NUMERICAL STUDY OF RADIATIVE IGNITION OF PYROLYSING SOLID FUELS

A numerical model of radiative ignition of pyrolysing solid fuels is d eveloped. The model is one-dimensional and transient. The following me chanisms are simultaneously accounted for: (i) the surface heat and ma ss transport, (ii) the surface oxidation chemical reaction, (iii) the in-depth pyrolysis, (iv) the gas-phase heating by absorption of the ra diation and by heat conduction/convection from the solid surface, and (v) the gas-phase chemical reaction. The solutions are obtained numeri cally with the method of lines. Using lignite and bituminous coal for the simulations, the results confirm that the pyrolysis products absor b a significant amount of the external radiation. Predictions of the i gnition times show that both the surface ignition time and the gas-pha se ignition time decrease rapidly with increasing radiation intensitie s. A good agreement between predictions and experiments is obtained. A sensitivity analysis is also carried out with the key kinetic paramet ers. This analysis establishes an upper limit for surface and pyrolysi s activation energies and a lower limit for gas-phase activation energ y. Within these limits, the radiative ignition of coals appears as an integration of two consecutive ignition modes: the surface ignition oc curs first, which is then followed by the gas-phase ignition. Beyond t hese limits, the single gas-phase ignition mode is the only ignition m ode to prevail.