| As one of heavy metals, mercury is a trace element in coal, it is highly volatile and emitted into the atmosphere following with flue gas in the process of combustion. Mercury poses a huge risk of health to humans and wildlife, and its control is arosed great attention in the field of environmental protection because of its high physiological and bioaccumulation. Coal is the major energy source in China, and it has been reported that mercury content in most Chinese coals is higher. Therefore, mercury contamination is a serious problem in our country and it demands immediate actions to control and research of mercury emission from coal-fired power plants.The paper simply introduces the major sources, physical and chenmical appearances, and the health hazard of mercury released from coal-fired power plants. It also emphatically describes the major progress of mercury control technologies and its measuring technologies for coal-fired flue gas at home and abroad. Meanwhile, discuss the structure, synthesis and modified methods, properties and the application in the treatment of pollutants of ZSM-5zeolite.In our experiment, HZSM-5zeolite possessing types of acid sites was used as adsorbent carrier. A series of HZSM-5zeolite adsorbents were prepared by incipient impregnation to investigate their removal characteristics of Hg0in experimental flue gas. Manganese acetate as modifier, MnOx/HZSM-5with different loadings (0～15%) was prepared at500℃calcinations temperature. In the following experiment, the Hg0removal ability of the adsorbents over time was investigated in a lab-scale fixed-bed system at different experiment condition. The experimental results showed that the HZSM-5had good activity on removing Hg0in the presense of6%O2. After loading active components MnOx on HZSM-5zeolite, the removal efficiency of Hg0could be increased, however, with the loading increasing, the removal efficiency first increased, then decreased, and the best loading amount was10%. Rising reaction temperature appropriately could increase the removal efficiency of Hg0, and the optimum temperature was300℃, where the removal efficiency could reach90%or more. As one kind of oxidents, O2in flue gas could promote the oxidation of Hg0while NO and SO2inhibited the mercury oxidation by poisoning and competing the activity sites on the MnOx/HZSM-5sorbents.Furthermore, it was studied that Hg0removal characteristics of Mn-Ce/HZSM-5sorbents prepared at different calcinations temperatures (350n450、550℃) over action temperature and reaction time. The experimental results displayed that the adsorbents prepared at different calcinations temperatures showed similar Hg removal performance. In comparison, the adsorbents prepared at450℃and550℃were better than the other on removal efficiency of Hg0in simulated flue gas. It was found that with the action temperature increasing, the removal efficiency of (0.5)Mn-Ce/HZSM-5first increased, then decreased, and the optimum action temperature was270℃which was lower than MnOx/HZSM-5’s. Besides, there were so many advantages that (0.5)Mn-Ce/HZSM-5was applied to Hg0removal, such as wide applied range, and high thermal stability. Compare the three kinds of adsorbents whose loadings both were6%, such as MnOx/HZSM-5,(0.5)Mn-Ce/HZSM-5and (2)Mn-Ce/HZSM-5. It was found that we could improve the performance of removal Hg by increasing the ratio of Mn and Ce, and the best ratio adsrbent was (0.5)Mn-Ce/HZSM-5.At last, a combination of technigues such as BET, XRD. SEM and TG were used to characterize the sorbents in order to research the changes in their physical and chemical properties. The results not only confirmed the results of adsorption tests, but also provided the theoretical basis for the improvement of adsorbent. |
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