| In recent years,with the increasing shortage of fossil energy,biomass energy,as a clean and renewable energy,has gradually attracted widespread attention.Among the many utilization methods of biomass,the method of thermochemical conversion has become an effective way to utilize biomass.In thermochemical conversion,biomass gasification is an effective way to convert biomass energy into high-grade energy.However,the biomass gasification process is also accompanied by problems such as high energy consumption,low energy utilization rate,and serious thermal pollution,which seriously restrict its large-scale application.Therefore,how to improve the utilization efficiency of thermal energy while ensuring the yield has become the focus of research.In this study,the biomass gasification model was established using the process simulation software Aspen Plus,and the biomass gasification principle was combined with the Gibbs minimum free energy principle to investigate the influence of different operating parameters on the gasification characteristics during the biomass gasification process.Research and analysis to determine the optimal conditions for biomass gasification;then under the optimal conditions,the system is optimized by using the outlet synthesis gas to heat the biomass raw materials and gasification agent,which is the basis for the design of the biomass gasification system for reference.Simulations were carried out using two different biomasses,oak and cow dung.The effects of gasifier temperature distribution,steam/biomass ratio,and gasification pressure on the gas composition,heating value(LHV)and H2/CO ratio of syngas were studied.Studies have shown that the increase of temperature can increase the content of H2 and CO,but when the temperature rises to 750℃,the reaction gradually stabilizes,and the content of H2 begins to stabilize and slightly decreases.Considering energy consumption and synthesis gas quality,the optimal temperature is 750℃.With the increase of water vapor flow rate,the H2 content continued to increase and the CO content decreased.As H2/CO and gas production continue to increase,adding too much water vapor is a waste because more energy is required to maintain temperature.Therefore,a water vapor/biomass ratio of 1 is considered optimal.Reactor pressure has little effect on syngas distribution,so operating the gasifier at atmospheric pressure is a reasonable choice.The energy flow study of the biomass gasification system was carried out.The effects of biomass gasification temperature,steam/biomass ratio and pressure on system heat load were studied respectively.The increase of gasification temperature will cause the increase of system heat load,which increases rapidly between 600-800℃,and then tends to be slow.An increase in the steam/biomass ratio will cause a continuous increase in the system heat load.The pressure will cause a reduction in the heat load of the system,but the reduction is small and the effect is not obvious.Finally,the energy flow optimization of the system is studied by means of heat recovery.When separately preheating biomass and gasification agent(steam)for reheating,the preheating gasification agent can effectively reduce the heat load of the system,and the phase change of steam generation can consume a large amount of syngas energy,reducing the heat load of the system.The load was finally reduced to 1.85 kW,a reduction of 31.7%.Using syngas to preheat the biomass and gasification agent at the inlet of the gasification system for recuperation in steps can not only preheat the biomass and gasification agent at the same time,but also effectively reduce the heat load of the system.However,when cascade utilization preheats biomass first,the biomass preheating temperature should not be higher than 260℃.When cascade utilization preheats the gasification agent first,the preheating temperature of the gasification agent should be higher than its boiling point. |
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