Centrifugal
section equipment Capacity Calculation in Sugar Industry Process
In this article explained about centrifugal
section and Sugar house equipment capacity calculation for process house of
sugar industry viz., Pug mills, Batch and continuous centrifugal machines,
Magma mixers, sugar melter, pumps for magma & molasses, Superheated wash
water system, Sugar hoppers, Sugar dryer, sugar elevator & grader.
Objectives of centrifugal
section
Once the mother liquor is exhausted to
practical limit only thing is remain to separate crystals in order to obtained
the commercial form. This operation is carried out in a centrifugal machine by
the principle of centrifugal force.
The basic function of centrifugal station is
separation of sugar crystal from mother liquor (molasses). In this process
required special attention for the following points to arrive centrifugal
section equipment capacity.
a) Effective separation of crystals from mother liquor
by avoiding of crystal damage for bagging sugar.
b) Minimum use of washing water.
c) Minimum use
of power consumption.
d) Control
systems used at Centrifugal.
The centrifugal section with sugar house
consists of the following major equipment
a) Pug mills
b) Batch centrifugal
c) Continuous Centrifugal
d) Magma mixers
e) Molasses receiving tank (runoff tanks)
f) Pumps for magma & molasses
g) Superheated wash water system
h) Transient Heater
i) Sugar receiving hoppers
j) Sugar dryer, sugar elevator and sugar
grader
k) Sugar bin
Pug Mill
Pugmill having ‘U’ shape and fixed in the
above centrifugal machines staging with drive. Generally, all pugmills are
equipped with agitator to keep the massecuite at constant motion in pugmill. (
Generally, agitator not required for ‘C’ fore worker centrifugal machine
and this pug mill is equipped with water jacket to circulation hot water for
treatment of massecuite.)
The level of massecuite in pug mill is always
maintained more than 70% to provide positive massecuite head when charging to
centrifugal machine.
The capacity of pug mill will be depended on
number of centrifugal machines and its capacity. The retention time in pug mill
is around 12 to 15 minutes.
For example 3 numbers of 1750 kg/charge
machines with 20 cycles/hour. Then
Massecuite quantity = 1.750 MT/cycle x 20
cycles/hour x 3 nos. = 105 MT/hr.
= 105 / 1.4 = 75 M3/hr = 1.25 M3/min.
Take 12 minutes of retention time then 1.25 x
12 = 15 m3 holding volume required.
Batch centrifugal
Batch centrifugal machines consist of
cylindrical basket design to receive the massecuite to be treated, and carried
on vertical shaft , driven from its upper part by a motor. The basket is
perforate with numerous holes to allow the molasses to escape.
The basket is open at the top to allow
massecuite to be feed in to it, and bottom opening allows sugar to discharge
when the machine is stopped.
Batch centrifugal machines
capacity requirement
Crushing
Capacity
– 5000 TCD ( 230
TCH on 22hr basis)
A massecuite %
cane
– 28 %
A m/c
quantity
– 230 x 28% = 64.4
T/hr
Consider 150% extra
– 64.4 x 150% =
96.6 T/hr
(To compensate breakdowns in sugar house)
Capacity of each
machine
– 1750 Kg/charge
Number of average
cycles
– 18 cycles/hr
Each Machine
capacity
– 1750 x 18 = 31.5
T/hr
No. of machines
required
– 82 / 31.5 = 3.06
Hence 3 nos. of Centrifugal machines are
required for A-Massecuite + 1 stand by = 4 nos.
(Practically 3 machines can handle that
capacity)
For more information on
Batch Centrifugal Machine Capacity and Gravity Factor with online calculator
Superheated wash water system
For better washing and get good quality sugar,
superheated water is used for batch centrifugal machines.
The superheated wash water system heat the
hot condensate water to 112 ± 3 oC by steam, and 5 to 7 kg/cm2 pressure
with high head centrifugal pump.
Quantity of water required
– 5 % on massecuite
or 10% on sugar produced
Continuous Centrifugal
Generally, Continuous centrifugal machines
are used for B and C massecuite curing. Continuous operation is obviously ideal
from the mechanical point of view, the machine runs at a constant speed without
stopping, is fed by a continuous stream of material, furnishes a constant
output of sugar, and requires less no. of operators.
Crushing
Capacity
– 4000 TCD (
182 TCH on 22hr basis)
B m/c %
cane
– 13 %
B m/c
quantity
– 182 x 13 % = 23.7
T/hr
Consider 150%
extra
– 23.7 x 150% = 36
T/hr
Capacity of
Machine
– 16 to 18 T/ hr
(Ø1500)
No. of machines
required
– 36 / 18 = 2 Nos.
C m/c %
cane
– 8 %
C m/c
quantity
– 182 x 8 % = 14.6
T/hr
Consider 150%
extra
– 14.6 x 150% = 22
T/hr
Capacity of Machine (CFW)
– 8 to 10 T/ hr
No. of machines
required
– 22 / 8 =
2.75 Nos. ≈ 3
nos.
CAW %
cane
– 3 %
C m/c
quantity
– 182 x 3 % =
5.5 T/hr
Consider 150%
extra
– 5.5 x 150% = 8
T/hr
No. of machines
required
– 1 No.
Transient Heater
The transient heater is used for heating of
low grade massecuite up to saturation temperature (50-52 0C) to reduce
the viscosity and easy purging of massecuite.
In transient heater low grade massecuite is
heated uniformly with vapour / steam or condensate water.
Low Grade Massecuite Treatment in Sugar
Crystallization Process
Cooling and reheating Process of low grade (B & C) massecuites
The mother liquor in low grade massecuite can
not be completely exhausted in vacuum pan this is due to decrease in
crystallization rate and high viscosity. Final stage in sugar recovery is
allowed to take place by cooling in crystalliser rather then during evaporation
in vacuum pans. Because evaporation in vacuum pans is more cost effective
procedure , therefore is to boil low grade massecuite in vacuum pan
for limited time, then discharge it to atmospheric crystallizes followed by
water cooled crystallizers.
The exhaustion of final molasses is directly
related to the economy of the sugar factory and hence more attention is given
being paid towards the processing of crystallisation in low grade massecuite.
The exhaustion of molasses will
depend on four successive parameters.
a) Boiling a massecuite to maximum
concentration in pan.
b) Cooling of the massecuite in the
crystalliser to crystallise the sucrose remaining in solution.
c) Re-heating of cooled massecuite to it’s
saturation temperature to reduce the viscosity of massecuite.
d) Separation of the crystals from exhausted
molasses in the centrifugal machine.
To judging pan boiling operation efficiency,
the use of %
exhaustion and Crystal % massecuite are found more
effective and informative.
Massecuite leaving a vacuum pan is
supersaturated and hot, in the range 63
to 67 oC. Crystal content is high, but it is still possible
to achieve additional exhaustion by cooling the massecuite prior to
centrifuging. As the massecuite is cooled the crystalliztion rate rate reduces,
but sufficient retention time in the cooling crystallizers will achieve
the additional crystallization desired.
The ideal condition for a low-grade
massecuite ” C m/c ” to crystallize more sugar from the mother liquor follow
the path as illustrated in the graph below.
Cooling Zone: The Cooling zone has water cooled surface area to
reduce the massecuite temperature from about 65ºC to 43 ºC within 18 to 20 hrs
of time. While designing the cooling zone the ratio of S / V should be
about 1.8 to 2.0 for C m/c and 1.2 for C m/c.
Ripening Zone: The Rippening zone comes after the cooling zone. This
zone has no cooling water surface, but may be provided with hot water coils to
take care of massecuite temp. In winter season, the retention time in this zone
is about 2 to 3 hrs.
Reheating Zone : Before centrifuge the massecuite, it should be
reheated upto 50 to 52ºC to reduce the viscosity and easy purging of
massecuite.
Exhaustion for “C” masseuite corresponding to
drop of 4 to 6 units in the purity of molasses is achieved in the crystalliser.
The overall exhaustion of mother liquor in C massecuite in pan and crystalliser
is shall be 24-27 units.
Exhaustion for “B” masseuite corresponding to
drop of 3 to 4 units in the purity of molasses is achieved in the
crystalliser. The overall exhaustion of mother liquor in B massecuite in
pan and crystalliser is shall be 20-22 units.
The massecuite is dropped in a crystalliser
having heating and cooling element the following treatment should be given to
get the maximum exhaustion for Low
Grade Massecuite .
·
Leave the massecuite in crystalliser for 2 to 4 hours allowing air
cooling.
·
Circulate the cold water in the element so as to cool the
massecuite at a rate not exceeding 1 to 2oC per hour. Quantity of cold water has to be adjusted accordingly.
Temperature of cold water should be 30 to 35o .
·
Cool the massecuite up to 42-43oC for C m/c and 50 to 55 oC for B m/c or till the purity of mother liquor becomes more or
less constant. ( Here using Nutch apparatus to check the purity of mother
liquor)
·
Allow the ripening time at lowest temperature for 2 to 3 hours.
·
Rate of stirring of massecuite has to be slow and not more than
0.5 rpm. ( 0.3 to 0.5 rpm for C m/c to 0.5 to 0.7 RPM for B m/c).
·
Reheat the massecuite up to the saturation temperature ( 51 to 52oC ) preferably using transient heaters by using hot as a heating
media.
Crystallizers generally divided in to two
types as follows.
Air cooled crystallizers
: It is a simple steel vessel, of “U” shaped cross-section,
fitted with an agitator permitting it to maintain the mass in slow and
continuous motion. open and horizontal containers type where atmospheric air is
employed for cooling the massecuite.
Water cooled
crystallizers : The various type of crystallisers either open or closed
type where water is employed for cooling the massecuite. It can be dived
furthers as Horizontal and vertical crystallizers.
The series Horizontal crystallizers
with water-cooled element and vertical type crystallizers were using for this
application of low grade massecuite treatment.
Magma Mixer
When massecuite is to be double cured or even
single cured ( in case of low grade massecuite), the centrifuged sugar is to be
mixed with syrup or clarified juice or hot water to form a magma. The magma
preparation is generally done in magma mixers. These mixers are double paddle
type with drive under centrifugal machines help in well mixing of sugar with diluting
liquid. The arm shall be strong enough to brake the lumps of sugar and mix well
with liquid.
The capacity of magma mixer will be depended
on number of centrifugal machines and its capacity. The retention time in magma
mixer is around 10 to 12 minutes.
For example take three numbers of 1500 mm dia
“ B” continuous machines having capacity of 16 T/hr to 18 T/hr.
Machine
capacity
– 16 T/hr each
Number of
machines
– 3
B sugar quantity per
machine
– 7.2 T/hr @ 100
brix ( 45% sugar considered)
B magma quantity per
machine- 9 T/hr @ 80 brix
Total B magma
quantity
– 27 T/hr @ 80 brix
(If used water for magma preparation)
Take 12 minutes of retention time then 5.5 T =
5.5 / 1.4 = 4 M3 holding volume required upto 80% level.
The length of the mixer shall be suitable for
all centrifugal machines.
Sugar Melter
Sugar Melter Application in Sugar Factory |
Sugar Melter design Calculation
In this article discussed about the role of sugar melter in sugar industry process house
and its capacity and design calculation. Also provided online calculator for
its capacity calculation.
Sugar Melter Capacity Calculation | Sugar Melting Feed Liquor
Calculation
The sugar melter simply can be defined
as it a equipment in which dissolving of sugar takes place. Generally the sugar
plants can be classified as Raw
sugar plant, Refined
sugar plant and white(
Suphited ) sugar plants. All
these type of sugar plants sugar
melter is one of the essential equipment in process house.
According to sugar melter application it is
called mainly two types.
·
B and C sugar mellter or low grade sugar melter
·
Raw Sugar melter
B & C sugar
mellter:
According to boiling
scheme adopted in sugar
process, some or total low grade sugars i.e B sugar and C double cured sugar
may be remelted. Its melt diverted to high grade massecuites.
B Massecuites cured in continuous
centrifugals or high gravity batch machines. The B sugar can be used directly
as a seed for A massecuite boiling and excess B sugar pumped to sugar melter
for remelting the sugar and it is used in A boiling.
For C massecuites double purging is
absolutely essential to reduce the colour load on final massecuite. The sugar
after second purging is dissolved in a melter and melt used in “A” boiling.
For B and C sugar melting purpose using hot water, clear juice or syrup for
melting
Raw Sugar Melter:
Affination process is the first step of refined sugar making.
This process helps to remove as much of the molasses film surrounding the raw
sugar. The affinated sugar sent to raw sugar melter to
prepare melt for further process. For less colour of raw sugar can be directly
sent to melter without affiniation process.
Raw sugar melting purpose using hot water or sweet water (low
brix water) for melting
Sugar melter design parameters
There are two basic approaches to equipment
for sugar melter
1. Horizontal cylindrical vessel with a horizontal
rotating stirrer ( Horizontal
sugar melter)
2. The second type is using number of vertical tanks
in series or compartments in the same vessel and having top mounted stirrers in
each tank ( Vertical
sugar melter)
The Sizing of melter mainly depends on
·
Size of the crystal to be melt
·
Final melt brix requirement
·
Temperature of the melter ( melt temperature )
For B and C sugar having the crystal size in
the range of 150
to 350 micron. According to Peter Rein recommendations 15 to 20 minutes holding volume required
for at 70 brix and 70 oC temperature.
For Raw sugar having the crystal size in the
range of 250
to 650 micron. So
for raw sugar melter required minimum 25 to 30 minutes holding volume
required for at 70 brix and 70 oC temperature.
Calculation of melter feed requirement and its vapour line sizing
Example – 1: ( Using Clear juice for both magma and melter)
|
S.No |
Particulars |
UOM |
Values |
Remarks |
|
Required Data |
||||
|
1 |
Crushing
Capacity |
TCH |
230 |
|
|
2 |
B
sugar % cane |
% |
5 |
4.5 to 6 % |
|
3 |
C sugar %
cane |
% |
1.5 |
1 to 2 % |
|
4 |
Rory
& Powder sugar |
% |
1 |
0.5 to 1.5 % |
|
5 |
Brix of
sugar |
% |
95 |
90 to 98 |
|
6 |
Magma
mixer oultet brix |
% |
90 |
88 to 92 |
|
7 |
Final
Melt Brix |
% |
65 |
60 to 70 |
|
8 |
Clear
Juice |
% |
14 |
Clear juice
brix |
|
9 |
Vapour temperature |
oC |
110 |
Consider 1st
vapour |
|
10 |
Velocity
of vapour |
m/sec |
30 |
Consider 1st
vapour |
|
11 |
Clear
Juice inlet temperature |
oC |
90 |
|
|
12 |
Melt
outlet temperature |
oC |
75 |
70 to 80 oC |
|
13 |
Inlet
Magma Temperature |
oC |
45 |
40 to 50 oC |
|
Calculation part |
||||
|
1 |
Specific
heat of Melt (Cp ) |
Kcal/oC |
0.65 |
|
|
2 |
Latent
heat of vapour (λ ) |
Kcal/kg |
532.51 |
As per the
steam table |
|
3 |
Specific
Volume of Vapour |
M3/kg |
1.210 |
As per the
steam table |
|
Magma |
||||
|
4 |
Quantity
of B seed + C seed |
T/hr |
17.25 |
230 x
(5+1.5+1)% |
|
5 |
Clear
juice required for Magma |
T/hr |
1.135 |
[(17.25 x 95) –
(17.25 x 90)] / (95 – 14) |
|
6 |
Final Qty
of magma |
T/hr |
18.385 |
17.25 + 1.135 |
|
Melter for B and C sugar |
||||
|
7 |
Clear
juice required for melting |
T/hr |
9.01 |
[(18.385 x 90)
– (18.385 x 65)] / (65 – 14) |
|
8 |
Total
Melt Quantity ( Q ) |
T/hr |
27.397 |
18.385 + 9.01 |
|
9 |
Vapour
required |
T/hr |
1.003 |
Q Cp ∆T / λ |
|
M3/sec |
0.337 |
1.003 x
1000 x 1.210 / 3600 |
||
|
0.405 |
20 % extra |
|||
|
10 |
Dia of
the vapour pipe |
mm |
131 |
SQRT(0.405/(0.785*30)))*1000 |
|
11 |
Melt
holding volume required |
M3 |
9.132 |
27.392 x 20 /
60 (20 min. retention time |
Note : In the above calculation clear juice temperature ( heat value) not consider. While using the
clear juice vapour requirement for melter is very less and some times almost
requirement is zero.
Example – 2: ( Using evaporated syrup for both magma and melter)
|
S.No |
Particulars |
UOM |
Values |
Remarks |
|
Required Data |
||||
|
1 |
Crushing
Capacity |
TCH |
230 |
|
|
2 |
B
sugar % cane |
% |
5 |
4.5 to 6 % |
|
3 |
C sugar %
cane |
% |
1.5 |
1 to 2 % |
|
4 |
Rory
& Powder sugar |
% |
1 |
0.5 to 1.5 % |
|
5 |
Brix of
sugar |
% |
95 |
90 to 98 |
|
6 |
Magma
mixer oulet brix |
% |
90 |
88 to 92 |
|
7 |
Final
Melt Brix |
% |
65 |
60 to 70 |
|
8 |
Syrup
using for melter |
% |
55 |
Syrup Brix |
|
9 |
Vapour
temperature |
oC |
110 |
Consider 1st
vapour |
|
10 |
Velocity
of vapour |
m/sec |
30 |
Consider 1st
vapour |
|
11 |
Syrup
Juice inlet temperature |
oC |
50 |
|
|
12 |
Melt
outlet temperature |
oC |
75 |
70 to 80 oC |
|
13 |
Inlet
Magma Temperature |
oC |
40 |
40 to 50 oC |
|
Calculation part |
||||
|
1 |
Specific
heat of Melt (Cp ) |
Kcal/oC |
0.65 |
|
|
2 |
Latent
heat of vapour (λ ) |
Kcal/kg |
532.51 |
As per the
steam table |
|
3 |
Specific
Volume of Vapour |
M3/kg |
1.210 |
As per the
steam table |
|
Magma |
||||
|
4 |
Quantity
of B seed + C seed |
T/hr |
17.25 |
230 x
(5+1.5+1)% |
|
5 |
Syrup
required for Magma |
T/hr |
2.464 |
[(17.25 x 95) –
(17.25 x 90)] / (95 – 55) |
|
6 |
Final
Quantity of magma |
T/hr |
19.714 |
17.25 + 2.464 |
|
Melter for B&C sugar |
||||
|
7 |
Syrup
required for melting |
T/hr |
49.29 |
[(19.714 x 90)
– (19.714x 65)] / (65 – 55) |
|
8 |
Total
Melt Quantity ( Q ) |
T/hr |
69.00 |
49.29 + 19.714 |
|
9 |
Vapour
required |
T/hr |
2.948 |
Q Cp ∆T / λ |
|
M3/sec |
0.990 |
2.948 x
1000 x 1.210 / 3600 |
||
|
1.189 |
20 % extra |
|||
|
10 |
Dia of
the vapour pipe |
mm |
225 |
SQRT(0.405/(0.785*30)))*1000 |
|
11 |
Melt
holding volume required |
M3 |
23.000 |
69.0 x 20 / 60
(20 min. retention time |
Note :
1. In the above calculation total syrup requirement is
2.46 + 49.29 = 51.75 T/hr. Here syrup brix having maintained below 55o then
available quantity will be sufficient for melting the sugar. Otherwise it may
be required some quantity of hot water or clear juice to maintained constant
melt brix.
2. While using the clear juice/syrup for melter then
it is better to use screener to strain out extraneous matter
3. In the energy conservation point of view some
designers using 4th vapour as a heating medium for melter. If we using
4th vapour then operate melter under vacuum condition or using DCH (Direct
Contact Heater) with melt recirculation pump.
Sugar melter automation
The main controlling parameters in the melter
is Brix and Temperature. So two control loops are required in melter automation
1 . Brix transmitter and control valve for feed (sweet
water or clear juice or syrup) inlet to maintained the constant melt brix
2. Temperature transmitter and vapour/ steam control
valve to maintain the constant melt temperature.
Pumps for molasses and magma
The ”B” magma is pumped to sugar melter for
melting or pan section for seed purpose. C fore worker magma is pumped to
either pug mill of after worker machine (in case of double curing) or sent to
seed crystallizer or melter depending on massecuite scheme with the help of
magma pumps.
The molasses pumps are used for pump the
molasses from molasses receiving tank to pan supply tanks for further process.
The C molasses is sent to final molasses storage tank with the help of molasses
pump.
Always Molasses and magma pumps capacity
shall be arrived on the basis of number of centrifugal machines in operation
and its capacity.
For examples
Capacity of each
machine
– 1750 Kg/charge
Number of centrifugal machines in
operation
– 3 nos.
Number of average cycles
– 20 cycles/hr
Each Machine
capacity
– 1750 x 20 = 35
T/hr
Total massecuite cured
– 31.5 x 3 = 105
T/hr
A-Heavy molasses %
massecuite
– 45% (maximum)
A-Light molasses %
massecuite
– 15% (maximum)
Quantity of A-Heavy
molasses
– 105 x 45% = 47.2
T/hr
Quantity of A-Light
molasses
– 105 x 15% = 16
T/hr
Hence two nos. (1 working + 1 standby) of
A-heavy molasses pumps are required with capacity of 60T/hr and two nos. (1
working + 1 standby) of A-Light molasses pumps are required with capacity of 20
T/hr.
The molasses receiving or runoff tanks of
usually 2 to 3 m3 capacity is required for each type of molasses.
B magma pump capacity
Machine
capacity
– 16 T/hr each
Number of
machines
– 3
B sugar quantity per
machine
– 7.2 T/hr @ 100
brix (45% sugar considered)
B magma quantity per
machine- 9 T/hr @ 80 brix
Total B magma
quantity
– 27 T/hr @ 80 brix
(If used water for magma preparation)
Total B magma
quantity
– 43.2 T/hr @ 80
brix (If used syrup @ 60 brix for magma preparation)
Hence two nos. (1 working + 1 standby) of B
magma pumps are required with capacity of 40 T/hr (Generally, for 5000 TCD
plant required 3 nos. (2 working + 1 standby) of B centrifugal machines with 16
T/hr capacity)
Hint: Quantity of magma calculation while using syrup in
magma preparation
Take syrup quantity required for magma = Q
T/hr
B sugar quantity = 21.6 T/hr
B sugar Brix = 100
Syrup Brix = 60
Final magma brix
Then
(100 x 21.6) + (Q x 60) = (21.6+Q) x 80
For the above equation Q = 21.6
Final magma quantity = 21.6+21.6 = 43.2 T/hr
Gross Hopper
The sugar after separation from molasses in
centrifugal machines is conveyed via sugar conveyor normally hoppers. The sugar
discharged from high grade centrifugal machine is still wet and to be dried and
further cooled, graded before bagging and stored in godown.
Generally, the grass hopper consist of a
wide, flat and shallow trough, supported on flexible strips inclined at 60
degree to horizontal. The trough is given repeated vibration by means of an
eccentric, rotating about 300 rpm.
The Capacity of hopper is calculated by the
formula
Q = S A n k d
Q = Output of sugar conveyor in kg/min.
S = use full vertical cross section area of
hopper through which sugar is discharged in m2
A = Moment of sugar per stroke in meters
n = rotational speed of eccentric, 300 rpm
k = coefficient of slip (0.5)
d = Apparent density of sugar, (800 to 950
kg/m3)
Sugar dryer
Crushing Capacity – 230 TCH
Recovery % cane – 12 %
Sugar Quantity – 230 x 12% = 27.6 T/hr
Consider 150% Extra – 27.6 x 1.5 = 41.4 T/hr ≈ 40 T/hr
(Note: Here considered 50% extra capacity
because it is single equipment and shall be absorbed loads and breakdowns in
process)
Sugar house equipment capacity is always
better to calculate on the existing number of “A” centrifugal machines
capacity.
Sugar elevator & Sugar Grader
Cooled and dried sugar has to be graded for
which it has to be elevated for delivering to grader. Elevator consists number
of buckets running on return pulley at bottom and driven by similar pulley at
the top of elevator.
The capacity of elevator is calculated as
Q = GVN
Q = Out put of sugar in kg/min.
G = Weight of sugar conveyed /
bucket in kg.
V = Speed of belt m/min.
N = No. of bucket per
mt of belt length.
Sugar grader
The sugar so obtained consists of
heterogeneous crystals and needs to be well sieved and graded before it is
marketed. The main aim is particle size
classification which is done by screens. The classification
is usually achieved by using wire mesh or perforated
plate through which particles smaller than screen aperture may pass, while largest fraction
is carried over the surface.
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