METHOD FOR CONTROLLING AMOUNT OF NH3 TO BE INJECTED INTO EXHAUST GAS DENITRIFICATION DEVICE

PURPOSE:To stably supply an optimum amt. of NH3 by estimating the NOX flow rate from the exhaust gas flow rate and NOX content in the exhaust gas, calculating the molar ratio corresponding to the exhaust gas flow rate, and determining the amt. of NH3 to be injected. CONSTITUTION:The exhaust gas flow rate is calculated 22 by a computing element 15 from the fuel flow rate 20 and O2 concn. 21 in the exhaust gas, and the corresponding molar ratio (NH3/NOX) is calculated 23. Meanwhile, the NOX flow rate is calculated 25 from the NOX concn. 24 in the exhaust gas and the calculated exhaust gas flow rate 22 at the inlet of an exhaust gas denitrification device, and the amt. of NH3 26 to be injected is determined as the feedforward manipulated amount from the calculated molar ratio and the NOX flow rate. Besides, the NOX concn. 27 in the exhaust gas on the outlet side of the denitrification device is measured, an NOX set value 28 of the outlet-side exhaust gas conforming to the environmental reference value and the NOX concn. are transmitted to a sample-value PI controller 29 to calculate the manipulated amount for feedback control. Both manipulated amount are added 30, and the NH3 supply system is controlled 32 with the obtained amt. 31 of NH3 to be supplied as the whole manipulated amount.