Steam-driven power stations have been used to drive most ships in most of the 20th century until recently. Shipboard power stations usually directly couple the turbine to the ship’s ash handling system in power plant pdf through gearboxes.
Power stations in such ships also provide steam to smaller turbines driving electric generators to supply electricity. London, reciprocating steam engines were used. 1884 provided larger and more efficient machine designs for central generating stations. After about 1905, turbines entirely replaced reciprocating engines in large central power stations. The largest reciprocating engine-generator sets ever built were completed in 1901 for the Manhattan Elevated Railway.
The energy of a thermal power station not utilized in power production must leave the plant in the form of heat to the environment. Currently most of the nuclear power stations must operate below the temperatures and pressures that coal-fired plants do, in order to provide more conservative safety margins within the systems that remove heat from the nuclear fuel rods. The direct cost of electric energy produced by a thermal power station is the result of cost of fuel, capital cost for the plant, operator labour, maintenance, and such factors as ash handling and disposal. Indirect, social or environmental costs such as the economic value of environmental impacts, or environmental and health effects of the complete fuel cycle and plant decommissioning, are not usually assigned to generation costs for thermal stations in utility practice, but may form part of an environmental impact assessment. On some units of about 60 MW, two boilers per unit may instead be provided.
200 largest power stations ranging in size from 2,000MW to 5,500MW. The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that drives the electrical generator. Heat exchangers may be used where the geothermal steam is very corrosive or contains excessive suspended solids. The water is pressurized in two stages, and flows through a series of six or seven intermediate feed water heaters, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Its walls are made of a web of high pressure steel tubes about 2.
The water circulation rate in the boiler is three to four times the throughput. It is separated from the water inside a drum at the top of the furnace. Lignite is a much younger form of coal than black coal. It has a lower energy density than black coal and requires a much larger furnace for equivalent heat output. The firing systems also differ from black coal and typically draw hot gas from the furnace-exit level and mix it with the incoming coal in fan-type mills that inject the pulverized coal and hot gas mixture into the boiler. From these headers the water rises through the water walls of the furnace where some of it is turned into steam and the mixture of water and steam then re-enters the steam drum.