CRYSTAL MANAGEMENT AT PAN BOILING STATION

1
CRYSTAL MANAGEMENT AT PAN BOILING STATION IS
THERE ROOM FOR IMPROVEMENT?ByMian Abdul
ShakoorProduction ManagerRanipur Sugar Mills
Limited
2
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.

3
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.

4
HOW DO GET GOOD QUALITY CRYSTALS AT PAN STATION
DURING BOILING.

• Compositional Factor
• 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.
• Operational factors
• Boiling scheme
• Cooling of C-Massecuite
• Re-heating of final cooled massecuite
• Circulation in Pan
• Selection of equipment of proper design and
  capacity.
• 6. Temperature of Massecuite and Heating media
  (steam/vapour)
• 7. Utilization of Jigger Steam in continuous Pan

5
1. Solubility of sucrose and Degree of super
saturation

• 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.
• 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 co-efficient will be
• Co-efficient of super saturation 72/68
• 1.05

6

• According to Classens Theory
• Co-efficient of super saturation value ranges
  1.10 1.60
• seeding high purity solution like at refinery
  boiling co-efficient of super saturation is 1.20
• For shock seeding value of co-efficient is 1.30 -
  1.40
• 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.

7
2. Viscosity

• The resistance produced by one layer of molecule
  of a liquid to the adjacent layer of molecules
  during its movement is called viscosity.
• One poise being a force required to two parallel
  surface of 1 cm² having distance of 1cm, apart to
  slide past each other at a velocity of one
  cm/sec.
• 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 55Cº.
• Viscosity of molasses reduced by 50 by the rise
  in temp by 5Cº.
• Viscosities limit the workability of Massecuite
  in pans and crystallizers and influence the
  formation of conglomerates, distorted grain and
  caking crystals.
• surface active chemicals ( visc-aid, sepran A-30,
  Hodage CB-6) _at_ 2kg/60 tons strike.

8
Crystal contents, Crystal surface areaand Size
of crystals.

• Crystal surface area is determined from crystal
  contents and crystal size.
• 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
• 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 0.04mm 0.06mm(40 and 60 microns).

9
impact of crystal size on purity of final
molasses
10
Uniformity of Crystal

• Un uniform crystals causes
• Reduced pore volume of crystals.
• Reduced molasses drainage during purging.
• 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.
• The crystal contents of various massecuite are to
  be-
• For A-Massecuite 60
• For B-Massecuite 50
• For C-Massecuite 40
• For Refine Massecuite 62 - 65

11
3.1 Slurry preparation

• Slurry /massecuite ratio is to be determined (can
  be done by experience)
• 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 2kg/6M³
  footing material.

12
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-
13
3.2 Routine measurement of Nutsch Molasses

• Routine monitoring through Nutsch pump is to be
  conducted.
• 60 to 75of the purity drop is gained in the pan.
• purity rise after the re-heater must be zero and
  some times can be negative

14
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

15
4.1.1 Sources of non sugars in cane juice.

1. With cane juice
2. Mills sanitation and Process House sanitation
3. Addition of raw water during processing of sugar
4. Usage of poor quality lime

16
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
• Immature and overripe cane contains more organic
  acids.
• Caused in production more scale and molasses
  cane.
• 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.
• Cultural practices, varietals differences, soil
  variations, planning and harvesting periods
  influences on clarification and subsequent
  exhaustion of molasses.

17
4.1.1.b. Mills and Process House sanitation

• 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.
• 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.

18
How Dextran entangles sucrose crystals.
19
How to avoid dextran formation.

• Dextran formation can be avoided
• Bleaching powder (25 Kgs/shift) at mills house.
• Pencillin 4 lac in imbibition water tank _at_ 3.50
  grams /shift.
• Pencillin 4 lac in defecation retention tank _at_
  3.50 grams /shift.
• Pencillin 4 lac in raw sugar remelter _at_ 3.50
  grams /shift.
• Pencillin 4 lac in A-H storage tank _at_ 3.50 grams
  /shift.
• Pencillin 4 lac in B-H storage tank _at_ 3.50 grams
  /shift.
• Pencillin 4 lac in syrup storage tank _at_ 3.50
  grams /shift.

20
4.1.1.c Addition of raw water during processing
of sugar

• Use of Raw water at mills house and at any stage
  of process house causes-
• Increase in 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.

21
4.1.1.d Usage of poor quality lime

• Good quality lime contains
• CaO _at_ 92
• Insoluble matters _at_ 2
• 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.

22
(No Transcript)
23
4.2 Reducing Sugars and RS/Ash ratio

• RS decreases solubility of sucrose in mother
  liqour.
• Crystallization becomes easy.

T RS/100gms of water Solubility of sucrose/100 gms of water
50ºC 0 260
50ºC 50 242
50ºC 100 222
50ºC 150 216
50ºC 200 208
24
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.

25
(No Transcript)
26
B. Operational Parameters

• 1. Boiling Scheme
• Conventional Boiling scheme-
• Sugar mills are using DRP,DCS process.
• 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.) .
• Blended boiling system and version boiling at
  refine massecuite boiling.
• Rejected run off (pty92-93) is sent back to Raw
  side in A-massecuite.
• In version boiling scheme rejected Run Off is 0.9
  1.10cane
• In blended boiling scheme rejected run off is
  3.10 3.50 cane

27
Comparison of Refine Materials at Version and
Blended boiling scheme.a. Version Boiling Refine
Massecuite production 4 2
1b. Blended Boiling Refine Massecuite
Production 2 1 1
S. No. Particular R-1 Material contribution in Total Refine Material R-1 Material contribution in Total Refine Material R-1 Material contribution in Total Refine Material R-2Material contribution in Total Refine Material R-2Material contribution in Total Refine Material R-2Material contribution in Total Refine Material R-3 Material contribution in Total Refine Material R-3 Material contribution in Total Refine Material R-3 Material contribution in Total Refine Material
S. No. Particular R-1 Mass RO1 R-1 Sugar R-2 Mass RO2 R-2 Sugar R-3 Mass RO3 R-3 Sugar
1. Blended Boiling 44 44 43 32 31 33 24 25 24
2. Version Boiling 50 54 52 37 39 37 13 7 11
28
Experience of Ranipur Sugar Mills

• Version boiling scheme adopted at Refine boiling.
• To produce maximum quantity of R1 sugar and to
  minimize the recirculation.
• 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.
• Massecuite Production remained as under
• A-Massecuite 20 - 21 (including A-1
  Massecuite)
• B-Massecuite 11 - 12
• C-Massecuite 7.50 - 8
• Final Molasses 3.90 - 4.50

29
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-
30
Successful story at Pan Boiling in Ranipur Sugar
Mills (A-1 and A-Massecuite Boiling Scheme)
31
B-Boiling Scheme
32
C-Massecuite Boiling Scheme
33
Refine Boiling scheme
34
2. Cooling of C-Massecuite

• C-Massecuites are cooled in the crystallizers to
  a final temperature as low as 35ºC to 38Cº.
• 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.

35
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 4.50M²/TCH for
  a ?T (water to massecuite temperature difference)
  of 3ºC.

36
4. Circulation in the Pan

• Circulation 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.

37
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

38
How to improve circulation

• By inducting mechanical circulator.
• By blowing low pressure steam below calendria.

39
Selection of the equipment of proper design and
capacity.

• 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.
• Therefore -
• keen study of process house (energy balance,
  material balance) for each stage.
• After that equipment is to be inducted of
  required capacity.

40
Capacity of Continuous Pan

• Two Designs are available 68M³, 102M³.
• Table by Fletcher and Stewart Limited

41
Ave Crushing rate A-Massecuite B-Massecuite C-Massecuite
Ave Crushing rate Cont Pan Size (M³) Cont Pan Size (M³) Cont Pan Size (M³)
80 22 30 20
100 30 30 30
125 40 40 30
150 40 50 40
200 60 60 50
250 70 70 60
300 80 90 70
350 100 100 80
400 100 120 100
450 120 2 x 60 100
500 2 x 70 2 x 70 120
42
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 68M³
• Capacity of pan 68M³
• 68 x 1.50
• 102 Tons
• Nos. of chambers 12 Nos.
• Capacity of each chamber 8.50 Tons
• a. 68M³ 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
• b. 68M³ 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
• c. 68M³ continuous pan working for C-Massecuite
  boiling

43
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.

44
Low boiling temperature can be achieved by,

• Increasing the vacuum in the shell of the pan.
• vacuum is to be raised up to 780 mm Hg by
  increasing injection water quantity.
• 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
  2nd or 3rd. vapours.
• If there is no possibility to bleed 2nd. Or 3rd.
  vapours due to heating surfaces at 3rd. or 2nd.
  Effects, then 1st. vapours are to be used under
  vacuum as discussed in option No.i.

45
7. Utilization of Jigger Steam in continuous Pan

• Jigger steam is being used in continuous pan to
  opening of chocked compartment.
• Pan boiler always kept open the jigger steam
  valve of all the compartments to increase the
  circulation of massecuite.
• 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.
• Low pressure and low temperature steam is to be
  used at jigger steam instead of 4-bar steam.

46
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 _at_
  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.

47
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

48
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 C-light is
  to be used in C-Massecuite.
• 8. Addition of pencilline 4lac in various stages
  of process house is to be conducted, as it has no
  adverse effect on sucrose contents of cane juice.

49
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 2nd.
  Or 3rd. vapour for the boiling of low grade
  massecuite.
• 15. Use 1st. 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.

50
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.

51
Thank You