Research On Biomass Gasification And Co-Combustion Process

With the rapid development of the global economy, Human's demand for energy is growing very fast. The world has begun to face the grim reality of resource exhaustion and environmental degradation. In order to achieve the coordination and sustainable development of economic and environmental, people hope there is some renewable resource that can replace fossil fuels for energy. Biomass with its inexhaustible, clean and green features has attracted worldwide attention and become a good alternative to fossil fuels. Based on the efficient utilization of biomass energy, the biomass gasification and co-combustion process has been studies in this paper. The main research contents are as followings:1. The model of biomass gasification was established under the conditions of air as gasification agent and in atmospheric circulating fluidized bed. Pine, cornstalk and sawdust were selected as gasification raw materials. The numerical simulation of biomass gasification process was carried out though ASPEN process simulation software.2. The performances of the gasification process were evaluated by exergy analysis, which were syngas molar fraction, gasifier temperature, syngas low heating value, carbon conversion, gasification efficiency and exergy efficiency. The optimal gasification parameters of biomass gasification were acquired.3. Biomass gasification processes were optimized to enhance the process exergy efficiency. The influence factors on the exergy efficiency are the types of biomass, biomass moisture content and gasifying agent temperature. Optimization schemes were determined though improving biomass gasification operating conditions, such as preheating biomass raw material, increasing gasifying agent temperature and so on. It shows that both preheating biomass raw material and increasing gasifying agent temperature could improve the gasifier's exergy efficiency obviously.4. The models of co-combustion of coal and biomass-gas were established. The thermal equilibrium analysis method based on the first law of thermodynamics and the exergy equilibrium analysis method based on the first and the second 1aw of thermodynamics were adopted. The thermal balanceable calculation and exergy equilibrium calculation of boiler were done. Main factors that influenced boiler efficiency were found though comparing heat losses with exergy losses. Heat efficiency, exergy efficiency, theoretical burned gas mass flow and theoretical air mass flow were calculated in pure coal burning process and co-combustion process with 5%~30% biomass-gas.By comparing co-combustion with pure coal burning, it shows that the theoretical burned gas mass flow will reduce and the theoretical air mass flow will increase and both boiler heat efficiency and exergy efficiency will decrease when there is more biomass gas co-combustion.In China, biomass gasification technology has a good foundation. Through gasification, biomass energy can be efficiently developed. The syngas co-combustion with coal in a traditional type of coal burning boiler can make the most utilization of the substantive investment and infrastructures of a modern coal burning power plant. Co-combustion is suitable for the transformation of coal-fired power plant in China. Developing biomass gasification technology and co-combustion technology in china can not only improve the environment quality, but also increase economic benefits to some extent. Accordingly, biomass gasification technology and co-combustion technology accord with our country national condition, and have very realistic significance to the development of green power and the promotion of new energy technologies.