CRYSTAL MANAGEMENT IN LOW GRADE MASSECUITE– IS

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
 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 coefficient will be
Co-efficient of super saturation
= 72/68
= 1.05
 According to Classen’s 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.
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) @ 2kg/60 tons strike.
3.
Crystal contents, Crystal surface area
and 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).
•
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
 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
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)
 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.
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
Sources of non sugars in
cane juice.
a. With cane juice
b. 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%
 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.
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.
•
False Pol reading during analysis of juice samples in the laboratory.
How Dextran entangles sucrose
crystals.
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 @ 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
 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.
4.1.1.d
Usage of poor quality
lime
 Good quality lime contains


CaO
Insoluble matters
@ 92%
@ 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.
4.2
Reducing Sugars and
RS/Ash ratio
 RS decreases solubility of sucrose in mother
liqour.
 Crystallization becomes easy.
T
50ºC
RS/100gms of water
Solubility of
sucrose/100 gms of
water
0
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

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 (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 : 1
R-1 Material contribution
in Total Refine Material
R-2Material contribution
in Total Refine Material
R-3 Material contribution
in Total Refine Material
R-1
Mass:
R-2
Mass:
R-2
Sugar
R-3
Mass:
S.
No.
Particular
1.
Blended
Boiling
44 %
44 %
43 %
32 %
31 %
33 %
24 %
25 %
24 %
2.
Version
Boiling
50 %
54 %
52 %
37 %
39 %
37 %
13 %
7%
11 %
RO1
R-1
Sugar
RO2
RO3
R-3
Sugar
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
=
 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)
RO3
Pty:(93-94)
B-Seed
Pty:(94-95)
A-1 Massecuite
(Pty: 92 – 93)
Syrup
Pty:(82-84)
C-Seed
Pty:(93-94)
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- 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-Mass:
Pty: (49-51)
B-H
(42-44)
C-Light
C-Cut
Pty: (54-55)
B-H
(42-44)
C-Mass:
Pty: (49-51)
Refine Boiling scheme
R-1 Mass:
R-1 Mass:
R-1 Mass:
R-1 Mass:
RO-1
RO-1
RO-1
RO-1
R-2 Mass:
R-2 Mass:
RO-2
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 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.
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 ΔT (water to massecuite temperature difference)
of 3ºC.
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.
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.
 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.
Capacity of Continuous Pan
 Two Designs are available 68M³, 102M³.
 Table by Fletcher and Stewart Limited
Ave:
Crushing
rate
A-Massecuite
B-Massecuite
C-Massecuite
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
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
a.
b.
c.
Capacity of pan
=
=
=
68M³
68 x 1.50
102 Tons
Nos. of chambers
=
12 Nos.
Capacity of each chamber
=
8.50 Tons
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
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
68M³ 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,
 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.
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.
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 4lac 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 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.
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