NOX DECREASING BOILER FOR BURNING PULVERIZED COAL BY PLURAL KIND OF FUEL

摘要

PURPOSE:To enable to maintain stable NOX reduction effect at all times without increasing unburnt content and consequently sharply reduce NOX in exhaust gas by a method wherein pulverized coal is supplied to main burners in one lower stage or in a plurality of stages, while coal oil mixture fuel, oil fuel or gas fuel is supplied to the uppermost stage. CONSTITUTION:In case of front firing, three stages of burners are provided at the front surface of a furnace 1 or the burners at the lowermost and middle stages consist of PG dual type pulverized coal burners and the burner at the uppermost stage consists of a PG dual type coal oil mixture burner. The air ratio of each burner is about 1.0 at the lowermost stage burner, about 0.7 at the middle stage burner, and about 0.5 at the uppermost stage burner. Consequently, the uppermost stage burner or coal oil mixture burner for NOX reduction produces a large quantity of intermediate produts stably in order to accelerate the reduction within the furnace. In addition, because the coal oil mixture burnr, contrary to pulverized coal burner, burns with a comparatively small amount of unburnt content even in low air ratio and has fast burning velocity, the fuel is burnt up enough completely by charging after air 5. In such a manner as mentioned above, the stable NOX reduction effect can be maintained at all times without developing unburnt content.