Study On Structure And Gasification Reactivity Of Coal Char During Co-pyrolysis Of Coal And Biomass

Co-gasification of coal and biomass is an important way to reduce fossil fuel use and efficient use of biomass,and char gasification reactivity is the key factor in the co-gasification process.In essence,the gasification reactivity of coal char is affected by the structure of the coal char,so the study on the structure and gasification reactivity of coal char during the co-pyrolysis of biomass and coal can provide theoretical guidance for the co-gasification and utilization of coal and biomass.In this work,anthracite and lignite and two kinds of biomass(cornstalk and sawdust)are co-pyrolyzed in the fixed tube furnace,respectively.And char mixture after co-pyrolysis of coal and biomass was separated based on different shape and size.The effects of biomass proportion,biomass type and coking temperature on the microcrystalline structure and surface functional groups of coal char were discussed,and the mechanism of co-pyrolysis was analyzed.The content of alkali metals on the surface of coal char after separation was measured by means of inductively coupled plasma emission spectrometer(ICP-OES),and the influence of biomass ratio and species on the CO₂ gasification reactivity of coal char was analyzed by thermogravimetry.Finally,the coal char gasification reactivity index was correlated with structural parameters and alkali metal content,and the coal char gasification reactivity prediction model was established.The main research results and conclusions are as follows:(1)X-ray diffraction and Fourier transform infrared spectroscopy were used to characterize and analyze the carbon microcrystalline structure and surface functional groups of coal char.The results showed that,with the increase of biomass proportion,the average stacking height L_c and the number of crystal surface layers N of anthracite char and lignite char decreased,and the graphitization degree decreased.The effect of corn straw on carbon microcrystal disorder was greater than that of sawdust.The addition of corn straw and poplar sawdust made the aromaticity and aromatic-ring condensation degree of coal char decrease gradually and the hydroxyl content increase.The higher the pyrolysis temperature,the more disordered the microcrystalline structure and the less the number of surface functional groups.(2)The results show that most of the alkali metals in biomass are intercepted by coal char through the interaction between coal char and volatiles during co-pyrolysis.The larger the proportion of biomass,the higher the content of alkali metals on coal char surface.The main alkali metal intercepted by corn stalks is potassium,and the alkali metal intercepted by sawdust is magnesium.The CO₂isothermal gasification characteristics of coal char under different conditions were studied by using thermogravimetric analyzer.The results showed that both corn straw and sawdust could improve the gasification reactivity of anthracite char,and the straw had a greater effect on the gasification reactivity of anthracite char.Corn straw promoted the gasification activity of lignite,and the reactivity index R_0.5 of lignite coke mixed with 80%corn straw was 1.12 times that of the original lignite char,while poplar sawdust inhibited the gasification reactivity of lignite,which attributed to sawdust was easy to melt and shrink in the pyrolysis process,hindering the gasification reaction.In addition,the pyrolysis temperature has a certain influence on the gasification reactivity.The higher the pyrolysis temperature,the less AAEMs content in coal char and the lower the gasification reactivity.(3)Under the condition of this study,the structural parameters of coal char are not strongly correlated with coal char gasification reactivity index,but have good consistency with coal char surface alkali metals.Therefore,a prediction model of coal char gasification reactivity based on the alkalinity index is established.