Transformation And Migration Of Selenium During Chemical-looping Gasification Of Coal

Coal is the main source of energy consumption in our country,in recent years,the pollution of atmospheric environment caused by the pollution gas and sulfur/nitrogen oxides,which produced in the process of coal utilization has attracted much attention from the society.It is necessary to develop an efficient and economical coal utilization technology,chemical looping gasification technology is a kind of high efficient,clean energy technology,it has the characteristics of improving energy efficiency.The release of selenium from coal into the atmosphere during combustion and gasification process is a great challenge for air cleaning.Through the combination of experiment and thermodynamic simulation,this research systematically investigated the behavior of selenium distribution and transformation,and the effects of reaction temperature,experimental coal types,oxygen-carbon ratio and cycles of oxygen carriers on the distribution of selenium in coal chemical looping gasification.The detailed contents of this study are as follows:1.Based on the minimum gibbs free energy method,the effects of CuO/Ben oxygen carriers on the release and migration of selenium during coal chemical looping gasification were investigated under the experimental conditions of temperature ranging from 100? to 1000? and the pressure was one atmosphere.The results of thermodynamic simulation showed that the existence form of selenium in coal chemical looping gasification was related to the reaction temperature,and H2Se(g)in gas phase was the main form of selenium in chemical looping gasification.As the temperature increased,the concentration of H2Se(g)in the gas phase increased,and CuO/Ben oxygen carrier would react with H2Se(g)to form Cu2Se.2.In the fluidized bed reactor,shaanxi bituminous coal and CuO/Ben oxygen carriers were selected to discover the migration distribution and transformation mechanism of selenium in gas phase,coal ash and oxygen carriers during traditional coal gasification and coal chemical looping gasification.The results showed that the content of gas-phase H2Se(g)was about 90%in traditional gasification,the main existence state of selenium in chemical looping gasifition was still the gas phase H2Se(g),the oxygen carrier oxidized and adsorbed selenium,which would reduce the content of selenium in the vapor phase,and the concentration of selenium in the oxygen carrier was about 19.07%,XPS characterization results showed that gaseous selenium migrated to oxygen carriers and existed in the form of Cu2Se and elemental selenium.3.This study investigated the effects of coal type,oxygen-carbon ratio,reaction temperature and cycle times of oxygen carrier on the distribution of selenium in gas phase,coal ash and oxygen carrier during coal chemical looping gasification.In coal chemical looping gasification,the distribution behaviors of selenium was universally applicable to the experimental coal from shaanxi,ningxia and Inner Mongolia.As the temperature increased from 850? to 950?,the more volatile H2Se(g)existed in the gas phase,high temperature in fuel reactor could promote the release of selenium from coal.In addition,as the oxygen/carbon ratio and cycle times increased,the concentration of gas phase H2Se(g)reduced,The adsorption capacity of oxygen carrier for selenium was enhanced,the content of retained selenium in oxygen carrier was increased,and the control of selenium in chemical looping gasification process provided a theoretical basis.