Heating furnace and its operating method

Abstract

To provide a method for operating a heating furnace which can elongate the service lives of radiant tubes used in the heating furnace.SOLUTION: Provided is a method for operating a heating furnace 1 which comprises plural sets of radiant tube burners 10 including a radiant tube 11 and a burner part 12 and executes heating by indirect heating from the plural radiant tubes 11 arranged in the furnace 1, in which the inspection of each radiant tube 11 is executed for deformation, and the burner part 12 for heating the inside of a detected radiant tube as the radiant tube 11 which has been detected as the one having deformation by the inspection and the burner part 12 for heating the inside of the adjacent radiant tube as at least one of the radiant tubes 11 adjacent to the detected radiant tube in an arrangement direction are respectively made into an extinguished state where firing is stopped or a low output fired stated where the temperature in the tube(s) is controlled to less than a furnace temperature.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a heating furnace that heats the interior of the furnace with multiple radiant tube burners, and a technique related to the operation of the heating furnace. The present invention is a technique suitable for industrial heating furnaces in which the material to be heated moves through the furnace while being heated, such as a continuous annealing furnace or a heating furnace that continuously heats galvanized steel sheets. [Background technology]

[0002] 2. Description of the Related Art Radiant tube burners equipped with a radiant tube and a burner unit are often adopted as heating devices for use in heating furnaces such as continuous annealing furnaces (see Patent Documents 1 and 2).

[0003] Patent Document 1 describes a W-type radiant tube as an example of a radiant tube of a radiant tube burner. The radiant tube described in Patent Document 1 has a tube structure with four straight tube sections with circular cross sections arranged vertically and three curved tube sections with circular cross sections that connect adjacent straight tube sections. A plurality of radiant tubes with such a tube structure are arranged along the conveying direction of the heated material such as a steel plate traveling in the heating furnace. As a result, the straight tube sections are arranged so that the side surfaces of the heated material face the surface of the heated material. Then, the combustion gas injected from the burner section passes through the inside of the radiant tube and is discharged from the downstream straight tube section as exhaust gas to the outside of the system. When the furnace is indirectly heated with this radiant tube, the temperature of the combustion gas may be extremely high, exceeding 1000°C. Therefore, each tube of the radiant tube undergoes thermal elongation in the tube axis direction.

[0004] In contrast, in Patent Document 1, the radiant tube is supported by a receiving metal fitting installed on the furnace wall and a curved pipe support member installed on the radiant tube side. The sliding part between the receiving metal fitting and the curved pipe support member slides by the amount of thermal elongation described above, so that the radiant tube is not subjected to thermal restraint. Furthermore, in order to reduce the thermal stress and deformation of the first straight pipe section and the first curved pipe section, which are particularly heavily subjected to the action of axial force and bending moment, a support receiving part is provided at the center of the tip of the first curved pipe section. As a result, the length of the first straight pipe section is made shorter than the length of the fourth straight pipe section, so that the support receiving part is located above the third curved pipe section. The structure proposed is one in which the support receiving part is supported by a support part protruding from the top of the third curved pipe section.

[0005] Furthermore, Patent Document 2 describes that the second straight pipe section and the third straight pipe section are connected to prevent the entire pipe from buckling.

[0006] In addition, as described in Patent Document 1, there is a problem in that the straight tube sections sag due to bending loads. That is, the gas temperature inside the radiant tube decreases the further downstream in the gas flow direction, so the straight tube sections do not thermally expand equally. As a result, the thermal expansion absorption function at the sliding section described above does not function properly, and the entire radiant tube is distorted, a bending load is applied, and each straight tube section may sag.

[0007] To address this issue, a radiant tube with an elliptical cross-sectional shape has been proposed (see Patent Document 2). In this document, the elliptical cross-section has a major axis in the vertical direction (the direction in which the material to be heated travels). By using a straight pipe section with an elliptical cross-section, the cross-sectional performance is improved compared to a straight pipe section with a circular cross-section, and sagging of the straight pipe section due to bending load can be reduced.

[0008] Furthermore, in recent years, the demand for high performance and quality for industrial products has increased, and the heating conditions in industrial heating furnaces have become stricter, so the thermal load on radiant tubes is also becoming greater. In addition to the W-shape, radiant tubes also come in U-shape (see Patent Document 3) and P-shape. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2020-101339 A [Patent Document 2] Japanese Patent Application Publication No. 9-303711 [Patent Document 3] Japanese Patent Application Publication No. 5-285533 Summary of the Invention [Problem to be solved by the invention]

[0010] The above-mentioned patent documents propose various methods for preventing deformation of radiant tubes, but even if such methods are implemented, it is not possible to completely prevent deformation of radiant tubes over time.

[0011] Here, the presence or absence of deformation in each radiant tube is checked, for example, when the furnace is stopped for periodic repair. At this time, deformation beyond a certain level (for example, deformation from an initial position equivalent to the straight tube diameter) may be found in the radiant tube, but not enough to warrant replacement this time. In this case, that radiant tube will be subject to replacement at the next repair. For this reason, if deformation is found in a radiant tube that was not subject to replacement at the previous repair because it had only minor deformation at the previous repair, it is often handled as follows. In other words, the radiant tube that was found to be deformed this time will often remain installed in the furnace without being replaced until the furnace is stopped for the next repair.

[0012] Here, the burner part of the radiant tube that was found to have been deformed beyond a certain level during the current inspection and is to be replaced next time will not be operated and will be extinguished to stop combustion.

[0013] The inventors conducted various investigations into the deformation behavior of the radiant tube to be replaced when it was in this extinguished state, and obtained the following findings.

[0014] The total length of the radiant tube is, for example, 3 to 5 m. Therefore, the temperature may be significantly different between the straight tube section connected to the burner section (the first straight tube section in the case of a W-type) and the straight tube section connected to the exhaust section (the fourth straight tube section in the case of a W-type). Here, assume that multiple radiant tubes are arranged side by side in the furnace. In this case, the straight tube section (the most downstream straight tube section) connected to the exhaust section of the radiant tube to be replaced is greatly affected by the radiant heat from the straight tube section connected to the burner section of the adjacent radiant tube. Therefore, it has been found that the radiant tube to be replaced next time may be deformed more than expected even if the burner is turned off. As shown in FIG. 7, a large deformation has been confirmed in the most downstream straight tube section 11D connected to the exhaust section of the radiant tube in an actual heating furnace.

[0015] The present invention has been made in light of the above-mentioned points, and has an object to provide a method of operating a heating furnace that can extend the life of the radiant tubes used in the heating furnace. [Means for solving the problem]

[0016] In order to achieve a further long life for radiant tubes, the inventors developed a high-precision simulator for an industrial heating furnace in which multiple radiant tubes are arranged vertically inside the furnace. The inventors then estimated the surface temperature distribution of the radiant tubes in the industrial heating furnace using the high-precision simulator. From the results, the inventors found that for a radiant tube in which deformation is progressing, the progression of deformation cannot be suppressed by simply stopping the combustion (extinguishing) of the burner part of that radiant tube. This occurs, for example, when the straight tube part on the exhaust side of the radiant tube in which deformation is progressing is adjacent to the straight tube part on the burner side of the adjacent radiant tube. Specifically, this is because the straight tube part connected to the exhaust part of the radiant tube in which deformation is progressing is heated by radiant heat from the adjacent radiant tube, and the temperature does not decrease. This means that high-temperature creep deformation of the tube cannot be suppressed. Therefore, the inventors found that the deformation of the radiant tube in which deformation is progressing can be suppressed by simultaneously extinguishing the radiant tube located next to the radiant tube in which deformation is progressing.

[0017] In order to solve this problem, one aspect of the present invention is a method of operating a heating furnace which has multiple sets of radiant tube burners, each of which has a radiant tube and a burner section that burns inside the tube to heat the inside of the tube, and heats the inside of the furnace with indirect heating from multiple radiant tubes lined up in a predetermined arrangement direction within the furnace, and which inspects the radiant tubes for deformation, and sets a burner section that heats the inside of a detected radiant tube, which is a radiant tube detected to be deformed in the inspection, and a burner section that heats the inside of an adjacent radiant tube, which is at least one of the radiant tubes adjacent to the detected radiant tube in the arrangement direction, to an extinguished state in which combustion is stopped, or a low-output combustion state in which the temperature inside the tube is below the furnace temperature. Effect of the Invention

[0018] According to the aspect of the present invention, the radiant heat from the other radiant tubes adjacent to the radiant tube undergoing deformation is suppressed. As a result, the deformation of the radiant tube undergoing deformation is prevented from being accelerated. As a result, according to the aspect of the present invention, it is possible to provide a heating furnace and an operating method thereof that can further extend the life of the radiant tubes used in the heating furnace. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of a heating furnace according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram for explaining the arrangement of radiant tubes according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a diagram illustrating a radiant tube burner according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a furnace temperature control unit. [Diagram 5] FIG. 2 is a perspective view showing a P-type radiant tube. [Figure 6] FIG. 13 is a schematic diagram showing another example of the arrangement of radiant tubes. [Figure 7] FIG. 13 is a diagram showing an example of a deformation of a radiant tube. [Figure 8] FIG. 13 is a diagram showing the relationship between normalized distance and surface temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, an embodiment of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments. In this embodiment, the radiant tube burner will be described with a W-shaped radiant tube (see FIG. 2) as an example. However, the shape of the radiant tube of the present disclosure is not limited to the W-shaped, and may be a U-shaped (see Patent Document 3) or P-shaped (see FIG. 5) with two straight tube sections, or a single-shaped with one straight tube section.

[0021] In addition, in the present embodiment, a continuous heating annealing furnace for heating a strip-shaped steel sheet will be described as an example, but the present disclosure may also be applied to other industrial heating furnaces.

[0022] (composition) In the heating furnace 1 of this embodiment, as shown in FIG. 1, the steel sheet 2, which is the material to be heated and unwound from the payoff reel, enters the furnace 1, is heated while moving along the pass line in the furnace 1, and is then extracted. Reference numeral 3 denotes a hearth roll that changes the direction of the conveying direction of the steel sheet 2. In this way, the continuous heating furnace 1 of this embodiment conveys the steel sheet 2 to be heated up and down as shown in FIG. 1 by a looper mechanism or the like. When the steel sheet 2 moves upward and downward, it is heated by radiant heat from the radiant tube 11. That is, the heating furnace 1 has multiple sets of radiant tube burners 10 along the conveying direction (pass line) of the steel sheet 2 as shown in FIG. 2. The conveying direction of the steel sheet 2 may be the horizontal direction as shown in FIG. 6. The multiple sets of radiant tube burners 10 may be arranged in the conveying direction of the steel sheet 2. In addition, the heating furnace is often configured to heat both sides of the steel sheet 2 in the plate thickness direction as shown in FIG. 6. In the case of Figure 6, when radiant tube burner 11A is the detection radiant tube, the adjacent radiant tube is radiant tube 11B. Similarly, when radiant tube burner 11C is the detection radiant tube, the adjacent radiant tube is radiant tube 11D.

[0023] As shown in Fig. 3, each radiant tube burner 10 includes a radiant tube 11 and a burner section 12. The burner section 12 is a heating device that heats the inside of the tube by combustion inside the tube.

[0024] As shown in Fig. 3, each radiant tube 11 in this embodiment has four straight pipe sections 11A, 11B, 11C, and 11D. Furthermore, radiant tube 11 has three curved pipe sections 11E, 11F, and 11G that connect adjacent straight pipe sections to form one combustion gas flow path. Also, burner section 12 is connected to one open end of radiant tube 11. In this embodiment, burner section 12 is connected to the most upstream straight pipe section 11A. Here, when distinguishing between the four straight pipe sections 11A, 11B, 11C, and 11D, they will be described as follows: As shown in Fig. 3, from the side closer to the burner section 12, they will be called the first straight pipe section 11A, the second straight pipe section 11B, the third straight pipe section 11C, and the fourth straight pipe section 11D.

[0025] As shown in FIG. 3, the radiant tube 11 is supported by the furnace wall 1A at the left and right ends, ie, the open end of the tube and the curved portions 11F and 11G. For this reason, the radiant tube 11 has multiple straight pipe sections 11A, 11B, 11C, and 11D that each extend laterally and are arranged vertically. During operation, the steel plate 2 to be heated moves along the arrangement direction of the straight pipe sections 11A, 11B, 11C, and 11D.

[0026] (Deformation prevention structure) Among the four straight pipe sections 11A, 11B, 11C, and 11D, the first straight pipe section 11A is subjected to the greatest thermal load due to its own heat, and is prone to deformation due to creep caused by its own weight and thermal effects. Deformation also occurs in the second and third straight pipe sections 11B and 11C, but the deformation associated with the deformation of the first straight pipe section 11A is greater.

[0027] In this embodiment, as shown in FIG. 3, the second straight pipe section 11B and the third straight pipe section 11C are connected vertically by the first reinforcing rib. As a result, the deformation of the first straight pipe section 11A is received by the second and third straight pipe sections 11B and 11C. In addition, a support member 20 is provided on the curved pipe section 11F that connects the second straight pipe section 11B and the third straight pipe section 11C, and the curved pipe section 11G that connects the third straight pipe section 11C and the fourth straight pipe section 11D, and the support member 20 is supported from below by a receiving metal fitting 21 attached to the furnace wall 1A. As a result, the deformation of the straight pipe sections 11A, 11B, 11C, and 11D is suppressed by receiving the bending moment associated with the deformation of the straight pipe sections 11A, 11B, 11C, and 11D.

[0028] Here, the deformation suppression structure for preventing deformation of radiant tube 11 due to the weight of straight tube portions 11A, 11B, 11C, and 11D, thermal effects, and the like is not limited to this, and other known structures may be adopted. This makes it possible to suppress downward deformation of the radiant tubes 11, thereby improving the life of the radiant tubes 11 and the yield of the furnace 1.

[0029] (Tube arrangement) As described above, the radiant tubes 11 of the multiple radiant tube burners 10 are arranged so as to line up along the moving direction of the steel plate 2, which is the material to be heated being transported. Specifically, as shown in Figures 2 and 3, the multiple radiant tubes 11 are arranged so as to line up along the conveying direction of the steel plate 2 traveling in the heating furnace 1, and so as to face the side surfaces of the straight tube sections 11A, 11B, 11C, and 11D to the surface of the steel plate 2. Each radiant tube 11 is heated by the combustion gas injected from burner section 12 passing through the inside of radiant tube 11 and being discharged as exhaust gas to the outside of the system from downstream straight tube section 11D.

[0030] 2 and 3, the steel plate 2 is transported in the vertical direction, which is the arrangement direction of the straight pipe portions 11A, 11B, 11C, and 11D.

[0031] (Burner section 12) Each burner section 12 adjusts the flow rate of fuel gas and combustion air based on instructions from the furnace temperature control section 30, and burns within the first straight tube section 11A of the radiant tube 11 to generate combustion gas that heats the inside of the tube. In FIG. 2, reference numeral 13 denotes an adjusting valve for adjusting the flow rate of fuel gas, and reference numeral 14 denotes an adjusting valve for adjusting the amount of combustion air.

[0032] (Control unit) The furnace temperature control unit 30 controls the furnace temperature. In FIG.

[0033] The furnace temperature control unit 30 controls the combustion of the burner unit 12 of each radiant tube burner 10 based on the furnace temperature and the furnace temperature target value (target extraction temperature). A burner control unit may be provided for each radiant tube burner 10, and a combustion command value may be supplied from the furnace temperature control unit 30 to each burner control unit. A known burner control method may be applied as the control method. As shown in FIG. 4, the furnace temperature control unit 30 includes a control unit main body 30A, a tube deformation detection unit 30C, a burner control change unit 30B, and an air blowing unit 30D.

[0034] <Control unit body 30A> The control unit main body 30A recognizes the radiant tube burners 10 that can be used for heating operation, and calculates the combustion state of each radiant tube burner 10 used for heating based on the furnace temperature and the target extraction temperature of the steel sheet 2, which is the material to be heated. Then, it controls each burner control unit so that the calculated combustion state is achieved. This control can be performed by applying a known control method, and the control method is not particularly limited.

[0035] <Tube deformation detection unit 30C> The tube deformation detection unit 30C is a detection unit that detects whether or not each radiant tube 11 is deformed. The tube deformation detection unit 30C detects the deformation of each radiant tube 11 based on a signal from a deformation detection sensor 31 that acquires information regarding the deformation of each radiant tube 11.

[0036] For example, when the operation of the furnace 1 is temporarily stopped for a periodic inspection, the tube deformation detection unit 30C acquires 3D image information of the inside of the furnace 1 acquired by a digital scanner device that 3D scans the inside of the furnace 1. Here, the digital scanner device constitutes the deformation detection sensor 31. Then, based on the acquired 3D image information, the tube deformation detection unit 30C obtains position information (e.g., central axis information of each straight pipe section) of each radiant tube 11, and judges whether or not a predetermined deformation or more has occurred in each radiant tube 11. Note that the judgment of deformation only requires the judgment of the deformation state of one of the multiple straight pipe sections 11A, 11B, 11C, 11D that constitute the radiant tube 11, for example, the straight pipe section 11D located at the bottom.

[0037] The deformation is, for example, equal to or larger than the outer diameter of the radiant tube 11. Alternatively, for example, a displacement meter that detects the displacement of receiving metal fittings 21 that receive support members 20 protruding from radiant tubes 11 is provided as deformation detection sensor 31. Then, tube deformation detection unit 30C determines the presence or absence of deformation of each radiant tube 11 from the amount of displacement of receiving metal fittings 21 that hold each radiant tube 11.

[0038] Alternatively, a furnace temperature distribution detection sensor may be provided to detect the temperature distribution inside the furnace 1. The tube deformation detection unit 30C may estimate (detect) the presence or absence of displacement of each radiant tube 11 from the temperature distribution around the arrangement of the radiant tubes 11.

[0039] <Burner control change unit 30B> Here, a radiant tube 11 that is determined to have a deformation based on the judgment of the tube deformation detection unit 30C is referred to as a detected radiant tube. Furthermore, at least one of the radiant tubes 11 adjacent to the detected radiant tube in the arrangement direction of the radiant tubes 11 (the vertical direction in this embodiment) is referred to as an adjacent radiant tube. In this embodiment, the radiant tube 11 located below the detected radiant tube is referred to as an adjacent radiant tube. The two radiant tubes 11 located on both sides of the detected radiant tube in the arrangement direction may both be referred to as adjacent radiant tubes.

[0040] Burner control change unit 30B first determines whether or not there is a detected radiant tube based on the determination of tube deformation detection unit 30C.

[0041] When the burner control change unit 30B determines that there is a detected radiant tube, it identifies the adjacent radiant tube for that detected radiant tube. If there are two or more detected radiant tubes, it identifies the adjacent radiant tube for each detected radiant tube. Note that if there are consecutive detected radiant tubes, some of the detected radiant tubes are also adjacent radiant tubes, but are processed as detected radiant tubes. The radiant tubes 11 can be identified, for example, by assigning identification numbers in the order of the radiant tubes 11.

[0042] Then, burner control change unit 30B changes the status of each burner unit 12 that heats the inside of each detection radiant tube and each burner unit 12 that heats the inside of each adjacent radiant tube to a non-heating control state. The non-heating control state is a state where the combustion of the burner section 12 is stopped and the burner section 12 is turned off, or a low-output combustion state where the temperature inside the tube is kept below the furnace temperature. The status of the detected radiant tube and the adjacent radiant tubes is set to a disabled state where they cannot be used for heating operations.

[0043] <Air blowing section 30D> Air blowing section 30D executes a process of flowing air at a temperature lower than the furnace temperature into at least one radiant tube 11 of radiant tube burner 10 that has been changed to the extinguished state by burner control change section 30B.

[0044] The air blowing section 30D is realized, for example, by stopping the pressure-feeding of the combustion gas and pressure-feeding the combustion air to the target burner section 12. The pressure-feeding combustion air has a temperature about the atmospheric temperature, which is generally lower than the furnace temperature. Generally, the combustion air is preheated (300 to 500°C) before the radiant tube inlet. However, since the heat source for preheating is the sensible heat of the combustion exhaust gas, when the pressure delivery of the combustion gas is stopped, the combustion air is not preheated.

[0045] A blower for blowing air into radiant tube 11 may be provided separately from burner section 12, and the blower may be used to blow air into radiant tube 11.

[0046] Here, air blower 30D may be omitted. Also, the processing of air blower 30D may be applied only to the adjacent radiant tubes, or only to the detection radiant tube. Additionally, the burner 12 of the detection radiant tube and the adjacent radiant tube do not have to be in the same non-heating controlled state. For example, the burner 12 of the detection radiant tube may be in an extinguished state only, while the burner 12 of the adjacent radiant tube may be in a low-output combustion state where the temperature is below the furnace temperature.

[0047] In addition, the air blowing section 30D may be configured to be operated when the temperature inside the tubes of the detection radiant tube burner and the adjacent radiant tube burner becomes higher than a predetermined value (e.g., higher than the furnace temperature) after the detection radiant tube burner and the adjacent radiant tube burner are put into an extinguished state.

[0048] Also, the presence or absence of deformation of each radiant tube 11 may be detected by visual inspection by an operator during regular inspection. In this case, the status is manually changed to the non-heating control state.

[0049] (Operation etc.) According to this embodiment, the radiant heat from the other radiant tubes 11 adjacent to the radiant tube 11 in which deformation is progressing is suppressed. As a result, the deformation of the radiant tube 11 in which deformation is progressing is prevented from being accelerated. This makes it possible to provide a heating furnace 1 and an operating method thereof that can further extend the life of the radiant tubes 11 used in the heating furnace 1.

[0050] Even when the radiant tubes 11 are in an extinguished state, they generate radiant heat due to heating from the heat inside the furnace 1. In response to this, it is possible to reduce the radiant heat from the radiant tubes 11 by circulating (pressuring) air at a temperature lower than the furnace temperature through the radiant tubes 11 in an extinguished state.

[0051] (others) The present disclosure may also have the following configuration. (1) A method for operating a heating furnace, which has a plurality of radiant tube burners each having a radiant tube and a burner section that burns inside the tube to heat the inside of the tube, and heats the inside of the furnace by indirect heating from a plurality of radiant tubes arranged along a predetermined arrangement direction in the furnace, Check whether the radiant tube is deformed or not. a burner unit for heating the inside of a detection radiant tube, which is a radiant tube detected as deformed in the above inspection, and a burner unit for heating the inside of an adjacent radiant tube, which is at least one of the radiant tubes adjacent to the detection radiant tube in the arrangement direction, are each put into an extinguished state in which combustion is stopped, or into a low-output combustion state in which the temperature inside the tube is equal to or lower than the furnace temperature; A method for operating a heating furnace comprising the steps of: (2) At least one of the burner sections that heat the inside of the detection radiant tube and the burner section that heats the inside of the adjacent radiant tube is extinguished, and air at a temperature lower than the furnace temperature is circulated through the radiant tube of at least one of the radiant tube burners that is in the extinguished state. (3) The arrangement direction of the plurality of radiant tubes is the vertical direction, The adjacent radiant tube is the radiant tube located below the detection radiant tube. (4) The radiant tube is a W-type radiant tube. (5) A heating furnace having a plurality of radiant tube burners each having a radiant tube and a burner portion that burns in the tube to heat the inside of the tube, and heating the inside of the furnace by indirect heating from a plurality of radiant tubes arranged along a predetermined arrangement direction in the furnace, a tube deformation detection unit for detecting the presence or absence of deformation of each radiant tube; a burner control change unit which, when it is determined based on the judgment of the tube deformation detection unit that there is a detected radiant tube, which is a radiant tube having a deformation, changes the burner unit which heats the inside of the detected radiant tube and the burner unit which heats the inside of an adjacent radiant tube, which is at least one of the radiant tubes adjacent to the detected radiant tube in the arrangement direction, to an extinguished state in which combustion is stopped, or to a low-output combustion state in which the temperature inside the tube is equal to or lower than the furnace temperature; Equipped with. (6) The burner control change unit turns off at least one of the burner unit that heats the detection radiant tube and the burner unit that heats the adjacent radiant tube, Furthermore, an air blowing section is provided which blows air at a temperature lower than the furnace temperature into the radiant tube of the radiant tube burner which has been put into an extinguished state by the processing of the burner control change section. (7) The arrangement direction of the plurality of radiant tubes is the vertical direction, The adjacent radiant tube is the radiant tube located below the detection radiant tube. (8) The radiant tube is a W-type radiant tube. EXAMPLES

[0052] In this example, a numerical simulation was created and executed in which a steel plate 2 was passed above and below two radiant tube burners 10 each having a W-shaped radiant tube 11, which were installed above and below each other, as shown in Fig. 3. The temperature of the steel plate 2 was assumed to be constant at 600°C.

[0053] (Sample conditions) <Case 1> In case 1, both of the radiant tube burners 10 are in a burner operation state.

[0054] <Case 2> In case 2, the upper radiant tube burner is in an extinguished state, and the lower radiant tube burner 10 is in a burner operation state. <Case 3> Case 3 is a case where both radiant tube burners 10 are in an extinguished state.

[0055] In the extinguished state, fuel gas and combustion air are not supplied and the burner is stopped. In the burner state, fuel gas and combustion air are supplied and burned in the radiant tube 11 to heat the tube.

[0056] (evaluation) The evaluation results are shown in Figure 8. The vertical axis indicates the surface temperature, and the horizontal axis indicates the temperature at the bottom of the fourth straight tube section 11D of the upper radiant tube 11 (the position indicated by the symbol T in FIG. 3), while the horizontal axis indicates the normalized value of the distance from the furnace wall 1A.

[0057] In case 2, the upper radiant tube 11 is in an extinguished state. However, as can be seen from Fig. 8, the difference in temperature at the temperature measurement position T in the fourth straight tube section 11D in case 1 and case 2 was small, at less than 30°C. This is because the temperature measurement position T receives radiant heat from the first straight tube section 11A of the lower radiant tube 11. As can be seen from this result, when deformation of the fourth straight tube section 11D of the upper radiant tube 11 is progressing, the deformation continues even when the upper radiant tube burner 10 is turned off. That is, in case 2, it is considered that the deformation of the upper radiant tube 11, especially the deformation of the lowest straight tube section 1D, continues.

[0058] On the other hand, by turning off the lower radiant tube burner 10 as in Case 3, the temperature measurement position T of the upper radiant tube 11 became almost the same temperature as the steel plate 2. In other words, it was found that, according to the present invention, it is possible to suppress the progression of deformation of the fourth straight tube section 11D of the upper radiant tube 11. [Explanation of symbols]

[0059] 1 Furnace 1A furnace wall 2 Steel plate (heated material) 10 Radiant tube burner 11 Radiant tube 12 Burner section 15 Furnace temperature detection sensor 20 Support material 21 Bracket 30 Furnace temperature control unit 30A Control Unit 30B Burner control modification part 30C Tube deformation detector 30D Air Blower

Claims

1. A method for operating a heating furnace, comprising a plurality of radiant tube burners each including a radiant tube and a burner section for heating the inside of the tube by combustion therein, and heating the inside of the furnace by indirect heating from a plurality of radiant tubes arranged in a predetermined arrangement direction within the furnace, comprising: Check whether the radiant tube is deformed or not. a burner section for heating the inside of a detection radiant tube, which is a radiant tube detected as deformed in the above inspection, and a burner section for heating the inside of an adjacent radiant tube, which is a radiant tube located on the exhaust side of the detection radiant tube among the radiant tubes adjacent to the detection radiant tube in the above arrangement direction, are each put into an extinguished state in which combustion is stopped, or into a low-output combustion state in which the temperature inside the tube is equal to or lower than the furnace temperature; A method for operating a heating furnace comprising the steps of:

2. At least one of the burner sections that heat the inside of the detection radiant tube and the burner section that heats the inside of the adjacent radiant tube is turned off, and air having a temperature lower than the furnace temperature is circulated through the radiant tube of at least one of the radiant tube burners that is turned off.

2. A method for operating a heating furnace according to claim 1.

3. The arrangement direction of the plurality of radiant tubes is the vertical direction, The adjacent radiant tube is a radiant tube located below the detection radiant tube.

3. A method for operating a heating furnace according to claim 1 or 2.

4. The radiant tube is a W-type radiant tube.

2. A method for operating a heating furnace according to claim 1.

5. A heating furnace has a plurality of radiant tube burners each including a radiant tube and a burner portion that heats the inside of the tube by burning the inside of the tube, and heats the inside of the furnace by indirect heating from the plurality of radiant tubes arranged in a predetermined arrangement direction in the furnace, a tube deformation detection unit for detecting the presence or absence of deformation of each radiant tube; a burner control change unit which, when it is determined based on the judgment of the tube deformation detection unit that there is a detected radiant tube, which is a radiant tube with a deformation, changes the burner unit which heats the inside of the detected radiant tube and the burner unit which heats the inside of an adjacent radiant tube, which is the radiant tube located on the exhaust side of the detected radiant tube among the radiant tubes adjacent to the detected radiant tube in the arrangement direction, to an extinguished state in which combustion is stopped, or to a low-output combustion state in which the temperature inside the tube is equal to or lower than the furnace temperature; A heating furnace comprising:

6. The burner control change unit turns off at least one of the burner unit that heats the detection radiant tube and the burner unit that heats the adjacent radiant tube, Further, an air blowing unit is provided that blows air having a temperature lower than the furnace temperature into the radiant tube of at least one of the radiant tube burners that has been put into an extinguished state by the processing of the burner control change unit.

6. A heating furnace according to claim 5.

7. The arrangement direction of the plurality of radiant tubes is the vertical direction, The adjacent radiant tube is a radiant tube located below the detection radiant tube.

7. A heating furnace according to claim 5 or 6.

8. The radiant tube is a W-type radiant tube.

6. A heating furnace according to claim 5.

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