Coal devolatized and partially gasified in a travelling grate reactor is dropped into a shaft furnace to form a downwardly moving stack which moves then downwardly to and through a fixed bed gasifier, wherein it is burned to ash. A gas stream from the travelling grate reactor is down-drafted through the shaft furnace and a gas stream is up-drafted through the fixed bed gasifier, and the two streams combined are drawn through a heat exchanger and fed to a gas burner, combustion air for the gas burner being heated in the heat exchanger.