Experimental And Numerical Simulation Of Coal/Biomass Fluidized Oxy-Fuel Combustion Characteristics

Oxy-fuel combustion is one of the most promising technologies for carbon capture.It transforms the traditional air combustion mode to O₂/CO₂ combustion,so that the concentration of CO₂ in flue gas is greatly increased,which is conducive to subsequent storage and utilization.Oxy-fuel co-firing of coal and biomass in fluidized beds,which combines the absorption of CO₂ by biomass growth and the capture of CO₂ by oxy-fuel combustion,is considered to be a new clean combustion technology expected to achieve negative CO₂ emissions,and has attracted great attention from academia and industry.In the past decade,important progresses have achieved in the study of oxy-fuel combustion in fluidized beds.However,the research on mixed fuels?such as mixture of coal and biomass?is still very limited,and many key basic issues are still unclear.In this work,the combustion characteristics of coal,coal and biomass blendings under oxy-fuel and fluidized conditions were studied through experiments and numerical simulations.A micro fluidization reaction-mass spectrometry experimental system?reactor diameter 10mm,combustion temperature 700°C-900°C?was constructed,and the characterization method of fluidized combustion process characteristics based on on-line mass spectrometry analysis was explored.Combustion behaviors of coal,biomass and their mixtures in oxy-fuel and fluidized conditions were studied with bituminous coal and Huali wood as fuels.The effects of coal to biomass mass ratio,combustion atmosphere,oxygen concentration,and combustion temperature on combustion characteristics,i.e.peak shape of CO₂ intensity spectrum,total reaction time,volume concentration of CO₂ enriched in flue gas,amount of CO₂ produced by coal combustion,relative generation rate of CO₂,NO formation and etc.,were investigated.A 3D mathematical and physical model and numerical simulation method,which couples of gas-solid flow and chemical reaction for coal/biomass fluidized bed oxy-fuel combustion,have been developed.The models under Euler-Lagrangian framework were established by MP-PIC method.LES model and discrete particle method were used to describe turbulent gas flow and particles flow,respectively.The chemical reaction model took into account of volatilization evolution and combustion,coke combustion,and pollutant generation.The coupling of gas-solid flow and chemical reactions was realized by setting the source terms of continuity equation,momentum equation,energy and component transport equation.In addition,a scientific numerical simulation verification strategy was designed,to verify the correctness and accuracy of the model qualitatively and quantitatively from two aspects:the gas-solid flow structure and the dynamic process of CO₂ enrichment.The distribution of combustion parameters and the evolution of time and space in coal/biomass fluidized bed combustion were revealed,and the intrinsic relationships between combustion parameters and flow structure were clarified.The dynamic characteristics of oxy-fuel combustion under fluidized conditions were obtained,through a large number of numerical simulations.The distributions of combustion parameters?i.e.gas-solid flow field,temperature field and component field?and their temporal and spatial evolution were analyzed.The characteristics of CO₂,SO₂ and NO spectral peaks?including peak shape,peak height,peak width and peak duration?were analyzed.The relationship between combustion parameters and flow structure?i.e.bubbling,fluidization,turbulent fluidization and pneumatic transport?was discussed.The present paper enriches the means of mechanism experiment and numerical simulation,obtains the data of fluidized oxygen-enriched combustion characteristics,and adds the basic theory of fluidized bed oxygen-enriched combustion.These achievements could provide useful references for the development of fluidized bed oxy-fuel combustion technology to capture CO₂.