Modelling spontaneous combustion in wet lignite

A model of self-heating of wet coal is presented. This involves coupled hea t and mass transport within a coal pile, together with an exothermic reacti on and phase changes of water. There are four state variables: temperature, oxygen, water vapour and liquid water concentrations. Heat and mass are co nducted or diffused through the pile, while simultaneously undergoing chemi cal reaction. As demonstrated by experiment, the heat release rate depends in a quadratic fashion on the liquid water content and this feature is a di stinctive aspect of the model. After development of the model, an illustrat ive spatially uniform model of just three state variables (temperature, oxy gen and liquid water concentrations) is analysed for its bifurcational stru cture of steady states, periodic solutions and their stability. By this mea ns, thresholds for the onset of ignition can be determined as a function of the physical and chemical parameters.