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SO2 emissions from China's steel industry have become one of the main sources of pollution after coal-fired power generation. Among them, the SO2 produced in the sintering process accounts for 60% to 90% of the total emissions of the steel industry. Therefore, the control of SO2 emissions from sintering machines has long been the focus of iron and steel enterprises in controlling pollution.
At present, the main flue gas desulfurization methods used in most sintering machines include: circulating fluidized bed semi-dry method, rotary spray semi-dry method and limestone-gypsum wet method. The desulfurizing agents used are generally quicklime, limestone, dolomite, etc. . Due to the different conditions of various enterprises in terms of investment costs, desulfurization efficiency, resource supply of desulfurization agents, and treatment of desulfurization by-products, in the past two years, companies have also begun to develop other methods, such as the additive method, ammonia-ammonium sulfate Method, steel slag dry method and so on. However, from the perspectives of low operating costs, high desulfurization efficiency, and relatively mature technology, most steel companies use the rotary spray semi-dry method and the limestone-gypsum wet process.
1. Basic process principles of two flue gas desulfurization methods
(1) Rotary spray semi-dry method
As shown in Figure 1 of the accompanying drawings, when hot (about 120 ° C) untreated flue gas is removed by an electric precipitator, it enters a rotary spray drying absorption tower through a flue gas distributor, and the prepared lime slurry mist droplets (Mist droplet diameter is not greater than 50 microns) When contacted, the acidic components in the flue gas are quickly absorbed and neutralized, and the moisture in the droplet is also evaporated and discharged along with the flue gas. The processed flue gas then enters a bag filter, and the suspended solids are removed by filtration, and is drawn to the chimney by an induced draft fan (pressurized fan) and discharged into the atmosphere.
(2) Limestone-gypsum wet method
As shown in Figure 2 of the accompanying drawings, when the hot (about 120 ° C) untreated flue gas is removed by an electric precipitator, it enters the absorption tower through a booster fan and is pumped with the slurry circulation during upward movement. The limestone slurry sprayed downward into the absorption tower is fully contacted, and a chemical reaction occurs to generate calcium sulfite. At the same time, the oxidizing air sent by the oxidizing fan enters the absorption tower after spraying water to cool down, forcibly oxidizes and crystallizes calcium sulfite to form gypsum. The flue gas passes through the demister to remove the contained droplets, and the net flue gas flowing out of the absorption tower is directly discharged into the atmosphere from the chimney.
2. The technical defects of the two flue gas desulfurization methods
Based on the analysis of the above principles and many years of practical experience, it is easy to see that whether it is a rotary spray semi-dry method or a limestone-gypsum wet desulfurization, there is an important process technical defect. That is, although the SO2 removal processes of both are relatively mature and have high desulfurization efficiency, water must be used as the medium to promote the chemical reaction between the desulfurizer and the sintering machine flue gas. In this way, although the treated flue gas has removed SO2, it carries a large amount of saturated steam and fine powder particles (after research, its main component is dust containing sulfate, nitrate, etc., which constitutes PM2.5 One of the main sources of pollution).
Because the smoke directly discharged into the atmosphere contains a large amount of water vapor and fine powder particles, white plumes will form after condensation, especially in winter. In some iron and steel enterprises with poor dust removal or defogging effect, even the phenomenon of thick white plumes and gypsum rain may seriously pollute the atmospheric environment and natural environment around the plant area.
How to improve the existing sintering machine flue gas treatment method. After the flue gas of the sintering machine head of the steel plant is subjected to a circulating fluidized bed, a rotary spray semi-dry method or a limestone-gypsum wet desulfurization treatment, the water-containing dust in the flue gas can be further reduced. The environmentally-friendly purification technology that effectively reduces pollutants such as PM2.5 and sulfates, nitrates, and visually eliminates "white smoke" from chimneys is a technical problem to be solved by the present invention.