Numerical modelling of the self-heating process of a wet porous medium

In this research, the shortcomings of some advanced models for heat and fluid flow and moisture transport within and around a reactive porous medium (a coal stockpile) are numerically investigated based on a local thermal non-equilibrium approach and results are compared with experimental data. A full account of the problem is presented, including transient variation of the maximum temperature in the medium and the time required to vaporize the water content. The former is the main parameter used in the study of spontaneous self-ignition of coal stockpiles and the latter is an indication of the last step of self-heating toward self-ignition. Correlations are developed for the maximum dimensionless temperature inside the pile when the moisture content is near zero and the time that it takes from the beginning of self-heating until this time as functions of porosity, permeability, moisture content and the overall size of the porous medium.