There are many occasions in industrial settings where the need arises for a specific source or supply of energy within the environment in which a steam power plant is being used to generate electricity. In such cases, it is appropriate to consider supplying this source of energy in the form of steam that has already been expanded through the high-pressure section of the turbine in the power plant cycle, thereby eliminating the construction and use of a second boiler or other energy source. Such an arrangement is shown, in which the turbine is tapped at some intermediate pressure to furnish the necessary amount of process steam required for the particular energy need—perhaps to operate a special process in the plant, or in many cases simply for the purpose of space heating the facilities.
This type of application is termed cogeneration. If the system is designed as a package with both the electrical and the process steam requirements in mind, it is possible to achieve a substantial savings in capital cost of equipment and in the operating cost, through careful consideration of all the requirements and optimization of the various parameters involved.
Cogeneration—also called combined heat and power (CHP)—is the simultaneous conversion of chemical energy of a single fuel source (e.g. natural gas) to produce useful energy (e.g. electricity) and propitous heat (e.g. boil a liquid for heating/cooling).