巴基斯坦Lakhra和Thar褐煤半焦的水蒸气催化气化

摘要

The catalytic effects of different catalysts, i.e., 3% Ca, 5%Na-BL, and 3% Ca+5% Na-BL catalyst, on carbon conversion, gasification reaction rate constant, activation energy, and relative amount of harmful sulfur containing gases, were investigated by thermogravimetry in steam gasification under temperature 700℃ to 900℃ at ambient pressure for two Pakistani Lakhra (LKH) and Thar (THR) lignite chars. High carbon conversion can be obtained by direct gasification of both LKH and THR chars, but the gasification rate became much fast using BL catalyst. THR char with high ash content was easy to form some complex silicates during BL catalytic gasification, leading to a lower conversion than that of LKH char with low ash content. SO2 and H2S as sulfur-containing gases produced by char and BL itself in steam gasification can be captured by the existence of Ca mixed with BL, which is more effective at temperatures less than 900℃. The shrinking core model (SCM) can be considered as a better choice to correlate the relations between conversion and time and to estimate the reaction rate constant (k) under different temperatures. The reaction activation energy (Ea) and pre-exponential factor (A) were predicted based on Arrhenius equation. The reaction activation energy of 44.7kJ/mol and 59.6kJ/mol for LKH chars with BL+Ca and BL catalysts were much lower than 114.6kJ/mol and 100.8kJ/mol for THR chars with the same catalysts, respectively. They were also lower than 161.2kJ/mol for LKH char and 124.8kJ/mol for THR char without catalyst.%采用热重法在常压与700℃~900℃条件下的水蒸气气化过程,对两种巴基斯坦Lakhra和Thar褐煤半焦进行了单一和混合催化剂(即3%钙和5%钠-黑液单一催化剂及一种3%钙和5%钠-黑液混合催化剂)对碳转化率、气化反应速率常数及活化能、有害污染含硫气体相对量的催化效应研究.两者Lakhra和Thar褐煤半焦经直接气化就可获得高的碳转化率,但采用纸浆黑液催化剂可使气化速率变得很快.含灰高的Thar褐煤半焦在纸浆黑液催化气化过程更易生成一些复杂的硅酸盐,从而导致比含灰低的Lakhra褐煤半焦出现一个更低的转化率.在水蒸气气化过程由半焦和纸浆黑液自身所产生的SO2 和 H2S含硫气体可为存在于纸浆黑液中的Ca盐所捕获而完成脱硫过程,但这一过程在低于900℃时更有效.缩芯模型 (SCM)可较好地用来关联转化率与时间的关系并给出不同温度下的反应速率常数k.基于阿累尼乌斯方程预测了反应活化能Ea 和指前因子A.在纸浆黑液和钙混合催化及纸浆黑液催化剂时,Lakhra褐煤半焦的Ea分别为44.7kJ/mol和 59.6kJ/mol明显小于Thar褐煤半焦的Ea=114.6kJ/mol 和 Ea=100.8kJ/mol,同样也小于无催化剂纯半焦气化时Lakhra褐煤半焦的Ea=161.2kJ/mol和Thar半焦的Ea=124.8kJ/mol.