Study On Fusion Characteristics And Slagging Characteristics Of Ash Produced By Biomass And Coal Under Gasification Condition

Biomass gasification is one of the important technical methods for efficient utilization of biomass resources.However,due to the problems of tar,agglomeration and slagging formation produced by biomass during gasification,a method by coal addition in biomass,which is called co-gasification of biomass and coal,was proposed by the research team to solve the above problems.Sawdust,rice husk,rice straw,rapeseed straw and lean coal were selected as raw materials,with biomass-to-coal mass ratio of 4 mixing.Biomass ashes and blend ashes composed of corresponding biomass and lean coal were research objects.By using of various experiments and simulation methods,the research on ash fusion characteristics and slagging characteristics of the biomass ash and blend ash was conducted.Firstly,to study fusion characteristics of biomass ash and blend ash of biomass and coal under reducing atmosphere,the experiments of X-ray fluorescence,ash fusion temperatures determination and X-ray diffraction were conducted.The results show that biomass has high content of alkali metals and alkaline earth metals,then the content of basic oxides is also high in biomass ash,but the total content of basic oxides in blend ash of biomass and coal is decreased.For low melting temperatures of biomass ashes,coal addition in biomass could provide good fusion characteristics of blend ashes.The softening temperatures of sawdust ash and rice straw ash are only 874?and 782?under reducing conditions,but the softening temperatures of their corresponding blend ashes are 1070?and 1083?,respectively.The preliminary analysis is that the significant increase the content of Al₂O₃ has a positive effect on the ash fusion characteristics.There are few high melting point minerals in biomass ashes,especially in rice straw ash,but high melting point minerals are formed in blend ashes at high temperature,the mineral transformation degree in the ash at different high temperatures is large,and a variety of minerals contained calcium and iron are formed,including wollastonite,larnite,clinoferrosilite,anorthite,et.al,which would produce the effects of low temperature etectic easily.Simultaneously,the equilib module and phase diagram module in FactSage are used to simulate and analyze ash fusion characteristics.Most of the slag-liquid line at high temperature is consistent with the actual flow temperature of ash.A variety of minerals containing potassium,calcium,magnesium and iron are formed in the ash samples,and most of them are based on silicon.Compared with the position of biomass ash in the phase diagram,the location of the blend ash moves to the mineral zone where the lean coal ash is located,and lean coal ash is located in the corundum mineral zone,which represents good ash fusion characteristics.The main reason for the change of fusion characteristics of blend ash is that the content of Al₂O₃ increases significantly.Sawdust ash,blend ash of rice straw and lean coal and blend ash of rapeseed straw and lean coal are all affected by the low temperature eutectic generated by different substances,which affects the ash fusion characteristics greatly.Then,combined with the above analysis of ash fusion characteristics,the experiments of manual decomposition and scanning electron microscope were used to investigate the slagging characteristics of ash at different temperatures.The results show that the microscopic morphology analysis of ash is basically consistent with the experimental results of manual decomposition.Under 815?reducing atmosphere rice straw ash shows a medium strong slagging tendency,while under the same condition,only blend ash of rapeseed straw and coal shows a slight tendency of slagging,which indicated that coal addition could improve slagging characteristics of ash samples,and the slagging characteristics are significantly related to softening temperature.Finally,to determine the slagging degree of the ash sample under gaification condition conveniently,the main factors of slagging under reducing atmosphere were emphatically considered,then the principal component analysis method was used to analyze and fit them to obtain the new slagging degree discrimination equation.SPSS software was applied to analyze data that represents those factors,four main components were achieved.Based on basic-acid ratio discriminant and correlation between various factors and slagging degree,?K₂O+Na₂O+FeO?/?SiO₂+Al₂O₃?,T/ST and SO₃/CaO are independent variables of the discrimination equation,which is gotten by Matlab software fitting.After examination,it basically meets the requirements for determining the slagging degree of biomass ash and blend ash of biomass and coal researched in this paper.