Patent ID: 8108073

Claim:
A method for controlling dosage of a reagent in a selective catalytic reduction (SCR) system comprising the steps of: a) providing the system with a plurality of reducing agent injection nozzles, each nozzle being configured and adapted to be independently calibrated during an SCR reaction when the system is in operation; b) determining an influence coefficient for each injection nozzle for a catalyst independently of the other injection nozzles, wherein the influence coefficient for each injection nozzle is based on a constant flow from the respective nozzle and a fraction of the constant flow that appears at each of a plurality of downstream grid points; and c) optimizing flow of reducing agent from each injection nozzle based on the influence coefficients to minimize a sum of deviation from the mean value of reducing agent to NO x ratio across a surface of the catalyst, wherein the flow of reducing agent is optimized based on the following equations: B i = ∑ j = 1 N ⁢ ⁢ K ij ⁢ X j AMM avg = ∑ i = 1 M ⁢ ⁢ B i M ∑ i = 1 M ⁢ ⁢ D i = ∑ i = 1 M ⁢ ⁢ ABS [ B i A i - AMM avg ∑ j = 1 M ⁢ ⁢ A j M ] ⁢ ⁢ ∑ j = 1 N ⁢ ⁢ X j = ∑ i = 1 M ⁢ ⁢ A i × η wherein: N=Number of Injection nozzles, M=Number of grid measurement points, X j =Flow rate of reducing agent at the j th injection nozzle, A i= NO x concentration at the inlet catalyst face in ppm at the i th grid measurement point, B i= Reducing agent concentration in ppm at the i th grid measurement point, K ij= Influence coefficient at the i th grid point for the j th injection valve, and is defined as the fraction of the flow at the j th injection valve that appears at the i th grid point, AMM avg= Average reducing agent concentration in ppm across the whole reactor cross section, D i= Absolute value of deviation from the mean value of reducing agent to NO x ratio at the i th grid point, and η=NOx Reduction Efficiency.