PURPOSE: To prevent a concretion phenomenon of solid balls to be used in removing soot, by successively pressurizing-sending or suction-transporting the solid balls extracted from a hopper to a separator tank by utilizing pressurized heated air supplied from a main engine or vacuum suction.

CONSTITUTION: A damper 8 is opened, and solid balls in a separator tank 7 are scattered from an upper portion of a boiler through a shoot pipe 9, a distributor 10 and diffusing instruments 11. The solid balls scattered fall into a hopper 17 while repeating collisions with the internal elements of the boiler. Thus, soot accumulated on the surfaces of the elements is exfoliated by means of the solid balls, and discharged from a chimney while being carried on the flows of gases. Since the solid balls are forwarded to a solid ball tank 4 by means of a screw conveyor 2 from the hopper 17, immediately sucked up by means of a suction nozzle 5 and lifted to the separator tank 7, there happens no danger that the solid balls concrete in the solid ball tank 4.