Most hydropower stations in the United States are about 90 percent efficient in converting the energy of falling water into electricity[6] while the efficiency of a wind turbine is limited by Betz's law, to about 59.3%, and actual wind turbines show lower efficiency. Demineralized water of low conductivity is used. Other types of power stations are subject to different efficiency limitations. The cooling water used to condense the steam in the condenser returns to its source without having been changed other than having been warmed. The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through cooling (OTC) water from a river, lake or ocean. This is because the heat inside the turbine casing tends to concentrate in the top half of the casing, making the top half portion of the shaft hotter than the bottom half. Barring gear (or "turning gear") is the mechanism provided to rotate the turbine generator shaft at a very low speed after unit stoppages. The entire rotating mass may be over 200 metric tons and 100 feet (30 m) long. An important class of thermal power station is that associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas, and in these plants freshwater production and electricity are equally important co-products. 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. This ensures that a highly explosive hydrogen–oxygen environment is not created. [19][20] In the case of existing flue gas stacks that exceed the GEP stack height, any air pollution dispersion modeling studies for such stacks must use the GEP stack height rather than the actual stack height. Natural gas is frequently burned in gas turbines as well as boilers. Other devices use catalysts to remove nitrous oxide compounds from the flue-gas stream. This system requires special handling during startup, with air in the chamber first displaced by carbon dioxide before filling with hydrogen. In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into small pieces and then conveyed to the coal feed hoppers at the boilers. Its walls are made of a web of high pressure steel tubes about 2.3 inches (58 mm) in diameter. Commercial electric utility power stations are usually constructed on a large scale and designed for continuous operation. The pulverizers may be ball mills, rotating drum grinders, or other types of grinders. The electricity flows to a distribution yard where transformers increase the voltage for transmission to its destination. Looks like you’ve clipped this slide to already. A simple cycle gas turbine achieves energy conversion efficiencies from 20 to 35%. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated. There is generally no permanent magnet, thus preventing black starts. Steam-driven power stations have been used to drive most ships in most of the 20th century[citation needed]. The considerable increase of the demand of electricity throughout the world has resulted in increased size of power plant.The process of electrical power generation, in a coal fired thermal power plant is one of the most widespread and conventional methods, of bulk power generation all over, as it vastly feeds the power requirement of a 7 billon plus population all across the globe. Almost all coal-fired power stations, petroleum, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as all natural gas power stations are thermal. If the water returns to a local water body (rather than a circulating cooling tower), it is often tempered with cool 'raw' water to prevent thermal shock when discharged into that body of water. [citation needed]. In some industrial settings, there can also be steam-producing heat exchangers called heat recovery steam generators (HRSG) which utilize heat from some industrial process, most commonly utilizing hot exhaust from a gas turbine. Seal oil is used to prevent the hydrogen gas leakage to atmosphere. The Primary air fan takes air from the atmosphere and, first warms the air in the air preheater for better economy. A DM plant generally consists of cation, anion, and mixed bed exchangers. 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. However, at times, manual intervention may be required. • TANYA MALVI (130110052) Sub-critical pressure fossil fuel power stations can achieve 36–40% efficiency. The piping and valves are generally of stainless steel. If you continue browsing the site, you agree to the use of cookies on this website. A central battery system consisting of lead–acid cell units is provided to supply emergency electric power, when needed, to essential items such as the power station's control systems, communication systems, generator hydrogen seal system, turbine lube oil pumps, and emergency lighting. • I.ALANGLA WALLING (130110058) This cleaning up of flue gases, however, only occurs in plants that are fitted with the appropriate technology. The dry steam then flows into the superheater coils. The energy efficiency of a conventional thermal power station is defined as saleable energy produced as a percent of the heating value of the fuel consumed. 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. In the nuclear plant field, steam generator refers to a specific type of large heat exchanger used in a pressurized water reactor (PWR) to thermally connect the primary (reactor plant) and secondary (steam plant) systems, which generates steam. The generator, typically about 30 feet (9 m) long and 12 feet (3.7 m) in diameter, contains a stationary stator and a spinning rotor, each containing miles of heavy copper conductor. The steam is obtained from high-pressure boilers. A system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter. Combined cycle power plant as in name suggests, it combines existing gas and steam technologies into one unit, yielding significant improvements in thermal efficiency over conventional steam plant. [17], The condenser tubes are made of brass or stainless steel to resist corrosion from either side. Clipping is a handy way to collect important slides you want to go back to later. As the combustion flue gas exits the boiler it is routed through a rotating flat basket of metal mesh which picks up heat and returns it to incoming fresh air as the basket rotates. Smaller units may share a common generator step-up transformer with individual circuit breakers to connect the generators to a common bus. The waste heat from a gas turbine, in the form of hot exhaust gas, can be used to raise steam by passing this gas through a heat recovery steam generator (HRSG). The hot reheat steam is conducted to the intermediate pressure turbine, where it falls in both temperature and pressure and exits directly to the long-bladed low-pressure turbines and finally exits to the condenser. The power plant covers an area of 454.86ha and is equipped with advanced pollution control equipment, including a 275m-high chimney, a dust extraction and suppression system, and low NOx burners. Nuclear-powered steam plants do not have such sections but produce steam at essentially saturated conditions. As the water in the boiler circulates it absorbs heat and changes into steam. A fossil fuel steam generator includes an economizer, a steam drum, and the furnace with its steam generating tubes and superheater coils. This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. The oil must kept warm (above its pour point) in the fuel oil storage tanks to prevent the oil from congealing and becoming unpumpable. A nuclear power plant is a thermal power plant, in which a nuclear reactor is used to generate large amounts of heat. In a nuclear reactor called a boiling water reactor (BWR), water is boiled to generate steam directly in the reactor itself and there are no units called steam generators. The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the waste heat is instead used for district heating, it is called cogeneration. After it passes through the turbine the steam is condensed in a steam condenser and recycled to where it was heated. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air. You can change your ad preferences anytime. 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. Nevertheless, they may become internally fouled during operation by bacteria or algae in the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce thermodynamic efficiency.