PURPOSE: To regulate NOx concn. at the exit of a denitrification device to be a predetermined value by a method wherein, when the NOx concn. at the entrance of the denitrification device is changed from the initial estimated value, the molar ratio is made changeable depending upon the degree of the change.
CONSTITUTION: In a function generator 5, at each change in the load on a boiler, the target value of NOx concn. at the exit of a denitrification device is subtracted from the estimated value of NOx concn. at the entrance thereof, the result thus obtained is divided by the estimated value of NOx concn. at the entrance of the denitrification device at each load change, the result thus obtained is made m (molar ratio) and (1-m) is generated. An integrator 6 adds the value of ratio from a divider 4 to the aforesaid (1-m). A subtracter 7 subtracts the result obtained by the integrater 6 from 1. An integrater 8 adds the total amt. of NOx in exhaust gas to the result obtained by the subtracter 7. A subtracter 9 subtracts the result obtained by the integrater 8 from the amt. of ammonia supplied to the denitrification device. A control valve 10 for the flow amt. of ammonia is regulated by the result obtained by the subtracter Q.
ESHITA TOYOHITO
HIRAKATA YUKIO
