Fossil fuel power plant
|A coal-fired power plant. Photo: DOE|
A fossil fuel power plant is a system of devices for the conversion of fossil fuel energy to mechanical work or electric energy. The main systems are the steam cycle and the gas turbine cycle. The steam cycle relies on the Rankine cycle in which high pressure and high temperature steam raised in a boiler is expanded through a steam turbine that drives an electric generator. The steam gives up its heat of condensation in a condenser to a heat sink such as water from a river or a lake, and the condensate can then be pumped back into the boiler to repeat the cycle. The heat taken up by the cooling water in the condenser is dissipated mostly through cooling towers into the atmosphere.
The gas turbine cycle relies on the Brayton cycle in which air compressed to high pressure, and heated to high temperature by the combustion of natural gas or light fuel oil, is the working fluid that expands in the turbine to provide the torque for driving both a compressor and the electric generator. The gas turbine demands clean fuels such as natural gas or light fuel oil. Combustion is the prevailing fuel utilization technology in both the above cycles. Coal is the preferred fuel for the steam cycle because of its low cost and broad and secure availability worldwide.
Combustion-generated pollutants, such as oxides of nitrogen (NO,x), of sulfur (SOx), and particulates, if uncontrolled and emitted into the atmosphere represent environmental and health hazards, such as acid rain. Environmental regulations supported by intensive research and developments have reduced pollutant emissions significantly. Improvements in efficiency and emissions come by increasing steam pressure and temperature in the steam cycle, and by increased turbine inlet temperature in the gas turbine cycle. Coal gasification produces a fuel gas that is capable of being used in the gas turbine. By integrating coal gasification with gas turbine and steam cycles, advantage can be taken of high efficiency and low pollutant emission while using coal, an inexpensive, secure and indigenous fuel in many countries throughout the world. A potential additional advantage of the Integrated Gasification Combined Cycle (IGCC) is the capability of capturing carbon dioxide (CO2) from the fuel gas and making it ready for high-pressure pipeline transportation to a carbon sequestration site. This will be key to the commercial and clean co-production of electricity and hydrogen from coal.
Further reading Fossil-Fuel Generation, Tennessee Valley Authority.