煤焦-CO_2/H_2O气化反应过程中灰的熔融特性

Ash Melting Behavior During Coal Char-CO2/H2O Gasification Reaction

利用TGA-51H型高温热天平、扫描电镜-X射线能谱研究了我国典型高、低灰熔点煤种煤焦-CO2／H2O气化反应过程中灰的熔融变化行为和熔融机制。研究结果表明：高温下煤中的灰主要在煤焦-CO2／H2O气化反应过程中的中、后期（碳转化率大于50％）开始发生熔融，且初始熔融部分的主要成分为Fe系硅铝酸盐矿物（如铁橄榄石、铁铝榴石等），随着煤灰的进一步熔融，熔融部分中Ca元素含量逐渐增加，大量钙系矿物的出现，导致了煤灰熔融进程的加速；对于同一煤种，煤焦-CO2气化反应过程中灰的熔融温度要比其在煤焦—H2O气化反应过程中的熔融温度约低50-100℃；高温下煤焦颗粒上熔融或半熔融状态的灰渣易粘附在煤焦颗粒上，从而堵塞了煤焦颗粒上的孔隙，减少了气化剂与煤焦表面的有效接触，导致高温下随温度的升高，高灰熔点煤的气化反应速率仍继续上升，而低灰熔点煤的气化反应速率则变化缓慢。

Ash melting behavior of Chinese typical high and low ash fusion temperature （AFT） coals during char-CO2/H2O gasification reaction was studied by thermogravimetry analysis（TGA） （TGA-51H） and scanning electron microscope （SEM） equipped with energy dispersive X-ray （EDX） analysis. It was found that the initial melting behavior of ash usually occurs at the middle or later stage of char-CO2/H2O gasification reaction （carbon conversion 〉50%） at high temperature. The initial molten parts of ash are mainly caused by iron bearing minerals, such as fayalite, almandite etc. Along with the process of ash melting, the molten parts in ash contain more and more Ca elements and the melting behavior appears to be accelerated by the presence of Ca bearing minerals. For the same coal, the AFT of coal under char-CO2 reaction condition is about 50-100~C lower than that under char-H2O reaction condition. When temperature is high, some molten or semi-molten parts of ash can easily adhere to the coal char surface, block some micro-pores on char and prohibit gasifying gas to diffuse into the macro- or micropore surface of char. Therefore, for chars with low AFT the char-CO2/H2O reaction rate leveled off as temperature increase while for chars with high AFT the reaction rate would continue increasing.