JP2004076083A - Heat treatment method in continuous non-oxidative furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method in a continuous non-oxidative furnace, which speedily changes an operating condition of lowering a treatment temperature of an article to be heated. <P>SOLUTION: In the heat treatment method in the continuous non-oxidative furnace for continuously heat-treating the article to be heated in an atmospheric non-oxidative gas generated by incomplete combustion of a fuel, by generating the atmospheric non-oxidative gas in at least one zone among several zones divided in a travelling direction of the article to be heated, in a main body of the furnace 10, and by introducing the atmospheric non-oxidative gas generated in the zone into a second combustion chamber arranged in other zones to burn it and heat each zone, the heat treatment method is characterized by introducing a cooling fluid into radiant tubes 12 and 13 when changing the operation conditions for lowering the treatment temperature of the article to be heated. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is applied to a non-oxidizing furnace of a continuous galvanizing facility or a direct-fired reducing furnace of a continuous annealing facility for continuously treating a heated object in a non-oxidizing atmosphere gas generated by incomplete combustion of a fuel. To a heat treatment method in a continuous non-oxidizing furnace.
[0002]
[Prior art]
In a steel heating furnace, in order to prevent the generation of scale, the fuel is incompletely burned at an air ratio of less than 1.0 to fill the furnace with incomplete combustion gas. Gas) may heat the steel. However, the non-oxidizing atmosphere gas generated as described above contains flammable and toxic gases such as unburned components and carbon monoxide. Because of the danger and the risk of gas poisoning due to the leakage of the gas, a process of burning the non-oxidizing atmosphere gas discharged from the furnace, so-called afterburning (secondary combustion) is performed. I have.
[0003]
FIG. 3 is a diagram showing a configuration of a conventional non-oxidizing furnace. In FIG. 3, reference numeral 70 denotes a furnace main body for heating a steel material X to be heated, 71 denotes a burner provided in the furnace main body, 72 denotes a secondary combustion chamber for performing after-burning, and 73 denotes a burner for the secondary combustion chamber. , 74 are combustion air fans. 80 indicates a flame.
[0004]
The heating of the steel material by the above-described non-oxidizing furnace is performed as follows. By supplying combustion air having an air ratio of less than 1.0 to the burner 71 of the furnace main body together with fuel to burn it, an oxidizing atmosphere gas is generated, and the inside of the furnace is maintained at a predetermined temperature by the oxidizing atmosphere gas. Is heated to a predetermined temperature. The non-oxidizing atmosphere gas discharged from the furnace body 70 is introduced into the secondary combustion chamber 72, where the unburned portion is burned, and then is released. In the secondary combustion chamber 72, since the non-oxidizing atmosphere gas is a gas having a low calorific value and it is difficult to burn this gas alone, a large amount of fuel is supplied to the burner 73 and a low calorific value gas is supplied. The temperature of the secondary combustion chamber is raised to a temperature at which even gas can be oxidized, and combustion is performed.
[0005]
By the way, by combusting after the non-oxidizing atmosphere gas is discharged from the furnace body, the problem that the energy that the fuel supplied to the heating furnace had was discarded without being used for heating the steel material was addressed. Conventionally, studies have been made on burning non-oxidizing atmosphere gas in a furnace body. For example, in Japanese Patent Publication No. 63-60094, an object to be heated is surrounded by a combustion gas burned at an air ratio of less than 1.0, and an unburned portion generated by this combustion is surrounded by the combustion gas. Combustion methods have been proposed. That is, in this method, the object to be heated is surrounded and heated by a non-oxidizing atmosphere gas burned at an air ratio of less than 1.0, and the oxidizing gas is blown outside the non-oxidizing atmosphere region to discharge the non-oxidizing atmosphere gas. Secondary burning.
[0006]
However, in the conventional heating furnace, since a boundary is not provided between the non-oxidizing atmosphere region and the secondary combustion region, when the combustion load changes and the flow rate of the gas in the furnace changes, Alternatively, if the heating furnace itself has a structure that impedes the flow of the combustion gas or oxidizing gas, the gas in the furnace is disturbed, and the gas in the oxidizing atmosphere generated by the secondary combustion contacts the object to be heated, The function of preventing scale generation is impaired.
[0007]
As described above, the above-described conventional heating furnace incorporates a means capable of forming a completely non-oxidizing atmosphere under a specific condition, and this means is applied to a general non-oxidizing furnace, It is difficult to form a completely non-oxidizing atmosphere around the heating object. Therefore, at present, a non-oxidizing furnace whose basic configuration is shown in FIG. 3 is used.
[0008]
[Problems to be solved by the invention]
The heat treatment method using the non-oxidizing furnace having the configuration shown in FIG. 3 has the following problems. Since the non-oxidizing atmosphere gas (incomplete combustion gas) generated in the non-oxidizing furnace is taken out of the furnace and subjected to secondary combustion, the heat energy generated in the secondary combustion becomes sensible heat of the exhaust gas and is radiated to the atmosphere. Energy efficiency is low.
[0009]
Moreover, since the non-oxidizing atmosphere gas discharged from the non-oxidizing furnace is a gas having a low calorific value that cannot be burned alone, the temperature of the secondary combustion chamber is raised to a temperature at which even a gas having a low calorific value can be oxidized due to the combustion. And a large amount of fuel is required separately. For this reason, energy efficiency is further reduced.
[0010]
In addition, the conventional heating furnace has a premix type in which a premixed air in which fuel and combustion air are premixed is blown into a burner, or fuel and combustion air are separately blown into a burner and diffused in the burner and in front of the burner. Although a nozzle mix type for mixing is provided, when these burners are used, soot is easily generated. In particular, in the combustion in a non-oxidizing furnace for incomplete combustion of fuel, the fuel must be burned in a range where the air ratio is very low, so that the combustion becomes unstable and soot is generated. For this reason, the combustion of the soot is performed, so that the energy of the supplied fuel is not effectively used. In addition, there is a problem that the soot generated contaminates the steel material and the inside of the furnace.
[0011]
An object of the present invention is to solve the above-mentioned problems and to provide a heat treatment method in a continuous non-oxidizing furnace capable of promptly changing operating conditions for lowering the processing temperature of an object to be heated.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a method for continuously heating an object to be heated in a non-oxidizing atmosphere gas generated by incompletely burning fuel, A non-oxidizing atmosphere gas is generated in at least one of the zones in which the main body is divided into a plurality of zones in the traveling direction of the object to be heated, and the non-oxidizing atmosphere gas generated in this zone is generated in another zone. In a heat treatment method in a continuous non-oxidizing furnace in which a heating target is continuously heated by introducing the fuel into a secondary combustion chamber provided in the furnace and burning each zone, the processing temperature of the heating target is controlled. The cooling fluid is introduced into the secondary combustion chamber when the operating condition is changed to lower the operating temperature.
[0013]
In the present invention, the secondary combustion of the non-oxidizing atmosphere gas is performed in the furnace. However, since the combustion is performed in the secondary combustion chamber provided in the secondary burning zone, the non-oxidizing atmosphere for heating the object to be heated is used. The secondary combustion gas, which is an oxidizing atmosphere gas, is not mixed with the atmosphere gas, and the atmosphere in the furnace main body is reliably maintained in a non-oxidizing atmosphere. In addition, heat is recirculated from the partition wall of the secondary combustion chamber into the furnace main body by radiant heat and is used as a part of a heating heat source for the object to be heated, so that energy efficiency is improved.
[0014]
In addition, when changing the operating conditions for lowering the processing temperature of the object to be heated, the cooling fluid is introduced into the secondary combustion chamber, so that the temperature of the zone provided with the secondary combustion chamber rapidly drops.
[0015]
According to a second aspect of the present invention, in the first aspect of the present invention, the cooling fluid is one or more kinds selected from air, combustion exhaust gas having exhaust heat recovered, nitrogen gas, and water. It is characterized by having.
[0016]
The type of cooling fluid to be used is selected based on the cooling rate, economy, difficulty in obtaining, and the like.
[0017]
The invention according to claim 3 is a method for continuously heating an object to be heated in a non-oxidizing atmosphere gas generated by incompletely burning a fuel, wherein the inside of the furnace main body is a moving direction of the object to be heated. A non-oxidizing atmosphere gas is generated in at least one of the zones divided into a plurality of zones, and the non-oxidizing atmosphere gas generated in this zone is introduced into a secondary combustion chamber provided in another zone. In the heat treatment method in a continuous non-oxidizing furnace that continuously heats the object to be heated by heating each zone and heating the inside of each zone, when changing the operating conditions to lower the processing temperature of the object to be heated Further, the combustion devices provided in the secondary combustion chambers of some of the zones provided with the secondary combustion chambers are stopped, and only the combustion air is supplied to the stopped combustion devices. I have.
[0018]
In the present invention, the temperature in the furnace is reduced by stopping the combustion devices in some of the zones provided with the secondary combustion chambers, and further, combustion air is supplied to the secondary combustion chambers. Thereby, the temperature in the furnace is reduced more quickly.
[0019]
The invention according to claim 4 is a method for continuously heating an object to be heated in a non-oxidizing atmosphere gas generated by incomplete combustion of a fuel, wherein the inside of the furnace main body has a moving direction of the object to be heated. A non-oxidizing atmosphere gas is generated in at least one of the zones divided into a plurality of zones, and the non-oxidizing atmosphere gas generated in this zone is introduced into a secondary combustion chamber provided in another zone. In the heat treatment method in a continuous non-oxidizing furnace that continuously heats the object to be heated by heating each zone and heating the inside of each zone, when changing the operating conditions to lower the processing temperature of the object to be heated Further, nitrogen gas is introduced into a furnace in a zone provided with a secondary combustion chamber.
[0020]
By cooling with nitrogen gas, the object to be heated can be prevented from being oxidized, and the yield and the quality during the operation of lowering the furnace temperature can be prevented.
[0021]
The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein in the zone for generating a non-oxidizing atmosphere gas, incomplete combustion of the fuel is performed using a tubular flame burner. Features.
[0022]
In the present invention, the tubular flame burner has the same basic configuration as that described in JP-A-11-281015, and refers to a burner as shown in FIG. The burner is configured such that fuel and oxygen-containing gas are swirled and burn in a tubular combustion chamber to form a tubular flame, and the combustion gas is discharged from an end of the combustion chamber. If this burner is used, a stable flame can be formed, and stable combustion can be performed in a combustion region of each flame with a uniform concentration of fuel and oxygen. Therefore, a local low-temperature region is not formed, and soot is not generated.
[0023]
The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein in the secondary combustion chamber, a nozzle for blowing fuel into a tubular combustion chamber having one end opened and an oxygen-containing gas are supplied. A non-oxidizing atmosphere gas is completely burned using a tubular flame burner provided such that a nozzle for blowing or a nozzle for blowing a premixed gas comprising fuel and an oxygen-containing gas is directed substantially tangentially to its inner wall surface. It is characterized by:
[0024]
In the present invention, a tubular flame burner is employed as a combustion device for performing secondary combustion. Since the non-oxidizing atmosphere gas is a gas having an extremely low calorific value, the fuel gas component is very dilute, it cannot be burned by a normal burner alone, but can be burned by a tubular flame burner. Since the tubular flame burner has a good mixability between the fuel and the oxygen-containing gas, has a high oxygen utilization efficiency, and does not need to supply extra oxygen, the combustion temperature can be raised. For this reason, in a steady operation state, it is possible to perform single combustion, and it is not necessary to supply fuel for secondary combustion. This greatly improves energy efficiency.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing an example of an embodiment relating to a configuration of a continuous non-oxidizing furnace for carrying out the present invention. The example shown in FIG. 1 shows a configuration when applied to a continuous non-oxidizing furnace arranged in a continuous annealing line. In FIG. 1, reference numeral 10 denotes a furnace main body for heating a steel strip X which is an object to be heated, the inside of which has a preheating zone A, a heating zone B, a soaking zone C, and a cooling zone in the traveling direction of the steel strip X. Zone D is divided into four zones. In FIG. 1, each zone in the furnace main body is shown by one section, but each zone is not limited to one section.
[0026]
In the heating zone B of the above zones, a tubular flame burner shown in FIG. 2 is provided as a combustion device 11 for incompletely burning fuel to generate a non-oxidizing atmosphere gas. This tubular flame burner will be described later.
[0027]
In the preheating zone A and the soaking zone C, radiant tubes 12 and 13 each having a tubular flame burner are provided as heating means. Numerals 14 and 15 are tubular flame burners provided on the radiant tubes 12 and 13, respectively. The tubular flame burners 14 and 15 are connected to branch pipes 17 and 18 of non-oxidizing atmosphere gas which are connected to an exhaust port 16 of the heating zone B and an exhaust port 39 of the preheating zone A, respectively. The non-oxidizing atmosphere gas discharged from the gas is introduced. For this reason, the radiant tubes 12 and 13 are secondary combustion chambers for a non-oxidizing atmosphere gas.
[0028]
Numerals 40 and 41 are pipes for introducing a cooling fluid into the radiant tubes 12 and 13 when changing operating conditions for lowering the processing temperature of the object to be heated. Reference numerals 42 and 43 denote flow control devices for the cooling fluid. As the cooling fluid, one or more selected from the group consisting of air from which the cooling fluid has sucked the atmosphere, combustion exhaust gas from which the cooling fluid has been recovered by exhaust heat, nitrogen gas, and water are introduced. In the case where water is used as the cooling fluid, it is preferable that the water is sprayed into an air current such as air, combustion exhaust gas, or nitrogen gas, and the gas-liquid mixed fluid is blown into the radiant tubes 12 and 13. This is to prevent oxidation when water is brought into contact with the object to be heated, thereby preventing deterioration in quality and yield.
[0029]
Reference numerals 44 and 45 denote pipes for blowing nitrogen gas into the furnace as needed when it becomes necessary to lower the furnace temperature more quickly.
[0030]
21, 22, and 23 are thermometers for measuring the furnace temperatures in the preheating zone A, the heating zone B, and the soaking zone C, respectively, and 24, 25, and 26 are the outlets of the preheating zone A and the outlet of the heating zone B, respectively. , A thermometer for measuring the temperature of the object to be heated at each outlet of the soaking zone C.
[0031]
Reference numeral 27 denotes a flow rate control device for fuel supplied to the tubular flame burner 11 in the heating zone B, reference numeral 28 denotes a flow rate control device for combustion air supplied to the tubular flame burner 11 in the heating zone B, and reference numeral 29 denotes a tubular flame in the preheating zone A. Reference numeral 30 denotes a combustion air flow control device supplied to the burner 14, and reference numeral 30 denotes a combustion air flow control device supplied to the tubular flame burner 15 in the soaking zone C.
[0032]
A controller 33 adjusts the flow rate of the fuel and the combustion air or the flow rate of the cooling fluid based on the measurement value of the thermometer for measuring the temperature in the furnace or the measurement value of the thermometer for measuring the temperature of the object to be heated. It is.
[0033]
Next, the tubular flame burner provided in the furnace body 10 will be described in detail. FIG. 2 is a diagram showing a basic configuration of a tubular flame burner provided in the continuous non-oxidizing furnace shown in FIG. (A) is a side view with a part cut away, and (b) is a cross-sectional view taken along the line AA in (a). Reference numeral 50 denotes a tubular combustion chamber, one end of which is open and serves as a discharge port for combustion gas. Around the combustion chamber 50, nozzles for separately blowing the fuel and the oxygen-containing gas or nozzles for blowing a premixed gas composed of the fuel gas and the oxygen-containing gas are provided. The nozzle 51 has an injection port opened on the inner surface of the combustion chamber, and is oriented such that the injection direction is substantially tangential to the inner peripheral surface of the combustion chamber. Therefore, a swirling flow is formed in the combustion chamber 50 by blowing the fuel or the oxygen-containing gas. Then, by forming the shape of the tip end portion of the nozzle 51 to be flat and narrowing the opening area, a high-speed swirling flow can be formed in the combustion chamber. 52 indicates a spark plug, and 60 indicates a flame.
[0034]
In the burner configured as described above, when the air-fuel mixture blown from the nozzle 51 and forming a swirling flow is ignited, the gas in the combustion chamber 50 is stratified by the density difference, and the density differs on both sides of the flame. A gas layer is formed. That is, high-temperature combustion gas exists on the axis side where the swirling speed is low, and unburned gas exists on the inner wall side where the swirling speed is high.
[0035]
Further, in the vicinity of the inner wall, the swirling speed is higher than the flame propagation speed, and the flame does not propagate to the vicinity of the inner wall, so that the flame is generated in the combustion chamber 50 in a tubular shape. Further, since unburned gas exists near the inner wall of the combustion chamber, the wall surface of the combustion chamber 50 is not directly heated and is not exposed to a high temperature. The gas in the combustion chamber 50 flows to the downstream side while swirling, during which the gas on the inner wall side burns sequentially, moves to the axial center side, and is discharged from the open end.
[0036]
The tubular flame burner having the above configuration has many advantages. Among them, the advantages relating to the present invention are as follows. Even when the fuel and the oxygen-containing gas are blown at a high speed, a stable flame is always formed because the swirling speed is low in the central portion in the combustion chamber 50. For this reason, in the combustion region of each part of the flame, combustion is performed in which there is no difference between the fuel concentration and the temperature, and there is no local low-temperature region, so that no soot is generated.
[0037]
In addition, since the fuel and the oxygen-containing gas are blown at a high speed to form a swirling flow, the mixing property between the fuel and the oxygen-containing gas is good, the oxygen use efficiency is high, and there is no need to supply extra oxygen. , The combustion temperature can be increased.
[0038]
The heat treatment in the continuous non-oxidizing furnace having the above configuration is performed as follows. Fuel is supplied from a fuel pipe to the tubular flame burner 11 provided in the heating zone B, and from the air pipe, the air ratio is usually set to a predetermined value in the range of 0.45 to 0.98. The combustion air whose flow rate has been adjusted is supplied, and the fuel is burned in the burner 11. Since this combustion is an incomplete combustion performed at an air ratio of less than 1.0, the inside of the furnace main body 10 becomes a non-oxidizing atmosphere.
[0039]
After the non-oxidizing atmosphere gas in the heating zone B is exhausted from the exhaust port 16 and the exhaust port 39 in the preheating zone A, it is introduced from the branch pipes 17 and 18 into the tubular flame burners 14 and 15 provided in the radiant tube, and is preheated. The combustion air is supplied and burns. By this combustion, radiant heat is radiated from the partition walls of the radiant tubes 12 and 13, and the preheating zone A and the soaking zone C are heated. At this time, since the combustion of the non-oxidizing atmosphere gas is performed in the radiant tubes 12 and 13, in the preheating zone A and the soaking zone C, the secondary combustion gas which is the oxidizing atmosphere gas is mixed with the non-oxidizing atmosphere gas. This does not occur, and the atmosphere in each zone is reliably maintained in a non-oxidizing atmosphere.
[0040]
In the controller 33, thermometers 21, 22, and 23 for measuring the furnace temperature in the heating zone A, the heating zone B, and the soaking zone C, or the outlet of the preheating zone A, the outlet of the heating zone B, and the soaking Based on the measured values of the thermometers 24, 25 and 26 for measuring the temperature of the object to be heated at the outlet of the zone C, the flow rates of the fuel and the combustion air supplied to the tubular flame burner 11 and the tubular flame burners 14 and 15 are determined. An instruction signal to be changed is transmitted, whereby the combustion amount of each burner is adjusted.
[0041]
As described above, the preheating zone A, the heating zone B, and the soaking zone C are heated so that the object to be heated has a predetermined temperature.
[0042]
Next, a method for changing the operating conditions for lowering the processing temperature of the object to be heated will be described. To lower the processing temperature of the object to be heated, one of the following methods is performed.
[0043]
{Circle around (1)} The valves of the cooling fluid flow controllers 42 and 43 are opened, and the introduction of the cooling fluid into the radiant tubes 12 and 13 in the preheating zone A and the soaking zone C is started. Lower. The introduction of the cooling fluid is continued until the furnace temperature in the preheating zone A and the soaking zone C reaches a predetermined temperature, and the introduction flow rate is adjusted based on the measurement values of the thermometers 21 and 23 for measuring the furnace temperature. Do. Alternatively, the process is continued until the temperature of the object to be heated reaches a predetermined temperature, and the introduction flow rate is adjusted based on the thermometers 24 and 26 for measuring the temperature of the object to be heated.
[0044]
(2) One of the tubular flame burners 14 and 15 provided in the radiant tubes in the preheating zone A and the soaking zone C is stopped. However, the supply of combustion air continues. Accordingly, in the zone where the combustion device is stopped, the temperature is reduced by stopping the supply of heat, and the radiant tube of the zone where the combustion device is stopped is supplied with low-temperature combustion air. Therefore, the radiant tube has a cooling function, and the temperature in the furnace is rapidly reduced.
[0045]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention mentioned above, energy efficiency is high and incomplete combustion of the fuel in a furnace main body can be continued stably. Further, when the operating conditions for lowering the processing temperature of the object to be heated are changed, the furnace temperature can be rapidly lowered.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an embodiment relating to a configuration of a continuous non-oxidizing furnace for carrying out the present invention.
FIG. 2 is a diagram showing a basic configuration of a tubular flame burner provided in the continuous non-oxidizing furnace shown in FIG.
FIG. 3 is a diagram showing a configuration of a conventional non-oxidizing furnace.
[Explanation of symbols]
Reference Signs List 10 Furnace main body 11 Tubular flame burners 12, 13 provided in furnace main body Radiant tubes 14, 15 Tubular flame burners 16, 39 provided in radiant tubes Exhaust ports 17, 18 Branch pipes 19, 20 for non-oxidizing atmosphere gas Fuel pipes Branch pipes 21, 22, 23 Thermometers 24, 25, 26 for measuring the temperature inside the furnace Thermometers 27, 31, 32 for measuring the temperature of the object to be heated Fuel flow control devices 28, 29, 30 Flow control device 33 Controllers 40, 41 Piping 42, 43 for introducing cooling fluid Flow control device 44, 45 for cooling fluid Nitrogen gas pipe 50 Combustion chamber 51 for tubular flame burner Blow-off nozzle 60 for tubular flame burner Tubular flame burner Flame of

Claims (6)

This is a method of continuously heating the object to be heated in a non-oxidizing atmosphere gas generated by incompletely burning the fuel, and the inside of the furnace main body is divided into a plurality of zones in the traveling direction of the object to be heated. A non-oxidizing atmosphere gas is generated in at least one of the zones, and the non-oxidizing atmosphere gas generated in this zone is introduced into a secondary combustion chamber provided in another zone and burned. In the heat treatment method in a continuous non-oxidizing furnace that continuously heats the object to be heated by heating, when changing the operating conditions to lower the processing temperature of the object to be heated, the cooling operation is performed to the secondary combustion chamber. A heat treatment method in a continuous non-oxidizing furnace, characterized by introducing a fluid. The heating in the continuous non-oxidizing furnace according to claim 1, wherein the cooling fluid is one or two or more kinds selected from air, exhaust heat recovered from exhaust heat, nitrogen gas, and water. Processing method. This is a method of continuously heating the object to be heated in a non-oxidizing atmosphere gas generated by incompletely burning the fuel, and the inside of the furnace main body is divided into a plurality of zones in the traveling direction of the object to be heated. A non-oxidizing atmosphere gas is generated in at least one of the zones, and the non-oxidizing atmosphere gas generated in this zone is introduced into a secondary combustion chamber provided in another zone and burned. In the heat treatment method in the continuous non-oxidizing furnace for continuously heating the object to be heated by heating, a secondary combustion chamber is provided when the operating condition for lowering the processing temperature of the object to be heated is changed. Heat treatment in a continuous non-oxidizing furnace, characterized in that a combustion device provided in a secondary combustion chamber of some of the zones is stopped, and only combustion air is supplied to the stopped combustion device. . This is a method of continuously heating the object to be heated in a non-oxidizing atmosphere gas generated by incompletely burning the fuel, and the inside of the furnace body is divided into a plurality of zones in the traveling direction of the object to be heated. A non-oxidizing atmosphere gas is generated in at least one of the zones, and the non-oxidizing atmosphere gas generated in this zone is introduced into a secondary combustion chamber provided in another zone and burned. In the heat treatment method in the continuous non-oxidizing furnace for continuously heating the object to be heated by heating, a secondary combustion chamber is provided when the operating condition for lowering the processing temperature of the object to be heated is changed. A method for heat treatment in a continuous non-oxidizing furnace, wherein nitrogen gas is introduced into the furnace in the zone where the heat treatment is performed. The heat treatment method in a continuous non-oxidizing furnace according to any one of claims 1 to 4, wherein in the zone where the non-oxidizing atmosphere gas is generated, the fuel is incompletely burned using a tubular flame burner. The heat treatment method in the continuous non-oxidizing furnace according to any one of claims 1 to 5, wherein in the secondary combustion chamber, the non-oxidizing atmosphere gas is completely burned using a tubular flame burner.

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