West Kenya Sugar Company

8/12/2019 West Kenya Sugar Company

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MAIN CAMPUS

SCHOOL OF ENGINEERING

DEPARTMENT OF CHEMICAL AND PROCESS ENGINEERING

NAME: SIBUCHI DENNIS KISAKA

REG NO.: CPE/26/09

DEPT: CHEMICAL & PROCESS ENGINEERING

CORSE CODE: CHP 392

TASK: LAB REPORT-DOUBLE PIPE HEAT

EXCHANGER

PRESENTED TO: MR. DENNIS OTIENO.

DATE: 12/04/2012

SIGN: .........................


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ContentsINTRODUCTION............................................................................................................................... 4

BACKGROUND INFORMATION ........................... ......................... .......................... .................... 4

Organizations structure.................................................................................................................... 5

INSPECTION AND WEIGHING.......................... .......................... ......................... ......................... 7

PRE-MILLING..................................................................................................................................... 8

MILLING.............................................................................................................................................. 9

JUICE TREATMENT......................................................................................................................... 12

Juice clarification.............................. .......................... ......................... .......................... .................. 15

Evaporators ..................................................................................................................................... 16

Function of parts ......................................................................................................................... 17

Operation ......................... ......................... .......................... ......................... ........................... ..... 18

Cleaning of the evaporators ......................... .......................... ......................... ......................... .. 20

Sulfur preparation .......................................................................................................................... 22

SUGAR HOUSE ................................................................................................................................ 23

Pan boiling ...................................................................................................................................... 24

A pan boiling ........................... .......................... .......................... ......................... ....................... 25

B-massecuite pan boiling............................................................................................................ 26

C-massecuite pan boiling ........................ .......................... ......................... ........................... ..... 26

Centrifugals ......................... ......................... .......................... ......................... ........................... ..... 27

Batch centrifugal ......................................................................................................................... 27

Continuous centrifugal ......................... ......................... ......................... .......................... .......... 29

EFFLUENT WATER TREATMENT................................................................................................ 31

Dosing room ........................ .......................... ......................... .......................... ........................... 31

Ponds ........................................................................................................................................... 31

Clarifier ........................................................................................................................................ 32

Constructed water lands ............................................... ......................... .......................... .......... 32

WATER TREATMENT..................................................................................................................... 33

Clarification ................................................................................................................................. 33

Bed filtration and decolourising ........................... ......................... .......................... .................. 33

Domestic water treatment ........................... .......................... ......................... ........................... ..... 33


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Boiler water treatment ......................... ......................... ........................... ......................... .............. 33

Removal of ions and dissolved gases ........................... .......................... ......................... .......... 33

BOILER............................................................................................................................................... 35

Flow of water in the boiler .......................... .......................... ......................... ........................... ..... 36

Flow of flue gases ........................................................................................................................... 36

Flow of air ....................................................................................................................................... 37

Flow of bagasse ........................... .......................... .......................... ......................... ....................... 37

LABORATORY.................................................................................................................................. 37

Test carried out in the laboratory ........................ .......................... ......................... ....................... 37

Sugar moisture test ..................................................................................................................... 37

Sugar colour test ......................................................................................................................... 38

pH determination ....................................................................................................................... 38

Determination of water insoluble matter in sugar ....................... .......................... .................. 39

Determination of moisture in bagasse................................................ ......................... .............. 39

Determination of sugar trace ..................................................................................................... 40

Determination of sugar ash .......................... .......................... ......................... ......................... .. 40

Determination of brix ................................................................................................................. 41

Determination of pol/sucrose content ......................... .......................... ......................... .......... 41


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WEST KENYA SUGAR COMPANY REPORT

INTRODUCTION

BACKGROUND INFORMATION

Company policy statement: we are committed to production and distribution of high

quality sugar and allied products at optimum cost without compromising the integrity

of our products and service in an attempt to satisfy our short term objectives.

Also, we are committed to long term profitability and employment of qualified

personnel and shall achieve this by utilizing business approach that makes our business

more competitive and continuously improving effectiveness of our quality management

system that takes to account and exceeds the needs of all our stakeholdersexpectations.

This encompasses the attitude of quality first.

Mission:to emerge as the premier producer of finest sugar and allied products whilst

continually striving to achieve long term sustainable growth and profitability. We aim

at rewarding our stakeholders by undertaking technological development, offering

competitive pricing focusing on diversification, providing safe, harmonious and

challenging working environment, and improving our relations with farmers by

working alongside the farming community and maximizing their produce ability.

Vision: to establish our self a market leader in the sugar industry in Kenya by

producing high quality sugar which meets international standards.


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Organizations structure

Managing

director

General Manager

Human resourceand administration

manager

Chief projectengineer

Financial

coordinator

Purchasingmanager

Chief

engineerChief process

manager

Head of

agriculture

Storesmanager

Roadsengineer

Board of directors

Auto-

workshop

manager

Transport

manager

Duty chief

engineerSoftware

engineer

Financial

accountant

Process

manager

Agriculture

service manager

Cane

development

manager


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General overview of the production process

Sugarcane Sugar cane fiber

Bagasse juice

Molasses Molasses &Sugar

Sugar

Cane Weighing

andInspection

MillingPre-mills

Drying

Separation of sugar

and molasses

Evaporation

StorageTransportation

Crystallization

Bagging

Boiler Juice treatment


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INSPECTION AND WEIGHING

Inspection: Sugar cane from out growers has to be first inspected before it is certified

for milling. This is done in order to maintain the quality of the sugar produced as well

as to ensure there is maximum derivation of sugar and itsby products from the crop.

Parameters taken into account during the inspection are; age, that is used to determine

the maturity of the crop, roots, disease, tops, trash and staleness.

If the sugar cane does not satisfy the minimum required conditions it is not allowed to

proceed for processing (i.e it is rejected).

For instance age of the crop is calculated by the formula:

=+

Note; This formula only applies if the roots and tops have been cut off, if they are not

then six is not added in the equation and if only one has been cut off, three instead of six

is added in the equation.

Its important to check for the staleness of the sugar since it affects other production

processes as milling.

The sugar cane should also have less trash for it to proceed in the production process.

Weighing: Is done on a weighing bridge by an automatic weighing machine. Weighing

of the trucks is done twice; when the truck is empty and when it is filled with cargo

which includes sugar cane, sugar, molasses, fertilizer baggasse et cetera.

Net weight= Gross Weight (total) Weight of the Truck- 160Kg (trash weight)


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For trucks carrying sugar cane, weight of the trash is also subtracted which was a

constant of 160kgs.

PRE-MILLING

Cane which has been weighed is carried to the cane yard. It is then unloaded from the

tracks to feed table by three different means which include; by use of a winch, by use

of a grabber and by use of a crane.

Cane loaded into the feed table is carried forward to the cane carrier by means of

conveyer. The conveyers are fitted with a hook that helps hold the sugar cane while its

being carried through the feed table.

The amount of sugar cane being carried into the cane carrier is specified (three quarters

full) and therefore has to be controlled in order not to stall the cane carrier. If there is

too much cane being carried into the carrier by the feed table akickeris employed that

pushes the cane back allowing only a moderate required amount through. Also, to

moderate the amount of cane entering the carrier, speed of the feed table conveyers is

moderated by the feed table operators. The feed table operators are in constant

communication with the cane carrier operators to prevent overloading of the cane

carriers.

The cane carrier carries the sugar cane forward into the pre-milling zone. Here they go

through a quick rotating chopper. The chopper moderates the amount of cane entering

to the other knives. It contains blades on a shaft that rotate backwards which throw

excess sugar cane backwards, maintaining the required level. They also cut the cane tosmall pieces.

The cane then proceeds to a first rotating leveler. The levelers work is to chop the long

cane stalks to shorter ones to allow for better processing.


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The short cane stalks are then carried forward to the heavy duty. The heavy duty

crushes the cane stalks to fibers, though not very fine fibers since bits of trash can still

be observed.

The cane fibers are then moved to the shredders. The shredders further pound the

fibers to finer fiber that is almost powdery.

The cane fibers are then moved to a belt conveyer.

Note: The product is of pre-milling is referred to as sugar fiber and not bagasse. This is

because it still contains the sugar juice in it.

MILLING

The cane in carried to the milling section by means of conveyer a belt. Before the cane

fibers are milled, metal impurities are removed from it by use of an electro-magnet

situated at the top of the conveyer.

Milling is done by means of rollers. A mill contains four rollers namely, top roller,

discharge roller, feed roller andunderfeed roller. The rollers are corrugated to prevent

the sugar fibers from sticking onto their surface.

Feed roller

Top roller motion of sugar fibers

Underfeed Discharge roller.


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The feed roller is the driver roller and it moves all the other rollers. The rollers are

coupled together using gears connected at the ends. The top gear is hydraulically

operated. High pressure water is the fluid used to press the roller down. The water is

applied to a piston which then presses the roller. The pressure applied by the steam is

contained byaccumulaters. The rollers are held into position by bearings. The bearings

are lubricated to slow wear and tear of the gears as well as to prevent overheating and

burning. The bearings are water cooled to prevent them from expanding and

overheating which would stall the mills.

The complete milling process contains five mills. In the first mill no water or juice is

added to the sugar fiber during the milling process and its juice is moved directly to the

storage tank. In the second mill juice from the third mills is added to it and juice from it

is stored in the storage tank. In the third mill juice from the fourth mill is added to it

and fourth mill juice from the fifth mills is added to it. In the fifth mill hot water is

added to its sugar fiber before milling. The process of recirculation of juice of one mill to

the other is called imbibition. The bagasse is carried from one mill to the next by an

intercarrier.

The product of milling is raw juice and the by product is bagasse. The raw juice is

pumped to the process house while the bagasse is carried by a hook conveyer to the

bagasse store to be later used in the boiler. The bagasse is first sieved to remove small

fine particles called bagacillo. The bagacillo is not a viable fuel and extinguishes the fire

in the boiler. The bagacillo is lifted by a vacuum to the process house where it is used as

a filter aid.


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Separation of roller lubrication oil and water

At times the cleaning water mixes with the lubricating oil and therefore need to

separate them.

A displacer systemis employed in which the difference in densities of the two liquids isused as the principle of separation.

It contains three chambers connected to each other by pipes as shown. Water oil

mixture entering the displacer first passes through a sieve that removes solid materials.

Water which is denser occupies the lower position and it therefore carried forward to

the next chamber by the pipe. Oil is collected from the chambers on a weekly basis.

Sieved water+oil in Oil connecting pipes

Oil out

Water. Water out


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JUICE TREATMENT

Layout of juice treatment

Raw juice

tank

Raw juice

/primary

heaters

Liming tank

Continuous

vacuum rotary

drum filter

Cyclone with

bagacillo

Flocculation

chamber

Filtrate tank

Clarified juice

tank

Limed juice

receiver tank

Limed

juice/Secondary

heater

Flash tank

Scum chamber

Clarifier

Mud juice

tank

Mud mixer

Evaporator

Telescopic

valve

Syrup clarifier

Syrup heater

Syrup storage

tank

Flocculation

chamber

Phosphoric

acid tank

Pans


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Juice from the mills is pumped to the raw juice tank. This juice is unprocessed. The pH

of the juice is about 5.0. The raw juice tank is contains two sensors used to detect the

level of juice in the tank. If the juice reaches the level of the first sensor an alarm goes off

giving off a warning of critical level. If the juice level reaches the second sensor, itindicates a critical warning level and hence automatically switches off the pumps at the

milling point stopping further intake of juice to the tank.

The juice is then pumped to the primary raw juice heaters. The juice heaters are heat

exchangers of the shell and tube design containing tubes two meters long. They are in

pairs. The first heater heats the juice to temperatures of 60 to 650c. It uses hot water 70o

Celsius as the heating fluid. The second heater uses third body vapor to heat the juice

(called third body because it comes from the 3rd evaporator). It heats the juice to

temperatures 75-80oC. The heat exchangers have a capacity of up to 120 m3/hr. The

heaters also contain a nozzle pipe that is used to test for leakage. This is done by closing

the outlet and passing cold water under pressure through the tubes. Cold water is also

used to clean the pipes through the nozzle by removing scales that may have

accumulated in the pipes. The process of cleaning is called brushing.

The purpose of heating the juice is to speed up the reactionswith the chemicals (lime

and R300) that would be added to it in latter stages of processing.

The juice is then pumped to the mond/raw juice receiver. It then flows under gravity to

the liming tank. The liming tank is where lime is added to raise the pH level of the

juice to between 7.3 and 7.5. The liming tank contains a stirrer that mixes the juice and

lime to form an even mixture. An overflow pipe is connected the liming tank at a height

where there is satisfactory mixing is achieved and therefore a satisfactory pH. The lime

addition system is automatic but control of how much lime is to be added is set by the

operators depending on the conditions. The tank also has pH sensors to detect the pH

of the juice.


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The limed juice is then moved to the limed juice receiver tank then pumped to the

secondary heaters/ limed juice heaters. Here their temperature is raised to 100 -1050c.

The heating fluid is second body vapor (that is from the second evaporator). Elevated

temperatures promote the process of flocculation and therefore improve juiceclarification.

The juice is then pumped to the flash tank. At the flash tank volume is increased

causing the liquid under high pressure to be flashed to liquid and vapor. The vapor is

let out through a vapor vent via a vapor box to the atmosphere. The purpose of flashing

is to reduce the pressure which may cause disturbance during clarification. The

remaining juice then leaves through a pipe which is connected with a flocculation

chamber via a valve. The valve controls the amount of flocculants added to the juice.

The juice and flocculants then mix co-currently. Flocculants used include R300. The

flocculants form nucleus that other suspended particles in the juice can grow, and

therefore they increase in mass and a settle in the clarifier. The ratio of juice to

flocculants is about one to a thousand by mass.

Mixing of flocculants is done in the flocculants chamber. A stirrer is employed to ensure

sufficient mixing of the flocculants with water.

The juice mixed with flocculants then moves to the scum chamber. The purpose of the

scum chamber is to reduce juice velocity so as it does not cause juice disturbance


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Juice clarification

Metal scrapers

Clear juice tank

Central rotating pipe

Mud drum

Mud remover pipe

Juice from the scum chamber flows into the clarifier through a central duct. The juice

flows downwards to the bottom most chamber of the clarifier and begins to rise. As the

juice level rises, flocs in it settle by sedimentation to the bottom. The juice rises through

the chambers. Also inside the chambers is a mud scraper. The mud scraper sweeps the

settled mud flocs on the floor of the chambers to the center where it flows down to the

next chamber. Clean clarified juice is removed from the top of each chamber via a clean

juice remover pipe situated at a point of satisfactory clarification. The clean juice is then

stored in the clear juice tank. Each chamber has a clean juice remover that is connected

with a valve to the clear juice tank. Flow through the pipes is controlled depending on

the level of clarity. Also at the bottom of each chamber is a mud remover pipe that is

connected to a mud tank. Its purpose is to remove juice filled with the settled mud.

Juice from the mud tank is transferred to the mud tank where it is stored momentarily

before being transferred to the mud mixer tank. At the mud mixed tank it is mixed with

bagacillo from the mills. The purpose of the bagacillo is to act as a filter aid during the

filtration in the rotary drum vacuum filter.


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The mud and bagacillo mixture is then pumped to the mud tank of the rotary drum

vacuum filter. Here the suspensions are kept in solution by an agitator to avoid settling.

The rotary drum is a horizontal slow rotating cylinder covered with a screen, with

radially separated compartments in which vacuum is applied. It is usually partiallysubmerged in the mud mixture. The vacuum absorbs both the juice and the suspension

in the juice. The juice passes through the screen into the radial compartments while the

mud does not. The absorbed juice is then passed out through outlet manifolds in the

compartments by action of vacuum. As the part of the drum which was submerged

moves out of the mud, water is sprayed on it with continued action of vacuum to wash

out any juice that may have remained on the cake that forms on the filter medium. The

cake is then scraped off using a knife onto a conveyer belt and transferred to a mud

boot. The filtrate is transferred to the filtrate storage tank and later pumped to the limed

juice tank to undergo processing again.

The clear juice from the clarifier is transferred to the clear juice heaters after which it is

transferred to the evaporators for concentration.

Evaporators

An evaporator is a vessel used to reduce the water content of juice to high concentration

of brix (both sugar and non-sugar soluble constituent). Evaporators receive juice from

the secondary juice heaters.


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Evaporator diagram Brick like material

Sweet juice remover catch hole

Sight glass boiling space

Steam/vapor in

Tubes Calandria

Deflector plate Saucer

Juice intake

Condensate remover

Juice outlet

Function of parts

Catcher: itsmade up of brick like material that prevents spurting boiling juice from

escaping through the vapor vent incase it jumps too high.

Calandria: is where the heating vapor or steam passes through the evaporator tubes.

The vapor then heats the tubes which intern heat the juice in the tubes causing it to boil.

Saucer:is where the juice is taken into the evaporator and where it remains while being

heated. It is also where the outlet pipe is situated.

Inlet pipe:allow entry of juice into the evaporator.


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Outlet pipe:It takes out already evaporated juice that has boiled and whose moisture

content has been reduced. It is connected to an outlet line with a valve that controls the

amount of juice leaving the evaporator.

Tubes: they provide a point of interaction between the heating vapor and the juice

hence maximum heat transfer between the two. They conduct the heat in the heating

vapor to the juice.

Non condensing gas remover: is to remove the non condensed gas from the boiling

space. This gas is removed from the evaporator since it reduces thermal conductivity

which is only by conduction and convection.

Deflector plate: It spreads the juice in brought in by the intake through the evaporator.

Condensate remover: it removed the condensed vapor or steam and directs it to the

condenser tank.

Sweet juice remover: removes sucrose containing water that has been condensed by the

catcher bricks. It is called sweet juice because it contains sucrose in it. It is usually

pumped to the pans where it is used for heating purposes.

Sight glass: it is used to view the level of juice in the evaporator as well as to monitor

the development of brix.

Operation

Juice from the secondary juice heaters is taken into the evaporators juice intake. This

intake juice contains about 15% brix and 85% water. The juice is then spread to the walls

of the saucer using the deflector plate that is of hemispherical shape. Steam is also

passed through the calandria simultaneously and is used to heat the juice. Hot boiling

juice is passes through the tubes depending on the level of boiling.

The boiled juice looses some of its vapor that is carried out through the vapor vent

where it is carried forward to be used in the next evaporator as the heating fluid. As it


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leaves some of it condenses. The condensate is transferred to the condenser tank where

it is then pumped to the boiler to top up the boiler water.

On heating the juice the steam looses some of its latent heat. It is then released to the

atmosphere to avoid build up of pressure.

There are a total of five evaporators; all operate under the same principle. The first

evaporator is of the semi Krestner type (does not have a downtake) and the other four

are Robert evaporators.

The quantity of brix in the syrup leaving from the fifth evaporators is between 60-65%

Table of summary of evaporator variables

VARIABLE

Exhaust steam pressure 0.9 to 1.2 kg/cm3

Exhaust steam temperature 1150c to 1200c

1 body vapor pressure 0.3 to 0.5 kg/cm3

1 body juice level boiling level half glass

1body outlet valve kept fully open

1 body boiling temperature 105 -108

2 body boiling temperature 103-105

2 body vapor pressure 0.2 -0.3

2 body juice level- boiling just at 1 glass level

2 body cut over valve fully open

2 body vapor temperature 93 -98


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3 body vapor vacuum 100 -150 mm (4-6 inches)

3 body juice level at 1 glass level

4 body temperature 80 -85

4 body vacuum 300-400mm (12 -16 inches)

5 body vapor temperature 60 65

5 body vacuum 500 600mm (22 24 inches)

Syrup brix 60 -65 %

Cleaning of the evaporators

The main purpose of cleaning is removal of scales that are formed in the evaporator

tubes during boiling as well as the evaporator inside. Scales are formed from

evaporated water containing lime juice that is they are lime salts that were in solution.

The evaporator is first filled with caustic soda which is heated to boiling by steam or

vapor for a period of four hours. Since the caustic soda is corrosive it softens the scales

from inside the tubes while eroding less of the metal tubes since they have a highercorrosion resistance. The caustic soda is then drained and the evaporators downtake

closed before it is steamed.

After the caustic soda has been drained, cold water is introduced into the evaporator.

The cold water not only serves the purpose of washing but also due to its low

temperature causes sudden contraction of the evaporator tubes. Sudden contraction

causes the scales in the tubes to crack. The cold water is then drained. This is repeated

three times.

After draining the tubes are cleaned by a rotating skatascola tool head connected to a

rotating motor by a rotating flexible shaft. Cold water is then again flashed through the

tank and then drained.


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Notes

The first second and third evaporators are operated under pressure while thefour and fifth evaporators are operated on vacuum. This is because the third

fourth and fifth evaporators are operated under vapor to reduce the evaporation

temperature of the juice or syrup. This is to prevent decomposition of the

sucrose.

Also as the temperatures reduce through the adjacent (that is from evaporator 1to 5) evaporators reduce. This is to prevent dissociation of sucrose in the sugar to

fructose and glucose. It also prevents caramolisation which is the burning of

sugar to form black carbon.

Also, the volume of the evaporators reduces from the first through to the fifth.This is because of reduces quantity due to loses by evaporation.

The evaporators are insulated with thick cotton material covered with shinyaluminum sheets to prevent heat losses to the environment.

From the evaporator the juice is transferred to the syrup heaters where its temperature

is further raised, it is then mixed with flocculants as R300. This helps to coagulate any

small suspensions in the syrup. Also phosphoric acid is added to reduce its viscosity.

The syrup is then pumped to the syrup clarifier. Its principle of separation is by

floatation, that is, the suspensions float on top of the syrup. The suspensions are then

removed by slow rotating scrapper at the top onto a side vent. The clarified syrup

moves to the bottom of the clarifier where there is a coiled pipe with orifices where it is

removed through a telescopic valve. The telescopic valve controls the level of the

clarifier. If the syrup coming in is clean the telescopic valve is opened more. This lowers

the juice level in the clarifier further away from the metal scrapper, hence no scrapping

but if there are many suspensions floating on the syrup the valve is closed reducing the

flow from the clarifier hence increasing its level to where they can be scraped.


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Sulfur preparation

Sulfur is prepared in order to be used in bleaching the sugar juice to produce white

sugar during the crystallization process.

Sulfur powder is added to the sulfur melting tank and moved to the sulfur melter

tank. Here steam is passed through the sulfur causing it to melt

The sulfur melt is then allowed to flow the sulfur burner tank and enclosed.

Compressed air is then added to the sulfur in presence of a hot metal catalyst causing

reaction between sulfur and oxygen in the air to occur. The product of the reaction is

sulfur dioxide.

Sulfur + oxygen sulfur dioxide

The reaction is exothermic and raised the temperature to 3500c.

The sulfur dioxide fumes are then passed through scrubbers. The scrubbers contain an

arrangement of bricks. The fumes are introduces from below and flow upwards. Sulfur

particles in the fumes are attracted and stick on the surface of the bricks by surface

adsorption.

The fumes are then water cooled by passing them through a heat exchanger reducing

the temperature from 3500c to 600c.

Sulfur not only causes bleaching of the juice but it also enhances crystallization by

bringing the pH down

The sulfur can either be applied directly to the syrup or to the limed juice. Sulphur is

applied from below and it rises upwards while bleaching the syrup or juice.


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SUGAR HOUSE

Sugar house overall layout

A-massecuite pan

boiling

Hopper

Syrup storage

tank

A wash receiver

tank

A-centrifugal

machine

Pug mill

C- Massecuite

pan boiling

B-molassesreceiver tank

C-sugar massecuite

receiver tank

Re-melter tank

B-centrifugal

Pug mill

B-sugar receiver

C-massecuite

crystallizer tank

B-massecuite Pan

boiling

B-massecuite

crystallizer

A-sugar

A molasses

receiver tank

Drier

Pug mill

Crystallizer

Storage

For lump and

powder sugar

Sugar bin for

commercial sugar

Grader

Weighing and

bagging

Vertical

crystallizer

C-centrifu

C-sug

receiv

Molasse

storage


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Pan boiling

It involves boiling of mother liquor with the aim of crystal growth to the required for

commercial consumption and increasing the brix. It is usually done in a pan boiler.

The heating fluid used is 2ndbody vapor for B and C massecuite boiling and 3rdbody

vapor for A massecuite. All the three pans are operated on vacuum to reduce the

boiling temperature of the massecuite and hence preventing caramalisation.

There are three types of pan boiling operations operating under the same principle.

They include A-massecuite pan boiling, B-massecuite pan boiling and C-massecuite pan

boiling. The difference between the three is the product and the mother liquor.

Diagram

Stirrer driver motor

Vapor body vapor vent

Catcher

Stirrer mother liquor intake boiling

NCG remover space

Heating vapor in

Calandria tube calandria

Condensate remover

Downtake


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A pan boiling

It involves evaporation of water from A-massecuite with addition of mother liquor. The

sugar crystals in the massecuite then grow by absorbing sucrose from the mother liquor

till they reach the required size. The heating fluid used is 3rdbody vapor and on heating

it is injected into the pan boiling space to enhance temperature.

It is divided into three stages which include;

a) Graining: it involves the introduction of B-magma into the pan A to the 350hllevel. The seed is then heated with continued controlled addition of hot water

and syrup. The purpose of the hot water is to dissolve tiny grains in the

massecuite called false grains, while the syrup provides other grains with syrup

for further growth. This is done for a period of about fifteen minutes to increase

the grain size to standard required size.

b) Boiling: it involves addition of mother liquor slowly to the massecuite whileboiling it. Mother liquor is a mixture of A-wash, remelt and syrup. Addition of

mother liquor causes the crystals to grow while at the same time increasing the

volume of the pan contents. The rate of addition of mother liquor should be

almost equal to the rate of absorption of sucrose from the mother liquor formaximum growth of the sugar crystals. If the addition rate is too fast there will

be dissolution of the crystals and hence formation of false grains. On the other

hand if the addition is too low the crystals may overbrix and dissociate to carbon

or create disruptions during striking. After the massecuite grow to a volume of

750HL the flow of mother liquor is stopped and the massecuite heated for a

while for it to brix.

c) Striking: it involves removal of massecuite from the pan to the receiver orcrystallizer. Depending on the level of growth of crystals, the massecuite may be

striked once twice or thrice. If the crystals grow to the required size they are

immediately dropped onto the crystallizer. This is called one strike. On

dropping the pan downtake is closed and vapour passed through it. This helps


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remove massecuite that might have stuck on the pan surface. The downtake is

then opened and massecuite allowed to flow out. This is done three times.

If the crystals grow to a slightly large but not expected level, half of it is sent to a

receiver tank. This is done by removing vacuum in the pan and applyingvacuum to the receiver then opening the valve between the two. The other half

left on the pan is retaken through the boiling stage before being dropped then the

other half is returned to the pan and taken through the boiling stage before being

dropped. This is called two strike.

However, if growth of the crystals during the first boiling is too small, a third is

separated from the pan to another pan. The remainder in the pan is boiled to the

top with addition of mother liquor till it fills then 2 strike process is performed to

it. The third transferred to the other pan is taken through the boiling process and

on filling it is dropped. This is called three strike.

B-massecuite pan boiling

Pan operations are similar to pan A. the difference is that A-heavy molasses is used

instead of mother liquor. Also the heating fluid is second body vapor.

The magma used is C-sugar and graining is done using hot water circulation (sweetwater from evaporators).

The product is B-massecuite.

C-massecuite pan boiling

Operation is similar to pan B boiling. The difference is that B-molasses is used during

the boiling process.

The magma used during seeding process is a mixture of slurry and A-molasses. Slurry

is microscopic crystals of sugar that provide nucleation site for growth of sugar crystals.

Its product is C-massecuite.

Massecuite is stored in the crystallizermomentarily before curing though A-massecuite

is can be cured immediately. The massecuite cools in the crystallizer from temperatures


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of about 610C. This further enhances formation of sugar crystals. Also, in the crystallizer

is a slow rotating stirrer that prevents the massecuite from settling and hardening.

C-massecuite is however passed through the vertical crystallizerwhere it is stored for a

minimum of 21 hours while water cooled before being moved to the C crystallizer. This

enhances further crystal formation in the C-massecuite which forms crystals slower.

The massecuite is then moved to the pug millwhere it is also stored momentarily with

continued stirring before entering the centrifugals.

Centrifugals

Centrifugal is a fast rotating vessels containing a screen as the inner chamber. Fast

rotation of the centrifugal causes the massecuite to be thrown onto the screen. Since the

crystals are of larger size they are trapped on the screen and molasses passes through

the screen hence separation. There are two types of centrifugals; batch centrifugal and

continuous centrifugals.

Batch centrifugal

It is called batch because massecuite addition into it is not continuous. It is majorly used

in the separation of A-massecuite to A-sugar A-wash and A-heavy molasses.


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Diagram

Driver motor

Motor brake

Pug mill

Charge sensor

Plough

Steam inlet pipe

water inlet pipe

bottom valve

molasses duct

The batch centrifugal is automatic and works as followThe valve is closes and massecuite is let into the centrifuge. The machine then

accelerates and run for a while a speed of 200rpm. This causes the massecuite to spread

evenly to the side of the screen. Also, excess molassesis separated via the screen to the

molasses storage tank.


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Massecuite is mixed with water at the funnel and flows into it from through the central

funnel duct into the distributor. The distributer distributes massecuite evenly around

the centrifugal as well as retains foreign material around the basket as nuts and bolts.

The molasses is then separated via the conical screens and moves to the molasseschamber while the magma is retained and moves upward the conical screen. Magma

from the B and C centrifugal is stored in receiver tanks and used as seed in A and B

sugar growth respectively.

A-sugar at the hopper is moved forward by shaking motion to the bucket elevators

where it is carried to the drier. The drier is a slow rotating horizontal cylinder. Inside it

there are hook like arms that mix the sugar while hot air form the radiator is being

blown into it hence reducing the water content. From the drier cold air is blown into the

sugar reducing its temperature to 40 degrees which is the required temperature for

bagging. The sugar is then carried with a belt conveyer to the grader via an

electromagnet which traps the metal impurities in the sugar.

The grader contains three screens which first separate lump sugar, then commercial

sugar and finally fine powdery sugar. The lump and powdery sugar is not suitable for

consumption and is therefore sent to the dissolution tank where water is added to it. It

is then pumped to the re-melter tank where its temperature is boosted which further

enhances dissolution then to the A-pan boiler.

The commercial sugar is carried by bucket elevators to the sugar bins where it is stored

momentarily while awaiting bagging.

Weighing and bagging is done by an automated system. The bag is placed into position

by the bagging operator. It is held to position by arms that employ a pressure system

and filled with sugar to the required weight. Pressure is the released which intern

releases the arms and the filled bag. Pressure release is done by a weight sensor, that is,

it releases only if the required weight has been reached. The bags are then carried by a

manually controlled conveyer and sewed, then carried by hand to a convey to the

storage room where it is stored before being transported to the market for sale.


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The water then moves to pond four. Pond four is aerated by a fast rotating motor with

blades. It contains aerobic bacteria which digest the sludge with use of oxygen. This

increases the pH of the water to 6.5-7.0.

Clarifier

Water then moves to the clarifier tank where particles settle by the sedimentation

process. The clarifier has a slow rotating metal rod fixed with brushes on it that sweep

the settled mud to a central outlet. The mud is pumped to pond 3 and 4 to increase the

number of bacteria as well as to balance the pH. If there is too much mud it is directed

to the drying plates to be dried.

The water then moves to pond 6 and is stored for about 15 days. The pond contains

algae. This indicates the ability of the water to sustain life. The level of green colour in

the water shows the amount of nutrients in the water which have to be absorbed before

release to the river. If the water is very green, nile cabbage is cultivated in this pond to

absorb some of the nutrients.

Constructed water lands

The water then moves to constructed water lands. They are six in number and contain

plants growing in them as water hyacinth. They are shallow to allow light to penetrate

through the water and allow growth of plants in the water. The plants also have long

fibrous roots that trap suspended particles and hence reduce the turbidity of the water.

Some of the plants also absorb heavy metals from the water. The water is carried by

meandered paths to reduce its velocity and increase the retention time.

The water is then tested at the end of the water lands for pH, turbidity and total

dissolved solids. Also, the river water is tested at the upstream and compared with the

conditions at the end of the water lands. This is to ensure the water from the factory is

not affecting the river water


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WATER TREATMENT

Water from the river is not suitable for use as it is, it therefore needs to be treated before

use both in the boiler and for domestic use. The water is pumped from the river into the

raw water storage tank for storage.

Clarification: It is then pumped to the clarifier, a flocculants called floquat is added to it

before entry into the clarifier.

It coagulates the small suspensions in the water and settles them at the bottom.

It is preferred to alum because it is an organic polymer and does not affect the pH of

the water. The settled particles are then swept to a central outlet pipe with a slow

rotating scraper.

The sediments at the bottom are removed momentarily through a discharge valve at thebottom of the clarifier. On the other hand clean water is removed from the top to a

storage tank.

Bed filtration and decolourising: It then moves through a sand bed filter that traps

other smaller particle in the water that cannot be separated in the clarifier. It then moves

to an activated carbon filter that removes colour and chlorine.

Domestic water treatment

From here domestic water is treated with calcium hypochlorite which disinfects the

water as well as removing colour that is in it. It is then stored in the domestic water

storage tank.

Boiler water treatment

Removal of ions and dissolved gases

Boiler water on the other hand is further treated to remove the reactive components in

it. First it is taken to the cationic unit where it is passed through a hydrogen ionexchange unit. This unit removes magnesium and calcium ions by exchanging them

with hydrogen ions to form an insoluble salt thus removing the water hardness.

The water then moves to the anionic unit that mainly removes chloride ions from the

solution and replaces it with hydroxide ions using a hydroxide exchange resin.


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The water is then moved to the degaser unit. This unit employs a pump rotating in an

opposite direction with the water. This removes gases in the water as oxygen. Oxygen is

removed since it reacts with the boiler tubes causing corrosion.

The water then moves to the mixed bed unit which contains a mixture of both cationand anion exchange resins that remove any remaining cations or anions. The water

then moves to the service tank while caustic soda is added to it to boost its pH to about

9.5 before use in the boiler.


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BOILER

A boiler is a vessel used for steam generation. The boiler here was a water tube boiler,

where water flowing in tubes is heated by flue gases flowing on the outer tube surface.

Water used in the boiler has to have minimal reactivity and also contain less dissolved

solids and therefore is treated in the dimineralisation plant or condensate water is used

from the process house.

Steam drum Primary superheater Secondary superheater

Flue gases to

Economizer and

air heaters

Downcomers

Mud drum

Blow down valve

Raisers

Common header

Grate

Motion of flue gases

fu

Bag

fee


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Flow of water in the boiler:water in the boiler is gotten from the service tank and

moves to the economizer where partly used flue gases are used to heat it to

temperatures of 1200C. The water then moves to the steam drumand if it contains any

vapor it evaporates due to increase in volume. The water then moves out through thedowncomer tubes, located at the bottom of the steam drum, where it is heated by flue

gases from the superheater region while flowing downward. The water then moves to

the mud drum. The mud drum has a blow down valvewhich serves the purpose of,

removing excess water in the boiler if its level is high, bleeding of water is has a high

TDS( total dissolved solutes), and draining the water out during maintenance. Also soot

scum is added to the water which serves several purposes as trapping any escaped

oxygen and keeping any scum in fluid state to enable easy removal through the

blowdown valve.

The water then moves to common headers which are connected to tubes on the furnace

walls called raisers. While it moves upwards it is heated by radiated heat from the

furnace to form a mixture of water and steam. This mixture is carried to another

common header before moving to the steam drum. Water being denser settles at the

bottom of the steam drum while steam removed upwards to a common header then to

the primary superheaters and secondary superheaters which are directly above the

furnace, where it is heated to temperatures of 4500C and a pressure of 45 psi and

transferred to the turbines through an outlet line. The line has a pressure controlled

spring valve that open to let out steam to the atmosphere when it rises above 45psi.

Flow of flue gases: flue gases from the furnace first move to the superheat region

where they are used to superheat steam. They then move to the downcomers where

they heat water in the downcomer tubes, then they are sucked by the induced draft fun

to the economizer where they heat the water to temperatures of 1200C. They are then

flowed into tubes where they are used to heat air flowing in the outside in the air

preheat region. The flue gases then flow to the main dust collector (MDC) region


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where dust particle in the gases are removed before being let out to the atmosphere via

a chimney.

Flow of air: air from the outside is by use of fast rotating forced draft (FD) fans. The air

then moves to the air preheaters to be heated in order not to reduce the temperature inof the furnace. Some of the heated air is let into the furnace from below while some is let

in via the secondary air fans near the point of entry of bagasse and is used to spread the

bagasse in the furnace. The ratio of air to bagasse in the furnace is 14:1 by mass.

Flow of bagasse: bagasse is moved from the bagasse storage via a chain conveyer to

the bagasse feeds. It is then spread to small pieces by the bagasse spreader which

employs the use of high speed rotating rollers before being fed into the furnace where it

is spread in the furnace by the secondary air fans.

Combustion is controlled by the rate of air flow into the boiler since most of the other

factors are kept constant.

Note:The boiler is started using firewood as the fuel before addition of bagasse.

LABORATORY

The work of the laboratory was to prepare reagents as well as to measure parameters of

various samples for quality control purposes. This was done by comparing the

parameters with the set values.

Test carried out in the laboratory

Sugar moisture test

Procedure 20 grams of sugar was accurately measured in an aluminum dish. It was then placed in an oven for 4 hours. The sample was the removed and placed in a desiccator.


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= ()

Sugar colour test

Procedure

50% sugar solution was made by weighing 50grams of sugar and it in water in a100ml volumetric flask.

Part of the sample was taken and its brix read from a refractometer. The solution was then filtered under vacuum through a membrane filter of pore

size 0.45mm

The first filtrate was discarded and the rest was covered to avoid evaporation. The spectophotmeter was switched on for about 30minutes It was then set at 420 nanometer wavelength and also zero absorbency was set

using a clean tube cell filled with distilled water.

The same cell was rinsed with the filtrate and filled, inserted and the absorbanceread.

=

pH determination

The electric method was used. This was carried out for the raw juice, limed juice, syrup,boiler water, service water and the condensate.

Procedure

The pH meter was calibrated using a buffer solution. The sample was then cooled to room temperature.


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The electrodes were then rinsed with the sample to be tested. The beaker was filled with enough sample to cover the bulb of the glass

electrode.

The system was then left to come to equilibrium and the pH read and recorded.

On reading the electrode was washed with distilled water and left in the distilledwater or buffer.

Determination of water insoluble matter in sugar

Procedure

Filter membranes of pole size 8 micrometers were prepared by boiling them indistilled water for a period of 30 minutes, put in a dish, dried in a hot air oven at

1050C for 1hour and cooled for 30 minutes in a dessicator and weighed. Weight was

recorded as W.

100 grams of sugar sampled was then weighed in 1000ml glass beaker, 700ml ofdistilled water added and boiled while stirring to dissolve completely.

Solution was then filtered through vacuum filtration apparatus fitted with theabove membranes.

The residue on membranes shall be dried in hot air oven at 1050C for 1hourcooled for 30 minutes in a dessicator and its weight was recorded as X

= /

Determination of moisture in bagasse

Procedure

Weight of the tray was taken and recorded as M.

100grams of bagasse or filter cake sample was measured while on the tray.

The tray with bagasse or filter cake was then placed in an oven at 1050C for 3 hours.

The sample was then removed and weighed immediately and recorded as P.

Calculation


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Weight of tray=M

Weight of sample on tray=N

Weight of sample dry=P-M=V

Weight loss=N-V

=

Determination of sugar trace

This was done on the condensate water to be used in the boiler.

Procedure

The sample was taken in a test tube and cooled.

5 drops of 1-naphtol were added and shaken well. Concentrated sulphuric acid was then slowly added from the side and checked

for the colour of the ring.

If it was purple then there were sugar traces else if it was green there were nosugar traces.

Determination of sugar ash

Procedure

5 grams of sugar were weighed in a platinum dish then moistened with 0.5ml ofconc. H2SO4.

The sample was then gently heated avoiding overflow of froth by heating bothbelow and above the dish until the sample is carbonized.

The sample was then place carbonized sample in muffled furnace at 6500C for3hours.

The sample was then removed, cooled and moistened again with conc. H2SO4,put in a furnace at 6500C and removed to cool in a dessicator to room

temperature.


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% = .

Determination of brix

Sample preparation

Sample was taken and weighed. Water equal to its weight was added to it. Samples

included A-massecuite, B-massecuite, C-massecuite, B-molasses and final molasses.

Procedure

The prepared whose brix was to be measured was used to clean the brixometerby rinsing it then it was wiped.

The sample was the put on the brixometer and the brix was read and the valuegotten was multiplied by two and recorded.

Determination of pol/sucrose content

Procedure

26 grams of sample prepared above was measured in a volumetric flask and theflask filled to mark. The flask was then shaken well to mix.

The mixture was then placed in a beaker and two spatulas of lead acetate addedto it. The lead acetate acts as a coagulant.

The mixture was then filtered by a filter paper onto a beaker and the residuedisposed.

The filtrate was first used to clean the pol tube then it was filled into the pol tubeto be used in the polarimeter

The pol meter is calibrated by distilled water to the zero level using distilledwater.

The flap was then replaced and rotated positively/negatively until the full moonwas reached.


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The pol reading was read multiplied by two and recorded.% =

Documents

West Kenya Sugar Company