Numerical study of radiative ignition of pyrolysing solid fuels

Abstract

AbstractA numerical model of radiative ignition of pyrolysing solid fuels is developed. The model is one‐dimensional and transient. The following mechanisms are simultaneously accounted for: (i) the surface heat and mass transport, (ii) the surface oxidation chemical reaction, (iii) the in‐depth pyrolysis, (iv) the gas‐phase heating by absorption of the radiation and by heat conduction/convection from the solid surface, and (v) the gas‐phase chemical reaction. The solutions are obtained numerically with the method of lines. Using lignite and bituminous coal for the simulations, the results confirm that the pyrolysis products absorb a significant amount of the external radiation. Predictions of the ignition times show that both the surface ignition time and the gas‐phase ignition time decrease rapidly with increasing radiation intensities. A good agreement between predictions and experiments is obtained.A sensitivity analysis is also carried out with the key kinetic parameters. This analysis establishes an upper limit for surface and pyrolysis activation energies and a lower limit for gas‐phase activation energy. Within these limits, the radiative ignition of coals appears as an integration of two consecutive ignition modes: the surface ignition occurs first, which is then followed by the gas‐phase ignition. Beyond these limits, the single gas‐phase ignition mode is the only ignition mode to prevail.