We analyze the heterogeneous ignition of a coal particle suspensión bounded by two parallel isothermal walls in the limit of large gas/particles thermal capacity ratio, in which the temperature difference between the particles and the gas is important. Radiative heat transfer is accounted for by using the Eddington differential approximation, and heat conduction between the particles and the gas is also included in the model. Heat reléase is assumed to occur at the surface of the particles through the heterogeneous reaction C(s) + 1/2 02 -* CO, obeying an Arrhenius law with large activation energy. Critical conditions for ignition are determined on the basis of a quasi-steady treatment. The effects of gas/wall temperature ratio, conduction/radiation parameter, and size of the reacting cloud relative to the óptica! length are explained.