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Domestic and foreign flue gas desulfurization facilities have been built mostly coal-fired power plants, desulfurization technology is also the main power plant research, petrochemical refinery desulfurization technology research to a certain extent, the power plant flue gas desulfurization existing mature technology. At present, according to the form of by-products, flue gas desulfurization technology can be divided into wet, dry, semi-dry three.
First, 14 kinds of flue gas desulfurization technology Xiangjie
Wet Flue Gas Desulfurization (WFGD) absorbent reacts with SO2 in a liquid state and the desulfurized product is also liquid. The method of high desulfurization efficiency, stable operation, but the high investment and operation and maintenance costs, system complexity, desulfurization products more difficult to deal with, easy to cause secondary pollution.
Dry flue gas desulfurization (DFGD) desulfurization absorption and product treatment are carried out in the dry state. The system is simple, no sewage and waste acid discharge, equipment corrosion, low operating costs, but lower desulfurization efficiency.
Semi-dry flue gas desulfurization technology (SDFGD) semi-dry method to absorb the advantages of wet and dry, desulfurization agent in wet desulfurization, desulfurization products to dry discharge. The method not only has the advantages of fast reaction rate of wet desulfurization, high desulfurization efficiency, but also has the advantages of dry sewage and waste acid discharge, easy product after sulfur treatment.
Wet flue gas desulfurization technology advantages: wet flue gas desulfurization technology for the gas-liquid reaction, fast reaction rate, high desulfurization efficiency, generally higher than 90%, mature technology, a wide range of applications. Wet desulfurization technology is relatively mature, safe and reliable operation of the production, in many desulfurization technology, has always dominated, accounting for more than 80% of the total installed capacity of desulfurization. Disadvantages: the resulting product is liquid or sludge, more difficult to deal with equipment, serious corrosion, washing after the flue gas to be reheated, high energy consumption, large area, high investment and operating costs, system complexity, large equipment, water consumption Large, one-time high investment, generally applicable to large power plants. Category: Commonly used wet flue gas desulfurization techniques are limestone - gypsum method, indirect limestone - gypsum method, lemon absorption method.
1, Limestone / Lime-Gypsum Principle: Limestone or lime slurry is used to absorb SO2 in flue gas to generate calcium sulfite. The separated calcium sulfite (CaO3S) can be discarded and can also be oxidized into calcium sulfate (CaSO4) Recycled in the form of gypsum. This is the most mature technology in the world, the most stable operating conditions desulfurization process, desulfurization efficiency of more than 90%.
2, indirect limestone - gypsum method common indirect limestone - gypsum method are: sodium and alkali double alkali method, alkaline aluminum sulfate method and dilute sulfuric acid absorption method. Principle: Sodium hydroxide, basic alumina (Al2O3? H2O) or dilute sulfuric acid (H2SO4) absorbs SO2, and the resulting absorption liquid reacts with limestone to regenerate and gypsum. The method is simple, less secondary pollution, no scaling and plugging problems, high desulfurization efficiency, but the resulting gypsum product quality is poor.
3, Lemon absorption method Principle: Citric acid (H3C6H5O7? 2O) solution has a good buffer performance, when the SO2 gas through the citrate liquid, SO2 in the flue gas and H + in water react to generate H2SO3 complex, SO2 absorption Rate above 99%. This method is only suitable for low concentrations of SO2 flue gas, but not for high concentrations of SO2 gas absorption, the application range is relatively narrow. In addition, there are seawater desulfurization, ammonium phosphate fertilizer, liquid-phase catalytic wet flue gas desulfurization technology.
Dry flue gas desulfurization technology advantages: Dry flue gas desulfurization technology for gas with the reaction, relative to the wet desulfurization system, with simple equipment, small footprint, lower investment and operating costs, easy operation, low energy consumption , The product easy to handle, no sewage treatment system and so on. Disadvantages: slow reaction, low desulfurization rate, advanced up to 60 ~ 80%. However, at present, the desulfurization efficiency of such a method is low, the utilization rate of the absorbent is low, the wear and scaling phenomenon is serious, the equipment maintenance is more difficult, the stability of the equipment is not reliable, and the service life is short, which limits the Application of this method. Category: Commonly used dry flue gas desulfurization technology activated carbon adsorption, electron beam radiation, dry charge injection method, metal oxide desulfurization method. A typical dry desulfurization system is the desulfurization agent (such as limestone, dolomite or hydrated lime) directly into the furnace. Taking limestone as an example, when calcined at a high temperature, the desulfurizing agent is calcined to form porous calcium oxide particles, which react with SO2 in the flue gas to generate calcium sulfate to achieve the purpose of desulfurization.
4, Activated carbon adsorption principle: SO2 is activated carbon adsorption and catalytic oxidation of sulfur trioxide (SO3), and then reacts with water to produce H2SO4, saturated activated carbon can be regenerated by washing or heating, while generating dilute H2SO4 or high concentrations of SO2. Available by-products H2SO4, liquid SO2 and elemental S, which can effectively control the emission of SO2, but also the recovery of sulfur resources. The technology of Xi'an Jiaotong University improved the activated carbon, developed a low cost, the choice of strong adsorption performance ZL30, ZIA0, to further improve the process of activated carbon so that flue gas SO2 adsorption rate of 95.8%, reaching the national emission standards.
5, Electron Beam Radiation Method: The high-energy electron beam irradiates the flue gas to generate a large amount of active substances, which oxidize the SO2 and nitrogen oxides in the flue gas into SO3 and nitrogen dioxide (NO2), further generate H2SO4 and nitric acid ) And absorbed by ammonia (NH3) or limestone (CaCO3) absorbers.
6, dry charge injection desulfurization method: the absorbent flows at high speed through the jetting unit to generate high voltage electrostatic corona charging zone, so that the absorbent with electrostatic charge, when the absorbent is sprayed into the flue gas flow, absorption Because agents with the same kind of charge and mutually exclusive, the surface is fully exposed, the desulfurization efficiency increased significantly. This method is dry process, no equipment pollution and scaling phenomenon, does not produce waste industrial flue gas desulfurization technology research waste water residue, by-product can also be used as fertilizer, no secondary pollutants, desulfurization rate greater than 90%, and equipment Simple, adaptable more extensive. However, this method desulfurization by electron beam accelerator to generate high-energy electrons; for the average large-scale enterprises, the need for high-power electron guns, harmful to human body, it also needs radiation shielding, so running and maintenance requirements. Chengdu, Sichuan Thermal Power Plant built an electronic desulfurization unit, SO2 in flue gas desulfurization reached the national emission standards.
7, the principle of metal oxide desulfurization: According to the characteristics of SO2 is a more lively gas, oxides such as manganese oxide (MnO), zinc oxide (ZnO), iron oxide (Fe3O4), copper oxide Strong adsorption, at room temperature or low temperature, the metal oxide on the adsorption of SO2, under high temperature, the metal oxide and the chemical reaction of SO2, generating metal salts. The adsorbent and the metal salt are then regenerated by thermal decomposition, washing or the like. This is a dry desulfurization method, although there is no sewage, waste acid, does not cause pollution, but this method has not been promoted, mainly because of relatively low desulfurization efficiency, large equipment, large investment, high operating requirements, high cost . The key to this technology is the development of new adsorbents. The above several kinds of SO2 flue gas treatment technology is widely used at present, although the desulfurization rate is relatively high, but the complex process, high operating costs, pollution prevention is not complete, resulting in secondary pollution and other deficiencies with our economy and environment to achieve the principle of harmonious development Do not adapt, it is necessary to explore new technologies and desulfurization.
Semi-dry flue gas desulfurization technology Semi-dry desulfurization including spray drying desulfurization, semi-dry semi-wet desulfurization, powder - particle spray bed desulfurization, flue gas desulfurization.
8, Spray drying method Spray drying desulfurization method is the use of mechanical or airflow power to disperse the absorbent into very fine droplets of mist, droplets and flue gas form a relatively large contact surface area between the gas-liquid two-phase A heat exchange, mass transfer, and chemical desulfurization methods that occur. Generally used absorbent is lye, lime milk, limestone slurry, etc., the vast majority of devices are currently using lime milk as an absorbent. Under normal circumstances, this method of desulfurization rate of 65% to 85%. Its advantages: desulfurization is carried out in gas, liquid and solid three-phase state, the process equipment is simple, the product is dry CaSO4, CaSO4, easy to handle, there is no serious equipment corrosion and clogging, water consumption is relatively small. Disadvantages: higher automation requirements, the amount of absorbent difficult to control, absorption efficiency is not high. Therefore, the choice of developing a reasonable absorbent is to solve this method is facing new challenges.
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