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1. SHORT HISTORY OF THE MILLS
The Amravati Co-operative Sugar Mills Limited was registered
under the Madras Co-op societies Act 1932 in December 1955.An
industrial license was granted for the sugar factory with an installed
capacity of 900MT per day in 1956. The mills commenced its
production in June 1960 with the imported G.H.H. Mills. The Mill
had expanded the crushing capacity from 900TCD to 1250TCD
during the year 1971-1972.The capacity was further increased to
2000TCD in 1976.since a decision was taken to run only Binny Mill
at the rate of 1250TCD, the G.H.H. Mills was discarded vide
commissioner of sugar letter No.3102/98E2 dated 09/05/1999.It was
also decided to crush up 1500MT with this capacity itself. The Board
of directors of the Mills was superseded in December 1963 and it is
under the management of the Special Officer since then.
1.1. Area of Operation
Tiruppur District
a) Entire Udumalpet Taluk
b) Entire Palladam Taluk
c) Entire Tiruppur Taluk
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d) Entire Dharapuram Taluk except Mulanur and Kannivadi Firkas
e) Entire Uthiyur Firka and Kangeyam and Kadaiyur Villages of
Kangeyam Firka
Dindigul District
a) Entire Palani Taluk
b) Entire Ottanchtram Taluk
Coimbatore district
a) Ramapattinam ,Kovilpalayam,Vadachitur and Kinathukadavu
Firkas of Pollachi Taluk
b) Entire Sulur Taluk
Mill area: Land = 222.715acres
Cane Farm: total Extent =20.70 acres ; Irrigated area = 10.00 acres
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2. GENERAL INTRODUCTION TO SUGAR INDUSTRY
Sugarcane is the best harvester of solar energy .It is the most
important commercial crop in Tamil Nadu and grows in almost all
districts of the state. Quantity of sucrose deposited by the solar energy
in sugar cane is highly dependent on the diurnal variation of
temperature. Wherever the difference between maximum and
minimum temperature is high, higher and highest, quantity of sucrose
in sugarcane is greater. In Tamil Nadu, as you go from East to West,
the difference is low in the East, higher in the mid area, and highest in
the West. Karnataka and Maharashtra are very fortunate in this regard.
The next important factor is the Sugarcane yield. India used to have a
proud record of highest yield of cane per hectare in the world .This
has declined in recent years due to various factors like selection of
varieties giving greater recovery, failure to combat pests and disease
effectively, lack of optimum irrigation, absence of drainage facilities,
absence of good seeding program, failure to select varieties suitable to
the area , lack of supervision over treatment of sugarcane sets for
distribution , rationing without any control , lack of suitable
application of organic manure and chemical fertilizers , untimely
harvesting ,lack of good weed management etc.
The farmer is naturally interested in quantity of Sugarcane and the
factory is interested in quality of sugarcane. Factory blames the
grower for the quality and grower blames the factory for failure to
recover the sugar to a greater extent. This can be solved to greater
extent by management which should have frequent meeting, with
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growers’ association and the technical staff inside the factory.
Measures and decisions taken should make both of them happy. Early,
mid, late varieties should be identified. The management should see
that the cane department has a very good scientific program to achieve
optimum results. Micronutrients and biological measures should be
discussed. Soil fertility should be looked into. Drainage is very
important. Rotation of crops is quite essential. Sugarcane gives sugar,
also serves as a fuel (bagasse), besides by products such as press mud
and molasses. It will be good if factory management harvests the cane
with its own labor, Chief executive should assess the quantum of Cane
required with reference to the crushing capacity of the factory month
wise and regulate the registration of cane accordingly. Transport of
cane should be subsidized equitably. Greater yield of quality cane
should be achieved but the cane should be harvested at the optimum
period and it should reach the factory within 24 hours of its harvest to
achieve greater results. Delayed harvest or premature harvest will
result in lesser yield and delayed arrival in the factory will lead to
inversion. Overall productivity of Cane has considerably increased in
TamilNadu in recent years , thanks to periodic science club meetings
held by world renowned Sugarcane Breeding Institute ,Coimbatore.
To produce quality cane and to get higher productivity per acre the
following should be adopted.
• Thorough preparation of land – by using tractor drawn ploughs.
• Introduction of new sugarcane varieties based on adoptive trials.
• Varietal scheduling –Based on the period of planting.
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• Staggered planting – To get regular and continuous supply of Cane
to mills.
• Registration of Cane area – To get assured supply of cane
• Seed nursery program – To get quality seed material.
• Adopting proper seed rate and proper planting method – To get good
yield
• Fertilizer management – Integrated fertilizer
• Irrigation management
• Weed Management – Integrated weed management
• Crop management by adopting improved proven agricultural
practices
• Pest and disease Management –Integrated Pest Management
• Harvest management – Harvest at proper age of crop and transport
arrangement
• Ratoon management – to get god quality cane in second crop-ratoon
• Use of labor saving
The above works will come under the following heads
(i) Preparatory cultivation
(ii) Seeds and sowing
(iii) Manures
(iv) Irrigation
(v) After cultivation – Gap filling, Weeding, Detrashing, Mulching,
Propping, etc.
(vi) Plant protection, Harvest and transport
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3. ABOUT SUGAR PRODUCTION
Cane Yard
Cane is brought to the factory from the field. Weighing of cane is a
very important factor that goes to prove or determine the productivity
of cane as well as that of operations in the factory. Correct weighing is
the pre-requisite in the factory. After weighing, cane is unloaded
inside the yard. For unloading cane into the carrier, mechanical
unloading either by sling or grab type has come to stay replacing
human labor. This sort of mechanical unloading has helped to load
fully and ensures efficiency in cane preparation and extraction.
Uniform feeding with optimum speed is a must. Leveling of cane
bundles without choking is a must. Leveler and cutter with or with out
reversal of knives should ensure better cane preparation.
Again automation has come to stay in this station and thus increase
the efficiency of uniform feeding leading to better mill extraction
Effective supervision is a must for maintenance of the slots in cane
carrier, steaming of the cane carrier and periodic washing of cane
carrier area should be ensured.
Mill house
Sugarcane contains juice and fiber. Juice is a mixture of sugar and
non-sugar besides water which is used to extract more sugar. Cut cane
goes up and falls on the rollers (Mill station) in an inclined fashion.
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Minimum of four mills with three rollers each will function. Sets of
three rollers with feed and discharge and top roller for applying
hydraulic pressure are present .Prepared cane is fed to these mills
which are kept in sequence to accept the cane mat of the previous mill
and so on. Juice squeezed is collected in the tray below and the
residue mat proceeds to the next set of three rollers and the same
action is repeated and juice is collected separately. Except for the I set
and II set of mills , all the other mills’ juices are pumped back to spray
on the cane mat for imbibing action to effect better juice extraction.
For the last mill of tandem feed alone, hot condensate water is used
for imbibitions.
The juice from I and II set alone (the ultimate “outlet gate” for the
juice from the milling station) is screened to remove the coarse
suspended matter (fiber) and screened juice sent to the process house.
The mat that gets out of the last mill is called bagasse (first by
product) practically containing no sugar (though we can’t remove cent
percent). The milling efficiency is the ratio of sugar extracted to sugar
present in cane on percentage basis called mill extraction.
Cane + added water = mixed juice + bagasse (material balance)
Sugar in cane = sugar in mixed juice + sugar lost in bagasse
Sugar in mixed juice =sugar bagged + sugar lost in filter cake +sugar
lost in molasses + unknown loss of sugar.
Bagasse rich in carbon fit for use as fuel and with moisture less than
49% is sent to the furnace of the boilers for generation of steam. Sugar
loss via bagasse has to be the acceptable minimum and depends on the
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milling efficiency. Bagasse is the first by-product of a sugar mill.
Earlier mountains of bagasse used to be common place.
Now-a-days , due to modernization , value for bagasse has increased.
In the present day process , better efficiency in burning and better
conservation of power , concept of co-generation has come which
leads to more profit. Paper mills take bagasse and give alternative fuel
to the sugar factory. What used to be a liability in the last decade now
proves to be money spinner.
Important factors like preparation of cane , mill setting , Imbibitions ,
hydraulic pressure , trash plate setting , grooving of rollers which
measured pitches , surface roughing of the rollers , maintenance of
inter-carriers , effective drainage of juice , specially in stainless steel
gutters , whirling of juice in juice tanks , screening of juice ,
avoidance of slippage etc. should be looked into. Besides effective
supervision on lubrication, sanitation of the Mill’s area is a very
important factor.
Proper planning for the number of roller shafts with grooved rollers
that should be kept in readiness, not only for the incoming crushing
season and for the sub sequent seasons, is quite essential. Periodical
ultrasonic X-ray of the shafts and the rollers is a must. There should
be no inhibition on imbibitions. Maximum up to 300% on fiber should
be attempted. Tackling of resultant moisture is an important task of
engineers. There should be minimum reabsorption. Hydraulics should
function effectively.DSM screen or rotary screens will reduce mill
load, reduce power consumption, and improve juice heating efficiency
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and clarification efficiency. Extraction through diffusion is also
another process.
Mills are normally run by steam turbines. The alignment of turbine
shafts with roller shafts and couplings is very important. Now-a-days
hydraulic drive variable speed AC drive, thyristor control DC drive is
also in vogue. Steam produced by the boiler rotates the turbines and
when it comes out, it gets the name “exhaust”. Exhaust steam ( or low
pressure steam ) is used in the process house for heating juices and for
evaporation and for crystallation.Sugarcane is well prepared ,
(preparation index) cut or shredded in to pieces and sent through
rollers. Juice extracted and the pressed cane mat is circulated in all the
mills and ultimately when the rampant after extraction of juice comes
out of the last mill, this cane residue is named as bagasse. Moisture in
the bagasse is a very important factor which influences the effective
burning in the furnace of boilers and resultant generation of steam.
Hot water imbibitions (maceration) will be more effective and the
resultant slippage in the last mill is mitigated by welding the grooves
of the rollers in the last mill through electrodes as the rollers rotate.
Good work by skillful welders is quite essential. Vibratory stress
relieving system can be adopted for all the units right from the cane
yard to the drier- house.
Boiler House
Bagasse that comes out of the mill station is fed into the furnaces
through carrier. Furnaces are of step-grate type, horse shoe type and
spreader striker type. Hot condensate water is sent to the drum and
ultimately through water tubes. Water inside the tubes is heated and
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the economizers should function well. Steam at prescribed pressure
and temperature is sent to all the stations in the factory. Forced draft
sends air to the furnace. Furnace and biogas from the biomethanation
plant is used together as a fuel for the main steam boiler. Proper
mixture of fuel to air ratio is essential. Quantum of steam with
adequate pressure, drum level maintenance, water flow and CO2
analysis are very important. Automation can be thought of. Steam
lines running through out should be lagged well on the exterior
preferably with glass wool and cement and ultimately aluminum or
stainless steel cladding to avoid or minimize the heat loss through
radiation.
A portion of the steam is sent to the turbines which move the rollers in
mill stations. Another portion is sent to the turbo-alternator which
produces power. Many are not aware that a sugar factory produces its
own power, although dependent on power grid for local electricity
board. Another portion is sent to processing sections in a limited way.
“Steam flow meter is a must”. Extraction of steam and power
generation by various units is concomitant. In the absence of a steam
flow meter, the boiler efficiency cannot be determined.
All the boilers require thorough overhaul and should get certified by
the boiler inspectorate. Any breakdown due to tube failure of the
boilers should be intimated to boiler inspectorate and should be
rectified as per the instructions of the boiler inspectorate.
Power House
Many are not aware hat a sugar factory besides producing sugar also
produces its own power to run its units .It also draws power from the
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electricity grid and it is quite essential for commencement of its
operations in the beginning and later on “change over “ to its own
power. During season, even the quarters situated on the same side of a
public road draw power from the factory. The unit is called “Turbo-
alternator”. The Amaravathi Mill generates 1.5 MW for its own
purpose. Live steam from the boilers goes into the turbine and rotates
its shaft. Gears which bear the shaft are very important and
supervision and maintenance of the gears is very important. The
correct alignment of turbine and the alternator is very essential and
this should be periodically checked.
Good foundation is another factor which stabilizes the productivity of
the unit. Effective lubrication goes a long way. Old thumb rule is that
you require 1kW of power to crush one tone of sugar cane. Modern
techniques enable crushing of one tonne of cane with less than 1 kw
of power (say 0.50 or so). Technocrats will try to have buffer for
everything to be on the safe side.
There will be double bus-bar which regulates the power from the grid
and also distributes factory’s power to various units. There should be
a diesel power generator (say 250 kW) as a standby.
Back pressure turbines are now-a-days replaced by the condensing
turbines. Co-generation has come into being.
Clarification
Mixed juice is weighed (even water is weighed before being sent to
Mills) and sent to the juice heaters for heating. Vapor from the
evaporator bodies will be utilized in juice heaters which used to be
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horizontal, now vertical. Mass flow rate of juice is an important
factor. Vapor condensates (hot water) if sent to the boiler feed tank
should be tested for “nil” sugar content. Exhaust utilized in the first
evaporator produces vapor which is utilized in juice heaters for
heating.
Juice output at 65°C as a result of primary heating will be sent for
liming to neutralize between alkalinity and acidity at a pH of 7.1 to
7.2 limestones or shell lime will also be used for preparation of lime
solution. Juice will also be treated with SO2 gas. Lime should contain
active CaO not below 80% and 10-12 Brix of lime solution. Effective
supervision should be on this station. Machinery items and the vessels
should be functioning properly.
Effective travel of SO2 gas is a must .Level at which sulphitation
vessel is fixed is a very important factor. Phosphate content should be
maintained at 300ppm. SO2 gas final temperature should be at 70°C.
Treated juice is again sent to juice heaters for secondary heating at a
temperature of 105°C.Temperature at which the raw juice and treated
juice is heated is very important and the gauges should function well
to indicate the required temperature in all the juice heaters. Such
heated sulphured juice goes to clarifier. Juice heating, liming and
sulphitation are for removing very minute suspended solids in
colloidal state.
Clarifier (used to be called as Dorr) will have a flash tank at the top
.Treated juice which comes out of juice heaters at 105°C output
reaches the flash tank and then enters the clarifier which will have
four compartments duly sealed with no inter connection. Juice enters
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the compartments on the bottom side and the level goes up gradually
.Perceptible non-sugars get coagulated and form huge flocks. Heavier
flocks settle down slowly leaving a clear transparent juice at the top of
each compartment. Tempering the juice is an important step in
plantation white sugar. This clear juice goes to the evaporators.
Magnoflac can be used as an aid for better settling.
The mud (settled heavier flocks) scraped by hinged scrapers is pushed
to the respective mud boots and then to the mud tank. It is then
pumped to the Rotary Vacuum filters having fine screens. Mud in
liquid form is mixed with a little of bagacillo(screened from the
bagasse that goes to the boiler and then blown to the vacuum filters by
air blowers). The drum rotates and through vacuum sucks the mud and
forms a blanket cake on the drum. Incidentally, juice is sucked from
the mud and dry mud (filter cake second by product) is scrapped and
sent out, which has manorial value and goes back to the agricultural
lands. The transparent clear juice sucked through the tubes inside the
drums is sent to the mixed juice tank for reprocessing.
Evaporation
Clear juice coming out of the clarifier and which is relieved of the
suspended and perceptible non-sugars from the original mixed juice is
now ready for the next stage. Evaporator is a unit which contains
“calendria” through which exhaust (power house steam) enters and
after its function of heating outside the tube through which the clear
juice flows , condenses as hot water and comes down which is sent to
the boiler feed water tank.
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There is adequate space on the top of the evaporator body. When juice
reaches the boiling point, water is naturally relived and goes above as
vapor in the available space on the top. This vapor is again sent to the
calendria of the second evaporator body. Also boiled juice from the
first to second is sent.
The same function continues in the second vessel. There will be
maximum four bodies. The ultimate vapor from the top space of the
final body is sent to the condenser and by pumping cold water in the
condenser , vapor is condensed totally thus creating absolute vacuum
and hot condensate water sent to spray pond for cooling and
recirculation and pumping to the condenser of the final body. On
account of above multiple effect, juice brix at 15 entering the first
body should come out as syrup with a brix at 58-60 . If brix of 58-60
is ensured in the last body, it minimizes the maximum problems in the
next stages, say crystallization (pans). Incidentally, vapors from the
evaporator bodies are sent to juice heaters and pans for heating.
Wherever exhaust is condensed, this hot water is pumped to boiler
feed water tank. Exhaust utilized in the secondary heating in juice
heaters and exhausts used in the first body of the evaporator are
examples. All the other vapor condensates are sent to boiling house.
The vessels (evaporator bodies) are all lagged to avoid heat loss
through radiation. Each vessel should have provision for pressure
vacuum gauges, inter-connecting pipelines and control valves etc.
Juice level gauge should be there and the optimum level of juices
should be maintained to achieve maximum efficiency. Through view
glasses, we are able to see the boiling of juice and note any
abnormalities. They are not storage vessels. The main purpose of the
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evaporator bodies is concentration of juice. Normally 100 tonnes of
clear juice input with 15 brix should come out as 25 tonnes of thick
syrup in terms of concentration at 60 brix . Concentrated juice/ syrup
is then pumped to sulphitation tower for bleaching with sulphur di
oxide gas .The sulphated syrup goes to “pan” for further evaporation
and to form crystals.
The tubes in the juice heaters and in the evaporator bodies (acting as
heat exchangers) accumulate scales inside on account of calcium,
silica etc. content of the juice. These scales shave to be removed
periodically. That is why factories have a shut down once in 25 days
to one month or so for cleaning tubes. Effective cleaning of the tubes
and efficient supervision there on during the shutdown is a must.
Instruments required for cleaning should be in a good shape and kept
ready even before shutdown.
Pan- Boiling and Curing
Sulphited syrup reaches the next stage for further water removal to be
carried out in single effect pans. The body of the pan is similar to that
of the evaporator except that the diameter of the tubes will get bigger.
Solid sugar has to be separated from the mother liquor in the syrup.
Vapor (steam) flows from the evaporator bodies individually to the
pans. We concentrate the virgin syrup and at a specific viscosity,
sugar starts crystallizing .Normally there will be crystal bed already
existing and then with further deposits on these crystals, the crystals
gradually grow in size and become fit for bagging or reuse as seed. As
the evaporation proceeds, crystals are formed. Contents stay in the
vessels. As and when it concentrates, further feed is given. Thus the
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material builds up in the volume to reach a full level. Then the vapor
is shut and the vacuum is released.
Product is discharged via the wider door provided at the bottom in the
conical portion. Product goes through wide gutters and falls in the
respective crystallizer. Product that comes out of pan is now called
massecuite. At one stroke, it is impossible to crystallize all sugar from
the syrup. It needs repeated boiling and concentration of the exhausted
mother liquor. this is the reason for “ three Boiling “ at least to extract
maximum possible sugar from the liquor until at the last stage ,
mother liquor separated is sent out as “ Final Molasses” , another
(third) by product. This product does contain some sugar and should
be kept at the minimum, a salutary duty of the process department.
Continuous Pans are also being tried in the place of batch pans. It has
been tried for “B” stage. People, who have reservations for “A” & “C”
stages earlier, have also started to operate conti-pans for “A” & “C”
stages. Good exhaustion is obtained. It may ensure optimal
exhaustion. Saving of power and sale of power to the grid thereby will
be worthy of the purpose. Steam consumption may be less and quality
of sugar may be better. A system will always have certain advantages
and disadvantages. If advantages far outweigh the disadvantages, the
system can be adopted with greater alacrity and devotion.
In pan boiling, there are three stages, viz. A, B and C stages. Products
produced by A Pan , B pan and C pan are called “A” massecuite, “B”
massecuite and “C” massecuite .The virgin sulphited syrup from the
tank is sucked into “A” pan . After boiling, the resultant “A”
massecuite goes down the gutter and then to crystallizer.(In
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crystallizer , the massecuites are cooled for a prescribed time).Designs
of crystallizers are different. Normally shaft with tubes (water will be
run through tubes) rotates and circulates the massecuite. This “A”
massecuite goes to the “Pug Mill” above “A” centrifugal. This
centrifugal is a batch type (not continuous).Now-a-days motors with
thyristor controls and automation have come into operation. Screens
with perforated slots are a significant phenomenon in the centrifugal
baskets. Speed at which the baskets rotate is terrific. Due to the
centrifugal force, liquid is pushed out of the basket. While coming
out, it passes through screens allowing the sugar to be retained in the
basket (solid-liquid separation).Spare screens should be available in
stores. Controls are set in such a way that “A” molasses (mother
liquor in syrup) and “A” heavy molasses are separately sent out.
Besides, sugar that comes out, goes out as commercial sugar for
bagging, “A” light molasses are sent and stored and again sucked into
“A” pans in the next operation. “A” heavy molasses are sent stored
and sucked into “B” pan. When boiling takes place in the pans, vapor
that goes up in the vessel is connected to the individual condenser
(conical body, nozzles, Venturi etc.), where vapor is condensed and
sent as hot water to cooling tower or spray pond as the case may be.
This hot water thus produced is cooled in the spray pond or cooling
water and again pumped through nozzles in the condenser. Each pan
has an individual condenser, unlike evaporator bodies and is termed as
single effect. It will be quite interesting to watch the flow of water in
hot water channel to a heavy duty pump that pumps hot water through
big pipes spread over in the pond. Pipes have a number of nozzles
through which water is sprayed to come in contact with the air and
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thus hot water gets cooled and comes back to the factory for being
pumped up to enter the individual condensers of the individual pans.
Cooling is necessary to condense the hot vapors. Vapors which go to
the condensers of the last evaporate body and condensers of each of
the three pans should contain no sugar. There should not be any
entrainment .Signs of foaming or hot water slightly brownish in color
is not good.
The next stage is “B “.Pan “B” receives the “A” heavy molasses from
the storage tank and boils it. Virgin syrup may be added to improve
the purity.”B” massecuite after drop in the crystallizer reaches the pug
mill over the “B” centrifugal. It is cured.”B” heavy molasses is stored
again and sucked into “C” pan.”B” sugar is melted and used as seed
and again sent to Pan “A”. Vapors as usual go to its condenser for
condensation as hot water.
“B” heavy molasses are further boiled in “c” pan. It is dropped in the
crystallizer and after cooling goes to the pug mill of “C” fore worker
(CFW) centrifugal machine for curing. Here the thick final molasses
are sent out as the “third” by product of the sugar factory. Loss of
sugar in this product should be reduced to the minimum. Separated
“C” sugar in this machine is sent to CAW (“C” after worker) machine
after storage in a pug mill.
After curing in CAW centrifugal machine and applying water wash,
“C” light molasses that come out are sent to “C” pan again for further
processing along with “B” heavy molasses. Vapors are sent to the
condenser.”C” after worker cured white sugar is sent for melting and
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sent to pan supply tank and then sucked into “A” pan for boiling along
with virgin syrup and “A” light molasses.
The above is the explanation of the process i.e. Pan boiling, vapor
condensation, spray pond, crystallizer cooling and centrifuging to
separate sugar from its mother liquor. Vertical crystallizers have also
come into operation. Continuous centrifugals are also in vogue for
“B” & “C” curing. Second vessel vapor drawn from evaporator bodies
helps in the boiling in the pans. People working in pan station should
be very vigilant. Gutters and crystallizers should be wide & slope.
Drawing of power by the centrifugals should be regulated. Baskets in
the centrifugals should be checked for dynamic balancing. Wear out
should be checked superheated water wash should be utilized in a
meticulous manner .Enough spares like screens, motors, shafts etc.
should be readily available. An efficient dust collector is must.
The final molasses are weighed, pumped and sent to the steel tanks.
The material with high viscosity requires special pumps for being sent
to the steel tanks. Proper maintenance of the steel tanks and the pumps
is a must. All the precautions are to be taken to avoid spontaneous
combustion in tanks. Temperature gauges should be there. Cool water
should be sprayed on the outer surface.
Molasses are sent to factory’s own distillery or other distilleries for
manufacture of alcohol, for manufacture of cattle feed, crushing of oil
seed etc.Now-a-days there is a free market for molasses. Molasses is
also exported.
Sugar sent out by “A” centrifugals goes on the hopper. Solid sugar
material has to be conveyed and dried. The long wide tray like is
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called “Hopper”. As sugar is moved by a hopping action by a special
eccentric drive, it is called hopper. Hot and cold air is blown on the
hopper down below and as the name clearly indicates, it hops and an
elevator takes the sugar above to the grader. Grader has the sieves.
The perforations of the sieves become smaller and smaller from first
to last one. Lumps are separated and the commercial size of the sugar
is also separately coming out. It is again sent to “bins” through an
elevator. It will have a capacity equivalent to 18 hours of production
of sugar. Sugar with the required size is bagged in terms of 100kg
each in “A” gunny bags and after stitching, bags are sent to godowns
for storing. Flooring and side walls of godown should be moisture
proof.
Sugar grades as per I.S.S are “S” (small) “M” (medium) and “L”
(large). Tamil Nadu bags mostly S30 (number indicates the color .
Color is 29, 30, 31 and “S” is size).For export purposes, the
recognized international method of procedure is to find ICUMSA
value.
Stores
This is a place where all the hardware, equipments, steel materials,
motors, pumps and the entire requirements of the factory are stored. A
separate godown will be for lime and sulfur. Store keeper in charge
will issue materials on indents signed by engineers and chemists.
Scientific system should be adopted not only for planning for
purchases but also for storage. Items should be classified according to
value and frequency of purchase and storage should be cost effective.
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Table.3.1.Sugar Godown Capacity
Godown
No.
Length
(in metres)
Breadth
(in metres)
Height
(in metres)
Capacity
(in
quintals)
A 56.25 35.55 7.75 75000
B 29.55 27.78 8.00 35000
B-
Extension
30.00 28.9 7.75 35000
C 55.60 29.80 7.60 70000
Total 215000
Workshop
This is the place where we have lathes , facilities for overhauling of
all machinery items ,inclusive of motors and pumps , manufacture of
small vessels , grooving of trash plates ,rollers etc. This is where one
has to remind himself about preventive maintenance and post-
maintenance. A factory has a season for about 6-7 months and the
other 5-6 months, the factory undertakes all the repair work. Overall
productivity of working season depends upon the good work done
during off-season. One has to analyze various reasons for breakdown
during season and the equipments should be kept in good shape to
minimize the break downs in subsequent seasons. Corrosion and
erosion of vessels should be set right .Scraps should be disposed of
annually.
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Laboratory
Every factory will have a laboratory. Laboratory is meant to help the
entire operations to run according to specified standard norms
.Samples should be taken from various stations at least once in an
hour and results communicated to engineers and chemists then and
there. Such process will minimize the loss of sugar in the respective
houses to a great extent.
Daily Manufacturing or Production Report
This is the daily summary of operations in a factory during the season
.It will be quite good , if the Chief Executive has a meeting with Chief
Engineer , Chief Chemist and Cane Manager daily for an hour or so
and record the minutes. Such discussions will have all the advantages
and ensure better co-ordination and smooth operation of the factory.
There are various norms and indices for different operations. Some of
those are indicated separately .All the sectors should take all sincere
efforts, and try to achieve those standards with devotion and mutual
co-operation.
23
Table.3.2.Molasses Storage Tank Capacity
SL.NO. Description of Molasses
Tank
Capacity(inMT)
1 Steel Tank No.1 3000
2 Steel Tank No.2 4000
3 Steel Tank No.3 4000
Total 11000
Table 3.3.Details of cane crushed,sugar produced,recovery,profit /loss
24
4.PERFORMANCE STANDARDS
1. Preparatory Index
I. Leveller and Cutter
II. Shredder and Fibrizor
65% +
85%+
2. Primary Extraction above preparatory
index
3. Reduced Mill Extraction
Four Mill Tandem
94%+
4. Imbibition % on fibre 250+
5. Moisture % bagasse -50%
6. Total Losses
(i)Pol Loss in Bagasse
(ii)Filter Cake
(iii)Final Molasses
(iv)Undetermined or Unknown
-0.60
-0.07
-1.15
-0.06
7. Time Lost
(i)Excluding general cleaning*
(ii)Including general cleaning
*Split up for 4.5
Mechanical
4.5%
10%
2.0
25
Electrical
Process
No Cane
Miscellaneous
0.5
0.5
1.0
0.5
8. Power Consumption
(i)Turbine driven and Fibrizor
(ii)Turbine driven mills
(iii)All units electrical driven
18kW/Hr
22kW/Hr
30kW/Hr
9 Steam Consumption
As per 1987 standard specification
HP boiler and quintuple effect
evaporator
Prior to 1987 specification
% on cane
max 50
max 55
10 Chemicals
I. Lime % Cane
II. Sulfur % Cane
0.20 to 0.25
0.06
11 Final Molasses 28 to 30 %
12 Syrup brix 58+
26
5.DISTILLERY UNIT
• Capacity
Rectified Spirit
a) Licenced Capacity : 55000 litre
b) Installed Capacity : 55000 litre
Extra-Neutral Alcohol
a) Licenced Capacity : 10 000 litre
b) Installed Capacity : 10 000 litre
• Date of trial Run : 16.03.1994
• Date of start of Commercial Production: 20.08.1994
• Erection of New Project
Ethanol Plant: 30kl/day
Annual Capacity: 90.00 lakh liter
27
• The Tankwise storage Capacity for Molasses and Alcohol
5.1.Molasses Tank Capacity in Distillery
Tank No. I 6000 MT
Tank No. II 6000 MT
Total 12000 MT
Table.5.2. Alcohol Receiver Tank (one day storage)
S.NO. DESCRIPTION QUANTITY
( in No’s)
CAPACITY
(in litre each)
1 Rectified spirit Tank 3 60000
2 Impure Spirit Tank 2 10000
3 Extra Neutral alcohol 3 12000
4 Technical Alcohol 2 10000
Table.5.3.Storage Tank ( Bulk Capacity)
S.NO. DESCRIPTION QUANTITY
(in No.s)
CAPACITY
(in litre each)
CAPACITY
(in Lakh litre )
1 Rectified spirit Tank 2 15,50,000.00 31
2 Impure Spirit Tank 2 1,80,000.00 3.6
28
3 Denatured Spirit Tank 2 50,000.00 1.0
4 Extra Neutral Alcohol 1 6,00,000.00 6.0
5 Rectified Spirit Holding
Tank(for ENA Raw
Material Tank)
1 20,000.00 0.2
6 Fusal Oil Tank 1 15,000.00 --------
Total 41.8
29
6.ALCOHOL PRODUCTION FROM MOLASSES
The production of alcohol involves two main process
• Fermentation
• Distillation
6.1.Fermentation
Fermentation is a process to which complex organic material is
broken down into smaller substances and decomposition is brought
about by the action of living organism which secrete the enzyme
catalyst suitable to the process.
Requirements : Molasses ,Water, Air,Yeast
The molasses from the Pre-Fermentor tank is diluted to required
concentration, mixed with Yeast , Water and Air. The initial gravity is
1.065 to 1.070. The nutrient such as DAP and Urea are added as a
food for yeast . The temperature is maintained from 30-31°C. After
10-12 hours the gravity falls from 1.065 to 1.035
Sucrose ----invertase---> Glucose + Fructose
Glucose ---zymase ------>Ethyl Alcohol +CO2
The fermentation process is carried out by continuous process in
fermentors (F1,F2,F3,F4,F5). The specific gravity varies in each
30
fermentors. In F5 the specific gravity should be 1.047-
1.048.Fermentation process completes with in 28-32 hours. The heat
exchangers are used to maintain the temperature.the wash from
fermentor F5 is pumped to wash settling tank.The settled sludge is
removed through a valve.The remaining wash is pumped to clarifying
wash tank. After reaching a minimum level in clarifying wash tank ,
the wash is transferred to the distillation section.
6.2.Distillation
Analyser Column
In the distillation process the analyser column separates alcohl from
the fermented wash.Steam is fed to the bottom of the column.this rises
to the top and it comes into contact with the wash flowing down over
the plates .Thus Alcohol is separated from the fermented wash.
Rectifier column
Vapors from the Analyzer column are fed to the bottom of the rectifier
column. The vapor are condensed and the spirit is obtained .The
rectified spirit has 94.68% of alcohol. It is used as alcohol beverage
and applied in paints , drugs ,oils, perfumes ,varnish, gums etc. In
pharmaceutical it is used as preservative for biological specimens and
used as fuel in spirit lamp.
The effluent left after distillation is used fro the production of Bio-Gas
.The Biogas is used for boilers. The secondary effluent is used as
manure.
31
7. TECHNOLOGY OF BIO-METHANISATION PLANT
7.1.Biomethanization Technology
In every distillery the Bio-Methanisation plant is installed for treating
the effluent generated from the distillation plant by an anaerobic
process.
Anaerobic treatments offers the capability of loading low , undiluted
stillage producing only low quantities of sludge and giving an effluent
that is readily treated in an anerobic system. Anaerobic treatment by
methanogenesis is widely used for stabilization of municipal solid
waste. More than 35 categories of industries ( including chemical
,fiber,food,milk and pharmaceuticals) are using anaerobic digestors
for waste water treatment. It is unique that most of the distilleries have
the digestors and they turn to improve the efficiency of the energy
recovery.
7.2.Bio chemical fundamental Process
Anaerobic waste water treatment involves the decomposition of
organic and inorganic matter of molecular oxygen. The micro
organism responsible for the decomposition of organic matter is
commonly divided into groups.
32
The first group hydrolyses and ferments complex organic compound
to simple organic acids, the most common acids are formic acid,
acetic acid and propionic acid. The second group of bacteria converts
the organic acids formed by the first group to methane & CO2.
The bacteria responsible for this conversion are strict anaerobes and
are called the methanogenesis. The figure in appendix shows the main
reaction performed by these bacteria. The most important bacteria of
this group are those which are degrading acetic acid and propionic
acid. They have very slow growth rate and as a result their
metabolism is usually considered as rate limiting in the anaerobic
treatment of organic wastes. In the second step the actual waste
stabilization is accomplished by the conversion of the organic acids
into methane and carbon dioxide. Methane gas is highly insoluble and
its departure from solution represents actual waste stabilization.
Anaerobic Treatment System
33
To maintain an anaerobic treatment system that will stabilize an
organic waste efficiently, the acid formers must be in a state of
dynamic equilibrium. To establish and maintain such a state , the
reactor should be void of oxygen and free from inhibiting
concentrations. The optimum temperature for the anaerobic treatment
ranges from 35°C to 40°C.The main nutrients for anaerobic bacteria’s
are phosphorus and nitrogen.
7.3.Process Description
The anaerobic Bio-methanisation plant is designed with the following
description.
Effluent Line
The hot stillage coming from the distillation column is transferred
through a pipe line to the effluent lagoon. The lagoon is referred to as
“Balancing Tank”. The effluent is transferred from the lagoon to feed
anaerobic reactor by feed pumps. The flow rate is maintained by flow
meter controlled by automatic control valve. Thermal pre-treatment is
designed to obtain a mean temperature of 37°C in the reactor. The
heat exchangers are used to cool the hot effluent. The flow rate of the
cooling water is manually controlled and monitored to achieve a
desirable temperature of the digester.
Digestor
The digestor is a fixed bed reactor with flocor “R” plastic media
having a large surface area upto 230 sq.m/m3.The recirculation pumps
collect the treated effluent at the bottom of the reactor through a pipe
works of assembly which permits uniform draw of the whole area.
34
Operation Methodology
The effluent to be methanised after pre-treatment is dispatched to the
digestor at recirculated loop level. The mixture (influent = treated
effluent) is distributed on the whole digestor via a distribution pot.
Treated effluent is carried away by overflow from the bottom of the
reactor to a hydraulic seal. The portion of the overflow determines the
liquid level in the digester.
A pH probe is installed on the recirculation loop to measure the pH of
the influent in the digester. A high and low threshold of pH sensor is
set to stop the digester feed (low pH-6.8 and high pH -7.8). A high
and low threshold for the digester inlet temperature alarms the
operator and stops the feed (low temperature of 35°C and high
temperature of 41°C).
Biomethanization flow chart
35
Gas Line
Biogas produced is collected at dome low. A biogas meter is provided
to continuously record biogas production. The biogas line is equipped
with two separate safety system.A vacuum breaker which allows
atmospheric air and a vent breaker which maintains a pressure lower
than the maximum pressure in the digester. The vent is equipped with
one submerged biogas line. The biogas when not used by the boiler is
discharged via the vent.
De-sludging System
If suspended solid concentration in the digester becomes very high.
The excess solid can be extracted via a pipe branched at the distance
of recycling pumps. The flow rate is adjusted manually. It is only
possible to use this line when the digester is not fed with stillage.
7.4.Biogas Generation and its cost Benefit Analysis
During the study of bio-methanisation plant operation, process and its
gas production and usage for reducing the fuel requirement and power
generation.
36
Description Detail
Capacity of distillery 55kL / day
Spent wash 750cu.m/day
COD load available 75 MT / day
Average COD reduction 60%
COD reduction 45 MT
Biogas production reduced 0.5 cu.m/ kg of
COD
Average Gas Production 45000x0.5 cu.m =22500cu.m
Each cubic metre of biogas 4500kCal/cu.m
Total Calorific Value 10125000kCal
Each cubic metre of gas 0.5 litre of
furnace oil
22500 cu.m of gas 11,250 litre of
furnace oil
11250 liter of furnace oil 112.5MT of
steam
55kL plant requires steam 115.50 MT of
steam
For running the 55kL rectified spirit plant there is no additional fuel
requirement . If we operate with 80% efficiency, the plant requires
1500-2000 litre for running the entire plant for providing entire
requirement of steam and to run the turbo-alternator.
37
7.5. Existing Digestor and its Performance
In Amaravathi Co-op Sugar Mills Ltd., a bio-methanisation plant is
installed with the capacity of 6000 cu.m and the daily feeding rate is
about 750 cu.m . This meets the treatment for entire effluent generated
from the distillery. This bio-methanisation plant is installed with an
out-lay of 3.25 crores and the plant is supplied by Messrs.Sakthi
Sugars Ltd with the collaboration of SGN of France and Germany.
The existing digester was commissioned in the year 1994 and the
plant is under operation since the inception. This plant was provided
with all control units for maintaining the feed rate, pH control, and
recirculation effluent and biogas booster. During the normal operation
the entire effluent generated from the distillery is stored in lagoons.
After cooling it is pumped for feeding the digester at required level to
meet the gas requirements and plant conditions.
Generally bio-methanisation plant is a cylindrical tank provided with
feeding pumps , recirculation pumps , biogas boosters and all other
required control units including the control panels , instruments for
measuring the feed of the effluent and biogas . This plant is connected
with more than 100HP motors.
Bio-methanisation plant is an anaerobic digester packed with PVC
media. This media contains circular rings with elasticity to provide
more occupying area for the growth of cell mass.
38
Table 7.1.The design and other factors of existing digester
S.No. Description Detail
1. Type of Reactor Anaerobic Biomethanisation
System
2. size 10m height x 28 m dia
3. Capacity 6000 cu.m
4. Inflow 750 cu.m / day
5. Hydraulic Retention time 8 days
6. Inlet design COD 100000mg/Lt
7. Inlet design BOD 50,000 mgs/Lt
8. COD reduction % 60%
9. BOD reduction % 90%
10. Type of Media PVC flocor
39
7.6.Performances
Pollutant removal
In stillage, soluble COD removal efficiency will not be less than sixty
percent and soluble BOD removal will not be less than 90.If higher
COD and BOD is in inlet effluent then dilution shall be practiced.
Biogas Production
The Stillage containing higher organic load , the biogas generation is
subject the theoretical value of 0.35 Nm3 CH4 per kg COD removed,
the biogas generation of the anaerobic unit will not be less than
0.53m3 biogas per kg of
COD removal.
Energy Production
Assuming the average biogas calorific value 4500kCal/m3, the
minimum yearly energy that can be recovered for a run of 300
days/year is 3480 tons fuel oil
40
8.AVENUES FOR CONSERVATION OF ENERGY
It has become the paramount need of the sugar sector at present to
become energy efficient for maximizing their profits as well as to
support the government, in their quest for additional energy resources.
Any augmentation from sugar sector will be a boon to any national
economy as it will not beat the expense of their fossil reserves.
Therefore for every unit in the sugar sector, a self introspection in the
form of a detailed energy audit will do a world of good at this
juncture, without waiting for the intervention of statutes. In this
context, sharing of experience based on the energy audits carried out
and the improvement made in some of the sugar factories in our
country will be very useful.
8.1.Steam Generation
At the outset the steam and power production areas will be
highlighted before going into the details of energy consumption areas.
For steam production bagasse being the only fuel, it is very important
to ensure that uniform feed of the fuel of not exceeding 50% moisture
content is assured always to the boilers. More than 60% of the
factories in India work with Boiler systems of less than 20 kg/sq.cm
pressure rating. Whatever may be the operating parameters of the
boilers, the need for maintaining the boilers in excellent health to
work at the rated efficiencies does not require over emphasis.
Typically in a well maintained boiler there is a variation of 0.8% in
the efficiency of boiler for every percentage of moisture variation in
bagasse. A moisture level of 50% in bagasse is generally taken as the
41
benchmark as all the sugar mills as well as boiler manufacturers adopt
this for their designs. Though bagasse drying can improve boiler
efficiency further, it has to be carefully planned in the heat balance of
the plant, while optimizing the power cycle.
It is important to take note of the following thumb-rules for
quantifying the energy conservation in boiler operations. Every 20°C
reduction in back end temperature: 1.0% increase in boiler efficiency.
10% reduction in excess air: 0.4% increase in boiler efficiency.1%
reduction in bagasse moisture: 0.8% increase in boiler efficiency. For
1TPH steam generation with 0.5% increase in boiler efficiency, there
is saving in 3 kg/hr of bagasse. For 1 TPH steam generation, by
installing flash steam recovery system for continuous blow down in
boilers, there is a saving of 1.5 kg/hr of bagasse. These figures may
vary according to boiler parameters.
The above details will emphasize the need for maintaining optimum
operational conditions required for efficient performance of mills and
boilers. The factory was quite old but with modern facilities in a
number of areas. The boilers (4 nos.) were also old and of low
pressure designs but retrofitted with system for efficiency
improvement. Because of poor state of maintenance the boiler
efficiencies recorded with the high moisture % in bagasse was ranging
from 50% to 56%. The bagasse steam ratio was 1.85 only against the
optimum of 2%.
It was found that by correcting some minor problems of maintenance
of boilers and by effecting some improvements like reduction in
excess air level, reduction in back end gas temperature, provision of
42
better bagasse feeding arrangement etc. the efficiencies could be
improved to 60% and above, which could reduce the bagasse
consumption
8.2. Power Generation
While dwelling on Energy audit, it will be relevant to highlight the
importance of improving productivity of bagasse. Moisture percentage
in bagasse is a critical factor in enhancing the productivity of bagasse
in addition to efficient boiler conditions.
Modern high efficiency boilers of high pressure designs i.e. pressures
upwards of 45kg/cm2 aim at efficiency of 70% plus for bagasse firing,
and with these boilers productivity of bagasse is further increased with
the increase of operating pressures. Adopting higher pressure power
cycle will increase the power output from the same bagasse.
It is seen that the bagasse steam ratio which used to be of the order of
1:2.0 with old low pressure, low efficiency systems have improved to
1:2.45 in the modern cogeneration systems which is a clear
improvement in the productivity of bagasse and a positive step
in energy conservation through improved boiler designs for higher
efficiency.
Thus this promises to be the key area in sugar industry for future
indexation of the statutory energy regulatory authority that has been
formed to monitor energy conservation
43
8.3. Steam Consumption
Steam consumption of the factory including refinery and distillery is
about 53.5% and for sugar factory alone it is around 49.5 to 50%. By
introducing continuous pans for B and C- massecuite and completely
avoiding the use of exhaust steam for pan boiling it is possible to
reduce steam consumption
44
9. CONCLUSION
Energy audit is a very important tool in transforming the fortunes of
any organization. Norms should be set and continuously reviewed
during the course of operations, just as any other financial or
production or commercial parameters. Particularly where
cogeneration of power is involved in a sugar industry, every unit of
power saved and every ton of bagasse saved will add to the additional
revenue of the organization.
Potential for energy conservation in sugar industry is immense
because of the fast developments that are taking place in the industry
as well as the traditionally conservative outlook of the Industry in
India and their present status.
The potential for saving cost per annum will be different in different
places and there are bound to be concern areas in all places if honestly
looked into, since no one could claim to have reached the state of
perfection. Therefore it will be prudent for all organizations to set
up energy committees within the organization, identify lacuna
dispassionately and rectify them immediately. Total commitment,
involvement and guidance of top managements are essential for this
and if implemented effectively, it will usher in prosperity not only to
the organization but also to the Industry and the Nation at large.
45
10.APPENDICES
(in the order of arrangement)
1. Factory flow chart of Amaravathi Sugar Mill
2. Schematics of Fermentation Process
3. Schematics of Distillation Process
4. Biomethanisation Plant
46
