Cogeneration with Definition and Principle

In the generation of electricity (except hydro-electric power), a large amount of heat energy remains in the exhaust steam from the steam turbine or hot gases from the gas turbine. On the other hand, many industrial processes use high – temperature heat: textile, cement, pulp and paper, food processing, fertilizer, petroleum refining, steel and glass industries are examples. There is often much heat energy left in the exhaust from such industries.
The waste heat in both the above cases in energetic, and is, therefore, potentially capable of producing useful in the form of process steam or electricity. Industrial managers are being urged to look at systems that “cogenerate” both heat and electric power.

Definition of cogeneration:

Cogeneration is an energy conversation technology. It is defined as the sequential production of electricity and steam (or) heat) energy from the same fuel source. It is employed to capture the heat energy availability which would otherwise be lost in the normal operation of a traditional power plant or an industrial process. For instance, heat from the exhaust gases of a gas turbine power plant could be made use of in the waste heat recovery boiler to produce process steam.

Principle of cogeneration:

congeneration principle

See the image 1. In the Conventional power plant, heat energy must be added to the boiler feed water in an amount sufficient to bring it up to point A. However, the turbine which drives the generator can utilize the amount of energy between points A and C only. A large amount of heat energy from point C back down to the feed water level E is rejected to the environment as shown in image 2.

See the image 3. In this industrial cogeneration system, the energy added from the feed water level up to point B is needed to generate process steam. On top of this, an extra amount of energy is added to bring the steam up to point A. the energy from A to B is now available for power generation and that from B down to D for process use as steam. A relatively small amount is rejected as waste heat as shown in image 4.


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