The multi-scale pore structure of superfine pulverized coal. Part 2. Mesopore and closed pore morphology

Abstract

Superfine pulverized coal exhibits extraordinary properties in thermal conversion processes like pyrolysis and combustion. The exploration of closed pores is of great significance for studying of the macromolecular structure, and developing advanced clean combustion technologies. In this work, the influences of coal rank and particle size on the mesopore characteristics (i.e., pore size, volume, and specific surface area), especially closed pores, were obtained by combining nitrogen adsorption and synchrotron-based small-angle X-ray radiation (SAXS). In addition, combined with the closed pore volume measured by He density and SAXS, research focuses on the formation and opening mechanisms of closed pores in different rank coals at a molecular level. The results indicate that both the bituminous (NMG) and anthracite coal (HN) have a few large open pores (>100 nm), with large amount of small mesopores and micropores (<2 nm). The HN coal has more open mesopores which have a smaller pore size than NMG coal. The closed pore proportion of HN coal in the studied pore size range is between 2 and 52 %, while that of NMG coal is between 47 and 67 %. In addition, both coals have a certain amount of closed pores formed by shear force and ash blockage, while the matrix compression also contribute to certain types of closed pores in NMG. These findings contribute to illustrating the closed pore structure in coal at the molecular level, which sheds light on constructing comprehensive macromolecular pore models of coal and thus promoting the development of clean coal utilization technologies.