煤田火区氧化煤分阶催化气化及作用机理

Staged catalytic gasification of oxidized coal in coal field fire area and itsaction mechanism

煤田火区热量较大,火区高温会对周围煤体造成影响,在火区受到有效控制或蔓延至其他区域后,往往在火区边缘或邻近煤层形成数量较大的氧化煤。与原始煤炭相比,氧化煤热值低、灰分高,难以作为常规燃煤利用,目前多与优质煤混合利用,导致混煤整体燃烧热值降低且炉渣量增加,严重影响电厂锅炉运行效率。为了更好地利用氧化煤,实现资源利用最大化,提出了氧化煤的分阶催化气化思路,并提出使用价格低廉的膨润土作为高温阶段的催化芯材,通过分阶式催化剂分别实现氧化煤气化过程的初期快速活化和后期催化气化,从而实现氧化煤高效气化利用。采用X射线衍射、扫描电子显微镜和孔隙分析表征氧化煤催化气化过程中关键结构演变特征,并利用热重质谱联用开展气化实验,通过特征参数分析气化前期和后期反应特点。结果表明:分阶式催化剂由外层K_(2)CO_(3)和内层膨润土构成,其表层K_(2)CO_(3)能明显促进氧化煤初期热解过程中孔隙结构的形成,在气化初期产生大量微孔结构,增加氧化煤与气化剂CO_(2)的接触面积,提高氧化煤反应活性;含Na+阳离子的膨润土可以在高温阶段发挥稳定催化作用,弥补了K_(2)CO_(3)在高温阶段易挥发和失活的缺陷。在分阶式催化剂作用下,碳晶格单元的生长速度减小。这表明分阶式催化剂可以插入碳芳环的边缘,导致内部晶格出现缺陷,从而有效抑制氧化煤焦的石墨化进程,保证连续催化气化反应。当K_(2)CO_(3)和钠基膨润土的质量比达到1∶1,整体催化气化效果最佳。分阶式催化剂在热解阶段也起到一定的催化作用,能促进氧化煤热解脱挥发分释放出氢气。在气化反应阶段,分阶式催化剂能有效降低氧化煤气化反应温度以及合成气产率峰值温度,提高气化反应速率。CO和H_(2)体积分数峰值对应温度的降低幅度分别达到97.4、129.1℃,具有明显的催化效果。氧化煤的分阶式催化气化高效制取合成气为火区氧化煤高效利用提供了新思路,可避免大量火区滞留煤炭资源的浪费。

Coal field fire can release massive amounts of heat,affecting the surrounding coal.When the fire area is effectively controlled or extended to other areas,a large amount of oxidized coal is formed at the edge of the fire area or adjacent coal seam.Compared with raw coal,oxidized coal has low calorific value and high ash content,which makes it difficult to be used as conventional coal for combustion.Currently,it is mostly mixed with high-quality coal,resulting in a decrease in the overall calorific value and an increase in the amount of slag,which seriously affects the operation efficiency of power plant boilers.To make a better use of oxidized coal and maximize the utilization of resources,the idea of staged catalytic gasification of oxidized coal is put forward.0x09It is proposed to adopt low-cost bentonite as the catalytic core material in the high-temperature stage.It can realize the high-efficiency gasification utilization of oxidized coal by the initial activation and the persistent catalytic gasification in the later stage.The X-Ray diffraction(XRD),Scanning electron microscope(SEM),and pore analysis are adopted to characterize the evolution of coal.The TG-MS analyzer is used to carry out gasification experiments.The results demonstrate that the staged catalyst is composed of an outer layer of K_(2)CO_(3) and an inner layer of bentonite.The surface layer of K_(2)CO_(3) can significantly promote the formation of pore structures in the initial pyrolysis of oxidized coal,and a large number of microporous structures are formed in the initial stage of gasification,increasing the amount of contact area of oxidized coal and gasifying agent CO_(2).Bentonite containing Na+can play a stable catalytic role at high temperatures,making up for the defects of K_(2)CO_(3) being volatile and deactivated.The growth rate of the carbon lattice unit is slower than that of raw coal char with the action of the staged catalyst.This indicates that the staged catalyst can be inserted into the edge of the carbon aromatic ring,resulting in defects in the internal lattice,thereby effectively inhibiting the graphitization process of oxidized coal char and ensuring the continuous catalytic gasification process.When the weight ratio of K_(2)CO_(3) and Na-based bentonite is 1∶1,the overall catalytic gasification effect is the best.The staged catalyst plays a catalytic role in the pyrolysis stage as well,which can promote the release of hydrogen from the pyrolysis of oxidized coal.During the gasification stage,the staged catalyst can effectively reduce the gasification reaction temperature of oxidized coal and the peak temperature of the synthesis gas yield,and increase the gasification reaction rate as well.The temperature values corresponding to the peak concentrations of CO and H_(2) decrease by 97.4℃and 129.1℃,respectively,showing an obvious catalytic effect.The high-efficiency production of syngas by the staged catalytic gasification proposed in this work provides a new way for the efficient utilization of oxidized coal in the fire area,which can avoid the waste of a large number of coal resources in the coal field fire area.