Patent ID: 7846405

Claim:
A method for monitoring and/or controlling performance of a selective catalytic reduction (SCR) emission control system, said method comprising: directing a combustion gas stream containing a pollutant gas over a catalyst bed; injecting a quantity of a pollution neutralizing gas into the combustion gas stream at a plurality of injection locations upstream from the catalyst bed to form a predetermined ratio of the pollution neutralizing gas to the pollutant gas, wherein the catalyst bed facilitates a reaction of the pollution neutralizing gas with the pollutant gas to produce an effluent; sampling the effluent at a plurality of sample locations across the catalyst bed; channeling at least one sample of effluent from each sample location of the plurality of sample locations to an enclosure, wherein the sample is heated to a first temperature; channeling the sample of effluent to an instrument at a second temperature that is approximately equal to the first temperature; measuring, substantially simultaneously, the concentration of the pollution neutralizing gas and the pollutant gas in the effluent; determining a ratio of the pollution neutralizing gas to the pollutant gas in the effluent at each of the plurality of sample locations; adjusting the quantity of injected pollution neutralizing gas at one or more of the plurality of injection locations to cause the determined ratio at each of the plurality of sample locations to be substantially equal to the predetermined ratio; and replacing at least a portion of the catalyst bed when the measured concentration of the pollution neutralizing gas or the pollutant gas exceeds a predetermined amount.