| The rational utilization of solid fuels,such as coal,oil shale and biomass,is related to the sustainable development of energy.Gasification,as a thermal conversion process,could be applied to industrial processing,which can not only produce clean fuel gas or syngas,but also greatly reduce the harmful gases and solid wastes to the environmental pollution.The gasification process of solid fuels mainly includes two processes,i.e.,fuel pyrolysis and char gasification.In this study,the gasification reaction process was decoupled into two reaction processes to be discussed,respectively.The influence of pyrolysis temperature on char gasification behaviors was also discussed.Furthermore,the reaction mechanism of different solid fuels was analyzed by calculating the kinetic parameters.In this study,the pyrolysis characteristics and kinetics of coal,oil shale and biomass were comparatively studied by using a micro-fluidized bed reaction analyzer(MFBRA).The results showed that the major gas components released from coal,oil shale and biomass had different initiating and ending time points under the isothermal condition,and the difference was more significant under the programmed heating conditions.The pyrolysis activation energy showed that the oil shale pyrolysis with high ash contents was somehow more difficult to take place in terms of higher activation energy.A consequent comparison on the kinetics of solid fuels obtained in the TG verified that the reliability of the pyrolysis and other rapid reaction kinetics obtained by MFBRA,and MFBRA could be a useful tool to give some insights into the intrinsic kinetics and reaction mechanisms of solid fuels pyrolysis.The sawdust char,straw char,ZD coal char and GB anthracite char obtained by pyrolysis were gasified in carbon dioxide,steam and their mixed atmosphere,respectively.The relationship between physicochemical properties and gasification activity was discussed.The results showed that the gasification activity was mainly controlled by the AAEM in ash content and the carbon crystal structure.The comparison of gasification activity in different atmosphere showed that the gasification activity in steam was about2-3 times that of carbon dioxide.Furthermore,due to the synergistic effect between steam and carbon dioxide,the char had higher gasification activity in mixed atmosphere.The gasification kinetics parameters of different char was calculated by model fitting.Among them,the random pore model had a better degree of fitting for the two kinds of biomass and ZD char,and the shrinking core model had a better degree of fitting for the GB anthracite char.The comparison on the gasification kinetics data in TG revealed that the gas diffusion limit could get smaller gasification rate.The higher gasification temperature was,the more severe gas diffusion limit could be.Finally,according to the gasification process of solid fuels,the effect of pyrolysis temperature on gasification reactivity was discussed.By using the elemental analysis,BET,FTIR and Raman spectrometer,the char produced at different pyrolysis temperatures was analyzed.It was found that the graphitization degree was gradually deepened with the pyrolysis temperature increased.The kinetic parameters of the char produced at different pyrolysis temperatures was carried out.The gasification activation energy of sawdust char had a linear relationship with the pyrolysis temperature,because the increasing of pyrolysis temperature only intensified the graphitization of sawdust char.The ZD char had a linear relationship with the pyrolysis temperature below 800℃,but no longer had a linear relationship when the pyrolysis temperature higher than 800℃.For the solid fuels which could be pyrolysis completely at low temperature,the graphitization degree was the main factor that the activation energy increased with pyrolysis temperature.For different types of solid carbonaceous fuels,the gasification kinetic parameters at different pyrolysis temperatures could be directly obtained by using MFBRA... |
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