Effects of Inertinite Content in Coal on Char Structure and Combustion

Abstract

This paper reports data on the combustion characteristics of seven high-volatile bituminous coals (VRr ≈ 0.65%) with increasing inertinite contents (10−68%). Structural parameters of pyrolysis chars are compared with the maceral compositions and distributions of maceral reflectances in the parent coals and with their combustion efficiencies. The microscopic study of pyrolysis chars obtained at 1000 °C reveals that inertinite-rich coal chars are much denser than those of inertinite-lean coals. The reactivity of these chars at low temperatures (500 °C) decreases with the increase of inertinite content of the parent coals, this being attributed to the highly cross-linked structure of the inertinites. However, at higher temperatures (1100 °C) the burnout levels of the inertinite-richest coals were clearly higher than those of medium-to-low inertinite coals. This cannot be explained from the assumption of a diffusional control of the combustion process. Thus, a chemical control of the process is suggested where the mechanism governing the overall reaction rate at 1100 °C would be the active site concentration in the molecular structure of pyrolysis chars, which, in turn, would depend on the aromaticity and degree of molecular ordering in the parent maceral structure.