Process and Apparatus for Low-NOx Combustion

Abstract

The invention relates to a process and an apparatus for low-NOx combustion with at least one burner ( 5 ) using fuel and oxidizing agent and/or furnace off-gases and/or carbon dioxide and/or steam. The low-NOx combustion according to the invention can be used in conventional melting and holding furnaces, in particular in aluminum holding furnaces or rotary drum furnaces and glass-melting furnaces, with the potential for considerable economies to be made.

1 - 27 . (canceled) 
   
   
       28 . A process for low-NOx combustion in a combustion chamber with at least one burner using fuel and oxidizing agent and furnace off-gas and/or carbon dioxide and/or steam,
 wherein the oxidizing agent and the furnace off-gases and/or the carbon dioxide and/or the steam are fed to the burner as a mixture which is produced by means of an injector,
 wherein the burner is connected by means of a pipeline:
 to the injector and 
 to a heat exchanger for heating oxidizing agent, carbon dioxide or steam, 
 
   wherein the heat exchanger is arranged in a stack which discharges the furnace off-gases from the combustion chamber and wherein the injector is arranged in the line.   
   
   
       29 . The process of  claim 28 , wherein the injector is operated with the oxidizing agent. 
   
   
       30 . The process of  claim 28 , wherein the mixture of oxidizing agent and furnace off-gases and/or carbon dioxide and/or steam which is fed to the burner has an oxygen content of at least 5% by volume of oxygen. 
   
   
       31 . The process of  claim 28 , wherein the mixture of oxidizing agent and furnace off-gases and/or carbon dioxide and/or steam which is fed to the burner at a temperature of from 20° C. to 1600° C. 
   
   
       32 . The process of  claim 28 , wherein the oxidizing agent used is oxygen or an oxygen-containing medium containing at least 10% by volume of oxygen at a pressure of from 0.2 to 40 bar and a temperature of from −20 to 40° C. 
   
   
       33 . The process of  claim 28 , wherein the combustion is carried out at a flame temperature of from 800° C. to 2700° C. 
   
   
       34 . The process of  claim 28 , wherein the burner has a burner mouth and the velocity at which the mixture of oxidizing agent and furnace off-gases and/or carbon dioxide and/or steam emerges at the burner mouth is between 20 and 80 m/s. 
   
   
       35 . The process of  claim 28 , wherein the burner has a burner mouth, and wherein:
 a) the mixture of oxidizing agent and furnace off-gases and/or carbon dioxide and/or steam flows out of the burner mouth at a velocity which is 0.3 to 4 times higher than the velocity at which the fuel flows out of the burner mouth;   b) a total momentum flux, based on the burner power, of from 1.5 to 8 N/MW is established;   c) a ratio of the momentum flux densities of the mixture of oxidizing agent and furnace off-gases and/or carbon dioxide and/or steam to fuel is from 0.8 to 31; and   d) a power density of from 0.2 to 0.5 KW/mm 2  is reached at the outlet of the burner block ( 4 ).   
   
   
       36 . The process of  claim 28 , wherein the burner comprises a fuel tube wherein partial self-carburization of the fuel takes place in the fuel tube through recuperative heat exchange with the mixture of oxidizing agent and furnace off-gases and/or carbon dioxide and/or steam. 
   
   
       37 . The process of  claim 28 , wherein the injector comprises an outflow nozzle wherein the oxidizing agent flows out of the outflow nozzle at a velocity of from 20 to 660 m/s. 
   
   
       38 . An apparatus for carrying out low-NOx combustion with at least one burner, which is arranged in a burner block of a furnace wall surrounding the combustion chamber and which is supplied with oxidizing agent and fuel, as described in one of the preceding claims,
 wherein the burner is connected by means of a line:
 to a heat exchanger for heating oxidizing agent, carbon dioxide or steam and 
 to an injector for producing a mixture of oxidizing agent and furnace off-gas and/or carbon dioxide and/or steam, 
   wherein the heat exchanger is arranged in a stack which discharges the furnace off-gases from the combustion chamber and whereby the injector is arranged in the pipeline.   
   
   
       39 . The apparatus of  claim 38 , wherein the injector has an axially displaceable outflow nozzle. 
   
   
       40 . The apparatus of  claim 38 , wherein the heat exchanger is a recuperator or regenerator. 
   
   
       41 . The apparatus of  claim 38 , wherein the burner has at least one connection for supplying the oxidizing-agent mixture and at least one connection for supplying the fuel. 
   
   
       42 . The apparatus of  claim 41 , wherein the fuel feed and/or oxidizing-agent mixture feed of the burner are arranged substantially coaxially with respect to one another. 
   
   
       43 . The apparatus of  claim 41 , wherein the furnace has an off-gas opening wherein the burner is arranged opposite the off-gas opening. 
   
   
       44 . The apparatus of  claim 38 , wherein the burner is arranged on the off-gas side of the furnace. 
   
   
       45 . The apparatus of  claim 44 , wherein the burner is arranged on the off-gas side of the furnace in the off-gas opening or in the stack. 
   
   
       46 . The apparatus of  claim 38 , wherein the media-carrying lines consist of a heat-resistant and corrosion-resistant NiCr or ODS alloy. 
   
   
       47 . The apparatus of  claim 42 , wherein the media-carrying lines have a thermal insulation on the outer side and/or a thermal protection on the inner side. 
   
   
       48 . The apparatus of  claim 47 , wherein the media-carrying lines have a thermal insulation on the outer side and/or a thermal protection on the inner side consisting of ceramic fibres or ceramic block. 
   
   
       49 . The apparatus of  claim 38 , wherein the burner block which includes the burner preferably has a cylindrical opening. 
   
   
       50 . The apparatus of  claim 38 , wherein the burner is equipped with a UV light receiver for flame monitoring. 
   
   
       51 . The apparatus of  claim 38 , wherein said apparatus is used in a furnace selected from aluminium holding furnaces, rotary drum furnaces or glass-melting furnaces. 
   
   
       52 . The process of  claim 28 , wherein said process is used in a furnace selected from aluminium holding furnaces, rotary drum furnaces or glass-melting furnaces.