Combustion System and Process

Abstract

A method and apparatus for reducing NO x emissions in a coal burning furnace of a power plant without utilizing techniques downstream of the furnace, such as SCR and SNCR, is provided. In a primary combustion zone, a fuel is combusted in the presence of a first oxidant gas comprised substantially of N 2 , to produce a first effluent gas that include one or more NO x species. Downstream a re-burn zone is operated in a sub-stoichiometric manner, combusting a second fuel in presence of the first effluent gas and a second oxidant wherein the second oxidant gas comprises a stream of oxygen. The effluent gas from the re-burn zone is introduced to overfire airflow so as to establish a super-stoichiometric zone prior to discharged from the furnace.

1 . In a combustion furnace comprising a plurality of air fired fossil fuel burners arranged in at least two rows, the improvement comprising replacing the uppermost row of air fired burners with a row of oxy-fired reburn burners. 
     
     
         2 . The combustion furnace of  claim 1 , wherein the burners are located on a single wall of the furnace and a over fire air port is located above the oxy-fired reburn burners. 
     
     
         3 . The combustion furnace of  claim 1 , wherein the burners are located on opposite walls of the furnace and a over fire air port is located above the oxy-fired reburn burners. 
     
     
         4 . The combustion furnace of  claim 1 , wherein the burners are located in a tangential firing pattern and a over fire air port is located above the oxy-fired reburn burners. 
     
     
         5 . A method of reducing the formation of nitrogen oxides emissions from the combustion of a fossil fuel in a nitrogen laden gas comprising
 providing a furnace wherein fossil fuel are combusted,   providing one or more rows of air fired burners,   providing a row of oxy-fired reburn burners downstream of the air fired burners,   providing a row of over fire air ports downstream of the row of oxy-fired reburn burners,   supplying the one or more rows of air fired burners with air and a fossil fuel at a stoichiometry of less than 1.0,   supplying the oxy fired reburn burners with a fossil fuel and a gaseous stream comprising at least 90 percent oxygen in sufficient quantity to produce a reburn stoichiometry between about 0.35 and 0.65, and   supplying the row of overfire air ports with sufficient air to produce a combustion stoichiometry above 1.10 downstream of the overfire air ports.   
     
     
         6 . The method of  claim 5  further comprising the step of operating the furnace as a single wall firing unit, wherein the air fired burners and oxy-fired reburn burners are located on a single wall of the furnace and a over fire air port is located above the oxy-fired reburn burners. 
     
     
         7 . The method of  claim 5  further comprising the step of operating the furnace as a opposed wall firing unit, wherein the air fired burners and oxy-fired reburn burners are located on multiple walls of the furnace and a over fire air port is located above the oxy-fired reburn burners. 
     
     
         8 . The method of  claim 5  further comprising the step of operating the furnace as a tangentially firing unit, wherein the air fired burners and oxy-fired reburn burners are located in a tangential firing pattern and a over fire air port is located above the oxy-fired reburn burners. 
     
     
         9 . In a method of controlling nitrogen oxides emissions resulting from the combustion of a fossil fuel in a utility boiler, the method including the step of staging combustion to prevent the formation of nitrogen oxides precursors by providing at least two rows of air fired burner, each of the burners being supplied with air and a fossil fuel and combusted at a stoichiometry of less than 1.0, and by providing a row of overfire air ports downstream of the last row of the at least two rows of air fired burners, wherein the overfire air ports provide sufficient air to create a combustion stoichiometry of greater than 1.10, the improvement comprising providing a oxy-fired reburn burner downstream of air fired burners and upstream of the over fire air ports, providing the oxy-fired reburn burner with a fossil fuel and a gaseous steam comprising at least 90% oxygen, and operating the oxy-fired reburn burner to produce a combustion stoichiometry of between about 0.35 and 0.85 at the outlet of the oxy fired reburn burner. 
     
     
         10 . The method of  claim 9  wherein the oxy-fired reburn burner is operated to produce a combustion stoichiometry of between about 0.35 and 0.65 at the outlet of the oxy fired reburn burner. 
     
     
         11 . The method of  claim 10  further comprising the step of operating the furnace as a single wall firing unit, wherein the air fired burners and oxy-fired reburn burners are located on a single wall of the furnace. 
     
     
         12 . The method of  claim 10  further comprising the step of operating the furnace as a opposed wall firing unit, wherein the air fired burners and oxy-fired reburn burners are located on multiple walls of the furnace. 
     
     
         13 . The method of  claim 10  further comprising the step of operating the furnace as a tangentially firing unit, wherein the air fired burners and oxy-fired reburn burners are located in a tangential firing pattern.