CFD simulation of thermodynamic and temperature effects on spontaneous combustion of coal stockpiles and dumps

Abstract

In this work the development of a numerical model capable of identifying suitable conditions responsible for spontaneous combustion of coal storage piles and carbonaceous waste dumps are presented. The developed model captured the mass, momentum and energy conservation equations through the porous media. Combustion processes under consideration included physical absorption and desorption of atmospheric species in the coal matrix, formation of coal-oxygen complexes and oxygenated carbon species through chemisorption as well as the formation of both CO2 and CO through coal oxygenation. The aim of this model was to predict the influence of parameters such as buoyancy driven flows, temperature, storage pile porosity and permeability distributions as well as storage pile geometrical dimensions on combustion characteristics of carbonaceous materials. Possible analysis of such a model is constructed from the basis of a volume averaged methodology instead of deriving governing equations on a pore scale since this has proven to be the best options both from the time and physical dimensions perspectives. In all the cases strong non-linear interactions between the mass, momentum, and energy balance equations complicated the solution attainment through numerical integration of stiff partial differential equations (PDE’s).The simulation results obtained from the twodimensional model provided useful information in characterising the thermal-flow and combustion properties of coal stockpiles and carbonaceous materials and as such proved to be beneficial in assessing the stability of the stockpiles and quantifying the amount of CO2 emitted during combustion. The qualitative correctness of the model was validated by comparing the predicted results with other available numerical data obtained from the literature. Good correlations between the predicted and numerical results were obtained.