Research On Characteristics Of Biomass Entrained Flow Gasification And Char Gasification Kinetics

With the fossil resource decreasing and the serious pollution caused by fossil fuel combustion, the biomass energy attracts more and more attention. Petroleum is the most needed resource in the energy resource, how to transform biomass to liquid fuels becomes a focus attention for research. In this paper, it put forward that the syngas is produced through entrained flow reactor after analyzing the advantages of biomass indirect liquefaction. On the base of demonstrating the feasibility for gasification using entrained flow reactor, a bench scale reactor was built. Combining experimental and theoretical analysis, the characteristics of biomass entrained flow gasification, kinetic study of semi-char gasification were investigated. The research results are of significance to understand the entrained flow gasification mechanism, and it can lay a solid foundation for the related technology research and development.In this paper, firstly, the feasibility for large scale gasification in the entrained flow reactor and the option of guideline were demonstrated, and it summarizes the current state of entrained flow gasification for biomass in foreign countries and home. Then a lab-scale entrained flow reactor was designed on the basic principle of gasification and its components and performance are introduced. The flow field and temperature field in the reactor were also simulated by the CFD software.Some biomass fuels were used as the feedstock for experiments. They were tested in the gasifier through pyrolysis, pure-oxygen gasification and steam gasification. The influence of particle size, O/B, S/B and temperature on product gas were investigated. The results indicate that the gas yields increases with the particle size decreasing; with the O/B increasing, carbon conversion ration increases, but H₂ yield decreases, CO yield has a maximum value. Different biomass has an optimal O/B value. The presence of steam can increase H₂ and CO₂ yield, H₂/CO value can reach 1.35, H₂ yield reaches the maximum value with the S/B during 0.6～0.8. The carbon conversion ratio, gas efficiency and H₂ yield increase with reactor temperature, H₂/CO value can reach 1.6 at 1400℃through steam gasification.The kinetics parameters of pyrolysis and gasification of biomass are important to design industrial gasifier and simulate the process of gasification, the reactivity of biomass chars was studied through steam gasification and CO₂ gasification. The results show that, for three biomass chars, the reactivity in steam and CO₂ has same trend. With carbon conversion, the reactivity increases and the reaction rate increases firstly, then decreases. The reaction rate of steam gasification is twice than that of CO₂ gasification. For steam gasification of biomass chars, the unreacted shrinking core model can used to describe their gasification behavior; but for CO₂ gasification, the mixture model can fit the gasification behavior exactly.The characteristics of biomass ash and its fusibility were studied to satisfy gasification in slagging-gasifier. The fusion point of ash was investigated after coal-based additive CaO, Fe₂O₃ and low melting point coal ash were respectively added as fusing agent. The results indicate that Fe₂O₃ and low melting point coal ash can lower the melting points of rice husk. And the fusing agent can catalyze char gasification, but the additive amount has an optimal value.