In recent years, China has implemented a policy of combining the total amount of air pollutants with that of emission concentration control, intensified efforts to control air pollution, implemented more stringent air pollution emission standards and charging system for sulfur emission and dust emission, Wet desulfurization and dust removal technology in our country has been rapid development, has made great progress, technically gradually becoming more mature. Wet flue gas desulfurization technology is particularly suitable for large and medium-sized industrial boiler flue gas desulfurization dust, and also has the advantages of simple equipment, easy operation, high desulfurization rate. One of the most used is the limestone-gypsum method. It is mainly mature technology for a wide range of coal, high desulfurization rate, wide range of sources of desulfurization agent, has now become China's key to promote a wet desulfurization method. However, in practice, there are problems such as scale fouling, corrosion and waste treatment. To completely solve these problems is to improve the core of wet FGD technology. The main reasons for the formation of the problem and countermeasures: 1. Fouling blockage In the wet flue gas desulfurization, whether the pipeline and the equipment are fouled or not has become a key issue of whether the desulfurization device can operate normally or not. To solve the problem of scaling and clogging, we need to understand the mechanism of scaling and the factors that affect scaling and clogging. Only then can we address these issues in terms of process design, equipment structure and operation control. There are three ways to cause fouling and blockage: ①The deposition of solids due to the evaporation of water from the solution or slurry; ② The deposition of Ca (OH) or CaCO, resulting in fouling by precipitation or crystallization; ⑧ CaSO or CaSO from the solution Crystallization, gypsum seed precipitation on the surface of the device and grow to cause fouling. However, in the operation of human factors also need to pay attention to the reasons, such as: ①not strictly in accordance with operating procedures, force d into the calcium desulfurizer excessive, causing the pH value of the washing liquid is too high, and promote the absorption of CO, generated too much Of CaCO, CsSO and other precipitation material; ② more dust-free flue gas into the absorption tower without strict dust removal desulfurization. There is no perfect way to solve this problem absolutely. Currently. Some common methods to prevent fouling blockage are: ①in the process operation, control absorption of liquid water evaporation rate and evaporation; ② appropriate control of the slurry pH value. Because with the pH value, CaSO significantly decreased solubility. So the lower the pH of the slurry, the less likely it is to scale. However, if the pH is too low, the solution has more CaSO, easy to passivate the limestone particle surface to inhibit the absorption reaction, and is too low and easy to corrode the equipment, so the slurry pH value should be properly controlled, the general When the limestone slurry is used, the pH value is controlled to be 5.8-6.2. ⑧ The easily crystallized material in the solution can not be supersaturated, and the solution has a certain seed; (barrier) Add CaSO 2H20 or CaSO seeds to the absorption liquid to control the absorption liquid Saturate and provide enough deposition surface to allow dissolved salts to preferentially precipitate on top. Reduce the deposition and growth of solids to the surface of the equipment; ⑤ for the insoluble calcium sorbents to use a smaller concentration and larger liquid-gas ratio. Such as: the concentration of limestone slurry is generally controlled less than l5%; ⑥ strict dust control, control the amount of smoke and dust in the flue gas; ④ equipment designed for special design, as much as possible to meet the absorption tower liquid holding capacity, gas- Large gas-liquid contact area, less internal components, pressure drop and other conditions. Also choose the surface smooth, non-corrosive materials production equipment, in the absorption tower selection should also be noted. For example: Fluidized bed scrubbers are more difficult to scale and clog than fixed packed scrubbers; ⑧ Use of additives is also an effective way to prevent equipment fouling. Currently used additives are CaC12, Mg (OH) 2, adipic acid and so on. Another reason for fouling is that O in the flue gas oxidizes CaSO to CaSO (gypsum) and supersaturizes the gypsum. This phenomenon occurs mainly in the natural oxidation of the wet system. The control measures are by means of forced oxidation and inhibition of oxidation regulation. It is necessary to oxidize all CaSO, CaSO, but also make it in the unsaturated state of crystallization, can effectively control the scale. Corrosion The cause of corrosion of equipment is very complicated, it is related to many kinds of factors. Such as: temperature of the solution, pH, coal combustion, chloride ion concentration. In addition to the generation of SO, a small amount of SO is also generated in the process of burning coal, while SO can generate sulfuric acid mist with the moisture in the flue gas (4% to 12%). When the temperature is low, the sulfuric acid mist condensation into sulfuric acid attached to the inner wall of the device, or dissolved in the washing liquid, which is wet absorption tower and related equipment, the main reason for the serious corrosion. At present, various parts of the wet desulfurization system, a reasonable selection of anti-corrosion materials and anti-corrosion materials inside and outside the device is to solve the main method of corrosion problems. Such as: to withstand high temperatures, corrosion, wear fast parts, can be used granite, ceramic or modified high-silicon cast iron; withstand low temperature and corrosion, Not serious wear parts, anti-corrosion coatings can be used for surface treatment. Japan's Hitachi's anti-corrosion measures are: In the flue gas reheater, absorption tower population flue, absorption tower flue gas inlet section, are heat-resistant glass flake resin coating, spraying tower spray area using stainless steel or carbon steel rubber lining. In addition the pH can be properly controlled to avoid corrosion, such as: the pH value of limestone slurry is generally controlled at 6.5 ~ 6.8t. 3. Flue gas dehydration Wet absorption tower in the operation process, easy to produce particle size lO ~ 6O m "fog." "Fog" not only contains water, it also dissolves sulfuric acid, sulfate, SO and so on. If not properly resolved, will bring flue gas, corrosion pipes and fans, and the fan impeller sticky ash, scaling, causing fan vibration, shorten the life of the fan. Therefore, wet dedusting equipment must be equipped with defogging, the performance of a direct impact on wet flue gas desulfurization system can continue the reliable operation. Mist eliminators usually consist of a defogger body and a flushing system. The role of demister body is to capture the droplets in the flue gas and a small amount of dust to reduce flue gas, to prevent fan vibration; flushing system is regularly rinsed by the demister trapped droplets of dust to prevent blade scaling, Maintain the system up and running. Demisters are mostly located at the top of the absorption tower. Normally, a two-stage demister should be provided, so that the residual moisture in the flue gas after decontamination is generally not more than 100mg / m, otherwise the heat exchanger, the flue and the fan will be corroded. Wastewater treatment After the lye absorbs the SO in the flue gas, it mainly produces the waste liquid in the form of colloidal suspension containing soot, sulfate and sulfite, which has a pH lower than 5.7 and is weakly acidic. Therefore, this type of wastewater must be properly treated before reaching efflux. Otherwise it will cause secondary pollution. The rational treatment of wastewater should be able to recover and comprehensive utilization of sulfate in the wastewater, so that the waste of resources. Such as: Japan and Germany due to the lack of gypsum resources, so in the wet limestone / lime-gypsum flue gas desulfurization, the success of the sulfate in the waste water into gypsum; also waste water sulfate into high Concentration of high purity liquid SO, as the raw material for the production of sulfuric acid. Now, the domestic and foreign power plants on limestone-gypsum desulfurization wastewater mainly chemical treatment. The waste water is first oxidized by air in a buffer pool to oxidize the low-priced metal ions to a high price (the purpose is to make the metal ions easier to precipitate and remove), then enter the neutralization pool, add the alkaline material lime milk in the neutralization pool, The metal ions in the neutralization tank to form a hydroxide precipitate, part of the metal ions to be removed. but