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Basic Principle of a heat and power engine

A combined heat and power generation can be realized by many technologies. Main principle is the decentralized use of (simultaneously) provided electricity and heat. The following figure illustrates the basic principle of an engine CHP.

Prinzip einer Kraft-Wärme-Kopplung


The internal combustion engine (eg, engine, gas turbine) drives a generator and makes electricity thereby available to the consumer. If necessary. The motor can also directly drive an engine or a compressor (for example in the production of compressed air). The heat, which accumulates in the engine block (coolant, oil) is used in a heat exchanger for heating water. The energy contained in the exhaust gas is used to generate steam if (process heat) and / or by means of heat exchanger service water heating.

Steam turbines, internal combustion engines and gas turbines are considered to be conventional technologies for the combined heat and power generation. Newer technologies such as fuel cells or Stirling engines broaden the existing cogeneration technologies.

The internal combustion engines (engine, gas turbine) differ mainly in the type of waste heat.  Internal combustion engines releases most of the waste heat  as cooling water , whereas heat is released in the gas turbine process to a higher temperature through exhaust gases. These results  among other things is influence considerably fields of application of these technologies. Thus gas turbines in particular in the field of industry are used to provide low-temperature process heat (500 ° C), while motor systems find their application especially in the deployment of field of space heating.

In most cases,  a cogeneration plant consists of the following main components:

  • Engine, gas turbine or Stirling engine as a generator / fuel cell
  • Electricity generator
  • Heat exchanger systems for the recovery of thermal energy from exhaust gases, engine heat and oil circuit
  • Various electrical switching and control equipment for power distribution and engine management
  • Hydraulic equipment for heat distribution

Especially in the field of space heating, the CHP system is usually accompanied by a peak boiler and a heat store.


Markus Gailfuß, BHKW-Infozentrum Rastatt