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Simultaneous production of two forms of energy Thermal Energy

Electricity / Mechanical Energy

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Conventional

Plant

Loses up to70%

Efficiency is30-40%

Fuel(100%)

CogenerationPlant

Loses up to10%

Efficiency upto 70-90%

Fuel(100%)

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Sector Potential, MW Realizable

Potential, MW

Distilleries 3500 2500

Cement 600 400

Chemicals 900 600

Fertilizers 1200 750

Metal Industry 1060 700

Sugar 5000 3000

Refineries 800 600Paper & Pulp 1000 750

Textile 1200 800

BCHP 650 400

Other Sector 750 500

Total 16000 11500

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Natural gas

CoalBiomassBagasse (waste product from sugar cane processing)

Waste gas

Sludge gas from sewage treatment plantMethane from landfills and coal bed methane

Liquid fuels (oil)

Renewable gases

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Steam turbine

Gas turbineReciprocating engine

Other classifications:

Topping cycle

Bottoming cycle

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Widely used in CHP applications

Oldest prime mover technology

Capacities: 50 kW to hundreds of MWs

Thermodynamic cycle is the Rankine cycle

that uses a boiler

Most common typesBack pressure steam turbine

Extraction condensing steam turbine

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Boiler Turbine

Process

HP Steam

Condensate LPSteam

Fuel

Steam exits the turbine at a higher pressure that

the atmospheric

Figure: Back pressure steam turbine

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BoilerTurbine

Process

HP Steam

LP Steam

Condensate

Condenser

Fuel

Figure: Extraction condensing steam turbine

Steam obtained by

extraction from an

intermediate stage

Remaining steam is

exhausted

Relatively high

capital cost, lower

total efficiency

Control of electrical

power independent of

thermal load

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Operate on thermodynamic Brayton cycle

atmospheric air compressed, heated, expanded

excess power used to produce power

Natural gas is most common fuel

1MW to 100 MW range

Rapid developments in recent years

Two types: open and closed cycle

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Open Brayton cycle:

atmospheric air at

increased pressure to

combustor

Old/small units: 15:1

New/large units: 30:1

Exhaust gas at 450-

600 oC

High pressure steamproduced: can drive

steam turbine Air

G

Compressor Turbine

HRSG

Combustor

Fuel

Generator

ExhaustGases

Condensate

from Process

Steam toProcess

Figure: Open cycle gas turbine cogeneration

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Working fluid circulates

in a closed circuit and

does not cause

corrosion or erosion

Any fuel, nuclear or

solar energy can be

used

Heat Source

G

Compressor Turbine

Generator

Condensate

from Process

Steam toProcess

Heat Exchanger

Figure: Closed Cycle Gas Turbine Cogeneration System

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Supplied fuel first produces power followed by

thermal energyThermal energy is a by product used for process

heat or other

Most popular method of cogeneration

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Primary fuel produces high temperature thermal

energy

Rejected heat is used to generate power

Suitable for manufacturing processes