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Waste heat
 
 
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Waste heat refers to heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
 produced by machine
Machine

A machine is any device that uses energy to perform some activity. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work....
s and industrial processes for which no useful application is found, and is regarded as a waste by-product
By-product

A by-product is a secondary or incidental product deriving from a manufacturing process, a chemical reaction or a biochemical pathway, and is not the primary product or service being produced....
. 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.

eas mechanical drives can be designed to run smoothly, with little dissipation of energy to heat, machines for conversion of energy
Energy conversion

In physics, the term energy describes the amount of work which may potentially be done by forces within a system. Changes in energy in systems can only be accomplished by adding or subtracting energy from them, as energy is a quantity which is conserved....
 contained in fuels to mechanical work
Mechanical work

In physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI of joules....
 or electric energy necessarily produce large quantities of the by-product heat (see: Second law of thermodynamics
Second law of thermodynamics

The second law of thermodynamics is an expression of the universal law of increasing entropy, stating that the entropy of an isolated system which is not in Thermodynamic equilibrium will tend to increase over time, approaching a maximum value at equilibrium....
).

The electrical efficiency
Electrical efficiency

The efficiency of an entity in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed , typically denoted by the Greek letter small Eta ....
 of thermal power plants, defined as the ratio between the input and output energy, most of the time only amounts up to 30%.






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Encyclopedia


Waste heat refers to heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
 produced by machine
Machine

A machine is any device that uses energy to perform some activity. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work....
s and industrial processes for which no useful application is found, and is regarded as a waste by-product
By-product

A by-product is a secondary or incidental product deriving from a manufacturing process, a chemical reaction or a biochemical pathway, and is not the primary product or service being produced....
. 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
Energy conversion

In physics, the term energy describes the amount of work which may potentially be done by forces within a system. Changes in energy in systems can only be accomplished by adding or subtracting energy from them, as energy is a quantity which is conserved....
 contained in fuels to mechanical work
Mechanical work

In physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI of joules....
 or electric energy necessarily produce large quantities of the by-product heat (see: Second law of thermodynamics
Second law of thermodynamics

The second law of thermodynamics is an expression of the universal law of increasing entropy, stating that the entropy of an isolated system which is not in Thermodynamic equilibrium will tend to increase over time, approaching a maximum value at equilibrium....
).

The electrical efficiency
Electrical efficiency

The efficiency of an entity in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed , typically denoted by the Greek letter small Eta ....
 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
SEA

See also: Sea and seasThe three-letter acronym SEA may refer to:People/organizations/businesses*Scientists and Engineers for America, a pro-science political advocacy group....
, lake
Lake

A lake is a terrain feature , a body of liquid on the surface of a world that is localized to the bottom of basin and moves slowly if it moves at all....
 or river
River

A river is a natural stream of water, usually freshwater, flowing toward an ocean, a lake, or another stream. In some cases a river flows into the ground or dries up completely before reaching another body of water....
. If sufficient cooling water is not available, the plant has to be equipped with a cooling tower
Cooling tower

Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the Wet-bulb temperature or rely solely on air to cool the working fluid to near the Dry-bulb temperature....
 to reject the waste heat into the atmosphere.

Cogeneration

Waste of the by-product heat is avoided if a cogeneration
Cogeneration

Cogeneration is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat.Conventional power plants emit the heat created as a by-product of electricity generation into the environment through cooling towers, flue gas, or by other means....
 system is used. Limitations to the use of by-product heat arise due to difficulties in heat transport
Heat transport

Articles on Heat transport include:* Heat* Heat pipe* Heat conduction* Convection* Coolant* Cogeneration...
 and heat storage
Heat storage

Articles on Heat storage include:* Energy storage* Thermal energy storage* Seasonal thermal store* Storage heater* Steam accumulator* Fireless locomotive...
.

Electrification of waste heat


Since there are huge potentials of the previously named waste heat they can not remain unused nowadays based on high fuel costs today. This fact leads to the need for more effective ways to use the input energies of every kind of power plant. The first and easiest opportunity is, to use this heat for heating purposes. In Germany this kind of combined cycle power plants is subsidised by the government. Most of the time a use of heat is not possible because the ambient temperature is to high or the heat nets can not take up additional energy. In such a case where no heat is needed, it can be converted to electricity by using the ORC-Process (Organic Rankine Cycle
Organic Rankine Cycle

Unlike the traditional steam Rankine cycle, the organic Rankine cycle uses a high molecular mass organic fluid. It allows heat recovery from low temperature sources such as industrial waste heat, geothermal heat, solar ponds, etc....
). The ORC is a process where an organic substance is used as working medium instead of water that can use lower temperatures for the production of electricity than the regular water steam cycle. By help of ORC-modules it is possible to turn this previously wasted energy economically into electricity.

See also

  • Heat recovery steam generator
  • District heating
    District heating

    District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating....