PURPOSE: To perform a recombustion of dust and make reduce remarkably an amount of waste material by a method wherein almost of all the oil coke dust discharged from a main body of boiler and a dust collector are supplied to the combustion chamber.

CONSTITUTION: Hoppers 12 to 14 for discharging the collected oil coke dusts 11 discharged and removed from the burnt exhaust gas are arranged below a main body 9 of the boiler, its air preheater 10 and a dust collector 2, respectively. In order to reignite almost of all the dust 11 in the combustion chamber 3, each of the hoppers is connected to the duct 16 having a reignition fan 15 therein and then the dust 11 is supplied to the main burner 6 for igniting the oil coke 4 arranged in the combustion chamber 3. With this arrangement, the reignition of a large amount of dusts generated under the combustion of the oil coke is performed to realize the saving of resource and saving of energy and at the same time a substantial amount of waste materials are reduced.