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Waste Heat Sources in Sugar Factory and Their

Utilization for Cooling Condenser Water

By

R.K.Kulkarni Dr. S.P.S. Rajput

Research Scholar Asst. ProfessorMechanical Engineering Department

M.A.N.I.T.

Bhopal(MP)

India

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Overview of Presentation

Introduction

Identifying Waste Heat Sources

Present System for Cooling Condenser Water

Proposed Cooling System Model

Working of Proposed System Benefits of Proposed System

Conclusions

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Introduction Sugar Industry- Second Largest processing industry

Stages in Sugar Manufacture-Extraction of Juice

-Clarification-Evaporation and Concentration

-Forming and separating crystals

Energy Consumed- Mill Driving Turbines- Mechanical

Driving auxiliary units- Electrical EnergyEvaporation and Concentration of juice- Heat Energy

Ways to Conserve Energy

1)Modernization of Old equipment/ machines

2)Adding of new systems like- Spiral juice heaters, Condensate flashingsystem, Continuous vacuum pans, Auto feeding of bagasse

3)Co generation.

4)Appropriate insulation of equipments

5)Efficient cooling system

6)Waste heat recovery systems

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Boilers40 T

15 T

15 T

Power

Turbines2000 kW

1600 kW

De Super heater

I II III IV

Boilers

20 T15 T

Feed Water Tank

Mill Turbines

375kW X 51500 kW X 1

Common

Header

Spray Pond

Jet Condenser

Evaporator Bodies

2 pumps

124 kW

3 pumps

189 kW

Fuel

Blow

down

Fuel

Flue Gas

Hot Condensate

Vapors

Identification of Waste Heat Sources

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Boiler Flue Gases

Waste heat content of flue gases

Q = 4.187K ((1-W) (1.4M-0.13) +0. 5) * tWhere

Q = Amount of waste heat in flue gases kJ/kg of sugar

K = k1*k2

K1 = percentage of bagasse in cane = 28 % from data of factory (min value)K2 = Quantity of cane required to get unit quantity of sugar. =11 from data of

factory

W = moisture content in bagasse average = 50 % according to data in factory.

M = ratio of actual air to theoretical air = 1.4

t = temp of fine gases going to chimney = 180 deg C.Thus waste heat content in flue gases can be calculated as

Q = (4.187)(0.28)( 11) ((1-0.5) (1.4*1.4-0.13) + 0.5 ) * 180

Q =3285 kJ/kg of sugar

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Boiler Blow down Water

Blow down- To control the amount of TDS in the boiler water for smooth

operationBlow down amount- varies form 2 to 3 % of evaporative capacity or steam

generation rate.

Heat content of blow down

Q = Mb.Cb. TbQ = Heat carried in KJ/kg of sugar

Mb = average quantity of blow down in kg/kg of sugar

= 2.5 % of evaporative capacity of boiler (Steam Generated)

= 0.025 of ( 50% of cane crushed)

= 0.025 of (0.5 * 11) per kg of sugar

Cb = Sp. Heat of water =4.187 kJ/kg K

Tb = temp of blow down. = 340 deg C

Q = 0. 025 (0.5 *11) * 4.187*340

= 195.7 kJ/kg of sugar

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Hot Water Overflow

Condensate from I and II evaporator body is used as feed water.

Condensate from III,IV body and pans is used as hot water for theprocess. Normally the condensate produced is more than that requiredfor the process. By measuring the excess quantity of hot water, heatcarried by excess water can be calculated.

Q = Mc.Cc.Tc

Mc = quantity of surplus condensate

= Average 7.5% on cane

= 0.075 * 11

Cc = specific heat of hot water = 4.187 kJ/ kg K

Tc = temp of hot water = 65 C

Q = (0.075) (11) (4.187) (65)Q = 224.5 kJ/kg of sugar

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Summary of Waste Heat Sources

S.No. Source Heat Content

kJ/kg of sugar

1 Flue gases 3285

2 Boiler blow down 195.7

3 Hot water 224.5

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IV

BodyPans

JetCondenser

Spray Pond

2 pumps

124 kW

3 pumps189 kW

Vapors

Hot water 40-

45 deg C

Cold water 30-35 deg C

Present Cooling System

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Present System of Cooling

Vapors from multiple effect evaporator and vacuum pans enter the condensers

at about 60-65 deg C The heat from vapors is absorbed by cold waterintroduced in the condenser. The temperature of this cold water is around 30-

35 deg C. The heat exchange between vapors and water is affected by-

1) Contact time of vapors with cold water

2) Contact surface offered by cold water to vapors

Water then flows out under gravity along with the condensed vapors at about

40-45 deg C. The temperature of incoming and outgoing water changes

according to ambient conditions.

Warm water leaving the condenser flows to the spray pond by gravity channeland it is cooled with the help of spray nozzles. Cold water at about 30 to 35

deg C returns through gravity channel and it is pumped to the condenser. Thus

it is a closed system.

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Limitations of Present System

The power consumption for pumps- 313 kW

Steam to Bagasse Ratio- 1.8 to 2

Increase in temperature of incoming water affects condensation of vapors in

condenser and in turn affects vacuum in evaporator body.

Increase in boiling point in the body increases the steam and bagasse

consumption.

Large quantity of cooling water is needed.

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Proposed System Model

Boilers

Flue gas

ScrubbingSystem

HeatExchanger

Absorption

Chiller

Flue Gases Water

Flue gases

to chimney

Hot Water

Cold Water

To condenser

Hot water from

condenser

Water

out

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Proposed System

Aim-Reduction in the inlet temp of cooling water by incorporating a vapor

absorption unit which runs on waste heat in boiler flue gases. Components-

1) Scrubbing system to remove suspended matter from hot flue gases.

2) A heat exchanger between flue gas and water.

3) Absorption cooling unit.4) Pumps and fans.

The hot flue gases from boiler contain soot etc. Full scrubbing of gas is not

needed at this stage and only large particles need be removed. The upper spraychamber is of standard construction for even distribution of working fluid.(scrubbing liquid return.)

A cross flow heat exchanger or shell and tube heat exchanger will be suitablefor the heat exchange between gas and water.

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A Typical Scrubbing System

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Ranges and Capacities of Absorption Chillers

Hot water driven Temperature Capacity Range

Low Temperature 70-110 deg C 100-650 NTR

Medium Temperature 110-150 deg C 100-1400 NTR

High Temperature 150-199 deg C 100-1400 NTR

Low Temperature 70-110 deg C 10-80 NTR

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Proposed System

Flue gases from boiler will be passed through a scrubbing system where the

suspended matter and un burnt particles will be removed. Then this gas will be passed through a heat exchanger where the water will be

heated by flue gases.

This hot water will be then used as heat source for the absorption refrigeration

system. The hot water from the condenser will be passed through theabsorption refrigeration machine where its temperature will be decreased.

This cold water will be then passed to the condenser for cooling purpose. The

low temperature hot gases can be then diverted towards chimney.

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Benefits from Proposed System

Proposed system will be able to cool the condenser cooling water tolower temperature.

The power required for spraying the water will be saved. The power will berequired for pumping the condenser water through the absorption chiller andheat exchanger. It is proposed to estimate the saving in power by thisarrangement.

It also expected because of low temperature of cooling water rate ofcondensation of cooling water will be more and it will create more vacuum inthe evaporator and pans. This will lower down the boiling point in theevaporator and it will reduce steam consumption and ultimately result in

bagasse saving.

As the particulate matter in gases is reduced due to scrubbing system, it willreduce the pollution at the factory site.

As the temperature of cooling water is less the quantity of water required forcondensing vapors will also be less. This will result in saving of water whenthere is scarcity of water. Low boiling temperature will improve the quality of

sugar.

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Conclusions

Energy audit is an important tool to identify the areas of energy conservation

in sugar factory. Waste heat sources in sugar factory are- Boiler flue gases

Boiler blow down

Hot condensate

Most important waste heat source- Boiler flue gas

Boiler flue gas heat can be utilized to run an absorption chiller.

The chiller will cool condenser water.

The power required in spray pond can be reduced. There will be improvement in condensation of vapors in condenser.

Low boiling point of juice in evaporator can save steam and bagasse.

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Acknowledgements:

1) The Malegaon Sahakari Sakhar Karkhana Ltd. Shivnagar , Tal. Baramati,

Dist.Pune.2) Vasantdada Sugar Institute Manjari (bk) Pune.

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References

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Thank You