Abstract: A simple pyrolysis method is presented,in which the coal is preheated with flue gas in a fixed bed. The high heat penetration into the packed bed of coal particles is described mathematically with a reaction and transport model. The temperature profiles for the particles,and the transient local distribution of volatile matter are examined under different conditions. The thermal penetration into the packed-bed particles by fluid flow is analyzed. The thermal penetration depth and coal pyrolysis zone moves along the bed with time. Increasing inlet gas temperature tends to enhance the temperature level in the thermal penetration zone and decrease the pyrolysis time. The model results are found to agree the experimental data available in literature.