Urea decomposition and improved SCR NOx reduction on industrial and small utility boilers

An apparatus providing a lean burn combustion source having reduced NOx emissions, said apparatus comprising:

• a furnace in which combustion takes place with a primary exhaust gas stream exiting said furnace;
• an economizer through which the primary exhaust gas stream flows, the economizer positioned downstream of said furnace and upstream of said at least one particulate control device;
• an air heater through which the primary exhaust gas stream flows, the air heater positioned downstream of said furnace and upstream of said at least one particulate control device;
• at least one particulate control device through which the primary exhaust gas stream flows positioned downstream of said furnace;
• a catalyst effective for NOx reduction through which the primary exhaust gas stream flows positioned downstream of said at least one particulate control device;
• a bypass duct providing a first side stream of hot exhaust gas through which a portion of the primary exhaust gas stream flows, said bypass duct comprising an inlet positioned downstream of said furnace and upstream said economizer and said air heater and an outlet positioned downstream of said economizer and said air heater and upstream of said at least one particulate control device, such that said bypass duct bypasses said economizer and said air heater;
• a decomposition duct providing a second side stream of hot exhaust gas through which a portion of the primary exhaust gas stream flows, said decomposition duct comprising:
• an inlet positioned downstream of said at least one particulate control device and upstream of said catalyst;
• a heat exchanger section passing through said bypass duct, whereby heat from the hot exhaust gas flowing through said bypass duct is transferred to the hot exhaust gas flowing through said decomposition duct;
• at least one injector positioned in said decomposition duct downstream of said heat exchanger section with respect to flow of hot exhaust gas through said decomposition duct, said at least one injector injecting aqueous based reagent into the hot exhaust gas flowing through said decomposition duct such that the aqueous based reagent decomposes to ammonia gas;
• a fan positioned in said decomposition duct upstream of said heat exchanger section with respect to the flow of hot exhaust gas through said decomposition duct;
• a supplemental heater positioned in said decomposition duct downstream of said heat exchanger section with respect to the flow of hot exhaust gas through said decomposition duct and upstream of said at least one injector with respect to the flow of hot exhaust gas through said decomposition duct;
• an outlet in fluid communication with a reagent distribution device positioned in the primary exhaust gas stream downstream of said at least one particulate control device and upstream of said catalyst;
• and
• wherein said decomposition duct comprises a continuous duct passing between the inlet of said decomposition duct and the outlet of said decomposition duct;
• and
• wherein the hot exhaust gas flowing through said decomposition duct, carrying the ammonia gas, is injected into the primary exhaust gas stream through the reagent distribution device, whereby a mixture of the hot exhaust gas flowing through said decomposition duct, carrying the ammonia gas, and the primary exhaust gas stream are caused to flow over said catalyst.