Tertiary air addition to solid waste-fired furnaces for nox control

Abstract

Through the addition of tertiary air and a reduction of secondary air, NOx emissions from a waste-to-energy (WTE) boiler may be reduced. The tertiary air is added to the WTE at a distance from the secondary air, in a boiler region of relatively lower temperatures. A secondary NOx reduction system, such as a selective non-catalytic reduction (SNCR) system using ammonia or urea, may also be added to the boiler with tertiary air to achieve desirable high levels of NOx reductions. The SNCR additives are introduced to the WTE boiler proximate to the tertiary air.

1 . A waste combustion furnace system for reducing NOx emission, the system comprising:
 a grate supporting a combusting waste bed;   at least one secondary nozzle introducing secondary air downstream from the combusting waste bed; and   at least one tertiary nozzle introducing tertiary air, the tertiary nozzles located at a distance downstream from said secondary nozzles, wherein the flue temperature at the distance is less than 1900° F.   
   
   
       2 . The system of  claim 1 , further comprising a post-combustion NOx control system positioned downstream from said tertiary nozzles. 
   
   
       3 . The system of  claim 2 , wherein the post-combustion NOx control system is a selective non-catalytic reduction (SNCR) system. 
   
   
       4 . The system of  claim 3 , wherein the flue temperature at the distance is between 1600 to 1900° F. 
   
   
       5 . The system of  claim 2 , wherein the tertiary air creates turbulence to improve effectiveness of a reagent introduced by the NOx reduction system. 
   
   
       6 . The system of  claim 1 , further comprising a primary air source introducing primary air upstream from the grate. 
   
   
       7 . The system of  claim 1 , further comprising means for allocating an amount of the secondary air to the secondary nozzles and an amount of the tertiary air to the tertiary nozzles. 
   
   
       8 . The system of  claim 7 , further comprising a primary air source introducing primary air upstream from the grate, wherein the allocation means further allocates an amount of the primary air to the primary air source. 
   
   
       9 . The system of  claim 7 , wherein the allocation means dynamically adjusts the amounts of the secondary air and the tertiary air to minimize NOx emissions. 
   
   
       10 . The system of  claim 9 , wherein the allocation means adjusts the amounts of the secondary air and the tertiary air to minimize Oxygen levels in the system upstream of the tertiary air addition. 
   
   
       11 . The system of  claim 7 , wherein the secondary air enters the system at a much lower velocity and stays close to a system wall to protect the wall from high system temperatures. 
   
   
       12 . A method for reducing NOx emission in a waste combustion system comprising furnace with a primary air source and a secondary air source for introducing, respectively, primary and secondary airs to a furnace, the method comprising the steps of:
 allocating a portion of the primary and secondary airs as tertiary air; and   supplying the tertiary air to the furnace air at a distance downstream from said secondary air, wherein the tertiary air reduces Oxygen levels in the furnace upstream of the tertiary air addition.   
   
   
       13 . The method of  claim 12 , wherein the tertiary air is supplied to a first region of the furnace of relatively low temperature in comparison to a second region supplied with the secondary air. 
   
   
       14 . The method of  claim 13 , wherein temperature at the first region is less than 1900° F. 
   
   
       15 . The method of  claim 12 , further comprising the step of positioning a post-combustion NOx control system downstream from said tertiary air. 
   
   
       16 . The method of  claim 15 , wherein the post-combustion NOx control system is a selective non-catalytic reduction (SNCR) system. 
   
   
       17 . The system of  claim 15 , wherein the tertiary air creates turbulence to improve effectiveness of a reagent introduced by the NOx reduction system. 
   
   
       18 . The method of  claim 12  further comprising the steps of:
 measuring performance of the furnace; and   adjusting allocations of the primary, secondary, and tertiary airs to achieve desired furnace operation.   
   
   
       19 . The method of  claim 18  wherein the step of adjusting the allocation of the primary, secondary, and tertiary airs allows the furnace to achieve stoichiometric conditions upstream of the tertiary air addition. 
   
   
       20 . The method of  claim 18  further comprising the step of adjusting the distance of said tertiary air from said secondary air. 
   
   
       21 . A system for reducing NOx emission in a municipal waste combustion furnace, the system comprising:
 means for supplying primary, secondary, and tertiary airs to the furnace, the tertiary air supplied downstream from said secondary air;   means for measuring the furnace environment;   means for the re-allocating the primary, secondary, and tertiary airs in response to said furnace environment measuring means.