JPS5726322A - Controlling system for concentration of oxygen in exhaust gas - Google Patents

Abstract

PURPOSE:To control the concentration of oxygen in the exhaust gas under the optimum condition especially in response to the variation of combustion load by unifying the setting of the excess air ratio and the setting of the concentration of oxygen in the exhaust gas lest they should interfere mutually. CONSTITUTION:Fuel flow rate signals Ff are inputted to a function computing element 19, and a correction coefficient f (Ef) of the excess air ratio corresponding to the amount of combustion is obtained. The coefficient is inputted to a multiplier 20, the excess air ratio muS1, the output of a computing element 18, is multiplied by the coefficient, and the excess air ratio muS2 that the amount of combustion is corrected in a low region is obtained. The theoretical amount of air, the output of a counter 16, is multiplied by the ratio by means of a multiplier 21, and actual air amount setting signals are acquired. The output signals muS2 of the multiplier 20 are inputted to a computing element 22 converting the excess of air into the concentration of oxygen in the exhaust gas, and the set value of the concentration of oxygen in the exhaust gas automatically corrected in response to the capacity of combustion is obtained. The set value is inputted as the set value of an exhaust gas concentration regulator 23, and compared, adjusted and computed with measuring signals from an exhaust gas oxygen concentration detector 13 of a boiler. The output signals of the multiplier 21, the actual air amount setting signals, are multiplied by the adjusting output signals by means of a multiplier 24 and corrected, and the concentration of oxygen in the exhaust gas is controlled.