Study On Gasification Reactivity And Kinetic Of Coal Char In Single Or Mixed Atmosphere Of H₂O And CO₂ At Eleveated Pressures

Due to the demand of energy and restriction of environment,coal gasification technology is developing into large-scale with high temperature and pressure.Char gasification in single CO₂ or H₂ O at elevated pressure is becoming a hot topic,but the conclusions are dissimilar.The study on char gasification in coexistence of CO₂ and H₂ O at elevated pressure is lack,the investigation into char gasification reactivity in single or mixed atmosphere of H₂ O and/or CO₂ at varying pressures is meaningful and valuable.Char gasification is rate-determining step,so the studies on char gasification reactivity are of great importance in improving char gasification efficiency.The purposes of this study are to investigate the effect of pressure and mineral matters on char gasification in various atmospheres,and the interactions during char gasification under mixture of H₂ O and CO₂ at elevated pressures.In this study,Ximeng lignite and demineralized Ximeng lignite were used as samples to prepare coal char（XMCC and DXMCC）by temperature-programmed pyrolysis with the final temperature of 1000 oC.The isothermal and non-isothermal gasification reactivities of coal char in H₂ O,CO₂,and mixed atmosphere of H₂O/CO₂ were evaluated by a pressured thermogravimetric analyzer,and the kinetic parameters were also calculated.The primary conclusions are as follows:（1）During the temperature-programmed gasification of XMCC in CO₂,the reaction rate increases with the increase of pressure,but the activation energy decreases.For H₂ O or H₂O/CO₂,the gasification rate of XMCC increases with the pressure increasing at low pressure,and then maintains at the level with the further increase of pressure.The temperature-programmed gasification of XMCC in H₂ O or H₂O/CO₂ can be divided into three stages,gasification is the chemical reaction controlling step in the first stage,which is catalyzed by the inherent mineral matters in the second stage,and the desorption of product or diffusion controlling is the main effect in the third stage.For the gasification of DXMCC in H₂ O,CO₂,or H₂O/CO₂,the results showed a linear increase in reaction rate with the increase of pressure,but a decrease trend for activation energy.（2）During the temperature-programmed gasification of XMCC in H₂O/CO₂,all the experimental values of gasification reaction rates are lower than calculated values at varying pressures,suggesting that there is inhibition effect between the char-H₂ O and char-CO₂ gasification.However,the experimental values of gasification reaction rates of DXMCC in H₂O/CO₂ at varying pressures are equal to calculated values,suggesting that the mineral matters have signification effect on interaction between char-H₂ O and char-CO₂.（3）During the isothermal gasification process of XMCC,gasification rate increases with the pressure increasing in CO₂,the pressure index is 0.24.While in the atmosphere of H₂ O and H₂O/CO₂,both the gasification rates and pressure index increase with the pressure increasing to 10 bar,and then remain unchanged with the further increase of pressure,which is due to the inhibiting effect of product gases on char gasification.The gasification reactivity of DXMCC in CO₂ and H₂ O shows a linear increase with the increase of tested pressure,and the effect of pressure on char-CO₂ is more significant.