Simulation Study Of High-efficiency Wood-chips Gasification Based On CFD

The fossil energy crisis and the environmental problem have promoted the research progress of alternative energy.Among them,biomass energy has huge reserves and low cost,that makes it become an important renewable clean energy.Therefore,its utilization technology is one of the important topics in the development of new energy.Based on the industrial demonstration method of the National Science and Technology Support Program,this paper conducts a simulation study on the gasification of biomass wood chips and optimizes the relevant gasification parameters.This thesis uses ANSYS 15.0 to proposes a three-dimensional model of biomass gasification using ANSYS 15.0.The grid independence is verified,and the previous experimental results are used to compare the model to verify the credibility.In this thesis,wood chips is used as the raw material to simulate the air gasification of biomass.The effects of gasification temperature,equivalent ratio ER,raw material particle size and air gasification agent temperature on gasification characteristics are analyzed.According to the simulation results,it can be known that the increase of the gasification temperature can make the gasification efficiency higher.The best gasification temperature obtained in this thesis is 1000-1100℃.When the amount of air gasification agent is increased,the contents of CO,H₂,and CH₄all show an increasing trend,but when the air is passed in excessively,the contents of CO and H₂begin to decrease,which makes each gasification index also decrease.Therefore,there is an optimal equivalent ratio,which is 0.3 in this thesis.The smaller the diameter of particle,the better the gasification reaction,the micron particles are the best choice.The air gasification agent temperature has less influence on the gasification result,the higher the temperature,there are more heat provided by the gasifier,the better the gasification performance.On the basis of air gasification research,the gasification characteristics of different gasification agents are studied.The results show that steam gasification agent has the best gasification performance.When the mass ratio of steam to biomass S/B reaches 1.1 and the gasification agent temperature is 800 K,the low heating value of synthesis gas LHVg and gasification efficiency can reach 10.29 MJ/m³and 90.26%.The gasification performance of oxygen is also better than that of air and carbon dioxide.The best O₂/B value is 0.3,and the effect of gasification agent temperature is the also small.Carbon dioxide gasification performance is slightly worse than other gasification agents.When the value of CO₂/B is 2.8,the highest gasification efficiency obtained is 43.86%,but carbon dioxide as a gasification agent can effectively reduce carbon emission.This thesis also studies the gasification performance of mixed gasification agents.Air-steam gasification agent is a more commonly used mixed gasification agent.The optimal gasification result can be obtained when the ER value is 0.3 and the S/B value is0.4,and the gasification efficiency is 76.47%.Air-CO₂mixed gasification agent is relatively less used,the gasification performance is not as good as air-steam gasification,but the introduction of carbon dioxide can promote the cracking of coke.The optimal CO₂/B and ER values obtained are 2.4 and 1.5 respectively.