Safety in thermal power plant pdf

Steam-driven power stations have been used to drive most ships in most of safety in thermal power plant pdf 20th century until recently. Shipboard power stations usually directly couple the turbine to the ship’s propellers 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.

The dry steam then flows into the superheater coils. The steam passes through drying equipment inside the steam drum on to the superheater, a set of tubes in the furnace. Here the steam picks up more energy from hot flue gases outside the tubing, and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves before the high-pressure turbine. Nuclear-powered steam plants do not have such sections but produce steam at essentially saturated conditions. Experimental nuclear plants were equipped with fossil-fired super heaters in an attempt to improve overall plant operating cost.

The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. Diagram of a typical water-cooled surface condenser. For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Thus leaks of non-condensible air into the closed loop must be prevented. The large decrease in volume that occurs when water vapor condenses to liquid creates the low vacuum that helps pull steam through and increase the efficiency of the turbines. The heat absorbed by the circulating cooling water in the condenser tubes must also be removed to maintain the ability of the water to cool as it circulates.

Many plants include an automatic cleaning system that circulates sponge rubber balls through the tubes to scrub them clean without the need to take the system off-line. The cooling water used to condense the steam in the condenser returns to its source without having been changed other than having been warmed. Another form of condensing system is the air-cooled condenser. Exhaust heat from the low-pressure section of a steam turbine runs through the condensing tubes, the tubes are usually finned and ambient air is pushed through the fins with the help of a large fan. The steam condenses to water to be reused in the water-steam cycle. Air-cooled condensers typically operate at a higher temperature than water-cooled versions. Power station furnaces may have a reheater section containing tubes heated by hot flue gases outside the tubes.

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