August 1, 2016 By Carl Weinschenk
Combined heat and power is a good deal: It is a fine way to drastically reduce waste and derive two uses from a single investment https:/

Combined heat and power (CHP, also known as cogeneration), is familiar to energy managers and building owners. The U.S. Energy Information Agency (EIA) last week posted a very interesting article that digs more deeply into various types of CHP systems and the industries that most often benefit from each.

The post says that there are two types of CHP: topping cycles and bottoming cycles. The difference is explained very well by The Office of Energy Efficiency and Renewable Energy (EERE). Topping cycle approaches use fuel first to generate electricity or mechanical power in a “prime mover” such as a gas turbine or reciprocating energy. Exhaust energy is captured and used for a secondary purpose, such as heating or cooling the facility.

Bottoming cycle systems – which the piece says also is known as “waste heat to power” – heat first is used “to provide thermal input to a furnace or other high temperature industrial process,” with a portion of the heat used for a secondary purpose. This, typically, is a waste heat boiler/steam turbine system, the post says.

The EIA piece has a very interesting chart depicting the industries using CHP and, further, the breakdown between bottoming and topping cycle approaches. In general, bottoming cycle are use in a slightly wider number of industries (chemical; paper, primary metal; petroleum and coal products; food, nonmetallic mineral; crop production; wood product and miscellaneous).

However, topping cycle approaches produce far more energy where they are used. For instance, in the chemical sector, last year bottoming cycle CHP only produced about 1 GW […]