PURPOSE: To improve carbon conversion rate by pulverizing unburned coal separated from the gas resulted from coal gasification and by making the pulverized coal into an aqueous slurry to convert the pulverized coal into a fuel of enhanced reactivity and then recirculating it into the gasification oven.

CONSTITUTION: The gas in a coal gasification oven 1 is cooled in a cooling section (1b), freed from slag, and further cooled by a crude cooling device 5. The ash (solid) allowed to fall runs in the form of an aqueous slurry, into a solid-liquid discharge line 7. Solid is separated from the gas discharged from the crude cooling device 5 through, e.g. a ceramic film 9 and joined into the aqueous slurry, from which a relatively large-sized particles are separated and removed by an electric screen solid separator 12, and the resultant slurry is subjected to a solid separator 13 of the same type to isolate the aimed solid, which is, in turn, pulverized together with water by a ball mill grinder 14; the resultant aqueous slurry is temporarily stored in a slurry tank 15. Thus, the aqueous slurry containing the pulverized solid is fed via a line 17 to the gasification oven 1.