Tan Bo, Cheng Gang, Zhu Xiaoman, Yang Xianbing
School of Emergency Management and Safety Engineering, China University of Mining and Technology -Beijing, Beijing, 10083, China.
Sci Rep. 2020 Apr 24;10(1):6946. doi: 10.1038/s41598-020-63988-4.
Coal is a porous medium. Oxygen molecules in the air penetrate through the pores of coal and are adsorbed on the coal surface. Low-temperature oxidation of coal then occurs, by which coal spontaneous combustion is promoted. Given this process, the authors analysed the physisorption characteristics of O in pulverized coal from the perspective of nanopore structure. In this study, five different kinds of coal samples (two lignites, one bituminous coal, and two anthracites) were selected, and the surface morphology, pore structure parameters and oxygen physisorption capacity of the pulverized coals were determined by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and oxygen adsorption with chromatography (OAC), respectively. The experimental results of SEM and MIP show that with the development of coal, the surface folds increase, and the pores increase in number and shrink, which leads to the nanopores of anthracite and bituminous coal being smaller and more complex than those of lignite. The experimental results of OAC show that adsorbed oxygen is physisorbed by pulverized coal in the order lignite > bituminous coal > anthracite. Analysis of the oxygen desorption curves shows that the oxygen desorption rates of the anthracites and bituminous coal are slower than those of the lignites. The results show that the amount of oxygen physisorbed by pulverized coal is proportional to the fractal dimension of the coal pores, proportional to the pore volume of the nanoscale pores, and inversely proportional to the number of closed pores in the coal. Based on the results of the analyses mentioned above, it is important to analyse the process of coal-oxygen chemisorption and the mechanism for low-temperature oxidation of coal to prevent coal spontaneous combustion.
煤是一种多孔介质。空气中的氧分子通过煤的孔隙渗透并吸附在煤表面。随后发生煤的低温氧化，进而促进煤的自燃。基于此过程，作者从纳米孔结构的角度分析了煤粉中氧的物理吸附特性。本研究选取了五种不同类型的煤样（两种褐煤、一种烟煤和两种无烟煤），分别通过扫描电子显微镜（SEM）、压汞法（MIP）和色谱氧吸附法（OAC）测定了煤粉的表面形态、孔隙结构参数和氧物理吸附容量。SEM和MIP的实验结果表明，随着煤化程度的提高，表面褶皱增加，孔隙数量增多且孔径减小，这导致无烟煤和烟煤的纳米孔比褐煤的更小且更复杂。OAC的实验结果表明，煤粉对吸附氧的物理吸附量顺序为褐煤>烟煤>无烟煤。对氧脱附曲线的分析表明，无烟煤和烟煤的氧脱附速率比褐煤慢。结果表明，煤粉物理吸附的氧量与煤孔隙的分形维数成正比，与纳米级孔隙的孔容成正比，与煤中封闭孔的数量成反比。基于上述分析结果，分析煤-氧化学吸附过程及煤低温氧化机理对于防止煤自燃具有重要意义。
