Abstract: A method of controlling the feeding of a reducing agent, such as urea or ammonia, to a selective catalytic reduction reactor, which is operative for removing NOx from a process gas of a process plant, comprising the steps of estimating a present value of at least one predetermined parameter which is indicative of the amount of NOx that needs to be removed from said process gas in the selective catalytic reduction reactor. The rate of increase of said at least one predetermined parameter is then estimated. When said estimated rate of increase of said at least one predetermined parameter is found to be positive, the amount of said reducing agent being supplied is increased to a higher value than would be the case if said at least one predetermined parameter were to be kept constant at the estimated present value thereof.

Abstract: A method of controlling the feeding of a reducing agent, such as urea or ammonia, to a selective catalytic reduction reactor, which is operative for removing NOx from a process gas of a process plant, comprising the steps of estimating a present value of at least one predetermined parameter which is indicative of the amount of NOx that needs to be removed from said process gas in the selective catalytic reduction reactor. The rate of increase of said at least one predetermined parameter is then estimated. When said estimated rate of increase pf said at least one predetermined parameter is found to be positive, the amount of said reducing agent being supplied is increased to a higher value than would be the case if said at least one predetermined parameter were to be kept constant at the estimated present value thereof.