Experimental Study On The Characteristics Of Char Gasification With CO₂

Coal accounts for a large proportion of Chinese energy structure,and it is also one of the main sources of my Chinese environmental pollution emissions.Under severe energy and environmental pressure,the development of efficient and clean coal conversion technology has become a strategic choice for our country's energy.Underground coal gasification is one of the effective ways to realize the clean utilization of coal.Its core is the reaction process of coke and gasification agent which is reduced by coal through pyrolysis.Therefore,this article mainly focuses on the gasification reaction characteristics of coke and CO₂ in the process of underground coal gasification.The coke is studied from various aspects such as coal type,gasification temperature,gasification agent partial pressure,and diffusion effect on CO₂ gasification reaction characteristics,then select an appropriate kinetic model,and analyze the kinetics of the coke-CO₂ gasification reaction from the three aspects of temperature,CO₂ partial pressure and ash content,and analyzed the compensation effect of reaction activation energy E and reaction pre-exponential factor k₀.Finally,combined with the coke-CO₂ gasification reaction experiment part,more suitable experimental conditions were selected,coal gangue and limestone were used to simulate the underground coal seam environment,and the influence of limestone and coal gangue on the coke-CO₂ reactivity in the underground coal gasification process was studied.The main research contents and conclusions of this paper are as follows:First,the experimental study on the characteristics of the char-CO₂ gasification reaction found that in a fixed bed reactor,the diffusion effect is significantly reduced when the CO2 flow rate is more than 160ml/min and the coke mass is less than 0.25g.The effect of the coke-CO₂ apparent gasification rate is significantly reduced.The gasification temperature has a significant effect on the gasification rate of coke-CO₂.When the temperature is increased from 900°C to 1200°C,the chemical reaction coefficient R increases from 0.057336 to 0.183762;when the temperature is lower than 1100°C,the apparent gasification rate is affected by the chemical The reaction kinetics is controlled,and the apparent gasification rate above 1100°C is mainly controlled by the diffusion rate.When the total flow of gasification agent is constant,increasing the CO₂ partial pressure will effectively improve the gasification activity of the coke-CO₂ reaction.At 1100°C,the gasification agent flow rate is 320ml/min,and the coke mass is 0.25g,when the CO₂ partial pressure is increased from 25%to 75%.When investigating the influence of coal types on the char-CO₂ gasification reaction,it was found that the order of the reaction activity of the three coal chars was:lignite coal char>bituminous coal char>deashed lignite coal char,the reactivity coefficient R is increased from 0.091 to about 0.155.When the temperature is 1100?and other experimental conditions are constant,the reactivity coefficient R is in order:0.147,0.128,0.1,indicating that the alkali metal in the ash has a more obvious influence on the char-CO₂ gasification reaction than the coke structure.Secondly,in this paper,the kinetic analysis of the char-CO₂ gasification reaction is carried out,and SCM,VRM,and RPM are selected to fit the chemical reaction rate constant k and reaction time.Studies have shown that the RPM model has the highest degree of fit R²,so this model is selected to describe the char-CO₂ gasification reaction,and the Arrhenius equation is used to obtain the reaction activation energy and pre-exponential factors under various experimental conditions.When studying the influence of ash on the char-CO₂ gasification reaction,it was found that after the deashing treatment,the reaction activation energy of the chemical reaction control stage increased from 65.13k J/mol to 98.02k J/mol,the activation energy of the reaction in the diffusion control stage increased from 29.9k J/mol to 38.8k J/mol.It can be seen that in the chemical reaction control stage,the ash content of coal has a greater impact on the CO₂ gasification reaction.The main reason is that lignite is a kind of high-sodium coal,and sodium has a higher catalytic effect on the char-CO₂gasification reaction,and it is in the chemical reaction.The control phase is more obvious.Whether the char-CO₂ gasification reaction is in the chemical reaction control stage or the diffusion control stage,its activation energy decreases with the increase of CO₂ partial pressure.When the gasification reaction is in the chemical reaction control stage,the activation energy range of three different CO₂ partial pressures(25%,50%,75%)is 41.78k J/mol-83.86k J/mol;When the gasification reaction is in the diffusion control stage,the activation energies of the three different CO₂ partial pressures range from 20.09k L/mol to 46.93k J/mol.At the same time,it is found through calculation that in the char-CO₂ gasification reaction,whether it is in the chemical reaction control stage or the diffusion control stage,there is an obvious compensation effect between the activation energy E and the pre-exponential factor k₀,and there is a good linear relationship between the two.The fit is as high as 0.9998.Finally,this paper uses limestone and coal gangue to simulate the underground coal gasification coal seam environment and carry out coal char-CO₂ gasification experiments.Studies have shown that adding limestone and coal gangue will increase the reactivity of coal.After the coal gangue is added,because the coal gangue contains alkali metal oxides,the alkali metals volatilize at high temperature,which plays a catalytic role by changing the internal structure of the coal,thereby reducing the reaction activation energy and improving the reaction activity of the coal.The coefficient R was increased from 0.0022 to 0.003.After limestone is added,the limestone will produce a large amount of CO₂ under high temperature calcination,thereby increasing the partial pressure of CO₂ in the gas atmosphere,enhancing the gas diffusion,thereby reducing the reaction activation energy and improving the reaction activity of coal.Compared with only adding coal gangue,its reaction coefficient R increased from 0.003 to 0.0042.