Steam-electric power plant

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A steam-electric power plant is a power plant in which the prime mover is steam. Water is heated, turns into steam and spins a turbine. After it passes through the turbine, the steam is cooled and condenses. Steam-electric plants are very similar to one another, only the heat source is different.

Almost all coal, nuclear, geothermal, solar thermal electric and many natural gas power plants are steam-electric. Natural gas is frequently combusted in gas turbines as well boilers, and it is possible to make coal and nuclear plants that are not steam electric, though all major plants are. Large solar power tower and solar parabolic trough type solar thermal electric plants are steam-electric, but solar dishes and solar ponds usually use a Stirling engine.

The vast majority of electricity is produced by steam-electric power plants. The only other types of plants that currently have a significant contribution are hydroelectric and gas turbine plants, which can burn natural gas or diesel. Photovoltaic panels, wind turbines and binary cycle geothermal plants are also non-steam electric, but currently do not produce much electricity.

A conventional steam-electric power plant is typically 33 to 35% efficient. Steam-electric power plants are generally this in- efficient due to the thermodynamics involved. Steam-electric power plants utilize a surface condenser cooled by water circulating through tubes. The steam which was used to turn the turbine is exhausted into the condenser. The steam is therefore condensed as it comes in contact with the cool tubes full of circulating water. This condensed steam falls down to the bottom of the condenser vessel into a collecting area most normally referred to as hotwell. This condensed steam is now water, commonly referred to as condensate water.

In the case of a conventional steam-electric station utilizing a drum boiler, the condenser removes the latent heat of vaporization from the steam as it changes states from vapor to liquid. The heat content (btu) in the steam is referred to as Enthalpy. The condensate pump now starts this condensate water on the move toward a train of feed water heaters. The series of feedwater heating equipment then raises the temperature of the water by utilizing extraction steam from various stages of the turbine. Once this water is again inside the boiler or steam generator, the process of adding the latent heat of vaporization or Enthalpy is underway. The boiler transfers energy to the water by the chemical reaction of burning some type of fuel. The water boils and turns to vapor. The vapor is passed through as series of steam and water seperators and then dryers inside the steam drum. The steam seperators and dryers remove the water droplets from the steam. The water droplets fall into the bottom of the drum and are recirculated through a series of large pipes typically referred to as down-comers. The down comers carry the water to the lower water wall headers. The water is again inside the tubes that are next to the burning fuel. These tubes actually make up the furnace walls of this water tube boiler. Steam bubbles form on the inside of these tubes and the bubbles rise up toward the drum and enter in to the steam seperators once again. This process is known as natural circulation.