PURPOSE: To prevent the occurrence of explosion even when CO gas flows to a recovery line and to enable execution of safe recovery by a method wherein a recovery line for ash and char forms a closed cycle to seal inactive gas, and ash and char are recovered in an ash silo as the pressure of inactive gas is controlled to a specified value and a ratio of an oxygen amount to inactive gas is controlled to a value lower than a specified value.

CONSTITUTION: In a recovery line 19, nitrogen gas is discharged in an ash silo 11 from a nitrogen gas feed source to an ash silo 11 through a gas feed pipe 21 having a pressure regulating valve 25 in an opened state. A pressure in a bag filter 12 is detected by means of a pressure control device 29, and when the detecting pressure is higher than a specified pressure, an exhaust pipe 30 is opened to discharge gas to the atmosphere to reduce the detecting pressure to a specified value. When the pressure if below the specified pressure, with a pressure regulating valve 25 in the pipe 21 opened, nitrogen gas is discharged to the ash silo 11 to reduce a ratio to a value lower than a specified value. This constitution enables execution of safe recovery even when CO gas flows to the recovery line.