Songhe Mine 17# Coal Underground Gasification Simulation Of Solid-liquid Product Characteristics And Trace Element Precipitation Law

Underground coal gasification（UCG）is a coal development technology that converts coal directly into gas fuel or raw material through controlled combustion in underground coal seams.Coal contains a variety of trace elements.Studying the occurrence state and migration rule of trace elements in coal during gasification will not only provide support for the environmental assessment of coal underground gasification,but also improve the theoretical basis for the recovery and utilization of key metal elements in coal.In this essay,the 17#coal seam of Songhe mining area in western Guizhou was taken as the research object,combined with the physical simulation experiment of coal underground gasification and the immersion experiment of solid products,the physical and chemical characteristics of solid-liquid products during gasification were analyzed,the occurrence characteristics and content changes of trace elements in raw coal and solid-liquid products were explored,and the migration process and precipitation rule of trace elements were revealed.Coal in the No.17 coal seam in Qianxi Songhe Mining area is low ash,medium volatile and low sulfur,with its R_o,max at 1.38%,and the macro coal rock type is from semi-dark to semi-bright.The maceral is mainly vitrinite（91.93%）,and the inorganic component is less,which is typical coking coal.The main minerals are pyrite,quartz,calcite,chlorite,kaolinite,zircon and other clay minerals.The physical simulation experiment of underground coal gasification was carried out.The results showed that with the increase of oxygen concentration in the gasification agent,the effective gas components and calorific value in the produced gas gradually increased,and tended to be stable when the oxygen concentration reached74%,indicating that the gasification effect was the best when the oxygen concentration was between 70%～80%.The surface morphology analysis of the residual coke showed obvious melting erosion phenomenon on its surface,and the development degree of pore and fissure increased.The residual coke immersion simulation experiment was carried out.The results showed that,with the increase of soaking temperature,the concentration of ammonia nitrogen in soaking solution gradually increased,while the concentration of volatile phenol and TOC gradually decreased,the concentration of Mn,Sb,V,Co,Cr,Ni,Cu and Zn in trace elements increased,and the concentration of Cd,Pb,As and Se showed a decreasing trend.With the extension of soaking time,the concentrations of ammonia nitrogen,volatile phenol and TOC in soaking solution increased rapidly in the early stage,but increased slowly and gradually tended to be stable in the late stage,while the trace elements showed an overall increasing trend.Combined with correlation analysis and statistics analysis,the occurrence state of harmful trace elements and rare earth elements in 17#raw coal and residual coke was studied.The results showed that Cr,Se and Ba in residual coke were mainly in silicate minerals,and Be,Co,Cu,Mo,Sb and V were mainly in clay minerals.As,Tl and Pb existed in organic compounds,while rare earth elements existed in silicate and phosphate minerals and rutile minerals.The distribution of trace elements in raw coal and gasification residual coke is obviously differentiated and enriched,indicating that trace elements have migrated to different degrees.The contents of trace elements in different residual coke shifted with the change of oxygen concentration of gasification agent.With the increase of oxygen concentration,the migration ability of Be,Co,As,Mo,V,Cd,Cu,Tl and Pb increased,while that of Ni,Zn,Ba and Cr gradually decreased.The concentration of oxygen in the gasifier had little effect on Sb migration ability.This study showed that the main factors affecting the migration of trace elements in underground coal gasification include the oxygen concentration ratio in the gasification agent,the characteristics of different trace elements and their occurrence states.