Effects Of Strong Stefan Flow On Char Particle Combustion In O₂/CO₂Atmosphere: An Experimental And Modeling Study

Oxy-fuel technology has been regarded as one of the most promisingcarbon capture and storage (CCS) methods for future coal power plant.Compared with conventional pulverized coal combustion, the feed gas inthe oxy-fuel technology is the mixture of O2and CO2instead of O2/N2andhas higher oxygen content. In this case, the Stefan flow occurs at carbonparticle surface may have a strong influence on surface reactions and bothheat and mass transfer mechanisms. Moreover, it may cause significanterror in model forecast if Stefan flow was neglected. However, the recentinvestigations on the effects of Stefan flow in carbon combustion are nextto none. In this work, a novel carbon particle combustion model andcertain experiments were conducted to study the effects of Stefan flow forthe integrated numerical analysis of oxy-fuel technology.A mathematical model of carbon particle with considering Stefanflow was presented for O2/CO2combustion. Furthermore, the experimentson the reaction kinetics and combustion of a char particle at various O2fractions and ambient temperatures were conducted. The verificationsbetween the model predictions and the experimental data from this workand literatures showed that the model considering Stefan flow can predictsurface temperature and burnout of char more accurately than the case ofneglecting Stefan flow.Further analyses of the experimental data and numerical simulationsindicated that the Stefan flow plays an important role in char particlecombustion. Greater effects of the Stefan flow on burnout time generally appear in the cases of lower oxygen concentration/char reactivity/gastemperature and larger particle size where the combustion is prone to becontrolled by reaction kinetic and gas diffusion simultaneously. Moreover,the presence of Stefan flow greatly accelerates the heat loss from theparticle. So a higher gas temperature and a larger oxygen mole fraction arerequired for the ignition of the char particle when Stefan flow is considered.It can be concluded that the effects of Stefan flow on the char particlecombustion cannot be neglected in the oxy-fuel combustion.