Study On Desulfurization, Denitrification And Adsorption Of Mercury By Catalytic Activated Carbon

Much contamination such as SO2,NOx,Hg and Pb comes from the coal-fired plants. After a series reaction by ultraviolet radiation and dust, SO2 and NOx are combined with H2O,at last form acid rain. Acid rain will do harm to environment and mankind health. The trace element such as Hg and Pb will have a series physics and chemic reaction in the low temperature flue gas. At last they escape from ESP, and at last emit to the air. Therefore it is very urgent to control the contamination, especially SO2 and NOx. In order to desulfurization ,denitrification ,adsorption of mercury, the paper uses activated carbon, adopt some method to catalyse it ,compares some method, discusses the mechanics and factor of desulfurization ,denitrification mercury adsorption by activated carbon.Activated carbon includes activated carbon fibers (ACF)and granular activated carbon(GAC), but the paper uses ACF, and adopts two manners to catalyse it. One is immersion in sulfuric acid before impregnated with ammonia, the other is immersion in ammonia before impregnated with sulfuric acid. The result shows that the first way is feasible, and can efficiently increase the oxygen functional group ,the nitrogen functional group. Furthermore after catalysis, the BET surface area and the capacity of pores become smaller, the average width of pores becomes bigger. The second way reduces the performance of activated carbon fibers.ACF adsorbs SO2 at active sites, then SO2 is converted to SO3, if there is water , sulfuric acid is formed. SO the performance of ACF is influenced by temperature,oxygen,moisture and so on. The results show that moisture is vital, controls the velocity of desulfurization. With the moisture increasing , the efficiency of desulfurization also improves, but when the moisture increases to 8%, the trend of augment is not visible . Oxygen is very important, and is adsorbed at the surface of ACF ,then C-O is formed. When the oxygen increases, the efficiency raises too, but after the oxygen increases to 5%, the trend is not obvious. We know that the ACF is a kind of low temperature adsorbent, so with temperature increasing, the vapor is not efficiently dewed and the efficiency of desulfurization decreases. With W/Q increasing, the activated sites that ACF supplies add , which can improve the efficiency. But we take into account the economics , we recommend that W/Q is 2.5×10-3～3×10-3Kg*min/L. Without ammonia, ACF converts NO into NO2. If there is water, NO2 goes on converting HNO3. There are many factors that influence the efficiency of conversion such as oxygen,temperature,water et al. The results show that the conversion increases with the oxygen, and the water is bad for conversion. Furthermore the temperature is also bad for conversion.If there is SO2 and NO, SO2 competes active sites with NO. According to the adsorption theory, the molecule diameter ,boiling point,dipole of SO2 are bigger than that of NO, so SO2 is adsorbed before NO, and influences the conversion of NO. Furthermore there is interaction between adsorbed SO2 and formed NO2, then intermediate product is formed. At last, H2SO4 and HNO3 are formed by water ,NO gives off. It is good for desulfurization by ACF.As is concerned for adsorption of mercury, the paper uses GAC and ACF. There are carbonyl group and lactone that are the active site for Hg0 capture. It involves an electron transfer process during Hg0 adsorption. Activated carbon is catalyzed by Na2S, which can enhance the adsorption of mercury. The result is compared with that of impregnated by ZnCl2. The paper concludes that activated carbon impregnated by ZnCl2 is better than by Na2S. ACF catalyzed by the first way also adsorb Hg and Pb.