Na_2CO_3催化剂对福建高变质无烟煤比表面及气化反应特性的影响

Effects of catalyst loading of Na_2CO_3 on specific surface area and gasification characteristics of Fujian high-metamorphous anthracite

基于对不同Na2CO3催化剂添加量煤样比表面积和热天平(800～950℃)的测定,分别进行了福建建欣混煤的吸附等温线和比表面积以及碳转化率和气化动力学的研究,Ⅱ型吸附、L3型脱附及H3型滞后环表明实验煤样具有明显两端开放的小孔和大孔、一端封闭的细颈瓶形及狭缝毛细孔的特征。催化剂在煤样微孔的填充和表面修平对气化反应活性起关键作用,在低催化剂(0～8%)区域,比表面积随添加量增加的递减致使碳转化率及反应速率增加;12%时,出现微孔比表面积最低、过渡孔比表面积最大及气化反应半衰期急剧下降的明显拐点,意味着煤样中主要发生气化反应的表面微孔达到催化剂充分填充的装载饱和度(LSL);15%～24%区域,超出微孔饱和填充的催化剂部分,进而填充过渡孔并相互覆盖,减小了表面修平与匀化作用而使碳转化率及气化速率基本达一定值。缩核模型可很好地模拟催化气化动力学过程,12%(LSL)时的反应活化能比原煤减少55%,呈现较高碳转化率及气化速率。

Based on the measurements of specific surface area and thermal balance （800--950°C） of coal samples at different catalyst loadings of Na2CO3, the adsorption isotherms and specific surface areas, carbon conversions and gasification kinetics of the “Fujian Jianxin mixed coal” were investigated. Type ]] adsorption, type L3 desorption and H3-type hysteresis loop produced in the adsorption-desorption process indicated that experimental coal samples exhibited such obvious characteristics of two-end opening holes, ink-bottle pore with one end closed and the slit pore configurations. The function of catalyst filling in micropore and smoothing the surface of coal played a key role in gasification reactivity. At the lower loading range from 0 to 8%, the decrease of specific surface area with increasing catalyst loading led to the enhancement of carbon conversion and reaction rate. When the catalyst loading was 12%, the minimum and maximum specific surface areas of the respective micropore and intergrading pore, and the distinct inflexionwith an abrupt decline of gasification reaction half-life implied that these microporous surfaces carrying out mainly gasification reaction could reach such a loading saturation level （LSL） by complete filling and sufficient covering of catalyst. However increasing the catalyst loading beyond the LSL from 15% to 24%, an excess of catalyst loading would fill the intergrading pore and overlap each other, which alleviated the smoothing and regularizing actions of coal surface and led to a basically constant, specific value of carbon conversion and reaction rate of gasification. The shrinking core model could be used to describe the kinetic process of catalytic gasification and to predict the reaction rate constant at different temperatures and catalyst loadings. At 12% of catalyst loading the activation energy of reaction reached a lower value of 92.89 kJ mol^1 and was 55% less than the 207.08 kJ ·mol^1 of the original pure coal, which demonstrated that in this case the micropore of coal sample sufficiently filled by catalyst could provide more reactive carbon seats and therefore a high carbon conversion and gasification rate could be obtained.