Method and apparatus to inject reagent in sncr/scr emission system for boiler

A boiler having a system to reduce nitrogen oxides in flue gas, the boiler comprising:

• a combustion chamber;
• a passage for flue gas generated in the combustion chamber;
• a SNCR system including at least one injector injecting a nitrogen oxides reducing reagent into the flue gas, wherein the nozzles are mounted to the passage;
• nozzles mounted to the passage downstream of the SNCR system and upstream of a SCR system, wherein the nozzles are mounted on at least one wall of the passage and are configured to inject a pressurized fluid into the flue gas;
• a source of the pressurized gas which is in fluid communication with the nozzles such that the pressurized fluid flows to the nozzles;
• a source of a NOx reducing reagent;
• a mixing device which mixes the reagent with the pressurized gas such that the pressurized fluid ti flowing to the nozzles includes the reagent, and
• the SCR system includes a support structure for a catalyst, wherein the support structure is in the passage and exposes to the flue gas.

A method to reduce airborne nitrogen oxides (NOx) in combustion gas comprising:

• generating combustion gas and directing the flow of combustion gas through a passage;
• reducing the airborne NOx by injecting via a SNCR system a NOx reducing reagent in the combustion gas flowing through the passage, wherein heat energy in the combustion gas promotes a chemical reaction between the reducing reagent and the NOx;
• injecting into the passage, downstream of the injection of the NOx reducing reagent, a mixture of steam and the NOx reducing reagent through an array of nozzles arranged on at least one side of the passage, wherein the mixture is formed upsteam of the array of nozzles and distributed to the array of nozzles, and
• further reducing the airborne NOx in the combustion gas by using a catalyst to promoting a reaction between combustion gas and the NOx reducing reagent injected with the steam.