Journal of Scicnti fi c & Industri al Rcsearch Vol. 58, February 1999, pp 76-82

Energy Conservation in Sugar Industries*

A N Pathak

Council of Science & Technology, UP, Yi gyan Bhavan, 9 Nabiull ah Road, Suraj Kund Park, Lucknow 226 018, India

Suggestive measures for minimizing energy and heat losses in Indian sugar industries are discussed. Suggestions are enumerated to achieve the target of effecti ve conservation of energy, heat and fu el through modernization of equ ipments and technology. Use of al ternat ive sources of energy like so lar energy, bioenergy, etc. for power generation and utihzati on of byproducts of sugar industry by value additi on, to increase the profitabi lit y of t'his sector is also di scussed.

Introduction

India is the top ranking sugar producing country in the world. Yet average size of sugar factories in our country continues to be undul y small. The capacity range of sugar factories varies from 400 TCD to 7000 TCD. The breakup of about 425 sugar factories accord­ing to their capac ity range is given in Table I.

The sugar consumption in India is increasing at the rate of about 7-8% per annum. The total internal con­sumption in India by the year 1999-2000 is expected to be 16.94 mi llion M.T. and per capita consumption is expected to grow to 16.75 kg per annum. Recovery in the sugar mills varies from 9 to 12%. A reduction in tota l sugar losses and energy consumption can be made pos­sible through implementation of n;odern equipment, modern technology, newer systems and techniques. The energy costs are ri sing steadily and the ava il ability of fuel is becoming scarce. Therefore, the conservati on of energy in sugar industry has become a matter of great signi ficance. The sugarcane bagasse is a renewable source of bioenergy . Many factories are using sugarcane bagasse with some add itional fuel to meet their energy requirements. The usage of this additional fuel can be avoided by modern ization and energy conservati on in sugar plants. The excess bagasse could be used as raw materi al for va rious va lue-added products. The other by-products like filtercake and molasses can be used for production of alcohol and down-stream products which can significantl y improve profitabi lity of the sugar in-d 1-) ustry -.

"This paper \Vas presented by the author on the occasion of Energy Conservation Day, 14 Dec 1997, at Shak ti Bhawan, Lucknow

The target of sugar production and the installed ca­pac ity needed to meet it for the 8th and 9th plan peri ods are given in Table 2.

The energy requirement in various un its of a sugar mill is given in Table 3.

Adoption of new systems and designs, as required for better performance and higher efficiency for improving the economics of sugar industry, is l}' 'must' , as sug­gested by Sood6,7.

Major Processes involved in a Sugar Mill

The units employed in a sugar mill are: I. Juice extraction Plant (JEP) The juice extraction plant in a cane sugar factory

primari ly consists of sugarcane unloading, conveying, cane preparati on and milling.

1.1 Cane Handling .- The cane unl oading can be done both manuall y and mechanically. The sugarcane is mechanically unloaded from trucks and bu ll ock carts on a moving slate conveyer through mechanical unloaders. Some sugar factories are also equipped with an arrange­ment of truck or wagon trippl ers which I ift the truck or

Table I - Break up of sug <lr fac tories of India accordin g to

their production capacity

S.No. Si ze Rangc, TCD Numbers

B ~l ow 1250 75

2 1250 140

3 125 i - 2000 80

4 200 1 - 2500 50

5 2501 - 3500 30

(j Above 3500 50

PATHAK: ENERGY CONSERVATION IN SUGAR INDUSTRIES 77

Table 2 - The target of sugar production and install ati on Table 3 - Energy requirement in different units of a sugar plant

capacity required for 8th and 9th Plan periods - COl/It!

S.No. Units Percentage

Plan/Period Target of Installed capacity production required 3.2. Energy Saving (million tonnes) (million tonnes) Alternatives

8/h Plall 3.3. Automation

1990-9 1 1147 1207 4. Sugar Crystallization 15-20%

1991-92 12.07 12.70 4.1. Energy Requirements at

1992-93 12.17 12.8 1 Vacuum Pans

1993-<:)4 12.78 !345 Design Selection

1994-95 1341 14. 12 Energy Savings At Vacuum System

91h Plall At Cooling System

1995-96 14.08 14.82 Continuous Pans

1996-97 14.79 15.57 Pan Automation

1997-98 15.53 16.34 Install at ion of

1998-99 16.30 17.17 Mechanical Circulators

1999-2000 17. 12 18.02 Molasses Conditioners

4.2. Energy Requirement at

Tab le 3 - Energy requ irement in dilTerent unit s of a sugar pl ant Crystal I izers

5. Sugar Centrifugals 10-15 % (Tota l Power-5000 kW)

5. 1. Energy Saving at 1 Continuous Centrifugals

S.No. Unit s Percentage 5.2. Selection of Process

I. Juice Extract ion Plant 40-45 % 5.3. Sugar Drying

1.1. Cane Handling 5-10% 54. Choice 0" Magma Liquoring

1.2. Cane Preparation 15-5.5. Schemes of sugar 20%

conveying and grading 13. Milling 25%

O. Steam Generation 5-10 % 0. of Mills

6.1. Efficient Usc and Mill Speeds Generat ion of Steam

Pressure Feeding Steam Pressure 42-45 kglcrn2g

Mill Transmission Geari ng Steam Temperature 4 15°C Power Requiremcnt Des ign of Boilers Automat ion Furnace Design

2. Juice Purilication Plant 10- 15 '1( Des ign of Accessories Energy/Steam Savings Heat Recovery units

2.1. Jui ce Heating Bagasse Drying 2.2. Treatment of Jui ce 6.2. Boiler Operation 2.3. Separation 6.3. Boiler Automati on 3. Saving of Steam During :1 0% 01 tot al 7. Powel' Gene.-ation

Evaporation steam required 7.1 . Cogeneration of Power for sligar pl allt

3. 1. Arrangement Models 7.2. Cogenerat ion Models

(' OI/1d

78 J SCI IND RES VOL 58 FEBRUARY 1999

wagon loaded with cane to an angle fac ilitat ing direct di scharge of sugarcane to the conveyer. From energy

saving view point, trippler arrangement is superior to others.

1.2 Preparation - The sugarcane is prepared into a

fibrous mass with the help of a set of cane cutting kni ves

or shredders. The bulk density of the whole cane is about 150 to 160 kg per cubic metre, whi Ie that of prepared cane ranges between 350 and 475 kg per cubi c met re.

A good preparation or cane is essenti all y required for (i) a higher through put, and (ii) reducing energy con­

sumption during the process of juice extracti on. In­stalled power requirement for preparation of cane can

be 50 to 100 HP tonnes fibre per hour. It is proved that app licali on of higher power in cane preparation results in overa ll reducti on in power and higher ex tracti on in

the cane mi li s. However, it is to be optimi zed. It has also been proved that a sequence of es tablishment of differ­

ent sets of cane kni ves results in proper cane preparati on and reducti on in energy consumption.

The energy can be saved by proper use of electroni c motors with 15 to 17% slip for dri ving cane kn ives.

Automat ic electroni ca lly regul ated cane feed ing equip­ment helps in reducing the power consumption. Steam

turbine drives are not beneficial in cane preparati on and ,

therefore, these shou ld not be used. 1.3 MiLling Operatioll - The prepared sugarcane is

passed th rough a set of 3 or 5 ro ll er cane mills for

ex traction of cane juice by high hydrauli c pressures . The mill s are operated at a speed of 10- 15 mt/minute through a steam or electric drive with the help of a set of reduct ion gears. The cane extract ion plant consumes about 40 to 45 % of total mechanical/electrica l energy required in sugar pl ant - 15-20% for cane preparation and the rest 25% for cane milling operati on .

Energy consumption can be optimi zed using 5 num­bers of ro ll s in 3-roller mill s, by adjusting the mill speed to 10-1 I metre per minute, by 2-roller pressure feeders and roughing hard surfaci ng of the mill ro ller ce ll s, optimi sing operating speed of the mill s in close proxim­it y or the rated speeds of the mill turbine and by using in close mult i-stage helical gear boxes to improve trans­mi ss ion efficiencies. However, the crown pin ion wou ld remain a major loss of power during transmiss ion which can be overcome by in stal l ing individual hydraulic mo­

tors on each rol ler of a mi ll.

Power Saving

During the milling of cane the power is consumed by the following un its:

(i) Bagasse (ii ) Fri ction between shafts and bearings of the rollers (iii ) Friction between bagasse and trash plate (iv) Friction of scrapers and toe of the trash plate

against the rollers, to which should be added the work of di slodging the bagasse at these points

(v) In driving of the intermediate carriers, and (vi) Gears . The consumption of power can be calcu lated by the

formulae given in Handbook of Cane Sugar Engineering by Dr E Hugo!. The sugar factory owner has to necess i­tate care in selection of the hydraulic loading at the mi li s, selection of mill bearings, des igning and s tting of the trash plate, des igning of the intermediate carrier gears, etc, such that all these result in minimum consumption of power during milling operation. However, automat­ion for controlling the milling operations may result in improved sugar ex tracti on and reduced energy cost. The areas of automati on can be: feeding, control of mill speeds, applicati on of maceration water fo r jui ce extrac­tion, etc.

Juice Purification Plant

The purifi cati on of juice in volves remova l of various non-sugar inorgan ic salts, colloid s, organic acids, co l­ouring matter, etc. This is achi eved by heating of juice and treatment wit h chemi cals li ke lime and sulphur and separation of the prec ipitated impurities.

The equipments deployed are heat-exchangers fo r heating of juice, equipment to prepare milk of li me , sulphur di ox ide, etc., reactors, settlers, clar ifi ers and industrial fi lters. The poss ibili ti es of energy saving dur­ing these steps are:

(i) Juice Healing - The exhaust steam from the pri me movers or vapours led from the evaporators is used fo r heating of juice in a set of mu lt iple pass juice

heat-exchangers where it is heated from 20 - 25°C to

102°C in one or more stages, depending upon the selec­tion of process of cleaning. Substanti al heat energy in the form of latent heat released on condensati on of steam/vapours is consumed for raising the temperature of the ju ice. Jui ce heaters should be properl y lagged and condensate shou ld be suitably recyc led. The automati on of steam/vapour entry for heating ju ice lTlay result in

PATHAK: ENERGY CONSERVATION IN SUGAR INDUSTRIES 79

energy savings. Total steam consumption should be

optimized in a sugar factory . (ii) Treatment of Juice - The loss of heat during

treatment of juice with various chemicals results due to

flashing and radiation practices of receiving juice in a

separate tank after treatment and before pumping to next

section of the plant. It should be discouraged. It should

directly be pumped from the reactor itself which should

be properly lagged to prevent heat loss due to radiation . (iii ) Separatioll - Settlers or industrial filters retain

juice for 2 to 3 hours which results in appreciable loss

of heat and drop in temperature to less than 90DC from

more than 100De. This heat loss can be minimized by

reducing the retention period and lagging the clarifier

shorter retention time with 30 to 45 minutes, which is

very common in the Australian Sugar Industry. It should

be adopted by sugar factories in India too . The factories in which the juice is filtered, the wash­

ing of filter cake should be done very carefully because

these washings have to be evaporated, resulting in more

consumption of steam. Minimum water for maximum

recovery of sugar from filter cakes should be used. This

can be achieved by maintaining cake porosity, by appli­

cation of water in a mist form from correctly designed

nozzles and by maintaining the desired pressure at the

wash nozzles. The quantity of filtrate return in case of rotary vac­

uum screen filters should be carefully controlled be­

cause its excess may result in heat loss. It has been

observed that this quantity may vary between 7-20% on

cane weight basis and, therefore, it offers a good scope

for reduction.

Evaporation

The various configurations of evaporators' arrange­

ment are possible to evaporate juice from 14-16 Brix to

60-65 Brix, which accounts for about 30% of the total

heat requirement in the process. The evaporator arrange­

ment should be such that it is possible to provide about

130-150 kg of vapours per tonne of juice for heating in

the juice heaters and about 230-270 kg of vapours/tonne

of juice for crystallization of sugar in the vacuum pans.

Therefore, a total of about 250-400 kg vapours/tonne of

juice additionally should be available from the evapora­

tor station to meet the requirement of juice heaters and

vacuum pans .

Further Reduction in Steam Consumption

It is possible to reduce further the consumption of steam through the use of thermo-compressors , mechani­cal vapour recompressors, liquid heat-exchangers for heating of juice, etc.

Automation

The automatic control sys tem of the evaporator should be designed in such way that the syrup, leavi ng the evaporators has a predetermined consistency. This design should also take care of the time-lag between the admittance of steam and exist of sy rup. The control of steam should also be linked with the flow of va pours for heating and boiling of juice.

The maintenance of consistent hi gher brix of syrup at the evaporators is essential in view of the multipl e effect advantage at this station compared to the other stati ons like juice heating and pan boiling.

Sugar Crystallization

Energy requirement by Va cuum pans

Through proper controls, energy can be saved at this stage which is estimated to be 15-18% of the total energy required in a sugar plant. This could be reduced to about 10-12% by taking remedial measures. The automation of vacuum pans can be of great advantage in reducing both the mechanical/electrical energy as also the heat energy requirement in this area of operation. Molasses conditioners should be installed in line to feed from the storage tank to the vacuum pans. The inline conditioning of the molasses avoids the chances of molasses cooling during the storage.

Energy Requirement by Crystallizers

The massecuite when discharged from the vacuum pans is received, stored and cooled in a set of cooling crystallizers, the massecuite is subjected to either air cooling in case of high grade massecuite or water cool­ing in case of low grade massecuite. The degree of supersaturation further increases during cooling, result­ing in deposition of more sugar on the avai lable/existing crystal surface. The energy requirement of crystallizers can be reduced by installing continuous vertical crystal­lizer which will then dispense with the use of a large battery of batch crystallizers. A large number of facto­ries are already making use of the continuous crystal­lizers and their use should be spread to as many more factories as possible.

80 J SCI IND RES VOL 58 FEBRUARY 1999

Sugar CentriJugals

The energy consumption at centrifugals is also re­lated to the selection of the process. The methods being used for cooling, conveying and grading of sugar can be modified to save energy. This primarily may require the use of fluidized bed drier for cooling and conveying. The design of the graders can also be modified so that a fewer number of graders can handle the required through put.

Steam Generation

The factors responsible for efficient use and genera-tion of steam are:

• Steam pressure • Steam temperature • Design of boilers • Design of accessories • Design of furnaces • Use of heat recov,ery units, and

• Bagasse drying. The commonly used furnaces in the sugar factory

boilers are : (i) Step grate furnace, (ii) Horse shoe fur­nace, and (iii) Spreader Stroker furnace .

Boiler Operation

The automation in boilers can be of immense use in achieving a higher boiler efficiency and hence reduced energy costs. The automation in boilers can include control of C02 and/or 0 2 per cent, steam flow, feed control, excess air control and excess 0 2 monitoring system, etc .

Power Generation Many sugar factorie· in the world are producing or

co-generating additional power for transfer to the grid or for use in the ancillary industry . Almost all factories are equipped with turbo generators which are generally of the back pressure type. Live steam from the boilers is used for operating turbo generators set for producing power. Exhaust steam is used for this process .

Use of Non-Conventional Energy in Sugar Industry

Solar energy and bioenergy can be used in the sugar industry for energy conservation. Water to be fed to boilers can be preheated through solar water heaters. Bioenergy in tenns of methane gas can be generated from sugar/distillery effluents which could supplement the fuel consumption by 50% in oil-fired or coal-fired

boilers. Energy can also be produced from bagasse and other byproducts of sugarcane industry8-IO

Energy Audits and Measurements in a Sugar Factory

An energy conservation project should be initiated with an energy audit of a sugar factory to achieve the most economical reduction of energy costs in order to save the maximum energy at the lowest cost. The man­ner in which the total energy utilization at the plant is managed between the different stages is determined by energy measurements, to be able to draw up an energy balance for the plant.

The energy audit comprises (a) Acquaintance with the energy systems of the

factory, (b) Infonnation collection regarding energy utiliza­

tion, production, etc. to base these energy balance, (c) Planning and execution of energy measurements,

and (d) Infonnation collection regarding the energy sys­

tems development to serve as a base for drawing up energy savmg measures.

Energy Saving in a Sugar Plant

The various means through which the Indian sugar industry is attempting to save energy and/or fuel are:

(a) Efficient production of steam (b) Efficient use of mechanical/electrical energy (c) Efficient use of steam This can be further elaborated as under: • Maximum generation of steam per unit bagasse

or fuel • Maximum generation of power set unit of steam • Minimum consumption of power • Minimum consumption of process steam • Minimum line losses both on account of steam

and power transmission • Maximum heat recovery through reclamation of

a hot condensate, flashing, etc. • Minimum usage of chilled water.

Technologies of the 21st Century in the Sugar Industry

Various new and futuristic technologies and proc­esses that could be used in (he sugar industry are:

'\

PATHAK: ENERGY CONSERVATION IN SUGAR INDUSTRIES 81

(i) Cane Handling - Computerized cane weighing

machines should be used . The present mechanical

weighing scale can be replaced by electrical scales . (ii) Cane Preparation- Many factories in Australia

and South Africa use heavy duty shredders to achieve

the preparatory index above 90% and this should be

evaluated under Indian conditions. (iii) Milling Juice Extraction Technologies - Mis

Taxmaco Ltd, Calcutta has collaborated with Walkers of Australia for a new design of a constant ratio 5-roller

mill. This design of the mill has capability to give higher

milling efficiency and low energy consumption. It has

already been commissioned in a sugar factory in Tamil

Nadu. The indigenous development in the field has not been

lagging behind . Mis WIL, Pune, have developed self

setting 3-roller mills and a milling tandem of this design

have already been commissioned in a sugar factory in

Tamil Nadu. The possibility of adopting diffusers in the cane sugar

industry should be reevaluated from the view point of

capital cost, maintenance cost, energy consumption and

extraction efficiencies. (iv) Low Pressure Extraction System - The power

requirement of the system is claimed to be about 0.6 kW

per TCD. (v) Cane Sugar Separation Technology-The indus­

try is rapidly replacing the steam turbine drives with

variable speed DC drive, which results in fuel saving and

gives a better flexibility in operational control. Hydrau­

lic motors for operating the mills can be a breakthrough

for the sugar industry in India in near future. Modifications in design of other accessories like im­

bibition equipment, etc. would also bring about saving

in energy and costs. (vi) Juice Treatmenl- Use of hydrogen peroxide for

treatment and removal of colour in syrups has been

found highly successful in Karnataka. This can be

adopted for a better removal of colour with reduced

sugar losses. The possibility to use short retention clari­

fier should be evaluated to avoid losses due to inversion.

Use of membrane filters and bag filters also offer good potential for achieving better quality of filtration in

future. Extensive studies have been conducted for c1ari-f· . f" b b f ' l . ))-) 3 IcatlOn 0 JUice y mem rane I tratlon .

(vii) Evaporation - The combination of extensive

vapour bleeding, condensate flashing and recirculation,

use of thermo-compressorsIMVR' s, etc. can reduce the

process steam consumption to about 30% on cane against the present 45% in the Indian Sugar Industry.

(viii) Sugar Crystallization - Use of continuous vacuum cooling crystallization system developed by a French Sugar Group (Beghisay) can improve the per­formance of crystallization section .

(ix) Centrifugals - To save energy, Mis Krupp, Germany, have developed a new design of continuous centrifugals where two centrifugal baskets are mounted on a common shaft and driven by a common motor.

(x) Sugar Handling - A firm in Bangalore has developed a sugar drier cum conveyor on the principle of fluidized-bed drier. It has been installed in Karnataka. The size of this equipment is 5m x 1.2m x 5m which can handle up to 150 bags of sugar/hour.

(xi) Steam Generation - The sugar industry can opt for modem design of boi lers and new furnaces based on following principles :

(a) Boiler with membrane wall construction (b) Furnace design for mixed fuel (c) Fluidized-bed furnaces Ponni Sugars at Erode has installed a Igni Fluid make

boiler of 25 tonneslh capacity and 45 kg/cm2 pressure which is very compact in design and is highly efficient. It can use coal, sugar pith and lignite and other alternate fuels too.

The concept of tap power directly from coal is under development of BHEL and BARC, Bombay. it is esti­mated that this technology can offer an overall effi­ciently of 60% against 30% at present through steam at turbo generators .

(xii) Power Generation - The conventional method of producing power through back pressure turbines can be replaced with production of power by extraction-con­densing turbines or by topping turbines. In this manner additional power can be produced for use in other indus­tries or for bleeding to state grid.

Automation at various sectors of sugar plant shall result in improved productivity, reducing sugar losses and energy cost. The author affirms that if the above mentioned improvements are incorporated, there could be 30% energy conservation in the sugar industry .

Conclusions

Recent developments in the sugarcane processi ng in the small scale sector have been reported by Gehlawat )4.

There are a number of other actions and precautions that can help to minimize energy and heat losses in a sugar plant. These include:

82 1 SCI IND RES VOL 58 FEBRUARY 1999

(a) All pipe lines, tanks which conveyor receive hot juices, steam, bled vapours, etc. should be properly lagged for avoiding radiation and condensation losses. Similarly, all heat-exchangers should be lagged.

(b) Pumps and motors should be carefully selected. it has been seen that many factories install over size pumps to cater to any future requirements during expansion. This is an incorrect approach and results in a recurring loss of power.

The type of pumps should be selected after matching the duty requirements with the performance curves of the pumps to achieve maximum efficiency. The use of screw pumps, wherever required, would also result in saving of power'.

(d) The slat and rake type conveyers should be re­placed with belt conveyers, if possible.

(e) The power factor of the electric distribution sys­tem should be maintained above 0.95 through use of capacitors, wherever possible.

(f) Hot condensate should be collected and suitably recycled to the boilers or to the process. A proper recy­cling of the condensate can totally eliminate the use of cold water in the process, and at the boilers. The flashing of condensates should also be recovered.

(g) A proposal to generate electric power at 3 k Y or 11 kY should also be considered and high tension motors at all major consuming ends, to reduce transmission losses.

Acknowledgement

The author is thankful to Dr (Mrs) Abha Srivastava for her help in preparing the manuscript.

References

By-products of Sugar Industry, Mauritius Chamber of Agri­culture, Memorandum to the Commission of Enquiry into the Sugar Industry, 1983.

2 A Master Plan for Modernization and Rehabilitation of the Sligar InduJt!}', Mauritius Chamber of Agriculture Specially prepared for the Sugar Enquiry Commission , 1983-84.

3 Dubey R S, Dther By-products Based Indllstries, Bhartiya Sugar Directory, 1983-84.

4 Sood R S, Staff Paper on Bye-products of Sligar In dllst I}'

(Sugar Expert to the Government of Mauritius) 1983-85 (un­published)

5 Development of the By-product Industries, Proceedings of All India Conference of Cooperative Sugar Mills, organized by National Federation of Cooperative Sugar Factories Ltd, New Delhi and National Cooperative Development Corporation, New Delhi, on 20th and 27th September 1989.

6 Sood H C, Modernization Programmes for Sugar Industry , in Modernization of Indian Sugar Industry , edited by J K Gehlawat (Arnold Publishers, New Delhi) 1990.

7 Sood H C, A plea for redesigning sugar machinery to maxi­mize production of sugar at low cost , Malwrashtra Sligar, 1987.

8 Sood H C, Staff Paper on Electric Genera/ion from Bagasse, for Sugar Enquiry Commission, Government of Mauritiu s 19!D-1985 (unpubli shed).

9 Particle Board Proj ect based on Bagasse, Bhartim Sligar, January 1990.

10 Mallritills SlIgarcane /3.v-prodllcts Stlldv, United Nations In­dustrial Development Organi zation Report l' 81/24 Appendi x 4&5, Nov 1981.

II Godbole M S, Potential or membrane applications in Indian Sugar Industry, Proc Indo-EC Workshop (Organized by DST), 1989.

12 Pathak R N, Ruikar A M, Bopardikar S V. Mal she Y C & Gehlawat J K, Achieve high Sugar Recovery and Steam Econ­omy in Sugar Industry Through Concentrati on of Secondary Juice by R 0 , Chem Ind News, (1983) 259.

13 Gehlawat J K, Clarification of cane juice by the membrane technology, Proc STAI Seminar, Bhubaneshwar (April 30 1995) pp 20-30.

14 Gehlawat J K, New developments in sugarcane processing­A boon to mini sugar plants and khandsari units, J Sci Ind Res, 57 (6) (1998) 299-305.