| The large-scale use of renewable energy which means biomass is an important path toalleviate energy shortages and environmental pollution.Biomass has the characteristics of being wide availability,renewable and low price,and its particles have attracted much attention because of its easy storage,easy transportation and high calorific value.At present,its thermochemical utilization technology is the focus of biomass utilization research.In this paper,the kinetics of the pyrolysis and gasification processes in CO2 are studied respectively by considering the problem of carbon dioxide emission reduction in greenhouse gas.Not only the kinetic study can grasp the reaction mechanism of its thermochemical process,but also can further predict the reaction rate and the degree of difficulty of the reaction.Also the proportion and their formation(methane,hydrogen and carbon monoxide)are studied,which can provide a reference for the preparation of combustible gas.The above study is designed to provide theoretical support for the simultaneous use of biomass and carbon dioxide.Therefore,both the kinetics of the pyrolysis stage and the gasification process in carbon dioxide atmosphere are discussed in this paper.The main contents and results of this paper are as follows:(1)The TG-DSC test was performed on the biomass powder by thermogravimetric analysis at different heating rates(10,15,20,30?/min)in a carbon dioxide atmosphere.The results show that the weight loss process of biomass powder can be divided into three stages.At different heating rates,the TG curves of the biomass move toward higher temperature zone.At the different heating rate(except 30?/min),the pyrolysis stage and the gasification stage are respectively exothermic reaction and endothermic reaction.;(2)Fit the data of the pyrolysis phase to reaction models at these four heating rates.The results show that the pyrolysis mechanism of the biomass powder in the CO2 atmosphere is in accordance with the Fn order reaction model,and the optimized reaction order is 1.61;(3)The curves of TG at four heating rates were studied by COATS-REDFERN,of single curve analysis method,and the corresponding kinetic parameters were obtained.The kinetic parameters of the pyrolysis stage were also calculated by using model-free method,of the multivariate curve analysis method(FRIEDMAN method,OZAWA-FLYNN-WALL method and ASTM E698 method).The results show that as the heating rate rises,the value of A decreases as the value of E does.The heating rate increases,the E reduces(except 20?/min);The results show that method of FRIEDMAN and OFW find that the activation energy and the value of the pre-index factor are close,the activation energy of the pyrolysis phase obtained by the model-FRIEDMAN method and OFW method are 181.75?213.51kJ/mol,197.02?205.83kJ/mol,respectively.The pre-exponential factors are 12.95?15.54 s-1,14.44?15.89 s-1,respectively.(4)The kinetic reaction characteristics of CO2 gasification were studied by using the conversion method.Meanwhile,the effects of the heating rate on the gasification reaction of the biomass char-CO2 were also investigated.The calculated E is 348.61?422.23kJ/mol while the conversion rate changes in 0.6?0.8.With the increase of heating rate,the rate of gasification reaction at different heating rates is similar,but the heating rate is higher,the more obvious change of gasification reaction rate;Both the gas of the pyrolysis stage and the gasification process in carbon dioxide atmosphere are also discussed in this paper.The main contents and achievements are as follows:(5)At the same time,the enlarge experiment of tube furnace was carried out to analyze the pyrolysis gas and gasification gas produced.The results show that the CO2 atmosphere affects the final production of gasification gas.Compared with the pyrolysis gas,the volume fraction of H2,CH4 and CO in the gasification gas increase significantly,and the volume ratio of H2,CH4 and CO are 25.03%,12.27%and 13.09%,respectively. |
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