Study On Iron-based Adsorbents For Mercury Removal And The Characteristic Of Mercury Emissions From Coal-fired Power Station

The traditional way of developing and using coal has impacted seriousiy on Chinese economy and environment. Developing clean coal-utilization technology to reduce coal-fired pollution is necessary now.Coal gasification is a technology which can convert the coal to gas,it is a efficient and clean way of coal utilization.Fuel gas generated from coal gasification also contains elemental mercury. This will not only impact on the gas turbine but also pollute the environment by emission into the atmosphere in the form of gaseous or compounds with the gas,fly ash or coke.To date,most of the research activities,both practical and fundamental,have focused on the removal and conversion of elemental mercury from real or simulated coal combustion flue gas.In contrast,very little attention has been paid to the capture of elemental mercury from coal-derived fuel gas.It is thought that coal gasification combined power generation will be a major utilization method of coal in the near future.Thus the development of an efficient method for the mercury removal of Hg0from the coal derived fuel gas is an urgent problem.This article relying on the National Natural Science Foundation and environmental welfare industry research and special project, Fe2O3sorbents synthesized by an ultrasonic-assisted precipitation method were employed to remove elemental mercury (Hg0) in coal gas. The samples were characterized by BET (Brunauer-Emmett-Teller), SEM (scanning electron microscope), XRD (X-ray diffraction) as well as XPS (X-ray photoelectron spectroscopy) analysis. The mercury removal performance and mechanism by iron oxide sorbent under nitrogen and simulated gas atmosphere was studied on a bench-scale fixed-bed apparatus by using mercury online analyzer. And the effect of various gas on Hg0removal performance by iron oxide sorbent was analysised.The result showed that:the adsorption performance of Fe2O3is relatively poor in nitrogen atmosphere, and physical adsorption is the dominating mechanism of mercury capture; when100×10-6H2S was introduced Fe2O3sorbents exhibited high Hg0removal activity at150℃, and more than95%of Hg0was removed. XPS surface analysis showed that the vast majority of mercury exist on the the surface of the iron oxide in the form of elemental mercury under the N2atmosphere while the vast majority of mercury exist in the form of Hg2+under the H2S atmosphere. In the presence of H2S, Hg0removal over Fe2O3was proposed to follow the Eley-Rideal mechanism, where adsorbed Sad reacts with gas-phase Hg0. The effect of the concentration of H2S on Hg removal was not observed in the range from100to400ppm,but the Hg removal did not occur without H2S. The effect of the presence of CO and H2was not observed at150℃. The oxidation of elemental mercury through gas phase reaction under a reducing atmosphere is difficult to happen.Because of the competitive adsorption,the presence of H2O suppressed the mercury removal at150℃The inhibitory effect is proportional to H2O concentration.The elemental mercury removal efficiency was influenced strongly by the adsorption temperature.With the adsorption temperature increases,the elemental mercury removal efficiency varies in the shape of a mountain.Using the Ontario sampling method of U.S. EPA standards for mercury emissions of a coal-fired utility boilers and the effects of conventional pollutant control device on the mercury emissions. Obtain data about mercury emissions from coal-fired boilers and the impact of conventional pollutant control device on the mercury emissions.