PURPOSE: To assure a safe and stable automatic operation of a solid fuel combustion device by a method wherein two adjusting valves are arranged in series with an outlet pipe for a primary air, a first adjusting valve may restrict an amount of air at an initial combustion of dry distillation and a second adjusting valve is automatically adjusted in response to a load of a waste heat recoverying device.

CONSTITUTION: When a drying reservoir 4 starts to perform a primary combustion, a first adjusting valve 22 for a primary air is initially controlled by a contact point 33 of an automatic controlling device 32 through a combustion furnace output temperature sensor 23 and a line 24. An amount of primary air is restricted and a supplying of oxygen at an initial dry distillation combustion is kept out of a limitation of explosion so as to prevent a phenomenon of explosion and then a safe operation is started. Then, a first adjusting valve 22 for primary air is controlled, an amount of primary air is gradually increased and an occurrence of dry distillation gas is promoted. In turn, a second adjusting valve 28 for the primary air is proportionally controlled for its opening or closing in response to an indicating valve from a load sensor 26 for a waste heat recovery device 25 and then a combustion output corresponding to a loading condition of the waste heat recovery device 25. An amount of secondary air is controlled in such a way as a signal of a remaining oxygen densitometer 11 for the chimney is fed back to a secondary air adjusting valve 13 so as to get a specified concentration of the remaining oxygen.