| Mercury pollution in coal-fired power plants has attracted more and more attention from domestic and foreign scholars in recent years.The state has introduced pollutant emission control standards and control of mercury emissions in coal to be imminent.At the same time,chemical looping conversion technology has gradually become a hot topic of domestic and foreign scholars as a new chemical transformation and energy utilization technology,which can realize chemical looping combustion process?CLC?and chemical looping gasification process?CLG?by controlling the amount of oxygen carriers.It was of great significance to study the morphological distribution and released of mercury during the conversion process for the removal and control of mercury in coal.In this paper,Fe4Al6 were used as oxygen carriers,Juye gas coal,Zhaotong lignite and Gaoping anthracite were selected as coal samples to investigate the mercury migration rule in the coal-chemical looping transformation process in the high temperature tubular furnace,in order to provide basic experimental data support for mercury emission control in the chemical looping conversion process.Effects of Fe4Al6 oxygen carriers on mercury release rate,gaseous mercury distribution and mercury release behavior in two reactors in coal chemical looping combustion/gasification process were investigated by Ontario-Hydro method in a tubular furnace.The result showed that Fe4Al6 oxygen carriers could affect the mercury release rate significantly.Compared with the traditional coal pyrolysis,Mercury release rate in CLC decreased,while that in CLG increased in 500?700?.However,mercury release rate in both CLC and CLG was more than that without oxygen carriers at 900?.Fe4Al6 oxygen carriers can significantly increase the relative content of Hg2+ from fuel reactor?FR?outlet.The relative content of Hg2+ increased with the increasing temperature.Besides the content of oxygen carriers,FR temperature was the primary influence factor on the distribution of mercury from fuel reactor and air reactor as well as the percentage of gaseous mercury speciation in the air reactor.In addition,the mercury release rate was different form different types of coal under the same condition,which related mainly to the composition of coal.This study will provide experimental evidence for revealing the influence mechanism of oxygen carriers on mercury migration in the coal and for the control of mercury in coal chemical looping conversion processes.The adsorption mechanism of mercury by oxygen at different temperatures and the oxidation mechanism of mercury by oxygen at different atmospheres were investigated in a high temperature tube furnace in order to fully verify the influence of Fe4Al6 oxygen carriers on mercury release rate and morphological transformation during chemical looping conversion The oxidation of Hg by oxygen carriers and the main valence state of Hg after adsorption were analyzed by using HSC thermodynamic equilibrium calculation and XPS.A model of oxygen carriers-mercury oxidation adsorption mechanism was established to further explain its mechanism.The adsorption/oxidation mechanism analysis of Fe4Al6 oxygen carriers transporter-mercury shows that oxygen transporter has certain adsorption and oxidation ability to mercury vapor,and the adsorption effect of oxygen transporter on mercury was obviously affected by temperature.The adsorption of oxygen carriers on mercury shown different characteristics at different temperatures:In 500?700?mainly physical adsorption and chemical adsorption quantity was less,in 700?900?weakened physical adsorption and chemical adsorption enhanced gradually,but still mainly physical adsorption;The oxygen carriers fixed part of mercury vapor to Hg2+ on the surface of oxygen carriers.Hg2+ was characterized by HgO?R?and HgO?Y?in the chemical adsorption process by means of XPS and thermodynamic equilibrium calculation.It was verified that the adsorption of Hg on the surface of oxygen carriers was mainly in the form of elemental mercury?Hg0?. |
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