EP1543271A1 - Method and apparatus for heat treatment - Google Patents

Method and apparatus for heat treatment

Info

Publication number
EP1543271A1
EP1543271A1 EP03798637A EP03798637A EP1543271A1 EP 1543271 A1 EP1543271 A1 EP 1543271A1 EP 03798637 A EP03798637 A EP 03798637A EP 03798637 A EP03798637 A EP 03798637A EP 1543271 A1 EP1543271 A1 EP 1543271A1
Authority
EP
European Patent Office
Prior art keywords
oxygen
fuel
gas
nozzle
gas containing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03798637A
Other languages
German (de)
French (fr)
Inventor
Anders Lugnet
Tomas Ekman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linde GmbH
Original Assignee
Linde GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Linde GmbH filed Critical Linde GmbH
Publication of EP1543271A1 publication Critical patent/EP1543271A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C9/00—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber
    • F23C9/006—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber the recirculation taking place in the combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C1/00—Combustion apparatus specially adapted for combustion of two or more kinds of fuel simultaneously or alternately, at least one kind of fuel being either a fluid fuel or a solid fuel suspended in a carrier gas or air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C15/00—Apparatus in which combustion takes place in pulses influenced by acoustic resonance in a gas mass
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/20—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone
    • F23D14/22—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone with separate air and gas feed ducts, e.g. with ducts running parallel or crossing each other
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/32—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid using a mixture of gaseous fuel and pure oxygen or oxygen-enriched air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2202/00—Fluegas recirculation
    • F23C2202/30—Premixing fluegas with combustion air

Definitions

  • the present invention relates generally to a method and an apparatus for heat treatment of materials, preferably metals, and more particularly to heat treatment involving low NOx emissions in open flame and radiant tubes as well as a very high thermal efficiency.
  • NOx nitrous oxides
  • a further problem when using a conventional oxy-fuel burner for heat treatment of metals using radiant tubes is that the high flame temperature of an oxy-fuel burner will damage the tube material, which of course is unacceptable.
  • An object of the present invention is to provide a method and an apparatus for heat treatment of metals wherein the drawbacks of prior art apparatuses are eliminated or at least mitigated.
  • a particular object is to provide a method and an apparatus wherein emission of nitrous oxides (NOx) is kept to a minimum while main- taining a high degree of thermal efficiency and providing technology to use oxy-fuel combustion in radiant tubes .
  • NOx nitrous oxides
  • the method provides for an environ- mentally friendly and at the same time cost effective process.
  • the invention is used in combination with radiant tubes, allowing the invention to be used in protective atmosphere processes.
  • These atmospheres are normally all atmospheres other than the atmosphere resulting form combustion of hydrocarbons .
  • Fig. 1 shows a longitudinal elevation sectional view through an apparatus according to the invention
  • Fig. 2 is a transverse cross sectional view from line II-II of Fig. 1;
  • Fig. 3 is an overall sectional view of a burner and radiant tube arrangement
  • Fig. 4 is a diagram showing typical temperature profiles for different types of combustion
  • Fig. 5 is a diagram showing flame and recirculation temperatures during operation of an apparatus according to the invention.
  • Fig. 6 is a diagram showing resulting equilibrium NO concentrations as well as two measured results .
  • Fig. 1 there is shown a sectional view of a burner arrangement, generally designated 1.
  • the burner arrangement comprises an insert 10 having a generally circular cross-section, see fig. 2.
  • the insert is arranged to be mounted through a hole in a wall 12 of a furnace (not shown), as is conventional. It is also preferred to arrange a heat insulating material 14 on the hot side of the burner mounting plate 12.
  • a fuel supply pipe 16 is centrally provided for supplying fuel, such as natural gas, to a burner reaction zone or flame 26, a portion of which is shown in figure 1.
  • the fuel supply pipe is in one end provided with a connector arranged to be connected to a source of fuel (not shown) and in the other end with a fuel nozzle 16a.
  • Oxygen is supplied through six equidistant pipes 18 placed at a constant distance from the centre axis of the insert 10, see fig. 2.
  • the oxygen supply pipes are in one end provided with a respective connector arranged to be connected to a source of oxygen (not shown) and in the other end with a respective oxygen nozzle 18a having a cross-sectional area of A3.
  • the oxygen nozzles are streamlined, thus minimizing turbulence of the oxygen leaving the nozzle, preferably at supersonic velocities. The effect of this will be explained further below.
  • An annular exhaust opening 20 is provided outside of the oxygen pipes 18. This opening is provided for accommodating recirculation of hot exhausts resulting from the heating process involving the burner.
  • the exhaust opening is separated from the oxygen pipes by a comparatively thin wall, thereby providing for a heat exchange between the hot exhausts from the burner process and the relatively cold oxygen supplied through the oxygen pipes 18.
  • This heat exchange provides for a high thermal efficiency, in all cases above 90%, resulting in a very energy efficient process, with low exhaust gas temperatures .
  • a circular flame tube 22 at the front end portion of the insert, having a cross- sectional area A2 and a diameter L2.
  • the flame tube surrounds the fuel and oxygen nozzles 16a, 18a and extends a distance Ll from the oxygen nozzles.
  • the primary function of the flame tube is to form a mixing compartment for oxygen and recirculated exhaust gas in a first mixing step and to direct the resulting jet momentum forwards.
  • the tube 22 preferably has a cross-sectional area of more than 100 times the cross-sectional area of each of the gas nozzles 18a.
  • equidistant apertures 24 each having an area Al, are provided in the flame tube — each one outside of a respective oxygen nozzle 18a. In that way, an ejector function is obtained whereby hot exhausts from outside of the flame tube 22 is sucked into the same.
  • the implication of that will be explained in the following in connection with the description of the method according to the invention.
  • fuel and oxygen are supplied from a respective source to the respective pipes.
  • the fuel can be any gaseous fuel, such as, natural gas, propane, coke oven gas, etc having a combustible content, or any liquid fuel, such as light to heavy fuel oil, emulsions containing carboneous substances , etc ..
  • oxygen is in this context meant a gas with an 0 2 content exceeding 80% by volume, and preferably exceeding 99.5%, i.e., essentially pure oxygen.
  • the oxidizing gas comprises other elements usually found in air, such as nitrogen and argon. It is preferred that the oxidizing gas comprises less than 5.5% by volume nitrogen and less than 4.5% by volume argon.
  • a pilot burner (not shown) is provided in the insert 20.
  • y is molefraction of Hydrogen (H) in fuel.
  • T rec i ro temperature of exhaust when recirculated
  • a mass flow of fuel
  • b mass flow of oxygen
  • c mass flow of recirculated exhaust.
  • the recirculation factor, c/b is typically above 10.
  • the exhausts created in the process can contain among 15 other things nitrogen, which, together with oxygen, forms unwanted NOx gases, mainly NO, which in nature is transformed into N0 2 .
  • the oxygen is supplied at high velocities, preferably at supersonic velocities, such as Mach 0.5 or above.
  • the oxygen is preferably injected to form a free jet to a distance of at least 15 nozzle diameters.
  • These velocities together with the configuration of the apertures 24 in the flame tube and the shape of the oxygen nozzles 18a and positions thereof relatively to the respective hole, create an ejector effect sucking the flame exhausts into the flame tube, as indicated by arrows in fig. 1.
  • the oxygen nozzles are Laval shaped and aerodynamic .
  • the oxygen containing mixture resulting from the primary recirculation Prior to being ignited, the oxygen containing mixture resulting from the primary recirculation is further mixed with the fuel and more exhaust gas in a second recirculation step. Due to the supersonic speed of the injected oxygen, preferably having a velocity of Mach 0.5 or above, this mixing is also effected at that hing velocity. This mixture is thus ignited and forms an extended reaction zone. It is thus realised, that the combination of among other things the parameters Al , A2 , A3, Ll, and L2 is of vital importance to effect the proper mixing of oxygen and exhausts. In a preferred embodiment, the following combination is provided: A1»A3, A2 ⁇ ⁇ Al (area of all apertures 24), and/or Ll ⁇ L2.
  • the higher oxygen content the higher temperature.
  • the high theoretical flame temperatures obtained with oxy-fuel burners could be disadvantageous in certain heat treatment processes wherein the material to be heated must be brought to very uniform temperatures.
  • the flame temperature is lowered to desired temperatures while the high NOx promoting temperatures are avoided, see Fig. 4.
  • a secondary recirculation of exhausts is also provided just down-stream of the flame tube 22, as indicated by the arrows in fig. 1.
  • This additional dilution of the oxygen content further helps to lower the temperatures of the flame.
  • the visible portion of the reaction zone 26 starts at a distance from the fuel nozzle, allowing for the recirculation of the exhausts prior to ignition.
  • the effect of the recirculation factor, as defined above, and of the temperature of the recirculated exhaust gases on the resulting flame temperature can be seen in Fig. 5.
  • a second preferred embodiment of a burner arrangement according to the invention will now be described with reference to fig. 3, wherein a burner and radiant tube arrangement is shown.
  • a burner insert 10 is provided in an aperture in a furnace wall 12.
  • a radiant tube, generally designated 30, is provided in front of the burner insert 10 and having a diameter exceeding that of the flame tube 22.
  • the use of a radiant tube is known per se and the radiant tube 30 com- prises an outer cylindrical tube 32 having a first open end facing the furnace wall 12 and a second closed end opposite of the first end.
  • an inner tube 34 having a diameter less than the inner diameter of the outer tube 32 so as to create an inner, essentially circular channel 36 and an outer, annular channel 38.
  • the inner tube is kept in position in any suitable way, such as by means of flanges (not shown) extending outwardly there from.
  • the inner tube 34 is positioned with its first end ending a dis- tance L3 from the front end of the flame tube 22 of the burner and with its second end ending spaced apart from the closed end wall of the outer tube 32, thereby providing a recirculation path for exhausts.
  • the reaction takes place in the inner channel 36. Exhausts created in the combustion process are guided through the inner channel, turn at the closed end of the outer cylinder 32, and return in the opposite direction through the outer annular channel 38.
  • the radiant tube forms an essentially closed system.
  • the exhausts returning to the burner 10 are guided either through the openings 24 in the flame tube, forming a primary recirculation path, or through the gap formed between the flame tube 22 and the inner tube 34, forming a secondary recirculation path.
  • the proportion of exhausts of the first and secondary recirculation paths is determined e.g., by the parameters Al, A2, Ll, L2, and L3 as well as by the velocity of the oxygen and the fuel.
  • the burner arrangement according to the invention allows very high degree of recirculation of exhausts. This in turn allows for extremely low NOx emissions; figures showing as low as 0-25 mg/MJ NOx have been obtained during test runs, depending on the N2 content. An oxygen content below 15% in the reaction zone has been found feasible.
  • a very high thermal efficiency is obtained, resulting in a cost-effective process.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Gas Burners (AREA)
  • Pre-Mixing And Non-Premixing Gas Burner (AREA)
  • Combustion Of Fluid Fuel (AREA)

Abstract

A method and an apparatus for heat-treatment of materials, preferably metals, are provided. The method comprises the following steps: providing and maintaining a flame by supplying a burner with fuel and gas containing at least 80 percent by volume oxygen; creating an oxygen-hot exhaust mixture by recirculating exhausts from the flame to the gas containing oxygen by means of an ejector effect; mixing the oxygen-exhaust mixture and the fuel; and providing a secondary recirculation by recirculating exhausts from the flame to the oxygen-exhaust-fuel mixture. The method and apparatus allow for extremely low NOx emissions and high efficiency, resulting in an environmentally friendly and at the same time cost effective process.

Description

METHOD AND APPARATUS FOR HEAT TREATMENT
FIELD OF INVENTION
The present invention relates generally to a method and an apparatus for heat treatment of materials, preferably metals, and more particularly to heat treatment involving low NOx emissions in open flame and radiant tubes as well as a very high thermal efficiency.
BACKGROUND Conventional oxy-fuel technology has successfully been used for many years . It provides great benefits regarding productivity and fuel consumption. Conventional oxy- fuel technology can also be used to achieve considerable reductions in NOx emissions compared to conventional air-fuel burner technology. However, oxy-fuel technology is relatively sensitive to air in-leakage into the combustion zone and requires good pressure control in the furnace. In some processes and furnace types it is very difficult to keep air from leaking into the system
Thus, fuel combustion in a furnace can result in large emissions of nitrous oxides (NOx). NOx (mainly N02) emissions have been found to have negative health effects, promote corrosion, and to be an environmental hazard, contributing among other things to eutrophi- cation.
Large quantities of nitrous oxides are emitted to the ambient air when treating products in a furnace using conventional and even modern air-fuel burner technology. In burner arrangements comprising radiant tubes, NOx contents of 200-250 mg/MJ are not uncommon, being far above the limits set by authorities to reduce the environment damaging emissions.
A further problem when using a conventional oxy-fuel burner for heat treatment of metals using radiant tubes is that the high flame temperature of an oxy-fuel burner will damage the tube material, which of course is unacceptable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and an apparatus for heat treatment of metals wherein the drawbacks of prior art apparatuses are eliminated or at least mitigated. A particular object is to provide a method and an apparatus wherein emission of nitrous oxides (NOx) is kept to a minimum while main- taining a high degree of thermal efficiency and providing technology to use oxy-fuel combustion in radiant tubes .
The invention is based on the realization that an oxy- fuel burner can be used for low NOx, high efficiency heat treatment of metals by providing for a recirculation of hot gas exhausts resulting from an ejector effect provided by the oxygen nozzles of the burner.
According to the invention there is provided a method of heat treatment of materials as defined in claim 1. There is also provided an apparatus for heat treatment of materials as defined in claim 11.
With the inventive method and apparatus the above- mentioned drawbacks of prior art are eliminated or at least mitigated. The method provides for an environ- mentally friendly and at the same time cost effective process.
In a particularly preferred embodiment, the invention is used in combination with radiant tubes, allowing the invention to be used in protective atmosphere processes. These atmospheres are normally all atmospheres other than the atmosphere resulting form combustion of hydrocarbons .
Further preferred features are defined in the dependent claims.
BRIEF DESCRIPTION OF DRAWINGS
The invention is now described, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 shows a longitudinal elevation sectional view through an apparatus according to the invention;
Fig. 2 is a transverse cross sectional view from line II-II of Fig. 1;
Fig. 3 is an overall sectional view of a burner and radiant tube arrangement;
Fig. 4 is a diagram showing typical temperature profiles for different types of combustion;
Fig. 5 is a diagram showing flame and recirculation temperatures during operation of an apparatus according to the invention; and Fig. 6 is a diagram showing resulting equilibrium NO concentrations as well as two measured results .
DETAILED DESCRIPTION OF THE INVENTION
In the following a detailed description of preferred embodiments of the present invention will be given. In Fig. 1 there is shown a sectional view of a burner arrangement, generally designated 1. The burner arrangement comprises an insert 10 having a generally circular cross-section, see fig. 2. The insert is arranged to be mounted through a hole in a wall 12 of a furnace (not shown), as is conventional. It is also preferred to arrange a heat insulating material 14 on the hot side of the burner mounting plate 12.
In the burner body, a fuel supply pipe 16 is centrally provided for supplying fuel, such as natural gas, to a burner reaction zone or flame 26, a portion of which is shown in figure 1. The fuel supply pipe is in one end provided with a connector arranged to be connected to a source of fuel (not shown) and in the other end with a fuel nozzle 16a.
Oxygen is supplied through six equidistant pipes 18 placed at a constant distance from the centre axis of the insert 10, see fig. 2. The oxygen supply pipes are in one end provided with a respective connector arranged to be connected to a source of oxygen (not shown) and in the other end with a respective oxygen nozzle 18a having a cross-sectional area of A3. The oxygen nozzles are streamlined, thus minimizing turbulence of the oxygen leaving the nozzle, preferably at supersonic velocities. The effect of this will be explained further below. An annular exhaust opening 20 is provided outside of the oxygen pipes 18. This opening is provided for accommodating recirculation of hot exhausts resulting from the heating process involving the burner. The exhaust opening is separated from the oxygen pipes by a comparatively thin wall, thereby providing for a heat exchange between the hot exhausts from the burner process and the relatively cold oxygen supplied through the oxygen pipes 18. This heat exchange provides for a high thermal efficiency, in all cases above 90%, resulting in a very energy efficient process, with low exhaust gas temperatures .
Finally, there is provided a circular flame tube 22 at the front end portion of the insert, having a cross- sectional area A2 and a diameter L2. The flame tube surrounds the fuel and oxygen nozzles 16a, 18a and extends a distance Ll from the oxygen nozzles. The primary function of the flame tube is to form a mixing compartment for oxygen and recirculated exhaust gas in a first mixing step and to direct the resulting jet momentum forwards. To this end, the tube 22 preferably has a cross-sectional area of more than 100 times the cross-sectional area of each of the gas nozzles 18a.
Six equidistant apertures 24, each having an area Al, are provided in the flame tube — each one outside of a respective oxygen nozzle 18a. In that way, an ejector function is obtained whereby hot exhausts from outside of the flame tube 22 is sucked into the same. The implication of that will be explained in the following in connection with the description of the method according to the invention. In order to start the burner, fuel and oxygen are supplied from a respective source to the respective pipes. The fuel can be any gaseous fuel, such as, natural gas, propane, coke oven gas, etc having a combustible content, or any liquid fuel, such as light to heavy fuel oil, emulsions containing carboneous substances , etc .. By oxygen is in this context meant a gas with an 02 content exceeding 80% by volume, and preferably exceeding 99.5%, i.e., essentially pure oxygen. Besides oxygen, the oxidizing gas comprises other elements usually found in air, such as nitrogen and argon. It is preferred that the oxidizing gas comprises less than 5.5% by volume nitrogen and less than 4.5% by volume argon. To ignite the flame, a pilot burner (not shown) is provided in the insert 20.
When ignited, the oxygen in the oxygen containing gas and the fuel maintains the reaction zone 26 so as to provide a heating source. The operation of the oxy-fuel burner 20 is controlled by means of the amount of fuel and oxygen supplied at high velocities through the fuel and oxygen pipes, respectively. The oxy-fuel mixture results in the reaction zone 26 having properties, such as length, temperature etc., that are controlled by the supply rate of fuel and oxygen. The higher the oxygen content is in the reaction zone, the higher the flame temperature will be, resulting in a theoretical flame temperature of 1200-2700°C.
In the flame, the oxygen and the fuel react according to the following formula:
xCyH + (x + y/4)02 => xC02 + y/2H20 + Energy (1) wherein x is molefraction of Carbon (C) in fuel, and
y is molefraction of Hydrogen (H) in fuel.
In addition to this the recirculated exhaust gas is influencing the flame temperature as described in the 5 following formula
a*Fuel+b*Oxygen+c*ExhaustTrecirc=>(a+b) *Prod+c*Exhaustτ£lamθ ( 2 )
wherein
T reciro = temperature of exhaust when recirculated,
Tfiamβ = temperature of exhaust after reaktion (l)and(2),
1 ■*■0v Tflame > T^reoαxc'
a = mass flow of fuel, b = mass flow of oxygen, and
c = mass flow of recirculated exhaust.
The recirculation factor, c/b, is typically above 10.
The exhausts created in the process can contain among 15 other things nitrogen, which, together with oxygen, forms unwanted NOx gases, mainly NO, which in nature is transformed into N02.
The formation of thermal NO is described by the Zeldovich mechanism according to the following formula:
20 O + N2 = NO + N k = 6.89E13 * exp(-75100/R/T)
N + 02 = NO + 0 k = 9 . 81E9 * exp ( -6610 /R/T )
N + OH = NO + H k = 4 . 20E13 Resulting equilibrium NO concentrations as a function of P02, PN2 and Temperature can be seen in Fig. 6.
As mentioned above, the oxygen is supplied at high velocities, preferably at supersonic velocities, such as Mach 0.5 or above. The oxygen is preferably injected to form a free jet to a distance of at least 15 nozzle diameters. These velocities, together with the configuration of the apertures 24 in the flame tube and the shape of the oxygen nozzles 18a and positions thereof relatively to the respective hole, create an ejector effect sucking the flame exhausts into the flame tube, as indicated by arrows in fig. 1. In a preferred embodiment, the oxygen nozzles are Laval shaped and aerodynamic .
After having been sucked into the flame tube 22, a minor portion of the recirculated exhausts leaves the burner arrangement through the exhaust pipe 20. In the exhaust pipe, the hot exhausts leave part of their heat energy to the oxygen being supplied to the burner in the oxygen pipes 18 in a heat exchange process. This heat exchange process contributes to the high efficiency of the burner arrangement and process according to the invention.
However, a major part of the exhausts are recirculated to the burner process by mixing thereof with the oxygen leaving the oxygen nozzles 18a, forming the primary recirculation mixture. This primary recirculation mixture preferably has a ratio by volume of oxygen to exhausts of at least six. The mixing of oxygen and exhausts is preferably effected over a distance of at least 20 nozzle diameters by allowing the gas containing oxygen to impinge on the walls of the flame tube 22.
Prior to being ignited, the oxygen containing mixture resulting from the primary recirculation is further mixed with the fuel and more exhaust gas in a second recirculation step. Due to the supersonic speed of the injected oxygen, preferably having a velocity of Mach 0.5 or above, this mixing is also effected at that hing velocity. This mixture is thus ignited and forms an extended reaction zone. It is thus realised, that the combination of among other things the parameters Al , A2 , A3, Ll, and L2 is of vital importance to effect the proper mixing of oxygen and exhausts. In a preferred embodiment, the following combination is provided: A1»A3, A2 < ∑Al (area of all apertures 24), and/or Ll ≥ L2.
As already stated, the higher oxygen content, the higher temperature. The high theoretical flame temperatures obtained with oxy-fuel burners could be disadvantageous in certain heat treatment processes wherein the material to be heated must be brought to very uniform temperatures. By lowering the oxygen content of the oxygen containing gas supplied to the burner, the flame temperature is lowered to desired temperatures while the high NOx promoting temperatures are avoided, see Fig. 4.
As mentioned above, a secondary recirculation of exhausts is also provided just down-stream of the flame tube 22, as indicated by the arrows in fig. 1. This additional dilution of the oxygen content further helps to lower the temperatures of the flame. This gives so- called fla eless combustion, which is accomplished by the high velocity fuel injection in combination with a streamlined fuel nozzle. As can be seen in fig. 1, the visible portion of the reaction zone 26 starts at a distance from the fuel nozzle, allowing for the recirculation of the exhausts prior to ignition. The effect of the recirculation factor, as defined above, and of the temperature of the recirculated exhaust gases on the resulting flame temperature can be seen in Fig. 5.
A second preferred embodiment of a burner arrangement according to the invention will now be described with reference to fig. 3, wherein a burner and radiant tube arrangement is shown. Thus, like in the first embodiment, a burner insert 10 is provided in an aperture in a furnace wall 12.
A radiant tube, generally designated 30, is provided in front of the burner insert 10 and having a diameter exceeding that of the flame tube 22. The use of a radiant tube is known per se and the radiant tube 30 com- prises an outer cylindrical tube 32 having a first open end facing the furnace wall 12 and a second closed end opposite of the first end. In the outer tube 32 there is provided an inner tube 34 having a diameter less than the inner diameter of the outer tube 32 so as to create an inner, essentially circular channel 36 and an outer, annular channel 38. The inner tube is kept in position in any suitable way, such as by means of flanges (not shown) extending outwardly there from. Also, the inner tube 34 is positioned with its first end ending a dis- tance L3 from the front end of the flame tube 22 of the burner and with its second end ending spaced apart from the closed end wall of the outer tube 32, thereby providing a recirculation path for exhausts.
In operation, the reaction takes place in the inner channel 36. Exhausts created in the combustion process are guided through the inner channel, turn at the closed end of the outer cylinder 32, and return in the opposite direction through the outer annular channel 38. Thus, the radiant tube forms an essentially closed system.
The exhausts returning to the burner 10 are guided either through the openings 24 in the flame tube, forming a primary recirculation path, or through the gap formed between the flame tube 22 and the inner tube 34, forming a secondary recirculation path. The proportion of exhausts of the first and secondary recirculation paths is determined e.g., by the parameters Al, A2, Ll, L2, and L3 as well as by the velocity of the oxygen and the fuel.
Several advantages are obtained with the described method. Firstly, the burner arrangement according to the invention allows very high degree of recirculation of exhausts. This in turn allows for extremely low NOx emissions; figures showing as low as 0-25 mg/MJ NOx have been obtained during test runs, depending on the N2 content. An oxygen content below 15% in the reaction zone has been found feasible. Secondly, and particularly in the second embodiment, a very high thermal efficiency is obtained, resulting in a cost-effective process.
Preferred embodiments of a method and an apparatus for heat-treatment of materials according to the invention have been described. A person skilled in the art realizes that these could be varied within the scope of the appended claims . Thus , although a preferred burner configuration having six oxygen nozzles has been shown, this configuration can be varied so that e.g. four nozzles or any other number or oxygen nozzles are provided.

Claims

1. A method of heat-treatment of materials , prefer- ably metals, said method comprising the following steps:
- providing and maintaining a flame by supplying a burner with fuel and gas containing at least 80 percent by volume oxygen, wherein said gas is supplied at supersonic velocities;
- creating an oxygen and hot exhaust mixture by recirculating exhausts from said flame to said gas containing oxygen by means of an ejector effect;
- mixing said oxygen-exhaust mixture and said fuel; and
- providing a secondary recirculation by recirculating exhausts from said flame to said oxygen-exhaust-fuel mixture.
2. The method according to claim 1, wherein the step of providing and maintaining a flame comprises the step of injecting the gas containing oxygen in at least one nozzle to form a free jet to a distance of at least 15 nozzle diameters.
3. The method according to claim 1 or 2, wherein the step of creating an oxygen-exhaust mixture comprises mixing said gas containing oxygen with at least six times the gas volume of hot exhausts.
4. The method according to any of claims 1-3, wherein the step of creating an oxygen-exhaust mixture comprises mixing said gas containing oxygen and said hot exhaust over a distance of at least 20 nozzle diameters by allowing the gas containing oxygen to impinge on walls of a mixing chamber.
5. The method according to any of claims 1-4, wherein the step of mixing said oxygen-exhaust mixture and said fuel comprises mixing at a velocity greater than Mach 0.5.
6. The method according to any of claims 1-5, comprising the additional step of effecting a heat exchange between exhausts leaving the process and the oxygen supplied to the burner.
7. The method according to any of claims 1-6, wherein the gas containing oxygen contains above 99.5% by volume oxygen.
8. The method according to any of claims 1-7, wherein the gas containing oxygen contains less than 4.5% by volume argon.
9. The method according to any of claims 1-8, wherein the gas containing oxygen contains less than 5.5% by volume nitrogen.
10. The method according to any of claims 1-9, wherein the heat treatment includes heat treatment of steel.
11. An apparatus for heat-treatment of materials, preferably metals, comprising:
- at least one fuel nozzle (16a) connectable to a fuel source; at least one gas nozzle (18a) connectable to a source of gas containing at least 80 percent by volume oxygen;
- wherein said at least one fuel nozzle and said at least one gas nozzle are arranged so at so provide a reaction zone (26);
characterized by
- means for supplying gas containing oxygen at supersonic velocities,
- means (24) for supplying hot exhausts from said flame upstream of said at least one gas nozzle to gas leaving said at least one gas nozzle by means of an ejector effect, thereby creating a oxygen-exhaust mixture, wherein said at least one fuel nozzle (16a) is provided downstream of said at least one gas nozzle (18a), and
a flame tube (22) arranged around said gas nozzles, wherein the flame tube is provided with openings (24) arranged outside of a respective of said at least one gas nozzle (18a).
12. The apparatus according to claim 11, comprising means for injecting the gas containing oxygen to form a free jet to a distance of at least 15 nozzle diameters.
13. The apparatus according to claim 11 or 12, comprising means for mixing said gas containing oxygen and said hot exhaust over a distance of at least 20 nozzle diameters by allowing the gas containing oxygen to impinge on walls of a mixing chamber.
14. The apparatus according to any of claims 11-13, comprising means for mixing said oxygen-exhaust mixture and said fuel at a velocity greater than Mach 0.5.
15. The apparatus according to any of claims 11-14, wherein said at least one fuel nozzle (16a) is centrally provided in the apparatus .
16. The apparatus according to any of claims 11-15, wherein said at least one gas nozzle comprises at least two, more preferably four or six equidistant nozzles (18a) provided at a constant distance from a centre axis of the apparatus.
17. The apparatus according to any of claims 11-16, wherein said at least one gas nozzle (18a) is Laval shaped and/or aerodynamic.
18. The apparatus according to any of claims 11-17, wherein said at least one fuel nozzle (16a) is streamlined so as to allow for flameless combustion.
19. The apparatus according to any of claims 11-18, comprising a tube (22) provided in front of the gas and fuel nozzles (16a, 18a), wherein the tube (30) comprises an outer cylindrical tube (32) having a first open end facing the gas and fuel nozzles and a second closed end opposite of the first end, and an inner tube (34) provided in the outer tube (32) and having a diameter less than the inner diameter of the outer tube (32) so as to create an inner, essentially circular channel (36) and an outer, annular channel (38).
20. The apparatus according to claim 19, wherein the inner tube is positioned with its first end ending a distance (L3) from a front end of the flame tube (22) and with its second end ending spaced apart from the closed end wall of the outer tube (32), thereby providing a secondary recirculation path for exhausts.
21. The apparatus according to claim 19 or 20, wherein said tube (22) has a cross-sectional area of more than 100 times the cross-sectional area of said at least one gas nozzle (18a).
EP03798637A 2002-09-25 2003-09-25 Method and apparatus for heat treatment Withdrawn EP1543271A1 (en)

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SE0202836A SE0202836D0 (en) 2002-09-25 2002-09-25 Method and apparatus for heat treatment
SE0202836 2002-09-25
PCT/SE2003/001492 WO2004029511A1 (en) 2002-09-25 2003-09-25 Method and apparatus for heat treatment

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JP (1) JP2006500543A (en)
KR (1) KR20050062556A (en)
AU (1) AU2003263721A1 (en)
BR (1) BR0314741A (en)
CA (1) CA2501062A1 (en)
MX (1) MXPA05003198A (en)
NO (1) NO20051955L (en)
PL (1) PL374499A1 (en)
RU (1) RU2005109915A (en)
SE (1) SE0202836D0 (en)
WO (1) WO2004029511A1 (en)
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Families Citing this family (37)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8794960B2 (en) * 2004-02-25 2014-08-05 John Zink Company, Llc Low NOx burner
DE102005005832B4 (en) * 2005-02-08 2006-11-02 Air Liquide Deutschland Gmbh Recuperative burner and method for heating an industrial furnace using the burner
US7670135B1 (en) * 2005-07-13 2010-03-02 Zeeco, Inc. Burner and method for induction of flue gas
US20070269755A2 (en) * 2006-01-05 2007-11-22 Petro-Chem Development Co., Inc. Systems, apparatus and method for flameless combustion absent catalyst or high temperature oxidants
RU2324745C2 (en) * 2006-02-26 2008-05-20 Игорь Михайлович Дистергефт Method of thermal processing of metal in combustion furnace of either direct or indirect reheating (variants), method of burning of mixture of liquid or gazeous fuel and heated air in combustion furnace of either direct or indirect reheating, heating mechanism (variants) and regenerative capping (variants) to implement these procedures
US8696348B2 (en) * 2006-04-26 2014-04-15 Air Products And Chemicals, Inc. Ultra-low NOx burner assembly
KR101063375B1 (en) 2006-12-22 2011-09-07 주식회사 케너텍 Oxygen Enriched Combustion Burner Using Forced Internal Recirculation
SE532339C2 (en) * 2007-12-10 2009-12-15 Aga Ab Burner method and apparatus
EP2080952A1 (en) * 2008-01-17 2009-07-22 L'AIR LIQUIDE, Société Anonyme pour l'Etude et l'Exploitation des Procédés Georges Claude Burner and method for alternately implementing an oxycombustion and an air combustion
FR2935040B1 (en) * 2008-08-13 2012-10-19 Inst Francais Du Petrole OXY-COMBUSTION CHAMBER
EP2295858A1 (en) * 2009-08-03 2011-03-16 Siemens Aktiengesellschaft Stabilising of the flame of a burner
SE534818C2 (en) * 2010-05-06 2012-01-10 Cortus Ab Method and apparatus for introducing powdered material into a gasification reactor, the apparatus comprising a laval nozzle
US8632621B2 (en) 2010-07-12 2014-01-21 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Method for melting a solid charge
US20120009531A1 (en) 2010-07-12 2012-01-12 L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Distributed combustion process and burner
SE535197C2 (en) * 2010-09-30 2012-05-15 Linde Ag Procedure for combustion in an industrial furnace
DE102010051347A1 (en) 2010-11-13 2012-05-16 Messer Austria Gmbh Apparatus and method for oxidizing fuels
US8915731B2 (en) 2010-12-30 2014-12-23 L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Flameless combustion burner
US20130095437A1 (en) * 2011-04-05 2013-04-18 Air Products And Chemicals, Inc. Oxy-Fuel Furnace and Method of Heating Material in an Oxy-Fuel Furnace
US20120282558A1 (en) * 2011-05-05 2012-11-08 General Electric Company Combustor nozzle and method for supplying fuel to a combustor
US20130122436A1 (en) * 2011-11-11 2013-05-16 General Electric Company Combustor and method for supplying fuel to a combustor
US8920159B2 (en) * 2011-11-23 2014-12-30 Honeywell International Inc. Burner with oxygen and fuel mixing apparatus
FR2986855A1 (en) * 2012-02-10 2013-08-16 Air Liquide Burner for use in vertical wall of boiler, has primary, secondary and fuel injectors mounted in main passage such that primary and secondary noses are drowned in dilution gas flowing in passage during operation of burner fuel noses
CN103277795B (en) * 2013-05-27 2015-05-20 中国科学院广州能源研究所 Gas burner capable of adjusting gas to be self-recycling
US10429072B2 (en) * 2013-09-23 2019-10-01 Bloom Engineering Company Inc. Regenerative burner for non-symmetrical combustion
US9593847B1 (en) 2014-03-05 2017-03-14 Zeeco, Inc. Fuel-flexible burner apparatus and method for fired heaters
RU2689654C2 (en) * 2014-04-10 2019-05-28 Софинтер С.П.А. Burner
US9593848B2 (en) 2014-06-09 2017-03-14 Zeeco, Inc. Non-symmetrical low NOx burner apparatus and method
US10281140B2 (en) 2014-07-15 2019-05-07 Chevron U.S.A. Inc. Low NOx combustion method and apparatus
EP2993397A1 (en) * 2014-09-02 2016-03-09 Linde Aktiengesellschaft Low-NOx-burner
FR3030689B1 (en) * 2014-12-23 2016-12-23 Air Liquide OXY-BURNER FOR COMBUSTIBLE GAS WITH LOW CALORIFIC POWER AND USE THEREOF
JP6399458B2 (en) * 2015-09-14 2018-10-03 大陽日酸株式会社 Oxygen burner and method of operating oxygen burner
JP6756248B2 (en) * 2016-11-25 2020-09-16 日本製鉄株式会社 Heating burner, radiant tube, and method of heating steel
EA032968B1 (en) * 2017-02-17 2019-08-30 Сергей Михайлович Кабишов Method for environment-friendly burning of hydrocarbon fuel
AU2018392602A1 (en) 2017-12-20 2020-07-02 Bd Energy Systems, Llc Micro reformer
EP3604923A1 (en) * 2018-07-31 2020-02-05 Linde Aktiengesellschaft Heat recovery system for an oven with one or several burners
EP3614049A1 (en) * 2018-08-22 2020-02-26 Linde Aktiengesellschaft A method of operating a burner for performing flameless combustion or at least semi flameless combustion and fluid supply system
IT201900003481A1 (en) * 2019-03-11 2020-09-11 Sacmi Forni Spa APPARATUS AND BURNER FOR COOKING CERAMIC PRODUCTS

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS55107811A (en) * 1979-02-14 1980-08-19 Daido Steel Co Ltd Radiant tube heating device
BR8405390A (en) * 1983-10-21 1985-09-03 Air Prod & Chem HEATING APPLIANCE
DE19600380A1 (en) * 1996-01-08 1997-07-10 Koerting Ag Burner for liquid or gas fuel
US6314896B1 (en) * 1999-06-10 2001-11-13 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Method for operating a boiler using oxygen-enriched oxidants
JP4174311B2 (en) * 2002-12-12 2008-10-29 バブコック日立株式会社 Combustion device and wind box
JP2004197970A (en) * 2002-12-16 2004-07-15 Miura Co Ltd Low-nox combustion method, and device thereof

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2004029511A1 *

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WO2004029511A1 (en) 2004-04-08
NO20051955L (en) 2005-06-24
SE0202836D0 (en) 2002-09-25
MXPA05003198A (en) 2005-09-12
US20050239005A1 (en) 2005-10-27
ZA200502379B (en) 2005-11-30
CA2501062A1 (en) 2004-04-08
NO20051955D0 (en) 2005-04-21
AU2003263721A1 (en) 2004-04-19
RU2005109915A (en) 2005-10-10
JP2006500543A (en) 2006-01-05
PL374499A1 (en) 2005-10-31
KR20050062556A (en) 2005-06-23
BR0314741A (en) 2005-07-26

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