Injector and method for reducing nox emissions from boilers, ic engines and combustion processes

Abstract

A system and method of reducing NOx emissions from a lean burn combustion source is provided. The system includes at least one injection lance having a elongated shaft with distal and proximal ends, a metering valve positioned at the distal end, an atomization chamber positioned between the metering valve and the distal end, a storage chamber for containing a reagent fluidly connected to the metering valve, an injection tip positioned at the proximal end for delivering the reagent, and at least one air port for supplying air to the atomization chamber. The injection lance is positioned in the combustion source, and the reagent is supplied from the storage chamber to the injection lance at an inlet pressure. The reagent is then injected into the combustion source via the injection lance, wherein a temperature of the reagent prior to the injection is maintained below a hydrolysis temperature of the reagent.

What is claimed is: 
     
         1 . A method of reducing NOx emissions from a fire tube boiler, comprising the steps of:
 positioning at least one injector between an outlet of a second pass and an entrance to a third pass of said fire tube boiler;   providing a reagent from a storage chamber to the at least one injector;   injecting the reagent into a combustion gas via the at least one injector; and   recirculating at least a portion of the reagent from the at least one injector to the storage chamber.   
     
     
         2 . The method of  claim 1  wherein said at least one injector comprises at least one injection lance having a distal end a proximal end, the proximal end positioned in the fire tube boiler, the at least one injection lance comprising an elongated shaft, a metering valve secured to the distal end, an atomization chamber positioned between the metering valve and the elongated shaft, and an injector tip removably secured to the proximal end. 
     
     
         3 . The method of  claim 2 , wherein the valve is a pulse width modulated solenoid valve. 
     
     
         4 . The method of  claim 2  wherein the reagent is provided to the at least one injector at a reagent inlet pressure and further comprising the step of providing air to the atomization chamber of the at least one injection lance at an air inlet pressure. 
     
     
         5 . The method of  claim 4 , wherein the reagent inlet pressure is between about 40 psi and about 120 psi. 
     
     
         6 . The method of  claim 4 , wherein air is provided at a flow rate between about 2 standard cubic feet per minute and about 20 standard cubic feet per minute. 
     
     
         7 . The method of  claim 4 , wherein air is provided to the at least one injection lance at an air pressure between about 5 psi and about 40 psi. 
     
     
         8 . The method of  claim 4 , further comprising the step of adjusting the air inlet pressure until the reagent is injected with droplet sizes between about 10 microns and about 50 microns. 
     
     
         9 . The method of  claim 1  wherein a temperature of the reagent prior to the injection is maintained below a hydrolysis temperature of the reagent and the reagent decomposes in the fire tube boiler to reduce NOx across a catalyst. 
     
     
         10 . The method of  claim 1 , wherein the reagent comprises a urea solution. 
     
     
         11 . The method of  claim 10 , wherein the urea solution comprises a solution of about 25% to about 50% of urea in water. 
     
     
         12 . The method of  claim 11 , wherein the urea solution comprises a solution of about 32.5% of urea in water. 
     
     
         13 . The method of  claim 1 , wherein the reagent is injected at a rate between about 0.04 gallon per hour and about 10 gallons per hour. 
     
     
         14 . The method of  claim 1 , wherein a combustion gas temperature at the injection point is between about 400 F and about 1100 F. 
     
     
         15 . The method of  claim 14 , wherein a combustion gas temperature at the injection point is between about 400 F and about 750 F 
     
     
         16 . The method of  claim 1 , wherein a quantity of the injected reagent is controlled via a metering valve in response to at least one of a combustor load, a fuel flow, a temperature and a NOx signal. 
     
     
         17 . The method of  claim 1 , further comprising the step of actuating the at least one injector on and off at a predetermined frequency. 
     
     
         18 . The method of  claim 17 , further comprising the step of modulating a pulse width of the injector to control injection rate of the reagent. 
     
     
         19 . A method of reducing NOx emissions from a fire tube boiler, comprising the steps of:
 positioning at least one injector in a cavity formed between an outlet of a second pass and an entrance to a third pass of said fire tube boiler;   providing a reagent from a storage chamber to the at least one injector; and   injecting the reagent into a combustion gas via the at least one injector.   
     
     
         20 . The method of  claim 19 , further comprising the step of recirculating at least a portion of the reagent from the at least one injector to the storage chamber or to an inlet of a recirculation pump. 
     
     
         21 . The method of  claim 19 , wherein the reagent comprises an aqueous solution of urea. 
     
     
         22 . The method of  claim 19 , wherein the reagent comprises an aqueous solution of ammonia. 
     
     
         23 . The method of  claim 19 , wherein the reagent comprises ammonia in gaseous form.