System and method for improving the performance of a selective catalyst reduction system in a heat recovery steam generator

A heat recovery steam generator, comprising:

• a gas inlet for receiving a flow of exhaust gas from a gas turbine;
• a gas outlet opposite the gas inlet and configured to transport the flow of exhaust gas to atmosphere;
• an ammonia injection grid having a generally planar array of injection ports configured to inject ammonia into the flow of exhaust gas at various locations along a cross-section of an exhaust gas flow path, the ammonia injection grid including a plurality of valves, each valve being associated with a respective subset of the injection ports;
• a measurement system located intermediate the ammonia injection grid and the gas outlet;
• and
• a control unit configured to:
• receive emission measurement data from the measurement system;
• to modify a position of each valve of the plurality of valves to thereby modify a spatial distribution of ammonia in the exhaust gas from the ammonia injection grid in dependence upon the emission measurement data;
• determine, at the modified spatial distribution, whether a NOx concentration in the exhaust gas is within a threshold range, wherein in the event the determined NOx concentration in the exhaust gas is not within the threshold range, the control unit is configured to further adjust the position of each valve of the plurality of valves, and wherein in the event the determined NOx concentration in the exhaust gas is within the threshold range, the control unit is further configured to record the respective valve position based on an operating condition at the time of the valve adjustment;
• and determine an optimum valve setting for each valve at the operating condition based on the recorded positions.