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Treatment of industrial waste gas from power plants

First, the source and characteristics of power plant exhaust
       1. Power plant types and exhaust emissions
       There are many types of power plants, such as thermal power plants, hydroelectric power plants, nuclear power plants, geothermal power plants, wind power plants, tidal power plants and solar power plants. These power plants use different amounts of power, so the amount of exhaust gas and the pollutants in the exhaust gas are not the same. Among them, hydropower, atomic energy, geothermal, wind, tidal and solar power plants use relatively clean energy, so their impact on the atmospheric environment is relatively small; and thermal power stations use exhaust gas because of the use of coal-fired boilers. The amount is large, the composition of the smoke is complicated, and the pollution caused to the atmosphere is serious. The flue gas of coal-fired boilers in thermal power plants is the most important source of pollution in the power industry.
       2. Sources and characteristics of waste gas from coal-fired power plants
       The waste gas from coal-fired power plants is mainly derived from the flue gas generated by boiler combustion, the exhaust gas in the middle ash storage of the pneumatic ash conveying system and the dust-containing exhaust gas generated by the coal yard, as well as the coal dust generated by coal yard, raw coal crushing and coal transportation. Among them, the amount of flue gas generated by boiler combustion and the pollutants contained in it are far greater than other exhaust gases, which is the focus of pollution control. The pollutants in the flue gas generated by boiler combustion are fly ash, SO2, NOx, CO, CO2, small amounts of fluoride and chloride. The ratio of them depends on the mineral composition of the coal. The main pollutants are fly ash, coal dust, SO2 and NOx. Boiler combustion produces a large amount of flue gas emissions, and the exhaust gas temperature is high, but the concentration of gaseous pollutants is generally low.
       3. Countermeasures for waste gas treatment in coal-fired power plants
       For the treatment of waste gas from coal-fired power plants, it is necessary to vigorously promote clean coal technology and carry out technological transformation and enterprise management as soon as possible to reduce coal consumption, which is one of the important ways for power plants to reduce emissions. In addition, we should actively develop and adopt high-efficiency exhaust gas treatment technology and comprehensive resource utilization technologies, such as the use of electrostatic precipitator with high dust removal efficiency for boiler flue gas dedusting, the development of efficient new technology for desulfurization and denitrification of power plants, and the use of cogeneration.
Second, power plant waste gas treatment
       (1) Dust control of boilers in coal-fired power plants
Coal-fired power plants use various types of dust collectors for boiler dust control: electrostatic precipitators, bag filters, wet dust collectors and cyclone dust collectors. Among them, the electrostatic precipitator has high dust removal efficiency and low operating cost, so the dust removal of coal-fired power plants is mainly electrostatic precipitators; the venturi and oblique bar grating wet precipitators have higher dust removal efficiency and lower cost, in water resources. There are still applications in richer areas; the efficiency of water film precipitators is generally 85%-90%, and the treated exhaust gas does not meet the emission standards, so it is being used less; and the inefficient dust collectors such as multi-tube and cyclone are being Electric dust is replaced.
       (II) Treatment of sulfur oxides in boilers of coal-fired power plants
       Coal-fired power plant boilers produce large amounts of sulfur dioxide when coal is burned. The control of sulfur dioxide technology can be basically divided into three categories: pre-combustion desulfurization, in-situ desulfurization and post-combustion desulfurization.
1. Desulfurization before combustion
       Pre-combustion desulfurization is the removal of a portion of the sulfur prior to combustion of the coal.
       (1) Physical law
       The physical methods for desulfurization before combustion mainly include a shaker method, a heavy medium method, a cyclone method, a flotation method, and a high gradient magnetic separation method. The first four methods are sorted by using different minerals in the coal and the density of the organic matter in the coal, and are suitable for coal particles having a particle diameter of more than 0.5 mm. The flotation method is sorted according to the difference in surface properties such as the hydrophilicity of coal and pyrite, and is suitable for fine granular coal. High gradient magnetic separation is based on the difference in magnetic susceptibility between coal and pyrite. The physical method generally only removes the inorganic sulfur on the surface of the coal particles, and its desulfurization effect usually only removes 20%-40% of the sulfur content in the coal.
       (2) Chemical method
       The chemical method for desulfurization before combustion is mainly an oxidation method, which can remove most of the inorganic sulfur and a considerable amount of organic sulfur. However, this method is costly and has strict reaction conditions, and is generally only used in some fields where coal quality is required to be high.
       2. Desulfurization during combustion
       Desulfurization during combustion is the addition of sulfur dioxide produced by the adsorption of adsorbents during the combustion of coal. A method of directly injecting a calcium-based absorbent into the furnace or a method of burning in a liquefied state may be employed.
       3. Desulfurization after combustion
       Desulfurization after combustion can be generally divided into dry process (including semi-dry process) and wet process.