水热及微波处理对我国典型褐煤气化特性的影响

Influence of the Hydrothermal Dewatering and microwave irradiation treatment on the Gasification Characteristics of Typical Chinese Lignite

选取了我国主要褐煤产区不同煤阶的三种典型褐煤分别用水热、微波处理对其进行了脱水改性并研究了改性前后褐煤CO2气化特性的变化。结果表明,经过水热处理后,褐煤中的水分大幅度下降,最高降幅达87.31%,固定碳和热值上升,氧含量下降,煤阶参数(O/C原子比)下降,褐煤煤阶上升。水热处理过程中煤质结构的复杂重整导致煤焦孔径向微孔方向发展,先降低后增加,而比表面积和孔容呈现先上升后下降的趋势。煤质结构深度变化和煤阶的上升使得改性后褐煤的气化特性曲线向高温区移动,碳转化率达到50%时的气化温度上升。动力学计算结果表明经过水热改性后气化反应活化能上升,反应级数发生变化。较高的水热处理终温和相对较低的原煤煤阶都使得水热脱水改性的效果更为显著。在对脱水改性前后褐煤煤质组成分析的基础上使用低温氮吸附法和热重着重分析了改性前后褐煤孔隙结构和CO2气化特性上的差异。结果表明,微波能够在较短的时间内大幅度降低褐煤中的水分,最高降幅达到87.93%,处理后褐煤中的水分含量都已在10%内,固定碳含量和热值上升。褐煤微波改性后孔隙结构向微孔方向发展,比表面积和孔容上升,平均孔径下降。CO2气化结果表明褐煤经过微波处理后气化速率上升,达到50%碳转化率时的特征温度降低,改性后褐煤的气化活性变好。动力学计算结果表明改性后褐煤气化活化能下降,反应级数发生变化。较高的微波处理终温使得微波脱水改性的效果更加明显,褐煤组成、结构和气化特性的变化也更大。煤阶相对较低含水量较高的褐煤脱水效果更显著,而煤阶相对较高含水量较少的褐煤改性造成结构和气化特性的变化更明显。

The influences of hydrothermal dewatering （HTD） and microwave irradiation performed at different temperatures on the gasification characteristics of typical lignites with different metamorphic grades in China were investigated in this paper. Results show that the upgrading process significantly decreases the inherent moisture at a maximum degree of 87.31% and oxygen content, and increases calorific value and fixed carbon content, According to the oxygen/carbon ratio parameter, the coal rank increases. The complex changes occurred on coal structure during the HTD process lead to pore size of coal char develop to the microporous region, and the surface area and volume increase at first but then decrease. Due to the development of coal structure and the increment of coal rank, the gasification process of upgraded coal is delayed towards high temperature region, the temperatures when carbon conversion rate reaches 50% increase. From the results of kinetic calculation, activation energy increases after treatment, and the reaction order＆amp;nbsp;of mechanistic model is changed. Besides, all the changes caused by HTD are more obvious when the upgraded temperature increased from 250 ＆#176;C to 300 ＆#176;C and when the rank of raw brown coal was lower. The upgrading process significantly decreased the inherent moisture content at a maximum degree of 87.31 % in a short time, and increased the calorific value and fixed carbon content. The moisture contents of all upgraded coals were less than 10 wt%. After upgrading, pore distribution extended to the micropore region, the surface area and volume increased, and the average pore size decreased. Based on thermo-gravimetric analysis, the temperature when carbon conversion rate reaches 50% decreased, and the gasification rate increased, indicating the increase of gasification activity. From the results of kinetic calculation,activation energy decreased after treatment, and the reaction order of mechanistic model changed. All the changes caused by MI were more obvious when the upgraded temperature increased from 130 ＆#176;C to 160 ＆#176;C. Besides, when the raw lignite had a lower coal rank with higher moisture content, the dewatering process was more evident.