Oxygen-enhanced combustion of unburned carbon in ash

Abstract

The unburned carbon content of ash is reduced by entraining a stream of the ash into a stream of oxidant and combusting the unburned carbon with oxygen in the oxidant.

1 . A method for reducing the carbon content of ash that contains unburned carbon, comprising
 entraining particles of ash containing unburned carbon into a flowing stream of gaseous oxidant that contains more than 21 vol. % oxygen to form a flowing mixed stream of said ash mixed with said oxidant and passing the flowing mixed stream through a combustion chamber wherein unburned carbon in the ash in the flowing mixed stream combusts to produce a flowing product stream of ash having a reduced carbon content entrained in a gaseous stream comprising combustion products,   wherein the heat contained in the stream of oxidant into which the particles of ash are entrained is enough to maintain said combustion of unburned carbon in the ash in said combustion chamber but is not so high that the particles of ash begin to melt,   optionally providing additional gaseous oxidant into the combustion chamber which, if provided, contacts unburned carbon in the ash after ignition thereof and combusts with additional unburned carbon in the ash or with combustion products, and   withdrawing said flowing product stream from said combustion chamber, feeding it to apparatus wherein ash having reduced carbon content is separated from said flowing product stream and obtaining from said apparatus ash having a reduced carbon content and a gaseous product stream comprising combustion products.   
     
     
         2 . A method according to  claim 1  wherein said flowing stream of oxidant is produced by mixing fuel and oxygen and combusting a portion of the oxygen in the mixture thus formed 
     
     
         3 . A method according to  claim 1  further comprising heating said flowing stream of gaseous oxidant before entraining said particles of ash into said flowing stream of oxidant. 
     
     
         4 . A method according to  claim 3  wherein said flowing stream of gaseous oxidant is heated before entraining said particles of ash into said flowing stream of oxidant by heat transfer from a heated chamber through which said flowing stream is passed. 
     
     
         5 . A method according to  claim 3  wherein said flowing stream of gaseous oxidant is heated before entraining said particles of ash into said flowing stream of oxidant by indirect heat exchange from a hotter stream. 
     
     
         6 . A method according to  claim 1  wherein said flowing stream of gaseous oxidant into which said particles of ash are entrained contains at least 50 vol. % oxygen. 
     
     
         7 . A method according to  claim 1  wherein additional gaseous oxidant is provided into the combustion chamber and contacts unburned carbon in the ash after ignition thereof and combusts with additional unburned carbon in the ash or with combustion products. 
     
     
         8 . A method for reducing the carbon content of ash that contains unburned carbon, comprising
 entraining particles of ash containing unburned carbon and particles of solid combustible matter having a lower ignition temperature than the ignition temperature of said unburned carbon into a flowing stream of gaseous oxidant that contains more than 21 vol. % oxygen to form a flowing mixed stream of said ash and solid combustible matter mixed with said oxidant and passing the flowing mixed stream through a combustion chamber wherein the solid combustible matter and unburned carbon in the ash in the flowing mixed stream combust to produce a flowing product stream of ash having a reduced carbon content entrained in a gaseous stream comprising combustion products,   wherein the heat contained in the stream of oxidant into which the particles of ash and solid combustible matter are entrained is enough to maintain said combustion of unburned carbon and solid combustible matter in said combustion chamber but is not so high that the particles of ash begin to melt,   optionally providing additional gaseous oxidant into the combustion chamber which, if provided, contacts unburned carbon in the ash after ignition thereof and combusts with additional unburned carbon in the ash, with additional solid combustible matter, or with combustion products, and   withdrawing said flowing product stream from said combustion chamber, feeding it to apparatus wherein ash having reduced carbon content is separated from said flowing product stream and obtaining from said apparatus ash having a reduced carbon content and a gaseous product stream comprising combustion products.   
     
     
         9 . A method according to  claim 8  wherein said flowing stream of oxidant is produced by mixing fuel and oxygen and combusting a portion of the oxygen in the mixture thus formed 
     
     
         10 . A method according to  claim 8  further comprising heating said flowing stream of gaseous oxidant before entraining said particles of ash into said flowing stream of oxidant. 
     
     
         11 . A method according to  claim 10  wherein said flowing stream of gaseous oxidant is heated before entraining said particles of ash into said flowing stream of oxidant by heat transfer from a heated chamber through which said flowing stream is passed. 
     
     
         12 . A method according to  claim 10  wherein said flowing stream of gaseous oxidant is heated before entraining said particles of ash into said flowing stream of oxidant by indirect heat exchange from a hotter stream. 
     
     
         13 . A method according to  claim 8  wherein said flowing stream of gaseous oxidant into which said particles of ash are entrained contains at least 50 vol. % oxygen. 
     
     
         14 . A method according to  claim 8  wherein additional gaseous oxidant is provided into the combustion chamber and contacts unburned carbon in the ash after ignition thereof and combusts with additional unburned carbon in the ash or with combustion products. 
     
     
         15 . A method according to  claim 1  wherein fuel other than unburned carbon in said ash is simultaneously being combusted in said combustion chamber, and unburned carbon in said ash comprises less than 50% of the total mass of combustible matter being combusted. 
     
     
         16 . A method according to  claim 15  wherein said flowing stream of oxidant is produced by mixing fuel and oxygen and combusting a portion of the oxygen in the mixture thus formed 
     
     
         17 . A method according to  claim 15  further comprising heating said flowing stream of gaseous oxidant before entraining said particles of ash into said flowing stream of oxidant. 
     
     
         18 . A method according to  claim 17  wherein said flowing stream of gaseous oxidant is heated before entraining said particles of ash into said flowing stream of oxidant by heat transfer from a heated chamber through which said flowing stream is passed. 
     
     
         19 . A method according to  claim 17  wherein said flowing stream of gaseous oxidant is heated before entraining said particles of ash into said flowing stream of oxidant by indirect heat exchange from a hotter stream. 
     
     
         20 . A method according to  claim 15  wherein said flowing stream of gaseous oxidant into which said particles of ash are entrained contains at least 50 vol. % oxygen. 
     
     
         21 . A method according to  claim 15  wherein additional gaseous oxidant is provided into the combustion chamber and contacts unburned carbon in the ash after ignition thereof and combusts with additional unburned carbon in the ash or with combustion products.