Simultaneous production of two forms of energy – Thermal Energy – Electricity / Mechanical Energy

Conventional Plant

Loses up to 70%

Efficiency is 30-40%

Fuel(100%)

Cogeneration Plant

Loses up to 10%

Efficiency up to 70-

90%

Fuel(100%)

Source: IEA, CHP: Evaluating the Benefits of Greater Global Investment (2008).

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 800 600

Paper & Pulp 1000 750

Textile 1200 800

BCHP 650 400

Other Sector 750 500

Total 16000 11500

Natural gas Coal Biomass

Bagasse (waste product from sugar cane processing)

Waste gas Sludge gas from sewage treatment plant Methane from landfills and coal bed methane

Liquid fuels (oil) Renewable gases

Steam turbine

Gas turbine

Reciprocating engine

Other classifications:

Topping cycle

Bottoming cycle

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 types Back pressure steam turbine

Extraction condensing steam turbine

Boiler Turbine

Process

HP Steam

Condensate LP Steam

Fuel

Steam exits the turbine at a higher pressure that the atmospheric

Figure: Back pressure steam turbine

Boiler Turbine

Process

HP Steam

LP SteamCondensate

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

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

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 steam produced: can drive steam turbine Air

G

Compressor Turbine

HRSG

CombustorFuel

Generator

Exhaust Gases

Condensate from Process

Steam to Process

Figure: Open cycle gas turbine cogeneration

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 to Process

Heat Exchanger

Figure: Closed Cycle Gas Turbine Cogeneration System

Supplied fuel first produces power followed by thermal energy

Thermal energy is a by product used for process heat or other

Most popular method of cogeneration

Primary fuel produces high temperature thermal energy

Rejected heat is used to generate power

Suitable for manufacturing processes

Increased efficiency of energy conversion and use

Reducing environmental impact

Conserving limited resources of fossil fuels

Saving money

On-site production of electricity generation

Promoting liberalization in energy markets

Industrial CHP Sugar industry – bagasse CHP Others

District system CHP IT industry Industrial parks Mixed residential/commercial districts

Small Scale Systems

Depends very much on tariff system

Heat Avoid cost of separate heat production

Electricity 1) Less purchase (kWh) 2) Sale of surplus electricity 3) Peak shaving (kW)

Carbon credits (future)

Lack of a clear definition of cogeneration or CHP

There has not been an economy-wide study of CHP potential (and associated benefits)

Lack of an approved methodology for calculating CO2 emission reductions from CHP

Limited availability of competitively priced turbines and engines for CHP

Lack of pipeline networks for district cooling

Energy Management, future CHP and Sell to Grid Base-load, and

Industrial Cooling, Heat and Power

Power Quality and CHP

Grid Ancillary Services

Remote Power and CHP

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Bulk Power

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Cogeneration improves energy efficiency…..…….if heat is used in a proper way

www.cogeneration.orgwww.uschpa.orgwww.iea.orgwww.cogenindia.orgwww.ieachp.org