Cogeneration

COGENERATION

1. PRINCIPLE OF COGENERATION

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, viz., textiles, pulp and paper, food processing, fertilizer, petroleum refining, glass industries, etc., use high-temperature heat energy. There is often much heat energy left in the exhaust from such industries.

In both the above cases, the waste heat is energetic. It is, therefore, potentially capable of producing useful work in the form of either process steam or electricity. Industrial managers are nowadays being urged to look at systems that cogenerate both heat and electric power.

Definition

Cogeneration is an energy conservation 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 of which would otherwise be lost in the normal operation of a traditional power plant or of an industrial process. For instance, heat energy 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.

2. APPLICATIONS OF COGENERATION

• Industrial cogeneration systems have received an impetus in recent years. The potential savings of cogeneration are significant. A gas turbine cogeneration system has been installed at ONGC, Uran with a capacity of 40 MW.

• Gas turbine with heat recovery, steam turbine with heat recovery and diesel engine with heat recovery are the different cogeneration schemes used in traditional power plants.

• Cogeneration systems are highly suitable for various process industries like rayon, pulp and paper, chemical process, textile, cement, glass and fertilizer where both power and process steam are used.

A few typical examples of industries where cogeneration systems could be utilized are:

(a) In industries, such as rayon, pulp and paper, chemical processing and textile, which require simultaneous steam and power, it is possible to meet either part or fuel heat and power requirements using steam turbine, gas turbine with heat recovery boiler.

(b) Cement kilns and brick kilns require a large amount of high temperature process heat. The gas turbine exhaust, with or without supplementary firing, can supply this heat and produce electric power for the factory.

(c) In glass melting furnaces, heat from the exhaust gases can be recovered in waste heat boiler to produce steam. The steam can be expanded in steam turbines to produce electrical power.