Combustion System Using Recycled Flue Gas to Boost Overfire Air

Abstract

The present application and the resultant patent provide a combustion system. The combustion system may include a combustion chamber for combusting a flow of fuel and a flow of air to a flow of flue gases, an overfire air system in communication with the combustion chamber, and a flue gas return line in communication with the overfire air system such that a recycled flue gas flow mixes with an overtire air flow before entry into the combustion chamber.

1 . A combustion system, comprising:
 a combustion chamber for combusting a flow of fuel and a flow of air to a flow of flue gases;   an overfire air system in communication with the combustion chamber; and   a flue gas return line in communication with the overtire air system such that a recycled flue gas flow mixes with an overfire air flow before entry into the combustion chamber.   
     
     
         2 . The combustion system of  claim 1 , wherein the flow of fuel comprises a supply of coal. 
     
     
         3 . The combustion system of  claim 2 , further comprising a mill in communication with the supply of coal. 
     
     
         4 . The combustion system of  claim 1 , further comprising one or more main burners positioned about the combustion chamber and in communication with the flow of fuel and the flow of air. 
     
     
         5 . The combustion system of  claim 4 , wherein the combustion chamber comprises a combustion zone about the one or more main burners. 
     
     
         6 . The combustion system of  claim 5 , wherein the overtire system is positioned downstream of the combustion zone. 
     
     
         7 . The combustion system of  claim 1 , wherein the overtire system comprises one or more overfire air injectors. 
     
     
         8 . The combustion system of  claim 1 , wherein the flow of air comprises a flow of combustion air and wherein the overtire air flow comprises a portion of the flow of combustion air. 
     
     
         9 . The combustion system of  claim 8 , further comprising one or more flue gas heat exchangers in communication with the flue gas return line and the flow of combustion air. 
     
     
         10 . The combustion system of  claim 1 , wherein the recycled flue gas flow comprises about ten percent (10%) of the flue gas flow. 
     
     
         11 . The combustion system of  claim 1 , wherein the recycled flue gas flow and the overfire air flow comprise an entry speed into the combustion chamber of about sixty (60) meters per second or more. 
     
     
         12 . A method of operating a combustion system, comprising:
 combusting a flow of air and a flow of fuel into a flue gas flow in a combustion zone of a combustion chamber;   diverting a portion of the flow of air as an overtire air flow;   recycling a portion of the flue gas flow;   mixing the overfire air flow and the recycled portion of the flue gas flow; and   injecting the overfire air flow and the recycled portion of the flue gas flow in the combustion chamber downstream of the combustion zone.   
     
     
         13 . The method of  claim 12 , further comprising the step of exchanging heat between the flow of air and the recycled portion of the flue gas flow upstream of the combustion chamber. 
     
     
         14 . The method of  claim 12 , wherein the step of recycling a portion of the flue gas flow comprises recycling about ten percent (10%) of the flue gas flow. 
     
     
         15 . The method of  claim 12 , wherein the step of injecting the overtire air flow and the recycled portion of the flue gas flow comprises injecting the overtire air flow and the recycled portion of the flue gas flow at about sixty (60) meters per second or more. 
     
     
         16 . A combustion system, comprising:
 a combustion chamber for combusting a flow of fuel and a flow of combustion air to a flow of flue gases in a combustion zone;   an overfire air system in communication with the combustion chamber downstream of the combustion zone for diverting a portion of the flow of combustion air as an overfire air flow; and   a flue gas return line in communication with the overtire air system such that a recycled flue gas flow mixes with the overtire air flow before entry into the combustion chamber.   
     
     
         17 . The combustion system of  claim 16 , further comprising one or more main burners positioned about the combustion zone and in communication with the flow of fuel and the flow of combustion air. 
     
     
         18 . The combustion system of  claim 16 , wherein the overtire system comprises one or more overfire air injectors. 
     
     
         19 . The combustion system of  claim 16 , wherein the flow of fuel comprises a supply of coal. 
     
     
         20 . The combustion system of  claim 16 , further comprising one or more flue gas heat exchangers in communication with the flue gas return line and the flow of combustion air.