Waste heat

Waste heat refers to heat produced by machines and industrial processes for which no useful application is found, and is regarded as a waste by-product. The biggest sources of waste heat originate from machines such as Gensets or industrial processes, such as the steel or glass melting. Nowadays those huge potentials mainly remain unused due to the small power outputs or the low temperatures.

Conversion of energy

Whereas mechanical drives can be designed to run smoothly, with little dissipation of energy to heat, machines for conversion of energy contained in fuels to mechanical work or electric energy necessarily produce large quantities of the by-product heat (see: Second law of thermodynamics).

The electrical efficiency of thermal power plants, defined as the ratio between the input and output energy, most of the time only amounts up to 30%. It is often difficult to find useful application for large quantities of low quality heat, so the heat is qualified as waste heat and rejected to the environment. Economically most convenient is the rejection of such heat to water from a sea, lake or river. If sufficient cooling water is not available, the plant has to be equipped with a cooling tower to reject the waste heat into the atmosphere.

Cogeneration

Waste of the by-product heat is avoided if a cogeneration system is used. Limitations to the use of by-product heat arise due to difficulties in heat transport and heat storage.

Electrification of waste heat

Since there are huge potentials of the previously named waste heat they can not remain unused nowadays. The first and easiest opportunity is, to use this heat for heating purposes. If no heat is needed, it can be converted to electricity by using the ORC-Process (Organic Rankine Cycle). By help of ORC-modules it is possible to turn this previously wasted energy economically into electricity. [ [http://www.gmk.info/Produkt_INDUCAL.523.html?; ORC - waste heat recovery] ]

ee also

* Heat recovery steam generator
* District heating

References