Fuel-Fired Furnace and Method for Controlling Combustion in a Fuel-Fired Furnace

Abstract

Fuel-fired furnace and a method for operating it, in which method: a main oxidizing agent is injected at a controlled flow rate into the combustion chamber of the furnace; the combustible material is burnt in the combustion chamber with the main oxidizing agent, producing thermal energy and flue gases at a temperature higher than 600° C.; the flue gases are removed via an exhaust duct, said removed flue gases possibly containing residual materials that could be oxidized, the exhaust duct being equipped with an inlet for a diluting oxidizing agent downstream of the combustion chamber; the residual materials that could be oxidized are burnt with the diluting oxidizing agent by means of a flame at the inlet for the diluting oxidizing agent; the flame intensity inside the exhaust duct is detected; and the flow rate at which the main oxidizing agent is injected into the combustion chamber is controlled according to the detected flame intensity.

1 - 15 . (canceled) 
     
     
         16 . A process for operation of a fuel-fired furnace comprising a combustion chamber, comprising the steps of:
 injecting a main oxidizing agent at a regulated flow rate into the combustion chamber;   burning a combustible material in the combustion chamber together with the main oxidizing agent, thus producing in the combustion chamber thermal energy and fumes at a temperature higher than 600° C.;   discharging the fumes from the combustion chamber by a discharge duct, said fumes discharged being able to contain residual materials which can be oxidized, the discharge duct being provided with an inlet for a dilution oxidizing agent downstream from the combustion chamber;   burning the residual materials together with the dilution oxidizing agent with a flame inside the discharge duct at the level of the inlet for the dilution oxidizing agent; wherein the flame intensity of said flame inside the discharge duct is detected and the injection flow rate of the main oxidizing agent into the combustion chamber is regulated according to the detected flame intensity.   
     
     
         17 . The process of  claim 16 , wherein:
 the injection flow rate of the main oxidizing agent into the combustion chamber is reduced when the detected flame intensity is lower than a predetermined lower limit; and   the injection flow rate of the main oxidizing agent into the combustion chamber is increased when the flame intensity thus detected is higher than a predetermined upper limit.   
     
     
         18 . The process of  claim 16 , wherein:
 the injection flow rate of the main oxidizing agent into the combustion chamber is reduced when the detected flame intensity is lower than the lower limit during a predetermined duration Δt 1  or when the mean value of the detected flame intensity during the predetermined duration Δt 1  is lower than the lower limit; and   the injection flow rate of the main oxidizing agent into the combustion chamber is increased when the detected flame intensity is higher than the upper limit during a predetermined duration Δt 2  or when the mean value of the detected flame intensity during the predetermined duration Δt 2  is higher than the upper limit.   
     
     
         19 . A process for operation of a fuel-fired furnace comprising a combustion chamber, comprising the steps of:
 injecting a main oxidizing agent and combustible material at regulated flow rates into the combustion chamber;   burning the combustible material in the combustion chamber together with the main oxidizing agent, thus producing in the combustion chamber thermal energy and fumes at a temperature higher than 600° C.;   discharging the fumes from the combustion chamber by a discharge duct, said fumes discharged being able to contain residual materials which can be oxidized, said discharge duct being provided with an inlet for a dilution oxidizing agent downstream from the combustion chamber;   burning the residual materials together with the dilution oxidizing agent with a flame inside the discharge duct at the level of the inlet for the dilution oxidizing agent, wherein:
 the flame intensity inside the discharge duct is detected; and 
 the injection flow rate of the main oxidizing agent, and optionally the injection flow rate of combustible material, into the combustion chamber, is regulated according to the detected flame intensity. 
   
     
     
         20 . The process of  claim 19 , wherein:
 the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber is reduced when the detected flame intensity is lower than a predetermined lower limit; and   the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber is increased when the detected flame intensity is higher than a predetermined upper limit.   
     
     
         21 . The process of  claim 20 , wherein:
 the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber is reduced when the detected flame intensity is lower than the lower limit during a predetermined duration Δt 1 , or when the mean value of the detected flame intensity during the predetermined duration Δt 1  is lower than the lower limit; and   the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber is increased when the detected flame intensity is higher than the upper limit during a predetermined duration Δt 2 , or when the mean value of the detected flame intensity during the predetermined duration Δt 2  is higher than the upper limit.   
     
     
         22 . The process of  claim 20 , wherein the injection flow rate of combustible material into the combustion chamber is varied according to the thermal energy requirement in the combustion chamber. 
     
     
         23 . The process of  claim 16 , wherein the flame intensity is determined by means of an optical detector selected from the group consisting of ultraviolet detectors, infrared detectors, and visible radiation detectors. 
     
     
         24 . A fuel-fired furnace comprising:
 a combustion chamber;   a burner or lance adapted and configured to inject a main oxidizing agent at a regulated flow rate into the combustion chamber;   a duct for the discharge of fumes from said combustion chamber, said duct comprising an inlet for a dilution oxidizing agent downstream from the combustion chamber; and   a detector to detect a flame intensity at the inlet for the dilution oxidizing agent inside the discharge duct.   
     
     
         25 . The fuel-fired furnace of  claim 24 , also comprising a control unit which is connected (a) to the detector, and (b) to the burner or lance, the control unit being programmed to:
 compare the flame intensity detected by the detector with a predetermined lower limit and a predetermined upper limit;   reduce the injection flow rate of the main oxidizing agent into the combustion chamber by the burner or lance, when the detected flame intensity is lower than the predetermined lower limit; and   increase the injection flow rate of the main oxidizing agent into the combustion chamber by the burner or lance, when the detected flame intensity is higher than a predetermined upper limit.   
     
     
         26 . The fuel-fired furnace of  claim 25 , wherein the control unit is programmed to:
 reduce the injection flow rate of the main oxidizing agent into the combustion chamber when the detected flame intensity is lower than the lower limit for a predetermined duration Δt 1  or when the mean value of the detected flame intensity during the predetermined duration Δt 1  is lower than the lower limit; and   increase the injection flow rate of the main oxidizing agent into the combustion chamber when the detected flame intensity is higher than the upper limit for a predetermined duration Δt 2  or when the mean value of the detected flame intensity during the predetermined duration Δt 2  is higher than the upper limit.   
     
     
         27 . The fuel-fired furnace of  claim 24 , wherein the burner or lance is a burner and the burner is adapted and configured to inject combustible material at a regulated flow rate into the combustion chamber. 
     
     
         28 . The fuel-fired furnace of  claim 27 , also comprising a control unit which is connected to the detector and the burner, the control unit being programmed to:
 compare the flame intensity detected by the detector with a predetermined lower limit and a predetermined upper limit;   reduce the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is lower than a predetermined lower limit; and   increase the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is higher than a predetermined upper limit.   
     
     
         29 . The fuel-fired furnace of  claim 28 , wherein the control unit is programmed to:
 reduce the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is lower than the lower limit during a predetermined duration Δt 1 , or when the mean value of the detected flame intensity is lower than the lower limit during the predetermined duration Δt 1 ; and   increase the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is higher than the upper limit during a predetermined duration Δt 2 , or when the mean value of the detected flame intensity is higher than the upper limit during the predetermined duration Δt 2 .   
     
     
         30 . The fuel-fired furnace of  claim 24 , wherein the flame detector is selected from amongst optical detectors, and preferably from amongst ultraviolet detectors, infrared detectors, and visible radiation detectors. 
     
     
         31 . The fuel-fired furnace of  claim 24 , wherein:
 the burner or lance is a lance; and   the furnace further comprises a lance adapted and configured to inject combustible material at a regulated flow rate into the combustion chamber.   
     
     
         32 . The fuel-fired furnace of  claim 31 , also comprising a control unit which is connected (a) to the detector, (b) to the lance for injection of the main oxidizing agent, and (c) to the lance for injection of combustible material, the control unit being programmed to:
 compare the flame intensity detected by the detector with a predetermined lower limit and a predetermined upper limit;   reduce the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is lower than a predetermined lower limit; and   increase the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is higher than a predetermined upper limit.   
     
     
         33 . The fuel-fired furnace of  claim 32 , wherein the control unit is programmed to:
 reduce the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is lower than the lower limit during a predetermined duration Δt 1 , or when the mean value of the detected flame intensity is lower than the lower limit during the predetermined duration Δt 1 ; and   increase the ratio between the injection flow rate of the main oxidizing agent and the injection flow rate of combustible material into the combustion chamber when the detected flame intensity is higher than the upper limit during a predetermined duration Δt 2 , or when the mean value of the detected flame intensity is higher than the upper limit during the predetermined duration Δt 2 .