PURPOSE: To prevent the adhesion of adhesive substances on the interior of a gas dispersion pipe or a gas dispersion cap by absorbing a part of fluid medium with the gas passing through said gas dispersion pipe and discharging the gas from the upper part.

CONSTITUTION: When a high moisture residual 12, such as beer dregs is burnt in a primary fluid combustion chamber 3, the combustion gas accompanied by the ash and unburnt substances flows into reducing parts 22 of a number of gas dispersion pipes 20 installed to a gas dispersion plate 6 and then a gas passage 20b for the pipes 20 at a high velocity. The combustion gas which has passed through the reducing part 22, and maintained the high velocity absorbs a fluid medium 4 filled in a fixed stationary part 24 from an opening end of an absorption pipe 23, and it is discharged from an upper end 21c. The combustion gas is dispersed and discharged from a clearance 21c of an entire periphery into a secondary fluid combustion chamber 4. In the mean time, a fluid medium 7 comes into collision or contact with an inner wall of the pipe 20 or an inner surface of a cap 21, and scales off adhesive substances and keeps clean the upper end of the pipe 20, a gas discharge part of the cap 21 or a reversing part where adhesive substances are easily adhered.