Modifying transport air to control nox

Abstract

Using oxygen-lean gas as the transport medium in which pulverized fuel solids are conveyed to the burner of a combustion system permits combustion at levels of combustion rate and NOx production under circumstances under which those levels would not be attainable if the transport medium were air.

1 . A combustion method comprising pulverizing solid carbonaceous fuel containing bound nitrogen, feeding the pulverized fuel to a burner, and combusting the pulverized fuel at said burner under conditions under which said combustion would produce a given amount of NOx if said fuel was mixed with air in said pulverizer and fed mixed with said air to said burner, but
 wherein said fuel is mixed in said pulverizer with a gaseous oxygen-lean stream that has an oxygen content sufficiently less than that of air that combustion of said fuel mixed with said gaseous stream produces less NOx than said given amount, and said fuel mixed with said gaseous stream is fed to said burner and is combusted at said burner.   
     
     
         2 . A method according to  claim 1  wherein the temperature of said gaseous oxygen-lean stream is 100° F. to 1000° F. when it is mixed with said fuel. 
     
     
         3 . A method according to  claim 1  wherein the primary stoichiometric ratio in said mixture of fuel and said gaseous oxygen-lean stream is 0.18 to 0.22. 
     
     
         4 . A method according to  claim 1  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         5 . A method according to  claim 1  wherein said fuel comprises coal. 
     
     
         6 . A method according to  claim 5  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         7 . A combustion method comprising providing a combustion system wherein solid carbonaceous fuel containing bound nitrogen can be pulverized and mixed with air, the mixture of fuel and air can be fed to a burner, and the mixture of fuel and air can be combusted at said burner under conditions under which said combustion produces a given amount of NOx and a given combustion rate,
 pulverizing in said pulverizer solid carbonaceous fuel containing bound nitrogen combustion of which at said burner to attain at least said given combustion rate when said fuel is pulverized, mixed with air, fed to said burner, and combusted at said burner, requires increasing the feed rate to said burner of air or fuel in said mixture thereby producing an amount of NOx higher than said given amount,   mixing said pulverized fuel with, instead of air, a gaseous oxygen-lean stream that has an oxygen content sufficiently less than that of air that combustion at said burner of said fuel mixed with said gaseous stream produces NOx in an amount equal to or less than said given amount, and combusting said fuel mixed with said gaseous stream at said burner.   
     
     
         8 . A method according to  claim 7  wherein the temperature of said gaseous oxygen-lean stream is 100° F. to 1000° F. when it is mixed with said fuel. 
     
     
         9 . A method according to  claim 7  wherein the primary stoichiometric ratio in said mixture of fuel and said gaseous oxygen-lean stream is 0.18 to 0.22. 
     
     
         10 . A method according to  claim 7  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         11 . A method according to  claim 7  wherein said fuel comprises coal. 
     
     
         12 . A method according to  claim 11  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         13 . A combustion method comprising providing a combustion system wherein solid carbonaceous fuel containing bound nitrogen can be pulverized and mixed with air, the mixture of fuel and air can be fed to a burner, and the mixture of fuel and air can be combusted at said burner under conditions under which said combustion produces a given amount of NOx and a given combustion rate, provided that the fuel has a moisture content below a predetermined value,
 pulverizing in said pulverizer solid carbonaceous fuel containing bound nitrogen which has a moisture content sufficiently higher than said predetermined value that attaining at least said given combustion rate when said fuel is pulverized, mixed with air, fed to said burner, and combusted at said burner, requires increasing the feed rate to said burner of the air in said mixture thereby producing an amount of NOx higher than said given amount,   mixing said pulverized fuel with, instead of air, a gaseous oxygen-lean stream that has an oxygen content sufficiently less than that of air that combustion at said burner of said fuel mixed with said gaseous stream produces NOx in an amount equal to or less than said given amount, and combusting said fuel mixed with said gaseous stream at said burner.   
     
     
         14 . A method according to  claim 13  wherein the temperature of said gaseous oxygen-lean stream is 100° F. to 1000° F. when it is mixed with said fuel. 
     
     
         15 . A method according to  claim 13  wherein the primary stoichiometric ratio in said mixture of fuel and said gaseous oxygen-lean stream is 0.18 to 0.22. 
     
     
         16 . A method according to  claim 13  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         17 . A method according to  claim 13  wherein said fuel comprises coal. 
     
     
         18 . A method according to  claim 17  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         19 . A combustion method comprising providing a combustion system wherein solid carbonaceous fuel containing bound nitrogen can be pulverized and mixed with air, the mixture of fuel and air can be fed to a burner, and the mixture of fuel and air can be combusted at said burner under conditions under which said combustion produces a given amount of NOx and a given combustion rate, provided that the fuel has a specific energy content above a predetermined value,
 pulverizing in said pulverizer solid carbonaceous fuel containing bound nitrogen which has a specific energy content sufficiently lower than said predetermined value that attaining at least said given combustion rate when said fuel is pulverized, mixed with air, fed to said burner, and combusted at said burner, requires increasing the feed rate to said burner of the fuel or the air in said mixture, thereby producing an amount of NOx higher than said given amount,   mixing said pulverized fuel with, instead of air, a gaseous oxygen-lean stream that has an oxygen content sufficiently less than that of air that combustion at said burner of said fuel mixed with said gaseous stream produces NOx in an amount equal to or less than said given amount, and combusting said fuel mixed with said gaseous stream at said burner.   
     
     
         20 . A method according to  claim 19  wherein the temperature of said gaseous oxygen-lean stream is 100° F. to 1000° F. when it is mixed with said fuel. 
     
     
         21 . A method according to  claim 19  wherein the primary stoichiometric ratio in said mixture of fuel and said gaseous oxygen-lean stream is 0.18 to 0.22. 
     
     
         22 . A method according to  claim 19  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99. 
     
     
         23 . A method according to  claim 19  wherein said fuel comprises coal. 
     
     
         24 . A method according to  claim 23  wherein said fuel is combusted in a combustion zone having a fuel rich zone, and further comprising injecting into said fuel rich zone one or more streams comprising at least 90 vol. % oxygen in an amount comprising less than 20% of the stoichiometric amount of oxygen required for complete combustion of said fuel, while feeding a stream of air through the burner into the fuel rich zone so that the stoichiometric ratio in the fuel rich zone is 0.1 to 0.99.