Spontaneous combustion of carbonaceous stockpiles. Part I: The relative importance of various intrinsic coal properties and properties of the reaction system

The likelihood of a coal stockpile or carbonaceous waste dump undergoing spontaneous combustion is strongly influenced by factors that relate to both the intrinsic properties of the material itself, as well as the properties of the reaction system. An understanding of these material properties is a pre-requisite for the simulation of the large-scale reaction system with the aim of preventing or containing this phenomenon. The first part of this paper investigates a range of coal properties that were considered to be the most critical in terms of heat ' generation ' in a bulk coal medium. Certain properties, such as the heat capacity, the heat of reaction with oxygen and the activation energy for this reaction, were found to vary to a relatively minor degree for coals of varying rank and geological origin. However, rates of reaction with oxygen were found to vary by orders of magnitude for different coals. The reaction kinetics is consistent with a diffusion-limited shrinking-core model. A study of the coal properties that most strongly influence these rates of reaction is the subject of part two of this paper. (c) 2005 Elsevier Ltd. All rights reserved.