Fossil fuel¬†power stations have rotating machinery to convert the heat energy of¬†combustion¬†into¬†mechanical energy, which then operates an¬†electrical generator. The¬†prime mover¬†may be a¬†steam turbine, a¬†gas turbine¬†or, in small plants, a reciprocating¬†internal combustion¬†engine. All plants use the¬†energy¬†extracted from expanding gas – steam or combustion gases. Very few¬†MHD generators¬†have been built which directly convert the energy of moving hot gas into electricity.
Byproducts of thermal power plant operation must be considered in their design and operation.¬†Waste heat¬†energy, which remains due to the finite efficiency of the¬†Carnot,¬†Rankine, or¬†Diesel¬†power cycle, is released directly to the atmosphere, directly to river or lake water, or indirectly to the atmosphere using a¬†cooling tower¬†with river or lake water used as a cooling medium. The¬†flue gas¬†from combustion of the fossil fuels is discharged to the air. This gas contains¬†carbon dioxide, water vapor, as well as substances such as¬†nitrogen oxides¬†(NOx),¬†sulfur oxides¬†(SOx),¬†mercury, traces of other metals, and, for coal-fired plants,¬†fly ash. Solid waste ash from coal-fired boilers must also be removed. Some coal ash can be recycled for building materials.
Fossil fueled power stations are major emitters of CO2, a¬†greenhouse gas¬†(GHG) which according to a¬†consensus opinion of scientific organisations¬†is a contributor to¬†global warming¬†as it has been observed over the last 100 years. Brown coal emits about 3 times as much CO2¬†as natural gas, and black coal emits about twice as much CO2¬†per unit of electric energy.¬†Carbon capture and storage¬†of emissions is not expected to be available on a commercial economically viable basis until government supported legislation is enacted.