Evaluation of the chemical properties of coals and their maceral group constituents in relation to combustion reactivity using multi-variate analyses

The factors affecting the combustion rates of coals have been investigated using multivariate analysis. Coals from Australia, Colombia, Germany, UK and USA and their separated maceral group constituents were subjected to detailed optical and chemical characterisation followed by the measurement of combustion reactivity at low temperatures (up to 1323 K) using TGA, and at high temperatures (1300-1900 K) in an entrained flow reactor. The derived activation energies and pre-exponential factors were used in conjunction with eighty-six detailed chemical and petrographic parameters as the basis for statistical analysis. This demonstrated that the parameters which significantly influence the combustion rate could be used to divide the coals and maceral groups into two classes. One class containing predominantly the northern hemisphere coals with their corresponding maceral groups and the other containing the Australian and Colombian coals with their maceral groups. No significant relationships were found between the reactivity of the coals and the maceral groups within that coal, or between the same maceral group for all the coals. However the chemical composition of the organic matter content was found to be an important parameter in determining coal reactivity and such information could be used to supplement classical petrographical classification and proximate and ultimate analyses in order to predict the reactivity of a given coal. The effect of ash on the burning rate of the individual maceral components was also investigated and the implications for burnout in practical combustion systems discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.