A char morphology system with applications to coal combustion

Abstract

A char morphology system is outlined, based on the physical and optical characteristics known to influence the burning of pulverized coal. Application of the system to high temperature char has established links between coal microlithotype predecessors and char types for subbituminous and bituminous coals. Quantities of high density and thick-walled char produced by pyrolysis at 1500 °C correlate with quantities of high density char in combustion residue, and with unburnt carbon content in fly ash for seven Australian energy coals. The proportions of different pyrolysis char types produced by any coal are shown to depend on coal rank, petrographic composition, maceral fusibility, and possibly ash content and composition, Quantities of high density chars in combustion residue can also be related to petrographic properties, including infusible inertinite content and percentage of microlithotypes of high inertinite content. Vitrinite reflectance is found to be a good parameter to differentiate burnout performance of coals with significant differences in rank. By comparing the proportions of high density, thick-walled pyrolysis char that form at 1500 °C, an estimate of burnout behaviour based on the combustion characteristics of char is obtained. Study of char types remaining after combustion also indicates potential for improvement of burnout performance, based on knowledge of the nature and origin of the unburnt carbon particles.