HYBRID BOOSTED OVERFIRE AIR SYSTEM AND METHODS FOR NOx REDUCTION IN COMBUSTION GASES

Abstract

A boiler incorporates an overfire air injection system for reducing NO x emissions. The boiler comprises a combustion device including a plurality of main burners supplied with fossil fuel and air for burning in a combustion zone, where the burners produce flue gases that flow from the combustion zone into a burnout zone. The boiler further comprises at least one overfire air injector for supplying overfire air to the combustion device and at least one booster overfire air injector for supplying high-pressure air to the combustion device.

1 . A boiler incorporating an overfire air injection system and a booster overfire air injection system for reducing nitrogen oxide (NO x ) emissions, the boiler comprising:
 a combustion device including a plurality of main burners supplied with fossil fuel and air for burning in a combustion zone, producing flue gases that flow from the combustion zone into a burnout zone;   at least one overfire air injector for supplying overfire air to the combustion device; and   at least one booster overfire air injector for supplying high-pressure air to the combustion device, wherein the overfire air from the at least one overfire air injector is at a lower pressure than the high-pressure air from the at least one booster overfire air injector.   
   
   
       2 . A boiler according to  claim 1 , wherein the at least one overfire air injector supplies overfire air to the burnout zone. 
   
   
       3 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector supplies high-pressure air to the burnout zone. 
   
   
       4 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector supplies high-pressure air to the plurality of main burners. 
   
   
       5 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector supplies high-pressure air to the burnout zone and the plurality of main burners. 
   
   
       6 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector supplies boosted overfire air as either one of heated air and ambient air or combinations thereof. 
   
   
       7 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector supplies boosted overfire air as heated air. 
   
   
       8 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector supplies boosted overfire air ambient air. 
   
   
       9 . A boiler according to  claim 1 , wherein the at least one booster overfire air injector and the at least one overfire air achieve air jet penetration and mixing in the combustion system to reduce NO x  emissions. 
   
   
       10 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion, said method comprising the steps of:
 providing a fossil fuel to a combustion device, where the combustion device includes a plurality of main burners supplied with the fossil fuel and air for burning fossil fuel and air in a combustion zone;   producing flue gases that flows from the combustion zone into a burnout zone;   supplying overfire air to the combustion device through at least one overfire air injector at a first pressure; and   supplying booster overfire air injector through at least one booster overfire air injector at a second pressure,   wherein the overfire air from the at least one overfire air injector at a first pressure is at a lower pressure than the second pressure from the at least one booster overfire air injector.   
   
   
       11 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising supplying overfire air to the burnout zone from the at least one overfire air injector. 
   
   
       12 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising supplying second pressure overfire air to the burnout zone from the at least one booster overfire air injector. 
   
   
       13 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising supplying second pressure overfire air to the plurality of main burners from the at least one booster overfire air injector. 
   
   
       14 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising supplying second pressure overfire air to the burnout zone and the plurality of main burners from the at least one booster overfire air injector. 
   
   
       15 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising supplying second pressure overfire air as either one of heated air and ambient air or combinations thereof. 
   
   
       16 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising supplying second pressure overfire air as heated air. 
   
   
       17 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10  further comprising supplying second pressure overfire air as air ambient air. 
   
   
       18 . A method for reducing nitrogen oxide (NO x ) emissions formed during the combustion according to  claim 10 , further comprising achieving air jet penetration in the combustion device and mixing in the combustion device to reduce NO x  emissions.