Low NOx combustion

Abstract

A furnace has a process chamber and a burner that is operative to fire a flame into the process chamber with the influence of a flame stabilizer. A bypass apparatus is configured to inject an unignited stream of premix into the process chamber without the influence of a flame stabilizer.

1 . An apparatus configured for use with a furnace process chamber and a burner that is operative to fire into the process chamber with flame stabilization, said apparatus comprising:
 a premix injection apparatus that is configured to inject unignited premix into the process chamber without flame stabilization.   
     
     
         2 . An apparatus as defined in  claim 1  wherein the premix injection apparatus includes a mixer chamber configured to form premix as fuel and oxidant streams mix together upon flowing into the mixer chamber, and includes a premix injector tube configured to extend from the mixer chamber to the process chamber to transmit the premix to the process chamber. 
     
     
         3 . An apparatus as defined in  claim 1  wherein the premix injection apparatus includes a premix injector tube configured to receive separate fuel and oxidant streams in an inner end of the tube, to form premix as the fuel and oxidant streams mix upon flowing through the tube, and to inject the premix into the process chamber from an open outer end of the tube. 
     
     
         4 . An apparatus as defined in  claim 1  further configured for use with a reactant supply system that controls the transmission of fuel and oxidant to the process chamber, and a temperature sensor in the process chamber, said apparatus further comprising a controller configured a) to operate the reactant supply system in a flame stabilization mode in which the reactant supply system transmits fuel and oxidant to the process chamber through the burner but prevents transmission of unignited premix to the process chamber through the premix injection apparatus, b) to operate the reactant supply system in a non-stabilization mode in which the reactant supply system blocks transmission of fuel and oxidant to the process chamber through the burner but transmits unignited premix to the process chamber through the premix injection apparatus, and c) to respond to the temperature sensor by shifting from the flame stabilization mode to the non-stabilization mode at a time when the temperature of the process chamber is not less than the autoignition temperature of the premix. 
     
     
         5 . An apparatus as defined in  claim 4  wherein the flame stabilization mode is a startup mode. 
     
     
         6 . An apparatus as defined in  claim 1  further configured for use with a reactant supply system that controls the transmission of fuel and oxidant to the process chamber, said apparatus further comprising a controller configured to operate the reactant supply system in a mode in which the reactant supply system transmits fuel and oxidant to the process chamber through the burner and simultaneously transmits unignited premix to the process chamber through the premix injection apparatus. 
     
     
         7 . An apparatus comprising:
 a furnace structure defining a process chamber;   a burner, which includes a flame stabilizer, that is operative to fire a flame into the process chamber; and   a bypass apparatus that is configured to inject unignited premix into the process chamber along a flow path that bypasses the burner and is free of a flame stabilizer.   
     
     
         8 . An apparatus as defined in  claim 7  wherein the bypass apparatus includes a mixer chamber configured to form premix as fuel and oxidant streams mix together upon flowing into the mixer chamber, and includes a premix injector tube extending from the mixer chamber to the process chamber to transmit the premix to the process chamber. 
     
     
         9 . An apparatus as defined in  claim 7  wherein the bypass apparatus includes a premix injector tube configured to receive separate fuel and oxidant streams in an inner end of the tube, to form premix as the fuel and oxidant streams mix upon flowing through the tube, and to inject the premix into the process chamber from an open outer end of the tube. 
     
     
         10 . An apparatus as defined in  claim 7  wherein the burner is a premix burner with a mixer tube and a burner tile that defines a reaction zone between the mixer tube and the process chamber, and the flame stabilizer is configured to obstruct the flow of unignited premix from the mixer tube into the reaction zone. 
     
     
         11 . An apparatus as defined in  claim 7  further comprising a reactant supply system configured to control the transmission of fuel and oxidant to the process chamber, a temperature sensor in the process chamber, and a controller configured a) to operate the reactant supply system in a burner mode in which the reactant supply system transmits fuel and oxidant to the process chamber through the burner but prevents transmission of unignited premix to the process chamber through the bypass apparatus, b) to operate the reactant supply system in a bypass mode in which the reactant supply system blocks transmission of fuel and oxidant to the process chamber through the burner but transmits unignited premix to the process chamber through the bypass apparatus, and c) to respond to the temperature sensor by shifting from the burner mode to the bypass mode at the time when the temperature of the process chamber is not less than the autoignition temperature of the premix. 
     
     
         12 . An apparatus as defined in  claim 11  wherein the burner mode is a startup mode. 
     
     
         13 . An apparatus as defined in  claim 7  further comprising a reactant supply system that controls the transmission of fuel and oxidant to the process chamber, and a controller configured to operate the reactant supply system in a mode in which the reactant supply system transmits fuel and oxidant to the process chamber through the burner and simultaneously transmits unignited premix to the process chamber through the bypass apparatus. 
     
     
         14 . A method of operating a furnace having a process chamber, a burner that is operative to fire into the process chamber with flame stabilization, and a reactant supply system configured to control the transmission of fuel and oxidant to the process chamber, said method comprising:
 forming unignited premix from the fuel and oxidant and injecting the unignited premix into the process chamber to induce autoignition and combustion of the premix in the process chamber without flame stabilization.   
     
     
         15 . A method as defined in  claim 14  wherein the unignited premix is injected into the process chamber in a non-stabilization mode of operation in which fuel and oxidant are not transmitted to the process chamber through the burner, and the non-stabilization mode is preceded by a flame stabilization mode in which fuel and oxidant are transmitted to the process chamber through the burner but the unignited premix is not injected into the process chamber, with the intervening step of shifting from the flame stabilization mode to the non-stabilization mode at a time when the temperature of the process chamber is not less than the auto ignition temperature of the premix. 
     
     
         16 . A method as defined in  claim 15  wherein the flame stabilization mode is a startup mode. 
     
     
         17 . A method as defined in  claim 14  wherein the unignited premix is injected into the process chamber to induce autoignition and combustion of the premix in the process chamber without flame stabilization in an operational mode in which the burner is simultaneously fired into the process chamber with flame stabilization. 
     
     
         18 . A method of operating a furnace having a process chamber, a burner that is operative to fire into the process chamber with the influence of a flame stabilizer, and a reactant supply system configured to control the transmission of fuel and oxidant to the process chamber, said method comprising:
 forming unignited premix from the fuel and oxidant and injecting the unignited premix into the process chamber along a flow path that bypasses the flame stabilizer to induce autoignition and combustion of the premix in the process chamber without flame stabilization.   
     
     
         19 . A method as defined in  claim 18  wherein the premix is injected into the process chamber in a bypass mode of operation in which fuel and oxidant are not transmitted to the process chamber through the burner, and the bypass mode is preceded by a burner mode in which fuel and oxidant are transmitted to the process chamber through the burner but the premix is not injected into the process chamber, with the intervening step of shifting from the burner mode to the bypass mode at a time when the temperature of the process chamber is not less than the autoignition temperature of the premix. 
     
     
         20 . A method as defined in  claim 19  wherein the burner mode is a startup mode. 
     
     
         21 . A method as defined in  claim 18  wherein the unignited premix is injected into the process chamber to induce autoignition and combustion of the premix in the process chamber without flame stabilization in an operational mode in which the burner is simultaneously fired into the process chamber with flame stabilization. 
     
     
         22 . A method of retrofitting a furnace having a process chamber and a burner that is operative to fire into the process chamber with flame stabilization, said method comprising:
 installing a premix injection apparatus that is configured to inject unignited premix into the process chamber without flame stabilization.   
     
     
         23 . A method as defined in  claim 22  wherein the apparatus further includes a reactant supply system configured to control the transmission of fuel and oxidant to the process chamber, and a temperature sensor in the process chamber, and said method further comprises installing a controller configured a) to operate the reactant supply system in a flame stabilization mode in which the reactant supply system transmits fuel and oxidant to the process chamber through the burner but prevents transmission of unignited premix to the process chamber through the premix injection apparatus, b) to operate the reactant supply system in a non-stabilization mode in which the reactant supply system blocks transmission of fuel and oxidant to the process chamber through the burner but transmits unignited premix to the process chamber through the premix injection apparatus, and c) to respond to the temperature sensor by shifting from the flame stabilization mode to the non-stabilization mode at a time when the temperature of the process chamber is not less than the auto-ignition temperature of the premix. 
     
     
         24 . A method as defined in  claim 23  wherein the flame stabilization mode is a startup mode. 
     
     
         25 . A method as defined in  claim 22  wherein the apparatus further includes a reactant supply system configured to control the transmission of fuel and oxidant to the process chamber, and said method further comprises installing a controller that is configured to operate the reactant supply system in a mode in which the reactant supply system transmits fuel and oxidant to the process chamber through the burner and simultaneously transmits unignited premix to the process chamber through the premix injection apparatus.