Research On The Effect And Regulation Of Ash Fusibility Under Sulfation During Oxy-biomass Combustion

With the rapid development of economy,the demand and consumption of energy are increasing.and carbon dioxide(CO2)emissions are also increasing year by year,which leads to the increasingly prominent problem of global warming.The use of"carbon-neutral" biomass fuel for power generation is one of the important ways to build a low-carbon power system,combined with oxy-fuel combustion of carbon capture technology,oxy-biomass combustion can achieve negative CO2 emissions.However,the accumulation of alkali metals and recirculating SO2 during oxybiomass combustion has caused a series of ash-related problems,which hinders the stable operation of power generation facilities.Primarily,the effects of sulfation on the ash fusibility were systematically investigated through ash fusion temperatures(AFTs)tests,scanning electron microscopy(SEM),inductively coupled plasma atomic emission spectrometer(ICP-OES),X-ray diffraction(XRD),and chemical thermodynamics calculation(FactSage).It was found that the presence of SO2 suppressed the release of K and Ca species,thereby changing the AFTs of corn straw,while increasing the SO2 concentration and extending the sulfation time both increased and then decreased the melting temperature of straw ash particles,reaching a maximum at SO2 concentration of 1000 ppm and sulfation time of 2 h,respectively,and for O2 concentration,sulfation elevated the straw ash melting temperature,with the most significant elevation at 21%O2 concentration.Furthermore,two reacting mechanisms for sulfation to change ash fusion characteristics,including moderate and excessive sulfation,were proposed in this work,and the relevance among minerals evolution,melting performance,and ash sulfation was successfully established.When the initial SO2 concentration was less than 1000 ppm,AFTs increased due to the transformation of alkaline chlorides to their sulfates and aluminosilicates with the presence of SiO2 and Al2O3 in ash samples,that was,moderate sulfation occurred.When the concentration of SO2 was higher than 1000 ppm.large amounts of KAISi3O8,CaAl2Si2O8,Ca2Al2SiO7 and CaSO4 were generated,causing the simultaneous eutectic and CaO-assisted melting,thereby decreasing the AFTs of corn straw,that was,excessive sulfation occurred.Based on the above-mentioned excessive sulfation aggravated the ash fusion problem,this study solved the ash fusion problem at high SO2 concentration by synergistically regulating the SiO2/Al2O3(Si/Al)and acid to basic oxides(A/B),and the individual effects of Si/Al and A/B as well as their interactions on ash melting performance of corn straw were explored.The results showed that the individual effects of Si/Al or A/B ratios on the AFTs were nonlinear due to the eutectic melting of minerals under excessive sulfation.In addition,a regression model was established by using for revealing the interaction of Si/Al and A/B on the on ash fusion characteristics by using the response surface analysis method with the softening temperature(ST)as the response factor and Si/Al and A/B as the dependent variables with the help of the Central Composite Design(CCD)principle..The results showed that the effect of A/B on ST was more significant than that of Si/Al.Furthermore,based on the regulation strategy obtained through the regression model,combined with experimental validation,after modifying the ratios of Si/Al and A/B to 8 and 1.0 simultaneously,the AFTs of corn stalk ash could be significantly improved,which in turn could effectively alleviate the ash fusion problem under high SO2 concentration of oxy-biomass combustion.