A method for controlling emissions from a power plant having an ammonia injection grid that includes a plurality of ammonia injection points, the method comprising the steps of: injecting ammonia into a flow of exhaust gas at an injection location, the injection of ammonia defining a spatial distribution of ammonia across an exhaust gas flowpath; measuring at least one parameter of the exhaust gas downstream from the injection location; comparing a measured value for the at least one parameter of the exhaust gas to a threshold value for the at least one parameter, wherein the at least one parameter is a plurality of parameters including nitrogen oxide, ammonia and oxygen within the exhaust gas; wherein the injection points of the ammonia injection grid are arranged in rows, each row having a control valve associated therewith for controlling a flow of the ammonia provided to the injection points; characterized in that the method further comprises the steps of: determining a position for at least one of the control valves prior to adjusting the position of the at least one of the control valves, determining positions for the control valves for a given operating condition based on previously acquired measurement data, controlling the control valves to the thus determined positions, if the measured value for the at least one parameter exceeds the threshold value for the at least one parameter, automatically modifying the spatial distribution of ammonia injection across the exhaust gas flowpath, wherein the step of modifying the spatial distribution of ammonia across the exhaust gas flowpath includes adjusting a position of at least one of the control valves, and determining, regularly updating and storing the thus adjusted positions for the control valves as a function of operating and boundary conditions based on newly acquired measurement data. injecting ammonia into a flow of exhaust gas at an injection location, the injection of ammonia defining a spatial distribution of ammonia across an exhaust gas flowpath; measuring at least one parameter of the exhaust gas downstream from the injection location; comparing a measured value for the at least one parameter of the exhaust gas to a threshold value for the at least one parameter, wherein the at least one parameter is a plurality of parameters including nitrogen oxide, ammonia and oxygen within the exhaust gas; wherein the injection points of the ammonia injection grid are arranged in rows, each row having a control valve associated therewith for controlling a flow of the ammonia provided to the injection points; characterized in that the method further comprises the steps of: determining a position for at least one of the control valves prior to adjusting the position of the at least one of the control valves, determining positions for the control valves for a given operating condition based on previously acquired measurement data, controlling the control valves to the thus determined positions, if the measured value for the at least one parameter exceeds the threshold value for the at least one parameter, automatically modifying the spatial distribution of ammonia injection across the exhaust gas flowpath, wherein the step of modifying the spatial distribution of ammonia across the exhaust gas flowpath includes adjusting a position of at least one of the control valves, and determining, regularly updating and storing the thus adjusted positions for the control valves as a function of operating and boundary conditions based on newly acquired measurement data. determining a position for at least one of the control valves prior to adjusting the position of the at least one of the control valves, determining positions for the control valves for a given operating condition based on previously acquired measurement data, controlling the control valves to the thus determined positions, if the measured value for the at least one parameter exceeds the threshold value for the at least one parameter, automatically modifying the spatial distribution of ammonia injection across the exhaust gas flowpath, wherein the step of modifying the spatial distribution of ammonia across the exhaust gas flowpath includes adjusting a position of at least one of the control valves, and determining, regularly updating and storing the thus adjusted positions for the control valves as a function of operating and boundary conditions based on newly acquired measurement data.