PURPOSE: To realize a superior flame shape and a better characteristic of combustion to restrict generation of NOx and at the same time to improve a turn-down characteris tic of fine powder coal combustion by a method wherein the number of fine powder coal injection pipes are adjusted in response to a required calorie of the fine powder coal, an amount of fed air is varied to keep a ratio of solid to gas in a specified range.

CONSTITUTION: In order to perform a stable combustion with low NOx, a shape of stable bright flame is required at a port of a burner and so a ratio between solid and gas is less than 2.5 and the lower the fuel having low volatile substance, the better of a low ratio of solid to gas. In reference to a maximum amount of combustion of the fine powder coal and the number of fine powder coal injection pipes 42d of a burner 10, the number of fine powder coal injection pipes to be opened in reference to a range of the amount of combustion of the fine powder coal is set in advance. For example, the number of the fine powder coal injection pipes 42d is three, the number of fine powder coal injection pipes to be opened is 3 to about less than 2/3, in a range over about 1/3, two to about less than 1/3, and one in a range more than a minimum combustion volume. The amount of air for feeding a powder coal is set in response to the number of fine coal injection pipes to be opened so as to be set within the specified range, and then a combustion is carried out.