Qut025 Srdc Tlop Report for Web

8/3/2019 Qut025 Srdc Tlop Report for Web

http://slidepdf.com/reader/full/qut025-srdc-tlop-report-for-web 1/21

Sugar Research & Innovation

Report on a visit to the White Sugar Mill

installation at Felixton Mill, South Africa

by

R.J. Steindl and R. Broadfoot

March 2008

QUT Job No. 3679

SRDC Project No. QUT025

ORGANISATION: Sugar Research & InnovationQueensland University of Technology

GPO Box 2434

BRISBANE Qld. 4001

CONTACT: Principal Investigator

Mr Rod Steindl

QUT, Brisbane Queensland

(07) 31381234

[email protected]

FUNDING: Sugar Research and Development Corporation

Queensland University of Technology

Sugar Research and Innovation, QUT is not a partner, joint venturer, employee or agent of SRDC and has

no authority to legally bind SRDC, in any publication of substantive details or results of this Project.

FINAL REPORT SUBMITTED TO THE SUGAR RESEARCH AND DEVELOPMENT CORPORATION AS PART OF

GRANT QUT025





i



Contents

Summary.......................................................................................................... iii

1. Introduction ............................................................................................. 1

1.1 Background.......................................................................................................... 1

1.2 Objective of the visit ........................................................................................... 2

2. The White Sugar Mill process ................................................................ 3 2.1 Ultrafiltration ....................................................................................................... 3

2.2 Refrigeration and heat recovery .......................................................................... 4

2.3 Demineralisation.................................................................................................. 5

2.4 Decolourisation.................................................................................................... 9

2.5 Evaporation, crystallisation, fugalling and drying .............................................. 9

2.6 Colour balance and sample analysis.................................................................. 10

2.7 Product handling................................................................................................ 11

2.8 Plant specification ............................................................................................. 12

2.9 Benefits.............................................................................................................. 12

2.9.1 Sugar recovery...................................................................................... 132.9.2 Reduced scaling.................................................................................... 13

2.9.3 Fermentation......................................................................................... 13

2.9.4 Fertiliser................................................................................................ 13

3. Acknowledgements ................................................................................ 15

4. References............................................................................................... 15

5. Other publications associated with WSM........................................... 16

6. Dissemination to the Australian industry ........................................... 16

List of figures

Figure 2.1 The White Sugar Mill process............................................................................. 3

Figure 2.2 Pumps and membrane modules for the ultrafiltration step.................................. 4

Figure 2.3 The heat recovery screen ..................................................................................... 6

Figure 2.4 One of the multi-port distributors used in the simulated moving bed ion-

exchange system.................................................................................................. 7

Figure 2.5 Some of the tanks holding ion-exchange resin.................................................... 8Figure 2.6 Device used to distribute permeate feed into a resin bed.................................... 8



ii

Figure 2.7 Image of the ion-exchange distribution system showing the current status in the

cycle of each resin vessel .................................................................................... 9

Figure 2.8 Snap samples of streams showing (L to R) UF feed, permeate, retentate,

deashed juice, decolourised juice, the resultant white sugar and raw sugar from

the normal process............................................................................................. 10Figure 2.9 White sugar stored in 1 t bags ready for transport............................................. 12

Figure 2.10 The status quo for cane flow to the factory and filter cake recycle back to the

canefields (Jensen et al., 2006).......................................................................... 14

Figure 2.11 The potential benefits in recycling both filter cake and fertiliser back to the

canefields to eliminate regenerant chemical disposal (Jensen et al., 2006) ...... 15

List of tables

Table 2.1 Analyses of process streams for three consecutive days (Jensen et al., 2006).. 11



iii



Summary

The purpose for visiting Felixton Mill while in South Africa for the ISSCT Congress was to

collect performance and operating/maintenance data for the White Sugar Mill (WSM)

plant.

After an initial meeting with some staff of Felixton Mill, Dr Craig Jensen of Tongaat-Hulett

Sugar Ltd accompanied the authors on a tour of the WSM plant installation and provided

sufficient information and data to permit an assessment of the WSM technology and itsimplications for Australian factories.

A production sized plant capable of processing 15 % of the Felixton Mill throughput

(equivalent to 12.5 t brix/h) and producing 36 000 tonnes of commercial EEC2 white sugar

per annum has been operating since 2005. The plant includes the following technologies:

• Ultrafiltration of 25 brix juice from a mixture of 1st and 2nd effect juice using ceramic

and stainless steel membranes operating in parallel;

• Juice refrigeration using flash cooling in a staged steam ejector system;

• Demineralisation using a combination of strong acid cation resins and weak base anionresins;

• Decolourisation of juice to about 400 IU using strong base resin in the chloride form;

and

• Evaporation, crystallisation, fugalling, drying and bagging using conventional

equipment.

Two crystallisation strikes are made to produce the white sugar product. A WSM molasses

suitable for fermentation to produce high value products is a by-product of the process.

The plant is capable of producing white sugar of less than 45 IU to meet EEC2 white sugar

standards.



1



1. Introduction

Following the ISSCT congress at Durban, South Africa, Dr Ross Broadfoot and Mr Rod

Steindl visited Felixton Mill on 3-4 August 2007 to inspect the White Sugar Mill (WSM)

installation and to discuss technical aspects of the process with Dr Craig Jensen. Dr.

Jensen, new technology group leader for Tongaat-Hulett and WSM project manager, has

been involved with the development of the WSM technology since its inception in the late

1990s.

1.1 Background

Development of the WSM technology was initiated in 1998 to prepare a high quality

fermentation feedstock for the production of lysine by South African Bioproducts Ltd

(SABP). Initial developments focused on de-ashing of refinery WSM molasses.

Subsequently, a joint development project between Tongaat-Hulett Sugar Ltd (THS) and

SABP shifted focus to processing clarified juice to produce white sugar to meet EEC2

standard, together with a high quality fermentation feedstock directly in a raw sugar

factory, without producing crystalline raw sugar as an intermediate product.

A pilot plant was installed at Felixton Mill in 1999 to prove the WSM process. Following

the success of the ‘proof of concept’ phase, a larger WSM plant called the ‘semi-

commercial’ plant was installed at Felixton Mill in 2002. This plant was capable of

processing 5 % of the mill throughput.

The original pilot plant was containerized and then used successfully for pilot trials in

Brazil at two sugar mills in 2004. The objective of the joint venture partners was to

establish the viability of the process under different conditions to those existing in South

Africa.

In 2005 a production sized plant capable of processing 15 % of the Felixton Mill

throughput (equivalent to 12.5 t brix/h) and producing 36 000 tonnes of commercial EEC2

white sugar per annum was commissioned.

The EEC2 white sugar specification includes the following quality parameters:

Polarisation >99.7

Colour <44.5 IU

Ash <0.03 %

Invert <0.04 %



2

1.2 Objective of the visit

• To collect performance and operating/maintenance data for the White Sugar Mill

(WSM) plant installed at Felixton Mill, South Africa.



3

2. The White Sugar Mill process

The WSM process is illustrated in Figure 2.1. The new process steps include ultrafiltration,

refrigeration of the permeate, and ion-exchange for decolourisation and demineralisation.

Evaporator

1st effect

Clear juice

Evaporator

2nd effect

Ultrafiltration

Juice

refrigerationEvaporator

Effects 3 to 5

Retentate

Ion-exchange

Demineralisation

& Decolourisation

White sugar

crystallisation

Two white

boilings

Two recoveryboilings

Chilled permeate

Wash water

Regen

chemicals

White juice

Fermentation

feedstock

White sugar

Permeate

19 brix

juice

25 brix

juice

30 brix

juice

Figure 2.1 The White Sugar Mill process

2.1 Ultrafiltration

Clear juice of about 25 brix is used as the feedstock for the WSM process. A rotating

wedgewire screen (80 μm openings) is used to remove suspended solids from the juice prior to the membrane filters. The ultrafiltration step (pore size 0.1 μm) removes high

molecular weight compounds from the juice to prevent fouling of the resin columns. The

use of 25 brix juice at 90 °C provides the best combination of volumetric flow rate,

permeate flux and pressure drop across the membranes. It also provides close to the

maximum solids flux (C. Jensen, pers. comm.; Steindl and Rackemann, 2002). Both

ceramic membranes from Applexion and stainless steel membranes from Graver

Technologies providing approximately equal areas of filtration surface are used in parallel.

A picture of the membrane plant and the pumps is shown in Figure 2.2.

Cross-flow velocities are in the range of 5-7 m/s. This is a trade-off between capital andoperating costs. Dropping from 7 to 5 m/s will halve the power consumption of the plant



4

per unit area of membrane, and increase the life of the membranes but the membrane area

required increases by approximately 20%. The membranes have provided about three years

service. THS expects to replace the membranes after five years service.

Figure 2.2 Pumps and membrane modules for the ultrafiltration step

The retentate from the ultrafiltration step is sent to the final molasses stream from the raw

sugar factory.

2.2 Refrigeration and heat recovery

The permeate is then cooled to minimise sucrose inversion losses during thedemineralisation and decolourisation treatments.

Refrigeration to about 10 °C is being achieved by flash cooling the juice in a single stage

with a head pressure of 1.2 kPa abs. This extremely low absolute pressure is achieved

through a staged steam ejector system (atmospheric pressure →20 kPa abs →7 kPa abs →

1.2 kPa abs).

Plate heat exchangers are used to exchange the heat between the cool white juice (juice

after decolourisation) and the hot permeate to improve the thermal efficiency. The

permeate is cooled to 22 °C before it enters the flash unit.





6

Figure 2.3 The heat recovery screen



7

Figure 2.4 One of the multi-port distributors used in the simulated moving bed ion-

exchange system



8

Figure 2.5 Some of the tanks holding ion-exchange resin

Figure 2.6 Device used to distribute permeate feed into a resin bed



9

Figure 2.7 Image of the ion-exchange distribution system showing the current

status in the cycle of each resin vessel

2.4 Decolourisation

Decolourisation of the deashed juice to about 400 IU colour is achieved in an ion-exchange

unit similar to those used for demineralisation. The resin used is a strong base resin in the

chloride form as commonly used in other fixed bed ion-exchange decolourisation plants in

the sugar industry. The pH of the juice exiting the ion-exchange unit is about 8.8. The resin

is regenerated with a caustic brine solution.

THS expects to replace the decolourising resins after two years. They expect that the cold

operating conditions will assist to extend the life of the resins.

2.5 Evaporation, crystallisation, fugalling and drying

The juice after decolourisation is at 15 brix and is evaporated to 70 brix in a 3 stage

evaporation plant comprising falling film evaporators. The first evaporator is supplied with

vapour 2 from the raw plant.

A single batch pan of 50 m3 capacity (unstirred, mild steel construction) is used for the two

white strikes and two recovery strikes. Each strike is slurry grained, run up and dropped.

The target size for the white sugar product is 500 μm. The mother molasses is of lowviscosity and strong circulation movement is obtained. There have been no problems with



10

settling of the crystals in the pan despite the pan being unstirred and the mother molasses

having low viscosity.

If the decolourised juice has colour less than 500 IU then the sugar from the two white

strikes becomes the product white sugar which satisfies the EEC2 grade.

A single batch fugal of 1.2 t charge is used to separate the white sugar crystal. A lot of

steam is injected into the fugal to assist the purging. Currently the WSM molasses from the

final recovery boiling is sent to the final molasses tank for the raw factory.

Drying of the sugar is undertaken using hot air at 55 °C initially followed by ambient air.

There is no conditioning step prior to bagging of the white sugar.

2.6 Colour balance and sample analysis

A photograph of snap samples of the various process streams through the WSM plant isshown in Figure 2.8. Typical colour values are as follows:

Clear juice 20,000 IU

Permeate juice 18,000 IU

Deashed juice 2,500 IU

Decolourised juice 400 IU

Some daily analyses are given in Table 2.1.

Figure 2.8 Snap samples of streams showing (L to R) UF feed, permeate, retentate,

deashed juice, decolourised juice, the resultant white sugar and raw

sugar from the normal process



11

Table 2.1 Analyses of process streams for three consecutive days (Jensen et al.,

2006)

Brix Pol Purity

(%)

pH Colour

(IU)

Ash (%)

Day 1

UF feed n.a.

IX feed 25.0 21.4 85.7 6.5 20,745 0.8

Interstage 18.5 16.4 88.3 7.0 1,360 0.02

White juice 16.2 14.5 89.7 8.1 78 0.01

White syrup 66.3 59.6 89.9 7.1 183 0.03

Day 2

UF feed 25.6 21.6 84.3 7.4 27,725 0.8

IX feed 25.1 20.9 83.5 7.1 16,587 0.8Interstage n.a.

White juice 15.8 14.3 90.5 7.9 118 0.01

White syrup 71.1 62.5 87.9 5.8 157 0.04

Day 3

UF feed 32.4 25.7 79.2 22,720 1.1

IX feed 25.8 20.7 80.2 6.4 21,640 0.8

Interstage 19.8 17.3 87.2 6.7 1,863 0.02

White juice 17.6 15.9 90.4 98 0

White syrup 72.2 65.3 90.5 180 0.01

2.7 Product handling

The white sugar is dried and bagged into 1 t bags (see Figure 2.9) on site. There is no sugar

conditioning step between the dryer and the bagging plant. The white sugar is sent to the

THS refinery for bagging in small bags for retail sale.



12

Figure 2.9 White sugar stored in 1 t bags ready for transport

2.8 Plant specification

The following specification for the plant was provided:

• Capacity: 200 t white sugar per day

• Capital cost: ~USD12M (2005 cost)

• Major equipment:

- 425 m2 membrane filtration area

- 90 m3 ion-exchange resin

- 1 MW refrigeration plant

- 5.5 MW liquid-liquid heat exchangers

- 2600 m2 triple effect falling film evaporation plant

- 2000 m2 fertiliser evaporation plant (double effect Kestner evaporators)

-

50 m

3

batch pan (unstirred, mild steel)- 1.2 t batch centrifugal

- Drying, storage and 1 t bagging plant

2.9 Benefits

For the conditions applying in South Africa, the WSM process has a number of benefits and

is claimed to be economically attractive.



13

2.9.1 Sugar recovery

If the whole throughput of a factory was to be treated through a WSM process the expected

improvement in sugar recovery from molasses is about 7 %. Laboratory tests have shown

that the target purity for the exhausted WSM molasses is ~25 purity. The crystallisation

rate for WSM treated syrup is considerably higher as a consequence of the higher purity

and lower viscosity and turbidity. This effectively provides a crystallisation capacity

increase.

This is similar to the benefits claimed from membrane filtration alone (Kochergin et al.,

2001; Kwok, 1996; Steindl, 2001; Steindl and Doyle, 1999; Steindl and Rackemann, 2002).

The extra sugar recovery from molasses must be balanced against sucrose losses of 0.5 to

1.0 % in the WSM process due to washing of membranes and resin.

The blended 1st and 2nd strike sugars boiled from the treated syrup will meet EEC2 qualitystandards. The sugar from two recovery boilings is remelted and recycled to the

decolourised juice stream.

2.9.2 Reduced scaling

The demineralisation step has a major impact on the amount of scaling deposited on the

heating surfaces in the evaporators, reducing the scale deposited to insignificant levels.

This results in a capacity increase as the HTCs in these vessels will not progressively

decline over time. Cleaning frequency, time to clean and chemical demand are drastically

reduced to provide savings in chemicals, downtime and throughput disruptions.

A similar but smaller effect would be found in the vacuum pans.

When used as a fermentation feedstock, the WSM molasses provides benefits of reduced

scaling in the distillation columns, reduced cleaning costs and improved operations. The

quantity of dunder produced by the distillery is much less when WSM molasses is used as

feedstock instead of conventional raw sugar factory final molasses.

2.9.3 Fermentation

The WSM molasses is a clean, high quality fermentation feedstock that should provide

opportunities for improved yields from a range of by-product opportunities. Experimental

work done in Brazil using the WSM pilot plant showed a 2 % increase in ethanol yield

compared to conventional clarified juice as the fermentation feedstock. When decolourised

juice was used as the fermentation feedstock, a 7 % improvement in ethanol yield was

obtained compared to using clarified juice.

2.9.4 Fertiliser

Figure 2.10 illustrates the current cycle between the canefield and the factory for those

South African factories with conventional milling tandems.



14

Figure 2.10 The status quo for cane flow to the factory and filter cake recycle back

to the canefields (Jensen et al ., 2006)

Disposal of the regenerant chemicals is a major issue with any ion-exchange installation.

THS has addressed this issue by using resins and developing CIP procedures that require

chemicals that can be directed to canefields to take advantage of their nutrient value.

Potassium is removed from the juice and nitrogen is recovered from the regenerant

chemicals. The Felixton WSM plant includes a two stage evaporator station to concentrate

the wash materials and regeneration chemicals from 5 brix to 50 brix, prior to use as

fertiliser. These chemicals can be applied directly to the canefields, substituting purchased

fertilisers, thereby reducing the operating costs of the WSM process and minimising the

environmental impact. The cycle for the flow of cane and nutrients for the WSM process is

illustrated in Figure 2.11.

K Fertiliser

N Fertiliser

Minerals

Raw Sugar

Blackstrap

Molasses

(Minerals)

Filter Cake

Cane



15

Figure 2.11 The potential benefits in recycling both filter cake and fertiliser back to

the canefields to eliminate regenerant chemical disposal (Jensen et al .,

2006)

3. Acknowledgements

The assistance provided by Mr Paul Schorn in providing the opportunity for the visit and

Dr Craig Jensen for making the time available to discuss the WSM plant were greatly

appreciated.

QUT gratefully acknowledges funding for this project from the Australian Government via

the Sugar Research and Development Corporation.

4. References

Jensen, C.R.C., Kitching, S.M., Rosettenstein, S. and Ahmed, F. (2006). The application of

WSM technology at Felixton Mill, South Africa. Proc. Process Workshop, Int. Soc.

Sugar Cane Technol., Louisiana, U.S.A., May.

Kochergin, V., Kearney, M. and Alvarez, J.F. (2001). Direct production of white sugar in

cane mills. Proc. Int. Soc. Sugar Cane Technol., 24:108-111.

K Fertiliser

N Fertiliser

Minerals

White Sugar

High Grade

Molasses

N Fertiliser

K Fertiliser

Minerals

N Chemicals

Cane

Filter Cake



16

Kwok, R.J. (1996). Ultrafiltration/softening of clarified juice The door to direct refining

and molasses desugarisation in the cane sugar industry. Proc. S. Afr. Sug. Technol.

Ass., 70: 166-170.

Steindl, R.J. (2001). Membrane filtration technology in the cane sugar industry. Proc. Int.

Soc. Sugar Cane Technol., 24: 3-10.

Steindl, R.J. and Doyle, C.D. (1999). Applications and benefits of membrane filtration for

the Australian sugar industry. Proc. Aust. Soc. Sugar Cane Technol., 21: 406-411.

Steindl, R.J. and Rackemann, D.W. (2002). Application of membrane filtration in raw

sugar factories. SRDC Project Report SRI096.

5. Other publications associated with WSM

Fechter, W.L., Kitching, S.M., Rajh, M., Reimann, R.H., Ahmed, F.E., Jensen, C.R.C.,

Schorn, P.M. and Walthew, D.C. (2001): Direct production of white sugar and

whitestrap molasses by applying membrane and ion-exchange technology in a cane

sugar mill. Proc. Int. Soc. Sugar Cane Technol., 24: 100-107.

Fechter, W.L., Brewer, P.A., Van De Pypekamp, G. and Smith, I.A. (2000). Treatment of

sugar juice. US Patent 6,709,527, March 31, 2000.

Jensen, C.R.C. and Kitching, S.M. (2007). Options for retrofitting white sugar milling

(WSM) technology into existing raw sugar factories. Proc. Int. Soc. Sugar Cane

Technol., 26: CD-ROM.

Jensen CRC (2007). Direct white sugar manufacture in the cane sugar industry via

membrane filtration and continuous ion-exchange demineralisation. Zukerindustrie

132(57), 446.

Rossiter, G., Jensen, C., and Fechter, W. (2002). White sugar from cane at the factory: The

impact of WSM. S.P.R.I. 2002 Conference Proceedings, 162

6. Dissemination to the Australian industry

A summary of the technologies associated with the WSM plant will be presented to

member mills during the Regional Research Seminars to be conducted in each of the major

centres in late April 2008.

A copy of this report will be made available to member mills of SRL.

Documents

Qut025 Srdc Tlop Report for Web