煤焦的高温高压反应动力学

Kinetics of char gasification at high temperature and pressure

采用不同压力、温度条件下制得的快速热解煤焦作为样品,使用热重分析仪在常压下进行煤焦-纯CO_2气化反应动力学测试,得到本征反应速率。采用Thiele模数表征反应/扩散相对强弱,并预测煤焦在高温高压反应中内扩散和本征反应对表观反应速率的影响。常压下制得的煤焦,随制焦终温的上升,煤焦的表观气化反应速率减小,而随制焦压力的上升,煤焦表观气化反应速率增大。随反应温度的升高,Thiele模数逐渐增大,表观反应从动力学控制区域逐渐进入内扩散影响过渡区域;增大反应压力(CO_2分压)可以使Thiele模数减小。增大制焦压力能够使煤焦气化反应的Thiele模数减小,使表观反应进入动力学控制区域,而制焦温度对Thiele模数影响较小,无明显规律。煤焦的平均孔径越小,在相同反应温度下,反应更容易进入内扩散影响过渡区域(Thiele模数Φ>0.4)。

In this paper,the char sample was made by the rapid pyrolysis of coal at different temperatures and pressures.The kinetics of CO2/char gasification reaction was measured by a thermogravimetric analyzer to get the data intrinsic reactions.The Thiele modulus was employed to characterize the relation of reaction/diffusion and to predict the effects of diffusion and intrinsic reaction in the apparent reaction at high temperature and pressure.The char sample made with a higher pyrolysis temperature or lower pressure has a faster apparent gasification reaction rate.With the increase of reaction temperature or the decrease of reaction pressure （CO2 partial pressure）,the value of Thiele modulus increases,and the apparent reaction moves from kinetic control to diffusion control.With the increase of pyrolysis pressure,the Thiele modulus of the whole reaction decreases,which makes the apparent reaction stay in kinetic control area;while the pyrolysis temperature has little influence on the Thiele modulus.At the same reaction temperature,for the char sample with smaller pore size,the diffusion is more likely to affect the apparent reaction （the Thiele modulus above 0.4）.