CO_2对煤升温氧化燃烧特性的影响

为了掌握CO2气体防治煤自燃的特性,采用TG-DSC联用分析系统测定煤样在不同CO2体积分数、不同升温速率时反应引起的质量、能量变化,研究CO2对煤升温氧化燃烧过程的影响。通过分析煤升温氧化燃烧过程的TG-DSC曲线,确定了煤氧化燃烧过程的特征温度变化规律,实验表明:煤样变质程度越高,TG曲线越向温度高的方向移动;特征温度T1,T2,T3在不同CO2/空气混合条件下失重曲线差异较小,在失重温度T4时,CO2体积分数越大,其TG,DTG曲线差异越大,着火温度、质量变化速率最大温度点及燃烬温度点延后。CO2体积分数影响了煤样放热强度,CO2体积分数越低,DSC曲线越陡,放热强度越高;CO2体积分数越高,曲线平缓,放热量小,燃烧点放热峰向高温区移动,反应得到了抑制。通过动力学分析计算得出:煤样在空气氛围下的活化能和频率因子均大于在通入CO2气体后,随着CO2体积分数的升高,表观活化能和指前因子减小速度加快,但反应速率常数也减小,表明CO2抑制了煤的氧化燃烧。

Effect of CO2 on characteristics of oxidation combustion for coal

In order to master the characteristics of CO2 gas prevention and control of coal spontaneous combustion，coal samples were measured the mass and energy changes caused by the reaction at four different atmosphere，different heating rates by the TG-DSC combination analysis system.Based on the analysis of curves of TG，DTG and DSC，the kinetics parameters of coal oxidation and decomposition reaction under the conditions of CO2/air mixture were calculated.With the increasing of CO2 concentration，the apparent activation energy and the pre-exponential factor of coal oxidation accelerate reduction，the reaction rate decreases，the releasing heat decreases.By analyzing the relationships between the curve of TG-DSC and the process of coal spontaneous combustion，the characteristic temperatures of the process of coal oxidation spontaneous combustion were determined.The experiments showed that：the higher the degree metamorphic of coal sample，coal sample weight loss curve is moving to the direction of high temperature.Between the weight loss curves of the T1，T2 and T3 of characteristic temperatures under the conditions of different CO2/air mixture have small differences.In the temperature T4 of weight loss，the more CO2 concentration increasing，the greater the difference of TG and DTG curves，the lower the oxygen concentration，the ignition temperature，maximum temperature point of weight loss rate and burnout temperature point are postponed.Heat liberation intensity of coal sample is affected by the concentration of CO2 gas，the lower the concentration of CO2，the steeper the DSC curve，the higher the heat release intensity;the higher the concentration of CO2，the gentler the curve，the smaller the heat quantity，the exothermic peak of burning point moves to higher temperature，the reaction is suppressed.By differential scanning calorimetry，the physical and chemical changes were studied in the process of coal samples heating oxidation.Releasing heat of coal samples，heat intensity of coal samples under different CO2 concentration conditions and coal samples heating intensity under different heating rates conditions were compared and analyzed.