A model of flame propagation in rich mixtures of coal dust in air

A two-phase combustion model describing fundamental coal dust flame propagation phenomena is developed to treat general fuel rich mixtures. The model includes heterogeneous combustion, pyrolysis of the coal, and homogeneous combustion of volatile matter and the optically thick limit for radiative heat transfer. Calculations for coal (fuel) rich mixtures in air were done for equivalence ratios of 3-8. Predicted burning velocities for 50 μm particles of coal with 36% volatile matter indicated a broad maximum of 37 cm/s at an equivalence ratio of 4 (0.367 kg/m³). The minimum computed velocity was 9 cm/s at φ = 8 (0.733 kg/m³). The burning velocity was found to increase as the particle size decreased. The chemical kinetics model was highly simplified, but based on experimental information. The predicted flame temperatures and structures compare well with recent experimental data published by the authors. The structure of the flames was found to be strongly influenced by radiative heat transfer. Flame thicknesses were predicted to exceed 10 cm for most conditions studied.