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Sintering flue gas of iron and steel enterprises has its own characteristics compared with flue gas of ordinary power plants: large amount of flue gas and uneven distribution. About 4,000-6000 m3 of flue gas is produced per ton of sintered ore produced, due to differences in gas permeability and uneven materials. In the end, the resistance of the flue gas system changes greatly, and the amount of flue gas becomes larger. Today, let's talk with you about how to choose the appropriate denitration technology for the sintering of flue gas in steel companies.
The difference between sintering flue gas in iron and steel enterprises compared with ordinary power plant flue gas
(1) The temperature variation range is large. It is generally 80-180 ° C, but does not reach the temperature required for the power plant boiler flue gas denitration SCR reaction 350 ° C. High oxygen content. Generally 15%-18% humidity. Large and unstable. In order to improve the gas permeability of the sintered mixture, the mixture must be added with an appropriate amount of water to form a pellet before sintering, so the moisture content is generally 10%-13%.
(2) The composition of pollutants is complex. The use of raw iron ore makes the corrosive gas such as HCl, HF, NOX contained in the flue gas, the dust concentration is high, and the SO2 content is large.
At present, flue gas denitration technology can be divided into catalytic decomposition, catalytic reduction, non-catalytic reduction, absorption method, adsorption method, electron beam method, etc. according to the removal principle. Today, we combine sintering technology from several widely used denitration technologies. The characteristics of the flue gas select a reasonable denitration technology.
The SCR process was first industrialized in Japan in the 1970s. It is mainly used in industrial boilers and power station boilers for flue gas denitrification. Under the action of catalysts, NH 3 is used as a reducing agent in a certain temperature range (generally 300-450 ° C). ), the NOX is reduced to produce N2 and H2O.
The technology has high denitration efficiency, generally 70%-90%, no secondary pollution, and the system is stable. More than 300 power plants in China use the SCR method, accounting for 98% of all denitration technologies. However, due to the low temperature of the sintering flue gas in China, the operating temperature of the SCR cannot be achieved and the investment operation cost is high, so it cannot be directly applied to the denitration of the sintering flue gas.
SNCR means that at a certain temperature, without the presence of a catalyst, an ammonia reducing agent such as ammonia or urea is selectively used to selectively reduce nitrogen oxides in the flue gas to N2 and H2O, and substantially does not interact with oxygen in the flue gas. The technology is mainly applied to flue gas denitrification in thermal power plants. The technology has low investment, simple equipment and no catalyst, but the denitration efficiency is relatively low, usually around 40%, and the reaction temperature is high, mainly used in kiln facilities, so it is not applicable. In the case of sintering flue gas.
NOX is removed by the selective injection of activated carbon functional groups and is removed by adsorption. The removal efficiency is 40%-60% without ammonia gas. The first advantage is that sulfur dioxide, nitrogen oxides, dioxins and other pollutants can be simultaneously removed; second, the flue gas temperature can meet the requirements of denitration reaction, no external heating source is needed; third, no process water and wastewater treatment is required.
Up to now, large steel companies using activated carbon dry-sintering desulfurization and denitrification include Japan's Nippon Steel & Sumitomo Metal, South Korea's Pohang Steel, Australia's BlueScope Steel and China Taigang. However, the construction cost and operating cost of the activated carbon device are very high, which is 3 to 5 times that of other sintering flue gas treatment devices. The consumption of activated carbon is large, and the sprayed ammonia increases the adhesion, resulting in uneven distribution of the gas flow in the absorption tower, coupled with environmental protection. The input efficiency is low and it is difficult to popularize.
The basic mechanism of the ozone oxidation denitration technology is to use the strong oxidizing ozone generated by the ozone generator to oxidize the poorly soluble NO to a high-valent nitrogen oxide such as NO2, N2O3, N2O5 which is easily soluble in water, and then in the washing tower. NOX is absorbed by the Ca(OH)2 of the absorbent to achieve the goal of denitrification.
Its denitration efficiency is 60-90%, and the reaction mechanism is:
NO + O3 → NO2 + O2
4NO2 + 2CA(OH)2→Ca(NO2)2 + Ca(NO2)2 + H 2 O
The ozone oxidation and denitration process is simple, the floor space is small, the operation and maintenance are simple, and SO2 and NOX can be simultaneously removed. Combined with the characteristics of sintering flue gas in iron and steel enterprises, the selected ozone oxidation denitration technology is the most suitable and reasonable, but this technology is less used in the domestic steel industry.
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