Types of cogeneration systems

There are two types of cogeneration systems: Topping cycle and Bottoming cycle.

Topping cycle system

Hot gases expand in the gas turbine to generate electricity. The still-hot rejected waste heat from the turbine is sent through a waste heat recovery boiler to produce low pressure process steam. The steam is sent to an industrial process requiring large quantities of hot steam (textile, paper and pulp, sugar, food processing, etc.).

An approach that circumvents the problem of distance is to bring the industry to the power plants; to create an industrial park in which the power plant provides both electricity and steam.

Bottoming cycle system

See the above image. In this the primary energy source is applied to an useful industrial process. The reject heat emerging from the process is then used for power generation.

In the next post I will explain the benefits of cogeneration.