Experimental And Mechanism Research On Entrained Flow Gasification Of Biomass For Syn-gas

The exploitation and utilization of biomass energy is an effective method for relieving the pressures of conventional energy resources shortage and serious environment pollution. How to effectively convert low quality biomass to higher quality liquid fuel has attracted more and more attention of the whole world. On the basis of the investigation of biomass indirect liquefaction to synthesize liquid fuel, technology options available on large scale to produce syngas from biomass by directional gasification have being discussed extensively, and a systematic research on both experimental and kinetic was performed on the biomass entrained flow gasification.The research background was introduced at the beginning of this paper. Based on the comparison among the several major biomass liquefaction technologies, the advantages of the biomass indirect liquefaction to synthesize liquid fuel were obtained. The key of biomass indirect liquefaction is the production of syn-gas. So focusing on the process of the biomass gasification combined with coal-based gasification technology, it summarizes that biomass entrained flow gasification for synthesizing the syn-gas on large scale is heading for a great future. Then an extensive review was made on the development of the technologies of biomass entrained flow gasification. From the analysis, it is shown that ash behavior, particle milling, feedstock feeding and system pressuring have been said to be the major hurdle if biomass is converted in a entrained flow gasifier. For developing a systematic experimental research on biomass entrained flow gasification, a lab-scale entrained flow reactor was designed and put up on the basic principle of the entrained flow gasification. Furthermore, the component and performance of the gasification system were introduced.In order to investigate the characteristics of biomass gasification in an entrained flow reactor, a lab-scale biomass entrained flow gasification system was characterized and was used to test sawdust gasification including gas composition, carbon conversion, products distribution and solid residue behavior with different reaction temperatures and oxygen/biomass ratio. The results reveal that syn-gas content increases and CH₄ content decreases with increasing reaction temperature; tar content can be considered very low; the carbon conversion rate and gas yield rate increase to a maximum value at high reaction temperature. In addition, a finite difference model was employed to simulate the fluidynamics, the energy balance and the mass transfer during the partial oxidation of biomass particles. The application of this model allows the residence time, the thermal history and the mass conversion of the particle inside the reactor to be estimated. The experimental and model results are in agreement.Considering the critical role of inorganic elements in biomass utilization, experiments of the sawdust gasification were done for studying emission behavior of inorganic elements with different reaction temperatures. The contents of different residues captured by cyclone and filter were measured. The composition and morphology of the residue ash were analyzed using ICP and EDX-SEM. The major emission mechanisms of inorganic elements at different temperatures were obtained.This work is very helpful to understand the inorganic elements transformation during biomass entrained flow gasification or combustion, as well as to find the solution of alkali problems.In order to investigate the influence of gasifying parameters in an entrained flow gasification, the effects of reaction temperature, oxygen/biomass (O/B) ratio, steam/biomass (S/B) ratio and residence time on gasification performance including gas composition, carbon conversion, H₂/CO ratio and CO/CO₂ ratio were tested in a lab-scale biomass entrained flow gasification system with rice husk, manchurian pine, korean pine and camphorwood as feed-stocks respectively. The results reveal that the reaction temperature is the most important effect in biomass entrained flow gasification. The optimum O/B ratio is in the range 0.2～0.3 at the gasification condition of 1300℃and atmospheric pressure, there is little CH₄ in the syngas at high reaction temperature and syngas composition becomes uniform while residence time exceed 1.6s. The H₂/CO ratio can increase with steam injected, and exceed 1 when S/B is more than 0.8. The steam injection affects the gasification efficiency but has little impact on the carbon conversion.A kinetic biomass gasification model combining chemical equilibrium was developed to evaluate and optimize gasifying parameters in entrained flow bed gasification. Model calculating results are in good agreement with the measurement data from previous gasification tests in entrained flow reactor. Model simulations of biomass gasification processes in entrained flow reactor were found to be reasonable. It implies the established model may be used to predict the effects of operation parameters on biomass entrained flow gasification.In order to research the torrefaction influence for biomass solid yield, energy yield, size reduction and overall efficiency during the gasification process, torrefaction experiments were carried out in a lab-scale reactor using four biomass feed-stocks. This paper also studied the size reduction and gasification characteristics of torrefied biomass experimentally. The results reveal that torrefaction can be applied with high biomass to solid energy yield with increasing the temperature and reaction time. The torrefaction temperature is more influential than the reaction time on the characteristics of torrefaction. Torrefaction can lead to a great decrease in power consumption since the destruction of fibrous structure and lead to a very substantial improvement of the grindability behavior. Torrefaction also can increase the overall efficiency of the gasification system. It therefore provides a solution to the problems concerned with entrained flow gasification related to size reduction of biomass and the subsequent pneumatic transport of the powder.