微型流化床与热重测定煤焦-CO2气化反应动力学的对比研究

对微型流化床反应分析仪(MFBRA)和热重分析仪(TGA)测定煤焦与CO₂的等温气化反应动力学进行了比较.在最小化气体扩散影响的条件下,半焦在MFBRA中的气化反应速率比TGA中大,且在转化率为0.15时有最大值.缩核模型能很好地描述半焦的气化行为.在760~1 000 ℃,半焦气化分两个阶段:在低温段,利用MFBRA和TGA求取的反应活化能基本相同,验证了MFBRA在求取反应动力学数据方面的有效性和可靠性;在高温段,MFBRA测定的反应活化能较大,说明其受扩散的抑制作用较小.相同温度下通过MFBRA求取的效率因子明显较大,这同其较快的反应速率相一致.上述差异充分说明了反应器类型对测试的(表观)反应动力学有显著影响.

Comparation of char gasification kinetics studied by micro fluidized bed and by thermogravimetric analyzer

The isothermal gasification kinetics of coal char with CO₂ was separately studied using a so-called micro-fluidized bed reaction analyzer (MFBRA) and a thermogravimetric analyzer (TGA). With minimized effects of heat and mass transfer, the reaction rate in MFBRA is much higher than that in TGA. And the maximal rate appears at a conversion of about 0.15 in MFBRA but at 0.45 in TGA. The shrinking core model can well describe the char gasification reaction both in MFBRA and in TGA. In the temperature range of 760~1 000 ℃, the char gasification reaction is investigated in two stages. At lower temperatures, the activation energy from MFBRA and TGA is very close, validating the reliability of MFBRA for gas-solid reaction kinetic studies. At higher temperatures, the estimated activation energy by MFBRA is obviously higher, showing a lower diffusion limitation in MFBRA. It is found that the measured frequency factor for the Arrhenius equation by MFBRA is much higher than that by TGA, complying with the higher reaction rate in MFBRA. As a consequence, MFBRA and TGA differ in diffusion and heating behavior, which can greatly affect the measurement of (apparent) kinetics.