TWO-STEP COMBUSTION CONTROLLING METHOD

PURPOSE:To lower the most of generation of NOX without increasing CO in the exhaust gas from a boiler and unburnt matter in the ash, by controlling the value of pressure difference between the pressure in a combustion chamber and the pressure of a blast box for two-step combustion to an optimum value. CONSTITUTION:A port 6 for two-step combustion is provided with a throat diameter varying apparatus 18 for adjusting the velocity of air so that when the amount of air supplied from said port is small, the diameter of the throat is decreased, while when the amount of the air is increased, the diameter of the throat is increased thereby increasing the velocity of air in the blast box 12 for two-step combustion to cause the flame gas in the combustion chamber and the air from the port to be mixed sufficiently. A signal from a two-step combustion air stream generator 19 via a charcteristic relay 21 and a signal from a two-step combustion draft generator 20 are inputted into a subtractor 22, and the output therefrom is processed in a proportional integrator 23, and is passed through a manual operation/automatic operation switch 24 to actuate a control drive 17 so that the desired control is performed.