A comparison of different methods for predicting coal devolatilisation kinetics

Knowledge of the coal devolatilisation rate is of great importance because it exerts a marked effect on the overall combustion behaviour. Different ap proaches can be used to obtain the kinetics of the complex devolatilisation process. The simplest are empirical and employ global kinetics, where the Arrhenius expression is used to correlate rates of mass loss with temperatu re. In this study a high volatile bituminous coal was devolatilised at four different heating rates in a thermogravimetric analyser (TG) linked to a m ass spectrometer (MS). As a first approach, the Arrhenius kinetic parameter s (k and A) were calculated from the experimental results, assuming a singl e step process. Another approach is the distributed-activation energy model , which is more complex due to the assumption that devolatilisation occurs through several first-order reactions, which occur simultaneously. Recent a dvances in the understanding of coal structure have led to more fundamental approaches for modelling devolatilisation behaviour, such as network model s. These are based on a physico-chemical description of coal structure. In the present study the FG-DVC (Functional Group-Depolymerisation, Vaporisati on and Crosslinking) computer code was used as the network model and the FG -DVC predicted evolution of volatile compounds was compared with the experi mental results. In addition, the predicted rate of mass loss from the FG-DV C model was used to obtain a third devolatilisation kinetic approach. The t hree methods were compared and discussed, with the experimental results as a reference. (C) 2001 Elsevier Science B.V. All rights reserved.