Study On Reaction Mechanism Of Iron-based Oxygen Carrier And Hydrogen Selenide Based On Coal Chemical Looping Gasification

As the pillar energy of our country,coal has also brought serious environmental pollution when promoting social development,especially the volatile elements such as mercury,selenium,arsenic,etc.,which cause serious harm to the environment and human body.Selenium,as an element closely related to human health,has always been the focus of research.As a new coal application technology,coal chemical looping gasification technology has the advantages of high energy utilization,low cost and low pollution,which is an important means of coal application in the future.Due to the introduction of oxygen carrier in coal chemical looping gasification technology,the release of pollution elements in the reaction process is different from that of conventional coal gasification.In this paper,the mechanism of the reaction between hydrogen selenide and iron-based oxygen carrier in coal gasification was systematically studied by simulation and experiment.The specific contents and conclusions are as follows:(1)The possible reaction between iron-based oxygen carrier and hydrogen selenide was simulated by using HSC chemistry 6.0 software in the temperature range of 300?1000?.Fe2O3,the active component of iron-based oxygen carrier,can oxidize and adsorb hydrogen selenide.With the decrease of Fe2O3 content and the increase of Fe3O4 and FeO content in iron-based oxygen carrier,the oxidation effect of iron-based oxygen carrier decreases gradually.With the deepening of reduction degree of ironbased oxygen carrier,the decomposition reaction of hydrogen selenide becomes the main reaction.(2)The reaction experiment of hydrogen selenide with iron-based oxygen carrier was carried out in tubular furnace.The effects of temperature,atmosphere and reduction depth of oxygen carrier on the reaction performance of iron-based oxygen carrier with hydrogen selenide were analyzed.The results show that high temperature is not conducive to the adsorption of hydrogen selenide,and the adsorption capacity decreases with the increase of temperature;The reduction degree of oxygen carrier affects the reaction mechanism;Hydrogen selenide mainly exists on the surface of oxygen carrier in the form of selenium,and there is a small amount of ferrous selenide.(3)Based on density functional theory,the stable adsorption configurations of H2Se and its dissociated species on Fe2O3 surface were calculated,and various possible reaction paths were studied.It was found that H2Se and its dissociated species,HSe and Se,were in the ?-Fe2O3(001)is preferentially adsorbed on the top of iron,and the adsorption energies are-59.74 kJ/mol,-170.78 kJ/mol,-239.28 kJ/mol,respectively.?-Fe2O3(001)surface has two functions in the reaction with H2Se:one is catalysis,which reduces the activation energy of H2Se dehydrogenation and makes the dehydrogenation easier;The second is to participate in the reaction as reactants,resulting in chemisorption.