table 4. 18 Mass balance around dryer .....................................................................................72

Table 5. 1 Enthalpy balance around diffuser ..............................................................................74

Table 5. 2 Enthalpy balance around Heat Exchanger 1 ..............................................................74


Table 5. 4 Enthalpy balance around evaporator ........................................................................ 76


Table 5. 6 Enthalpy balance around Heat Exchanger 4. .............................................................77

Table 5. 7 Enthalpy balance around a boiling pan ......................................................................79

Table 5. 8 Enthalpy balance around Centrifuge .........................................................................80

Table 5. 9 Enthalpy balance around the Dryer ...........................................................................80


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Table 6. 1 Equipment Specifications ..........................................................................................81

Table 7. 1 Mechanical Engineering design summary ................................................................ 109

Table 7. 2 Auxiliary equipment design summary ..................................................................... 115

Table 7. 3 Properties of heating and cooling fluids of Heat Exchanger 1 .................................. 124

Table 7. 4 Chemical properties of the plate heat exchanger to be designed ............................ 133

Table 7. 5 Mechanical design summary of the plate heat exchanger ....................................... 137

Table 7. 6 Summary of Chemical Engineering design ............................................................... 156

Table 7. 7 Summary of mechanical design ............................................................................... 161

Table 9. 1 Purchased equipment cost ..................................................................................... 171

Table 9. 2 Total capital cost estimates .................................................................................... 173

Table 9. 3 Total capital cost .................................................................................................... 173

Table 9. 4 Annual raw material cost estimates ....................................................................... 175

Table 9. 5 Utility Cost Estimates (Annual) ............................................................................... 176

Table 9. 6 Annual Depreciation ............................................................................................... 177

Table 9. 7 Total product cost estimates .................................................................................. 179

Table 9. 8 Annual sales from the product ............................................................................... 180

Table 9. 9 Cumulative cash flow ............................................................................................. 185

Table 11. 1 HAZOP Analysis around a Rotary Drum Dryer ........................................................ 203

Table 11. 2 HAZOP Analysis around Heat Exchanger 1 ............................................................. 204

Table 11. 3 HAZOP Analysis around the Filter Press ................................................................. 205

Table A- 1 Specific heat Capacities of Various Component ...................................................... 214

Table A- 2 Overall heat transfer coefficients ............................................................................ 214

Table C- 1 Summary of mass balance around diffuser ............................................................. 218

Table C- 2 Summary of mass balance around Liming Unit ........................................................ 220

Table C- 3 Summary of mass balance around carbonation unit ............................................... 221

Table E- 1 Summary of lime tank specifications ....................................................................... 226


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CHAPTER ONE

1.1 INTRODUCTION

Sugar beet is a crop that is considered an option in the plan to raise farming in Kenya to a

profitable level, reduce poverty and create new employment opportunities (Mandere et al.

2009). The cultivation of sugar beet in tropical regions of Africa, and in this case Kenya,

is a new venture. The crop is predominantly cultivated in the temperate climatic regions of

Europe and North America (Draycott and Christenson, 2003). It is until recently, Syngenta AG

has developed a tropical sugar beet. This has allowed the plant to be grown in tropical and sub-

tropical regions. In Kenya, sugar beet cultivation was introduced in Nyandarua District

(Nyandarua County) on a trial basis to assess whether it would be a suitable cash crop

for being adopted in the region to help improve the farmers’ livelihoods (Geita, 2004).

The sugar beet crop is still under trial, so no commercial cultivation of the crop is yet

taking place in the District. The yield achieved in these trials is 70 tons/ha of wet root

weight and 17% sugar content. The yields compare well with published yield ranges in

tropical climates (Doorenbos and Kassam, 1979). Therefore, the sugar beet trials in the

Nyandarua District indicate that despite being associated with temperate climates (Draycott

and Christenson, 2003), the crop has the potential for successful cultivation in some

tropical conditions.

The processing starts by slicing the beets into thin chips. This process increases the surface area

of the beet to make it easier to extract the sugar. The extraction takes place in a diffuser where

the beet is kept in contact with hot water for about an hour.

Sugarbeet processing operations comprise also other steps, including juice purification,

evaporation, crystallization, dried-pulp manufacture, and sugar recovery from molasses.

1.2 OBJECTIVE

This project aims to design a plant for the production of granulated-refined sugar from sugar

beet. The plant is designed to process 85,000 Kg/h of raw beet.


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CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 INTRODUCTION

The word sugar comes from the Indian sarkara. The chemical name of sugar is sucrose. The

‘ose’ suffix in sucrose, glucose, raffinose and so on, identifies the sugars. Sugar (sucrose,

C12H22O11) is one of the families of sugars (saccharides). All sugars belong to a larger group,

known as carbohydrates (sugars, starches, and dietary fibers). The term sugar substitute refers

to all natural and synthetic (artificial) sugars other than sucrose. (Beet sugar Technology by R. A.

McGinnis, Reinhold Publishing Corporation, 1951).

Sugar is the generalized name for a class of sweet-flavored substances used as food. They are

carbohydrates and as this name imply, are composed of carbon, hydrogen and oxygen. There

are various types of sugar derived from different sources. Simple sugars are

called monosaccharides and include glucose, fructose and galactose. The table or granulated

sugar most customarily used as food is sucrose, a disaccharide. Other disaccharides include

maltose and lactose.

Sugars are found in the tissues of most plants but are only present in sufficient concentrations

for efficient extraction in sugarcane and sugar beet.

Sucrose (sugar), glucose (dextrose), and fructose (levulose) are examples of sweet-tasting

sugars. The quantity of hydroxyl groups (OH) in molecules of sugars contributes to their

sweetness. However, not all sugars are sweet in taste. In general, sugars with at least two

hydroxyl groups (OH) in their molecules are sweet. About 50 compounds have a sweet taste.

Beet sugar (sugar made from sugarbeet), cane sugar (sugar made from sugarcane), and refined

sugar (sugar made from raw sugar) are similar in shape, taste, and other chemical and physical

properties.

It is difficult to recognize whether a sugar is made from sugarbeet or sugarcane. Advanced

laboratory instruments and techniques are required to find the difference in beet and cane

http://en.wikipedia.org/wiki/Carbohydrate

http://en.wikipedia.org/wiki/Monosaccharide

http://en.wikipedia.org/wiki/Glucose

http://en.wikipedia.org/wiki/Fructose

http://en.wikipedia.org/wiki/Galactose

http://en.wikipedia.org/wiki/Sucrose

http://en.wikipedia.org/wiki/Disaccharide

http://en.wikipedia.org/wiki/Maltose

http://en.wikipedia.org/wiki/Lactose

http://en.wikipedia.org/wiki/Sugarcane

http://en.wikipedia.org/wiki/Sugar_beet


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sugar by the content of carbon isotope ratio, which is the ratio of C13 (reads carbon 13) to C12.

This ratio is about 25% in beet sugar and 11% in cane sugar (Bubnik et al. 1995). Another

differential marker is based on the raffinose content in these sugars (to a much higher extent in

cane sugar) determined by chromatographic method (Eggleston, 2005).

2.2 BRIEF HISTORY OF SUGAR PRODUCTION

Sugarcane cultivation and the technique of sugar production began in India probably around

2000 BC and moved to Persia (now Iran) around AD 600. In Persia, the technique was improved;

milk was used as the purifying agent; and the filtered syrup was crystallized. Then the Persians

invented a cone-shaped clay mold for the production of cone sugar (loaf sugar).

The mold had a small dripping hole in the middle of its bottom so that the syrup around the

crystals slowly drips from the mold. The crystals were then left to dry for few days. (Similar

cone-sugar molds made of sheet metal are still used in some countries.)

In AD 800, sugarcane cultivation spread from Persia to Egypt, Syria, and as far as Morocco and

Spain. By the fourteenth century, Egypt was Europe’s main supplier, via the port of Alexandria,

of sugar made from sugarcane.

Sugar became popular in tea in Britain by the end of the seventeenth century. In those days,

sugar was available in large cone shapes that had to be broken first into large pieces with a

cast-iron pincer and then into regular cube size with a little chopper. Sugarbeet cultivation on a

research scale began in 1747 when Andreas Marggraf (a German chemist) discovered sugar in

sugarbeet varieties (Bruhns, 1997). Later, Franz Achard (Marggraf’s student) in Germany and

Ya. S. Esipov in Russia were simultaneously engaged in the cultivation of sugarbeet varieties.

They also continued independently with research on the processing of sugar from sugarbeet in

industrial scale. The first beet-sugar factory was built in Cunern (in Germany) in 1802 by Achard

and in Alyabevo (in Russia), shortly thereafter.


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Beet sugar technology developed rapidly, resulting in more than 400 beet-sugar factories in

European countries by 1830 (including several factories in France by the order of Napoleon

Bonaparte).

2.3 FUNCTIONALITIES OF SUGAR

People like sugar for its sweetness. But the sweetness is only one of the functionalities (the

factors improving the characteristics of other products) of sugar. Following are some of sugar’s

other functionalities:

Improves the flavor of food products

Improves the sparkle in candy products

Improves the shelf life of food products

Improves the bulking property of food products

Improves the color and texture of baked products

Improves the preserving property of food products

Improves the texture (mouth-feel) of food products

Improves the foam in egg white in meringue products

Improves the release of pectin of fruits in jam products

Improves the heating rate of food products in the microwave

Improves the flavor and color of food products by caramelization

Improves the taste of the food products

2.4 SUCROSE PROPERTIES

The sucrose molecule (C12H22O11) consists of 12 carbon atoms (C), 22 hydrogen (H), and

11oxygen atoms (O). In percentages, the molecule contains 51.5% oxygen, 42.0% carbon, and

6.5% hydrogen. The molecular mass (weight) of sucrose is 342.3 g.


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The properties of sugar are as follows;

Density: Fine sugar 880 kg/m3, Medium sugar 860 kg/m3, Coarse sugar 840 kg/m3,Cube

sugar 850 kg/m3, Powdered sugar 650 kg/m3

Melting point: 185C. It undergoes caramelization at temperatures close to the melting

point to form fructose, glucose and finally caramel (coloring substance)

Colorless and odorless

The freezing-point depression (FPD) of sucrose at 50% solution is -7.6 C

It is a non-reducing sugar (unlike most other sugars) because its molecule does not have

a free functional group in either of its two rings.

It has monoclinic crystals

It is non-ionic

It is hygroscopic and can absorb up to 1% moisture

It is hydrolyzed by dilute acids and invertase (yeast enzyme) to form glucose and

fructose

It is fermentable but will resist bacterial decomposition at high concentrations

The specific heat of pure and impure sucrose solutions decreases when their

concentration and temperature are increased.

The solubility varies as follows;

Figure 2. 1 Molecular structure of sucrose molecule


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2.5 SUGAR BEET

Sugar beet, a cultivated plant of Beta vulgaris, is a plant whose tuber contains a high

concentration of sucrose. It is grown commercially for sugar production. Sugar beets and other

Beta vulgaris cultivars such as beetroot and chard share a common wild ancestor, the sea beet

(Beta vulgaris maritima).

Sugar beet is a conical, white, fleshy root with a flat crown. The plant consists of the sugar beet

root and a rosette of leaves. Sugar is formed through a process of photosynthesis in the leaves,

and it is then stored in the root. Sugar can represent between 15% and 21% of the sugar beet

root’s total weight; however, depending on the cultivar and growing conditions, the sugar

content can vary from 12 to above 20%.

Figure 2. 2 Solubility of sugar at different temperatures (Mosen Asadi, 2007)

Figure 2. 3 Sugar beet (Beta vulgaris L): the root, leaf and flowering patterns (Wikipedia.com)

http://en.wikipedia.org/wiki/Beta_vulgaris

http://en.wikipedia.org/wiki/Tuber

http://en.wikipedia.org/wiki/Sucrose

http://en.wikipedia.org/wiki/Sugar

http://en.wikipedia.org/wiki/Beetroot

http://en.wikipedia.org/wiki/Chard

http://en.wikipedia.org/wiki/Sea_beet


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The root of the beet (taproot) contains 75% water and the rest is dry matter. The dry matter is

about 5% pulp and about 75% sugar. This pulp, insoluble in water and mainly composed of

cellulose, hemicelluloses, lignin and pectin, is used in animal feed. Sugar is the primary value of

sugar beet cash crop. The by-products of the sugar beet crop such as pulp and molasses add

another 10% to the value of the harvest.

Sugar beet grows exclusively in the temperate zone, in contrast to sugar cane which grows

exclusively in the tropical and subtropical zones. The beet, unlike sugar cane, grows below the

ground. The average weight of sugar beet ranges between one and two pounds. Sugar beet

foliage has a rich, brilliant green color and grows to a height of about 14 inches. The leaves are

numerous and broad and grow in a tuft from the crown of the beet, which is usually level with

or just above the ground surface.

2.5.2 Other uses of sugar beet

Beverages

Sugar from sugar beet is used to make a rum-flavored hard liquor which is now known

as tuzemak. On the Aland Islands, a similar drink is made under the brand name KobbaLibre. In

some European countries, especially in the Czech Republic and Germany, sugar beet is also

used to make rectified spirit and vodka.

Sugar beet syrup

Unrefined sugary syrup can be produced directly from sugar beet. This thick, dark syrup is

produced by cooking shredded sugar beet for several hours, then pressing the resulting sugar

beet mash and concentrating the juice produced until it has the consistency similar to that of

honey. This syrup is used as a spread for sandwiches, as well as for sweetening sauces, cakes

and desserts.

Betaine

Betaine can be isolated from the by-products of sugar beet processing. Production is chiefly

through chromatographic separation, using techniques such as the "simulated moving bed".

http://en.wikipedia.org/wiki/Solubility

http://en.wikipedia.org/wiki/Sugar_cane

http://en.wikipedia.org/wiki/Rum

http://en.wikipedia.org/w/index.php?title=Tuzem%C3%A1k&action=edit&redlink=1

http://en.wikipedia.org/wiki/%C3%85land

http://en.wikipedia.org/wiki/Rectified_spirit

http://en.wikipedia.org/wiki/Vodka

http://en.wikipedia.org/wiki/Honey

http://en.wikipedia.org/wiki/Betaine

http://en.wikipedia.org/wiki/Chromatography


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Uridine

Uridine can be isolated from sugar beet. Uridine in combination with omega-3 fatty acids has

been shown to alleviate depression in rats.

Alternative fuel

They are used to produce bioethanol. The feedstock-to-yield ratio for sugarbeet is 56:9.

Therefore it takes 6.22 kg of sugarbeet to produce 1 kg of ethanol (approximately 1.27 litres at

room temperature).

2.5.3 Sugar beet composition

Sugarbeet (the raw material of the beet-sugar factory) composition is important to both the

sugarbeet farmer and the processor (factory). Sugar (sucrose) and non-sugar (non-sucrose)

content determine the quality of the sugarbeet (high sugar and low non-sugar content is

desirable).

The basic unit of sugarbeet (like other plants) is the cell. A beet cell consists of

Cell wall: Protects the cell and consists mainly of cellulose and pectin.

Protoplasm (cell membrane): Controls the movement of molecules in and out of the

vacuole. The protoplasm consists of protein and is non-permeable to sucrose and non-

sucrose substances but semi-permeable to water.

Vacuole (cell nucleus): Stores beet juice, containing sucrose and non-sucrose

substances.

As shown in the figure below, the dry substance of sugarbeet consists of beet juice and beet

marc (beet pulp). Beet juice contains both sucrose and non-sucrose (impurities).

http://en.wikipedia.org/wiki/Uridine

http://en.wikipedia.org/wiki/Omega-3_fatty_acid

http://en.wikipedia.org/wiki/Depression_(mood)


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Sugar beet juice is mainly made up of saccharides (sugars), which are sucrose (15 to 20%),

raffinose (0.2 to 0.5%), glucose and fructose (0.05 to 0.1%), and planteose, stachyose, and

verbascose (in trace amounts). Beet juice always contains more glucose than fructose. The

raffinose (a trisaccharide) content can vary largely depending on the location. Usually, sugar

beets with high sucrose content have less raffinose. The level of nitrogen in the fertilizer also

affects the raffinose content (the higher the nitrogen used, the higher is the raffinose content).

Dextran and levan are the main polysaccharides present in sugar beet juice. Their content

increases when beets are damaged because microorganisms, particularly the Leuconostoc

group, consume the sugar and convert some of it to dextran and levan. High contents of

dextran and levan create difficulties during sugar beet processing because of their colloidal

nature.

Sugar beet

Dry substance 75.0% water

20.0% beet juice 5.0% beet marc

17.5% sucrose

1.1% Nitrogenous (0.2% amino acids, 0.1% betaine, etc.)

0.9% Non-nitrogenous (0.3% invert sugar, 0.2% raffinose, etc.)

0.3% Minerals (K+, Na+, Ca2+, Mg2+, SO42−, PO4

3−)

0.2% Others

2.5% Non-sucrose 1.2% cellulose

1.1%Hemicellulose

0.1% Protein

0.1%Saponin

0.1% Minerals

Figure 2. 4 Sugar Beet Compositions


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Nitrogenous compounds (in amounts of 1 to 2%) are other components of beet juice. Almost all

amino acids (compounds that contain an amino group (NH2) and a carboxyl group (COOH), both

groups joined to the same carbon) are present in beet juice and beet pulp (marc).

Glutamine is present in the largest amount. Most amino acids are soluble in water and in

alkaline solutions, so they do not precipitate in lime and end up in molasses. Betaine (in

amounts considerable amount of high-purity betaine can be recovered.

Minerals in beet juice are referred to as ash. Analytical tests of sugar beets have shown trace

amounts of barium, boron, calcium, copper, lead, magnesium, molybdenum, nickel, selenium,

silicon, and zinc.

Beet pulp (beet marc) consists of fibrous materials that are water insoluble and remain almost

the same shape after the diffusion process. During sugar beet growth in the field, some of the

sugar is spent in producing pulp (the main component of cell walls) and the protoplasm. The

pulp content of sugarbeet ranges from 4 to 6%, but it can differ depending on the growing

conditions and the variety of sugarbeet. Some scientists have proved that high-sugar content

beets contain higher pulp content as well (Van der Poel, 1998).

Pulp consists mainly of pectin, cellulose, and hemicellulose:

Pectin: A gel-type substance that is insoluble in cold water but soluble gradually in

boiled water, and stable during the diffusion process

Cellulose: A wood-type substance that is insoluble in hot water, diluted acids, and alkalis

solutions, and stable during the diffusion process

Hemicellulose: A wood-type substance that is insoluble in hot water but soluble in hot

diluted acid solutions, and stable during the diffusion process.

Sugarbeet pectin has lower gelling power than apple or citrus pectin, because the molecular

mass of sugarbeet pectin (15000 to 50000) is smaller than apple or citrus pectin (70000 to

90000).


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Cellulose is a polysaccharide made of several thousand molecules of glucose (C6H12O11).We

humans cannot digest cellulose and hemicellulose because we do not have an enzyme that can

break the polymer’s chain. However, cattle, for example, have bacteria containing this enzyme

in the stomach. The bacteria convert cellulose and hemicellulose into small digestible molecules

that can be used by animals as a nutrient. (Pulp is a good food ingredient for some animals).

Post harvested beets piled in beet storage contain some tare (clay, sand, stone, and trash mixed

with the beets). The impurities that make up the tare differ depending on a field’s properties,

the harvesting method, and the size of the beets, all of which make it difficult to estimate beet-

pile density. Following is the mass and density of a typical washed beet (beet without tare):

2.6 TYPES OF SUGARS

The following are some of the categories of sugar and are achieved by different sugar-end

processes;

Icing: very small crystals that quickly dissolve in liquids or can be used for decorating

desserts, like confectioners' sugar.

Caster: larger crystals than icing.

Granulated: basic table sugar, with larger crystals than caster or icing.

Preserving: very coarse sugar used as a preserve in jams and similar confections.

2.7 OVERVIEW OF BEET SUGAR PRODUCTION

Sugar production depends on large-scale operations that consist of several unit operations.

Successive unit operations are involved in separating sugar (sucrose) from non-sugars (non-

sucrose). The non-sugars (impurities) are the undesirable substances.

Mass 0.5-2.0 Kg

Bulk density 650-700 Kg/m3

Density 1050-1100 Kg/m3


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Evaporator

Evaporation

Cossette Purity = 87%

Diffusion juice Purity = 88%

Thin juice Purity = 90%

Diffusion

Molasses purity = 60%

Sugar

Purity = 100%

Crystallization

Thick juice Purity = 90%

Separation of sugar from non-sugars in fact is the aim of almost every step of sugar production.

The sugar separation is gradual and is accomplished in several stations. The improvement in

each station is expressed by the purity (sugar content as % of dry substance) of the product

from that station. As Figure 2.5 shows, the ultimate goal is to produce sugar with almost 100%

purity.

In sugarbeet processing, the term station is used to denote the section of the factory that does

a particular job.

Sugar production is a large-scale operation divided into smaller unit operations. To process

sugarbeet and produce sugar, several unit operations will be employed. These include;

Fluid transportation

Heat transfer

Diffusion

Filtration

Sedimentation

Evaporation

Crystallization

Centrifugation

Drying

Figure 2. 5 Purity profile during Sugar production


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To change raw material (sugarbeet) into sugar, the sugar has to be separated from the non-

sugars (all soluble substances except sugar) in the beet juice from sugar. Several stations are

required to separate non-sugars (unwanted components) from sugar (wanted component).

Sugarbeet processing is subdivided into 20 stations, which are explained in a systematic order

in later chapters. As table 2.1 shows, the first 13 stations (through the evaporation station)

make up the beet-end of the factory; the remaining stations are in the sugar-end.

Each station consists of two or more steps, totaling 80 to 85 steps. For example, the purification

station (the station with highest number of steps) consists of the following 13 steps: juice

heating, preliming, prelimed-juice heating, main liming, limed-juice heating, first carbonation,

mud separation, mud thickening, first-carbonation, filtration, first-carbonation juice heating,

second carbonation, second-carbonation, filtration, and second-carbonation safety filtration.

Table 2. 1 Stations for beet sugar production

Beet-end Sugar-end

1 Beet receiving and storage 14 Juice decolourization and sulfitation

2 Beet dry-cleaning 15 Juice storage

3 Beet conveying and fluming 16 Crystallization

4 Stone and trash separation 17 Molasses exhaustion

5 Beet washing and flume- water treatment 18 Centrifuging

6 Beet slicing 19 Sugar drying, storing and packing

7 Diffusion process 20 Production of specialty sugars

8 Pulp treatment

9 Milk of lime and carbonation gas production

10 Juice purification

11 Juice sedimentation and filtration

12 Steam production

13 Juice evaporation


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Figure 2.6 below shows a simplified flow diagram of a typical beet-sugar production plant (the

numbers in parentheses indicate the stations). In this figure, in-process products (juices, syrups,

liquors, and massecuites) go through the factory along the solid line. By-products (pulp,

carbonation- lime residue, and molasses) and other materials (e.g. limestone, coke, and steam

used in processing) are also shown.

2.8 JUSTIFICATIONS FOR SUGAR BEET USE AS RAW MATERIAL

The following are some of the reasons as to why sugar beet has been chosen as the raw

materials for sugar production;

The sugar content in sugarbeet is approximately 30% more than sugarcane.

The cost of crop of sugarbeet is lesser than sugarcane.

Sugarcane crop takes around 1 year to mature while sugarbeet can be harvested in 7

months.

Sugar beet requires 6 to 8 irrigation cycles on the other hand, sugarcane requires at

least 16 irrigation cycles.


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Waste water

Sludge/mud

Molasses

Ca(OH)2

CO2

Wet pulp

Water

Beet receiving & storage

Dry cleaning Loose soil & grit

Stone and trash separation

Stone & trash

Beet washing

Diffusion

Diffusion water

Purification

Cossettes

Diffusion juice

Filtration

Pressing

Drying

Pelleting

Sulphitation Evaporation Pellets

Crystallization

Centrifuging

Drying

Screening Sugar

Water SO2

Slicing

Fluming

Fresh water

Figure 2. 6 Flow diagram for beet sugar production


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CHAPTER THREE

3.0 PROCESS DESCRIPTION

3.1 HARVESTING

The timing of the harvest is determined by sugarbeet ripeness, average root size, and weather

conditions. Before harvesting, the mass of the root must be almost twice that of the crown, and

the leaves start to turn yellow. Harvesting time is the function of the following factors:

Air temperature

Length of sugarbeet storage

In places where temperatures do not permit long-term storage, the harvest is conducted on an

as-needed basis. Sugarbeet is harvested (dug) out of the ground by a harvester.

Beets are usually transported by large trucks or (depending on the proximity to the railroad), to

be stockpiled in the beet-storage areas (beet piling grounds) in piles 5 to 12 m high. Beets are

usually piled by mobile pilers.

Once harvested and transported to the factories, the beets are topped and scalped. Topping is

the removal of beet tops (petiole and leaves). Scalping is the cutting of the crown that follows

the topping process. Defoliators remove the tops from the beets immediately after harvesting.

Figure 3. 1 Topped beet (Wikipedia.com)


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This is accomplished by two or three sets of flails, of which usually one or two sets are made of

rubber, but one set is made of steel. The beets are cut uniformly below the green leaf stalks of

the crown. Cutting the beets at the right level leaves a cut surface area of about 5 cm in

diameter. If beets are cut above the normal level, the beet tonnage increases but so does the

amount of non-sugars, which makes processing at the factory difficult. This also brings down

the average sugar content of the beets, causing a decrease in factory efficiency and sugar

production. In general, sugar losses during storage increase when beets are cut below or above

the normal level.

3.2 RECEIVING AND STORAGE

Sugar beets are delivered to the factory mostly by truck or by railcar (in some areas). Farmers

who are close to the factory might bring beets by tractor. Planning beet delivery to the

receiving station, particularly in those areas with short-period storage (due to high

temperatures) is of utmost importance.

3.2.1 Beet unloading and sampling

Beets arriving at the factory are unloaded into the receiving hoppers or piled on the beet-

storage area. Two types of unloading systems are available:

Wet unloading

Dry unloading

Wet unloading is not popular because of high water usage and damage to beets if extensive

high-pressure equipment is used. In wet unloading, beets are pushed from the vehicle into the

flume by an overhead spray nozzle (fire hose). The nozzles are usually operated from the

control room. The correct adjustment of water pressure is important in preventing beet

damage, so a pressure of about 2.5 bar (36.7 psi) is usually used. The amount of water used is in

the range of 225 to 550% on beet (van der Poel 1998).


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Dry unloading is carried out in any of the following ways: Hydraulic side-dumping truck,

Hydraulic back-dumping truck, Side-tilting platform, back-tilting platform and Bottom-dump

trailer.

In the hydraulic side-dumping and back-dumping operation, hoisting equipment on the truck

lifts the bed of the truck to unload the beets. In the side-tilting operation, the vehicle moves to

a tilting platform.

The platform is then raised on one side to unload the beets from the lower side of the vehicle.

In the back-tilting operation the platform is raised from the front and the beets are unloaded

from the back of the vehicle. (Note: Bottom-dump trailers are not popular in beet

transportation.)

Pilers are used to pile beets and are usually mobile. A beet piler consists of a swing-around

receiving hopper that is positioned to receive the beets from the truck. It also contains a belt

conveyor and a large boom (up to 30 m). Some pilers are further equipped with an automatic

sampling device.

After a truck is emptied, the receiving hopper swings to admit the next truck. From the hopper,

beets drop onto the conveyor and are then lifted to another conveyor that carries them to a

screen where soil and trash are removed. A larger conveyor (up to 30 m), called a boom, carries

the beets to the storage piles. Sugar factories can pile beets 5 to 12 m high.

As the beets are passed over a screen, a portion of the soil is filtered out. The amount of

removed soil is typically about 50% of the soil attached to the beets.

To determine the beet gross weight (weight of beets and beet tare) at the receiving station,

each beet truck or railcar is weighed before unloading, and the weight (weight-in) is recorded

by a computer. After unloading of beets, beet tare from the piler is transferred back to the

truck and the vehicle is weighed again (weight-out). The difference of the weight gives the gross

beet weight.


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Beet sampling is performed at the receiving station by a sampling device that is installed after

the weighing equipment. Beet sampling is performed automatically or manually from sugarbeet

loads. In the automatic method, a tube (called a sample tube) is lowered through the beet load

to take a sample of about 10 to 12 kg, which is sent to the beet lab. The following tests are

carried out:

Soil tare - the amount of non-beet delivered.

Crown tare - the amount of low sugar beet delivered.

Sugar content ("pol") - amount of sucrose in the crop.

Nitrogen content - for recommending future fertilizer use to the farmer.

3.2.2 Beet tare

Beets delivered to the factory contain tare (impurities) that has to be separated from the beets

during early steps of the process. Beet tare consists mostly of soil stuck to the beets after they

are removed from the ground. Other components in beet tare are clay, sand, stone, and trash

(leaves and weeds). Under good harvesting conditions, the tare varies from 2 to more than 8%

OB (on beet). In clay-type soil areas or if farmers harvest beets in wet weather, the tare can

increase significantly.

3.2.3 Beet storage

Delivered beets are piled and stored in beet-storage areas (beet piling grounds). Four types of

beet storage are available:

Factory beet storage: This type of storage is located in the factory. It is open and differs

in size (a few thousands to hundreds of thousands of tons of beets).

Remote beet storage: This type of storage is located near the factory (between the field

and the factory). Is open, and medium to large size. It is used for long-period storing

until the beets are gradually transferred to the factory storage.

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Clamp beet storage: This type of storage is located in the beet field, is open, and is of

small size. It is used for short-period storing during the harvest, until the beets are

gradually delivered to the factory.

Deep-freezing storage: This type of storage is located in the factory, is open or closed,

and is of medium to large size. It is used for long-period storing. Forced-air ventilation is

used to cool and deep-freeze the beet piles.

3.2.4 Sugar and mass losses during storage

Sugar loss during storage is any sugar-content reduction that occurs from the time the beets

are weighed at the delivery to the storage and the time they are reweighed during processing

(usually after beet slicing). Post-harvested beets are still alive and continue to consume sugar.

The losses result from

Beet respiration

Microorganisms

The sugar loss during beet storage occurs in a two-step process.

Step 1: (𝐶12𝐻22𝑂11 ) is decomposed to produce invert sugar

𝐶12𝐻22𝑂11 + 𝐻2𝑂 → 𝐶6𝐻12𝑂6 + 𝐶6𝐻12𝑂6

Step 2: The invert sugar is decomposed to produce carbon dioxide (CO2), water and energy.

𝐶6𝐻12𝑂6 + 6𝑂2 → 6𝐶𝑂2 + 𝐻2𝑂 + 𝐸𝑛𝑒𝑟𝑔𝑦 (674 𝑘𝑐𝑎𝑙)

Later during processing, part of the invert sugar will decompose to some acid (e.g. lactic acid)

and the coloring substances will negatively affect the process. Invert sugar formation during

storage can be high (100 to 200 g per ton beet per day under normal storage conditions).

The intensity of sugar loss during storage depends on the following factors:

Microorganisms


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Temperature

Dirt content

The following preventive actions can be taken to reduce sugar losses in beet piles:

Using forced-air ventilation: Is helpful during early and late stages of storage. During

the early days of storage, when the temperature is high, the forced air removes the

respiration heat from the piles. In this system, several ducts (channels) are installed

under the piles and air is forced through the piles by blowers.

Deep-freezing the beets: Is used in open and closed storages. The closed storages are

known as beet sheds.

3.3 BEET DRY-CLEANING

Beet Dry-cleaning of sugarbeet processing station includes a hopper, conveyor, and a large

vibrating screen. The equipment is installed outside the main processing building next to the

flume system.

The beet-dry-cleaning (dry-screening) station is to separate stone, sand, and part of soil from

the beets. Any clay (moistened soil) stuck to the beets cannot be separated by the dry-cleaning

system. Materials larger than about 12 mm, such as large stones and weeds are also excluded

from the separation at this station. But loose soil, sand, small stones, beet tops, and leaves can

be separated from the beets by their screening.

Figure 3. 2 Effects of temperature on sugar loss in beets (van der Poel 1998)


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The separated materials are usually trucked to the field. In the dry-cleaning station, the beets

are first transferred from the storage area into the beet hopper using front-end loaders or

trucks. Beets can also be unloaded into the hopper of the dry-cleaning belt directly from the

truck or rail car when they are delivered to the factory. From the hopper, the beets are

elevated by a conveyor to a vibrating screen. Here, part of impurities is separated from the

beets by vibration (shaking). Then, a belt conveyor delivers the dry-cleaned beets to the flume

channel.

In the dry-cleaning station, three types of screening systems are usually used:

Cable screen

Grab-roller screen

Spiral-roller screen

The beet-dry cleaning station provides cleaner beets to the beet washer, so less wash water is

needed in the beet-washing process. This is an environmental advantage and a cost savings for

the factory.

3.4 BEET CONVEYING

Beets are conveyed using the dry-conveying system; front-end loaders transport the beets from

the factory beet storage to the beet hopper which is installed in front of the beet flume. The dry

system offers the following advantages over wet transportation:

Less loss of sugar during transportation

Less water usage


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3.5 BEET FLUMING

The beet-flume system (water-transport system) transports the beets to the stone and trash

separators by the force of water. Fluming is possible because the sugarbeet has a density

slightly greater than that of water (beet density is about 1.1 Kg/m3).

Fluming requires water in the range of 300 to 500% on beet (OB). To save water and to control

the quantity of mud, flume water is treated for mud separation in the factory’s waste water

ponds, and the treated water is returned to the flume. A flume-water clarifier can be used;

which allows several returns (recycles) of the water to the flume, while part of the water is

discharged to the ponds at each cycle. In the clarifier, the majority of the mud and solids are

removed. The flume-water clarification reduces considerably the amount of discharged

wastewater of the plant.

The beet flume is made of concrete or sheet metal; its U-shaped bottom has a slope of about

1.5%. Flumes are 1.0 to 1.3 m wide and about 1.0 m deep, depending on the processing

capacity of the factory. Flumes are built with a bypass that allows the fluming to continue if a

plug occurs.

The fresh water used in fluming is generally condenser water. During fluming, high pressure

water should not be used because it damages the beets.

Figure 3. 3 Beet conveying operation (Mosen Asadi, 2007)


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3.5.1 Stone separator

Stone separators (stone or rock catchers) are installed around the flume system to separate

large stones (rocks) from beets. The stone separator operates based on the density difference

between beets and stones. In a water–beet–stone mixture, stones have higher density than

water and beet, causing the stones to drop and separate from the beets in the stone separator.

A bucket stone separator is used for this operation.

3.5.2 Trash separator

Trash (sugarbeet leaves and weeds) can clog the slicer’s knives, plug the diffuser, and bring

many impurities into the process. Therefore, the flume system contains a trash separator to

remove trash flowing with the beets. A number of types of trash separators are used in sugar

processing. In the rake trash separator, the trash is caught on rakes that move against the flow

of the flume in an endless chain. The speed of the chain is a slow speed of about 0.2 m/s. The

trash is released from the rakes as the rakes are tilted outside the flume. In general, trash

separators can remove a large part of trash but not small trash and beet-chips (small beet

particles). Beet chips and small trash can be removed by using a vibrating chip separator which

is usually installed after the trash separator or the beet washer.

Figure 3. 4 Beet flume (Mosen Asadi, 2007)


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3.6 BEET LIFTING TO BEET WASHER

Once inside the plant building, the beets are lifted from the fluming channel into the beet

washer. The beet washer is located several meters higher than the flume to make the delivery

of washed beet to the slicers easier. Beets are lifted to the beet washer by one of the following

means:

Belt conveyor

Pump

Bucket conveyor

The most common way of feeding the beet washer is by way of the beet pump for following

reasons: it has lower initial investment, it’s easy to maintain, it needs less room.

The amount of wash water needed for fluming and cleaning beets is high (about 200 to 500%

OB), depending on the beet-handling and cleaning system of the plant.

3.7 BEET WASHING AND FLUME-WATER TREATMENT

Beets that have been separated from stones and trash and partially washed during fluming are

now moved to the main processing building of the plant by fluming. Once inside the plant

building, the beets are lifted from the fluming channel to feed the beet washer for the final

cleaning.

The beet washer is installed in an open area next to the trash separator, and the washed beets

are transferred to the main building by a conveyor to feed the beet slicers. In the beet washer,

Figure 3. 5 Rake trash separator (Mosen Asadi, 2007)


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soil and clay stuck to the beets and sand are washed away before the beets enter the slicing

process. The beet washer not only cleans the beets but also removes most of the microbes

coming with the beets.

The main job of the beet-washing station is to supply the slicing station with a steady flow of

clean beets. The beet washer is the last point for removing remaining tare, so its operation is

important to the performance of the further stations. In many ways, the beet-washing station

controls the slice rate of the factory because any stones or excess weeds can damage slicer

knives and cause delays in beet slicing.

The washing station must be maintained in a way that ensures that enough (but not overfilled)

clean beets are always in the slicer’s hopper. Beets are cleaned in two separate washers.

Water discharged from the beet washer and from the flume system contains:

Small beet particles (chips)

Small trash particles

Mud

Wash water from the beet washer and flume system is pumped to a mud settling pond. The

upper flow from the pond is mixed with makeup water (usually condenser -water) to be reused

in the fluming and beet washer.

The wash water is first sent to the chip separator to separate beet -chips and trash particles

from the water. The separator removes the heavier beet chips from trash particles. After

Figure 3. 6 Beet washing operations (Mosen Asadi, 2007)


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separation, the beet chips are sent to the beet hopper and then to the slicers, and trash

particles are sent to the pulp presses to be pressed with pulp.

The water from the chip separator is discharged to the wastewater treatment system to be

cleaned and reused in the flume and beet washer.

3.7.1 Flume-water treatment

A coarse metal grate (a screen with large openings) is installed at the end of the beet washer to

separate water from the beets. The beets are then sprayed with fresh water. The chips are then

separated. Here, the flume water is directed to the chip-separation system and then to the

wastewater-treatment system. Otherwise, the flume water is directly sent to the wastewater

system.

3.7.1.1 Chip Separation from Flume Water

Beet chips are small, broken particles of beets that could not be separated in the earlier stages

of operation. A chip separator removes beet chips and small trash particles (weeds) left in the

water discharged from the beet washer.

The separator is a drum screen filter consisting of a vibrating screen with openings of about 0.2

mm, followed by a separating belt that separates the heavier beet chips from weeds by a rolling

mechanism (chips have the ability of rolling, while weeds do not).

After separation, the beet chips are sent by a conveyor to the beet hopper, which feeds the

slicers. Weeds are sent to the pulp presses. Chip separation has the following advantages:

It increases sugar recovery by recovering beet chips.

It decreases the load of solids entering the factory’s wastewater system.

It increases the income by recovering beet chips and trash that would otherwise be

wasted.

3.7.1.2 Mud Separation from Flume Water

Used wash water from the beet washer or from the chip separator contains mud as well as

dissolved sugar leached from beets during fluming and washing. The flume water is sent to the


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mud-separation system (mud centrifuge), where the mud, sand, and trash (weeds) residue are

separated.

Muddy water from the beet washer and flume system is pumped to the mud-settling pond,

which has a short retention time (several days). The upper flow from the pond is mixed with

fresh water (usually condenser water) to be used in the beet flume and beet washer. The mud-

separation system consists of the following elements:

Flume clarifier

Mud-settling pond

Flume filter (trash filter)

Cake filter (usually filter press or centrifuge filter)

In this system, muddy water first goes to the flume clarifier. The clarifier uses the density

difference between dirt and water for separation. The overflow from the clarifier is clean

enough to be sent to the fluming and washing system. The underflow from the clarifier, which

contains mud and fine trash materials, is sent to the mud-settling pond and from there to the

flume filter (trash filter) to remove any trash and fiber material from the mud and to prevent it

from entering the water treatment system.

The mud is then filtered by a filter press centrifugal filter to produce cake to ease its handling

process. The material recovered by the trash filter is returned to the pulp presses to become

part of the pulp production from the factory. Water from the trash screen is sent to the flume

pond and then to the wastewater treatment system. Trash separation prevents the mud ponds

from producing odor.

The flume clarifier is used to remove mud from flume water. It consists of a large tank with a

shallow cone bottom that is 50 to 100 m in diameter and 2 to 4 m deep. The clarifier contains a

slow-moving rake driven from a central shaft. There are arms connected to the rake.

The feed enters the center of the clarifier, and the heavier particles flow downward and

gradually make a mud layer where the clear liquid stays on top. The clear water spills over the


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edge of the tank into a trough. The rake arms gently move the mud to the center of the tank,

where it flows through a large opening and is pumped by the mud pump.

3.8 BEET SLICING

Slicing beets is the process of cutting beets into long, thin strips, called cossettes. In the slicing

station, a conveyor (usually the belt type) continuously delivers clean beets from the beet

washer to the beet hopper (a cone-shaped container) that feeds the beets to the slicers.

When equipped with the chip separator, the separated beet chips are also sent to the beet

hopper. The main function of the beet-slicing operation is to improve the diffusion operation

and the removal of sucrose from the beets. This is achieved mainly because of the increase of

the surface area of the beets. Increasing the surface area maximizes the following:

The contact area between the beet cells and the water in the diffuser

The movement of sugar from the cells to the diffusion juice

3.8.1 Cossette Quality

For complete removal of sugar by the diffusion process, the size and quality of the cossettes are

important. Generally, for the same result, thick cossettes need more diffusion time, or a higher

amount of diffusion water than thinner cossettes. Therefore, thin cossettes are desirable. The

desired characteristics for high-quality cossettes are as follows:

Uniform width (3 to 6 mm thick, square or V shape)

Uniform length (30 to 60 mm long)

The cossettes are then transferred to the diffuser.

3.9 JUICE DIFFUSION

3.9.1 The diffusion process

This process takes place in the diffuser (as shown in the diagram below), in which sliced beets

(cossettes) are kept in contact with hot water for about an hour to diffuse the juice from the

beet cells. The hot water (about 70 C) used in the diffusers destructs the beet cells to make the


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movement of diffusing components possible. As the water moves ahead, it collects sugar

(sucrose) and non-sugars (non-sucrose) from the cossettes and becomes a concentrated impure

sucrose solution, known as diffusion juice (raw juice). The diffusion juice (with 85 to 88% purity)

is sent to the purification station for the removal of certain non-sugars (impurities). In the

meantime, the cossettes in the diffuser gradually lose almost all (about 98%) of their sucrose

and turn into pulp (de-sugared cossettes). The wet pulp is sent to the next station (Pulp

Treatment) to be pressed, dried, and pelletized and sold as a by-product of the process.

3.9.2 Denaturation

Denaturation (changing the nature), in chemistry, means destruction (alteration) of the cell

protoplasm by coagulation of its main component, protein, to make it permeable. In beet

processing, heat is generally used in the diffuser for denaturing the beet cells.

In a continuous-countercurrent diffuser (see Figure above), rotating equipment moves the

cossettes continuously from one end, while water travels in the opposite direction. The

cossettes gradually lose their sucrose (about 98%) and turn into pulp (de-sugared cossette),

while the water gradually gains the sucrose and turns into diffusion juice, which usually

contains about 15% DS (dry substance) with a purity (%sucrose in dry substance) of 85 to 88%.

The rest of the sucrose (about 2%) stays with the pulp.

Figure 3. 7 Juice diffusion process (Mosen Asadi, 2007)

Figure 3. 8 Counter-current diffusion (Mosen Asadi, 2007)


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During diffusion, the juice is continuously pumped from the head-end (cossette side) of the

diffuser, and the wet pulp is discharged from the opposite side, known as the tail-end (pulp

side). The pulp is sent to pulp presses to be pressed. The pulp-press water from pulp presses is

heated and returned to the diffuser as part of the diffuser water supply.

3.9.3 Factors influencing the diffusion process

Factors influencing the diffusion operation are the following:

pH: Beet juice has a pH of 6.0 to 6.5. The optimum pH of diffusion juice is 5.8 to 6.0. At this pH,

sucrose inversion to invert sugar is at the lowest level. The acidification of diffusion water and

sometimes pulp-press water is commonly practiced in the diffusion operation to slightly lower

the juice pH and achieve the optimum value to prevent microbiological activity. Acidification

also helps in the pulp-pressing operation.

Draft: is the mass of diffusion juice leaving the diffuser relative to the mass of cossettes

entering the diffuser. It is expressed as percent on beet (% OB). For example, a draft of 120%

means that 120 t of juice is produced from 100 t of processed beets. Draft not only indicates

the amount of the diffusion juice but also helps determine the amount of diffusion water

entering the diffuser.

Low draft slows the movement of the cossettes-juice mixture and increases the risk of plugging

the diffuser. High draft means extra water has been added to the process and will need to be

evaporated later during evaporation. A draft of 110 to 130 is considered an optimum range

when processing undamaged beets.

Temperature: The optimum temperature for the diffusion operation of undamaged beets is 70

to 73 C.

Retention time: is the amount of time cossettes are in contact with beet juice. A complete

diffusion process takes place over a certain period. The retention time, used by diffuser

manufacturers for undamaged beet, ranges from 60 to 110 minutes.


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Cossette quality: High-quality cossettes are necessary to produce good diffusion juice with high

purity without regard to the type of diffuser.

Microbial activity: Cossettes are a good medium for the growth of many kinds of microbes,

particularly thermophile bacteria (grows around 50C). This type of bacteria converts sugars to

acids (mainly lactic acid), which aids in pulp pressing but increases sugar losses. In addition, it

increases the soluble non-sugar content of the diffusion juice, which increases the amount of

lime used in juice purification and juice softening. As a rule, the lowest microbial activity is

observed when the diffuser is kept at 70 to 73C and at a pH of 5.8 to 6.0.

3.9.4 Adding pressing aids to the diffuser

Pressing aids (pressing agents) are chemicals added to the diffusion water to improve pulp

press-ability (the dewatering of pulp by pulp presses). The following chemicals are used as

pressing aids: gypsum, calcium sulfate, calcium chloride, and aluminum chloride or aluminum

sulphate.

3.9.5 Adding antifoaming agent to the diffuser

Foam (a colloid-type material, consisting of small bubbles of a gas trapped in a liquid) slows the

movement of cossettes and juice in the diffuser, so an antifoaming agent is added to the

diffuser to break up the foam molecules and improve the movement of the cossettes-juice

mixture. The required amount of antifoaming agent is about 100 g/t of beet.

3.9.6 Adding biocide to the diffuser

Bacterial activity can lead to considerable sugar loss during the diffusion process. The use of a

biocide during the diffusion process helps reduce microbial problems, prevents inversion of

sucrose, and reduces acid (e.g., acetic, butyric, and lactic acids) formation.

Sulfitation is used because sulfur dioxide is a good biocide, which improves sugarbeet

processing by: disinfecting the diffusion juice, lowering the pH of the diffuser and improves the

pressing qualities of the wet pulp.


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3.9.7 Diffuser type

The type of the diffuser used is the Silver-DDS slope diffuser. The Silver-DDS diffuser consists of

a U-shaped vessel, inclined at an angle of 11 to the horizontal. The cossettes move upward

with the help of two rotating-parallel screws. The speed of the screws can be varied between

0.5 and 1.3 RPM depending on the slice rate. The wet pulp is discharged by double scrolls from

the top-end (tail-end or pulp-end) where the diffusion water enters. The diffusion juice moves

downward through the cossettes and, at the low-end (head-end or cossettes side) of the

diffuser, passes through a screen before it is pumped to the next step of the process. The

screen separates the juice from the entering cossettes. There is no baffle or partition in this

diffuser. Steam jackets keep the temperature of the diffuser at around 70C. The cossettes are

heated at the low-end by the passing diffusion juice as the juice is cooled to about 25°C.

3.9.8 Product and by-product of the diffusion process

Diffusion juice is the product and wet pulp is the by-product of the diffusion process. Before the

diffusion juice is directed to the purification process, it is screened to remove sand and pulp

particles.

Wet pulp is the by-product of the diffusion process. Wet pulp has a high moisture content of

about 90%. It is pressed to about 80% and dried to a moisture content of about 10% before

storage and transport. The dried pulp is valuable cattle feed, supplying carbohydrates, proteins,

and minerals. Pulp pressing, drying, and pelleting are the subject of the next section.

3.10 PULP TREATMENT

3.10.1 Introduction

This Station (see Figure below) consists of two steps: pulp pressing and pulp drying. When the

exhausted (de-sugared) beet cossettes leave the diffuser, they are called wet pulp, containing

about 90% water (10% dry substance [DS]) and almost all the beet pulp (beet’s fibrous

materials). The wet pulp still contains a considerable amount of sugar (sucrose). To recover the

sugar from the wet pulp and handle, store, and market the wet pulp economically, it must be

pressed and dried to decrease its moisture content to about 10% (90% DS). This is achieved in a


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Cassettes

Diffusion Pulp drier

Pellet press

Livestock feed (storage and

shipment)

Wet pulp

Pressed pulp

Pulp press Dried pulp

Press water

Pressing aid

Molasses

Diffusion (raw) juice

two-step process. First, the wet pulp is pressed in pulp presses to about 75% moisture content

(25% DS). The juice pressed from the pulp, called press water, is screened, heated, and

returned to the diffuser as part of the diffusion water. In the second step, the pressed pulp is

dried in pulp dryers to about 10% moisture content (90% DS).

3.10.2 Pulp pressing

The wet pulp leaving the diffuser is transported by a screw conveyor to the pulp-pressing

section. In the pulp presses, the wet pulp is pressed to a smaller volume with about 75%

moisture content (25% DS). (With the use of a pressing aid, pulp press-ability improves,

resulting in moisture content reduction to about 65 %.) The press water is collected in a tank

and the pumped to a screen, where fine pulp particles are removed and returned to the pulp

presses for repressing. The screened press water, called pulp press water, is then heated to 70

to 90C before being returned to the diffuser. The amount of pulp-press water is about 75 to

85% OB (on beet). Heating disinfects the press water before it is returned to the diffuser,

preventing sugar losses due to microbial activity.

It is cheaper to remove water from the wet pulp mechanically by pressing than by thermally

drying. The water content of the wet pulp can be reduced by the presses as much as practicable

before feeding the pressed pulp to the pulp dryer. The pulp-pressing operation is important

because it;

Removes about 80% of the total water present in the wet pulp

Provides part of the needed water for the diffusion process

Figure 3. 9 Pulp treatment operations


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Reduces the load to the waste water treatment system

Saves energy in pulp drying

The pulp press to be used is a horizontal twin screw pulp press.

3.10.3 Pulp drying

Pressed pulp is directed by a belt conveyor to the pulp dryer to produce dry pulp with about

10% moisture content. Wet-pulp particles are highly porous, so moisture can be easily removed

in the dryer, where heat is formed by the combustion of fuel with air to evaporate water from

the pulp.

Coal, oil, or natural gas can be used as the fuel in the pulp dryer. The type of dryer used is the

steam dryers.

Steam dryers use superheated steam from the boiler house for pulp drying. The vapor removed

from the pulp then serves as heat in the vapor users of the factory. Steam dryers do not

demand changes in the boiler house. Pulp drying by steam dryer provides the following

advantages compared with fuel-burning dryers:

Savings on energy cost

Reduction in air pollution

3.10.4 Pulp Pelleting

The dry pulp is transferred to pellet presses (pelletizers) to produce pelleted pulp (pellets).

Molasses is also added. The pellets are round, 6 to 16 mm in diameter and 25 to 50 mm in

length. Pelleting puts the pulp in a compact form (the bulk density of pellets is about triple that

of dry pulp).

The dry pulp from the dryer is supplied to a surge tank above the pellet presses. Then, the pulp

is mixed with steam or hot water to increase its temperature to 90C. For pelleting, dry pulp

must have 8 to 12% moisture content. The moist pulp is fed to the center of a rotating die in

the pellet press, and then forced to the die openings by the rollers. Knives, positioned on the


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side of the die, cut the pellets to the desired length. The length can be changed by adjusting the

clearance between the die and the roller.

3.10.5 Pulp storage

The pulp storage is adjusted for temperature and humidity by ventilation and air circulation to

maintain the moisture content of the stored product at a desired level. When the air moves

through the pellets, it absorbs moisture and increases in temperature. Inadequate air

circulation and a cold climate cause moisture migration (due to the temperature difference

between the top and bottom of the pile), resulting in a hardening of the pellets. In addition,

there is the risk of mold formation

3.11 MILK-OF-LIME AND CARBONATION GAS PRODUCTION

This section involves preparation of two important chemicals used in Juice purification: milk-of-

lime (MOL) and carbonation gas (CO2 gas). It consists of two sections: calcining (the

decomposition of limestone in the limekiln to produce quicklime) and slaking (the mixing of

quicklime with water in the slaker to produce milk-of-lime). Raw materials for the limekiln are

limestone (CaCO3) and coke (C).

Figure 3. 10 Carbonation gas production (Mosen Asadi, 2007)


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The milk-of-lime (MOL, carbonation lime or simply lime) and carbonation-gas (simply gas)

station consists of two steps:

Calcining: The decomposition of limestone (CaCO3) to quicklime (CaO) and carbon

dioxide gas (CO2) in the limekiln (solid-fired kiln) at about 1100C by using the heat

energy of the limekiln’s fuel

𝐶𝑎𝐶𝑂3 + 𝐻𝑒𝑎𝑡 → 𝐶𝑎𝑂 + 𝐶𝑂2

Slaking: The mixing of quicklime with water or a diluted juice (often sweet water from

filters) in the slaker to produce lime, a suspension of Ca(OH)2 in water.

𝐶𝑎𝑂 + 𝐻2𝑂 → 𝐶𝑎(𝑂𝐻)2

In the limekiln operation, limestone and coke are weighed automatically, mixed together into

buckets in a limestone-to-coke ratio of about 10 to 1, and transported by a bucket elevator to

the top of the kiln. Then, the feed is discharged into the kiln through a hopper in an equal

distribution. The feed moves slowly down the kiln through three zones namely; preheating,

calcining and cooling.

Each zone occupies about one-third of the kiln’s height. The temperature in the middle of the

calcining (burning) zone is kept at about 1100C (the hottest of the three zones) to completely

convert the CaCO3 to CaO and CO2. After discharge from the bottom of the kiln, the quick-lime

(CaO) is transported by a belt conveyor to the lime slaker.

In the slaker, the CaO is mixed with water to produce lime. The lime is kept in a supply tank for

about 30 minutes to complete the reaction between lime and water. At this point, the lime is

ready to be used in the juice-purification station.

Carbonation gas is collected at the top of the kiln and piped to the gas scrubber (dust collector)

where lime particles are removed and the gas is cooled. The clean gas is directed to the gas

compressor to increase its pressure to about 1.7 atm. At this point, the carbonation gas is ready

for use.


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3.12 JUICE PURIFICATION

3.12.1 Introduction

The diffusion juice from the diffusion process contains a considerable amount of non-sugars

(non-sucroses). In the juice-purification station, milk of lime (MOL) is added to the heated

diffusion juice in a few steps to precipitate and destabilize the non-sugars. Carbonation gas is

also added in two steps to precipitate the lime as calcium carbonate (CaCO3) and to adjust the

pH and alkalinity of the juice. During operation, the precipitated calcium carbonate (PCC) is

separated from the juice in the clarifier, dewatered in the cake filters (filter presses or rotary-

drum filters), and sold as carbonation-lime residue (CLR, one of the by-products of the factory)

in soil fertilizer, as a pH adjuster, and for other uses.

The purpose of juice purification is to remove certain non-sugars, suspended particles, and

colloids (e.g., dextran and colorants with high-molecular mass) from the diffusion juice to

produce a high-purity, colloid-free, and low-color juice with minimum hardness (lime salts).

During a typical purification process, a non-sugar elimination (NSE) efficiency of 20 to 30% is

achieved, and the remaining non-sugars become destabilized to the point where they are

harmless to the later operation and finally end up in molasses. Thin juice is the product of the

purification station, and carbonation-lime residue is its by-product.

In the liming step, the diffusion juice is limed (i.e. lime is added) to a certain alkalinity and pH to

precipitate some non-sugars. For example, sodium oxalate reacts with lime to precipitate (↓)

calcium oxalate (CaC2O4):

𝐶𝑎(𝑂𝐻)2 + 𝑁𝑎2𝐶2𝑂4 → 𝐶𝑎𝐶2𝑂4 ↓ +2𝑁𝑎𝑂𝐻

In the carbonation step, the limed juice is carbonated (i.e., gas is added) to a certain alkalinity

and pH to convert the un-reacted lime to precipitate calcium carbonate:

𝐶𝑎(𝑂𝐻)2 + 𝐶𝑂2 → 𝐶𝑎𝐶𝑂3 + 𝐻2𝑂


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The precipitated calcium carbonate (PCC) is removed from the juice by settling and filtration to

produce clear juice. The goals of juice purification are as follows:

Removal of all insolubles substances

Removal of certain soluble substances (insolubles)

Production of thermo-stable juice with minimum hardness

In the purification station, 20 to 30% of non-sugars, such as invert sugar, colloids and coloring

substances, are removed. As a rule, each kg (ton or any mass unit) of non-sugars carries 1.5 kg

(ton or any mass unit) of sugar to molasses. This means that non-sugars elimination saves the

30 to 45% of sugar. In addition, during purification, all insoluble substances (diffusion juice

contains about 2% insoluble solids) are removed, making further operations easier. The product

of the purification station is a juice, known as thin juice.

3.12.2 Pre-liming

Pre-liming is the step of purification where a small amount of lime (about 0.2 to 0.7% on juice)

is added to the heated diffusion juice (about 86C) until optimum conditions for the pre-liming

operation (pH of about 8.5 and an alkalinity of about 0.1) are reached. The liming time of the

juice in this step is about 10 to 15 minutes.

The non-sugars that are removed during pre-liming cannot be removed adequately in main

liming. If pre-liming is controlled properly, most of the colloids, invert sugar, proteins,

phosphates and sulfates in the diffusion juice are precipitated and removed later by

sedimentation and filtration.

3.12.3 Main liming

Main liming (main defecation) is the step of purification where lime (at about 1.0 to 2.5% OB) is

added to the heated prelimed juice (about 88C).

Unlike preliming, in main liming the lime used is much more than can be dissolved in the juice

for the following reasons:


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To act as an adsorbent for the adsorption of non-sugars (lime has a high adsorption

capacity).

To act as an aid for the filtration process to improve the filterability of the juice.

The most important reactions occurring during main liming are the following:

Decomposition of invert sugar into colorants and acids and the formation of oxalic acid

Decomposition of amino acids such as glutamine and asparagine into their ammonium

salts

3.12.4 First carbonation

First carbonation is the step of purification where the carbonation gas is added to the heated

limed juice (about 90C) until the optimum conditions for the first-carb juice (pH of 10.8 to 11.0

and alkalinity of 0.08 to 0.11) are reached. The gassing time of the juice in this step is about 10

minutes.

After the first-carbonation process, the juice becomes slurry, named first-carbonation slurry. In

the juice are suspended solids visible to the naked eye as individual substances. Carbonation

slurry consists of calcium carbonate (55 to 60%), organic compounds (10 to 15%), and water. To

separate the solids from the juice, the first-carbonation slurry is treated in clarifiers (settlers) or

thickening filters. The separation of the solids converts the first-carb slurry into clarified juice,

which is nearly free of suspended solids, and a thickened by-product called carbonation mud.

First-carb juice separated from mud in the clarifier or thickening filters is filtered to remove the

remainder of solid particles in pressure-leaf filters because these solids would otherwise partly

re-dissolve in the second carbonation.

3.12.5 Second carbonation

Second carbonation is the step of purification where carbonation gas is added to the filtered

and heated first-carb juice until optimum conditions for the second-carb juice (pH of 9.0 to 9.2

and alkalinity of 0.02 to 0.03) are reached. Before the filtered first-carb juice is entered into the

second-carb tank, it is heated to about 92C in the second-carb heaters to prevent formation of

calcium bicarbonate in the juice. The main functions of the second carbonation are:


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To precipitate still-existing un-reacted lime

To decrease the hardness content of the juice to minimum

To decrease the pH of the juice to an optimum level for the next station

After second carbonation, the juice is filtered in second-carb filters (pressure-leaf filters) to

form the thin juice which is transferred to the next stage for evaporation.


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SO2

Carbonation gas

Milk- of- lime (MOL)

From diffuser (raw juice)

Heating

(86C)

Preliming (0.2-0.7 CaO OB)

Heating

(88C)

Main liming (1.0-2.5 Cao OB)

Heating

(90C)

First carbonation 0.08-0.11 alkalinity

Mud separation

Mud thickening

1st carb filtration

Heating

(92C)

Second carbonation 0.02-0.03 alkalinity

2nd carb filtration

Thin juice to evaporators

Lime kiln

Lime slaker

Sulphur stove

Figure 3.11 Flow diagram for juice purification operation(Mosen Asadi, 2007)


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3.13 SULPHITATION

Juice sulfitation is the process of adding sulfur dioxide (SO2) to the juice to reduce color and

prevent color formation in the next steps of operation. SO2 inhibits the browning (Maillard)

reaction that forms coloring compounds during evaporation and crystallization. It is usually

used before the evaporation (to thin juice) and crystallization (to thick juice or standard liquor)

process at about 30 ppm on juice.

Sulphur dioxide gas is produced in a “sulphur stove”. The sulfur stove is an apparatus in which

sulfur is burned to form sulfur dioxide, in accordance with the following reaction;

𝑆 + 𝑂2 → 𝑆𝑂2

Sulfur dioxide made with the sulfur stove may be introduced into the juice with a steam injector

or with the aid of gas pumps.

3.14 EVAPORATION

3.14.1 Introduction

Evaporation (vaporization) is the process of concentrating a solution by boiling to convert some

of the liquid to vapor. The temperature difference between the heating medium (steam) and

feed is the driving force (cause) of evaporation. In concentrating a solution there’s two classes

of evaporation involved:

Heating evaporation (conversion of liquid to vapor by heating under normal pressure)

Flashing evaporation (conversion of liquid to vapor by heating under vacuum)

In the sugar processing, flashing evaporation is used to obtain a lower boiling temperature of

the juice, which decreases the required heat. Low pressure decreases the boiling point (BP) of

water (at a lower pressure, water boils at a lower temperature), resulting in a heat-efficient

operation (saves energy). To save more energy, heat exchangers preheat the feed before it is

introduced to the evaporators. For evaporation, heat (flow of energy from a hotter object to a

colder object) is needed to convert molecules of the solution to the vapor state. Evaporators

are mainly used to concentrate the solution.


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In the sugar factory, water is evaporated from juice in two stations:

Evaporation station

Crystallization station

In the evaporation station, thin juice with about 15% dry substance (DS) and about 8.8 pH is

concentrated to produce a thickened juice with about 60% DS and about 8.7 pH, which is called

thick juice. Thin juice consists of nonvolatile solutes (sucrose and non-sucrose substances) and a

volatile solvent (water). During evaporation, only the solvent (water) evaporates; solute (sugar

and non-sugars) does not. This is the reason why the purity of the juice does not change during

evaporation (purity is not relevant to water content), assuming no decomposition of sucrose

occurs.

To obtain a low boiling temperature in the evaporators, a condenser keeps the juice under

vacuum, usually with the help of a vacuum pump placed between the evaporator and the

condenser. This means that the juice must be pumped out of the evaporators. The steam

pressure to the first effect is 300 kPa. The final effect operates at near atmospheric pressure.

The concentrator uses vapor from the second-effect or third-effect evaporator and operates at

a slightly negative pressure (about 70 kPa).

As mentioned previously, the functions of the evaporation station in a sugar plant can be

summarized as follows:

Concentrates thin juice

Produces condensate for boilers

Produces vapor and condensate for heat and condensate users

The proper integration of these three functions results in efficient energy usage in the plant.

(Steam production in the boiler house, its distribution, and its utilization in the heat exchangers

and evaporators, are important to the energy efficiency of sugar plant.

Besides economic aspects, the color increase between thin juice and thick juice during

evaporation is important. In normal beet processing and with SO2 applied to the thin juice

before entering the evaporators, a reasonable color rise (below 20%) between the thin juice

and the thick juice is an indicator of proper evaporation operation.


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In the evaporation station, thin juice with about 15% DS is heated in the thin-juice heaters to

about 90C. Then it is pumped into the evaporators to increase its concentration to about 60%

DS. The steam gives up its heat to the juice and leaves the evaporators as vapor and

condensate.

The concentration of the thin juice is usually achieved in the multiple effect evaporators.

3.14.2 Multiple effect evaporators

A multiple-effect evaporation station in sugar beet processing consists of usually five effects

(quintuple-effect evaporators). Often, each effect consists of two evaporators, called bodies.

For example, a five-effect evaporation station with two bodies in each effect contains 10

evaporators.

A single-effect evaporation operation is not efficient because the vapor has a large amount of

energy and low pressure hence multiple effect evaporators are used. It is universal practice to

feed the thin juice into the first effect, throttle juice from the first effect into the second effect,

throttle juice from the second effect into the third effect, and so on to the last effect. Water is

evaporated in each effect and so as the juice progresses through the evaporators, its density

increases. Juice from the last effect is called thick juice and is pumped to high melter for further

preparation prior to crystallization process.

Figure 3. 11 Multi-effect evaporator system (Mosen Asadi, 2007)


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It is also a general practice for the steam and vapor flow to be parallel to the juice flow. Exhaust

steam is piped into the first-effect steam chest. On condensing, this steam gives most of its heat

to the juice in the first effect. The exchange of heat causes the juice to boil. Vapor from the

boiling first-effect juice collects in the evaporator dome and is piped into the vapor or steam

chest of the second effect. First-effect vapor in the set-and-effect vapor chest gives most of its

heat to the juice in the second effect, and so produces second-effect vapor. This process

continues down through the evaporators until the vapor from the last effect is led to a

condenser.

This condenser maintains the last vapor at a low pressure, usually below atmospheric pressure

and so under a vacuum, and consequently at a low temperature. As a result, each evaporator

effect acts as a condenser for the preceding effect. Hence each succeeding vapor pressure, and,

of course, temperature, is proportionately lower, with the lowest vapor pressure in the last

effect under control by the condenser.

Single-effect evaporation needs roughly 1 kg of steam to evaporate 1 kg of water in the

product. But in multiple-effect evaporation, 1 kg steam entering the first effect can evaporate

as many kilograms of water as there are effects in the system.

After evaporation, the percentage of sucrose in the "thick juice" is 50-65 %. Crystalline sugars,

produced later in the process, are added to the juice and dissolved in the high melter (thick

juice treatment)

3.15 SYRUP CRYSTALLIZATION

Crystallization, in sugar technology, is mass transfer of sugar molecules from the syrup to the

solid particles (seeds) to form crystals. Crystallization leaves impurities in the syrup (known as

mother liquor). Crystallization is one of the most effective separation techniques, providing an

impurity-elimination effect of up to 99.9%. In other words, impurities are excluded from the

crystallization process and pure solute is the only substance that crystallizes (granulated-refined

sugar contains above 99.9% sucrose and raw sugar (96 to 99%). Crystallization occurs when the

syrup is supersaturated and other conditions are met.


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In beet sugar processing, crystallization occurs when solute (in our case, sucrose) moves from a

supersaturated solution (in our case, impure sucrose solution) and attaches to the crystal

structure. This crystallization process can be achieved through two classes:

Flashing crystallization (crystallization by evaporation under vacuum)

Cooling crystallization (crystallization by cooling)

In flashing crystallization, water is evaporated under vacuum (at about 74˚C) and seed is

applied, causing crystallization to occur because the water present in the mother liquor is not

enough to hold sugar molecules. In flashing crystallization, the presence of a vacuum decreases

the boiling point (BP) of the syrup, preventing the inversion of sucrose and saving energy.

In cooling crystallization, the temperature of the massecuite lowered to about 40˚C, causing

crystallization to occur because the water present in the mother liquor holds less sugar

(solubility decreases with decreasing temperature).

3.15.1 Beet sugar syrup crystallization

The crystallization process is described below:

3.15.1.1 Thick juice treatment

The purity of the evaporator thick juice is increased by dissolving in it crystalline sugars. This

takes place in the melter.

The intermediate sugar crystals are always dissolved in the thick juice provided they are higher

in purity than the thick juice with the intermediate sugar dissolved in it. In the melter there is

also addition of filter aid in the form of diatomaceous earth. This material is best added to one

of the melter sugar scroll conveyors, very complete dispersion being obtained in this manner.

The thick juice is filtered to produce standard liquor, which is then pumped to the vacuum-pan

storage tanks.

Also addition of sugar crystals makes the thick syrup saturated. This is necessary in sugar

production process as it will facilitate faster crystallization process in the vacuum pan.


Page | 48

3.15.1.2 Crystal formation

Super-saturation must be established in a solution for crystallization to occur. A state of super-

saturation is attained by boiling the standard liquor under vacuum (flash evaporation). Also

evaporation is done under vacuum for the following reasons:

To reduce the boiling point (BP): The presence of the vacuum increases the

temperature difference (ΔT) between steam and the boiling material, so the material

boils at a lower temperature (the higher the DT, the lower is the BP). Toward the end of

crystallization, the massecuite contains about 90% DS, which equals a boiling-point

elevation (BPE) of about 20°C. This raises the BP to 120°C, which causes a high color

formation if the process was not performed under vacuum.

To avoid inversion: At low temperatures, the inversion of sucrose to invert sugar is

minimal.

To save energy: The energy is saved because of the lower BP of the syrup.

High-green syrup

Sugar

Low green syrup

C-sugar

B- Sugar

Standard liquor

Thick juice

White pan A

High raw pan B

Low pan C

Mixer A

Evaporator

Mixer B

Centrifuge B

Melter

Mixer B

Cooling crystallization

Centrifuge C

Molasses

Centrifuge A

Figure 3. 12 Three-stage crystallization


Page | 49

The vacuum in the vacuum pan is maintained to correspond to a syrup boiling point of 75-80 °C.

The vacuum occurs by a condenser and a vacuum pump placed between the vacuum pan and

the condenser.

The standard liquor (with purity of about 93%) from the vacuum pan storage tanks is pumped

to the vacuum pan. The liquor is boiled at a reduced boiling temperature until it becomes

supersaturated. To begin crystal formation, the liquor is either "shocked" using a small quantity

of powdered sugar or is "seeded" by adding a mixture of finely milled sugar (200g in 50m3 of

liquor) and isopropyl alcohol. The seed crystals are carefully grown through control of the

vacuum, temperature, feed-liquor additions, and steam. When the crystals reach the desired

size, the mixture of liquor and crystals, known as massecuite or fillmass, is discharged to the

mixer. From the mixer, the massecuite is poured into high speed centrifuges, for separation of

crystals from mother liquor.

3.15.2 Centrifugation and washing of crystals

3.15.2.1 Centrifugation

Centrifugation separates the sugar crystals from the mother liquor (liquid around the crystals)

in the massecuite by using centrifuges. A centrifuge is a machine that separates solid from

liquid by centrifugal force (FC), which is produced by high speed rotation (about 1200

revolution per minute, RPM). The FC pushes the mother liquor through the screen of the

basket. Sugar crystals are too large to pass through and retain on the screen. During

centrifuging, the mother-liquor components stay intact because the centrifugal operating has

no effect on solutions. Centrifuges with a higher FC can handle more concentrated massecuites.

In the centrifugal operation, the following factors are important:

Centrifugal force

Massecuite temperature

Massecuite concentration

The centrifugal force (FC) pushes the rotating material from the center of rotation to the side.

FC is developed by rotation (the faster the spinning, the greater the FC).


Page | 50

Massecuite is centrifuged directly after it is discharged from the pan. When crystallization is

complete, the massecuite from the pan is discharged into the mixer (a cylindrical tank with a

mixing device) to wait for the centrifuging process. When the loading step of the centrifuge

starts, the gate of the mixer is opened, and the massecuite is discharged into the centrifuge. In

the centrifuge, the massecuite is rotated in the centrifuge basket, which has a perforated wall

covered with a metal screen.

Revolution per minute of the centrifuge increases constantly to a predetermined speed to

increase the FC, which is evenly distributed over the entire height of the basket. FC pushes the

massecuite toward the basket’s wall, discharging the mother liquor through the basket screen.

The sugar crystals are too large to pass through and build up a layer 150 to 180 mm (6 to 7 in.)

thick on the basket. In the meantime, most of the mother liquor, known as high-green (A-

green) syrup, is removed. However, the crystals still contain a thin layer of mother liquor and

appear yellow, so the crystals must be washed.

3.15.2.2 Washing

Sugar crystals are washed because of the following reasons:

Increase the purity of the sugar

Decrease the ash content of the sugar

Decrease the color of the sugar

For washing, wash water at about 80C is used. The amount of wash water used depends on

the type of massecuite, the sugar color, and the ash content requirements of the white sugar.

White crystals are usually washed twice, which increases the purity of the sugar and decreases

its color.

The crystals are sprayed for a few seconds with hot water, while the basket rotates at

maximum revolution per minute. During washing, the spray nozzle is moved up and down to

wash the crystals uniformly. The runoff syrup discharged during this period is directed to a

separate tank. This syrup is called wash syrup and has a higher purity than high-green syrup


Page | 51

because part of the crystals is dissolved during washing. Constant rotation continues until the

preset mass (or volume) of sugar crystals is reached.

The wash water, which contains a small quantity of sucrose, is pumped to the vacuum pans for

processing. Also the syrup that was separated from the sugar crystals in the centrifuge is serves

as feed liquor for the "second boiling" and is introduced back into the vacuum pans along with

standard liquor and recycled wash water. The process is repeated once again, resulting in the

production of molasses, which can be further desugarized using an ion exchange process called

deep molasses desugarization. Molasses that is not desugarized can be used in the production

of livestock feed or for other purposes.

As the washing process continues, more liquor and wash water pass through the basket to

achieve the desired moisture content (about 0.3%). The rotation is slowed and mechanical

brakes stop the basket. RPM decreases to discharge speed, the discharging device opens to

discharge the crystals from the machine. A plow (blade) removes all remainders of the crystals

from the basket. The wet sugar falls onto a screw conveyor, which moves the sugar to an

elevator to feed the sugar dryer. At this time, the centrifuge is ready to start the next cycle.

3.16 SUGAR DRYING AND COOLING

The wet sugar discharged from the centrifuge has moisture content of 0.1 to 1% (depending on

the amount of washing during centrifuging and the centrifuge’s efficiency) and a temperature

of about 60 °C. This moisture is removed by drying in the sugar dryer.

The process of drying and cooling sugar consists of removing water from wet sugar to the

desired level and cooling the sugar to the norm. As wet sugar dries, the surface moisture is

actually evaporating from the sucrose solution around the crystals.

Most of the water in wet sugar is on the surface of the crystals in the form of a saturated

sucrose solution with high purity (very close to 100%) and high concentration (about 80%).

The wet sugar is dried and cooled in the sugar dryer to a moisture content of about 0.05% and a

temperature below 35˚C. The sugar loses more moisture and cools during transportation from


Page | 52

the dryer to the silo or in the packing station. To ensure that the sugar is safe for packing and

shipping, it is usually held for 24 to 72 hours (depending on its moisture content) under

sufficient air current with low relative humidity. During this process, known as sugar

conditioning, the sugar reaches the equilibrium moisture content, and its temperature is

reduced. The conditioned sugar has a moisture content of about 0.03%, has an ambient

temperature, and is free flowing. Sugar with such properties is safe for storing, shipping in bulk

form, or shipping in a bag.

After the wet sugar is discharged from the centrifuges, a screw conveyor, belt conveyor, or

bucket elevator moves it into the wet sugar box (bin). The wet box works as a hopper feeding

the wet sugar to the sugar dryer. In the dryer, the heat of the wet sugar usually evaporates the

water in the sugar. If the moisture content of the wet sugar is higher than normal (more than

1%), additional heat is necessary to dry the sugar.

Water exists in wet sugar in three forms:

Surface (free) moisture: Exists on the crystal surface. The surface layer contains most of

the water present in the crystal.

Interior (bound) moisture: Exists near the surface of the crystal. It takes about 24 to 72

hours for the bound moisture to escape, depending on the properties of the

conditioned air (flow rate, temperature, and relative humidity).

Inherent moisture: Exists completely inside the crystals. The amount of inherent

moisture is extremely small and is difficult to remove but does not create any problem

in packing or storing of the sugar.

Most of the moisture in wet sugar is surface moisture, so the main part of the heat is used to

vaporize surface water, which is easily removed in the dryer. Almost all the remaining moisture

left in the crystals is bound moisture present inside crystals and is removed only over time.

Therefore, the removal of bound moisture to a desired level (below 0.03%) continues during

the cooling and conditioning of the sugar.


Page | 53

Usually, the sugar is cooled to 25 to 35C, depending on the dryer-cooler availability in the plant

and the temperature of the weather. A louver dryer with a cooling zone at the last section to

cool the dried hot sugar is used.

In the rotary louver dryer, sugar crystals are in partial fluidization by the action of the louvers

mounted on a rotating drum. Air passes a heater to give the optimum conditions for drying and

then is forced by a fan into the dryer. In the dryer, the air moves upward at about 0.5 m per

second through the screen and then through the sugar, leaving at the discharge end. The

countercurrent movement of the sugar and air in the dryer prevents the dry sugar dust from

mixing with the wet crystals. The dried and cooled sugar leaves the discharge end at an inclined

angle to the air discharge.

3.17 PACKAGING AND STORAGE

After the sugar leaves the dryer, it is ordinarily screened to remove very coarse or very fine

materials, or both, and is then either sent to bulk storage, or more usually is placed in packages

suitable for distribution to the trade and stored until required.

During bulk storage, sugar conditioning is also achieved. Sugar conditioning refers to holding

sugar in a current of adequate air for a certain period after the sugar is discharged from the

dryer so that the crystals can lose their bound water and reach the equilibrium moisture

content. (Sufficient time is needed to move bound water out of the crystals.) If bound water is

not removed and sugar is stored in a place without air ventilation, caking occurs. Therefore,

sugar must be conditioned to a safe temperature (about 25C) and moisture content (about

0.03%) in the cooler or in the silo with a complete ventilation system. The properties and the

amount of airflow through the crystals are important. Conditioned air with 20 to 25C and 55 to

60% relative humidity (RH) creates the best conditioning environment and corresponds to a

sugar moisture-content of about 0.03%. In addition, the airflow rate is also important to

achieve a complete conditioning operation and prevent condensation.


Page | 54

Scales: Automatic scales are normally used for all weighing, and although they are capable of

considerable accuracy, the filled packages must be check weighed at regular intervals, and

minor adjustments made to ensure continued accuracy.

Granulated-refined (GR) sugar is packed in different sizes from a 5 g (teaspoon) bag, called a

packet (for use in restaurants and other commercial places), up to 1000 kg. In general, sugar

packs (packages) are divided into two sizes:

Industrial size: Packs more than 10 kg

Retail size: Packs up to 10 kg


Page | 55

CHAPTER FOUR

4.0 MASS AND MATERIAL BALANCES

Basis: 85,000 Kg/ hr.

We have 300 working days in a year.

Analysis of beet without tare (typical washed beet)

Mass = 0.5- 2.0 kg

Density 105-1100 kg/m3

Bulk density = 650-700 kg/m3

Beet tare 2-8% on beet (OB), (Mosen Asadi 2007)

Average beet tare (non-beet material) of 5.2% is used in material balance.

4.1 STORE

The store keeps the raw beet temporarily to ensure continuity of supply to the cleaning section.

The period of storage is usually up to a maximum of 30 days. Also, temperatures are kept low

(1-30C) to avoid sugar losses due to temperature decomposition:

Sugar loss per day per ton beet (Ms)

𝑀𝑠 = 140 × 100.0343 ×𝑇 (Vukov, 1977)

T= temperature ℃

Assumptions:

Sugar loss on the beet during storage amount to 1.5% OB due to microbial action

Store 83,725 kg/hr raw beet

85,000 kg/hr raw beet

S2 S1

Storage


Page | 56

Table 4. 1 Mass balance for storage section

Components Input (kg/hr) Output (kg/hr)

Stream S1 S2

Raw beet 85,000 83,725

4.2 DRY SCREENING

In dry screening, the beets are pre-cleaned without using water just before being washed in the

beet washer. The purpose of this station is to remove any beet tare (Stones, sand and part of

the soil) that could otherwise enter the flume system and the beet washer with the beets so

that less wash water is needed later in the beet-washing process.

Assumptions:

1.7% OB containing stones, sand and soil are removed.

Table 4. 2 Mass balance around dry screener


Stream S2 S3 S4

Raw beet 83,725 82,302 -

Stones, Sand & Soil - - 1,423

Total 83,725 82,302 1,423

S4

S3 S2

1,423 kg/hr Stones



Dry screening


Page | 57

4.3 FLUME

The fluming system uses wet system (water) to transport beets from the dry screening area to

the next station (stone and trash separation).

Assumption:

Sugar loss of 0.4% OB to water (Fort Collins, 1982)

400% OB of water is introduced in the flume (Fort Collins, 1982)

Table 4. 3 Mass balance around flume

4.4 STONE SEPARATOR

The mixture of beets and water in the flume goes through the stone separator for removing

stones. These coarse impurities must be removed completely to prevent damage to the beet

slicers.

Assumptions:

1 % OB of stones is removed


Stream S3 S5 S6

Raw beet 82,302 - 81,890

Water - 329,208 329,620

Total 82,302 329,208 411,510

Flume

329,208 kg/hr Water

S5 Purity = 100%

Raw beet = 82,302 kg/hr

Water = 329,620 kg/hr

Total = 411510 kg/hr

82,302 kg/hr raw beet S6

S3 Purity = 60%

Flume

Stones = 1,232 kg/hr

Raw beet = 82,302 kg/hr


Total = 411,922 kg/hr S8

S7 S6 Raw beet = 81,070 kg/hr


Total = 410,690 kg/hr

Stone separator


Page | 58

Table 4. 4 Mass balance around stone separator

4.5 TRASH SEPARATOR A trash separator removes trash (sugar beet leaves and weeds) flowing with the beets.

Assumptions:

0.5% OB of trash is removed

Table 4. 5 Mass balance around trash separator

Components Input(kg/hr) Output(kg/hr)

Streams S6 S8 S9

Beet 81,070 80,664 -

Water 329,620 329,620 -

Trash - - 406

Total 410,690 410,284 406

4.6 WASHER

The beets are lifted from the fluming channel to feed the beet washer for the second last

Cleaning. Soil and clay stuck on the beets, and sand are washed away. Beet washing also

removes most of the microbes coming with the beet.


Stream S6 S7 S8

Raw beet 82,302 81,070 -

Water 329,620 329,620 -

Stones - - 1,232

Total 411,922 410,690 1,232

Water=329,620kg/hr

Beet=81,070kg/hr

Total=410,690kg/hr

S10

S9 S7

Trash separator

Trash=406 kg/hr

Water=329,620kg/hr

Beet=80,644kg/hr

Total=410,284kg/hr


Page | 59

Assumptions:

2.1 % OB of tare is removed.

10 % OB of water is left with the material exiting the washer.

Table 4. 6 Mass balance around washer


Streams S9 S11 S12

Beet 80,664 79,211 -

Water 329,620 7,921 321,699

Tare+ beet particles - - 1453

Total 410,284 87,132 323,152

4.7 DEWATERING SCREEN

The main job of dewatering screen is to supply the slicing station with a steady flow of clean

beets. At this station fresh water is introduced resulting in further removal of soil and clay on

beet.

Assumptions:

Washer

Water=329,620kg/hr

Beet=80,644kg/hr

Total=410,284kg/hr

S12

S11 S9

Mud, small beet particle & small trashes= 1,453 kg/hr

Water= 321,699 kg/hr

Total= 323,152kg/hr

Water=7,921 kg/hr

Beet=79,211 kg/hr

Total=87,132 kg/hr


Page | 60

150% OB of fresh water is introduced into the dewatering screen.

98% of the water from the washer station is removed

0.3% OB of tare (mud and small trashes) and small beet particles are removed from the

incoming beet.

Table 4. 7 Mass balance around dewatering screen

Components Input (kg/hr) Output(kg/hr) Streams S11 S13 S14 S15

Beet 79,211 - 78,973 - Water 7,921 - 158 -

Fresh water - 118,817 - - Discharge water - - - 126,580

Tare+ beet particles - - - 238 Total 87,132 118,817 79,131 126,518

Water=7921 kg/hr

Beet=79,211 kg/hr

Total=87,132 Kg/hr

Fresh water= 118817 kg/hr

S13

Dewatering screen

S15

S14 S11

Mud, small beet particle & small trashes= 238 kg/hr

Discharge water= 126580 kg/hr

Total= 126,518kg/hr

Water=158 kg/hr

Beet=78,973 kg/hr

Total=87,131 kg/hr


Page | 61

4.8 CHIP SEPARATOR

In the chip separator small, broken particles of beets that could not be separated in the earlier

stages of operation are recovered. Water discharged from the washer and dewatering screen is

pumped through a chip separator with 0.2mm screen where small, broken particles are

retained.

Assumptions:

Chip separator has an efficiency of 90%

99.9% of water is removed

S17

Tare + small beet particles= 1,691 Kg/hr

Water= 448,279 Kg/hr

Total= 449,970 Kg/hr

Water= 321,699Kg/hr

Tare + small beet particles=1453 Kg/hr

Total = 323,152 Kg/hr

Tare+ small beet particle = 238 Kg/hr

Discharge water= 126580 Kg/hr


S12

Chip separator

S18

S15

Water=448 Kg/hr

Beet=1,522 Kg/hr

Total=1970 Kg/hr

S16

Tare + small beet particles= 169 Kg/hr

Water= 447,831 Kg/hr



Page | 62

4.9 SLICER

In the slicing station, a belt conveyor continuously delivers clean beets from the beet washer to

the beet hopper (a cone-shaped container) that feeds the beets to the slicers. The main

function of the beet-slicing operation is to improve the diffusion operation and the removal of

sucrose from the beets. The beets are reduced to small sizes known as cossettes of uniform

width, 4 mm thick and 40 mm long (Mosen Asadi, 2007).

Assumption:

Negligible mass loss of beet


Streams S12 S15 S16 S17 S18

Water 321,699 126,580 448,279 448 447,831

Tare+ small beet particles.

1,453 238 1,691 - 169

Broken beet - - - 1,522 -

Total 323,153 323,153 449,970 1,970 480,000

Slicer Water= 606 kg/hr

Beet =80,495 kg/hr


Water=606 kg/hr

Cossettes=80,495 kg/hr

Total=81,101 kg/hr

Water= 448kg/hr

Beet =1,522kg/hr

Total = 1,970 kg/hr

Water= 158kg/hr

Beet =78,973kg/hr


S17

S20 S14 S19

Slicer

Table 4. 8 Mass balance around chip separator


Page | 63

Table 4. 9 Mass balance around slicer

Components Input(kg/hr) Output(kg/hr) Streams S14 S17 S19 S20

Water 158 448 606 606 Beet 78,973 1,522 80,495 -

cossettes - - - 80,495 Total 79,131 1,970 81,101 81,101

4.10 DIFFUSER

In diffusion station, the sliced beets are kept in contact with hot water (70°C) for about an hour

to diffuse the juice from the beet cells. The hot water is introduced counter currently. As water

moves ahead, it collects sugar (sucrose) and non-sugar (non-sucrose) from the cossettes and

become a concentrated impure sucrose solution known as diffusion juice. Also in this station

the following are added:

Sulphur (iv) oxide

Calcium chloride

Antifoaming agent

Assumptions (Mosen Asadi, 2007):

Diffusion juice contains 85% water and 15 % dry substance (DS)

The dry substance consists of 86.5% sucrose, 1.0 % insolubles and 12.5 % non-sucrose.

100g/ton. Of antifoaming agent is added.

0.23kg/ton. Of SO2 is added.

0.125% OB of CaCl2 is added

96% of sucrose is removed based on 15% sucrose content in cossettes.

Diffusion water content is based on the following formula

𝑀𝐷𝐼𝐹𝐹 .𝑊 = 𝑀𝐷𝐼𝐹𝐹 .𝐽 + 𝑀𝑃𝑃 −𝑀𝐶

Where:

Mc=Mass of cossettes

MDIFF.J =Mass of diffusion juice (18.4%OB)

MPP=Mass of pressed pulp (111% OB)


Page | 64

Table 4. 10 Mass balance around diffuser


Streams S20 S21 S22 S23 S24 - S28 S26 S27

Cossettes 80,495 - - - - - - - -

Water 606 - - - - - - 75,947 -

SO2 - 24 - - - - - - -

Antifoaming

agent

- - 8 - - - - - -

CaCl2 - - - - 100 100 - - -

Diffusion water - - - 23,665 - 23,665 - - -

Wet pulp water - - - - - - 63,583 - 72,388

Dry substance - - - - - - 1,298 - 8,043

Sucrose - - - - - - - 11,593 -

Non sucrose - - - - - - - 1,673 -

Insolubles - - - - - - - 134 -

Total 81,101 24 8 23,665 100 23,765 64,881 89,349 80,431

S22

S23

Wet pulp Water=72,388 kg/hr

Dry substance= 8,043 kg/hr

Total= 80,431 kg/hr

Wet pulp Water=63, 583 kg/hr

Dry substance= 1,298 kg/hr

Total= 64,881 kg/hr

S24

S20

S21

S25

S27

S28

S26

Diffusion water= 23665 kg/hr

SO2= 24 kg/hr

Cossettes= 80,495 kg/hr

Water= 606 kg/hr

Total= 81,101 kg/hr

Anti foaming agent=8 kg/hr

Water=75,947 kg/hr

Sucrose=11,593 kg/hr

Non sucrose=1,675 kg/hr

Insolubles = 134 kg/hr

Total= 89,349 kg/hr

CaCl2=100 kg/hr

Diffuser


Page | 65

4.11PULP PROCESSING

In this section, the quantity of water in the pulp emanating from the diffuser is reduced.

Assumptions:

The quantity of water is reduced from 90% to 60% (Mosen Asadi, 2007).

Table 4. 11 Mass balance for pulp processing

4.12 JUICE PURIFIER

Juice purification is used to remove certain non-sugars, suspended particles and colloids from

the juice to produce a high purity, colloidal-free and low-color juice with minimum hardness. In

the juice-purification station, the thin juice goes through liming followed by carbonation

substations.


Stream S27 S28 S29

Water 72,388 63,583 8,805

Dry substance (DS) 8,043 1,298 6,745

Total 80,431 64,881 15,550


DS = 1,298 kg/hr



DS = 8,043 kg/hr


S28

S29 S27

Water = 63,583

DS = 1298

Total = 64881

S27

S27

Water = 8,805 kg/hr

DS = 6,745 kg/hr


Pulp Processing


Page | 66

4.12.1 Liming

Milk of lime (MOL) is added to the heated diffusion juice to precipitate and destabilize the

nonsugars.


35% of non-sugars is removed

4% OB of milk of lime is used

Invert sugars forms the major fraction of the nonsugars removed.


Stream S26 S30 S31

Water 75,947 - 76,181

Sucrose 11,593 - 11,593

Non-sucrose 1,675 - 1,089

Insoluble 134 - 967

Milk of lime - 536 55

Total 89,349 536 89,885

MOL= 536 kg/hr S31 S30

S26

Water= 75,947 kg/hr

Sucrose= 11,593 kg/hr

Non sucrose= 1,675 kg/hr

Insoluble= 134 kg/hr

Total= 89,349 Kg/hr

Water= 75,947 kg/hr




Total= 89,349 kg/hr

Liming

Water= 76,181 kg/hr


Non-sucrose= 1,089 kg/hr


MOL= 55 kg/hr

Total= 89,885 kg/hr

Table 4. 12 Mass balance for liming


Page | 67

4.12.2 Carbonation

CO2 is added to diffusion juice to precipitate excess lime and adjust pH and the alkalinity of the juice

Assumptions:

0.7 % OB( to purification section) CO2 is used

Table 4. 13 Mass balance for carbonator


Stream S31 S32 S33 S34

Water 76,181 - 76,194 -

Sucrose 11,593 - 11,593 -

Non-sucrose 1,089 - 1,089 -

Insoluble 967 - 1,041 -

Milk of lime 55 - - -

CO2 - 94 - 62

Total 89,885 94 89,917 62

4.13 FILTRATION

After the first and second carbonations, the precipitated calcium carbonate (PCC) and non-

sucrose substances (non-sugars) are filtered to produce clear juice, known as thin juice.

In the filtration section, the raw juice is passed through membrane filter press followed by

rotary drum filter which brings about the separation of PCC and non-sugars from clear juice.

CO2= 62 kg/hr

S34

CO2= 94 kg/hr

Water= 76,181 kg/hr



Insolubles= 967 kg/hr

MOL= 55 kg/hr

Total= 89,885 kg/hr

S33 S31

S32

Carbonation

Water= 76,194 kg/hr

Sucrose= 11,593kg/hr


Insolubles= 1,041 kg/hr

Total= 89,917 kg/hr


Page | 68

Assumptions:

The carbonation lime residues produced by filter press contains 70% solid content and

that produced by rotary drum filters has about 50% solid content.

Negligible amount of sucrose and non-sucrose are lost during filtration.

4.14 EVAPORATOR

This is unit is the heat center and is concerned with concentrating the thin juice.

Assumptions:

In this operation, thin juice with about 15% dry substance (DS) is concentrated to

produce a thickened juice with about 60% DS. (Mosen Asadi, 2007)


Stream S33 S35 S36 S37 S38

Water 76,070 76,194 - 76,194 -

Sucrose 11,593 11,593 - 11,593 -

Non sucrose 1,089 1,089 - 1,089 -

Insolubles 1,041 312 729 156 156

Total 89,917 89,188 729 89,032 156

Water= 76,194 kg/hr



Insolubles= 1,041 kg/hr

Total= 89,917 kg/hr


Water= 76,194 kg/hr




Total= 89,136 kg/hr

Water= 76,194 kg/hr




Total= 89,188 kg/hr

S35

S33

S38

S36

S37


Rotary drum

Filter press

Table 4. 14 Mass balance for filter system


Page | 69

Scale formation is negligible, hence no loss of non-sucrose content of thin juice.

No sugar loss during evaporation

Table 4. 15 Mass balance on evaporator

Component Input (kg/hr) Output (kg/hr)

Stream S39 S40 S41

Water 76,194 67,635 8,559

Sucrose 11,593 - 11,593


Insoluble 156 - 156

Total 89,032 67,635 21,397

4.15 CRYSTALLIZER

The crystallizer carries a mass transfer of sugar molecules from the syrup to the solid particles

to form crystals. Crystallization system involves both the boiling system and the centrifuging.

4.15.1 Boiler system

Boiling concentrates the syrup under vacuum (at about 74˚C) to the desired DS and super-

saturation for seeding.


Evaporator Evaporator

S40


Sucrose = 11,593 kg/hr

Non-sucrose = 1,089 kg/hr

Insoluble = 156kg/hr

Total =89,032 kg/hr

S39


S41

Water = 8,559 kg/hr



Insoluble = 156 kg/hr

Total = 21,397kg/hr

Evaporator


Page | 70

95% water is lost in the evaporation in the boiler

No sugar losses in the process

Amount of seeding is negligible

Purity of crystals attained is 100%

Table 4. 16 Mass balance around boiling pan

4.15.2 Centrifuge

The centrifugal station is used to separates the sugar crystals from the mother liquor (liquid

around the crystals) in the massecuite by using centrifuges.


Molasses purity is 58%

3% (per weight of massecuite) wash water is used.

82% 0f crystals are separated.


Streams S41 S42 S43

Water 8,559 8,131 428

Sucrose 11,593 - 11,593

non-sucrose 1,089 - 1,089

insoluble 156 - 156

Total 21,397 8,131 13,266

S42

Water 428 kg/hr


Non-sucrose = 1,089 kg/hr.



Water = 8,559 kg/hr


Non-sucrose = 1,089 kg/hr.



Water = 8,131 kg/hr.

S41 S43

Boiling Pan


Page | 71

11% of water remains with the sugar crystals

Table 4. 17 Mass balance around centrifuge



Water 428 398 91 735

Sucrose 11,593 - 9,533 2,060

Non-sucrose 1,089 - - 1,089

Insoluble 156 - - 156

Total 13,266 398 9,624 4,040

Molasses


Water = 735kg/hr

Non- sucrose =1,089 kg/hr


Total = 4,040 kg/hr

Water = 398kg/hr

Water 428 kg/hr





S46

S45

S47

S44


Water = 91 kg/hr

Total =9,624 kg/hr

Centrifuge


Page | 72

4.16 DRYER

In this unit, the moisture content of sugar is reduced to about 0.05% (Mosen Asadi, 2007)

Table 4. 18 Mass balance around dryer

Component Output (kg/hr) Output (kg/hr)

Stream S46 S48 S49

Water 91 46 45

Sucrose 9,533 - 9,533

Total 9,624 46 9,578


Water= 91kg/hr

Total= 9,624 kg/hr

S49

S49


Water= 45 kg/hr

Total= 9,578 kg/hr

Total = 9,578 Kg/hr

Water = 45 kg/hr


Total = 9,578 kg/hr

S48

S46

S46

Water vapour = 46 kg/hr

Dryer Dryer


Page | 73

Pulp water (70°C) 80,431 kg/hr

Steam (140°C) 7,802 kg/hr

Cossettes (25°C) 81,101 kg/hr

Diffuser water (70⁰C) 23,266 kg/hr

Diffuser Thin juice (70⁰C)

89,349 kg/hr

Wet pulp (70℃) 80,431 kg/hr Steam (140⁰C)

7,802 kg/hr

Pulp water (65°C) 64,881 kg/hr

QL

5.0 ENTHALPY BALANCES

5.1 ASSUMPTIONS

A reference temperature of 25℃ is used in the analysis

Correlation for the heat capacity of water as a function of temperature is given:

𝐶𝑝 𝑀𝑜𝑙𝑒−1 .𝐾 = 32.243 + 19.239 × 10−4𝑇 + 10.555 × 10−6𝑇2 − 3.59 × 10−9𝑇3

Steam for heating is available at 4 bar ( low pressure boiler)

Latent heat steam at 4 bar = 2133.40 kJ/kg.

The heat capacity of the streams do not vary with temperature

The specific heat of the juice is calculated using the dry substance of the juice (DSjuice)

based on the formula below:

𝐶𝑝 ,𝑗𝑢𝑖𝑐𝑒 = 4.187 (1 − 0.006𝐷𝑆𝑗𝑢𝑖𝑐𝑒 ) 𝑘𝐽/𝑘𝑔.℃

Enthalpy changes associated with precipitation reaction is negligible

5.2 DIFFUSER

In this unit, the sliced beets are kept in contact with hot water (700C) for about an hour to

diffuse the juice from the beet cells. The hot water is introduced counter currently.

Cp of thin juice = 4.1832 kJ/kg.℃

Cp of diffusion water = 4.187 kJ/kg.℃

Cp of wet pulp = 4.184 kJ/kg.℃

Sensible heat loss = 0.04%


Page | 74

5.3 HEAT EXCHANGER 1

This unit is used to raise the temperature of thin diffusion juice from 70°C to 86°C for optimal liming process.

Cp of thin juice = 4.187 kJ/kg.℃

Losses=0.06%

Components Input (kJ/hr) Output (kJ/hr)

Thin juice 16,819,413 23,997,354

Heat provided by steam 7,182,250 -

Losses - 4,309

Total 24,001,663 24,001,663


This unit is used to raise temperature from 86°C to 90°C for optimal carbonation process.

Components Input (kJ/hr) Output (kJ/hr)

Cossettes 0 -

Thin juice - 16,819,413

Diffusion water 4,458,840 -

Wet pulp - 15,143,548

Pulp water 10,864,972 -

Heat supplied by steam 16,645,808 -

Losses - 6,658

Total 31,969,620 31,969,620

Table 5. 1 Enthalpy balance around diffuser

Thin juice (70℃) 89,349 kg/hr

Steam condensate (80℃) 3,011 kg/hr


Steam in (140℃) 3,011.91kg/hr

QL

Heat Exchanger 1

Table 5. 2 Enthalpy balance around Heat Exchanger 1


Page | 75

Heat Exchanger 2

Thin juice (900C)

89,032 kg/hr

Condensate steam (90℃) 954 kg/hr

QL

Thin juice (86°C) 89,032 kg/hr

QL

Evaporator

Evaporated water = 67,635 kg/hr

Saturated steam in (140°C) 77,472 kg/hr

Thick juice (130°C) 21,397 kg/hr

Steam condensate out (140°C) 77,472 kg/hr


Steam (140°C) 954 kg/hr

Cp of water = 4.187 KJ/kg.℃

Cp of thin juice = 4.1832 KJ/kg.℃

Losses = 0.04 %

5.5 EVAPORATOR

This is unit is the heating center and is concerned with concentrating the thin juice. In this

operation, thin juice with about 15% dry substance (DS) is concentrated to produce a thickened

juice with about 60% DS.

In this unit, the temperature of the diffusion is raised from 90°C to 130°C by using saturated

steam at 4 bars from the low pressure boiler. Saturated steam at 140°C was used.


Component Input (kJ/hr) Output (kJ/hr)

Thin juice 21,973,881 24,208,513

Heat provided by steam 2,235,526 -

Losses - 594

Total 24,209,407 24,209,407


Page | 76

Cooling water out (80°) 15,379 kg/hr

Exchanger 3

Cooling water (25°C) 15,379 kg/hr


QL


Table 5.4 Enthalpy balance around the Evaporator

𝑇𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 𝑝𝑟𝑜𝑣𝑖𝑑𝑒𝑑 𝑏𝑦 𝑠𝑡𝑒𝑎𝑚 = 166,162,456 kJ/hr

𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 = 𝑄

(𝐻𝑆 −𝐻𝐶)=

166,162,456

2144.8= 77,472 𝑘𝑔/𝑟


This unit reduces the temperature from 130°C to 90°C to facilitate the decolourization process

and to stop milliard reactions which lead to colour formation.

Losses = 0.04%

Cp of thick juice = 4.1719 kJ/kg. °C


Diffusion Juice 24,208,513 9,372,945

Evaporated water - 180,998,023

Steam 166,162,455 -

Total 190,370,968 190,370,968


Page | 77

Heat Exchanger 4

Cooling water (25°C) 18,268.18 kg/hr

Cooling water (60°C) 18,268.18 kg/hr



QL


This unit reduces the temperature further to 60°C to avoid melanization reaction which leads to

brown colour formation.

Losses = 0.04%

Cp of thick juice = 4.1719 kJ/kg.°C



Thick Juice 9,372,945 5,829,837

Cooling water 0 3,541,690

Losses - 1,417

Total 9,372,945 9,372,945

Table 5. 6 Enthalpy balance around Heat Exchanger 4.


Thick Juice 5,802,299 3,124,315

Cooling water 0 2,676,377

Losses - 1,606

Total 5,802,299 5,802,299


Page | 78

Boiling pan

Saturate steam (140°C) 9,153.47 kg/hr

Evaporated water (74°C) 8131 kg/hr

Massecuite (74°C) 13266 kg/hr

Standard liquor (60°C) 21,397 kg/hr

Steam condensate (140°C) 9,153.47 kg/hr

QL

5.8 CRYSTALLIZATION

5.8.1 Boiling pan

Boiling concentrates the syrup under vacuum (at about 74˚C) to the desired DS and super-

saturation for seeding.

Solubility of sucrose (at 90% purity and 74°C) = 3.36 kg sucrose/kg water

Heat of crystallization = 136.36 kJ/kg (Kilmartin and Van Hook, 1950)

Losses = 0.04%

Hv, latent heat of vaporization of steam at 74°C = 2635.3 kJ/kg

Enthalpy of steam in at 140°C = 2733.9 kJ/kg

Enthalpy of steam condensate out at 140°C = 589.1 kJ/kg

Cp of massecuite = 4.1627 kJ/kg. °C


Page | 79

Centrifuge

Sugar (60℃) 9,624 kg/hr

Molasses (60℃) 4,040 kg/hr

Massecuite (74℃) 13,266 kg/hr

QL

Wash water (80℃) 398kg/hr

5.8.2 Centrifuge

The centrifugal station is used to separates the sugar crystals from the mother liquor (liquid

around the crystals) in the massecuite by using centrifuges.

Cp of massecuite = 4.162 kJ/kg.℃

Cp of molasses = 1.775 kJ/kg.℃ (Rovillard E. E. A, 1985)

Cp of wash water = 4.187 kJ/kg.℃

Cp of wet sugar (Bubnik et al., 1995)

𝐶𝑝 = 4.187 −𝐷𝑆 × 0.0297 − 4.6 × 10−5 × 𝑇 + 7.5 × 10−5 × 𝐷𝑆 × 𝑃

Where: DS = Dry substance content (for pure sucrose solutions, DS = S)

T = temperature (℃)

P = purity (for solutions P=100)

Cp of sucrose = 2.15 kJ/kg.℃

Component Input (kJ/h) Output (kJ/h)

Standard liquor 3,124,315.05 -

Massecuite - 2,705,896.53

Evaporated water - 21,427,624.30

Crystals 1,384,691.04 -

Steam 19,632,367.69 -

Losses - 7,852.95

Total 24,141,373.78 24,141,373.78

Table 5. 7 Enthalpy balance around a boiling pan


Page | 80

5.9 DRYER

In this unit, the moisture content of sugar is reduced to about 0.05% (Mosen Asadi, 2007)

Cp, Air= 1.006 kJ/kg.℃

Cp, Sugar =2.15 kJ/kg.℃

Latent heat of vaporization of water = 2140 kJ/kg. ℃

Losses = 0.004%

Table 5. 8 Enthalpy balance around Centrifuge


Massecuite 2,705,896 -

Wash water 91,653 -

Sugar - 1,723,050

Molasses - 1,046,523

Losses - 27,975

Total 2,797,549 2,797,549

Table 5. 9 Enthalpy balance around the Dryer

Components Input (kJ/hr) Output(kJ/hr)

Wet sugar 72,4206 -

Hot air 1,129,863 826,566

Dry sugar - 926,768

Water vapour - 98,716

Losses - 121

Total 1,854,070 1,854,070

QL

Wet sugar (60°C) 9,624 kg/hr

Dry sugar (70°C) 7,579 kg/hr

Dryer

Hot air (80°C) 14,975 kg/hr

Hot air + water vapour (80°C) 15,021 kg/hr


Page | 81

CHAPTER SIX

6.0 EQUIPMENT SIZING AND SPECIFICATION

The sizing and specification of various equipment used in beet sugar processing plant, are

shown in the table below.

Table 6. 1 Equipment Specifications

1. Hopper Equipment code H1

Service Temporal storage of sugar beets.

Type Wedged shaped with elongated outlet.

Material Stainless steel

Capacity 23.6 m3

Length 12.4m

Width 6.5m

Height 3.8m

Number 1

2. Belt conveyor 1 Equipment code BC1

Service Conveying raw sugar beets from the hopper to the screen.

Belt width 0.5m

Belt inclined length 6m

Belt speed 9.2m/s

Material Two-ply polyester fabric with polyurethane.

Belt inclination 40°

Driver motor type 0.25 HP shaft-mounted gear motor

3. Screen 1 Equipment code SR1

Service Removal of loose soil and small stones from the sugar beet.

Type Screener-Rectangular Deck

Length 3.8m

Width 1.5m

Material Stainless steel 304

Screen action Vibratory/screen action

4. Stone Separator Equipment code SS

Service Separation of large stones(rocks) from sugar beets

Type Bucket stone separator

Length of chain 4.75m

Width 1.25m

Height 1.88m


Page | 82

Material Carbon steel

Size of the opening 0.1m

5. Trash Separator Equipment code TS

Service Removal of trash flowing with the beets.

Type Rake trash separator

Material Carbon Steel

Length of chain 7.5m

Speed of the chain 0.2m/s

6. Beet pump Equipment code BP

Service Pumping of the flume from the trash separator to the beet washer

Type Rotary lobe pump

Power 50.1 kWhr/tone feed

Material Cast iron

7. Washer Equipment code WS

Service Removal of the soil stuck on the beets.

Type Arm washer

Material Carbon Steel

Capacity 34.36m3

Diameter 2.5m

Length 7m

Arm speed 5 rpm

8. Screen 2 Equipment code: SR2

Service Separation of beets from water and sprinkling with clean water.

Type Screen-Rectangular Deck


Length 2.5m

Width 1.5m


Service Conveying of beets from the dewatering screens to the slicer.

Belt width 0.5m


Belt speed 8.8m/s




10. Screen 3 Equipment code SR3

Service Recovery of broken beets.



Page | 83


Length 2.5m

Width 1.5m

Screen action Vibratory/shaking action


Service Conveying recovered broken beets from recovery screens to belt conveyor 2.

Belt width 0.5m


Belt speed 8.8m/s




12. Slicer Equipment code SL

Service Cutting of beets into long, thin strips(cossettes)

Type Drum slicer

Slicing capacity 3200 tonnes/day

Number of knives boxes

22

Number of knives per box

6

Length of knives 200mm

Width of knives 5.6mm



Service Conveying the cossettes to the diffuser

Belt width 1m


Belt speed 100m/min.

Material Two-ply polyester fabric with polyurethane cover.



14. Diffuser Equipment code DF

Service Contacting of sliced beets with hot water to diffuse the juice out of the beet cells.

Type Sliver-DDS slope diffuser

Description U-shaped vessel, inclined to the horizontal, with two rotating horizontal screws.


Page | 84

Inclination 11°

Speed of screw 0.9 rpm

Capacity 2,145 tonnes/day


15. Heat Exchanger 1 Equipment code HE1

Service Raising the temperature of diffusion water to 70°C

Type Plate and frame

Equivalent length 1.2m

Equivalent width 0.5m

Area 70 m2

Number of plates 400

Material for plate Stainless steel 316

Material for frame Carbon steel


Service Raising the temperature from 70°C to 86°C for optimal liming process.




Area 80m2




17. Lime Tank Equipment code LT

Service Addition of milk of lime to heated diffusion juice to precipitate and destabilize the non sugars.

Type Dome topped with a stirrer

Holding time 30 minutes

Capacity 26.39m3

Diameter 2.56m

Height 5.51m


Number 2


Service Raising the temperature from 86°C to 90°C for optimal carbonation.


Equivalent length 1m


Area 50m2



Page | 85



19. Carbonation Tank Equipment code CT1

Service Addition of CO2 to the diffusion juice.



Capacity 23.86m3

Diameter 2.4m

Height 4.8m


Number 3

20. Rotary Drum Filter Equipment code RDF

Service Removal of mud from thin diffusion juice.

Area 23.52m2

Diameter 2m

Height 3.74m


Number 3


Service Maintaining temperature at 90°C for optimal second carbonation process.




Area 70m2




Number 2

22. Press Filter Equipment code PF

Service Removal of solid particles to produce a clear thin juice (safety filtration).

Area 12m2

Thickness of frame 20mm

Number of frames 6

Filtration time 3136 seconds


Flow rate 0.0235 m3/s

Material for plate and frame

AISI 321 Stainless steel

Material for rack AISI 304 Stainless steel

Material for filter Polypropyrene


Page | 86

cloth

Number 2

23. Sulphitation Tank Equipment code ST

Service Addition of SO2 for decolourization.

Type Dome topped with agitator


Capacity 23.54m3

Diameter 2.465m

Height 5m


Number 1

23. Syrup Tank 1 Equipment code SYT1

Service Holding of thin diffusion juice temporarily.

Type Dome topped


Capacity 14.5m3

Diameter 3m

Height 6m


Number 1

24. Evaporator Equipment code EV

Service Concentration of the thin juice.

Type Four effect evaporator

Area 47.26m2

Capacity 14.5m3

Capacity per effect 17,806.4 kg/hr


25. Syrup Tank 2 Equipment code SYT2

Service Holding thick juice temporarily

Type Dome topped


Capacity 14.5m3

Diameter 1.35m

Height 5.4m


Number 2

26. Melter Equipment code MLT

Service Dissolving intermediate sugar crystals.

Type Cuboidal shaped


Capacity 14.5m3

Length 2.4m


Page | 87

Width 2.4m

Height 2.4m


Number 1

27. Boiling Pan Equipment code BP

Service Concentrating syrup under vacuum.

Type Vacuum boiling pan

Area 26.45m2

Capacity 14.5m3

Capacity per effect 7,132.3 kg/hr


28. Mixer Equipment code MX

Service Holding thick juice temporarily

Type Dome topped tank with agitator.


Capacity 8.5m3

Diameter 1.75m

Height 3.5m


Number 3

29. Centrifuge Equipment code CF

Service Separation of sugar crystals from mother liquor

Type Continuous centrifuge.

Speed 1200 rpm

Loading capacity per cycle

2000 kg

Diameter 1m

Height 1.25m


Number 3

30. Screw Conveyor 1 Equipment code SC1

Service Conveying of high green syrup from the first centrifuge to the second boiling pan

Type LS screw conveyor.

Speed 1200 rpm

Conveying length 2.5m

Spiral diameter 0.2m

Screw speed 50 rpm

Standard power 1.5 kW/2 HP

Material Stainless steel AISI 304



Page | 88

Service Conveying of low green syrup from the second centrifuge to the third boiling pan


Speed 50 rpm



Screw speed 50 rpm




Service Conveying of molasses from the third centrifuge to the molasses exhaustion unit.


Speed 50 rpm



Screw speed 50 rpm




Service Conveying of sugar from the first centrifuge to the rotary drum dryer.


Speed 75 rpm

Conveying length 8m


Screw speed 75rpm



34. Feeder

Equipment code FD

Service Directing and controlling flow of sugar to the dryer.

Area 1.03m2

Diameter 1.15m

Cylinder height 4.6m

Height of bottom frustrum

1m

35. Rotary dryer Equipment code RD

Service Reducing moisture content of sugar.

Area 35.03m2

Diameter 2.06m


Page | 89

Length 10.51m

Retention time 15.71 minutes

Solid hold up 9%

Height of flights 0.2575m

Width of flights 0.1262m

Number of flights 13

Peripheral speed of the shell

4.06rpm

Shell thickness 11.56mm

Drum orientation 4°


Service Raising temperature of air to 100°C

Type Shell and tube

Area 16.65m2

Length 8m

Shell diameter 171mm

Tube diameter 15.75mm



Service Conveying of dried sugar to the size separation screens.


Speed 70 rpm

Conveying length 10m




38. Screen 4 Equipment code: SR4

Service Separating oversized and undersized sugar particles.


Length 4m

Width 2m

Inclination 40°

Rate of sugar movement

1.4m/s

Screen action Vibratory/shaking action



Page | 90

CHAPTER SEVEN

7.0 EQUIPMENT DESIGN

7.1 DESIGN OF A ROTARY DRUM DRYER BY MOSE O. LAMECK- CPE/41/08

7.1.1 INTRODUCTION

Drying

Drying of solids is the removal of relatively small amount of water or other liquids in the solid;

so as to reduce the amount of liquid to an acceptable low value. Drying is usually done prior to

the packaging after the final overall process.

The removal of the liquid from the solids by drying is achieved by thermal vaporization. In

contrast to the vaporization where liquid is removed by boiling; thermal vaporization uses air to

remove water in the form of vapour.

Drying is usually governed by the principle of transport of heat and mass. When a moist solid is

heated to an appropriate temperature, moisture vaporizes at or near the solid surface and the

heat required (sensible heat and heat of vaporization) for drying is usually supplied by a hot

gas. As soon as some of the surface moisture vaporizes, more moisture is transported from

inside the solid to its surface. Moisture can be removed from within a solid by a variety of

mechanisms depending upon the nature and type of the solid and its state of agglomeration.

The mechanism of moisture transport in different solids may be broadly classified into:

transport by capillary forces

liquid diffusion

pressure induced transport

vapour diffusion

The mechanism that dominates depends on the nature of the solid, its pore structure and the

rate of drying. In granular solids like sugar, moisture transport occurs due to capillary forces so

long as there is enough moisture on the bulk of the solid.


Page | 91

Drying of sugar

The deterioration of sugar is retarded and the loss in the test is reduced if the moisture content

of the sugar is reduced. The water content of raw sugar is generally within the range 0.5-2%.

Within the dryer, this may be reduced to between 0.2- 0.5%. This gives saving in two directions:

the sugar keeps better

the polarization and the titre increases immediately in proportion to the water removed, and if

for example the polarization increases from 97.8° to 98.2°, the financial gain so realized is much

greater than the loss of weight due to the water evaporated.

The enthalpy present in wet sugar entering the sugar dryer sometimes is usually sufficient to

dry itself to the desired level without need for additional heat. But, in normal operation,

additional heat is provided in form of hot air to ensure that there is sufficient enthalpy to

achieve the desired drying.

7.1.2 ROTARY DRUM DRYER

A typical adiabatic counter current air heated rotary drum dryer is commonly used in drying of

wet sugar. A rotary drum dryer consists of a slowly rotating, slightly inclined cylindrical shell fed

with the moist sugar at the upper end. The sugar flow along the rotating shell gets dried and

leaves the dryer at the lower end.

Supply of heat to the wet solid may be done directly or indirectly. Accordingly, a rotary dryer is

called ‘direct heat rotary dryer’ or ‘indirect heat rotary dryer’. In a dryer of the former type, the

wet solid is dried in direct contact with a hot gas flowing parallel or counter current with the

wet solid. In an indirect heat dryer, on the other hand, heat is supplied through the shell wall of

the dryer by a hot flue flowing outside. A low flow rate of air is maintained within the shell to

carry away the evaporated water.

For drying of sugar, direct heat rotary dryer with counter current flow of hot air is used.


Page | 92

Why rotary drum dryer

There are different types of dryers which can be used in the drying of sugars. They include:

rotary louver dryer, rotary tray dryer, fluidized bed dryer and rotary drum dryer.

The following salient features of rotary drum dryer, justifies why it qualifies to be used over the

other types of dryers. They include:

Ideally suited for large capacity applications and uneven particle size distribution.

Continuous operation and versatile application.

Low operating & maintenance cost.

Low energy consumption.

Dry and moisture control, minimum up to 5% or less, and meet the material widely.

Reliable, simple operation, convenient maintenance, safe, and durable.

Figure 7. 1 Schematic picture of a direct-heat counter current rotary dryer


Page | 93

Construction and operating features of a rotary drum dryer

Figure 7. 2 Countercurrent rotary drum dryer assembly

The major parts of a direct heat counter current rotary dryer assembly are shown in the figure

above. The shell is made of a suitable metal or alloy. The major ‘internals’ are the ‘flights’

running along the shell of the dryer. It is essential to keep the solid mixed up as it flows in order

to avoid agglomeration or formation of lumps.

The flights do this job. As the shell rotates, the flights lift the flowing solid and shower it in the

air stream so as to avoid agglomeration. This also ensures a good contact between the solid and

the hot gas and continuously exposes the solid so that drying of the particle occurs uniformly.

The flights project radially from the shell wall.

The operating features of a rotary drum dryer are described as follows:

a. Flow types

Countercurrent flow which is used in the design of this rotary dryer ensures more uniform

distribution of the temperature driving force along the shell; there is a substantial temperature

difference between the gas and the solid all through. Nearly dry solid comes in contact with


Page | 94

fresh hot gas and the temperature of the solid is substantially raised to complete drying if there

is some bound moisture.

Parallel flow unit can also be used. The wet solid comes in contact with the fresh hot gas.

Because the solid has enough moisture in it, its temperature remains close to wet bulb

temperature of water till most of the moisture is removed. By that time the gas temperature

decrease significantly because of supply of heat for drying.

b. Gas heating

Hot flue gases may sometimes be directly used for drying. But because of the possibility of the

sugar being contaminated in contact with the flue gas, a clean heating gas is necessary.

Therefore, air is heated in a tubular heat exchanger and fed to the dryer.

c. Solid feeding

The solid-feeder should push the wet solid into the dryer at the top end but should not allow

the drying gas to escape through it. A screw feeder is most convenient because it acts as a ‘gas-

seal’ too. A chute extending into the shell may also be used for feeding.

d. Dust collection

The exit gas from a rotary dryer often carries over or entrains considerable amounts of fines. If

the carryover of dust is substantial, the gas is led to a cyclone or bag filter to separate the fines.

If there is excessive dusting, the mass flow rate of the hot gas in the dryer is kept low. In this

design, a cyclone is designed as a recovery system.

e. Support and drive of the dryer

A full-scale rotary dryer has a huge weight and is supported on assemblies of trunnion and

thrush roll. Anti-friction pillow blocks can also be used. A motor of high rating rotates the dryer

through a speed reduction device and a girth gear on the periphery of the shell. The shell is

properly insulated against heat loss to the ambient.

f. Heat efficiency

This is the fraction of the thermal energy of the hot gas that is utilised for drying. It is also

referred to as thermal efficiency. The rest of the supplied energy leaves the dryer with the gas


Page | 95

or is lost to the ambient. The heat efficient of a rotary dryer may vary from about 20% to 80%

depending upon the operating temperature.

7.1.3 CHEMICAL ENGINEERING DESIGN

Introduction

The objectives of chemical engineering design are to determine:

Mass and energy balance calculations.

Shell diameter and length.

The solid hold up and the retention time.

Mass balance

Data

Feed stream: 9,624 kg/hr to be dried from 1% moisture content to 0.5%

Assumption (Mosen Asadi, 2007):

50% of water in the feed stream is removed as vapour.

Taking a basis of 1 hour:

Amount of water present in the feed stream= 91 kg

The amount of water removed from wet sugar as vapour= 50

100× 91 = 46 𝑘𝑔

The amount of water present in the dry sugar exit stream= 91-46 = 45 kg

Quantity of hot air into the dryer:

= 3.188 𝑘𝑔

𝑠= 11,477 𝑘𝑔/𝑟 (𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑢𝑛𝑑𝑒𝑟 𝑠𝑒𝑙𝑙 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑎𝑛𝑑 𝑙𝑒𝑛𝑔𝑡 𝑏𝑒𝑙𝑜𝑤)

Total amount of exit gas from the drier = 𝑜𝑡 𝑎𝑖𝑟 𝑖𝑛𝑡𝑜 𝑑𝑟𝑦𝑒𝑟 + 𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑒𝑑 𝑤𝑎𝑡𝑒𝑟

= 11,477 + 46 = 11,523 𝑘𝑔


Page | 96

S50

S46 S49

S48

Dryer

Wet sugar Sucrose= 9,533 kg/hr

Water= 91 kg/hr Total= 9,624 kg/hr

Dry Sugar Sucrose= 9, 533 kg/hr

Water= 42 kg/hr Total= 9,578 kh/hr

Hot air + Water vapour = 11,523 kg/hr

Hot Air= 11,477 kg/hr

Amount of dry sugar from the dryer= 𝑤𝑒𝑡 𝑠𝑢𝑔𝑎𝑟 𝑖𝑛𝑡𝑜 𝑑𝑟𝑦𝑒𝑟 − 𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑒𝑑 𝑤𝑎𝑡𝑒𝑟

= 9,624 − 46 = 9578 kg

Enthalpy balance

Data

Cp, Air= 1.006 kJ/kg.℃

Cp, Sugar =2.15 kJ/kg.℃

Latent heat of vaporization of water = 2140 kJ/kg. ℃

Reference temperature= 25°C



Sucrose 9,533 - - 9,533

Water 91 - 46 45

Hot air - 11,477 11,477 -

Total 9,624 11,477 11,523 9,578

Table 7.1 Mass balance around the dryer


Page | 97

Energy carried into the dryer can be calculated as follows:

𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 = 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑤𝑒𝑡 𝑠𝑢𝑔𝑎𝑟 + 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑜𝑡 𝑎𝑖𝑟

𝐸𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑤𝑒𝑡 𝑠𝑢𝑔𝑎𝑟 = 𝑀𝑆 𝐶𝑃𝑆 𝑇 − 𝑇0 + 𝐶𝑝𝑤𝑎𝑡𝑒𝑟 𝑥𝑓(𝑇 − 𝑇0)

= 9624 2.15(60 − 25) + 4.18 × 0.009(60− 25) = 736,878 𝑘𝐽/𝑟

𝐸𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑜𝑡 𝑎𝑖𝑟

= 𝐺𝑎 𝐶𝑃 𝑎𝑖𝑟 𝑇 − 𝑇0 + 𝐻𝜆0 + 𝐶𝑃 𝑣𝑎𝑝𝑜𝑢𝑟 𝐻 𝑇 − 𝑇0

= 11,477 1.006 100− 25 + 0.01 × 2140 + 1.884 × 0.01(100− 25) = 1,127,764 𝐾𝐽/𝑟

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 = 736,878 + 1,127,764 = 1,864,642 𝑘𝐽/𝑟

Energy carried out of the dryer can be calculated as follows:

𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡 = 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑑𝑟𝑦 𝑠𝑢𝑔𝑎𝑟 + 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑜𝑡 𝑎𝑖𝑟

𝐸𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑑𝑟𝑦 𝑠𝑢𝑔𝑎𝑟 = 𝑀𝑆 𝐶𝑃𝑆 𝑇 − 𝑇0 + 𝐶𝑝𝑤𝑎𝑡𝑒𝑟 𝑥𝑓(𝑇 − 𝑇0)

= 9578 2.15(70− 25) + 4.18 × 0.005(70 − 25) = 835,680 𝑘𝐽/𝑟

𝐸𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑏𝑦 𝑜𝑡 𝑎𝑖𝑟

= 𝐺𝑎 𝐶𝑃 𝑎𝑖𝑟 𝑇 − 𝑇0 + 𝐻𝜆0 + 𝐶𝑃 𝑣𝑎𝑝𝑜𝑢𝑟 𝐻 𝑇 − 𝑇0

11,477 1.006 74− 25 + 0.015 × 2140 + 1.884 × 0.015(74 − 25) = 950,052 𝑘𝐽/𝑟

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡 = 935,680𝑘𝐽 𝑟 + 950,052𝑘𝐽 𝑟

= 1,785,732 𝑘𝐽/𝑟

Energy loss to the environment can also be calculated as follows:

𝐸𝑛𝑒𝑟𝑔𝑦 𝑙𝑜𝑠𝑠 = 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑖𝑛 − 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑟𝑟𝑖𝑒𝑑 𝑜𝑢𝑡

= 1,864,642 − 1,785,732 = 78,910 𝑘𝐽 𝑟


Page | 98

SHELL DIAMETER AND LENGTH

Data

Wet sugar inlet temperature = 60°C

Dry sugar outlet temperature= 70°C

Inlet gas temperature= 100°C

Outlet gas temperature= 74°C

Inlet solid mass flow rate= 9624 kg/hr = 2.673kg/s

Solid inlet moisture content= 0.01 kg/kg dry solids

Components Input (kJ/hr) Output(kJ/hr)

Wet sugar 736,878 -

Hot air 1,127,764 950,052

Dry sugar - 835,680

Losses - 78,910

Total 1,864,642 1,864,642

QL

Wet sugar (60°C) 9,624 kg/hr

Dry sugar (70°C 9,578 kg/hr

Hot air + water vapour (74°C) 15021 kg/hr

Dryer

Hot air (100°C) 14,975 kg/hr

Table 7.2 Enthalpy balance around the dryer


Page | 99

Solid outlet moisture content= 0.005 kg/kg dry solids

Specific heat capacity of sugar= 2.15 kJ/kg.℃

Specific heat capacity of water vapour= 1.88 KJ/kg.℃

Specific heat capacity of air = 1.006 kJ/Kg. °C

Latent heat of vaporization = 2257.1 kJ/kg

For a counter current flow rotary drum dryer, the diameter and length of this dryer are

calculated as follows:

For a mass flow of solid of 2.673 kg/s and inlet and outlet moisture of 0.01 kg/kg dry solids and

0.005kg/kg dry solids respectively, the mass of water evaporated = 2.673(0.01-0.005)=

0.013365 kg/s.

For a unit mass of solids, the heat duty includes (Ref. temperature=25℃):

𝑒𝑎𝑡 𝑖𝑛 𝑡𝑒 𝑖𝑛𝑙𝑒𝑡 𝑠𝑜𝑙𝑖𝑑 = (𝐶𝑃𝑆 + 𝑥𝐶𝑃𝑊) 𝑇𝑆.𝑖𝑛 − 𝑇𝑟𝑒𝑓 = 2.15 + 0.01 × 4.18 60 − 25

= 76.713 𝑘𝐽/𝑘𝑔

𝑒𝑎𝑡 𝑖𝑛 𝑡𝑒 𝑜𝑢𝑡𝑙𝑒𝑡 𝑠𝑜𝑙𝑖𝑑 = (𝐶𝑃𝑆 + 𝑥𝐶𝑃𝑊) 𝑇𝑆.𝑜𝑢𝑡 − 𝑇𝑟𝑒𝑓 = 2.15 + 0.005 × 4.18 70− 25

= 97.6905 𝑘𝐽/𝑘𝑔

𝑙𝑎𝑡𝑒𝑛𝑡 𝑒𝑎𝑡 𝑜𝑓 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

= 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑒𝑑 × 𝑙𝑎𝑡𝑒𝑛𝑡 𝑒𝑎𝑡 𝑜𝑓 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛

= 0.01 − 0.005 × 2257.1 = 11.2855 𝑘𝐽/𝑘𝑔

𝑒𝑎𝑡 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑏𝑦 𝑜𝑡 𝑎𝑖𝑟

= 𝑒𝑎𝑡 𝑖𝑛 𝑡𝑒 𝑜𝑢𝑡𝑙𝑒𝑡 𝑠𝑜𝑙𝑖𝑑 + 𝑙𝑎𝑡𝑒𝑛𝑡 𝑒𝑎𝑡 𝑜𝑓 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

− 𝑒𝑎𝑡 𝑖𝑛 𝑡𝑒 𝑖𝑛𝑙𝑒𝑡 𝑠𝑜𝑙𝑖𝑑

= 97.6905 + 11.2855− 76.713 = 32.263 𝑘𝐽/𝑘𝑔


Page | 100

Converting this heating duty to kilo Watts:

Heating duty, Q= 32.263×2.673=86.24 kW

The humid heat of the entering air is 1.03 kJ/kg.℃ and making heat balance:

𝐺1 1 + 𝑌 =𝑄

𝐶𝑃1(𝑇1−𝑇2)……………………… (7.1.1)

Where:

𝐺1 𝑘𝑔

𝑠 𝑖𝑠 𝑡𝑒 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑖𝑛𝑙𝑒𝑡 𝑎𝑖𝑟

𝑌 𝑘𝑔

𝑘𝑔 𝑖𝑠 𝑡𝑒 𝑢𝑚𝑖𝑑𝑖𝑡𝑦 𝑜𝑓 𝑖𝑛𝑙𝑒𝑡 𝑎𝑖𝑟

𝑄 𝑘𝑊 𝑖𝑠 𝑡𝑒 𝑒𝑎𝑡 𝑑𝑢𝑡𝑦

𝐶𝑃1 KJ

Kg.℃ 𝑖𝑠 𝑡𝑒 𝑢𝑚𝑖𝑑 𝑒𝑎𝑡 𝑜𝑓 𝑖𝑛𝑙𝑒𝑡 𝑎𝑖𝑟

And: 𝑇1 𝑎𝑛𝑑 𝑇2 𝑎𝑟𝑒 𝑡𝑒 𝑖𝑛𝑙𝑒𝑡 𝑎𝑛𝑑 𝑜𝑢𝑡𝑙𝑒𝑡 𝑎𝑖𝑟 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑟𝑒𝑠𝑝𝑒𝑐𝑡𝑖𝑣𝑒𝑙𝑦

In this case:

𝐺1 1 + 0.01 =86.24

1.03(100− 74)= 3.22𝑘𝑔/𝑠

and: mass flowrate of air, 𝐺1 =3.22

1.01= 𝟑.𝟏𝟖𝟖 𝒌𝒈/𝒔

The dryer diameter is then found from the allowable mass velocity of air and the entering air

flow and for a mass velocity of 0.95 kg/m2s (Richardson and Coulson Chemical Engineering;

Volume 2), the cross sectional area of the dryer is:

3.188

0.95 = 3.3558𝑚2

Equivalent to a diameter of 4×3.3558

𝜋

0.5

= 𝟐.𝟎𝟔 𝒎


Page | 101

The length of the dryer is also calculated as follows:

𝑙𝑜𝑔𝑎𝑟𝑖𝑡𝑚𝑖𝑐 𝑚𝑒𝑎𝑛 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒(𝐿𝑀𝑇𝐷) =∆𝑇1 − ∆𝑇2

ln ∆𝑇1

∆𝑇2

𝐴𝑡 𝑡𝑒 𝑖𝑛𝑙𝑒𝑡: ∆𝑇1 = 74 − 60 = 14°𝐶

𝐴𝑡 𝑡𝑒 𝑜𝑢𝑡𝑙𝑒𝑡: ∆𝑇2 = 100 − 70 = 30°𝐶

𝐴𝑛𝑑 𝑡𝑒 𝐿𝑀𝑇𝐷 =14 − 30

ln 14

30

= 21°𝐶

𝑇𝑒 𝑙𝑒𝑛𝑔𝑡 𝑜𝑓 𝑎 𝑑𝑟𝑦𝑒𝑟 𝑖𝑠, 𝐿 𝑖𝑠 𝑡𝑒𝑛:

𝐿 =𝑄

0.0625𝜋𝐷𝐺0.67∆𝑇𝑚……………………… (7.1.2)

where: 𝐷 𝑚 𝑖𝑠 𝑡𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

𝐺 𝑘𝑔 𝑚2𝑠 𝑖𝑠 𝑡𝑒 𝑎𝑖𝑟 𝑚𝑎𝑠𝑠 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

In this case:

𝑇𝑒 𝑙𝑒𝑛𝑔𝑡 𝑜𝑓 𝑡𝑒 𝑑𝑟𝑦𝑒𝑟 𝐿 =86.24

0.0625𝜋 × 2.06 × 0.950.67 × 21= 𝟏𝟎.𝟓𝟏 𝒎

This gives a length ratio of (10.51/2.05)= 5.2, which is a reasonable value for a rotary drum dryer.

Heat

100°C

70°C

60°C

74°C


Page | 102

Retention time and solid hold up

There are four components of particle movement along the drum dryer:

Gravitational, due to slope of the drum

Drag of the gas on the particle

Bouncing of the particle on impact with the bottom of the dryer

Rolling of the particles in the bed at the bottom of the dryer

The time of passage in the rotary dryer resulting from the four components above can be

estimated by the relationship developed by Friedman and Marshall (1949) as shown below:

𝜏 = 𝐿 0.3344

𝛼𝑁𝑅0.9𝐷

+ 0.6085𝐺

𝑊𝑑𝑝0.5

……………………… (7.1.3)

Where:

𝜏 𝑚𝑖𝑛. 𝑖𝑠 𝑡𝑒 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑟𝑒𝑠𝑖𝑑𝑒𝑛𝑐𝑒 𝑡𝑖𝑚𝑒

𝐿 𝑚 𝑖𝑠 𝑡𝑒 𝑑𝑟𝑦𝑒𝑟 𝑙𝑒𝑛𝑔𝑡

𝛼 𝑟𝑎𝑑. 𝑖𝑠 𝑡𝑒 𝑑𝑟𝑦𝑒𝑟 𝑖𝑛𝑐𝑙𝑖𝑛𝑎𝑡𝑖𝑜𝑛

𝑁𝑅 𝑟𝑝𝑚 𝑖𝑠 𝑡𝑒 𝑠𝑒𝑙𝑙 𝑟𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑠𝑝𝑒𝑒𝑑

𝐷 𝑚 𝑖𝑠 𝑡𝑒 𝑑𝑟𝑦𝑒𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

𝐺 𝑚3 𝑚𝑖𝑛 𝑖𝑠 𝑡𝑒 𝑔𝑎𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒

𝑊 𝑘𝑔 𝑚𝑖𝑛 𝑖𝑠 𝑡𝑒 𝑠𝑜𝑙𝑖𝑑 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒

𝑑𝑝 𝑚𝑖𝑐𝑟𝑜𝑛𝑠 𝑖𝑠 𝑡𝑒 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

In this design, the following data is used:

𝐿 = 10.51 𝑚

𝛼 = 0.07 𝑟𝑎𝑑.

𝑁𝑅 = 4.06 𝑟𝑒𝑣/min(𝑎𝑠 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑢𝑛𝑑𝑒𝑟 𝑝𝑒𝑟𝑖𝑝𝑒𝑟𝑎𝑙 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓𝑡𝑒 𝑠𝑒𝑙𝑙)


Page | 103

𝐷 = 2.06𝑚

𝐺 = 191.28 𝑘𝑔 𝑚𝑖𝑛

𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑖𝑛𝑔 𝑡𝑖𝑠 𝑣𝑎𝑙𝑢𝑒 𝑡𝑜 𝑚3 𝑚𝑖𝑛 , 𝑖𝑡 𝑖𝑠 𝑑𝑖𝑣𝑖𝑑𝑒𝑑 𝑏𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑎𝑖𝑟 (= 1.225 𝑘𝑔/𝑚3)

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝐺 =191.28

1.225= 156.14 𝑚3/𝑚𝑖𝑛

𝑊 = 160.4 𝑘𝑔/𝑚𝑖𝑛

𝑑𝑝 = 0.5 𝑚𝑖𝑐𝑟𝑜𝑛𝑠

Substituting these values in the residence time equation:

𝜏 = 10.51 0.3344

0.07 × 4.060.9 × 2.06+

0.6085 × 156.14

160.4 × 0.50.5

𝜏 = 𝟏𝟓.𝟕𝟏 𝒎𝒊𝒏𝒖𝒕𝒆𝒔

The residence time is defined as holdup divided by feed rate (Kelly and O’Donnell, 1977). This

definition can be given by the expression:

𝜏 =𝐻∗

𝑊………………… . (7.1.4)

Where:

𝐻∗ 𝑖𝑠 𝑡𝑒 𝑜𝑙𝑑𝑢𝑝, 𝑎𝑛𝑑 𝑖𝑠 𝑢𝑠𝑢𝑎𝑙𝑙𝑦 𝑑𝑒𝑡𝑒𝑟𝑚𝑖𝑛𝑒𝑑 𝑏𝑦 𝑠𝑢𝑑𝑑𝑒𝑛𝑙𝑦 𝑠𝑡𝑜𝑝𝑝𝑖𝑛𝑔 𝑡𝑒

𝑑𝑟𝑢𝑚 𝑎𝑛𝑑 𝑠𝑢𝑏𝑠𝑒𝑞𝑢𝑒𝑛𝑡𝑙𝑦 𝑤𝑒𝑖𝑔𝑖𝑛𝑔 𝑖𝑡𝑠 𝑐𝑜𝑛𝑡𝑒𝑛𝑡𝑠.

𝑤 𝑖𝑠 𝑡𝑒 𝑠𝑜𝑙𝑖𝑑 𝑓𝑒𝑒𝑑𝑟𝑎𝑡𝑒 (𝑘𝑔/𝑚𝑖𝑛)

Substituting in the expression:

15.71 =𝐻∗

160.4

𝑇𝑢𝑠 𝑜𝑙𝑑𝑢𝑝,𝐻∗ = 15.71 × 160.4 = 𝟐,𝟓𝟐𝟎 𝒌𝒈


Page | 104

Expressing this solid holdup in terms of the fraction of the shell volume occupied by the solid at

any time:

𝑆𝑜𝑙𝑖𝑑 𝑜𝑙𝑑𝑢𝑝 =𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑡𝑒 𝑠𝑜𝑙𝑖𝑑

𝑠𝑒𝑙𝑙 𝑣𝑜𝑙𝑢𝑚𝑒

𝑆𝑒𝑙𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 =𝜋𝐷2𝐿

4=𝜋 × 2.062 × 10.51

4= 35.03 𝑚3

𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 =𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 𝑜𝑙𝑑𝑢𝑝

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑

𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑠𝑢𝑔𝑎𝑟 = 800 𝑘𝑔/𝑚3

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒, 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 =2,520

800= 3.15 𝑚3

𝑇𝑢𝑠, 𝑠𝑜𝑙𝑖𝑑 𝑜𝑙𝑑𝑢𝑝 % =3.15

35.03= 𝟗%

The rotary drum dryer operates with 8-15% of their volume filled with materials (Miskell and

Marshall, 1956), hence this sold holdup percentage is within the expected range.

7.1.3.6 Summary of Chemical Engineering Design

7.1.4 MECHANICAL DESIGN

In the mechanical design of a rotary drum dryer, the chemical engineer is responsible for

developing and specifying the basic design information for the specialist engineer.

In this design of rotary drum dryer, the following areas are covered:

Quantity of hot air to the dryer 11,477 kg/hr

Energy supplied by hot air 950,052 kg/hr

Dryer diameter 2.06m

Dryer length 10.51m

Retention time 15.71 minutes

Solid hold up 9%

Table 7.3 Chemical engineering design summary


Page | 105

Materials of construction.

Size and number of lifting flights.

Shell thickness of the rotary drum dryer.

The peripheral speed of the shell.

The orientation of the rotary drum.

Materials of construction

The most important characteristics to be considered when selecting a material of construction

are: (Coulson and Richardson’s Chemical Engineering Vol. 6)

1. Mechanical properties:

Strength-tensile strength.

Stiffness-elastic modulus (Young’s modulus).

Toughness-fracture resistance.

Hardness-wear resistance.

Fatigue resistance.

Creep resistance.

2. The effect of high and low temperatures on the mechanical properties.

3. Corrosion resistance.

4. Any special properties required; such as, thermal conductivity, electrical resistance, magnetic

properties.

5. Ease of fabrication forming, welding, casting.

6. Availability in standard sizes plates, sections and tube.

7. Cost.

Material of construction chosen for this design will be AISI 316 stainless steel on product

contact parts and AISI 304 stainless steel on the outside parts.


Page | 106

The size and number of lifting flights

A sufficient number of flights must be distributed across the drum. The volume of material

transported by the flights should be between 8% and 15% of the total volume inside the dryer

(Baker, 1983). This fact is related to the optimum dryer loading. Values below this range will

lead to wastage of energy and values above this range will lead to heterogeneity of the final

product.

The flight height in a direct dryer is one-eighth of the dryer diameter and the flight count per

circle is 2D, where D is the diameter in feet (Perry and Green, 1999).

The ratio between the area occupied by the solids in the flights (S) and the load of the solids in

the flight (h*) may be given by the following relationship (Schofield and Glikin, 1962):

∗ 𝜃𝑖 = 𝑆𝑖𝐿𝜌𝑠 ………………… (7.1.5)

Where:

∗ 𝑘𝑔 𝑖𝑠 𝑡𝑒 𝑓𝑙𝑖𝑔𝑡 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑙𝑜𝑎𝑑

𝜃 𝑟𝑎𝑑 𝑖𝑠 𝑡𝑒 𝑎𝑛𝑔𝑙𝑢𝑙𝑎𝑟 𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡𝑒 𝑓𝑙𝑖𝑔𝑡 𝑒𝑑𝑔𝑒

𝑆𝑖 𝑚2 𝑖𝑠 𝑡𝑒 𝑡𝑟𝑎𝑛𝑠𝑣𝑒𝑟𝑠𝑎𝑙 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑎𝑟𝑒𝑎 𝑜𝑐𝑐𝑢𝑝𝑖𝑒𝑑 𝑏𝑦 𝑡𝑒 𝑓𝑙𝑖𝑔𝑡 𝑠𝑜𝑙𝑖𝑑𝑠

𝐿 𝑚 𝑖𝑠 𝑡𝑒 𝑑𝑟𝑦𝑒𝑟 𝑠𝑜𝑙𝑖𝑑

𝜌𝑠 𝑘𝑔

𝑚2 𝑖𝑠 𝑡𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦

Based on the above formula, the following data is used:

𝑇𝑒 𝑓𝑙𝑖𝑔𝑡 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑙𝑜𝑎𝑑, ( ∗) = 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑡𝑟𝑎𝑛𝑠𝑝𝑜𝑟𝑡𝑒𝑑 × 𝑠𝑜𝑙𝑖𝑑 𝑜𝑙𝑑𝑢𝑝

= 0.125 × 2,748.54 = 348.07 𝑘𝑔

𝐴𝑛𝑔𝑢𝑙𝑎𝑟 𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛 𝑜𝑓 𝑓𝑙𝑖𝑔𝑡 𝑒𝑑𝑔𝑒,𝜃 = 450 = 0.7854

𝐿𝑒𝑛𝑔𝑡 𝑜𝑓 𝑡𝑒 𝑑𝑟𝑦𝑒𝑟,𝐿 = 10.51 𝑚


Page | 107

𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑠𝑢𝑔𝑎𝑟, 𝜌𝑠 = 800 𝑘𝑔/𝑚2

Thus, substituting in formula:

348.07 × 0.7854 = 𝑆𝑖 × 10.51 × 800

𝑆𝑖 = 0.0325𝑚2

𝐻𝑒𝑖𝑔𝑡 𝑜𝑓 𝑓𝑙𝑖𝑔𝑡 =1

8𝐷 =

1

8× 2.06 = 𝟎.𝟐𝟓𝟕𝟓 𝒎

𝑇𝑟𝑎𝑛𝑠𝑣𝑒𝑟𝑠𝑎𝑙 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 = 𝐻𝑒𝑖𝑔𝑡 × 𝑤𝑖𝑑𝑡

0.0325 = 0.2575 × 𝑤

Solving:

𝑤𝑖𝑑𝑡 𝑜𝑓 𝑡𝑒 𝑓𝑙𝑖𝑔𝑡,𝑤 = 𝟎.𝟏𝟐𝟔𝟐 𝒎

Solving for the number of flights:

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑙𝑖𝑔𝑡𝑠 = 2𝐷

𝐷 = 2.06 𝑚 = 6.76 𝑓𝑡

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑙𝑖𝑔𝑡𝑠 = 2 × 6.76 = 𝟏𝟑 𝒇𝒍𝒊𝒈𝒉𝒕𝒔

Shell thickness of a rotary drum dryer

The thickness of the wall of the cylinder (shell) is calculated based on the following expression:

𝑠𝑒𝑙𝑙 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠 =𝑃𝐷𝐷𝑡

2𝑗𝑓 − 𝑃𝑡…………………… (7.1.6)

Where:

𝑃𝐷 𝑘𝑁 𝑚𝑚2 𝑖𝑠 𝑡𝑒 𝑠𝑒𝑙𝑙 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒

𝐷𝑡 𝑚𝑚 𝑖𝑠 𝑡𝑒 𝑠𝑒𝑙𝑙 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

𝑗 𝑖𝑠 𝑡𝑒 𝑗𝑜𝑖𝑛𝑡 𝑓𝑎𝑐𝑡𝑜𝑟


Page | 108

𝑓 𝑘𝑁 𝑚𝑚2 𝑖𝑠 𝑡𝑒 𝑠𝑒𝑙𝑙 𝑑𝑒𝑠𝑖𝑔𝑛 𝑠𝑡𝑟𝑒𝑠𝑠

The design internal pressure is 10% above normal pressure

𝑃𝐷 = 1.1 × 𝑁𝑜𝑟𝑚𝑎𝑙 𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒

The rotary drum operates at atmospheric pressure i.e. 101.32 Kpa

Therefore, the design pressure is:

𝑃𝐷 = 1.1 × 101.32 = 111.45 𝐾𝑝𝑎

Also, from standard tables, typical design stress at 21° C (LMTD) is 14.2 N/mm2 and the

recommended joint factor is 0.85.

Substituting in the formula above for shell thickness;

𝑠𝑒𝑙𝑙 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠 =0.1115 × 2060

2 × 0.85 × 14.2 − 0.1115= 9.56 𝑚𝑚

Adding the corrosion allowance of 2 mm

The shell thickness= 9.56 + 2= 11.56 mm

Peripheral speed of the shell

The speed of rotation of a rotary drum dryer is given by the following formula (Hugot, 1986)

𝑛 =10 − 1.63

𝐷 𝑟𝑝𝑚………………………… . . (7.1.7)

Where D is the diameter of the drum in meters

For this design, the speed of rotation is:

𝑛 =10 − 1.63

2.06= 𝟒.𝟎𝟔 𝒓𝒑𝒎


Page | 109

Orientation of the drum dryer

The rotary drum is usually set at a slope to the horizontal, which will facilitate the movement of

the sugar from end to end of the drum, being repeatedly lifted and dropped through the

counter current air flow.

For this design an orientation of 4° (0.07 rad.) to the horizontal is used (Key, 1972).

Summary of Mechanical Engineering Design

7.1.5 DESIGN OF AUXILIARY EQUIPMENT OF A ROTARY DRUM DRYER

For efficient and effective operation of rotary drum dryer, some auxiliary components are

needed. These auxiliary equipment include:

Air heater

Recovery system

Thermal design of air heater

A single-pass shell and tube heat exchanger will be used.

For the air to be heated, the following data is used:

Air inlet temperature= 25° C

Air outlet temperature = 100°C

Material of construction AISI 316 Stainless steel

Height of lifting flights 0.2575m

Width of lifting flights 0.1262m

Number of lifting flights 13

Shell thickness 11.56mm

Peripheral speed of the shell 4.06 rpm

Drum orientation to the horizontal 4°

Table 7. 1 Mechanical Engineering design summary


Page | 110

Specific heat capacity of air = 1.006 kJ/kg. °C

𝐻𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑟𝑎𝑡𝑒,𝑄 = 𝑀𝐶𝑃∆𝑇 = 11,477 × 1.006 100− 25 = 865,939.65 𝑘𝐽

𝑆𝑖𝑚𝑖𝑙𝑎𝑟𝑙𝑦,𝑄 = 𝑈𝐴∆𝑇𝑀

𝑈 = 680𝑊 𝑚2𝐾

For a counter current heat exchanger, logarithmic mean temperature difference (∆𝑇𝑀 ) is

calculated as follows:

𝑙𝑜𝑔𝑎𝑟𝑖𝑡𝑚𝑖𝑐 𝑚𝑒𝑎𝑛 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒(𝐿𝑀𝑇𝐷) =∆𝑇1 − ∆𝑇2

ln ∆𝑇1

∆𝑇2

𝐴𝑡 𝑡𝑒 𝑖𝑛𝑙𝑒𝑡: ∆𝑇1 = 145 − 25 = 120°𝐶

𝐴𝑡 𝑡𝑒 𝑜𝑢𝑡𝑙𝑒𝑡: ∆𝑇2 = 145 − 100 = 45°𝐶

𝐴𝑛𝑑 𝑡𝑒 𝐿𝑀𝑇𝐷 =120 − 45

ln 120

45

= 76.5°𝐶

𝐴 =𝑄

𝑈∆𝑇𝑀=

865,939.65

680 × 76.5= 16.65 𝑚2

Tube details

Taking a triangular pattern with a 1.25do pitch

145°C

25°C

145°C

100°C

Air

Steam


Page | 111

Tube pitch

According to TEMA (Tubular Exchangers Manufacturers Association) standards the

recommended tube pitch for a triangular pattern tube arrangement is given by:

𝑃𝑡 = 1.25𝑑𝑜 = 1.25 × 19.05 = 23.81 𝑚𝑚

Tube dimensions

The tube thickness (gauge) is selected to withstand the internal pressure and give an adequate

corrosion allowance. Steel tubes for heat exchangers are covered by British Standards (BS 3606)

cover.

Taking standard tube length and outside diameter:

L=8 m (8000mm)

do = ¾’’ (19.05mm)

Standard tube thickness for steel tubes:

Fir the outside diameter TEMA standards give a thickness of 0.065 in (1.65mm)

The tube inside diameter is given by:

19.05 − 2 1.65 = 15.75𝑚𝑚

Tube count

The number of tubes is given by:

𝑁𝑡 =𝐴𝑇

𝑎𝑡………………… (7.1.8)

Where:

AT is the total heat transfer area of the tubes

at is the heat transfer area of one tube


Page | 112

𝑎𝑡 = 𝜋𝑑0𝑙

= 𝜋 × 19.05 × 10−3 × 8 = 0.4788 𝑚2

𝐴𝑇 = 16.65𝑚2

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒, =16.65

0.4788= 35 𝑡𝑢𝑏𝑒𝑠

Shell diameter

The shell diameter must be selected to give a fit to the tube bundle as is practical; to reduce

bypassing round the outside of the bundle. The clearance required between the outermost

tubes in the bundle and the shell inside diameter will depend on the type of exchanger and the

manufacturing tolerances.

The shell diameter is calculated from the bundle diameter and the shell bundle clearance as

follows:

𝐵𝑢𝑛𝑑𝑙𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟,𝐷𝑏 = 𝑑0 𝑁𝑡

𝐾1

1

𝑛

……………………… (7.1.9)

Where k1 and n are constants of particular tube passes and arrangements

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝐵𝑢𝑛𝑑𝑙𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 (𝐷𝑏) = 19.05 × 10−3 35

0.319

1

2.142

= 0.171𝑚 𝑜𝑟 171 𝑚𝑚

𝑠𝑒𝑙𝑙 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟,𝑑𝑠 = 𝑏𝑢𝑛𝑑𝑙𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟,𝐷𝑏 + 𝑠𝑒𝑙𝑙 𝑏𝑢𝑛𝑑𝑙𝑒 𝑐𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒

Using shell- bundle clearance charts for fixed heat exchangers:

At Db= 305 mm

𝑠𝑒𝑙𝑙 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 − 𝑏𝑢𝑛𝑑𝑙𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 11 𝑚𝑚

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒, 𝑠𝑒𝑙𝑙 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 𝑏𝑢𝑛𝑑𝑙𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 + 11


Page | 113

= 171 + 11 = 182 𝑚𝑚

Baffle spacing

Baffles are used in the shell to direct the fluid stream across the tubes, to increase the fluid

velocity and so improve the rate of transfer. The baffle spacing is taken as 0.3 times the shell

diameter. In this design the spacing is:

= 0.3 × 182 = 54.6 𝑚𝑚

This baffle spacing leads to a very high pressure drop on the shell side; it is therefore doubled to

yield 109.2 which gives an acceptable pressure drop.

Design of a recovery system

In the operation if a rotary drum dyer, the exit air has sugar particles in form of dust which if

left to the atmosphere will cause loss of sugar and pollution of the atmosphere. A cyclone has

been used as recovery system of this sugar from the exit air.

Cyclone separators provide a method of removing particulate matter from air streams at low

cost and low maintenance that would otherwise end up in the atmosphere. In general, a

cyclone consists of an upper cylindrical part referred to as the barrel and a lower conical part

referred to as cone.

The volumetric flowrate of the cyclone chamber can be calculated based on the following

relationship (Simpson and Parnell, 1995):

𝑉 = 𝐿𝑑𝑟𝑦 𝑎𝑖𝑟

𝑀𝑊1+𝐿𝑠𝑜𝑙𝑣𝑀𝑊2

× 22.4 ×273 + 𝑇𝑎𝑐𝑡𝑢𝑎𝑙

273×

10330

10330 + 𝑃𝑎𝑐𝑡𝑢𝑎𝑙 𝑚3

𝑟……………… (7.1.10)

Where:

𝐿𝑑𝑟𝑦 𝑎𝑖𝑟 𝑖𝑠 𝑡𝑒 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑡𝑒 𝑑𝑟𝑦𝑖𝑛𝑔 𝑚𝑒𝑑𝑖𝑢𝑚.

𝐿𝑠𝑜𝑙𝑣 𝑖𝑠 𝑡𝑒 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒 𝑜𝑓 𝑡𝑒 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑖𝑛 𝑓𝑒𝑒𝑑, 𝑖𝑛 𝑡𝑖𝑠 𝑐𝑎𝑠𝑒 𝑤𝑎𝑡𝑒𝑟.


Page | 114

𝑇𝑎𝑐𝑡𝑢𝑎𝑙 𝑖𝑠 𝑡𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑡𝑒 𝑑𝑟𝑦𝑖𝑛𝑔 𝑚𝑒𝑑𝑖𝑢𝑚 𝑖𝑛 °𝐶.

𝑃𝑎𝑐𝑡𝑢𝑎𝑙 𝑖𝑠 𝑡𝑒 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑖𝑛 𝑡𝑒 𝑑𝑟𝑦𝑖𝑛𝑔 𝑐𝑎𝑚𝑏𝑒𝑟 𝑖𝑛 𝑚𝑚𝑊𝐺

𝑀𝑊1 𝑖𝑠 𝑡𝑒 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔𝑡 𝑜𝑓 𝑎𝑖𝑟

𝑀𝑊2 𝑖𝑠 𝑡𝑒 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

From the online cyclone operating pressure calculator P actual = 22,262 mmWG.

The following data is used for the calculation of volume:

𝐿𝑑𝑟𝑦 𝑎𝑖𝑟 = 11,477𝑘𝑔 𝑟

𝐿𝑠𝑜𝑙𝑣 = 91 𝑘𝑔 𝑟

𝑇𝑎𝑐𝑡𝑢𝑎𝑙 = 100°𝐶

Substituting in the equation above:

𝑄 = 11,477

28.84+

91

18.02 × 22.4 ×

273 + 100

273×

10330

10330 + 22,262 𝑚3/𝑟

𝑄 = 3,909𝑚3

𝑟= 1.086 𝑚3/𝑠

The area of the chamber can be obtained by the relationship below:

𝐴 = 𝑣𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒

𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑎𝑖𝑟

The velocity of exit air from the dryer in a countercurrent flow = 1.05 m/s (Hugot, 1986)

𝑇𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝑎𝑟𝑒𝑎 𝐴 = 1.086

1.05= 1.03 𝑚2

𝐴 =𝜋𝐷2

4


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𝐷 = 4𝐴

𝜋 =

4 × 1.03

𝜋 = 𝟏.𝟏𝟓𝒎

Using an aspect ratio of 4:1 for cylindrical height to diameter we can obtain the dimension for

the height of the cylindrical shell part of the cyclone as:

𝐻 = 4 × 1.15 = 𝟒.𝟔𝒎

Using a cylindrical cone of 60° (www. niro.com):

𝑇𝑒 𝐻𝑒𝑖𝑔𝑡 𝑜𝑓 𝑡𝑒 𝑏𝑜𝑡𝑡𝑜𝑚 𝑐𝑜𝑛𝑒 =𝐷

2tan 60

𝑇𝑢𝑠, 𝑒𝑖𝑔𝑡 𝑜𝑓 𝑡𝑒 𝑏𝑜𝑡𝑡𝑜𝑚 𝑐𝑜𝑛𝑒 =1.15

2× tan 60 = 𝟏.𝟎 𝒎

Summary of design of auxiliary equipment

AIR HEATER

Area 16.65 m2

length 8 m

Tube diameter 15.75 mm

Number of tubes 35

Shell diameter 171 mm

Baffle spacing 54.6m

RECOVERY SYSTEM

Area 1.03 m2

Diameter 1.15 m2

Cylindrical height 4.6 m

Height of the bottom cone 1 m

Table 7. 2 Auxiliary equipment design summary

http://www.niro.com/


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7.2 DESIGN OF A PLATE HEAT EXCHANGER BY KIMATHI HARRISON MUTHIORAH - CPE/16/08

7.2.1 INTRODUCTION

Heat transfer predicts the energy transfer which may take place between material bodies as a

result of temperature difference. This energy transfer is defined by thermodynamics as heat.

Heat transfer supplements the first and second principles of thermodynamics by providing

additional experimental rules which may be used to establish energy-transfer rates. The science

of heat transfer explains how and at what rate the exchange will take place.

Three modes of heat transfer are conduction, convection and radiation. When heat flows

through a body by the transference of momentum of individual atoms or molecules without

mixing, it is said to flow by conduction.

When heat flows by actual mixing of warmer portions with cooler portions of the same

material, the mechanism is known as convection. Convection is restricted to the flow of heat in

fluids. Radiation is term given to the transfer of energy through space by means of

electromagnetic waves. Radiation is transmitted, reflected, or absorbed when matter appears

in its path while it is passing through a space.

The transfer of heat to and from process fluids is an essential part of most chemical processes.

The application of the principles of heat transfer to the design of equipment to accomplish a

certain engineering objective is of extreme importance, for in applying the principles to design,

the individual is working toward the important goal of product development for economic gain.

Plate heat exchangers are used extensively in the food and beverage industries, as they can be

readily taken apart for cleaning and inspection. Their use in the chemical industry will depend

on the relative cost for the particular application compared with a conventional shell and tube

exchanger.

In this design problem, it is needed to raise the temperature of the thin beet juice from a

temperature of 76°C to a temperature of 86°C to enable optimum liming process. A plate heat


Page | 117

exchanger was chosen because of its advantages over the shell and tube design which are

discussed later in this section.

A gasketed plate heat exchanger consists of a stack of closely spaced thin plates clamped

together in a frame. A thin gasket seals the plates round their edges. The plates are normally

between 0.5 and 3 mm thick and the gap between them 1.5 to 5 mm. Plate surface areas range

from 0.03 to 1.5 m2, with a plate width: length ratio from 2.0 to 3.0. The size of plate heat

exchangers can vary from very small, 0.03 m2, to very large, 1500 m2. The maximum flow-rate

of fluid is limited to around 2500 m3/h. Corner ports in the plates direct the flow from plate to

plate. The plates are embossed with a pattern of ridges, which increase the rigidity of the plate

and improve the heat transfer performance. Plates are available in a wide range of metals and

alloys; including stainless steel, Aluminium and titanium.

Figure 7. 3 Gasketed plate heat exchanger (Heat Exchangers, Kevin D. Rafferty, 2002)


Page | 118

Advantages

1. Superior thermal performance.

Plate heat exchangers are capable of nominal approach temperatures of 10 °F compared to a

nominal 20 °F for shell and tube units. In addition, overall heat transfer coefficients (U) for plate

type exchangers are three to four times those of shell and tube units.

2. Compact design.

The superior thermal performance of the plate heat exchanger and the space efficient design of

the plate arrangement results in a very compact piece of equipment. Space requirements for

the plate heat exchanger generally run 10% to 50% that of a shell and tube unit for equivalent

duty. In addition, tube cleaning and replacing clearances are eliminated.

3. Ease of maintenance.

The construction of the heat exchanger is such that, upon disassembly, all heat transfer areas

are available for inspection and cleaning. Disassembly consists only of loosening a small number

of tie bolts.

4. Expandability and multiplex capability.

The nature of the plate heat exchanger construction permits expansion of the unit should heat

transfer requirements increase after installation. In addition, two or more heat exchangers can

be housed in a single frame, thus reducing space requirements and capital costs.

5. Availability of a wide variety of corrosion resistant alloys.

Since the heat transfer area is constructed of thin plates, stainless steel or other high alloy

construction is significantly less costly than for a shell and tube exchanger of similar material.

6. Plates are attractive when material costs are high.

Plates are less expensive to fabricate when the materials costs tend to be high.


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Disadvantages

1. Temperature limitation

The maximum operating temperature is limited to about 250 °C, due to the performance of the

available gasket materials.

2. Gasket selection

The selection of a suitable gasket is critical.

3. Low pressure operation

A plate is not a good shape to resist pressure and plate heat exchangers are not suitable for

pressures greater than about 30 bar.

Flow of heat exchanger fluids

Figure 6.2 illustrates the nature of fluid flow through the plate heat exchanger. The primary and

secondary fluids flow in opposite directions on either side of the plates.

Figure 7. 4 Nature of fluid flow through the plate heat exchanger (www.alfalaval.com)

7.2.2 DESIGN PROCEDURE

The design procedure is similar to that for shell and tube exchangers.

1. Calculate duty, the rate of heat transfer required.

2. If the specification is incomplete, determine the unknown fluid temperature or fluid

flow rate from a heat balance.

3. Calculate the logarithmic mean temperature difference, 𝛥𝑇𝑙𝑚


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4. Determine the logarithmic mean temperature correction factor, 𝐹𝑡.

5. Calculate the corrected mean temperature difference, 𝛥𝑇𝑚 = 𝐹𝑡 × ∆𝑇𝑙𝑚 .

6. Estimate the overall heat transfer coefficient.

7. Calculate the surface area required.

8. Determine the number of plates required (𝑇𝑜𝑡𝑎𝑙 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎

𝑎𝑟𝑒𝑎 𝑜𝑓 𝑜𝑛𝑒 𝑝𝑙𝑎𝑡𝑒)

9. Decide the flow arrangement and the number of passes.

10. Calculate the film heat transfer coefficients for each stream.

11. Calculate the overall coefficient, allowing for fouling factors.

12. Compare the calculated with assumed overall coefficient, if satisfactory, say -0% to

+10% error, proceed. If unsatisfactory, return to step 8 and increase or decrease the

number of plates.

13. Check the pressure drop of each stream

Heat exchanger duty

The heat exchanger duty, (Q) is given by the following expression:

𝑄 = 𝑚 𝑖 𝐶𝑝𝑖 ∆𝑇……………………………………… 7.2.1

Where,

𝑄 = 𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒,𝑊,

𝑚 𝑖 = 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑡𝑒 𝑜𝑡 𝑜𝑟 𝑐𝑜𝑙𝑑 𝑓𝑙𝑢𝑖𝑑, 𝑘𝑔/𝑟,

𝐶𝑝𝑖 = 𝑒𝑎𝑡 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑡𝑒 𝑓𝑙𝑢𝑖𝑑, 𝑘𝐽/𝑘𝑔.𝐾,

∆𝑇 = 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑟𝑖𝑠𝑒 𝑜𝑟 𝑓𝑎𝑙𝑙 𝑜𝑓 𝑡𝑒 𝑓𝑙𝑢𝑖𝑑,𝐾.

The general equation for heat transfer across a surface is:

𝑄 = 𝑈𝐴∆𝑇𝑚 …………………………………… 7.2.2

Where,

𝑄 = 𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒,𝑊,

𝑈 = 𝑡𝑒 𝑜𝑣𝑒𝑟𝑎𝑙𝑙 𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡,𝑊/𝑚2 ℃,


Page | 121

𝐴 = 𝑒𝑎𝑡 − 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑎𝑟𝑒𝑎,𝑚2,

∆𝑇𝑚 = 𝑡𝑒 𝑚𝑒𝑎𝑛 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒, 𝑡𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑟𝑖𝑣𝑖𝑛𝑔 𝑓𝑜𝑟𝑐𝑒,℃

Logarithmic mean temperature difference

This is normally calculated from the terminal temperature differences: the difference in the

fluid temperatures at the inlet and outlet of the exchanger. For counter-current flow the

logarithmic mean temperature is given by:

∆𝑇𝑙𝑚 = 𝑇1 − 𝑡2 − (𝑇2 − 𝑡1)

ln 𝑇1 − 𝑡2 /(𝑇2 − 𝑡1)…………………… 7.2.3

Where,

∆𝑇𝑙𝑚 = log𝑚𝑒𝑎𝑛 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒,

𝑇1 = 𝑜𝑡 𝑓𝑙𝑢𝑖𝑑 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒, 𝑖𝑛𝑙𝑒𝑡,

𝑇2 = 𝑜𝑡 𝑓𝑙𝑢𝑖𝑑 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒,𝑜𝑢𝑡𝑙𝑒𝑡,

𝑡1 = 𝑐𝑜𝑙𝑑 𝑓𝑙𝑢𝑖𝑑 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒, 𝑖𝑛𝑙𝑒𝑡,

𝑡2 = 𝑐𝑜𝑙𝑑 𝑓𝑙𝑢𝑖𝑑 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒, 𝑜𝑢𝑡𝑙𝑒𝑡.

Temperature correction factor

To estimate the “true temperature difference” from the logarithmic mean temperature by a

correction factor is applied to allow for the departure from true counter-current flow:

∆𝑇𝑚 = 𝐹𝑡 × ∆𝑇𝑙𝑚 …………………………………… 7.2.4

Where,

∆𝑇𝑚 = 𝑡𝑟𝑢𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑛𝑐𝑒

𝐹𝑡 = 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟

For plate heat exchangers, it is convenient to express the logarithmic mean temperature

difference correction factor,𝐹𝑡 , as a function of the number of transfer units, NTU, and the flow

arrangement (number of passes) as shown in figure 7.3 below.

The number of transfer units is given by:


Page | 122

𝑁𝑇𝑈 =𝑇1 − 𝑡1

∆𝑇𝑙𝑚……………………………………… 7.2.5

Figure 7. 5 Log mean temperature correction factor for plate heat exchangers (Chemical Engineering Design, Coulson & Richardson’s, Volume 6, pg. 760)

Heat transfer coefficient

The equation for forced-convection heat transfer in conduits is used for the plate heat exchangers.

𝑝𝑑𝑒𝑘𝑓

= 0.26 𝑅𝑒0.65 𝑃𝑟0.4 (𝜇𝜇𝑤 )0.14 ……………… .7.2.6

Where

𝑝 = 𝑃𝑙𝑎𝑡𝑒 𝑓𝑖𝑙𝑚 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡.


Page | 123

𝑅𝑒 = 𝑅𝑒𝑦𝑛𝑜𝑙𝑑 𝑛𝑢𝑚𝑏𝑒𝑟 𝜌𝑢𝑝𝑑𝑒

𝜇=

𝐺𝑝𝑑𝑒

𝜇

𝑢𝑝 = 𝐶𝑎𝑛𝑛𝑒𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦.

𝑑𝑒 = 𝐸𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 (𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐) 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟, 𝑡𝑤𝑖𝑐𝑒 𝑡𝑒 𝑔𝑎𝑝 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡𝑒 𝑝𝑙𝑎𝑡𝑒𝑠,𝑚.

𝐺𝑝 = 𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑐𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 = 𝑤/𝐴𝑓 ,𝑘𝑔𝑚−2𝑠−1

𝑤 = 𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒 𝑝𝑒𝑟 𝑐𝑎𝑛𝑛𝑒𝑙, 𝑘𝑔/𝑠

𝐴𝑓 = 𝑐𝑟𝑜𝑠𝑠𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝑓𝑜𝑟 𝑓𝑙𝑜𝑤,𝑚2

There is no heat transfer across the end plates, so the number of effective plates will be the

total number of plates less two.

Pressure drop

The plate pressure drop can be estimated using a form of the equation for flow in a conduit.

This equation is given below.

∆𝑃𝑃 = 8 𝑗𝑓 𝐿𝑃

𝑑𝑒

𝜌𝑢𝑝2

2…………………… .7.2.7

Where, 𝐿𝑃 = 𝑝𝑎𝑡 𝑙𝑒𝑛𝑔𝑡

𝑢𝑝 = 𝐺𝑝/𝜌

The value of the friction factor 𝑗𝑓 will depend on the design of plate used. For preliminary

calculations the following relationship can be used for turbulent flow:

𝑗𝑓 = 0.6 𝑅𝑒−0.3.…………………… . .… .7.2.8

The pressure drop due to the contraction and expansion losses through the ports in the plates

must be added to the friction loss. This is calculated by the equation below.

∆𝑃𝑝𝑡 = 1.3 𝜌𝑢𝑝𝑡

2

2𝑁𝑝 …………………… .7.2.9

Where 𝑢𝑝𝑡 = 𝑡𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑟𝑜𝑢𝑔 𝑡𝑒 𝑝𝑜𝑟𝑡𝑠,𝑤

𝜌𝐴𝑝,𝑚

𝑠

𝑤 = 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑡𝑟𝑜𝑢𝑔 𝑡𝑒 𝑝𝑜𝑟𝑡𝑠, 𝑘𝑔/𝑠


Page | 124

𝐴𝑝 = 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡𝑒 𝑝𝑜𝑟𝑡 =𝜋𝑑2

𝑝𝑡

4,𝑚2

𝑑𝑝𝑡 = 𝑝𝑜𝑟𝑡 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟,𝑚

𝑁𝑝 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑎𝑠𝑠𝑒𝑠

7.2.4 PROCESS DESIGN

The design is based on the plate heat exchanger 1, which is used to heat the thin juice from

70°C to 86°C using steam at 4 bar. A schematic of the heat exchanger is shown in the diagram

below.

Property Thin Beet Juice (cooling fluid) Steam (heating fluid)

Mass flow rate (kg/s) 24.82 0.837

Density (kg/m3) 1580.00 2.163

Viscosity (Ns/m2) 0.057 1.377 x 10-5

Specific heat capacity (kJ/kg.K) 4.1719 2.340

Prandlt number 5.6 1.051

Inlet temperatures (°C) 70.00 140.00

Outlet temperatures (°C) 86.00 140.00

Thermal conductivities (W/m. °C) 0.18 0.031

Steam in (140°C)

3,011 kg/hr

Thin Juice (86°C)

89,349 kg/hr

Thin Juice (70°C)

89,349 kg/hr

Condensate out (140°C)

3,011 kg/hr

QL

Heat Exchanger 1

Table 7. 3 Properties of heating and cooling fluids of Heat Exchanger 1


Page | 125

Calculations

Heat Exchanger duty

The heat exchanger duty is calculated using equation 7.2.1.

𝑄 = 24.82 × 4.1719 × 16

= 1656.69 𝑘𝑊

Logarithmic mean temperature difference

The LMTD is determined using equation 7.2.3

∆𝑇𝑙𝑚 = 140 − 70 − (140 − 86)

𝑙𝑛 140−70

(140−86)

∆𝑇𝑙𝑚 = 61.65℃

Mean temperature difference (MTD)

The Number of Transfer Units (NTU) is determined by equation 7.2.5:

𝑁𝑇𝑈 = 143.61 − 40

81.99= 1.264

A 1: 1 pass arrangement is selected.

From figure 7.3, the temperature correction factor 𝐹𝑡 is determined.

𝐹𝑡 = 0.96

The mean temperature difference is determined using equation 7.2.4:

∆𝑇𝑚 = 0.96 × 61.65 = 59.18℃

The overall heat transfer coefficient is estimated to be 350 𝑊 𝑚2 .℃ . (Chemical Engineering

Design, Coulson & Richardson’s, Volume 6)

Area of heat transfer

The area of heat transfer is calculated using the equation 7.2.2,


Page | 126

𝐴 =𝑄

𝑈 × ∆𝑇𝑚

𝐴 =1656.69 × 103

350 × 59.18≅ 80 𝑚2

Number of plates

Selecting an effective plate area of 0.75 m2, effective length of 1.5 m and width of 0.5 m, the

number of plates is then determined. (Actual plate size will be larger to accommodate the

gasket area and ports).

𝑁𝑜.𝑜𝑓 𝑝𝑙𝑎𝑡𝑒𝑠 = 𝑇𝑜𝑡𝑎𝑙 𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑎𝑟𝑒𝑎

𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑜𝑛𝑒 𝑝𝑙𝑎𝑡𝑒……………… 7.2.10

=80

0.75≅ 107 𝑝𝑙𝑎𝑡𝑒𝑠

Number of channels per pass

Allowing for an end plate,

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑛𝑛𝑒𝑙𝑠 𝑝𝑒𝑟 𝑝𝑎𝑠𝑠 =107 − 1

2= 53

A plate spacing of 3mm, a typical value (Chemical Engineering Design, Coulson & Richardson’s,

Volume 6.) is chosen, then:

𝐶𝑎𝑛𝑛𝑒𝑙 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 = 𝑝𝑙𝑎𝑡𝑒 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 × 𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑤𝑖𝑑𝑡 𝑜𝑓 𝑝𝑙𝑎𝑡𝑒… .7.2.11

= 3 × 10−3 × 0.5 = 0.0015 𝑚2

𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑚𝑒𝑎𝑛 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 2 × 3 × 10−3 = 6 × 10−3 𝑚

Thin juice

Channel velocity


Page | 127

The channel velocity 𝑢𝑝 is given by the expression below:

𝐶𝑎𝑛𝑛𝑒𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒

𝑑𝑒𝑛𝑠𝑖𝑡𝑦×

1

𝑐𝑎𝑛𝑛𝑒𝑙 𝑐𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎×

1

𝑛𝑜. 𝑜𝑓 𝑐𝑎𝑛𝑛𝑒𝑙𝑠… 7.2.12

𝑢𝑝 = 24.82

1580×

1

0.0015×

1

53= 0.198 𝑚/𝑠

Reynolds’s Number (Re)

𝑅𝑒 = 𝜌𝑢𝑝𝑑𝑒𝜇

=1580 × 0.198 × 6 × 10−3

0.0567= 33.04

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4 ……………………… 7.2.13

= 0.26 × 33.0400.65 × 5.60.4 = 5.03

Plate film coefficient

From expression for Nusselt number, the plate film coefficient 𝑝𝑐 is calculated.

𝑝𝑐 =𝑘𝑓 .𝑁𝑢

𝑑𝑒………… .………………… .7.2.14

= 0.6 × 5.3

6 × 10−3 = 530 𝑊 𝑚2.℃

Steam

Channel velocity

𝑢𝑝 = 0.837

2.163×

1

0.0015×

1

53= 4.867 𝑚/𝑠

Reynolds’s number (Re)


=2.163 × 4.867 × 6 × 10−3

1.377 × 10−5= 4587.5

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4

= 0.26 × 4587.50.65 × 1.0510.4 = 63.63


Page | 128


𝑝 = 0.031 × 63.63

6 × 10−3 = 328.76𝑊 𝑚2.℃

Overall heat transfer coefficient

The overall heat transfer coefficient is given is given by the expression below:

1

𝑈=

1

𝑝𝑐+

1

𝑅𝑐+

𝑑𝑡𝑘𝑝

+1

𝑝+

1

𝑅…………………………… .7.2.15

Where,

𝑈 = 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡

𝑝𝑐 = 𝑝𝑙𝑎𝑡𝑒 𝑓𝑖𝑙𝑚 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑛 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑠𝑖𝑑𝑒

𝑝 = 𝑝𝑙𝑎𝑡𝑒 𝑓𝑖𝑙𝑚 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑛 𝑡𝑒 𝑒𝑎𝑡𝑖𝑛𝑔 𝑠𝑖𝑑𝑒

𝑅𝑐 = 𝑓𝑜𝑢𝑙𝑖𝑛𝑔 𝑓𝑎𝑐𝑡𝑜𝑟 𝑜𝑛 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑠𝑖𝑑𝑒

𝑅 = 𝑓𝑜𝑢𝑙𝑖𝑛𝑔 𝑓𝑎𝑐𝑡𝑜𝑟 𝑜𝑛 𝑡𝑒 𝑒𝑎𝑡𝑖𝑛𝑔 𝑠𝑖𝑑𝑒

𝑑𝑡 = 𝑝𝑙𝑎𝑡𝑒 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠

𝑘𝑝 = 𝑡𝑒𝑚𝑎𝑙 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑡𝑒 𝑝𝑙𝑎𝑡𝑒

1

𝑈=

1

530+

1

1800+

0.6 × 10−3

16.2+

1

328.76+

1

10000= 0.005622

𝑈 = 177.88 𝑊 𝑚2 .℃

This value of 𝑈 is too low compared to the initial estimate of 350 𝑊 𝑚2 .℃ , therefore the

number of channels per pass is increases to 120.

Number of plates

𝑁𝑜. 𝑜𝑓 𝑝𝑙𝑎𝑡𝑒𝑠 = 2 × 120 + 1 = 241 𝑝𝑙𝑎𝑡𝑒𝑠

Thin juice

Channel velocity

𝑢𝑝 = 24.82

1580×

1

0.0015×

1

120= 0.087 𝑚/𝑠



Page | 129


=1580 × 0.087 × 6 × 10−3

0.0567= 14.55

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4 = 0.26 × 14.550.65 × 5.60.4 = 2.95




𝑑𝑒= 0.6 ×

2.95

6 × 10−3 = 295 𝑊 𝑚2 .℃

Steam

Channel velocity

𝑢𝑝 = 0.837

2.163×

1

0.0015×

1

120= 2.15 𝑚/𝑠



=2.163 × 2.15 × 6 × 10−3

1.377 × 10−5= 2026.34

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4

= 0.26 × 2026.340.65 × 1.0510.4 = 37.41

Plate film coefficient 𝑝 = 0.031 × (37.41/ 6 × 10−3) = 193.29𝑊 𝑚2.℃

The overall heat transfer coefficient

1

𝑈=

1

295+

1

1800+

0.6 × 10−3

16.2+

1

193.29+

1

10000= 0.00926

𝑈 = 108.04 𝑊 𝑚2 .℃

Overall coefficient required, = 350 ×53

120= 154.58 𝑊 𝑚2.℃

Increasing the number of channels per pass is increases to 210.

Number of plates


Page | 130


Thin juice

Channel velocity

𝑢𝑝 = 24.82

1580×

1

0.0015×

1

210= 0.05 𝑚/𝑠



=1580 × 0.05 × 6 × 10−3

0.0567= 8.34

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4 = 0.26 × 8.340.65 × 5.60.4 = 2.06




𝑑𝑒= 0.6 ×

2.06

6 × 10−3 = 205.56 𝑊 𝑚2.℃

Steam

Channel velocity

𝑢𝑝 = 0.837

2.163×

1

0.0015×

1

210= 1.23 𝑚/𝑠



=2.163 × 1.23 × 6 × 10−3

1.377 × 10−5= 1157.80

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4

= 0.26 × 1157.800.65 × 1.0510.4 = 26

Plate film coefficient 𝑝 = 0.031 × (26/ 6 × 10−3) = 134.33 𝑊 𝑚2.℃


Page | 131


1

𝑈=

1

134.33+

1

1800+

0.6 × 10−3

16.2+

1

205.56+

1

10000= 0.013

𝑈 = 76.91 𝑊 𝑚2 .℃


210= 88.33𝑊 𝑚2 .℃

Increasing the number of channels per pass to 250;

Number of plates


Thin juice

Channel velocity

𝑢𝑝 = 24.82

1580×

1

0.0015×

1

250= 0.04 𝑚/𝑠



=1580 × 0.04 × 6 × 10−3

0.0567= 6.69

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4 = 0.26 × 6.690.65 × 5.60.4 = 1.78




𝑑𝑒= 0.6 ×

2.06

6 × 10−3 = 178𝑊 𝑚2.℃

Steam

Channel velocity

𝑢𝑝 = 0.837

2.163×

1

0.0015×

1

250= 1.03 𝑚/𝑠


Page | 132



=2.163 × 1.03 × 6 × 10−3

1.377 × 10−5= 1001.65

Nusselt number (Nu)

𝑁𝑢 = 0.26 𝑅𝑒0.65 × 𝑃𝑟0.4

= 0.26 × 1001.650.65 × 1.0510.4 = 23.66

Plate film coefficient 𝑝 = 0.031 × (23.66/ 6 × 10−3) = 122.24𝑊 𝑚2 .℃


1

𝑈=

1

178+

1

1800+

0.6 × 10−3

16.2+

1

122.24+

1

10000= 0.014

𝑈 = 71.42 𝑊 𝑚2 .℃


250= 74.20𝑊 𝑚2 .℃

The value of 𝑈 obtained (71.42𝑊

𝑚2.℃) is satisfactory.

𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒄𝒉𝒂𝒏𝒏𝒆𝒍𝒔 𝒑𝒆𝒓 𝒑𝒂𝒔𝒔 = 𝟐𝟓𝟎

𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒑𝒍𝒂𝒕𝒆𝒔 = 𝟓𝟎𝟏

Pressure drops

The plate pressure drop is estimated using equation 7.2.7

Thin juice

The friction factor 𝑗𝑓 is determined using equation 7.2.8

𝑗𝑓 = 0.6 (6.69)−0.3 = 0.34

𝑃𝑎𝑡 𝑙𝑒𝑛𝑔𝑡, 𝐿𝑃 = 𝑝𝑙𝑎𝑡𝑒 𝑙𝑒𝑛𝑔𝑡 × 𝑛𝑜. 𝑜𝑓 𝑝𝑎𝑠𝑠𝑒𝑠 = 1.5 × 1 = 1.5𝑚

∆𝑃𝑃 = 8 × 0.34 1.56 × 10−3

1580 × 0.042

2 = 852.52

𝑁

𝑚2


Page | 133

𝑇𝑒 𝑝𝑜𝑟𝑡 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑙𝑜𝑠𝑠, 𝑡𝑎𝑘𝑖𝑛𝑔 𝑝𝑜𝑟𝑡 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑎𝑠 100𝑚𝑚,𝑎𝑟𝑒𝑎 = 0.00785 𝑚2

𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑟𝑜𝑢𝑔 𝑝𝑜𝑟𝑡 = (24.82/1580)/0.00785 = 2.00𝑚/𝑠

∆𝑃𝑝𝑡 = 1.3 × 1580 ×22

2= 4,108

𝑁

𝑚2

𝑇𝑜𝑡𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑑𝑟𝑜𝑝 = 852.52 + 4,108 = 𝟒,𝟗𝟔𝟕.𝟓𝟐 𝑵/𝒎𝟐

Steam

The friction factor 𝑗𝑓 is determined using equation 7.2.8

𝑗𝑓 = 0.6 (1001.65)−0.3 = 0.075

𝑃𝑎𝑡 𝑙𝑒𝑛𝑔𝑡, 𝐿𝑃 = 𝑝𝑙𝑎𝑡𝑒 𝑙𝑒𝑛𝑔𝑡 × 𝑛𝑜. 𝑜𝑓 𝑝𝑎𝑠𝑠𝑒𝑠 = 1.5 × 1 = 1.5𝑚

∆𝑃𝑃 = 8 × 0.075 1.56 × 10−3

2.163 × 1.032

2 = 167.09𝑁/𝑚2

𝑇𝑒 𝑝𝑜𝑟𝑡 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑙𝑜𝑠𝑠, 𝑡𝑎𝑘𝑖𝑛𝑔 𝑝𝑜𝑟𝑡 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑎𝑠 100𝑚𝑚,𝑎𝑟𝑒𝑎 = 0.00785 𝑚2

𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑟𝑜𝑢𝑔 𝑝𝑜𝑟𝑡 = (0.837/2.163)/0.00785 = 49.29 𝑚/𝑠

∆𝑃𝑝𝑡 = 1.3 × 2.163 ×49.292

2= 3,416.40 N/m2

𝑇𝑜𝑡𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑑𝑟𝑜𝑝 = 167.09 + 3,416.40 = 𝟑,𝟓𝟖𝟑.𝟒𝟗𝑵/𝒎𝟐

Design parameter Specification

Number of plates 501 plates

Number of channels per pass 250 channels

Pressure drop on thin juice side 4,967 N/m2

Pressure drop in steam side 3,584 N/m2

Overall heat transfer coefficient 71.42 W/m2.°C

Table 7. 4 Chemical properties of the plate heat exchanger to be designed


Page | 134


The plate heat exchanger consists of a pack of corrugated metal plates with portholes for the

passage of the two fluids between which heat transfer will take place.

The plate pack is assembled between a fix frame plate and a movable pressure plate and

compressed by tightening bolts. The plates are fitted with a gasket which seals the interpolate

channel and directs the fluids into alternate channels. The plate corrugations promote fluid

turbulence and support the plates against differential pressure.

The plate and the pressure plate are suspended from an upper carrying bar and located by a

lower guiding bar, both of which are fixed to a support column.

Figure 7. 6 Gasketed plate heat exchanger components (www.graham-mfg.com)

Upper bar Column

Follower

Head Plate package

Tie bolts

Lower bar


Page | 135

Frame

The heat exchanger consists of a frame plate (Head), a pressure plate (Follower), a carrying bar,

a lower bar and a column. Tightening bolts are used to press the plates together. The frame is

constructed from carbon steel.

Plates

The plate package consists of plates with a groove along the rim of the plate and around the

ports. The plates are constructed from stainless steel alloy 316. The chevron plate design is

used as shown below. The chevron angle is 25°.

Figure 7. 7 The chevron plate used in the gasketed plate heat exchanger (www.graham-mfg.com)

Gaskets

The groove provided in the plates holds the special gasket. The purpose of this gasket is to

prevent intermixing of the media and leakage to the outside. The gaskets are selected to suit

the actual combination of temperature, chemical environment and fluid properties. Nitrile

(NBR) clip-on gaskets shown in Figure 6.6 below are used in the plate heat exchanger as they

are oil resistant and fat resistant.


Page | 136

Wall shear stress

The wall shear stresses on the plates can be calculated from the equation below:

𝜏 =𝑓𝜌𝑤2

2………………………………… . .7.2.16

Where,

𝜏 = 𝑠𝑒𝑎𝑟 𝑠𝑡𝑟𝑒𝑠𝑠,𝑁

𝑓 = 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟

𝑤 = 𝑓𝑙𝑜𝑤 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦,𝑚/𝑠

𝜌 = 𝑓𝑙𝑢𝑖𝑑 𝑑𝑒𝑛𝑠𝑖𝑡𝑦, 𝑘𝑔/𝑚3

The friction factor 𝑓 can be estimated from the equation developed by Shah and Bhatti, 1988.

𝑓

2∅𝑤 =

𝑁𝑢𝑃𝑟−1

3

𝑅𝑒………………………………………………………………………………… 7.2.17

Where,

∅𝑤 = 𝑓𝑢𝑛𝑐𝑡𝑖𝑜𝑛 𝑡𝑎𝑡 𝑚𝑜𝑑𝑖𝑓𝑖𝑒𝑠 𝑎𝑛𝑎𝑙𝑜𝑔𝑦 𝑑𝑒𝑝𝑒𝑛𝑑𝑖𝑛𝑔 𝑜𝑛 𝑑𝑢𝑐𝑡 𝑔𝑒𝑜𝑚𝑒𝑡𝑟𝑦 𝑎𝑛𝑑 𝑓𝑙𝑜𝑤 𝑡𝑦𝑝𝑒

Figure 7. 8 Clip-on gasket used in the plate heat exchanger


Page | 137

Thin juice side

The friction factor is calculated as,

𝑓 =2 × 1.78 × 5.6−

1

3

6.69= 0.30

The shear stress from equation 7.16 is then:

𝜏 =0.30 × 1580 × 0.042

2= 0.38 𝑁

Steam side

The friction factor is calculated as,

𝑓 =2 × 23.66 × 1.051−

1

3

1001.65= 0.05

The shear stress from equation 7.2.16 is then:

𝜏 =0.05 × 2.163 × 1.032

2= 0.06 𝑁

Table 7. 5 Mechanical design summary of the plate heat exchanger


Equivalent length of plate 1.5m

Equivalent width of plate 0.5m

Plate thickness 0.6mm

Material of construction of plate Stainless Steel 316

Plate spacing 3mm

Pass Arrangement 1 : 1

Number of channels per pass 250 channels

Plate configuration Chevron with chevron angle of 25°

Gasket material Nitrile (NBR) or EPDM

End plate thickness 50mm

Port diameter 100mm

Tightening bolts M39

Number of tightening bolts 4 short, 4 long.

Material of construction of frame Carbon Steel


Page | 138

Filtrate

Filtration

equipment

Suspension

Driving force (Pressure drop ΔP)

Medium

7.3 DESIGN OF A PLATE AND FRAME FILTER (FILTER PRESS) BY NTAHER MOHAMED SALEH- CPE/20/07

7.3.1 INTRODUCTION

In the simplest of terms, filtration is a unit operation that is designed to separate

suspended particles from a fluid media by passing the solution through a porous

membrane or medium. As the fluid or suspension is forced through the voids or pores of

the filter medium, the solid particles are retained on the medium's surface or, in some

cases, on the walls of the pores, while the fluid, which is referred to as the filtrate,

passes through. A filtration system can be shown schematically as in the figure below;

In order to obtain fluid flow through the filter medium, a pressure drop ΔP has to be

applied across the medium; it is immaterial from the fundamental point of view how this

pressure drop is achieved but there are four types of driving force:

Gravity

Vacuum

Pressure

Centrifugal

There are basically two types of filtration used in practice: the so-called surface filters are

used for cake filtration in which the solids are deposited in the form of a cake on the up-

stream side of a relatively thin filter medium, while depth filters are used for deep bed

Figure 7. 9 Schematic diagram of a filtration system


Page | 139

filtration in which particle deposition takes place inside the medium and cake deposition on

the surface is undesirable.

In a surface filter, the filter medium has a relatively low initial pressure drop and, as can

be seen in Figure 7.3.2, particles of the same size as, or larger than, the openings wedge

into the openings and create smaller passages which remove even smaller particles from

the fluid. A filter cake is thus formed, which in turn functions as a medium for the

filtration of subsequent input suspension.

In a depth filter - Figure 7.3.3 - the particles are smaller than the medium openings and

hence they proceed through relatively long and tortuous pores where they are collected

by a number of mechanisms (gravity, diffusion and inertia) and attach to the medium by

molecular and electrostatic forces.

Of the two types of filtration, cake filtration has the wider application, particularly in the

chemical industry (because of the higher concentrations used).

Suspension

Filter medium

Figure 7. 10 Mechanism of cake filtration (Ladislav Svarovsky, 2000)

Figure 7. 11 Mechanism of deep bed filtration (Ladislav Svarovsky, 2000)


Page | 140

7.3.2 FILTRATION FUNDAMENTALS

In filtration the bed steadily grows in thickness. It may be noted that there are two quite

different methods of operating a batch filter. If the pressure is kept constant then the rate of

flow progressively diminishes, whereas if the flow rate is kept constant then the pressure must

be gradually increased. Because the particles forming the cake are small and the flow through

the bed is slow, streamline conditions are almost invariably obtained, and, at any instant, the

flow rate of the filtrate may be represented by the following form of equation;

𝑈𝑐 =1

𝐴

𝑑𝑉

𝑑𝑡=

1

5

𝑒3

(1 − 𝑒)2

−∆𝑃

𝑆2𝜇𝑙………………………………… . . (7.3.1)

Where, 𝑈𝑐 − 𝑆𝑢𝑝𝑒𝑟𝑓𝑖𝑐𝑖𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑡𝑒 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 (𝑚/𝑠)

𝑉 – 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 𝑤𝑖𝑐 𝑎𝑠 𝑝𝑎𝑠𝑠𝑒𝑑 𝑖𝑛 𝑡𝑖𝑚𝑒, 𝑡 (𝑚3/𝑠)

𝐴 – 𝑇𝑜𝑡𝑎𝑙 𝑐𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡𝑒 𝑓𝑖𝑙𝑡𝑒𝑟 𝑐𝑎𝑘𝑒 (𝑚2)

𝑙– 𝐶𝑎𝑘𝑒 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠 (𝑚)

𝑆 – 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑜𝑓 𝑡𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 (𝑚−1)

𝑒 – 𝑉𝑜𝑖𝑑𝑎𝑔𝑒

µ − 𝑉𝑖𝑠𝑐𝑜𝑠𝑖𝑡𝑦 𝑜𝑓 𝑡𝑒 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 (𝑘𝑔/𝑚𝑠)

𝛥𝑃 –𝐴𝑝𝑝𝑙𝑖𝑒𝑑 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 (𝑘𝑁/𝑚2)

𝑡 − 𝑡𝑖𝑚𝑒

In deriving this equation it is assumed that the cake is uniform and that the voidage is constant

throughout.

For incompressible cakes e in equation (1) may be taken as constant and the quantity,

𝑒3 [5(1 – 𝑒)2𝑆2] is then a property of the particles forming the cake and should be constant

for a given material.

Thus,

1

𝐴

𝑑𝑉

𝑑𝑡=

(−ΔP)

𝑟𝜇𝑙……………………… .…………… (7.3.2)

Where,


Page | 141

𝑟 =5(1 – 𝑒)2𝑆2

𝑒3

Equation (2) is the basic filtration equation and r is termed the specific resistance which is seen

to depend on e and S. For incompressible cakes, r is taken as constant.

7.3.2.1 Flow rate- pressure drop relationships

Clean medium

At the beginning of batch cake filtration, the whole pressure drop available (i.e. the driving

force) is across the medium itself since as yet no cake is formed. As the pores in the medium

are normally small and the rate of flow of filtrate is low, laminar flow conditions are almost

invariably obtained.

Darcy's basic filtration equation relating the flow rate Q of a filtrate of viscosity μ

through a bed of thickness L and face area A to the driving pressure ΔP is

𝑄 = 𝑒𝐴Δ𝑃

𝜇𝐿……………………………………… (7.3.3)

Where 𝑒 is a constant referred to as the permeability of the bed. Equation (3) can be written as,

𝑄 =𝐴Δ𝑃

𝜇𝑅……………………………………… . . (7.3.4)

Where R is called the medium resistance.

Medium with a cake forming on its face

The filtrate flow rate at constant driving pressure becomes a function of time because the liquid

is presented with two resistance in series, one of which, the medium resistance R may be

assumed constant and the other, the cake resistance 𝑅𝑐 increases with time.

𝑄 =𝐴Δ𝑃

𝜇(𝑅 + 𝑅𝑐)………………………… .……… (7.3.5)


Page | 142

As the resistance of the cake may be directly proportional to the amount of cake deposited (for

incompressible cakes) it follows that

𝑅𝑐 = 𝑟𝑤………………………… . .…… .…… . (7.3.6)

Where 𝑤 the mass of cake is deposited per unit area (kg m-2) and 𝑟 is the specific cake resistance (m kg-1).

Substitution of equation (6) in (5) gives

𝑄 =𝐴Δ𝑃

𝜇𝑅 + 𝑟𝜇𝑤…………………… . .…………… (7.3.7)

Pressure drop

The pressure drop ΔP may be constant or variable with time depending on the characteristics

of the pump used or on the driving force applied. If it varies with time the function

Δ𝑃 = 𝑓(𝑡) is usually known.

Face area of the filter medium

The face area of the medium A is usually constant, but with a few exceptions such as in the

case of equipment with an appreciable cake build-up on a tubular medium or a rotary

drum.

Liquid viscosity

The liquid viscosity μ is constant provided that the temperature remains constant during

the filtration cycle and that the liquid is Newtonian.

Specific cake resistance

The specific cake resistance 𝑟 should be constant for incompressible cakes but it may

change with time as a result of possible flow consolidation of the cake and also, in the

case of variable rate filtration, because of variable approach velocity.

Average specific cake resistance 𝑟𝑎𝑣can be determined as follows


Page | 143

1

𝑟𝑎𝑣=

1

Δ𝑃𝑐

𝑑(Δ𝑃𝑐)

𝑟

Δ𝑃𝑐

0

…………………………………… . (7.3.8)

where Δ𝑃𝑐 is the pressure drop across the cake.

An experimental empirical relationship can sometimes be used over a limited pressure range

𝑟 = 𝑟0(Δ𝑃𝑐)𝑛 …………………… .………………… . (7.3.9)

where 𝑟0 is the resistance at unit applied pressure drop and n is the compressibility index

obtained from experiments.

Using equation (9), the average cake resistance 𝑟𝑎𝑣 can be shown to be (from equation 7.3.8)

𝑟𝑎𝑣 = (1 − 𝑛)𝑟0(Δ𝑃𝑐)𝑛 …………… .………………… (7.3.10)

Mass of cake deposited per unit area

The mass of cake deposited per unit area w is a function of time in batch filtration

processes. It can be related to the cumulative volume of filtrate V filtered in time t by

𝑤𝐴 = 𝑐𝑉 ………………………………………… . (7.3.11)

where c is the concentration of solids in the suspension (mass/unit volume of the filtrate).

Medium resistance

The medium resistance R should normally be constant but it may vary with time as a

result of some penetration of solids into the medium and sometimes it may also change

with applied pressure because of the compression of fibres in the medium.

7.3.3 FILTER SELECTION

Filtration equipment is commercially available in a wide range. Proper selection must be based

on detailed information of the slurry to be handled, cake properties, anticipated capacities and

process operating conditions. One may then select the preferred operational mode (batch,

semi-batch or continuous), and choose a particular system on the above considerations and

economic constraints.


Page | 144

The most suitable filter for any given operation is the one which will fulfill the requirements at

minimum overall cost. Since the cost of the equipment is closely related to the filtering area, it

is normally desirable to obtain a high overall rate of filtration. This involves the use of relatively

high pressures although the maximum pressures are often limited by mechanical design

considerations.

Although a higher throughput from a given filtering surface is obtained from a continuous filter

than from a batch operated filter, it may sometimes be necessary to use a batch filter,

particularly if the filter cake has a high resistance, since most continuous filters operate under

reduced pressure and the maximum filtration pressure is therefore limited. Other features

which are desirable in a filter include ease of discharge of the filter cake in a convenient

physical form, and a method of observing the quality of the filtrate obtained from each section

of the plant. These factors are important in considering the types of equipment available.

The main factors to be considered when selecting equipment and operating conditions are:

i) The properties of the fluid, particularly its viscosity, density and corrosive properties.

ii) The nature of the solid—its particle size and shape, size distribution, and packing

characteristics.

iii) The concentration of solids in suspension.

iv) The quantity of material to be handled, and its value.

v) Whether the valuable product is the solid, the fluid, or both.

vi) Whether it is necessary to wash the filtered solids.

vii) Whether very slight contamination caused by contact of the suspension or filtrate with

the various components of the equipment is detrimental to the product.

viii) Whether the feed liquor may be heated.

ix) Whether any form of pre-treatment might be helpful

Cake filters are used when the desired product of the operation is the solids, the filtrate, or

both. When the filtrate is the product, the degree of removal from the cake by washing or

blowing with air or gas becomes an economic optimization. When the cake is the desired


Page | 145

product, the incentive is to obtain the desired degree of cake purity by washing, blowing, and

sometimes mechanical expression of residual liquid.

In the operational sense, some filters are batch devices, whereas others are continuous. The

variety of solid-liquid separation equipment is so great that only a brief selection are presented

here.

a) Batch filters. Examples include:

Nutsche filters

Horizontal plate filters

Filter press

Liquid bag filter

Pressure leaf filter

Centrifugal discharge filter

b) Continuous cake filters include:

Rotary drum filter

Scraper-discharge filter

String-discharge filter

Coil-filter

The type of equipment chosen for the filtration operation is the filter press. A filter press is

suitable because the solid content is not so high that frequent dismantling of the press is

necessary. The reason being that the amount of precipitate produced during the first

carbonation is much higher than during the second carbonation hence the use of a filter press

in filtering the juice in the second-carb juice.

Plate-and-frame filter

Plate-and-frame presses operate discontinuously and use pressure to filter and press the mud

to produce cake. At the start of filtration in a plate-and-frame press, some solid particles begin

to deposit on the filter medium to form a layer of thin cake. After this brief initial period, the


Page | 146

cake does the filtration, not the filter medium. When a certain amount of cake is built up, the

cake is washed to remove the remaining sugar.

A plate-and-frame press consists of several sets of two square plates (one for juice and the

other for water inlet) and a frame. The face of the plates is covered with filter cloth. The

arrangement of plates and frame starts with a solid head and continues in the following way:

juice plate, frame, water plate, frame, juice plate, frame, water plate, and so on. The sets sit

vertically in a metal rack, and a screw squeezes them together.

Figure 7. 12 Scheme to show the principle of plate-and-frame presses (Svarovsky, 2000)

Figure 7. 13 A typical filter press (Mosen Asadi, 2007)


Page | 147

Filter press has been chosen over a rotary drum filter for the following reasons:

1. Sugar loss: Sugar loss to cake produced by filter presses accounts for about 0.7% on

sugar entering the factory. With vacuum filters, the losses are 0.9 to 1.4%. Less sugar is

left in the cake produced with filter presses because of better de-sweetening and better

pressing mechanisms.

2. High dry substance content: Filter presses produce cake with about 70% DS, but rotary-

drum filters produce cake with about 50% DS. Therefore, while in the lime pond, the

product of drum filters need decanting to reduce its moisture content. This costs extra

expenses.

3. Quality of filtrate: Filter presses can produce clear juice, but filtrate from rotary-drum

filters still contains some suspended solids

Design equations for batch filter cycles

A typical cycle can be represented by;

𝑡𝑇 = 𝑡𝑓 + 𝑡𝑐 + 𝑡𝑤 + 𝑡𝑑𝑛 = 𝑡𝑓 1 +𝑡𝑐𝑡𝑓

+𝑡𝑤𝑡𝑓

+𝑡𝑑𝑡𝑓

+𝑡𝑑𝑛𝑡𝑓 ………………………… . . (7.3.12)

Where the subscripts f, c, d and w are used to respectively indicate values during the filtration,

consolidation, de-liquoring and washing phases of a cycle of total duration 𝑡𝑇 : the term 𝑡𝑑𝑛

denotes filter downtime, for cake discharge and cloth cleaning.

Process design calculations for filtration are based on the general filtration equation stated as

𝑑𝑉

𝑑𝑡=

𝐴2Δ𝑃

𝜇 (𝑟𝑎𝑣𝑐𝑉 + 𝐴𝑅)…………………………………… . (7.3.13)

Where 𝑉 is the cumulative volume of the filtrate, 𝐴 the filter medium area, Δ𝑃 the filtration

pressure, 𝜇 the viscosity of liquid, 𝑐 the effective feed concentration and 𝑅 the medium

resistance.

The cake properties are related to the filtration pressure according to (Wakeman and Tarleton,

1994) the following equations


Page | 148

𝑟𝑎𝑣 = 𝑟0(1 − 𝑛)Δ𝑃𝑛

𝐶𝑎𝑣 = 𝐶0Δ𝑃𝛽

𝑚𝑎𝑣 = 1 +𝜌𝑙𝜌𝑠

1 − 𝐶𝑎𝑣𝐶𝑎𝑣

𝑐 =𝑠𝜌𝑙

1 −𝑚𝑎𝑣𝑠

Where 𝜌𝑙 is the density of liquid, 𝑚𝑎𝑣 the ratio of mass wet/ dry cake, 𝑠 the mass fraction of

solids in the feed and 𝑟0,𝑛,𝐶0 and 𝛽 are empirical constants.

The cake thickness is given as

𝑙 =𝑉

𝐴

𝑆[𝜌𝑠 𝑚𝑎𝑣 − 1 + 𝜌𝑙 ]

𝜌𝑠(1 −𝑚𝑎𝑣𝑠)

Substituting 𝑄 = 𝑑𝑉 𝑑𝑡 into equation (12) yields the volume of the filtrate

𝑉 =𝐴

𝑟𝑎𝑣𝜇𝑙𝑐 𝐴

Δ𝑃

𝑄− 𝜇𝑙𝑅

The filtration time is obtained from

𝑡 = (1/𝑄)𝑑𝑉

𝑉

0

Which can be approximated using trapezium rule integration by:

𝑡𝑓 ≈ (𝑉)𝑖 − (𝑉)𝑖−1

2

𝑉

0

1

𝑄𝑖+

1

𝑄𝑖−1

The mass of solids on the filter medium is given as

𝑀𝑠 = 𝐴𝑙𝐶𝑎𝑣𝜌𝑠


Page | 149

For a given 𝑀𝑠 , the mass of cake liquid (𝑀𝑙), mass of cake solute (𝑀𝑠𝑜𝑙 ) and cake moisture

content (𝑀) are respectively given by

𝑀𝑙 = 𝐴𝑙𝑒𝜌𝑙

𝑀𝑠𝑜𝑙 = 𝐴𝑙𝑒∅𝑜

𝑀 = 100 𝑀𝑙

𝑀𝑙 + 𝑀𝑠

Where ∅𝑜 is the solute concentration in the feed.

7.3.4 CHEMICAL ENGINEERING DESIGN

The objectives for the chemical engineering design is to determine:

1. Number of frames

2. Plate thickness

3. Time of filtration

4. Cake deposition/discharge

5. Feed temperature

6. Filtration pressure

7. Mass of cake solute

8. Mass of cake liquid

9. Cake moisture content

After the second carbonation, the small amount of precipitated calcium carbonate (PCC) and

insoluble compounds are filtered to produce clear juice, known as thin juice. The impurities

removed as Insolubles include; oxalates, phosphates, sulphates, colloids, pectins, nitrogenous

compounds, organic non-sucroses and inorganic non-sucroses.

The design is determined for the equipment used in filtering carbonation mud to remove

Insolubles.

Assumptions made are;


Page | 150

Wet cake

Water= 70 kg/hr


Total= 226 kg/hr

Filtrate

Water=76,124 kg/hr

Sucrose=11,593 kg/h

Non-sucrose=1089 kg/hr

Insolubles= 156kg/hr

Total= 88,962 kg/hr

Slurry Water= 76,194 kg/hr Sucrose= 11,593 kg/h

Non-sucrose= 1089 kg/hr Insolubles= 312 kg/hr Total= 89,188 kg/hr

Filter press

i) The cake is compressible.

ii) The slurry feed is at constant temperature. This ensures constant viscosity of slurry.

iii) Sucrose and non-sucrose (soluble) losses are negligible in the cake

Data necessary for process design calculations:

Concentration of solids in the entering stream 𝑐 (𝑐 > 𝑐𝑜 )

𝑐 =312 𝑘𝑔/𝑟

89,188 𝑘𝑔/𝑟× 100% = 0.3498%

Concentration of solids in the wet cake

𝑐𝑜 =156 𝑘𝑔/𝑟

226 𝑘𝑔/𝑟× 100% = 69.03%

Rate of wet cake formation

𝑀𝑐 =𝑀. 𝑐

𝑐0

Where 𝑀 is the mass flow rate of entering stream = 24.77 kg/s

Hence,

𝑀𝑐 =24.77 × 0.35

69.03= 𝟎.𝟏𝟐𝟔 𝒌𝒈/𝒔

Additional data necessary (Mosen Asadi, 2007):


Page | 151

Mass flow rate of solids = 226 kg/hr

Mass flow rate of clarified juice = 88,962 kg/hr

Time necessary to dismantle = 900 s

Time to reassemble = 900 s

Time to drop cake from each plate = 30 s

Density of slurry = 1090 kg/m3

Density of cake, 𝜌𝑐 = 2700 kg/m3

Density of filtrate, 𝜌𝑓 = 1050 kg/m3

Viscosity of filtrate = 0.075 kg/m.s

Specific cake resistance, r av = 2.21×1011 m/kg

Porosity of cake, 𝑒 = 0.225

Pressure drop across cake, ΔP = 4 bar

Plate thickness

Let,

𝑛 = Number of frames

𝑏 = Frame thickness

The time to complete one batch cycle is given by equation (7.3.11)

𝑡𝑇 = 𝑡𝑓 + 𝑡𝑐 + 𝑡𝑤 + 𝑡𝑑𝑛 = 𝑡𝑓 1 +𝑡𝑐𝑡𝑓

+𝑡𝑤𝑡𝑓

+𝑡𝑑𝑡𝑓

+𝑡𝑑𝑛𝑡𝑓

Time to remove cake from all the plates (Chemical Engineering Design, Coulson, Volume 2)

= 𝑛 × 𝑡𝑐

Time to complete one cycle

𝑡𝑇 = 𝑡𝑓 + 1800 + 30𝑛

Overall rate of filtration


Page | 152

=𝑉

𝑡𝑓 + 1800 + 30𝑛…………………………… 7.3.14𝑖)

The total volume of filtrate per cycle 𝑉 is given as

𝑉 =𝑇𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑟𝑎𝑚𝑒𝑠

𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐𝑎𝑘𝑒 𝑑𝑒𝑝𝑜𝑠𝑖𝑡𝑒𝑑 𝑏𝑦 𝑢𝑛𝑖𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒, 𝑣………………… . (7.3.15)

Rate of filtration

=𝑚𝑎𝑠𝑠 𝑜𝑓 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒

𝜌𝑓

Mass of filtrate

=88,962 𝑘𝑔/𝑟

3600 𝑠× 𝑟 = 24.71 𝑘𝑔/𝑠

Rate of filtration

=24.71 𝑘𝑔/𝑠

1050 𝑘𝑔/𝑚3= 0.0235 𝑚3/𝑠

Volume of cake deposited by unit volume of filtrate is given as (Chemical Engineering Design,

Coulson: Volume 2)

𝑣 =𝑐𝜌𝑓

1 − 𝑐 1 − 𝑒 𝜌𝑐 − 𝑐 𝑒 𝜌𝑓

Concentration of the insoluble in the entering stream

𝑐 =312 𝑘𝑔/𝑟

89,188 𝑘𝑔/𝑟= 0.003498

Volume of cake deposited by unit volume of filtrate is therefore

𝑣 =0.003498 × 1050

1 − 0.003498 1 − 0.225 2700− 0.003498 × 0.225 × 1050

𝑣 = 0.001762

The frames are assumed to be square with side of 1m,


Page | 153

Volume of frames

= 𝑛 × 𝐴 × 𝑏 × 2

Where 𝐴 = 1 × 1 = 1 𝑚2

Volume of frames= 𝑛 × 1 × 𝑏 × 2 = 2𝑛𝑏

Using equation (7.3.13),

𝑉 =2𝑛𝑏

𝑣=

2𝑛𝑏

0.001762= 1135.07𝑛𝑑

Given equation (7.3.12),

𝑑𝑉

𝑑𝑡=

𝐴2Δ𝑃

𝜇 (𝑟𝑎𝑣𝑐𝑉 + 𝐴𝑅)

Upon integrating at V=0 when t=0 and V=V when t=tf yields,

𝑉

2

2

= 𝐴2 ∆𝑃 𝑡𝑓𝑟𝑎𝑣𝜇𝑣

Substituting the values obtained in the above equation yields

(1135.07𝑛𝑏)2

2=

(2 × 1)2 × 6 × 105 𝑡𝑓2.21 × 1011 × 0.075 × 0.001762

6.442 × 105 × 𝑏2 = 2.4 × 106

29.205 × 106𝑡𝑓

𝑡𝑓 = 78.39 × 105𝑏2 …………………………… . .……… (7.3.15𝑖)

Substituting the above results into equation (7.3.13i)

0.0235 =1135.07𝑛𝑏

78.39 × 105𝑏2 + 1800 + 30𝑛

Making 𝑛 the subject of the above equation

184216.5𝑏2 + 42.3 + 0.705𝑛 = 1135.07𝑛𝑏

Hence


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𝑛 =184216.5𝑏2 + 42.3

1135.07𝑏 − 0.705………………………………… . (7.3.16)

𝑛 is a minimum when 𝑑𝑛 𝑑𝑏 = 0, that is when:

209.099 × 106𝑑2 − 259745𝑑 − 48013 = 0

Solving the above quadratic equation yields:

𝑏 = 𝟎.𝟎𝟏𝟓𝟖𝟎 𝒎 𝑜𝑟 𝟏𝟓.𝟖𝟎 𝒎𝒎

Number of frames

It is determined by using equation (7.3.14) and substituting the obtained values from the above

calculations for the plate thickness:

𝑛 =184216.5 × 0.01582 + 42.3

1135.07 × 0.0158 − 0.705

𝑛 = 5.12

Therefore a minimum of 6 frames must be used.

The sizes of frames which will give exactly the required rate of filtration when six are used are

given by substituting the value of 𝑛 = 6 into the equation:

0.0235 =1135.07 × 6𝑏

78.39 × 105𝑏2 + 1800 + 30 × 6

Or: 184216.5𝑏2 − 6810.42𝑏 + 46.53 = 0

Solving the above equation yields:

𝑏 = 0.0090 𝑜𝑟 0.0279 𝑚

Thus, 6 frames of thickness either 9 mm or 27.9 mm will give exactly the required filtration rate;

intermediate sizes give higher rates.

Thus any frame thickness between 9 mm and 27.9 mm will be satisfactory. In practice, however

20 mm (0.78 in) frames have been chosen.

Filtration area

The area of filtration is determined as follows:


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𝐴 = 2 × 𝑥 × 𝑥 × 𝑛

= 2 × 1 𝑚 × 1 𝑚 × 6

𝑨 = 𝟏𝟐 𝒎𝟐

Where 𝑥 is the length and width of the square plates.

Time of filtration

This is determined using equation (7.3.14i):

𝑡𝑓 = 78.39 × 105𝑏2

Since the chosen thickness is 𝑏 = 0.020 𝑚,

𝑡𝑓 = 78.39 × 105 × 0.022

𝑡𝑓 = 𝟑𝟏𝟑𝟔 𝒔𝒆𝒄𝒐𝒏𝒅𝒔

Total time for filter batch cycle

The time to complete one batch cycle is given by equation (7.3.11) written here as

𝑡𝑇 = 𝑡𝑓 + 1800 + 30𝑛

𝑡𝑇 = 3136 + 1800 + 30 × 6

𝑡𝑇 = 𝑡𝑓 + 1800 + 30𝑛

𝑡𝑇 = 𝟓𝟏𝟏𝟔 𝒔𝒆𝒄𝒐𝒏𝒅𝒔

Cake deposition

This is determined using the following equation:

𝑙 = 𝑣𝑉

𝐴

𝑙 = 0.001762 ×0.0235

12

𝑙 = 3.450 × 10−6 𝑚/𝑠


Page | 156

Volumetric flow rate of liquid in the exit stream

This is determined as follows:

𝑉𝑓 =𝑀𝑐

𝑊

Where 𝑊 = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑎𝑘𝑒 𝑝𝑒𝑟 𝑚3𝑜𝑓 𝑡𝑒 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 (𝑘𝑔/𝑚3)

𝑊 =𝜌𝑐

1 𝑐 − 1 𝑐1 =

2700

1 𝑐 − 1 𝑐1 = 9.493 𝑘𝑔/𝑚3

𝑉𝑓 =24.77 × 0.003498

9.493

𝑉𝑓 = 9.13 × 10−3 𝑚3 𝑠


The plate-and-frame press consists of several sets of two square plates (one for juice and the

other for water inlet) and a frame. The face of the plates is covered with filter cloth. The

arrangement of plates and frame starts with a solid head and continues in the following way:

juice plate, frame, water plate, frame, juice plate, frame, water plate, and so on. The sets sit

vertically in a metal rack, and a screw squeezes them together. Each cycle consists of the

following steps:

Table 7. 6 Summary of Chemical Engineering design


Rate of cake formation 0.126 kg/s

Filtrate volumetric flow rate 0.0235 m3/s

Total filtration area 12 m2

Filtration time 3136 seconds

Total time for filter batch cycle 5116 seconds

Number of frames 6

Thickness of frame 20 mm

Filter pressure difference 4 bar

Filter operating temperature 80 °C


Page | 157

1. Filtration: Feed is pumped into one end of the assembly and passes through an inlet channel,

which runs through the entire assembly. The channel feeds the frames, where the solids

gradually are collected. The juice passes the filter cloth and the plates, enters the juice-outlet

channel, and goes out from the discharge end. Filtration continues until juice no longer flows

out the discharge end. When the frames are full of solid (it usually takes one hour), the press is

said to be jammed.

2. Cake washing: The inlet for feed is closed and wash water (about 60°C) enters to de-sweeten

the cake.

3. Cake drying: Low-pressure steam or compressed air is blown through the cake to reduce the

water content of the cake.

4. Cake emptying: The assembly is opened manually to drop the cake from the plates.

5. Cleaning: The plates, frames, and filter cloths are cleaned for next cycle.

Material of construction

Many factors have to be considered when selecting engineering materials, but for chemical

process plant the overriding consideration is usually the ability to resist corrosion.

The most important characteristics to be considered when selecting a material of construction

are (Coulson and Richardson’s Chemical Engineering Vol. 6):

1. Mechanical properties:

Strength-tensile strength.

Stiffness-elastic modulus (Young’s modulus).

Toughness-fracture resistance.

Hardness-wear resistance.

Fatigue resistance.

Creep resistance.

2. The effect of high and low temperatures on the mechanical properties.

3. Corrosion resistance.


Page | 158

4. Any special properties required; such as, thermal conductivity, electrical resistance,

magnetic properties.

5. Ease of fabrication forming, welding, casting.

6. Availability in standard sizes plates, sections, tube.

7. Cost

The structural frame and other external parts of the filter which is used to support the entire

filter press will be made of AISI 304 stainless steel. This material contains the minimum Cr and

Ni that give a stable austenitic structure.

The plates and frames which are 1 m × 1m in dimension will be constructed using AISI 321

stainless steel. It has a slightly higher strength than type 304, and is more suitable for relatively

high-temperature use.

In construction of the liner pipes, AISI 321 stainless steel is used.

Filter medium/cloth

The filter cloth must meet general requirements for any type of filter and particular

requirements for individual filters. In general, the filter cloth must have the following

properties:

Retains solids

Not plug easily

Produce clear filtrate

Be not expensive

Be thermally resistant

Be chemically resistant

Be strong and not wear easily

Allow solids to be discharged easily


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The filter cloth made from polypropylene meets all the above requirements. Hence it is chosen

as the material for the filter medium. It is resistant to hydrochloric acid less than 3% (used for

cleaning).

Filter plate type

The type of frame and plate used is the caulked and gasketed shown below.

Slurry inlet pipe diameter

The slurry inlet pipe diameter is calculated from the equation of economic pipe diameter

(Coulson and Richardson’s Chemical Engineering Vol. 6).

For stainless steel pipe:

𝑑,𝑜𝑝𝑡𝑖𝑚𝑢𝑚 = 260𝐺0.53𝜌−0.37

Where,

𝐺 = 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 , 𝑘𝑔/𝑠 𝜌 = 𝑑𝑒𝑛𝑠𝑖𝑡𝑦, 𝑘𝑔/𝑚3

𝑑 = 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑝𝑖𝑝𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟,𝑚

𝑑,𝑜𝑝𝑡𝑖𝑚𝑢𝑚 = 260 × 24.770.53 × 1090−0.37

𝑑, 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 = 𝟏𝟎𝟕.𝟏 𝒎𝒎,𝑁𝑜𝑚𝑖𝑛𝑎𝑙 𝑠𝑖𝑧𝑒 𝑐𝑜𝑠𝑒𝑛 𝑖𝑠 𝟏𝟐𝟓 𝒎𝒎

Filtrate outlet pipe diameter

The outlet pipe diameter is calculated from the equation of economic pipe diameter (Coulson

and Richardson’s Chemical Engineering Vol. 6).

Figure 7. 14 Caulked and gasketed frame (www.durcofilters.com)


Page | 160

For stainless steel pipe:

𝑑,𝑜𝑝𝑡𝑖𝑚𝑢𝑚 = 260𝐺0.53𝜌−0.37

Where,

𝐺 = 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 , 𝑘𝑔/𝑠

𝜌 = 𝑑𝑒𝑛𝑠𝑖𝑡𝑦, 𝑘𝑔/𝑚3

𝑑 = 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑝𝑖𝑝𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟,𝑚

𝑑,𝑜𝑝𝑡𝑖𝑚𝑢𝑚 = 260 × 24.710.53 × 1050−0.37

𝑑,𝑜𝑝𝑡𝑖𝑚𝑢𝑚 = 𝟏𝟎𝟖.𝟓 𝒎𝒎 ,𝑁𝑜𝑚𝑖𝑛𝑎𝑙 𝑠𝑖𝑧𝑒 𝑐𝑜𝑠𝑒𝑛 𝑖𝑠 𝟏𝟐𝟓 𝒎𝒎

Flanges

Standard flanges (Coulson and Richardson’s Chemical Engineering Vol. 6) are used in the plate

and frame filter to join the pipes to the filter structure. The following is a detail of the

specifications.

𝑃𝑖𝑝𝑒 𝑜𝑢𝑡𝑒𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 139.7 𝑚𝑚

𝐷 = 240 ,𝑏 = 18,1 = 48,𝑑4 = 178,𝑓 = 3,𝑑2 = 18,𝑘 = 200,𝑑3 = 155, 𝑟 = 8 (All dimensions in mm)

Bolting type M16 with 8 bolts.

Figure 7. 15 Steel welding neck flanges, 6 bar


Page | 161

Valves

A valve selected for shut-off purposes should give a positive seal in the closed position and

minimum resistance to flow when open. Since the filter will be cleaned on an hourly basis a

plug valve is chosen for the filter press. This valve is also directional.


Motor type Hydraulic

Material of construction for rack (supporting) AISI 304 stainless steel

Material of construction of liner pipes AISI 321 stainless steel

Material of construction of plates and frames AISI 321 stainless steel

Inlet pipe diameter 125 mm

Outlet pipe diameter 125 mm

Filter cloth Polypropylene

Plate and frame type Caulked and gasketed

Pump type Centrifugal

Pumping pressure 6 bar

Pipe inlet and outlet thickness 7.35 mm

Table 7. 7 Summary of mechanical design


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CHAPTER EIGHT

8.0 PROCESS CONTROL AND INSTRUMENTATION

8.1 INTRODUCTION

The measurement of a process variable, the comparison of that variable with its respective set

point, and the manipulation of the process in a way that will hold the variable at its set point

when the set point changes or when a disturbance changes the process is known as process

control. Process control is used to maintain a variable in a process plant at a set point or to

cause it to respond to a set point change. The most common method used in process control is

the PID (proportional, integral, derivative) control algorithm.

Instruments are provided to monitor the key process variables during plant operation. They

may be incorporated in automatic control loops, or used for the manual monitoring of the

process operation. They may also be part of an automatic computer data logging system.

Instruments monitoring critical process variables will be fitted with automatic alarms to alert

the operators to critical and hazardous situations.

A control system consists of four stages. First, the item to be controlled must be measured. This

reading must then be compared with some desired value, called the set point. Depending on

the result of this comparison, a decision must be made whether some variable(s) in the process

should be changed. Then if a change is indicated, the amount of change required must be

determined and it must be instituted. The comparison, decision making and size change

determination are considered part of the controller.

8.2 INSTRUMENTATION AND CONTROL OBJECTIVES

The primary objectives of the designer when specifying instrumentation and control schemes

are (Coulson and Richardson, volume 6),

1. Safe plant operation:

a) To keep the process variables within known safe operating limits.


Page | 163

Controlled

variable

Load

-

Set point + Controller Valve

+ Process

Measurement

b) To detect dangerous situations as they develop and to provide alarms and

automatic shut-down systems.

c) To provide interlocks and alarms to prevent dangerous operating procedures.

2. Production rate: To achieve the design product output.

3. Product quality: To maintain the product composition within the specified quality

standards.

4. Cost: To operate at the lowest production cost, commensurate with the other

objectives.

8.3 THE FEEDBACK CONTROL LOOP

Feedback control utilizes a loop structure with negative feedback to bring a measurement to a

desired value, or set point. A block diagram of a typical process control loop is shown in Figure

below, with key elements of the loop being the controller, valve, process, and measurement.

Note that in addition to the set point entering the loop, there is also a load shown. Changes in

set point move the process to anew value for the controlled variable, whereas changes in load

affect the process resulting in a disturbance to the controlled variable.

The control loop must respond to either a change in set point or a change in the load, by

manipulating the valve in a manner that affects the process and restores the controlled variable

to its set point. Reacting to set point changes is called servo operation, and reacting to load

Figure 8. 1 Block diagram of a control loop


Page | 164

changes is called regulator operation. Control loop performance is determined by the response

characteristics of the block elements in the loop: the controller, valve, process and

measurement.

The components of the feedback control loop system will include:

Primary sensors: thermocouples, resistance temperature detectors (RTD) or

thermometers for temperature; orifice plates, turbine, magnetic flow meters for flow

and differential pressure cells for pressure or level.

Transmitters: Transmitters convert the sensor signal into a control signal for use by

recorders, indicators or controllers (for flow, temperature, pressure, etc.)

Controllers: typically proportional (P), proportional-integral (PI) or proportional-integral-

derivative (PID) forms or model based controllers.

Signal conditioning: ensuring signals are normalized for processing (based on range and

zero of instruments).

Final control elements: normally control valves and the diaphragms or motors that drive

the valve stem, plus the basic valve characteristic (proportional, equal percentage, quick

opening).

8.4 TYPICAL CONTROL SYSTEMS

Flow, level, and pressure are process variables that can be controlled by manipulating their own

process stream. Flow control is typically used to establish throughput, whereas level and

pressure are measures of liquid and gas inventory, which must be maintained to establish the

overall process material balance.

8.4.1 Flow controller

Flow control is probably the most common control loop in most processes. Typically a liquid or

gas flow rate is maintained in a pipe by a throttling valve downstream of the measurement.

These consist of flow meters (liquid and gas) which measure, report and record fluctuating flow

variables for the necessary counter action to be taken.


Page | 165

8.4.2 Pressure controller

Pressure in a pipe line may be controlled by manipulating either the inlet or outlet flow.

Pressure is an integrating process, usually with negligible dead time; therefore high gain and

long integral time are recommended tuning. A pressure regulator is a self-contained valve and

field controller with high gain about a preset set point.

Figure 8. 2 Flow controller used to control the flowrate of CaCl2 and anti-foaming agent to the diffuser

Figure 8. 3 Figure showing a pressure controller used to maintain the correct pressure in a boiling pan


Page | 166

8.4.3 Temperature controller

Various thermal sensitive instruments are used to regulate this parameter; they may be thermostats,

thermocouples or digital thermometers. These transmit temperature data to controllers which then

regulate the amount of steam or cooling water supplied to the equipment in question.

8.4.4 Level controller

Level control can be designed into the process with gravity, pressure and elevation determining

outlet flow. They are installed to detect rising levels of fluids in holding vessels and prevent

spillage upon attaining the maximum capacity.

Figure 8. 4 showing a temperature controller used to control the flow of steam to heat exchanger thus controlling the temperature of exit stream flowing to carbonation tank 1

Figure 8. 5 showing a level controller used to maintain thin juice level inside the carbonation


Page | 167

CHAPTER NINE

9.0 ECONOMIC AND PROFITABILITY ANALYSIS

9.1 INTRODUCTION

Chemical plants, like any other investment are built to make a profit, and an estimate of the

investment required and the cost of production are needed before the profitability of a project

can be assessed.

An acceptable plant design must present a process that is capable of operating under

conditions which will yield profit. Since ‘net profit = total income – all expenses’, it is essential

that the chemical engineer be aware of different types of costs involved in manufacturing

process. Capital must be allocated for ‘direct plant expenses’ (e.g. raw material, labour,

equipment) and ‘indirect expenses’ (e.g. administration, sales). The ‘total investment’ for any

project consists of ‘fixed capital investment’ and the ‘working capital’.

Factors affecting investment and production costs

(i) Equipment cost – is a major cost in a chemical process industry. A reduction can be

made by the use of idle equipment capacity, purchase of second hand equipment, use

of standard type equipment. For fabricated equipment, invite quotations.

(ii) Price fluctuations in salaries and wages - wages fluctuate from time to time and place to

place.

(iii) Company policies - about labour, safety regulations, depreciation calculations etc.

(iv) Rate of production and operating time - when equipment stands idle labour costs are

usually low but other costs such as maintenance, protection and depreciation continue.

Fixed costs remain the same irrespective of production rate. Total product cost

increases as rate of production increases. At ‘Break-even point’

Total product cost = Total income (all products sold)

(v) Government Policies on imports and exports - rate of depreciation, income tax, and

environment regulations etc.


Page | 168

9.2 PLANT DEVELOPMENT TIMELINE

9.2.1 Expected Dates

Commencement of construction : June 2014

Completion of construction: June 2016

Commencement of operation: January 2017

9.2.2 Plant Operation Specifications

Daily Operation Time: 24 hrs

Number of shifts: 3

Weekly Operation Time: 6 days with every 7th day used for equipment cleaning and maintenance.

9.3 CAPITAL INVESTMENT

9.3.1 Fixed Capital Investment (FCI)

This is the capital needed to supply the necessary manufacturing and plant facilities. It can be

manufacturing or non-manufacturing cost. It includes:

Direct cost

Purchased equipment

Purchase equipment installation

Instrumentation and control

Piping

Electrical equipment and materials

Buildings (including services such as heating, air-conditioning etc)

Yard improvement

Service facilities :

- Utilities - steam, water etc.

- facilities e.g. electric, substation, ref. Plant

- non-process equipment - e.g. office furniture

- distribution and packaging


Page | 169

Land

Indirect cost

Engineering and supervision

Construction expenses

Contractor's fee

Contingency

9.3.2 Working Capital (WC)

Working capital is the additional money needed, above what it cost to build the plant to start

the plant up and run it until it starts earning income. It includes the cost of:

1. Value of raw material inventory – usually estimated as 2weeks’ delivered cost of raw

materials;

2. Value of product and by product inventory – estimated as 2weeks’ cost of production;

3. Cash on hand – estimated as 1 week’s cost of production;

4. Accounts receivable – products shipped but not yet paid for–estimated as 1month’s cost

of production;

5. Credit for accounts payable – feedstock, solvents, catalysts, packaging, etc. received but

not yet paid for – estimated as 1 month’s delivered cost;

6. Spare parts inventory

Most of the working capital is recovered at the end of the project. Working Capital is estimated

to be 14.2% of the FCI.

Total Capital Investment

The total investment needed for a project is the sum of the fixed capital investment (FCI) and

working capital (WC).i.e.

𝑇𝐶𝐼 = 𝐹𝐶𝐼 + 𝑊𝐶


Page | 170

9.3.3 Estimation of the Cost of Purchased Equipment

Before the plant is fully operational, all the necessary equipment components must be

purchased and installed. The costs for all the equipment in our plant is obtained based on the

formula below, Chemical Engineering Design Principles Practice and Economics of Plant and

Process Design, 1983.

𝐶𝑒 = 𝑎 + 𝑏𝑆𝑛

Where:

𝐶𝑒 = 𝑝𝑢𝑟𝑐𝑎𝑠𝑒𝑑 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑐𝑜𝑠𝑡

𝑎, 𝑏 = 𝑐𝑜𝑠𝑡 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡𝑠

𝑆 = 𝑠𝑖𝑧𝑒 𝑝𝑎𝑟𝑎𝑚𝑒𝑡𝑒𝑟

𝑛 = 𝑒𝑥𝑝𝑜𝑛𝑒𝑛𝑡 𝑓𝑜𝑟 𝑡𝑎𝑡 𝑡𝑦𝑝𝑒 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡

Based on Marshall and Swift Equipment Cost Indexes

2006 = 499.6

2011 = 585.7

𝐶𝑜𝑠𝑡 𝑒𝑠𝑡𝑖𝑚𝑎𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 = 585.7499.6 = 1.1723 (𝑇𝑒 𝑏𝑎𝑠𝑒 𝑦𝑒𝑎𝑟 𝑢𝑠𝑒𝑑 𝑖𝑠 2006. )


Page | 171

Table 9. 1 Purchased equipment cost

EQUIPMENT SIZE, S a b n Sn Ce(BASE YEAR

2006), $ Ce(CURRENT YEAR

2011), $ NUMBER OF EQUIPMENT

TOTAL , $

Hopper 177.00 5500 500 0.6 22.3246 16,662.31 19,533.22 1 19,533.22

Belt conveyor 1 12.00 21000 340 1 12 25,080.00 29,401.28 1 29,401.28

Belt conveyor 2 14.00 21000 340 1 14 25,760.00 30,198.45 1 30,198.45

Belt conveyor 3 10.00 21000 340 1 10 24,400.00 28,604.12 1 28,604.12

Belt conveyor 4 16.00 21000 340 1 16 26,440.00 30,995.61 1 30,995.61

Screen 1 3.80 400 120 2 14.44 2,132.80 2,500.28 1 2,500.28

Screen 2 2.50 400 150 2 6.25 1,337.50 1,567.95 1 1,567.95

Screen 3 2.50 400 150 2 6.25 1,337.50 1,567.95 1 1,567.95

Screen 4 4.00 400 150 2 16 2,800.00 3,282.44 1 3,282.44

Stone separator 4.75 400 300 2 22.5625 7,168.75 8,403.93 1 8,403.93

Trash separator 7.50 200 240 2 56.25 13,700.00 16,060.51 1 16,060.51

Beet pump 121.10 3300 48 1.2 316.063 18,471.00 21,653.55 1 21,653.55

Pump 1 26.00 3300 48 1.2 49.8848 5,694.47 6,675.63 1 6,675.63

Pump 2 26.16 3300 48 1.2 50.2534 5,712.16 6,696.37 1 6,696.37

Pump 3 26.20 3300 48 1.2 50.3456 5,716.59 6,701.56 1 6,701.56

Pump 4 26.20 3300 48 1.2 50.3456 5,716.59 6,701.56 1 6,701.56

Pump 5 25.80 3300 48 1.2 49.4247 5,672.38 6,649.74 1 6,649.74

Pump 6 25.80 3300 48 1.2 49.4247 5,672.38 6,649.74 1 6,649.74

Pump 7 7.20 3400 52 1.5 19.3196 4,404.62 5,163.54 1 5,163.54

Washer 33.00 900 400 0.8 16.3988 7,459.51 8,744.78 1 8,744.78

Slicer 81.10 1220 990 0.9 52.2539 52,951.37 62,074.89 1 62,074.89

Diffuser 25.99 100 14000 0.7 9.78058 137,028.05 160,637.99 1 160,637.99

Heat exchanger 1 70.00 1100 850 0.4 5.47065 5,750.06 6,740.79 1 6,740.79


Page | 172

Heat exchanger 2 80.00 1100 850 0.4 5.7708 6,005.18 7,039.87 1 7,039.87

Heat exchanger 3 50.00 1100 850 0.4 4.78176 5,164.50 6,054.34 1 6,054.34

Heat exchanger 4 70.00 1100 850 0.4 5.47065 5,750.06 6,740.79 1 6,740.79

Lime tank 23.92 5900 900 0.7 9.22854 14,205.68 16,653.32 2 33,306.64

Carbonation tank 1 23.86 5900 900 0.7 9.21233 14,191.09 16,636.22 3 49,908.66

Carbonation tank 2 15.90 5900 900 0.7 6.93391 12,140.52 14,232.33 2 28,464.65

Sulphitation tank 23.54 5900 1200 0.7 9.12566 16,850.80 19,754.19 1 19,754.19

Syrup tank 1 31.40 5700 700 0.7 11.1648 13,515.36 15,844.05 3 47,532.16

Syrup tank 2 14.50 5700 700 0.7 6.50066 10,250.46 12,016.62 2 24,033.24

Rotary drum filter 23.52 -45000 57000 0.3 2.57888 101,996.18 119,570.12 1 119,570.12

Filter press 0.60 32000 18000 0.5 0.7746 45,942.74 53,858.67 2 107,717.35

Evaporator 47.26 18000 14000 0.6 10.1087 159,522.10 187,007.76 4 748,031.03

Melter 14.50 14000 15400 0.7 6.50066 114,110.20 133,771.39 1 133,771.39

Boiling Pan 8.82 17500 13500 0.6 3.69217 67,344.23 78,947.64 3 236,842.93

Mixer 14.53 5500 620 0.8 8.50771 10,774.78 12,631.27 3 37,893.82

Centrifuge 1.00 24000 26000 0.8 1 50,000.00 58,615.00 3 175,845.00

Screw conveyor 1,2,3 2.50 21000 340 1 2.5 21,850.00 25,614.76 3 76,844.27

Screw conveyor 4 8.00 35000 378 1 8 38,024.00 44,575.54 1 44,575.54

Screw conveyor 5 10.00 35000 391 1 10 38,910.00 45,614.19 1 45,614.19

Feeder 1.03 2700 500 0.7 1.02091 3,210.45 3,763.61 1 3,763.61

Rotary drum dryer 35.03 -7400 5400 0.9 24.5469 125,153.10 146716.9771 1.00 146,716.9771

Total purchased equipment cost,

IE

2,577,226.63


Page | 173

Table 9. 2 Total capital cost estimates

Direct cost Purchased Equipment cost Cost ($)

purchased Equipment cost 100.00% 2,577,226.63

Equipment Delivery cost 10.00% 257,722.66

Delivered Equipment cost, ID 2,834,949.29

Direct Cost % of ID Cost ($)

Purchased Installation 39.00% 1,105,630.22

Instrumentation and control 13.00% 368,543.41

Piping installed 31.00% 878,834.28

Electrical 10.00% 283,494.93

Buildings 29.00% 822,135.29

Yard Improvement 10.00% 283,494.93

Service Facilities 55.00% 1,559,222.11

Land 6.00% 170,096.96

Total Direct Plant Cost 8,306,401.42

Indirect cost % of ID Cost ($)

Engineering & supervision 32.00% 907,183.77

Construction 34.00% 963,882.76

Contractors fee 18.00% 510,290.87

Contingency 36.00% 1,020,581.74

Startup expense 35.00% 992,232.25

Total indirect cost 4,394,171.40

Total FCI (Fixed Capital investment) 12,700,572.82

% of TCI Cost ($)

Total FCI 14.29% 12,700,572.82

Working capital 85.71% 2,097,862.47

Total Capital investment (FCI) 14,798,435.29

Table 9. 3 Total capital cost


Page | 174

9.3.4 Total Product Cost

This is the cost involved in the manufacture of goods and sale of products. It can be estimated

on one of the three bases:

Daily basis

Unit-of-product basis

Annual basis

The annual basis is chosen for the calculation of the total product cost because it smoothes the

effect of seasonal variations; if the equipment are not in use full time, it takes care of; more

convenient to calculate cost for plant operation on less full capacity; convenient for infrequent

but large production expenses.

Total production cost is made up of:

1. Manufacturing costs and

2. General Expenses.

Manufacturing cost is divided into:

Direct production costs

Raw material cost

Power and utilities cost

Operating labour

Royalties

Maintenance and repair

Laboratory charges

Catalysts and solvents

Fixed charges

These are costs not affected by the level of production and include

Depreciation

Taxes(property)

Insurances


Page | 175

Rent

Plant overheads costs

Medical

Safety and protection

General plant overhead- payroll, packaging, restaurant, recreation, salvage, labs and

storage.

The general expenses

These are costs associated with management and administrative activities not directly related

to the manufacturing process. They include:

Administration cost

Ware housing

Distribution and marketing costs

Research and development

Raw Materials Cost Estimates

Table 9. 4 Annual raw material cost estimates

Name of material Price, $/tonne Annual amount

tonne/yr. Annual raw

material, $/yr.

Raw sugar beet 49.40 612,000.00 30,232,800.00

Carbon dioxide 20.00 676.80 13,536.00

Anti-foaming agent 220.00 57.60 12,672.00

Calcium hydroxide 180.00 3,859.20 694,656.00

Sulphur dioxide 850.00 192.80 163,880.00

Calcium chloride 150.00 720.00 108,000.00

Total raw material cost 31,225,544.00


Page | 176

Utilities Cost Estimates

Table 9. 5 Utility Cost Estimates (Annual)

Depreciation

Initial expenses in equipment, buildings etc. is written off as a manufacturing expense. A decrease in value (depreciation) is assumed to occur throughout the usual life of the material possessions.

Depreciation (D) is calculated based on declining balance method:

𝑉𝑆 = 𝑉(1 − 𝑓)𝑛

Where:

𝑉𝑆𝑖𝑠 𝑡𝑒 𝑎𝑠𝑠𝑒𝑡 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑡𝑒 𝑒𝑛𝑑 𝑜𝑓 𝑦𝑒𝑎𝑟 𝑛 𝑠𝑒𝑟𝑣𝑖𝑐𝑒 𝑙𝑖𝑓𝑒

𝑉 𝑖𝑠 𝑡𝑒 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑡𝑒 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡

𝑓 𝑖𝑠 𝑡𝑒 𝑓𝑖𝑥𝑒𝑑 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑓𝑎𝑐𝑡𝑜𝑟

𝑛 𝑖𝑠 𝑡𝑒 𝑠𝑒𝑟𝑣𝑖𝑐𝑒 𝑙𝑖𝑓𝑒 𝑖𝑛 𝑦𝑒𝑎𝑟𝑠

The table below gives the depreciation values for all the years, including the salvage value(𝑉𝑠)

at the end of the plant life(20 𝑦𝑒𝑎𝑟𝑠).

Utilities % of FCI Cost ($)

Electricity 1.00% 127,005.73

Fuel 0.10% 12,700.57

Waste disposal 1.50% 190,508.59

Steam 1.00% 127,005.73

Raw material storage 0.50% 63,502.86

Finished product storage 1.50% 190,508.59

Safety installation 0.40% 50,802.29

Hot water 1.00% 127,005.73

Process water 0.80% 101,604.58

Hot air 1.00% 127,005.73

Communication 0.20% 25,401.15

Total 1,143,051.55


Page | 177

Table 9. 6 Annual Depreciation

V n Va D

12,530,475.86 1 11,167,798.37 1,362,677.49

11,167,798.37 2 9,953,310.77 1,214,487.60

9,953,310.77 3 8,870,897.56 1,082,413.21

8,870,897.56 4 7,906,195.77 964,701.79

7,906,195.77 5 7,046,404.40 859,791.37

7,046,404.40 6 6,280,114.53 766,289.87

6,280,114.53 7 5,597,157.97 682,956.56

5,597,157.97 8 4,988,472.29 608,685.68

4,988,472.29 9 4,445,980.61 542,491.68

4,445,980.61 10 3,962,484.39 483,496.22

3,962,484.39 11 3,531,567.93 430,916.46

3,531,567.93 12 3,147,513.23 384,054.70

3,147,513.23 13 2,805,224.12 342,289.11

2,805,224.12 14 2,500,158.63 305,065.49

2,500,158.63 15 2,228,268.72 271,889.91

2,228,268.72 16 1,985,946.59 242,322.13

1,985,946.59 17 1,769,976.76 215,969.83

1,769,976.76 18 1,577,493.45 192,483.31

1,577,493.45 19 1,405,942.52 171,550.93

1,405,942.52 20 1,253,047.59 152,894.93


Page | 178

Operating Labour Cost Estimates

Department Job description Number Monthly pay($) Annual pay($)

Administration General manager 1 2700 32,400.00

Human resource manager 1 2000 24,000.00

Marketing manager 1 2000 24,000.00

Procurement Manager 1 2000 24,000.00

Clerk 2 400 9,600.00

Secretary 4 300 14,400.00

Receptionist 1 250 3,000.00

Tea girl 1 150 1,800.00

Accounting Finance manager 1 2000 24,000.00

Clerk 1 400 4,800.00

Accountant 2 750 18,000.00

Secretary 2 300 7,200.00

Sales and marketing Sales representative 1 750 9,000.00

Clerk 1 400 4,800.00

Secretary 1 300 3,600.00

Production Production manager 1 2200 26,400.00

Engineers 5 1800 108,000.00

Supervisors 8 800 76,800.00

operators 22 500 132,000.00

Technicians 10 500 60,000.00

Casuals 50 150 90,000.00

Quality control Chemists 4 400 19,200.00

Supporting staff Chief security officer 1 1000 12,000.00

Guards 8 150 14,400.00

Cafeteria 10 250 30,000.00

Drivers 4 315 15,120.00

Total Operating Costs($) 788,520.00

Table 9.7 Annual Operating labour cost estimates


Page | 179

Total Product Cost

Table 9. 7 Total product cost estimates

Direct product costs Factor Cost ($)

Raw material - 31,225,544.00

operating labour costs - 788,520.00

Utilities - 1,143,051.55

Maintenance (5% of FCI) 7% 889040.0972

Laboratory charges (10% of OLC) 10% 78852

Operating supplies (15% of maintenance) 15% 133356.0146

Total direct product cost 34,258,363.67

Fixed charges Depreciation (10% of FCI) - 563,871.41

Property taxes (3% of FCI) 3.0% 381,017.18

Insurance (2% of FCI) 2% 254,011.46

Total fixed charges 1,198,900.05

General expenses Plant overhead costs (7% of TPC) 7.00% 3,259,795.70

Administrative costs (10% of TPC) 10.00% 4,656,851.00

Distribution and marketing (2% of TPC) 2.00% 931,370.20

Research and development (2% of TPC) 2.00% 931,370.20

Financing (9% of TCI) 9.00% 1,331,859.18

Total general expenses 11,111,246.28

Total Product cost 46,568,510.00

Profit margin, 20% (of TPC) 20% 9,313,702.00

Total product sales 55,882,212.00


Page | 180

9.4 ANNUAL CASH FLOW ANALYSIS

9.4.1 Annual Sales

The annual sales for our product (sugar) are shown in the table below:

Table 9. 8 Annual sales from the product

Annual cash flow analysis is based on the formulas below:

𝑆𝑡𝑎𝑟𝑡 𝑢𝑝 𝑒𝑥𝑝𝑒𝑛𝑠𝑒 = 35% 𝑜𝑓 𝑃𝑢𝑟𝑐𝑎𝑠𝑒𝑑 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑐𝑜𝑠𝑡 = 9,020,029.3205

𝐴𝑛𝑛𝑢𝑎𝑙 𝑇𝑃𝐶 = 𝑇𝑜𝑡𝑎𝑙 𝑇𝑃𝐶 × 𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦

𝐺𝑟𝑜𝑠𝑠 𝑝𝑟𝑜𝑓𝑖𝑡 𝑓𝑜𝑟 𝑓𝑖𝑟𝑠𝑡 𝑦𝑒𝑎𝑟 = 𝑇𝑜𝑡𝑎𝑙 𝑠𝑎𝑙𝑒𝑠 – 𝑇𝑃𝐶 − 𝑆𝑡𝑎𝑟𝑡 𝑢𝑝 𝑐𝑜𝑠𝑡

𝐺𝑟𝑜𝑠𝑠 𝑝𝑟𝑜𝑓𝑖𝑡 𝑎𝑓𝑡𝑒𝑟 𝑓𝑖𝑟𝑠𝑡 𝑦𝑒𝑎𝑟 = 𝑇𝑜𝑡𝑎𝑙 𝑠𝑎𝑙𝑒𝑠 − 𝑇𝑜𝑡𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝑐𝑜𝑠𝑡𝑠

𝑁𝑒𝑡 𝑝𝑟𝑜𝑓𝑖𝑡 = 𝐺𝑟𝑜𝑠𝑠 𝑝𝑟𝑜𝑓𝑖𝑡 ∗ 1 − 𝑡𝑎𝑥 𝑟𝑎𝑡𝑒

𝐴𝑛𝑛𝑢𝑎𝑙 𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝐶𝑎𝑠 𝑓𝑙𝑜𝑤 = 𝑁𝑒𝑡 𝑃𝑟𝑜𝑓𝑖𝑡 + 𝐷𝑒𝑝𝑟𝑒𝑐𝑖𝑎𝑡𝑖𝑜𝑛

𝐶𝑢𝑚𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝐶𝑎𝑠 𝑓𝑙𝑜𝑤

= 𝑁𝑒𝑡 𝑃𝑟𝑜𝑓𝑖𝑡 𝑎𝑓𝑡𝑒𝑟 𝑡𝑎𝑥𝑒𝑠 + 𝐷𝑒𝑝𝑟𝑒𝑐𝑖𝑎𝑡𝑖𝑜𝑛 − 𝑇𝑜𝑡𝑎𝑙 𝐶𝑎𝑝𝑖𝑡𝑎𝑙 𝐼𝑛𝑣𝑒𝑠𝑡𝑚𝑒𝑛𝑡

The following assumptions were also used for the calculation:

Income tax is charged at 30% of the gross profit

The production capacity in the first year is only 75%

All the products are on demand.

The annual cash flow is tabulated below:

Price, $/tonne Annual amount, tonne/yr Annual value of product

810.3381012 68961.6 55,882,212


Page | 181

Table 9.10 Annual cash flow

Year Capacity of plant

Annual sales, $ Annual TPC, $ Annual

depreciation, $ Gross income, $ Net income, $

Annual Cash flow, $

Cumulative cash flow, $

0 0% 0.00 0.00 0.00 0.00 0.00 0.00 -14,798,435.29

1 75% 41,911,659.00 34,926,382.50 1,362,677.49 5,622,599.01 3,935,819.30 5,298,496.80 -9,499,938.49

2 100% 55,882,212.00 46,568,510.00 1,214,487.60 8,099,214.40 5,669,450.08 6,883,937.68 -2,616,000.81

3 100% 55,882,212.00 46,568,510.00 1,082,413.21 8,231,288.79 5,761,902.15 6,844,315.36 4,228,314.55

4 100% 55,882,212.00 46,568,510.00 964,701.79 8,349,000.21 5,844,300.15 6,809,001.94 11,037,316.48

5 100% 55,882,212.00 46,568,510.00 859,791.37 8,453,910.63 5,917,737.44 6,777,528.81 17,814,845.30

6 100% 55,882,212.00 46,568,510.00 766,289.87 8,547,412.13 5,983,188.49 6,749,478.36 24,564,323.66

7 100% 55,882,212.00 46,568,510.00 682,956.56 8,630,745.44 6,041,521.81 6,724,478.37 31,288,802.03

8 100% 55,882,212.00 46,568,510.00 608,685.68 8,705,016.32 6,093,511.43 6,702,197.10 37,990,999.13

9 100% 55,882,212.00 46,568,510.00 542,491.68 8,771,210.32 6,139,847.22 6,682,338.90 44,673,338.03

10 100% 55,882,212.00 46,568,510.00 483,496.22 8,830,205.78 6,181,144.05 6,664,640.27 51,337,978.30

11 100% 55,882,212.00 46,568,510.00 430,916.46 8,882,785.54 6,217,949.88 6,648,866.34 57,986,844.64

12 100% 55,882,212.00 46,568,510.00 384,054.70 8,929,647.30 6,250,753.11 6,634,807.81 64,621,652.45

13 100% 55,882,212.00 46,568,510.00 342,289.11 8,971,412.89 6,279,989.02 6,622,278.13 71,243,930.58

14 100% 55,882,212.00 46,568,510.00 305,065.49 9,008,636.51 6,306,045.56 6,611,111.05 77,855,041.63

15 100% 55,882,212.00 46,568,510.00 271,889.91 9,041,812.09 6,329,268.47 6,601,158.37 84,456,200.00

16 100% 55,882,212.00 46,568,510.00 242,322.13 9,071,379.87 6,349,965.91 6,592,288.04 91,048,488.04

17 100% 55,882,212.00 46,568,510.00 215,969.83 9,097,732.17 6,368,412.52 6,584,382.35 97,632,870.39

18 100% 55,882,212.00 46,568,510.00 192,483.31 9,121,218.69 6,384,853.08 6,577,336.39 104,210,206.78

19 100% 55,882,212.00 46,568,510.00 171,550.93 9,142,151.07 6,399,505.75 6,571,056.68 110,781,263.46

20 100% 55,882,212.00 46,568,510.00 152,894.93 9,160,807.07 6,412,564.95 6,565,459.88 117,346,723.34

Total 1,103,673,687.00 919,728,072.50 11,277,428.27 172,668,186.23 120,867,730.36 132,145,158.63 1,073,204,764.18

Average profit 8,633,409.31

Average depreciation 563,871.41


Page | 182

Graphical Cumulative Cash Flow Analysis

Figure 9. 1 Cumulative Cash Flow Curve

9.5 PROFITABILITY ANALYSIS

Profitability analysis is a measure of the attractiveness of the project. Absolute profit is of little

significance; instead the rate of return on invested capital is to be looked into.

The methods used for profit analysis of this design include:

Rate of return

Pay out period

Discounted cash flow based on full life performance

-20

0

20

40

60

80

100

120

-5 0 5 10 15 20 25

Cu

mu

lati

ve c

ash

flo

w

Mill

ion

s

Year

Cumulative cash flowW

C+F

C+L

and

Break-even point

Pay-out period


Page | 183

9.5.1 Rate of Return

Rate of return (ROR), which is the ratio of annual profit to investment, is a simple index of the

performance of the money invested.

𝑅𝑂𝑅 =𝐴𝑛𝑛𝑢𝑎𝑙 𝑝𝑟𝑜𝑓𝑖𝑡

𝑇𝑜𝑡𝑎𝑙 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝐼𝑛𝑣𝑒𝑠𝑡𝑚𝑒𝑛𝑡

For our plant, the rate of return was calculated as:

𝑅𝑂𝑅 =5,313,702

14,798,435.29× 100% = 35.91 %

9.5.2 Payout period

This is the period of time theoretically necessary to recover the original capital investment in

the form of cash flow to the project based on total income minus all costs except depreciation.

Generally for this method, original capital investment means only the original, depreciable,

fixed-capital investment, and interest effects are neglected. Thus,

𝑃𝑎𝑦𝑜𝑢𝑡 𝑝𝑒𝑟𝑖𝑜𝑑 (𝑦𝑒𝑎𝑟𝑠) = 𝑑𝑒𝑝𝑟𝑒𝑐𝑖𝑎𝑏𝑙𝑒 𝑓𝑖𝑥𝑒𝑑 − 𝑐𝑎𝑝𝑖𝑡𝑎𝑙 𝑖𝑛𝑣𝑒𝑠𝑡𝑚𝑒𝑛𝑡

𝑎𝑣𝑔 𝑝𝑟𝑜𝑓𝑖𝑡𝑦𝑟 + 𝑎𝑣𝑔 𝑑𝑒𝑝𝑟𝑒𝑐𝑖𝑎𝑡𝑖𝑜𝑛

𝑦𝑟

𝑃𝑎𝑦𝑜𝑢𝑡 𝑝𝑒𝑟𝑖𝑜𝑑 (𝑦𝑒𝑎𝑟𝑠) = 𝑑𝑒𝑝𝑟𝑒𝑐𝑖𝑎𝑏𝑙𝑒 𝐹𝐶𝐼 − 𝐿𝑎𝑛𝑑 𝑐𝑜𝑠𝑡

𝑎𝑣𝑔 𝑝𝑟𝑜𝑓𝑖𝑡𝑦𝑟 + 𝑎𝑣𝑔 𝑑𝑒𝑝𝑟𝑒𝑐𝑖𝑎𝑡𝑖𝑜𝑛

𝑦𝑟

For our plant, based on the above formula;

𝑃𝑎𝑦𝑜𝑢𝑡 𝑝𝑒𝑟𝑖𝑜𝑑 = 16,798,435.29− 170,096.96

6,633,409.31 + 563,871.31= 2.3 𝑦𝑒𝑎𝑟𝑠

9.5.3 Discounted cash flow rate of return

This method of approach for a profitability takes into account the time value of money and is

based on the amount of the investment that is unreturned at the end of each year during the

estimated life of the project.


Page | 184

A trial-and-error procedure is used to establish a maximum after-tax interest rate at which

funds could be borrowed for the investment and just break even at the end of the service life.

The trial and error calculations are tabulated in the next page.


Page | 185

Table 9. 9 Cumulative cash flow

Trial for 15% Trial for 25% Trial for 34% Trial for 35%

1+i 1.15 1+i 1.25 1+i 1.34 1+i 1.35

Year Cash flow 1/(1+i)n Present worth 1/(1+i)n Present worth 1/(1+i)n Present worth 1/(1+i)n Present worth

1 5,298,496.80 0.869565217 4607388.52 0.8 4238797.439 0.746269 3954102.088 0.740741 3924812.443

2 6,883,937.68 0.756143667 5205245.882 0.64 4405720.114 0.556917 3833781.287 0.548697 3777194.885

3 6,844,315.36 0.657516232 4500248.451 0.512 3504289.466 0.41561 2844563.395 0.406442 2781817.96

4 6,809,001.94 0.571753246 3893068.956 0.4096 2788967.193 0.310156 2111855.817 0.301068 2049974.145

5 6,777,528.81 0.497176735 3369629.648 0.32768 2220860.641 0.23146 1568727.033 0.223014 1511480.435

6 6,749,478.36 0.432327596 2917985.753 0.262144 1769335.255 0.172731 1165846.623 0.165195 1114981.338

7 6,724,478.37 0.37593704 2527980.493 0.209715 1410225.326 0.128904 866812.1943 0.122367 822852.9329

8 6,702,197.10 0.326901774 2190960.122 0.167772 1124442.085 0.096197 644731.3806 0.090642 607501.0708

9 6,682,338.90 0.284262412 1899537.775 0.134218 896888.3455 0.071789 479717.2246 0.067142 448667.4685

10 6,664,640.27 0.247184706 1647397.146 0.107374 715610.2996 0.053574 357049.7465 0.049735 331466.0308

11 6,648,866.34 0.214943223 1429128.758 0.085899 571133.2695 0.03998 265824.3866 0.036841 244949.2697

12 6,634,807.81 0.18690715 1240093.02 0.068719 455940.5209 0.029836 197956.9559 0.027289 181060.254

13 6,622,278.13 0.162527957 1076305.334 0.054976 364063.5905 0.022266 147450.0887 0.020214 133865.4267

14 6,611,111.05 0.141328658 934339.4521 0.04398 290759.7388 0.016616 109851.8247 0.014974 98992.36345

15 6,601,158.37 0.122894485 811245.9598 0.035184 232257.6124 0.0124 81855.55864 0.011092 73217.28571

16 6,592,288.04 0.10686477 704483.3435 0.028147 185556.4123 0.009254 61004.15293 0.008216 54162.14793

17 6,584,382.35 0.092925887 611859.5683 0.022518 148267.1095 0.006906 45470.89158 0.006086 40071.99621

18 6,577,336.39 0.080805119 531482.4493 0.018014 118486.7589 0.005154 33897.1889 0.004508 29651.19638

19 6,571,056.68 0.070265321 461717.4055 0.014412 94698.90693 0.003846 25272.25787 0.003339 21942.87918

20 6,565,459.88 0.061100279 401151.43 0.011529 75694.59882 0.00287 18843.8303 0.002474 16240.14049

Total 36353860.95 21373197.24 14860511.84 14340089.23

Ratio 2.456601676 1.444287644 1.004194805 0.969027397


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Based on the above tabulation, for an Initial investment of $ 14,798,435.29, the DCFROR was

established to be 34%. For a project to be viable, DCFROR should be at least 10% more than the

current bank lending rate. Estimating the Bank Lending Rate (BLR) to be approximately 18%,

the difference between the DCFROR and the bank lending rate is 16% an indication that the

venture is very profitable.

9.6 BREAK-EVEN POINT (BEP) ANALYSIS

This is the point at which the total sales and the total cost of production are equal. It marks the

production rate below which the plant is operating at a loss and must therefore be exceeded.

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑒𝑙𝑙𝑖𝑛𝑔 𝑝𝑟𝑖𝑐𝑒 = 𝐴𝑛𝑛𝑢𝑎𝑙 𝑆𝑎𝑙𝑒𝑠

𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑒 = $ 810.3381/𝑢𝑛𝑖𝑡

𝑃𝑟𝑜𝑑𝑢𝑐𝑡 𝐶𝑜𝑠𝑡 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 = 𝑇𝑃𝐶

𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑒 = $ 675.2818/𝑢𝑛𝑖𝑡

𝐷𝑖𝑟𝑒𝑐𝑡 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑐𝑜𝑠𝑡 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 = 𝐷𝑖𝑟𝑒𝑐𝑡 𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝐶𝑜𝑠𝑡

(𝑇𝑜𝑡𝑎𝑙 𝐴𝑛𝑛𝑢𝑎𝑙 𝑆𝑎𝑙𝑒𝑠 𝑃𝑟𝑜𝑑𝑢𝑐𝑡 𝐶𝑜𝑠𝑡 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 )

= 34,258,363.67

55,882,212/675.2818

= $ 413.98/𝑢𝑛𝑖𝑡

The break-even point is calculated as:

𝐺𝑒𝑛𝑒𝑟𝑎𝑙 𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠 + 𝐹𝑖𝑥𝑒𝑑 𝑐𝑎𝑟𝑔𝑒 + 𝐴𝑣𝑎𝑟𝑎𝑔𝑒 𝑠𝑒𝑙𝑙𝑖𝑛𝑔 𝑝𝑟𝑖𝑐𝑒

= 𝐴𝑣𝑎𝑟𝑎𝑔𝑒 𝑠𝑒𝑙𝑙𝑖𝑛𝑔 𝑝𝑟𝑖𝑐𝑒 × 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑜𝑛𝑛𝑒𝑠

11,111,246.26 + 1,198,900.05 + 413.98𝑛 = 810.338/𝑛

𝑛 = 31,058.15 𝑡𝑜𝑛𝑛𝑒/𝑦𝑒𝑎𝑟

The break-even point (QB) is at 45.03% of the maximum production capacity as shown below.

𝑄𝐵 = 31,058.15

68,961.6= 45.03%


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The table below shows a detailed breakdown of how Total Production Cost and Sales Revenue

vary with the variable output quantities between production rates of 0 tonnes/year and

100,000 tonnes/year.

Table 9. 11 Break-even point analysis table

Output units (tonnes/yr) Total Product cost,

$ Total sales, $

0 12,310,146.33 0.00

5000 14,380,046.33 4,051,690.50

10000 16,449,946.33 8,103,381.00

15000 18,519,846.33 12,155,071.50

20000 20,589,746.33 16,206,762.00

25000 22,659,646.33 20,258,452.50

30000 24,729,546.33 24,310,143.00

35000 26,799,446.33 28,361,833.50

40000 28,869,346.33 32,413,524.00

45000 30,939,246.33 36,465,214.50

50000 33,009,146.33 40,516,905.00

55000 35,079,046.33 44,568,595.50

60000 37,148,946.33 48,620,286.00

65000 39,218,846.33 52,671,976.50

70000 41,288,746.33 56,723,667.00

75000 43,358,646.33 60,775,357.50

80000 45,428,546.33 64,827,048.00

85000 47,498,446.33 68,878,738.50

90000 49,568,346.33 72,930,429.00

95000 51,638,246.33 76,982,119.50

100000 53,708,146.33 81,033,810.00


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Figure 9. 2 Break-even Point Chart

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

0 20 40 60 80 100 120

Pro

du

ctio

n c

ose

an

d s

ale

s re

ven

ue

($)

Mill

ion

s

Rate of production(Tonnes/year)

Thousands

Break-even point analysis

Loss zone

Break Even point

Profit Zone

Sales revenue

Production Costs


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CHAPTER TEN

10.0 SAFETY, HEALTH AND ENVIRONMENTAL IMPACT ASSESSMENT

10.1 INTRODUCTION

The chemical industry has contributed tremendously to economic growth globally.

Unfortunately, chemical wastes and discharges have caused extensive environmental pollution

and damage to human health. Toxic chemicals pose environmental problems which require a

multidisciplinary effort to be resolved.

Currently the disciplines involved in management of toxic chemical chemistry, toxicology,

engineering, economics, sociology and political science and from the viewpoint of industry, we

have: government, academic and non-government organizations.

The concept of ecological sustainable industrial development motivates producers and

consumers to use products and operate industry using the best technologies to minimize

adverse environmental impact

The significance of safety and health in chemical industries is a vital issue in achieving

productivity. Industries are faced with the task of producing and using their products in a

manner that is safe for:-

Persons involved with production.

Persons using the products.

Persons living near the process plants.

The environment i.e. land, air, water, plants and animals.

Industrial operations and products must undergo proper hazard assessment and industries

must put in place appropriate standards and procedures to ensure that chemical risks are kept

to a minimum.

Any manufacturing industry has a legal and moral obligation to safeguard the health and

welfare of its employees and the surrounding populace. All manufacturing processes are to


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some extent hazardous and the designer should ensure, through the application of sound

engineering practices, that the risks are reduced to acceptable levels.

10.2 SAFETY

Safety generally means being safe or freedom from danger or risk. It is an area

of safety engineering and public health that deals with the protection of workers' health,

through control of the work environment to reduce or eliminate hazards.

Chemical process safety refers to the application of technology and management practices;

To prevent accidents in plants

To reduce the potential for accidents.

Work place hazards can generally be grouped into:-

Mechanical hazards

Chemical hazards

Physical hazards

Biological hazards

Psycho-Social hazards

Unsafe working conditions and production may lead to industrial accidents and can result in:

Temporary or permanent injuries.

Fatalities.

Loss of future productivity by training new personnel

Loss of valuable work hours

Cost implications due to compensation, medical fees, insurance etc.

The Occupational Safety and Health Act (OSHA, 2007) stipulates the guidelines for ensuring

favorable and bearable working conditions in Kenya. The Act establishes occupational, safety

and health standards to be adhered to in places of work.

Major provisions of this Act include:

Inspection of work places


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Maintenance of accurate records of employees

Maintenance of accurate records of any toxic or harmful material whose levels

exceed those prescribed by an applicable standard.

Provides for the rights of employees to be informed of any violations by

employers cited by inspectors of work places.

The provisions of this Act are enforced by inspection officers who carry out inspections for work

places.

10.2.1 Safety Management in the beet sugar processing plant

Potential hazards in the beet sugar processing plant include the following:

Waste water from beet washer

Electrical components malfunction, electrocution and risk of electrical fires

Failure of instruments and process equipment

Risk of fires

Toxicity of the chemicals used e.g. SO2, CaCl2

Odour

Sludge and mud from the filtration operation

Leakages from equipment causing spills

High pressure steam especially in the evaporators and the crystallizer

Slips, trips and falls

Corrosion

Dust explosions

Fire Detection and Evacuation systems

Smoke and fire detectors and sensors will be installed across the plant area. A sensor, on

detecting heat or smoke, should let off an alarm to allow evacuation. The workers must always

be inducted once hired so as to know the procedures of evacuation of fire scares and periodical

training should be done as well as fire and evacuation grills.


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Proper Housekeeping

Sugar being a human consumable product has to be produced under the highest levels of

cleanliness and hygiene. Proper housekeeping in the beet-sugar plant includes:

Storage of material as CaCO3, SO2 and others only in authorized places or neatly and

without obstruction. No material should be stored outside the demarked area.

Marking escape and transport routes e.g. The working area, pathways, corridors,

passages, rest rooms, control rooms, sub stations and wash rooms should be free from

rubbish and unwanted material.

Tidiness and clear marking of areas during plant construction.

All construction equipment to follow safety requirements.

No ignition sources

Marking equipment for identification

Good access to the site should be maintained.

All machinery and equipment should be maintained clean.

Materials should be stored and stacked in such a way as not to cause any obstruction at

the workplace or which could cause.

No materials should in such a way that it obstructs the accessibility to fire extinguishers,

first aid boxes, electrical switches, walk paths aisles and roads.

Spillages and wastes

Spillages are to be taken note off, contained and collected.

When opening valves, the risk of spillages should be considered.

Any spillage is to be reported to the Health Safety & Environment Department

immediately while possible control and containment of the spill is carried out.

All departments are provided with spill control kits. Emergency safety cupboards are

located at various locations containing personal protective equipment and spill control

kit.


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First Aid

All emergency handling team members are trained in first aid.

First Aid boxes are available in all departments

Safety Signs and Instructions

To create the Health, Safety and Environment awareness at all levels of management and to

communicate the specific risk / hazards, at relevant locations Health, Safety and Environment

Signs, Warning Labels, Instruction to be displayed.

Labeling

All equipment and chemicals should be classified according to their risk and labeled accordingly.

Lighting

Illumination sufficient for maintaining safe working conditions are provided where ever

personnel is required to work or pass , including in passageways, stairways and landings.

No work area has illumination of less than 50 lux or otherwise specified.

Chemical Safety

All employees know the hazards of the chemicals they may deal or work with.

All employees make sure that they have a copy of the MSDS (Material Safety and Data

Sheets), read and understand it.

All employees use appropriate personal protective equipment while handling the

chemicals.

All chemical containers and bottles are labeled correctly.

Store the chemical as per the incompatibility.

Obey warning and danger signs.

Try to stop the spillage, if any, and report the same to the shift in-charge and safety

department simultaneously through your colleagues earliest possible.


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Spacing

There should be adequate spacing between equipment and pipelines.

Emergency Contact Numbers

List of key personnel is available at emergency control center, main gate.

Safety Relief Vents, Interlocks and trip systems

For pressure vessels, relief vents are installed. Interlocks and trip systems should also be

installed in case of failure of the instruments.

Control valves

There are remote control valves to isolate equipment and areas of the plant in case of

emergency.

Inspection of equipment

Regular inspection of equipment such as evaporators, storage vessels, heat exchangers,

crystallizer (boiling pans and mixers) and pipelines helps to avoid explosions and mechanical

failure through thermal vibrations, corrosion and stresses. Frequent testing to confirm

compliance to design parameters should be conducted on the relevant equipment.

Training of workers

Specialized training of workers on chemical safety, personal protection equipment, fire

prevention and protection techniques, accidents prevention and safety management can

contribute significantly to risk management in the plant.

Accident Documentation

All accidents should be reported to the relevant section managers and eventually to the safety

manager for effective investigation.


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Laboratory Safety

All chemicals and regent bottles are clearly labeled. They are stored in their appropriate

places.

Volatile, combustible, flammable chemicals must are stored away from direct flame and

other sources of heat.

Poisonous material must be kept locked.

Fuming cupboard must be used where toxic, irritating and flammable vapours are

involved. Exhaust fans and blowers must be kept continuously on to drive out any fumes

or vapours if present.

While handling toxic and corrosive chemicals, proper personal protective equipment.

Do not throw used solvents into the sink but, collect them in containers for recovery or

disposal.

There are energy lines and taps in laboratory. Get them inspected periodically and see

that leaks are detected and rectified quickly.

While pouring solvents which develop static charges from bigger container to smaller

container, both of them must be earthed and bonded in order to prevent fire and

explosion due to static charge buildup. Pour in manner such that the free fall of the

solvent is minimal.

Equipment Safety

All new equipment are procured as per user's safety requirement and designed

accordingly.

The equipment should be qualified for installation, operation and performance.

The Persons working on the equipment should undergo the operation training.


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Employee Requirements

It shall be a requirement for each worker to have the following PPEs (personal protective

Equipment) within the factory premises.

Masks: for protection against solvent vapour or fumes more so those at or around the

sulphiting operation.

Protective clothing: these include overalls and dust coats to be replaced weekly for cleaning

purposes.

Protective shoes: special shoes to prevent any damage due to falling objects and also to prevent

falling or sliding.

Ear plugs: Prevent damage caused by vibration or noise produced by equipment.

Safety helmet: mandatory inside the factory to protect the head from metal objects.

Management and Safety

We as the engineers are better placed to help achieve a safe environment for the society since

we have the skills and knowledge.

Management should be at the forefront in enforcing safe engineering practices.

Organizing safety trainings and safety promotional campaigns.

Enacting rules and policies to be adhered to concerning safety, for which there are

repercussions for violations committed.

Management should ensure that they get a safety report periodically.

There should be an independent inspector doing regular safety audits.

Ensuring there is proper and regular inspection and maintenance of equipment.

10.3 ENVIRONMENTAL IMPACT ASSESSMENT (EIA)

An environmental impact assessment is a study of the possible positive and negative impact

that a proposed project may have on the environment. It is also the process of identifying,

predicting, evaluating and mitigating the biophysical, social, and other relevant effects of

development proposals prior to major decisions being taken and commitments being made.


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Environmental Impact Assessment (EIA) aims to ascertain:-

The degree of impact of a proposed activity on the environment.

Whether impacts could be avoided or mitigated by any means or not.

All chemical process industries have chemical wastes and discharges which could cause

extensive environmental pollution and damage to human health if not controlled.

In Kenya, the government set up the National Environmental Management Authority (NEMA)

under the Environmental Management and Coordination Act (EMCA) No.8 of the 1999, as the

principal instrument of government in the implementation of policies relating to the

environment.

NEMA has to collaborate with experts in production industries to come up with standards for

Environmental Impact Assessments and also what is called Environmental Audits.

Other organization which deals with awareness, training and waste reduction audits is Kenya

National Clearer production Center at KIRDI.

10.3.1 Environmental concerns

In the beet sugar processing plant, the bulk of the chemicals used are not toxic. The

environment areas which are prone to pollution are the soil, water and air. Generally the main

sources of pollutants are:

Waste and sludge from filters in the filtration and sulfitation operation.

Sugar dust from the rotary dryer.

Effluents from washing operation.

Vent gases released from the multiple evaporators.

Excessive water consumption and water pollution - cultivating and processing sugar crops is a

relatively water intensive process involving a number of stages that use water. Processing beets

consumes a large amount of water as they need to wash off the soil from the beets at harvest.

Waterways and aquatic habitats can be polluted by agrochemicals and other sediments used in

the cultivation process.


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10.3.2 Waste treatment practices

These refer to the control and management of toxic substances by the application of various

treatment technologies, which include pre-treatment, waste minimization and waste disposal.

10.3.2.1 Minimization of wastes

Recycling of Used Water

Recycling of water is required so as to reduce the amount of waste water effluent generation

from the plant. All waste water pipeline systems should be checked regularly and any fault

corrected immediately.

Molasses

This is the by-product of the centrifugation operation. Molasses can be used as an animal feed

or in production of ethanol for lab and industrial use.

10.3.3.2 Disposal of wastes

Solid wastes

The main solid wastes are:

Pellets from the wet pulp pressing section

Loose soil and grit from dry screening

Little stones from the stone and trash separator

Colloids, invert sugar, proteins, phosphates and sulfates in the diffusion juice which are

precipitated and filtered out

These wastes should be properly disposed of by burying or incineration.

Liquid wastes

Liquid wastes include:

Washing solvents used to clean the vessels

Washing water used for cleaning floors and beet washing

Juice spillages from intermediate holding tanks

Sludge or mud from filtration


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These should be treated prior to disposal into sewerage streams. This is done by treating with

the appropriate chemicals to reduce toxicity levels of the waste stream before discharge into

sewerage systems. Biological treatment methods may also be used.

Gaseous wastes

The main sources of gaseous wastes are:

Vapor Fumes from the evaporators

Dust from the dryer and loading in the warehouse

These wastes should be removed from the gaseous streams before discharge into the

atmosphere. Dust separating mechanisms can be used such as bag filters and electrostatic

precipitators. Operators should also be provided with masks to prevent exposure to fumes.


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CHAPTER ELEVEN

11.0 HAZARD AND OPERABILITY ANALYSIS (HAZOP)

11.1 INTRODUCTION

A hazard and operability study is a procedure for the systematic, critical, examination of the

operability of a process. When applied to a process design or an operating plant, it indicates

potential hazards that may arise from deviations from the intended design conditions.

The HAZOP process is based on the principle that a team approach to hazard analysis will

identify more problems than when individuals working separately combine results.

Hazard - any operation that could possibly cause a catastrophic release of toxic, flammable or

explosive chemicals or any action that could result in injury to personnel.

Operability - any operation inside the design envelope that would cause a shutdown that could

possibly lead to a violation of environmental, health or safety regulations or negatively impact

profitability.

11.2 PURPOSE OF HAZOP

HAZOP is carried out for the following reasons:

• HAZOP identifies potential hazards, failures and operability problems.

• It encourages creativity in design concept evaluation.

• Its use results in fewer commissioning and operational problems and better informed

personnel, thus confirming overall cost effectiveness improvement.

• Necessary changes to a system for eliminating or reducing the probability of operating

deviations are suggested by the analytical procedure.

• HAZOP provides a necessary management tool and bonus in so far that it demonstrates

to insurers and inspectors evidence of comprehensive thoroughness.

• HAZOP reports are an integral part of plant and safety records and are also applicable to

design changes and plant modifications, thereby containing accountability for

equipment and its associated human interface throughout the operating lifetime.


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11.3 HAZOP PROCESS

The HAZOP process is undertaken in the following procedure:

1. Divide the system into sections (i.e., reactor, storage)

2. Choose a study node (i.e., line, vessel, pump, operating instruction)

3. Describe the design intent

4. Select a process parameter

5. Apply a guide-word

6. Determine cause(s)

7. Evaluate consequences/problems

8. Recommend action: What? When? Who?

9. Record information

10. Repeat procedure (from step 2)

11.4 HAZOP CONCEPTS

a) Node

A node is a specific location in the process in which (the deviations of) the design/process intent

are evaluated.

Examples might be: separators, heat exchangers, scrubbers, pumps, compressors, and

interconnecting pipes with equipment.

b) Design Intent

The design intent is a description of how the process is expected to behave at the node; this is

qualitatively described as an activity (e.g., feed, reaction, sedimentation) and/or quantitatively

in the process parameters, like temperature, flow rate, pressure, composition, etc.

c) Deviation

A deviation is a way in which the process conditions may depart from their design/process

intent.


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d) Parameter

The relevant parameter for the condition(s) of the process to be used (e.g. pressure,

temperature, composition).

e) Guideword

A short word used to create the imagination of a deviation of the design/process intent. The

most commonly used set of guide-words is: no, more, less, as well as, part of, other than, and

reverse.

The guidewords are applied, in turn, to all the parameters, in order to identify unexpected and

yet credible deviations from the design/process intent.

Guide-word + Parameter Deviation

f) Cause

The reason(s) as to why the deviation could occur. Several causes may be identified for one

deviation. It is often recommended to start with the causes that may result in the worst

possible consequence.

g) Consequence

The results of the deviation, in case it occurs. Consequences may both comprise process

hazards and operability problems, like plant shut-down or reduced quality of the product.

h) Safeguard

These are facilities that help to reduce the occurrence frequency of the deviation or to mitigate

its consequences.

11.5 SAMPLE HAZOP ANALYSIS

As an illustration a HAZOP analysis was carried out on three equipments; rotary drum dryer,

heat exchanger 2 and filter press. The results of the analysis are tabulated as follows.


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Study node: Rotary Drum Dryer Exit

Deviation Causes Consequences Safeguard Action required Assigned to

Less temperature

- Decreased flow of hot air - Low temperature of hot air - Increased moisture in feed sugar - Increased flow rate of material

- High moisture content in final sugar - Low quality sugar

- Conducting temperature profiles for the dryer to monitor desired temperature. -Monitoring of material and hot air flow rate. - Install sensors to monitor material and hot air flow rates -Install low temperature alarms

- Repair/replace malfunctioning sensors and valves. - Clean fouled air heater tubes - Replace worn out air induced draft fan

Process engineer

More temperature

-Temperature control failure -Increased flow of hot air. -High initial material temperature - Increased temperature of hot air -Less flow rate of material

- Less moisture than required in final sugar. - High energy consumption.

- Conducting temperature profiles for the dryer to monitor desired temperature. -Monitoring of material and hot air flow rate. - Install sensors to monitor material and hot air flow rates -Install high temperature alarms

- Repair/replace malfunctioning sensors and valves. - Maintenance of alarm systems

Process engineer

Table 11. 1 HAZOP Analysis around a Rotary Drum Dryer


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Study node: Heat Exchanger 1 Exit

Deviation Causes Consequences Safeguard Action required Assigned to

Less pressure

-Failure of pressure control valves -Scaling of inlet pipe -Malfunctioning of the inlet pump

-Under heating of the juice -More pumping energy required in the subsequent stages

-Regular inspection and maintenance of heat exchanger plates -Regular maintenance and inspection of valves and sensors

-Replace worn out plates -Repair/ replace malfunctioning sensors and valves -Clean fouled plates -Install sensors to monitor material and steam flow rates

Process Engineer

More pressure

-Pressure control failure

-Increased flow of steam

-High juice entry pressure

-Low temperature of outlet juice

-High energy consumption

-Monitoring of material and steam flowrate

-Regular maintenance and inspection of valves and sensors

-Repair/ replace malfunctioning sensors and valves

-Maintenance of alarm systems

Process Engineer

Table 11. 2 HAZOP Analysis around Heat Exchanger 1


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Study node: Filter press exit

Deviation Causes Consequences Safeguard Action Assigned to

No flow - Absence of juice in 2nd carbonation tank - Failure of pump 4 - Clogging of filter medium - Wrong path flow - Blockage of pipe - Burst pipe - Isolation in error - Failure of control valve after pump 4

- No filtration occurring - Over heating and damage of downstream heat exchangers

- Human operator detection - Alarm and level detectors for the 2nd carbonation tank - Regular maintenance of pumps and valves - Maintenance and repair of pipes - Regular inspection of cake removal system

- Inspection and repair of burst pipes - Repair faulty valves and pumps - Inspection and repair or replacement of faulty level detectors. - Unclogging of filter medium - Rectifying any wrong isolation

Process engineer

Less flow - Leakages from the inlet pipe - Leakages from the filter press pipe lines - Clogged filter medium - Faulty plates and frames due to high pressure build up - Valve stuck in partial closed position - Blockage of inlet pipe and filter press pipelines

- Decreased efficiency of downstream operations - Less removal of precipitates - Overheating of downstream heat exchangers - Reduced filter press output

- Human operator detection - Regular maintenance of control valves - Maintenance and repair of pipes - Regular inspection of cake removal system

- Repair faulty valves and pumps - Regular checks of pipelines - Installation of flow alarms and detectors - Unclogging of filter medium

Process Engineer

More flow - Increased pumping capacity - Reduced delivery head - Greater fluid density - Cross connection of systems - Flow Control faults

- Overloading of filter press and failure - Poor efficiency of filter

-Regular inspection of flow

control systems.

-Maintenance of pump

- Regular maintenance of flow

controllers

- Repair of pump in case of increased capacity - Repair and replacement of faulty valve

Process Engineer

Table 11. 3 HAZOP Analysis around the Filter Press


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CHAPTER TWELVE

12.0 PLANT LOCATION AND LAYOUT

12.1 PLANT LOCATION

Plant location refers to the choice of region and the selection of a particular site for setting up a

business or factory. The geographical location of the plant plays an important role in the

profitability and success of the plant. The proposed site for beet sugar production plant is in

Nyandarua County in Kenya’s Central Province. The choice is determined by the following

reasons:

1. Raw Material

The availability and price of suitable raw material will often determine the site location. Sugar

beets are available in Nyandarua County due to the favorable climatic conditions. The location

of the plant in this region will ensure a considerable reduction in transport and storage costs of

the raw materials.

2. Climate

Beet grows in temperate climates. Nyandarua county being on the wind ward side of Abadare

Ranges is has a temperate climate. Adverse climatic conditions at a site will increase costs.

Abnormally low temperatures will require the provision of additional insulation and special

heating for equipment. Stronger structures will be needed at locations subject to high winds

(cyclone/hurricane areas) or earthquakes. Nyandarua County is ideal in that it does not

experience any adverse climatic conditions to discourage growth of beets.

3. Market

Central Kenya which harbors Nyandarua Count is the most populated region in the country. Its

environs provide a huge market for sugar. Also being 187km away from Nairobi- the capital city

provides a larger region of marketing sugar.


Page | 207

4. Labour availability

Owing to the region’s high population and high rates of unemployment in the country, unskilled

labour which takes most of our human resource is available. Labour is cheap and readily

available with unemployment rates of 45%. Prevailing pay rates stand at Kshs. 400 per 8-hour-

working day on unskilled labour, which is cheap.

5. Availability of utilities

Beet sugar production calls for enough electric power to run machinery and water. Fuel is

required to supply these utilities. The plant should therefore be located in an area already

covered by electrical energy supply to avoid the high cost site power generation or need for

power installation. Nyandarua is well covered by the national electrical power grid.

Beet sugar processing requires a lot of water for cooling and steam generation purposes.

Nyandarua County has adequate supply of water since it in the slopes of Abandare range. In

addition, a number of wells are present in Nyahururu district, which is a neighboring town. This

ensures adequate flow of water.

6. Site Characteristics

Sufficient and suitable land should be available for plant location and possible future expansion.

The preferred location should be well drained, ideally flat and have good load bearing

characteristics. It should also be easier for movement of modern machinery during construction

and operation and thus low initial cost of investment.

7. Environmental impact and effluent disposal

All industrial processes produce waste products. Nairobi has a well-developed sewerage

system. Effluent from the plant is not toxic and can be discharged directly into the sewerage

system.

8. Local Community

The proposed plant must fit in with and be acceptable to the local community. This plant can be

located close to the community as it does not pose a significant risk to the community owing to


Page | 208

the nature of its products and environmental impact. The plant will be located close to Ol-Kalou

town which will provide social amenities like hospitals, churches, schools and recreational

facilities which will enable the plant to attract and accommodate employees from different

parts of Kenya and thus making them more efficient.

12.2 PLANT LAYOUT

Plant layout is used to describe the arrangement of various parts of a plant.

The process units and ancillary buildings should be laid out to give the most economical flow of

materials and personnel around the site. Hazardous processes must be located at a safe

distance from other buildings. Consideration must also be given to the future expansion of the

site.

A good plant layout should meet the following general principles:

Principle of smooth flow

Principle of overall integration of resources

Principle of minimum distance moved; for both material and personnel

Principle of satisfaction and safety.

Thus the plant layout should be such that the following are minimized:

Damage to persons or property in case of fire, explosion or toxic release.

Maintenance costs

The number of people required to operate the plant

Construction costs

The cost of planned future expansion

Other operating costs

The direction of prevailing wing should be considered such that the administrative buildings, car

park and utilities are on the upwind side while the processing plant, tank farms and burning

flames on the downwind side.

When roughing out the preliminary site layout, the process units will normally be sited first and

arranged to give a smooth flow of materials through the various processing steps, from raw


Page | 209

material to final product storage. Process units are normally spaced at least 30 m apart; greater

spacing may be needed for hazardous processes.

The location of the principal ancillary buildings should then be decided. They should be

arranged so as to minimize the time spent by personnel in travelling between buildings.

Administration offices and laboratories, in which a relatively large number of people will be

working, should be located well away from potentially hazardous processes. Control rooms will

normally be located adjacent to the processing units, but with potentially hazardous processes

may have to be sited at a safer distance. The siting of the main process units will determine the

layout of the plant roads, pipe alleys and drains. Access roads will be needed to each building

for construction, and for operation and maintenance.

Utility buildings should be sited to give the most economical run of pipes to and from the

process units. Cooling towers should be sited so that under the prevailing wind the plume of

condensate spray drifts away from the plant area and adjacent properties.

The main storage areas should be placed between the loading and unloading facilities and the

process units they serve.

Important plant layout keywords include;

Raw material Storage

Product Storage

Process Site

Laboratories

Workshop

Canteen & Change house

Fire Brigade

Central Control Room

Security office

Administrative Building


Page | 210

Site for Expansion Project.

Effluent treatment plant

Power house

Emergency water storage

Plant utilities

The beet processing plant has the following layout.


Page | 211

SECURITY HOUSE B

WEIGH BRIDGE CLEANING

PROCESSING AREA

EXPANSION

WA

STE

WA

TER

TREA

TMEN

T

MAIN CONTROL ROOM

PLANT QUALITY OFFICES CONTROL

PLANT UTILITIES

SUGAR SILOS

SUGAR PACKAGING

AND SHIPMENT

BEET STORAGE FIRE

STATION

PARKING

ADMNISTATION BLOCK

GARAGE STORE ROOM

WORKSHOP

WASH ROOMS CANTEEN

SECURITY HOUSE A

SECURITY HOUSE C

DUMP YARD

PREVAILING WIND

DIRECTION


Page | 212

CHAPTER THIRTEEN

13.0 REFERENCES

Mosen Asadi. (2007), “Handbook of Beet Sugar Technology”, 2nd edition, John Wiley & Sons

McGniss, R.A. (1951), “Beet Sugar Technology”, 2nd edition, Reinhold Publishing Corporation

Hugot, E. (1986), “Handbook of Cane Sugar Engineering”, 3rd edition, Elsevier Publishing

Corporation

Sinnot, R.K. (2005), “Coulson and Richardson’s Chemical Engineering Design”, 4th edition,

volume 6, Elsevier Publishing Corporation

Walker, Lewis, McAdams and Gilliland. (1926), “Principles of Chemical Engineering”, 3rd

edition, Reinhold Publishing Corporation

Perry, R.H., Green, D.W. and Maloney, J.O. (1997), “Perry’s Chemical Engineer’s Handbook”,

7th edition, Mc-Graw Hill

Willia, D.B. (1974), “Preliminary Chemical Engineering Plant Design”, 1st edition, Elsevier

Publishing Corporation

Bubni, K. Z. & Kadlec, P. (1996), “Program for calculation of sucrose properties, other sugars

and their solutions”, Berlin, (pp.22–29)

Sugar Technologists manual (1978), “Chemical and physical data for sugar manufacturers and

users” Berlin, Germany: Bartens Publishing Company

Koolen, J.L.A. (2002), “Design of simple and Robust Process Plants”, 1st edition, Wiley-VCH

Verlag GmbH & Co.

Walas, S.M and et al, (2012), “Chemical Process Equipment: Selection and Design”, 3rd edition,

Elsevier Publishing Corporation


Page | 213

Steve, T and Wakeman R. (2007), “Solid-Liquid Separation: Equipment Selection and Process

Design”, 1st edition, Elsevier Publishing Corporation

Rousseuau, R. W. (1987), “Handbook of Separation Process Technology”, 1st edition, John

Wiley & sons

Sugar Properties. http://www.sugartech.co.za/

Wang, L. (2004), “Theoretical Study of Cyclone Design”, Texas A & M University. 1: 55-79

Timmerhaus, K.D. & Peters, M.S. (1991), “Plant Design and Economics for Chemical Engineers”,

4th Edition, McGraw Hill Inc

Beet sugar. http://en.www.wikipedia.org/wiki/beetsugar/

Cost index. http://www.matches.com/

McCabe, W.L. Smith, J.C. & Harriott, P. (1993), “Unit Operations of Chemical Engineers”, 5th

Edition, McGraw-Hill, Inc

Oliver D. C. (2004), “Environmental Impacts of Sugar Production: The Cultivation and

Processing of Sugarcane and Sugar Beet”, Sugar Technology. 1: 44-55

Nadia M A. and Mahmood A K. (2006), “Study on Effluent from Selected Sugar Mill in Pakistan:

Potential Environmental, health and Economic Consequences of an Excessive Pollution Load”,

Sugar Technology. 2: 22-30

Albright L. F. (2008), “Albright’s Chemical Engineering Handbook”, 1st edition, CRC Press

(1999), “Tubular Exchanger Manufacturer’s Association (TEMA) standards”, 8th edition

Engineering tools. http://www.engineeringtools.com/

Seborg D. E, Edgar T. F and Duncan M. A. (2004), “Process Dynamics & Control”, 2nd edition, John Wiley & Sons, Inc.

http://www.sugartech.co.za/

http://en.www.wikipedia.org/wiki/beetSUGAR/

http://www.matches.com/

http://www.amazon.com/dp/0851999816/?tag=finmybli-20



http://www.engineeringtools.com/


Page | 214

APPENDICES

APPENDIX A: DATA

Table A- 2 Overall heat transfer coefficients

Table A- 1 Specific heat capacities of various components

Components Cp (kJ/kg.°C)

Thin juice 4.1832

Water 4.1870

Thick juice 4.1719

Massecuite 4.1627

Molasses 4.1620

Wet sugar 2.1500

Air 1.006


Page | 215

APPENDIX B: FORMULAE

(i) Calculation of specific heat capacity of wet sugar

Specific heat capacity of wet sugar is calculated based on the formula below (Bubnik et al.

1995):

𝐶𝑝 = 4.187 −𝐷𝑆 × 0.0297 − 4.6 × 10−5 × 𝑇 + 7.5 × 10−5 × 𝐷𝑆 × 𝑃

Where: DS = Dry substance content (for pure sucrose solutions, DS = S)

T = temperature (℃)

P = purity (for solutions P=100%)

(ii) Heat of crystallization of sucrose

Extrapolation for heat of crystallization at various temperatures is based on the formula below:

𝑦 𝑥∗ = 𝑦𝑘−1 +𝑥∗ − 𝑥𝑘−1

𝑥𝑘 − 𝑥𝑘−1(𝑦𝑘 − 𝑦𝑘−1)

Available data (Kilmartin and Van Hook, 1950)

Heat of crystallization at 30°C is 30.61 kJ/kg

Heat of crystallization at 57°C is 95.50 kJ/kg

Upon carrying out linear interpolation,

Heat of crystallization at 74°C= 136.36 kJ/kg


Page | 216

APPENDIX C: DETAILED SAMPLE MASS BALANCE CALCULATIONS

(1) Diffuser

In diffusion station, the sliced beets are kept in contact with hot water (70°C) for about an hour

to diffuse the juice from the beet cells. The hot water is introduced counter currently. As water

moves ahead, it collects sugar (sucrose) and non-sugar (non-sucrose) from the cossettes and

become a concentrated impure sucrose solution known as diffusion juice. Also in this station

the following are added:

Sulphur iv oxide

Calcium chloride

Antifoaming agent


Diffusion juice contains 85% water and 15 % dry substance (DS)

The dry substance consists of 86.5% sucrose, 1.0% Insolubles and 12.5% non-sucrose.

100g/ton. Of antifoaming agent is added.

0.23 kg/ton (cossettes stream+ diffusion water) Of SO2 is added.

0.125% OB of CaCl2 is added

96% of sucrose is removed based on 15% sucrose content in cossettes.

Diffusion water content is based on the following formula:

𝑀𝐷𝐼𝐹 .𝑊 = 𝑀𝐷𝐼𝐹𝐹 .𝐽 + 𝑀𝑃𝑃 −𝑀𝐶

Where:



MPP=Mass of pressed pulp (111% OB)

The equation of conservation of mass with no accumulation is expressed as:

𝑀𝑎𝑠𝑠 𝑖𝑛 = 𝑀𝑎𝑠𝑠 𝑜𝑢𝑡


Page | 217

Overall mass balance

Stream 20(kg/hr) + Stream 21(kg/hr) + Stream 22(kg/hr) + Stream 25(kg/hr) + Stream 28(kg/hr)

= Stream 26(kg/hr) + Stream 27(kg/hr)

Component mass balance

i. Cossettes

𝑀𝑎𝑠𝑠 𝑖𝑛 (𝑆20) = 80495 𝑘𝑔/𝑟

ii. Water

𝑀𝑎𝑠𝑠 𝑖𝑛 (𝑆20) = 606 𝑘𝑔/𝑟

𝑀𝑎𝑠𝑠 𝑜𝑢𝑡 𝑆26 = 0.85 × 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑗𝑢𝑖𝑐𝑒 = 0.85 × 89349 = 75947 𝑘𝑔/𝑟

iii. Sulphur dioxide

𝑀𝑎𝑠𝑠 𝑖𝑛 𝑆21 = 0.23 × 81,101 + 23799 = 24 𝑘𝑔/𝑟

iv. Antifoaming agent

𝑀𝑎𝑠𝑠 𝑖𝑛 𝑆22 = 0.0001 × 80495 = 8 𝑘𝑔/𝑟

v. Calcium chloride

𝑀𝑎𝑠𝑠 𝑖𝑛 𝑆24 = 0.00125 × 80495 = 100 𝑘𝑔/𝑟

vi. Diffusion water

𝑀𝑎𝑠𝑠 𝑖𝑛 (𝑆23)

𝑀𝐷𝐼𝐹 .𝑊 = 𝑀𝐷𝐼𝐹𝐹 .𝐽 + 𝑀𝑃𝑃 −𝑀𝐶

Where:



MPP=Mass of pressed pulp (111% OB

𝑀𝐷𝐼𝐹 .𝑊 = 0.184 × 80495 + 1.11 × 80495 − 80495 = 23665 𝑘𝑔/𝑟


Page | 218

vii. Wet pulp water

𝑀𝑎𝑠𝑠 𝑖𝑛 (𝑆28) = 63,583 𝑘𝑔/𝑟

𝑀𝑎𝑠𝑠 𝑜𝑢𝑡 𝑆27 = 72,388 𝑘𝑔/𝑟

viii. Dry substance

𝑀𝑎𝑠𝑠 𝑖𝑛 (𝑆28) = 1,298 𝑘𝑔/𝑟

𝑀𝑎𝑠𝑠 𝑜𝑢𝑡 𝑆27 = 8043𝑘𝑔/𝑟

ix. Sucrose 𝑀𝑎𝑠𝑠𝑜𝑢𝑡 𝑆26 = 0.865 × 0.15 × 89349 = 11593 𝑘𝑔/𝑟

x. Non sucrose

𝑀𝑎𝑠𝑠 𝑜𝑢𝑡 𝑆26 = 0.125 × 0.15 × 89349 = 1675 𝑘𝑔/𝑟

xi. Insolubles

𝑀𝑎𝑠𝑠 𝑜𝑢𝑡 𝑆26 = 0.125 × 0.15 × 89349 = 1675 𝑘𝑔/𝑟

Table C- 1 Summary of mass balance around diffuser


Streams S20 S21 S22 S23 S24 - S28 S26 S27

Cossettes 80,495 - - - - - - - -

Water 606 - - - - - - 75,947 -

SO2 - 24 - - - - - - -

Antifoaming agent - - 8 - - - - - -

CaCl2 - - - - 100 100 - - -

Diffusion water - - - 23,665 - 23,665 - -

Wet pulp water - - - - - - 63,583 - 72,388

Dry substance - - - - - - 1,298 - 8,043

Sucrose - - - - - - - 11,593 -

Non sucrose - - - - - - - 1,673 -

Insolubles - - - - - - - 134 -

Total 81,101 24 8 23,665 100 23,765 64,881 89,349 80,431


Page | 219

(2) Liming and carbonation

(i) Liming

Milk of lime (MOL) is added to heated diffusion juice to precipitate and destabilize the non-

sugars.

Assumptions:

35% on non-sugars are removed

4% of milk of lime is used

Invert sugars forms the major fraction of the non-sugars removed

𝐻2𝐶2𝑂4 + 𝐶𝑎(𝑂𝐻)2 → 𝐶𝑎𝐶2𝑂4 + 2𝐻2𝑂

Non- sugars removed = 35

100× 1675 = 5.86 kg/hr

Moles of 𝐻2𝐶2𝑂4 =5.86

90= 6.511

𝐶𝑎(𝑂𝐻)2 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 = 481.82

Unreacted milk of lime=536- 481.82= 54.18 kg/hr

𝐶𝑎𝐶2𝐻4 𝑝𝑝𝑡 𝑓𝑜𝑟𝑚𝑒𝑑 = 6.511 × 128 = 833.40 kg/hr

𝐻2𝑂 𝑓𝑜𝑟𝑚𝑒𝑑 = 2 × 6.511 × 18 = 234.4 kg/hr


Page | 220


Stream S26 S30 S31

Water 75,947 - 76,181

Sucrose 11,593 - 11,593


Insolubles 134 - 967

Milk of lime - 536 55

Total 89,349 536 89,885

Table C- 2 Summary of mass balance around Liming Unit

MOL= 536 kg/hr S31 S30

S26

Water= 75,947 kg/hr




Total= 89,349 kg/hr

Liming

Water= 76,181 kg/hr




MOL= 55 kg/hr

Total= 89,885 kg/hr


Page | 221

(ii) Carbonation

CO2 gas is added to precipitate excess lime and adjust pH and alkalinity of the juice.

Assumptions

0.7% OB of CO2 is used (S26) The precipitation reaction and calculations based on the reaction are as follows:

𝐶𝑎(𝑂𝐻)2 + 𝐶𝑂2 → 𝐶𝑎𝐶𝑂3 + 𝐻𝑂2

𝑀𝑎𝑠𝑠 𝑜𝑓𝐶𝑎(𝑂𝐻)2 𝑢𝑠𝑒𝑑 = 55𝑘𝑔/𝑟

𝑀𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑎(𝑂𝐻)2 𝑢𝑠𝑒𝑑 =55

73= 0.75𝑘𝑔/𝑟

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝐶𝑂2𝑢𝑠𝑒𝑑 𝑢𝑝 = 𝑚𝑜𝑙𝑒𝑠 × 𝑅𝑀𝑀 = 0.75 × 44 = 33 𝑘𝑔/𝑟

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝐶𝑂2 𝑟𝑒𝑚𝑎𝑖𝑛𝑖𝑛𝑔 = 94 − 33 = 61 𝑘𝑔/𝑟

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝐻2𝑂 = 𝑚𝑜𝑙𝑒𝑠 × 𝑅𝑀𝑀 = 0.75 × 18 = 13.5 𝑘𝑔/𝑟

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝐶𝑎𝐶𝑂3𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 = 0.75 × 99 = 74.25 𝑘𝑔/𝑟



Water 76,181 - 76,194 -

Sucrose 11,593 - 11,593 -

Non-sucrose 1,089 - 1,089 -

Insolubles 967 - 1,041 -

Milk of lime 55 - - -

CO2 - 94 - 62

Total 89,885 94 89,917 62

Table C- 3 Summary of mass balance around carbonation unit


Page | 222

Steam condensate (80℃) 3,011 kg/hr


Thin juice (86℃) 89,349kg/hr

Steam in (140℃) 3,011.91kg/hr

QL

Heat Exchanger 1

APPENDIX D: DETAILED SAMPLE ENTHALPY BALANCE CALCULATIONS

(i) Heat Exchanger 1( before liming)

This unit is used to the raise the temperature of the crude castor oil from 70°C to 90°C by using

saturated steam at 4 bars from the low pressure boiler.

Sensible heat loss to the environment is assumed to 0.06%.

A schematic of the unit is shown in the diagram below:

The amount of energy required to effect temperature rise is given by the expression below.

𝑄 = 𝑚 𝑗𝑢𝑖𝑐𝑒 × 𝐶𝑝𝑗𝑢𝑖𝑐𝑒 × ∆𝑇

Where,

𝑄 = 𝐻𝑒𝑎𝑡𝑙𝑜𝑎𝑑𝑖𝑛𝐾𝐽/ 𝑟

𝑚 𝑗𝑢𝑖𝑐𝑒 = 𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒 𝑜𝑓𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑗𝑢𝑖𝑐𝑒 𝑖𝑛 𝑘𝑔/𝑟

𝐶𝑝𝑗𝑢𝑖𝑐𝑒 = 𝐻𝑒𝑎𝑡 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑗𝑢𝑖𝑐𝑒 𝑖𝑛 𝐾𝐽/𝑘𝑔.℃

∆𝑇 = 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑐𝑎𝑛𝑔𝑒 𝑖𝑛 𝑑𝑒𝑔𝑟𝑒𝑒 𝑐𝑒𝑙𝑐𝑖𝑢𝑠

∴𝑄 = 89349.00𝑘𝑔

𝑟× 4.1832

𝐾𝐽

𝑘𝑔 .°𝐶× 90 − 70 𝐶 = 7,177,941.26 𝐾𝐽/𝑟

Accounting for sensible heat loss (QL), the total energy to be supplied by the latent heat of

vaporization of steam at 4 bar is given by;


Page | 223

Evaporator

Evaporated water 67,635 kg/hr

Saturated steam in (140°C) 77,472 kg/hr


Steam condensate out (140°C) 77,472 kg/hr

Thin juice 89,032kg/hr

𝑄𝑇 = 7,177,941.26

(1 − 0.0006)= 7,182,250.61 𝐾𝐽/𝑟

Mass flow rate of steam required is calculated as,

𝑚 𝑠 =𝑄𝑇

𝐻𝑙𝑣

Where 𝐻𝑙𝑣 = 𝑙𝑎𝑡𝑒𝑛𝑡 𝑒𝑎𝑡 𝑜𝑓 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚 𝑎𝑡 4 𝑏𝑎𝑟 = 2144.8 𝐾𝐽/𝑘𝑔

∴ 𝑚 𝑠 =7,182 ,250 .61 𝐾𝐽 /𝑟

2144 .80 𝐾𝐽 /𝑘𝑔= 𝟑𝟑𝟒𝟖.𝟔𝟖 𝒌𝒈/𝒉𝒓

(ii) Evaporator

This is unit is the heating center and is concerned with concentrating the thin juice. In this

operation, thin juice with about 15% dry substance (DS) is concentrated to produce a thickened

juice with about 60% DS.

In this unit, the temperature of the diffusion is raised from 90°C to 130°C by using saturated

steam at 4 bars from the low pressure boiler.

Sensible heat loss to the environment is assumed to 0.04%.

A schematic of the evaporation unit is shown in the diagram below:

The mass flow rate of steam used to effect the concentration is calculated as follows:

(Heat)F + (Heat)S= (Heat)V +(Heat)P+ (Heat)C


Page | 224

Where:

F- Feed

S- Steam

V- Vapour

P- Product

C- Condensate

𝑀𝐹 𝐶𝑃𝐹 𝑇𝐹 − 𝑇𝑟𝑒𝑓 + 𝐻𝑆𝑀𝑆

= 𝑀𝑉 𝐻𝑉 + 𝑀𝑃

𝐶𝑃𝑃 𝑇𝑃 − 𝑇𝑟𝑒𝑓 + 𝑀𝑆 𝐻𝐶

𝐶𝑃 𝑗𝑢𝑖𝑐𝑒 = 4.187 1 − 0.006𝐷𝑆𝑗𝑢𝑖𝑐𝑒 𝑘𝐽/𝑘𝑔

For feed, 𝐶𝑃𝐹 = 4.187 1 − 0.006 × 0.15 = 4.1832kJ

kg.℃

For product, 𝐶𝑃𝑃 = 4.187 1 − 0.006 × 0.6 = 4.1719kJ

kg.℃

The heat contents of steam (HS) and the heat content of condensate (HC) at 140°C are:

HS = 2733.9 kJ/kg

HC= 589.1 kJ/kg

The enthalpy of vapor (HV) at 100°C is 2676.1 kJ/kg

Calculating for heat supplied by steam to the product:

89032 × 4.1832 90 − 25 + 𝑀𝑆 × 2733.9

= 67635 × 2676.1 + 21397 × 4.1719 × 130 − 25 + 𝑀𝑆 × 589.1

2144.8𝑀𝑆 = 166,162,455.6 𝑘𝐽/𝑟

Accounting for sensible heat loss and getting the total heat supplied by steam;

2144.8𝑀𝑆 =166,162,455.6 𝑘𝐽/𝑟

(1 − 0.0004)= 166,228,947.19 𝑘𝐽/𝑟

Therefore mass flow rate of steam required,

𝑀𝑆 =

166228947.1788

2144.8= 77503.24 𝑘𝑔/𝑟


Page | 225

APPENDIX E: EQUIPMENT SIZING CALCULATIONS

Lime Tank

This equipment is used for the addition of milk of lime (Calcium hydroxide) to the heated

diffusion juice to precipitate and destabilize the non-sugars for easy removal. The design

chosen for this vessel is a cylindrical tank with a dome shaped top.

𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑡𝑒 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑗𝑢𝑖𝑐𝑒 = 89,349 𝑘𝑔/𝑟

𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑗𝑢𝑖𝑐𝑒 = 940.371 𝑘𝑔/𝑚3

𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑡𝑒 𝑗𝑢𝑖𝑐𝑒 =𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒

𝐷𝑒𝑛𝑠𝑖𝑡𝑦=

89,349

940.371= 95.01 𝑚3/𝑟

Assumptions

The tank should be 90% full

The height to diameter ratio chosen is 2: 1 (𝑖. 𝑒. = 2𝑑)

A basis of 30 minutes is taken

Two tanks are used

For 30 minutes hold up;

𝑇𝑒 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑡𝑒 𝑡𝑎𝑛𝑘𝑠 =95.01

2= 47.51𝑚3

When the tank is 100% full;

𝑇𝑒 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑡𝑒 𝑡𝑎𝑛𝑘𝑠 =47.51

0.9= 52.79𝑚3

𝑇𝑒 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑜𝑛𝑒 𝑡𝑎𝑛𝑘 =52.79

2= 26.394𝑚3

𝑇𝑒 𝑉𝑜𝑙𝑢𝑚𝑒 =𝜋𝐷2𝐻

4

Assume H=2D


Page | 226

𝑇𝑒 𝑉𝑜𝑙𝑢𝑚𝑒 =𝜋𝐷3

2

Thus,

26.394 =𝜋𝐷3

2

Solving,

𝐷 = 2.56 𝑚

𝐻 = 5.12 𝑚

The mixing in the lime tank should be severe to ensure contact between the diffusion juice and

milk of lime. To effectively carry this out, an agitator with 4 baffles is selected.

The power requirement for baffled agitated tank is selected as 1.5 kW/m3 for slurry suspension.

(Chemical Engineering Design, Coulson vol. 6, page 490).

A summary of the sizing calculations is given below:

Lime Tank Equipment code LT

Service Addition of milk of lime to heated diffusion juice to precipitate and destabilize the non sugars.



Capacity 26.39m3

Diameter 2.56m

Height 5.51m

Agitator power 1.5 kW/m3


Number 2

Table E- 1 Summary of lime tank specifications

Documents

Production of Sugar From Suugar Beet