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Cogeneration
“Combined Heat and Power (CHP)”
Definitions
Cogeneration can be defined as simultaneous
production of heat and power from one source.
The idea of cogeneration is the recovery of the waste
heat resulting form a power unit to generate steam
or hot gas stream which can be used to cover part or
all of the thermal demand of a plant in addition to
the electrical demand which is satisfied by the power
unit.
A cogeneration unit is characterized by its thermal to
electric ratio which is the quantity of recovered
thermal energy to the electrical energy generated
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Comparison Between Cogeneration
and Conventional System
Waste Energy
10.03 MW Waste Energy
5.05 MW
Fuel Input Output Power
18.9 MW Output Power
6.88 MW
6.88 MW
Fuel Input
Power Unit (GT) = Process Steam
24.66 MW
Waste Energy 12.73 MW
3.19 MW
Cogeneration
Fuel Input
Process Steam
15.2 MW
12.73 MW Reduction in Fuel Input
Process Heating Energy by 27.6%
Conventional System
Advantages of Cogeneration
Plant perspective:
Fuel savings and its associated cost
savings
Improve the environment through the
reduction of harmful emissions
Improve the reliability of power supply to
the plant
Reduce the plant venerability toward
changes in energy cost
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Advantages of Cogeneration (contd.)
From National Perspective:
Avoid distribution losses, which represents
10-12% of the total power tansmitted.
More cost effective than a central power
station
Reduce the grid peak demand
Reduce air pollution due to the
improvement in fuel utilization
Types of Cogeneration Cycle
Fuel
Heat Industrial Use
Source (e.g. Furnace)
Engine Generator
Electrical
Energy
Bottoming Cycle
Thermal Energy
Heat Exchanger
(Hot gases, Steam, Hot
water)
Fuel Engine Generator
Electrical Energy
Topping Cycle
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Types of Topping
Cogeneration
Cogeneration types is usually defined
according to the type of power generation
unit. These types are:
Steam turbine based cogeneration unit such as:
back pressure turbine or extraction turbine
Gas turbine based cogeneration unit
Reciprocating engine based type which may be
gas or diesel engine. This category of
cogeneration can take several forms such as:
ebullient system for low pressure steam and two
recovery cycles for both steam and hot water
Steam Turbine Cogeneration Systems
Input Steam Input Steam
Output Output
Power Power
To Steam
Condenser
Process Steam Process Steam
Back Pressure Turbine Extraction Turbine
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Gas Turbine Cogeneration System
Exhaust Process
Steam
Exhaust
Combustion Chamber By-pass
Output
Power Supplementary
Firing
Combustion Chamber
Inlet Air Diverting
Valve HRSG
Output
Power
Gas Turbine With HRSG
Inlet Air Direct Use of Exhaust
Gases in Heating
Direct Recover of Thermal
Energy in GT Exhaust
Reciprocating Engine Cogeneration
System
Exhaust Exhaust Gas Steam To User
Gas Heat Engine Coolant Heat
Recovery Recovery Condensate
Engine Coolant
Return from
Engine User Return from
Engine Generator Coolant Engine User
Heat Generator Coolant
Engine
Electricit Exchanger Heat
Hot Water Electricity Exchanger
y to User
Lube. to User to User
Oil Lube. Hot Water to
Engine Coolant Oil User
Engine Coolant
Warm Water to User
Warm Water to User
Water From
Water From User
User
Lube. Oil
Heat
Exchanger
Steam and Hot Water
Hot Water Arrangement
Arrangement
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Engine Energy Balance
Cooling water circuit is usually
divided into High temperature
circuit which is used to cool the Cooling
engine cylinder and low Exhaust Water out
Gases
temperature circuit which is
used to cool the lubricating oil Fuel
and the AC or IC (if any) Output
Power
Cp w T w ,o T w ,in
o Air
Q cw m cw
Qex mof mao Cpg ,av (Tex Ta )
Cooling Radiation, Vibration
Water in and Unaccounted
losses
1
Qex mof 1 Cpg ,av (Tex Ta )
f th
Qlosses mofQHV P Qcw Qex
Energy Balance of SIE and CIE
Heat Balance of a Large Medium Speed Enerby BALANCE FOR SMALL Small Diesel Engine
Diesel Engine
Radiation
Lube Oil Radiation
intercooler 1% Lub. Oil 13% Power
4%
15% 7%
Cooling Power 34%
Water 41%
10%
Cooling
Water
Exhaust 24% Exhaust
29% 22%
Energy Balance for Large Energy Balance for Small SIE
Medium Speed SIE
Air Cooler Lub. Oil Radiation Radiation
Cooling 5% 2% 1% Lube Oil 7%
Water 5% Power
Power 32%
19%
44%
Cooling
Water
33% Exhaust
Exhaust 23%
29%
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Considerations of Cogeneration
Systems
Type Available Process Thermal To Fuels
Heat Electric Ratio
Steam Turbine 120oC to 400 oC 2:1 to 30:1 Residual, Distillate,
Gaseous, Combustible
Waste
Gas Turbine 120oC to 500 oC 1.2:1 to 4:1 Residual, Distillate,
Gaseous
Reciprocating 80oC to 120 oC 0.8:1 to 2:1 Residual, Distillate,
Engine Gaseous
Efficiency of Cogeneration System
Efficiency of Cogeneration
E H
co
Q A
Combined efficiency for Separate Generation
1
c
e / e 1 e / h
Where
E
e
E H
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Advantages of Cogeneration
Better energy utilization efficiency
Provide additional source for power supply
Lower environmental impact
Avoiding distribution losses
Cost effective
Possible power exchange with the utility
Industries Suitable for Cogeneration
Applications
Most industries use both electrical and thermal
energies simultaneously.
Thermal to electric ratio differs from one industry to
another furthermore it depends on the details of the
industrial process for the same industry.
The thermal to electric ratio is highest for textile and
food industries (i.e. 5 –30) while it is the lowest for
engineering industries (less than 1).
Food, Textile, Chemical, Building material and
Petrochemical are the most suitable industries for
cogeneration
Also cogeneration is suitable for commercial building
such as hotels and resorts
