CRYSTAL MANAGEMENT AT PAN BOILING STATION – IS THERE ROOM FOR IMPROVEMENT? By Mian Abdul Shakoor Production Manager Ranipur Sugar Mills Limited
ABSTRACT The recommendations are addressed for molasses exhaustion keeping in view of equipment design and process parameters at each stage during pan boiling station. Equipment design focused on the flow pattern to give the required retention time for crystal growth, mass and heat transfer. Recommended process parameters for solid concentration, temperature, retention time, crystal contents and crystal size distribution which are necessarily to improve the molasses exhaustion at each stage of the low grade station. Cane quality and a good performance of each process stage prior to the pan station, are fundamentals to maximize sugar recovery. These informations are the basis to define the required materials and methods, and to analyze the results of this presentation.
INTRODUCTION § The art of pan boiling is difficult and requires much skill and experience. Dr. Classen and Dr. J. G Theim have no doubt given a scientific approach to the subject as a result of which, the art of pan boiling has become easier to follow more correctly. Still it requires skill and experience on the part of pan boiler to make crystals of required, numbers and of pre-determined size, free from false grain and conglomerates or twinned grains. § Besides the skill and experience of pan boiler, so many factors impart their effect on sugar loss in final molasses of any sugar factory. Amongst them one major factor is characteristics of the crystals. During sugar boiling grains should be of right numbers and of uniform size free from false grains and conglomerates. The crystal contents or grain contents of Massecuite should be such as to give maximum crystal surface for sugar adsorption from the mother liquor. The fact of size of the crystal (fine coarse or bold) is immaterial; the important thing is the uniformity of the grains. Trouble arises when grains of different dimensions (coarse and fine) occur together, as irregular grain prevents the mother liqour to pass exterior during purging.
HOW DO GET GOOD QUALITY CRYSTALS AT PAN STATION DURING BOILING. A. Compositional Factor 1. 2. 3. 4. Solubility of sucrose and Degree of super saturation. Viscosity Crystal contents, Crystal surface area and Size of crystals. Effect of Non sugars, Reducing sugars and RS/Ash ratio on crystal formation and exhaustibility of molasses. B. Operational factors 1. 2. 3. 4. 5. 6. 7. Boiling scheme Cooling of C-Massecuite Re-heating of final cooled massecuite Circulation in Pan Selection of equipment of proper design and capacity. Temperature of Massecuite and Heating media (steam/vapour) Utilization of Jigger Steam in continuous Pan
1. Solubility of sucrose and Degree of super saturation Ø The amount of sucrose dissolve per unit part of solvent (pure water) is called solubility at a given temperature. § Non sugars increases the solubility of sucrose. Ø The ratio of sucrose present in the supersaturated solution at a given temperature and the sucrose present in saturated solution at the same temperature is called degree of super saturation or co-efficient of super saturation. § Co-efficient of super saturation = Sucrose % water in supersaturated solution Sucrose% water in saturated solution For example at temperature 28ºC, 100 parts water contains 72 parts of sucrose to make it supersaturated, and 68 parts of sucrose to make it saturated, then the coefficient will be Co-efficient of super saturation = 72/68 = 1. 05
§ According to Classen’s Theory Ø Co-efficient of super saturation value ranges 1. 10 – 1. 60 § § For shock seeding value of co-efficient is 1. 30 - 1. 40 § Ø seeding high purity solution like at refinery boiling co-efficient of super saturation is 1. 20 For spontaneous (waiting method) seed formation the required value of co-efficient of super saturation is 1. 60. Boiling zones based on degree of super saturation: § Metstable zone nearest to super saturation, existing crystals increases in size, no new crystal grows. § Intermediate zone new crystals can grow in the presence of existing crystals. § Labile Zone new crystals can grow in the absence of existing crystals.
2. Viscosity Ø The resistance produced by one layer of molecule of a liquid to the adjacent layer of molecules during its movement is called viscosity. Ø One poise being a force required to two parallel surface of 1 cm² having distance of 1 cm, apart to slide past each other at a velocity of one cm/sec. Ø Non sugars, gums, waxes colloidal matters enhances viscosity. § In general it may be stated that: § § For a particular Massecuite higher the brix, higher will be the viscosity. Viscosity of molasses is doubled with the increase in total solids by 0. 80% Rising the temp: lower down the viscosity. Minimum viscosity observed at saturation temperature that is 55 Cº. Viscosity of molasses reduced by 50% by the rise in temp: by 5 Cº. Ø Viscosities limit the workability of Massecuite in pans and crystallizers and influence the formation of conglomerates, distorted grain and caking crystals. Ø surface active chemicals ( visc-aid, sepran A-30, Hodage CB-6) @ 2 kg/60 tons strike.
3. Crystal contents, Crystal surface area and Size of crystals. Ø Crystal surface area is determined from crystal contents and crystal size. Ø Smaller sized crystals have greater surface area then larger sized crystals. But • • Smaller sized crystal may pass through the working screens of centrifugals, causing high purity of final molasses. Purging capacity decreased and recirculation of molasses increased Ø For low grade massecuite recommended crystal sizes are: • for C Massecuite grains ((C Massecuite seed) are between 180 and 200 microns • for C-massecuite leaving the pan are between 250 and 300 microns • for C Massecuite leaving the C crystallizers are between 300 and 350 microns. • Crystal width has to be 1. 50 to 2. 0 times larger than the width of screen slot. • Slot size of working liner for low grade massecuite 0. 04 mm – 0. 06 mm(40 and 60 microns). • Minimum crystal width is recommended as 120 micron • Crystal size of slurry is maintained up to 5 micron.
impact of crystal size on purity of final molasses
Uniformity of Crystal Ø Un uniform crystals causes • Reduced pore volume of crystals. • Reduced molasses drainage during purging. Ø Uniform crystals are produced: • Constant production rate in case of batch pans and continuous pans. • regular injection of seed (grain) in continuous pan. • Seed/massecuite ratio is to be maintained by crystal size distribution (CSD) analytical tool. • 35% - 40% grain is to be injected in continuous pan. Ø The crystal contents of various massecuite are to be: § § For A-Massecuite For B-Massecuite For C-Massecuite For Refine Massecuite = = 60% 50% 40% 62% - 65%
3. 1 Slurry preparation § Slurry /massecuite ratio is to be determined (can be done by experience) Ø EXPERIENCE AT RANIPUR SUGAR MILLS. • Conventional slurry machine contains porclain balls of various sizes, was used up to 2008 – 2009. • Design of slurry machine revisited. • Porclain balls were replaced with SS rods. • Slurry prepared in myth elated spirit. • Slurry preparation time was maintained at 48 hours. • Slurry was injected at the rate of 2 kg/6 M³ footing material.
Impact of slurry on Final Molasses Purity S. No Season Purity of FM Type of slurry machine used 1. 2008 – 2009 33. 736 Conventional machine with porclain balls 2. 2009 – 2010 32. 865 Slurry machine with SS rods 3. 2010 – 2011 31. 811 -do- 4. 2011 – 2012 31. 779 -do-
3. 2 Routine measurement of Nutsch Molasses § Routine monitoring through Nutsch pump is to be conducted. § 60 to 75%of the purity drop is gained in the pan. § purity rise after the re-heater must be zero and some times can be negative
4. Effect of Non sugars, Reducing sugars and RS/Ash ratio on crystal formation and exhaustibility of molasses. 4. 1 Non Sugars § Non sugar increases the solubility of of sucrose in molasses. § Chlorides and carbonates decreases the rate of crystallization. § Sulphates slightly increases the rate of crystallization. § Research shows that 5. 5% crystallization rate is decreased in the presence of gummy matters and waxes with concentration 0. 50%
4. 1. 1 a. b. Sources of non sugars in cane juice. With cane juice Mills sanitation and Process House sanitation c. Addition of raw water during processing of sugar d. Usage of poor quality lime
4. 1. 1. a With cane juice § The constituents of normal cane juice fall with in the following limits. Water 75 -88% Sucrose 10 – 21 % Reducing sugars 0. 25 – 0. 35% Organic matters other than sugars 0. 5 – 1. 00 % Inorganic compounds 0. 2 – 0. 6% Nitrogenous bodies 0. 5 – 1. 00% Ø Immature and overripe cane contains more organic acids. § Caused in production more scale and molasses % cane. Ø Staled cane or frosted cane produces juice with lower purity, less sucrose, high titrateable acidity and abnormal amount of dextran or gums • effects adversely on molasses exhaustibility. Ø Cultural practices, varietals differences, soil variations, planning and harvesting periods influences on clarification and subsequent exhaustion of molasses.
4. 1. 1. b. Mills and Process House sanitation Ø Leuconostoc Bacteria enter in the cane: • At farm into the exposed tissues caused by mechanical harvesting. • At site in prepared cane, cutting , burning, freezing and via disease and pests. • Polymer of glucose “Dextran” is produced after conversion of sucrose. • Dextran has needle shaped crystals. Ø Effect of Dextran: • Increases the viscosity at various stages of process house. • • • Increases the loss of sucrose in the final molasses by entangling recoverable sucrose. Slots of centrifugal screens get chocked due to its crystal shape. • Every 300 ppm dextran in syrup increases 1% in molasses purity. • False Pol reading during analysis of juice samples in the laboratory.
How Dextran entangles sucrose crystals.
How to avoid dextran formation. Ø Dextran formation can be avoided • Bleaching powder (25 Kgs/shift) at mills house. • Pencillin 4 lac in imbibition water tank @ 3. 50 grams /shift. • Pencillin 4 lac in defecation retention tank @ 3. 50 grams /shift. • Pencillin 4 lac in raw sugar remelter @ 3. 50 grams /shift. • Pencillin 4 lac in A-H storage tank @ 3. 50 grams /shift. • Pencillin 4 lac in B-H storage tank @ 3. 50 grams /shift. • Pencillin 4 lac in syrup storage tank @ 3. 50 grams /shift.
4. 1. 1. c Addition of raw water during processing of sugar Ø Use of Raw water at mills house and at any stage of process house causes: § Increase in inorganic salts in the form of TDS § Has adverse effect on molasses exhaustibility and scale formation on heating surface area of heat changers.
4. 1. 1. d Usage of poor quality lime Ø Good quality lime contains § § Ca. O Insoluble matters @ 92% @ 2% Ø Poor quality of lime caused: § High percentage of silica in lime retards the settling of juice in juice clarifier, thus poor clarification effect is achieved. § High percentage of magnesia retards filtration and rate of settling again poor clarification effect. Darkening in juice. § § Increases gummy substances. § Increases ashes%. § Adverse effect on exhaustibility of final molasses.
4. 2 Reducing Sugars and RS/Ash ratio § RS decreases solubility of sucrose in mother liqour. § Crystallization becomes easy. T Solubility of sucrose/100 gms of water 0 50ºC RS/100 gms of water 260 50 242 100 222 150 216 200 208
RS/Ash Ratio § Higher value of ratio, lesser will be sucrose in final molasses. § Ratio varies from 0. 90 to 2. 50 in different regions. § beet molasses contains high ashes and very low RS, thus high loss of sugar in final molasses.
B. Operational Parameters 1. Boiling Scheme Ø Conventional Boiling scheme: § Sugar mills are using DRP, DCS process. Ø It Involves • • three boiling system on Raw side (to minimize the loss of sugar in final molasses with least recirculation. Refine boiling (To produce good quality of white refines sugar and least recirculation. ). Ø Blended boiling system and version boiling at refine massecuite boiling. Ø Rejected run off (pty: 92 -93) is sent back to Raw side in A-massecuite. • • § In version boiling scheme rejected Run Off is 0. 9 – 1. 10%cane In blended boiling scheme rejected run off is 3. 10 – 3. 50 % cane Massecuite production remained as: § A-Massecuite § B-Massecuite § C-Massecuite § R-Massecuite § Molasses production = = = 23% - 25% cane 14% - 15% cane 9% - 10% cane 20% - 22% cane 4. 50% - 5. 25% cane
Comparison of Refine Materials at Version and Blended boiling scheme. a. Version Boiling Refine Massecuite production = 4 : 2 : 1 b. Blended Boiling Refine Massecuite Production = 2 : 1 R-1 Material contribution in Total Refine Material R-2 Material contribution in Total Refine Material R-3 Material contribution in Total Refine Material R-1 Mass: R-2 Sugar R-3 Mass: S. No. Particular 1. Blended Boiling 44 % 43 % 32 % 31 % 33 % 24 % 25 % 24 % 2. Version Boiling 50 % 54 % 52 % 37 % 39 % 37 % 13 % 7% 11 % RO 1 R-1 Sugar RO 2 RO 3 R-3 Sugar
Experience of Ranipur Sugar Mills Ø Version boiling scheme adopted at Refine boiling. • To produce maximum quantity of R 1 sugar and to minimize the recirculation. Ø Adopted four strike boiling system on raw side i, e besides the conventional A, B , C massecuite , A-1 massecuite boiling. § A-1 massecuite is boiled by taking 75% of B-seed and rejected run off. § A-1 sugar is mixed with A-sugar remelt and A-Light (pty: 83 - 84) is return back to A-Massecuite in footing. Ø Massecuite Production remained as under § A-Massecuite = § § § = = = B-Massecuite C-Massecuite Final Molasses 20% - 21% (including A-1 Massecuite) 11% - 12% 7. 50% - 8% 3. 90% - 4. 50%
Loss of sugar in Final Molasses S. No Season Loss of sugar F. M Remarks 1. 2008 -2009 1. 452 Three strike Boiling scheme on raw side and cut boiling scheme at refine boiling 2. 2009 -2010 1. 353 Four strike boiling scheme on raw side and version boiling scheme on refine massecuite 3. 2010 -2011 1. 2504 -do- 4. 2011 -2012 1. 2667 -do-
Successful story at Pan Boiling in Ranipur Sugar Mills (A-1 and A-Massecuite Boiling Scheme) RO 3 Pty: (93 -94) B-Seed Pty: (94 -95) Syrup Pty: (82 -84) C-Seed Pty: (93 -94) A-1 Massecuite (Pty: 92 – 93) A- Light (Pty: 84 -85) A- Sugar (Pty: 98 -98. 50) B-Seed Pty: (94 -95) A- Mass: (Double) (Pty: 85 -87) A- Mass: (Pty: 84 -85) A- H (Pty: 62 -64) A- Sugar (Pty: +97. 50)
B-Boiling Scheme A-H Pty: (62 -64) C-Seed Pty: (93 -94) B-Mass (Double) (Pty: 76 – 77) B-Mass (Pty: 71 -72) A-H (Pty: 62 -64) B-Mass (Pty: 71 -72) B-H B-Sugar (Pty: 42 -44) (Pty: 94 -95)
C-Massecuite Boiling Scheme Preparation of C-Grain C-Light Pty: (61 -63) Preparation of C-Mass: C-Cut Pty: (54 -55) Syrup Pty: (82 -84) C. G Material (Baby Pan) Pty: (68 -69) C-Light C-Mass: Pty: (49 -51) B-H (42 -44) C-Cut Pty: (54 -55) B-H (42 -44) C-Mass: Pty: (49 -51)
Refine Boiling scheme R-1 Mass: RO-1 R-2 Mass: RO-2 R-3 Mass:
2. Cooling of C-Massecuite § C-Massecuites are cooled in the crystallizers to a final temperature as low as 35ºC to 38 Cº. § Cooling is to be conducted steadily, (cold water is to be circulated counter current to massecuite flow in vertical crystallizer) § Recommended cooling rate is 1. 50 – 2ºC/hour. § Minimum residence time is recommended as 48 hours.
3. Re-heating of final cooled massecuite § C-massecuite should be re-heated to a temperature lower than its saturation temperature (55ºC). § Re-heating is to be conducted steadily (Counter current flow of hot water to flow of massecuite). § Temp: of hot water is to be kept up to 62ºC – 65ºC. § Re-heater areas are approximately 4. 50 M²/TCH for a ΔT (water to massecuite temperature difference) of 3ºC.
4. Circulation in the Pan ØCirculation of massecuite in the pan while boiling play a prime role in proper growth of crystals and exhaustion of molasses by: § Prevent cake formation on the heating surface, which on further heating convert into caramel. § Crystals are stationary, not free to move, so circulation helps them to grow. § Proper mixing of molasses in side the pan held, thus good exhaustion of molasses occurs.
Reasons for poor circulation of massecuite in Pan. § Design of the pan, specially the angle of the lower cone of pan i, e it should be 19º – 20º. § Defective position/arrangement of feed pipe. § High viscosity
How to improve circulation § By inducting mechanical circulator. § By blowing low pressure steam below calendria.
5. Selection of the equipment of proper design and capacity. Ø Experience shows that a lot of problem is being faced: • after the induction of new equipments (Heaters, evaporators and continuous pans). • The process house becomes unbalanced, in energy point of view. • Resulting in inadequate operation of equipments. • Impacts on the sugar boiling adversely. • Overall losses of the factory increased not only in terms of sucrose in final molasses but also consumption of fuel enhanced. • In the end of the day higher management makes some unpopular decisions. Ø Therefore : • keen study of process house (energy balance, material balance) for each stage. • After that equipment is to be inducted of required capacity.
Capacity of Continuous Pan § Two Designs are available 68 M³, 102 M³. § Table by Fletcher and Stewart Limited
Ave: Crushing rate A-Massecuite B-Massecuite Cont: Pan Size (M³) 80 22 30 20 100 30 30 30 125 40 40 30 150 40 200 60 60 50 250 70 70 60 300 80 90 70 350 100 80 400 120 100 450 120 2 x 60 100 500 2 x 70 120
Alternate method to calculate capacity of continuous pan § Capacity of continuous pan can also be calculated on various positions (A, B, C) by another alternate method. Which is as under: - § Taking the example for continuous pan 68 M³ Capacity of pan c. = 12 Nos. Capacity of each chamber b. 68 M³ 68 x 1. 50 102 Tons Nos. of chambers a. = = 8. 50 Tons 68 M³ continuous pan working for A-Massecuite boiling No. of syrup feeds = 06 Nos. Capacity of pan on A-Massecuite = 6 x 8. 50 = 51 Tons/Hr 68 M³ continuous pan working for B-Massecuite boiling No. of A-H feeds = 04 Nos. Capacity of pan on A-Massecuite = 4 x 8. 50 = 34 Tons/Hr 68 M³ continuous pan working for C-Massecuite boiling No. of B-H feeds = 02 Nos. Capacity of pan on A-Massecuite = 2 x 8. 50 = 17 Tons/Hr
6. Temperature of Massecuite § Solubility of sucrose is directly proportional to the temperature. § Low grade massecuite contains comparatively very less amount of sucrose in the mother liquor which is to be crystal out during boiling. § low temperature is to be kept during boiling of low grade massecuite. § Conventionally, the boiling temp: of pan remains + 60ºC. § recommended low grade massecuite is to be boiled at temperature 57ºC - 58ºC.
Low boiling temperature can be achieved by, Ø Increasing the vacuum in the shell of the pan. • vacuum is to be raised up to 780 mm Hg by increasing injection water quantity. Ø Decreasing temperature of calendria in case of continuous pan. • Temperature of calendria can be decreased by, • Creating vacuum in the calendria up to 10 mm of Hg to 12 mm of Hg. This vacuum corresponds to temp: 84ºC - 85ºC. • Low grade Massecuites are to be boiled through 2 nd or 3 rd. vapours. • If there is no possibility to bleed 2 nd. Or 3 rd. vapours due to heating surfaces at 3 rd. or 2 nd. Effects, then 1 st. vapours are to be used under vacuum as discussed in option No. i.
7. Utilization of Jigger Steam in continuous Pan Ø Jigger steam is being used in continuous pan to opening of chocked compartment. Ø Pan boiler always kept open the jigger steam valve of all the compartments to increase the circulation of massecuite. Ø Practice • dissolve the crystals specially in compartment No. 1, 2 and 3, where the size of crystals are comparatively small. • Increases the temperature of massecuite which effects adversely on the exhaustion of the molasses. Ø Low pressure and low temperature steam is to be used at jigger steam instead of 4 -bar steam.
CONCLUSION AND RECOMMENDATIONS 1. To get maximum crystal surface available for adsorption of sugar, appropriate crystal contents are to be maintained in massecuite boiling by uniform feeding of grain in continuous pans @ 35 -40%. 2. Conventional slurry machine is to be replaced with new design of slurry machine. 3. Routine analysis of mother liquor through Nutsch pump either under pressure or under vacuum to be carried for improvement of pan boiling.
CONCLUSION AND RECOMMENDATIONS 4. § § § § § Process house is to be boiled on high purity. Following purities are to be kept at various stages. a. A-Massecuite purity = 84 – 85 b. B-Massecuite purity = 71 – 72 c. C-Massecuite Purity = 49 - 51 d. B-Seed Purity = 94 – 95 e. C-Sugar Purity = ± 80 f. C-Seed Purity = 93 – 94 g. A-H Purity = 62 – 64 h. B-H Purity = 42 – 44 i. C-Light purity = 61 - 63
CONCLUSION AND RECOMMENDATIONS 5. A-1 Boiling is to be inducted in three boiling scheme to minimize the shifting of Pol to raw side by using 75% B-seed and rejected run off. A-light molasses is to be use in footing rather in massecuite. 6. Version boiling scheme is to be adopted for the production of white refined sugar, to minimize the recirculation of rejected run off. 7. In Case of Batch pans, A massecuite is to be boil on cut system, in case of continuous pan, syrup is not to be feed more than 6 chambers for proper molasses exhaustion and to get maximum massecuite : molasses purity drop. C-seed is to be melted in footing and graining is to be conducted through B-seed. B-Massecuite boiling is to be conducted in case of batch pan on cut system. In case of Continuous Pan, A-H molasses is to be feed not more than 4 chambers. In case of C-Massecuite boiling, Purity of C-Grain is to be kept 67 – 68, Whole Clight is to be used in C-Massecuite. 8. Addition of pencilline 4 lac in various stages of process house is to be conducted, as it has no adverse effect on sucrose contents of cane juice.
CONCLUSION AND RECOMMENDATIONS 9 After each three days, RS are to be checked at various stages of the house. 10. Before purging, the temperature of massecuite is to be raised up to 52ºC, temperature of hot water is to be kept at 62ºC - 65ºC. 11. Thorough study is to be conducted of pans for proper circulation of massecuite. 12. Keen study is to be carried out (energy balance, material balance) for each step of the process, then induct equipment in process stream as per requirement. 13. Temperature of low grade massecuite is to be kept at 57ºC - 58ºC, while it is boiled. 14. Priority is to be given for the usage of 2 nd. Or 3 rd. vapour for the boiling of low grade massecuite. 15. Use 1 st. vapour for boiling of low grade massecuite under vacuum, if necessary. 16. Jigger steam is to be used occasionally where it requires. 17. Low pressure and low temperature (first vapour) is to be used instead of 4 bar steam.
Acknowledgement First of all I am thankful to “Almighty Allah”, who made me able to conduct this presentation. I am also thankful to the Mian Nadeen Khalique, Executive Director RSM who give me permission to present this paper. In the last but not least, I am thank full to Engr: Abdul Aziz Tahir (Technical Director), who always gives me technical and moral guidance in each step of my life.
Thank You
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