Centrifugal section equipment Capacity Calculation in Sugar Industry

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.

Centrifugal Section and Sugar House Equipment in Boiling House of Sugar Factory

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 – 96.6 / 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)

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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

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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.

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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

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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.

Sugar grader capacity shall be considered 2 nos. having 20 T/hr each