Method for Carrying Out combined Burning in a Recovering Furnace

Abstract

The invention relates to a burning method carried out in furnace provided with energy recovering means and burners, wherein a part of burners are embodied in the form of aero-combustible burners and the other part thereof are embodied in the form of oxy-combustible burners which are placed under the air ducts of the aero-combustible burners and carry out a staged combustion method.

1 - 13 . (canceled) 
   
   
       14 : A combustion method carried out in a furnace provided with energy recovery means and burners, in which:
 a) the heat of the flue gases is alternately recovered by one part of the energy recovery means and then by the other part of the energy recovery means;   b) at least some of the burners are air-fuel burners consisting of at least one air duct under which or at the center of which at least one injector of a first fuel is placed, said injector being perpendicular to the furnace wall; and   c) two phases are alternately implemented:
 1) a first phase in which only one part of the energy recovery means operates and only the air-burners capable of sending their flames to said operating energy recovery means are in operation; and 
 2) a second phase in which only the other part of the energy recovery means operates and only the air-burners capable of sending their flames to said operating energy recovery means are in operation, 
   wherein at least one oxy-fuel burner is placed under the air duct of at least one air-fuel burner, said oxy-fuel burner comprising fluid injectors perpendicular to the furnace wall and implementing a method of staged combustion of a second fuel and of an oxygen-rich gas, said staged combustion method being carried out in such a way that at least one jet of the second fuel and at least one jet of oxygen-rich gas is injected, the jet of oxygen-rich gas comprising a primary jet of oxygen-rich gas and a secondary jet of oxygen-rich gas,   the primary jet of oxygen-rich gas being injected close to the jet of the second fuel in order to cause a first incomplete combustion, the gases issuing from this first combustion still comprising at least part of the second fuel,   while the secondary jet of oxygen-rich gas is injected at a distance I 2  from the jet of the second fuel which is greater than the distance between the jet of the second fuel and the primary jet of oxygen-rich gas closest to the jet of the second fuel, in order to enter into combustion with the part of the second fuel present in the gases issuing from the first combustion,   the primary jet of oxygen-rich gas being divided into at least two primary jets: at least a first primary jet of oxygen-rich gas which is injected in contact with the jet of the second fuel, and at least a second primary jet of oxygen-rich gas injected at a distance I 1  from the jet of the second fuel, said distance I 2  being greater than the distance I 1 .   
   
   
       15 : The method of  claim 14 , wherein the furnace is a melting furnace in which the energy recovery means are placed on the sides and in that at least one oxy-fuel burner is placed under an air duct located in the furnace melting zone. 
   
   
       16 : The method of  claim 14 , wherein the flow rate of oxygen-rich gas injected by the oxy-fuel burner is between 20 and 100% of the flow rate of oxygen-rich gas and air injected by said burner and the air duct under which it is placed. 
   
   
       17 : The method of  claim 14 , wherein, for each oxy-fuel burner placed under the air duct of an operating air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 70 to 80% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       18 : The method of  claim 14 , wherein, for each oxy-fuel burner placed under the air duct of an operating air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 45 to 55% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       19 : The method of  claim 14 , wherein only the oxy-fuel burners placed opposite the energy recovery means recovering the heat from the flue gases are in operation. 
   
   
       20 : The method of  claim 14 , wherein, for each oxy-fuel burner placed under the air duct of a stopped air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 70 to 80% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       21 : The method of  claim 14 , wherein, for each oxy-fuel burner placed under the air duct of a stopped air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 45 to 55% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       22 : The method of  claim 14 , wherein the combustion carried out by the air-fuel burners is substoichiometric and in that the combustion carried out by the oxy-fuel burners is superstoichiometric. 
   
   
       23 : The method of  claim 15 , wherein the flow rate of oxygen-rich gas injected by the oxy-fuel burner is between 20 and 100% of the flow rate of oxygen-rich gas and air injected by said burner and the air duct under which it is placed. 
   
   
       24 : The method of  claim 15 , wherein, for each oxy-fuel burner placed under the air duct of an operating air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 70 to 80% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       25 : The method of  claim 15 , wherein, for each oxy-fuel burner placed under the air duct of an operating air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 45 to 55% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       26 : The method of  claim 25 , wherein the combustion carried out by the air-fuel burners is substoichiometric and in that the combustion carried out by the oxy-fuel burners is superstoichiometric. 
   
   
       27 : The method of  claim 15 , wherein the combustion carried out by the air-fuel burners is substoichiometric and in that the combustion carried out by the oxy-fuel burners is superstoichiometric. 
   
   
       28 : The method of  claim 27 , wherein the flow rate of oxygen-rich gas injected by the oxy-fuel burner is between 20 and 100% of the flow rate of oxygen-rich gas and air injected by said burner and the air duct under which it is placed. 
   
   
       29 : The method of  claim 27 , wherein, for each oxy-fuel burner placed under the air duct of an operating air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 70 to 80% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       30 : The method of  claim 27 , wherein, for each oxy-fuel burner placed under the air duct of an operating air-fuel burner, the flow rate of oxygen-rich gas in the jet of secondary oxygen-rich gas represents 45 to 55% of the total quantity of oxygen-rich gas injected by said oxy-fuel burner. 
   
   
       31 : A system for carrying out a combustion in a furnace comprising:
 a) at least one air-fuel burner composed of:
 1) an air duct; and 
 2) at least one fuel injector placed under or at the center of the air duct and perpendicular to the furnace wall; and 
   b) at least one oxy-fuel burner placed under the air duct of the air-fuel burner and composed of at least one set of injectors comprising:
 1) at least one fuel injector; 
 2) at least one oxygen-rich gas injector placed so as to inject said oxygen-rich gas in contact with the fuel injected by the injector of the oxy-fuel burner; 
 3) at least one oxygen-rich gas injector placed at a distance I 1  from the fuel injector of the oxy-fuel burner; and 
 4) at least one oxygen-rich gas injector at a distance I 2  from the fuel injector of the oxy-fuel burner, where I 2 >I 1 , 
   said injectors of the oxy-fuel burner being perpendicular to the furnace wall.   
   
   
       32 : The system of  claim 31 , wherein the injector of the first fuel of the air-fuel burner is placed under the air duct and in that said injector and the injectors of the oxy-fuel burner are placed substantially in the same horizontal plane. 
   
   
       33 : The system of  claim 31 , wherein the oxy-fuel burner is composed of two sets of injectors, said sets being arranged symmetrically about the center of the air duct under which the burner is placed. 
   
   
       34 : The system of  claim 33 , wherein at least one fuel injector of the air-fuel burner is placed between the two sets of injectors of the oxy-fuel burner.