PURPOSE: To extremely facilitate removal of scale, by a method wherein 0.1W 3wt%, based on oil coke powder, of an alumina material, for example, Al2O3, is added and burnt.

CONSTITUTION: When oil cokes are burnt in a boiler, 0.1W3wt%, based on oil coke powder, of an alumina material, for example Al2O3 is added and burnt. The added alumina material reacts to FeV2O4 being a low melting point compound to produce FeAl2O4 being a high melting point compound. A part, where scale makes contact with a water pipe, is formed in an uneven state with a width of 1W3mm, and arching with scale on an adjoining water pipe is prevented from occurrence. Through decrease of a boiler load during operation, the temperature of a combustion chamber is reduced to about 600W800°C, and this enables scale to easily fall off naturally for removal.