Low velocity staged combustion for furnace atmosphere control

Abstract

An improved staged combustion method useful with oxy-fuel combustion and in a furnace which contains a charge, wherein substoichiometric combustion and low velocity injection of fuel and primary and secondary oxidant are carried out in an orientation which forms a reducing atmosphere proximate the charge surface.

1 . A method for carrying out combustion comprising:
 (A) injecting into a furnace which contains a charge, at a point above the charge, fuel and primary oxidant in a substoichiometric ratio not exceeding 70 percent of stoichiometric, said primary oxidant being a fluid comprising at least 50 mole percent oxygen, both of said fuel and primary oxidant being injected into the furnace at a velocity of 100 feet per second or less;   (B) combusting fuel and primary oxidant within the furnace to produce heat and combustion reaction products including unburned fuel;   (C) injecting secondary oxidant into the furnace above the injection point of the fuel and primary oxidant, said secondary oxidant being a fluid comprising at least 50 mole percent oxygen, at a velocity of 100 feet per second or less;   (D) establishing a fuel rich gas layer proximate the charge, said fuel rich gas layer being more reducing to the charge than the secondary oxidant; and   (E) combusting secondary oxidant with unburned fuel to provide additional heat and combustion reaction products within the furnace.   
   
   
       2 . The method of  claim 1  wherein the fuel and primary oxidant are injected into the furnace in a substoichiometric ratio within the range of from 5 to 50 percent of stoichiometric. 
   
   
       3 . The method of  claim 1  wherein combustion reaction products are withdrawn from the furnace at a point not below the point where fuel and primary oxidant are injected into the furnace. 
   
   
       4 . The method of  claim 1  wherein the charge comprises oxidizable material. 
   
   
       5 . The method of  claim 1  wherein the charge comprises iron in its fully reduced state. 
   
   
       6 . The method of  claim 5  wherein the charge further comprises coke or charcoal. 
   
   
       7 . The method of  claim 1  wherein the secondary oxidant is provided at a flowrate sufficient to provide oxygen into the furnace so that the stoichiometric ratio of the primary and secondary oxidant to the fuel injected into the furnace is at least 90 percent. 
   
   
       8 . A method for carrying out combustion comprising:
 (A) injecting into a furnace which contains a charge, at a point above the charge, fuel and primary oxidant in a substoichiometric ratio not exceeding 70 percent of stoichiometric, said primary oxidant being a fluid comprising at least 50 mole percent oxygen, both of said fuel and primary oxidant being injected into the furnace at a velocity of 100 feet per second or less;   (B) combusting fuel and primary oxidant within the furnace to produce heat and combustion reaction products including unburned fuel;   (C) injecting secondary oxidant into the furnace below the injection point of the fuel and primary oxidant, said secondary oxidant being a fluid comprising at least 50 mole percent oxygen, at a velocity of 100 feet per second or less;   (D) establishing a oxygen rich gas layer proximate the charge, said oxygen rich gas layer being more oxidizing to the charge than the combustion reaction products within the furnace; and   (E) combusting secondary oxidant with unburned fuel to provide additional heat and combustion reaction products within the furnace.   
   
   
       9 . The method of  claim 8  wherein the fuel and primary oxidant are injected into the furnace in a substoichiometric ratio within the range of from 5 to 50 percent of stoichiometric. 
   
   
       10 . The method of  claim 8  wherein combustion reaction products are withdrawn from the furnace at a point not below the point where fuel and primary oxidant are injected into the furnace. 
   
   
       11 . The method of  claim 8  wherein the charge comprises oxidizable material. 
   
   
       12 . The method of  claim 8  wherein the charge comprises molten glass. 
   
   
       13 . The method of  claim 8  wherein the secondary oxidant is provided at a flowrate sufficient to provide oxygen into the furnace so that the stoichiometric ratio of the primary and secondary oxidant to the fuel injected into the furnace is at least 90 percent.