Impact Of Biomass Alkalis Migration On Coal Char During Co-pyrolysis Of Coal And Biomass

Biomass co-gasified with coal is an important way to realize utilization of biomass effectively,and rich alkali metals in biomass can be used as catalyst for co-gasification of biomass and coal,then improve the system element utilization.However,biomass alkalis in thermal conversion process are easy to volatile and will cause a series of problems such as equipment corrosion.If the released alkali metal can be fixed in the solid phase to reduce the concentration of alkali metal in the gas phase,not only alleviate the corrosion problems of the equipment,but also improve the gasification efficiency of char.Therefore,if there is a clear understanding of the migration and distribution of biomass alkali metals in different gas-solid phase during co-gasification process,which will have a greater value to the biomass alkali metal catalytic coal gasification process in a certain extent.In this paper,rice straw and Jincheng anthracite were selected as the main research object.The effects of different pyrolysis conditions such as reaction temperature,blending ratios and reaction atmosphere on the migration and distribution of biomass alkalis were investigated by means of fixed bed reactor.The influence of coal structure on the migration and immobilization of alkali metals were studied,and the catalytic effect of alkali metal immobilized on coal char were performed by thermal balance.The following conclusions can be drawn from research results:1.In the case of co-pyrolysis at inert atmosphere,when the temperature is higher than 600 °C,the biomass alkalis begins to migrate to the coal char,and the oxygen content of co-pyrolysis coal char is higher than that of seperated pyrolysis.And when the biomass alkalis does not migrate to the coal char,the oxygent content of co-pyrolysis char is less than individual pyroysis char.During co-pyrolysis process of Jincheng anthracite coal and rice straw,oxygen compounds produced from biomass pyrolysis will be deposited on the surface of coal char to improve the oxygen dispersion of coal char surface,then promote the biomass alkals allocation in coal char.2.Due to different atmosphere occurred in varing degrees of interaction with biomass and coal char during co-pyrolysis of Jincheng anthracite and rice straw at three different atmosphere such as nitrigen?carbon dioxide and steam.under the steam atmosphere,the biomass alkalis K and Na migrate to the coal char higher than that of nitrigen and carbon dioxide atmosphere,while the alkali K and Na retained in the biochar were lower than that of nitrigen and carbon dioxide atmosphere.3.The change of coal structure has a significant effect on the migration and distribution of biomass alkalis K and Na during co-pyrolysis stage of coal and biomass.Reducing the oxygen content of coal and the minerals content in coal are not conducive to the migration and distribution of biomass alkali metal to coal.4.Biomass alkali metal as a catalyst for coal gasification,its catalytic ability not only determined by the amount of biomass alkali metal migration,but also depend on the structure of coal char and the active alkalis content.