Determination Of Kinetic Parameters Of Carbon Gasification Reaction And Its Influencing Factors

Coal/biomass gasification is one of the important methods to efficiently and cleanly utilize energy,so it is crucial to research on the kinetics of gasification reaction.In this paper,Mongolian brown coal coke and coffee slag coke were used as experimental materials,and the gasification reaction kinetics was studied based on TGA.The research content of the subject is divided into two parts: first,the effects of the external diffusion caused by the sidewall of the crucible and the bed diffusion caused by the sample bed on the kinetic parameters of the gasification reaction were discussed in detail based on the isothermal thermogravimetric analysis method.Second,the gasification reaction kinetic parameters were solved by Coats–Redfern method and distributed activation energy model based on the non-isothermal thermogravimetric analysis method,and the results obtained by the two methods were compared and analyzed.In the isothermal gasification experiment,it is found that with the increase of gasification temperature,the reaction order of coffee coke increases,the reaction order of lignite coke decreases,and the variation of reaction order with temperature is related to the nature of the material itself.After eliminating the influence of external diffusion and bed diffusion,the reaction order,activation energy and pre-exponential factors are basically constant with the increasing conversion.However,the effect of external diffusion caused by the crucible sidewall will reduce the gasification reaction rate,apparent activation energy and pre-exponential factor.As the partial pressure of the gasifying agent increases,the effect of outdiffusion increases.The existence of bed diffusion also leads to the reduction of apparent activation energy and preexponential factor,and the influence of bed diffusion on gasification reaction rate,apparent activation energy and pre-exponential factor is much greater than that of external diffusion.In addition,when there is diffusion resistance,the activation energy and pre-exponential factor of coffee coke decrease gradually with the increasement of conversion rate,while the activation energy and pre-exponential factor of lignite coke increase gradually,and the variation of activation energy and pre-exponential factor with conversion rate is also related to the raw material.Regardless of the diffusion effect,the activation energy of the coffee coke and lignite coke and the pre-exponential factor showed good compensatory effects with the increase of the conversion rate.In the non-isothermal gasification study,the reactivity of coffee coke at each heating rate was higher than that of lignite coke.When the Coats–Redfern method is used to solve the reaction kinetic parameters,the increasement of the heating rate and the effects of the external diffusion and bed diffusion resistance will result in the reduction of the activation energy and the pre-exponential factor,but the influence of the bed diffusion is greater than that of the external diffusion.Regardless of the existence of the diffusion effect,the activation energy and the pre-exponential factor obtained by the Coats–Redfern method show good compensation effects as the heating rate increases.When the distributed activation energy model is used to solve the kinetic parameters,the activation energy of coffee coke and lignite coke is basically constant with the increase of conversion rate after the influence of external diffusion and bed diffusion is eliminated.When the diffusion resistance exists,both the external diffusion and the bed diffusion resistance will lead to the reduction of the activation energy and the preexponential factor,but the influence of the bed diffusion is significantly greater than the external diffusion.Whether it is isothermal gasification or non-isothermal gasification,the effect of diffusion on activation energy at different conversion rates is consistent.The activation energy obtained by the distributed activation energy model is linearly fitted with the preexponential factor by selecting the appropriate conversion rate interval,and a significant compensation effect can be obtained.After eliminating the effects of external diffusion and bed diffusion,the activation energy of coffee coke solved by isothermal method is much larger than that of non-isothermal method.When there is external diffusion or bed diffusion,the activation energy of coffee coke solved by non-isothermal method is close to that of isothermal method.Regardless of the reaction kinetic parameters solved by isothermal or non-isothermal methods,the influence of bed diffusion on the reaction kinetic parameters is greater than the external diffusion.