Experimental Study On Removal Of Gas-phase Elemental Mercury By Sorbents Derived From Biomass And PVC

Mercury emission from the coal combustion process is the main artificial source of atmospheric mercury pollution. Adsorption of mercury by activated carbon injection is a simple way of removal mercury after combustion. Because of its high cost, activated carbon is not widely used in coal-fired power plants. Thus, development of new type adsorbent what is environmental protection, high efficiency and low cost becomes the current hot research topic. This paper presents waste-derived sorbent as a new idea of mercury removal sorbents. Biomass waste as the carbon substrate and PVC as the active chlorine precursor,Cl-activated sorbents by thermal treatment of the mixture were obtained in this paper. The mercury removal property of waste-derived sorbents was studied.First, the feasibility of waste-derived sorbents was discussed in this paper. Paper and PVC as the raw materials and pyrolysis chars were prepared by different temperatures,mixing ratios, atmospheres in this study. The experiments showed that paper has an obvious interaction with PVC. The absence of PVC increased the yield of pyrolysis char and formed the functional group C-Cl in the surface. The mercury removal property of these pyrolysis chars showed that the chemical adsorption capacity greatly enhanced at 110℃. It was mainly through a combination of C-Cl surface functional groups and Hg0, following the formation of a substance similar to HgClx.Following contents studied the comparison of mercury removal capacity about the two waste-derived sorbents paper/PVC and wood/PVC. Waste-derived sorbents were prepared by three different ways with temperature at 700℃(N2 atmosphere, Barrier pyrolysis)and temperature programmed(N2 atmosphere). In view of the yield and adsorption efficiency of the sorbents, the two substances were suitable as raw materials of this sorbent. The wood/PVC sorbents had higher adsorption efficiency when the quality of sorbents was the same. Different preparation methods lead to different number of C-Cl functional groups inthe surface and the sorbents that prepared under barrier pyrolysis at 700℃ made itself the highest absorption efficiency. Waste-derived sorbents had a good mercury removal property in a wide temperature rang. There was an optimum adsorption temperature. CO2 and NO in the feed gas had negligible effect on the efficiency of mercury removal. Under certain conditions of concentration, O2 was favored for the removal of mercury, but SO2 had an inhibition of the efficiency, and when O2 and SO2 exist the same time, the influence canceled each other.Depending on the nature of the adsorbents, this paper made some research about mercury removal performance of the sorbents improved by physical, chemical activation and plasma. The results indicated these three types of treatments all can enhance the absorption efficiency of the sorbents. The order of degree promotion was plasma, chemical activation, and physical activation, respectively. Plasma treatment resulted in forming more C-O functional groups and transforming the distribution of C-Cl functional groups in the surface of sorbents.