JP3549981B2 - Furnace support structure of radiant tube with alternating heat storage - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an in-furnace support structure of a W-type heat storage alternate combustion radiant tube used in a heating furnace such as a continuous annealing furnace and a continuous galvanizing.
[0002]
[Prior art]
FIG. 6 shows a state in which a W-type heat storage alternating combustion radiant tube attached to a furnace wall such that a burner is at a vertical position is supported by a conventional typical W-type radiant tube support structure. The upper burner 43 and the lower burner 44 are provided with an upper burner storage zone 45 and a lower burner storage zone 46 for preheating the combustion air, respectively, and the two burners alternately repeat combustion and heat storage. Therefore, in the conventional radiant tube, the temperature difference between the burner side and the recuperator side greatly increases, but in this case, the combustion conditions are symmetrical with respect to the vertical direction of the tube, and the temperature distribution of the tube is also symmetrical with the vertical direction. The W-type heat storage alternate combustion radiant tube realizes extremely high heating and combustion efficiency.
[0003]
In order to prevent oxygen from entering the furnace, both the upper burner 43 and the lower burner 44 of the burner side end (upper) 2 and the burner side end (lower) 10 of the radiant tube 1 are connected to the burner bank 11. The burner banks 11 are welded to the furnace wall, and are fixed respectively. In the furnace, the third bend tip support receiving portion 41 at the tip of the third bend 8 is supported by a furnace wall support jig 42 from the furnace wall 13 on the side opposite to the burner. Further, a saddle 39 between radiant tubes is provided between the lower part of the first bend 4 or the second straight pipe 5 and the upper part of the third bend 8 or the third straight pipe 7, and the second bend 6 or the third straight pipe is provided. A radiant tube saddle 40 is provided between the seventh straight tube 9 and the fourth straight tube 9.
[0004]
By the way, the radiant tube is constrained by the above-mentioned support and mounting structure against thermal expansion due to high-temperature heating, and thermal stress and deformation occur. Since it becomes unusable due to deformation such as contact, it must be replaced each time. This thermal stress and deformation will be described in detail with reference to FIGS. Note that, as the heat load state on the radiant tube, two states of normal operation and furnace heating are considered.
[0005]
FIG. 7 shows a state during normal operation. The temperature in the furnace reaches around 900 ° C., and the temperature of the radiant tube 1 increases by several tens of degrees or more. At this time, the temperature of the burner bank 11 is usually 200 ° C. to 300 ° C., whereas the temperature of the radiant tube 1 in the furnace is higher than 950 ° C., so that the furnace wall support jig 42 at the tip of the third bend 8 is used. , The distal end of the first straight pipe 3 is forced to be considerably upwardly deformed by thermal expansion in the height direction (vertical direction) 47 reaching the third bend 8, the saddle 39, and the first bend 4. For example, in the case of a radiant tube in which the distance between the axis of the first straight tube 3 and the fourth straight tube 9 is 900 mm, the temperature of the burner bank is 250 ° C., the temperature of the radiant tube in the furnace is 950 ° C., and the thermal expansion of the radiant tube is Assuming a rate of 17 × 10 ⁻⁶ , the vertical extension of the burner bank portion is about 3.8 mm and the vertical extension of the tip portion is about 14.5 mm, resulting in a difference of 10 mm or more.
[0006]
As described above, due to the upward deformation of the distal end of the first straight pipe 3 due to thermal expansion, an extremely large first straight pipe bending moment (during normal operation) 48 is generated in the first straight pipe 3. Further, because of the restraint by the saddle 39, a large first bend bending moment (during normal operation) 49 also occurs in the first bend 4, and the straight pipe portion near the saddle has a large vertical force, which is a large vertical force. Receive 50. Further, a large bending moment 51 is applied to the support receiving portion 41 at the distal end of the third bend 8 which supports about one-third of its own weight. Further, at high temperatures, the saddles 39 and 40 bear a part of the weight of the tube, so that the vicinity of the saddles of the third straight pipe 7 and the fourth straight pipe 9 is caused by vertical loads 50 and 52 which are vertical forces. Is received constantly.
[0007]
The radiant tube 1 is exposed to a high temperature for a long time, and is subjected to creep deformation due to the above-mentioned stress and the influence of its own weight. As shown in FIG. 8, a saddle upper straight pipe buckling 53 and a saddle lower straight pipe buckling 54 are provided on the second straight pipe 5 and the third straight pipe 7 near the saddle 39, and a third straight pipe near the saddle 40. The saddle upper straight pipe buckling 55 and the saddle lower straight pipe buckling 56 occur in the pipe 7 and the fourth straight pipe 9. Also, the second straight pipe 5 sags 57 due to a reduction in cross-sectional rigidity due to the buckling 53 of the second straight pipe 5. Further, the support receiving portion 41 at the tip of the third bend 8 generates the third bend tip support receiving portion rotation deformation 58 which is an upward deformation, in accordance with the bending moment 51. Along with the rotational deformation 58 and the buckling 56 of the fourth straight pipe 9, the fourth straight pipe sag 59 is also caused, and the service life of the radiant tube is reached.
[0008]
FIG. 9 shows a state when the furnace is heated from normal temperature to a normal operation state. However, the radiant tube is deformed over time, and the support receiving portion 41 at the tip of the third bend 8 is deformed upward. When the temperature is raised in this state, the first straight pipe 3 generates a large axial force (when the temperature is raised) 60, which is a large compressive force, because the thermal expansion of the tip of the third bend 8 is hindered. The first straight pipe bending moment (at the time of temperature rise) 61 is generated by the bend portion. As a result, a large stress is generated in the first straight pipe 3. Further, a large first bend bending moment (at the time of temperature rise) 62 is generated in the first bend 4 by the deformation restraint by the saddle 39. As a result, stress concentration occurs on the side surface of the bend portion, and a large force is applied to the upper portion of the saddle. Furthermore, temperature deviation due to aging deterioration of the material, oxidation thinning, accumulation of thermal fatigue, generation of scale, etc. is added, and when the above-mentioned large stress is generated, the first straight pipe burner side crack 63 is formed on the first straight pipe burner side. Alternatively, a first bend side surface crack 64 is generated on the first bend side surface.
[0009]
As described above, when the heat storage alternating-combustion radiant tube is supported by the conventional support structure, the temperature distribution is vertically symmetric, but the support structure is vertically asymmetric, causing various problems, such as cracks and deformation. , Causing buckling and longevity. Therefore, reducing the bending moment due to the thermal expansion and alleviating the restraining force by the saddle to prevent the occurrence of buckling greatly extends the life of the radiant tube.
[0010]
In order to solve the problem of the heat storage alternating combustion type radiant tube, there has been no example of a means for preventing deformation and cracks. As a method of stress relaxation, Japanese Patent Application Laid-Open No. 5-272708 discloses a structure in which a bellows is attached to an end portion of a burner side at the burner side to absorb the axial elongation of the straight pipe on the burner side. At the side end, a bellows is provided in the axial direction of the tube, and in the height direction, there is a bellows provided with a burner and a spring supporting a part of the tube's own weight, thereby presenting a structure capable of freeing thermal expansion. . Japanese Patent Application Laid-Open No. 3-226519 discloses a method in which the diameter of the first straight pipe or the first and second straight pipes is made larger than other parts, and the tip of the first bend is supported from the furnace wall.
[0011]
[Problems to be solved by the invention]
However, in the heat storage alternating combustion type radiant tube, although the combustion conditions and the temperature distribution are vertically symmetric, the conventional support structure is not vertically symmetric and has no effect of reducing the thermal stress due to deformation and restraint. Further, in the structures disclosed in JP-A-5-272708 and JP-A-1-38415, although the bellows is effective in relieving stress, not only is it necessary to simultaneously support a considerable weight of the burner including the tropics, The installation of the bellows increases the cost, and there is a problem in the durability of the bellows. Further, the method of supporting the tip of the first bend from the furnace wall disclosed in Japanese Patent Application Laid-Open No. Hei 3-226519 inhibits thermal expansion when the temperature is repeatedly lowered and raised by furnace repair or the like at the time when the supporting portion is deformed. And cause buckling.
[0012]
Accordingly, an object of the present invention is to provide a heat storage alternating combustion type radiant tube that significantly reduces thermal stress and deformation during normal operation and furnace heating at low cost, and reduces the buckling of the straight tube near the support and the support portion. An object of the present invention is to provide an in-furnace support structure for a heat storage alternate-combustion radiant tube that can prevent the entire tube from buckling due to thermal expansion inhibition due to deformation and can achieve a longer life than a conventional radiant tube.
[0013]
[Means for Solving the Problems]
The gist of the present invention is that a fixing jig having a horizontal slit is provided in a furnace supporting structure of a W-type heat storage alternate combustion type radiant tube arranged so that a mounting position on a burner bank is arranged vertically. Is protruded from the furnace wall opposite to the burner bank so as to be located on the vertical center axis of the radiant tube, and a pin movable on the slit and a receiving jig protruded from the tip of the first bend. The first bend is supported while connecting the pins provided at the first and second ends with a rod so that both ends become a rotary joint, and the pin movable on the slit and a receiving jig protruding from the tip of the third bend. The third bend is suspended from the pin provided on the fixture by connecting the rod with a rod so that both ends become a rotary joint. Further, a fixing jig having a horizontal slit is provided on the slide. And a receiving jig protruding from the tip of the second bend via a pin that can move on the slit. As a structure for supporting the second bend while being connected to form a rotary joint, the support structure is vertically symmetrical, and is a support structure in a furnace of a heat storage alternating combustion type radiant tube.
[0014]
In the present invention, the support position from the furnace wall and the burner bank is set as the vertical center axis of the radiant tube, thereby realizing a vertically symmetrical furnace support structure, and the first, second, and third bend end portions. Is supported as a rotary joint, so that thermal expansion of the tube due to deformation of the support portion is not hindered. In addition, there is no buckling because the straight pipe portion has no support portion.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described based on examples.
[0016]
FIG. 1 is a diagram showing the entire embodiment, and FIGS. 2 and 3 are detailed diagrams thereof.
[0017]
First, a furnace wall side fixing jig 14 having a horizontal furnace wall side fixing jig upper slit 15 is protruded from a furnace wall 13 opposite to the burner bank 11. The height center position of the slit 15 is on the vertical center axis 16 of the radiant ant tube. Next, the first bend receiving jig 17 having the pin hole 18 is protruded from the distal end of the first bend 4, and the third bend receiving jig 22 having the pin hole 23 is protruding from the distal end of the third bend 8. . The centers of the pin holes 18 and 23 are vertically symmetric with respect to the vertical center axis 16.
[0018]
The first bend support rod 19 has a first bend side pin hole 20 and a furnace wall side fixing jig side pin hole 21 at both ends. The pin hole 20 of the rod 19 and the pin hole 18 provided in the receiving jig 17 are connected through a first bend tip pin 27, and the pin hole 21 is slit through a furnace wall side fixing jig pin 29. 15 can move. Further, the third bend suspension rod 24 has a third bend side pin hole 25 and a furnace wall side fixing jig side pin hole 26 at both ends. The pin hole 25 of the rod 24 and the pin hole 23 provided in the receiving jig 22 are connected via a third bend tip pin 28, and the pin hole 26 is connected to the pin 29 and can move on the slit 15. The pin 29 is located closer to the furnace wall 13 than the pins 27 and 28 are. The depth L1 of the slit 15 from the position of the pin 29 before heating the radiant tube is set substantially equal to the maximum value of the thermal expansion in the axial direction of the tube.
[0019]
The burner bank 11 is provided with a burner bank side fixing jig 30 having a slit 31 on the burner bank side fixing jig in the horizontal direction. The height center position of the slit 31 is on the vertical center axis 16. Next, a second bend tip receiving jig 32 having a pin hole 33 at the tip of the second bend 6 is protruded. The pin hole 33 is movable on the slit 31 via the second bend tip pin 34. The depth L2 of the slit 31 from the position of the pin 34 before the heating of the radiant tube is set equal to the maximum value of the thermal expansion in the axial direction of the tube.
[0020]
The diameter of the pin 27 is determined so that the pin does not bend and deform even if the deformation of the first bend 4 is restricted. The diameter of the pin 28 is the same as that of the pin 27. The diameter of the pin 29 on the furnace wall side fixing jig 14 projecting from the furnace wall 13 is determined in consideration of all loads applied to the first bend 4 and the third bend 8. The diameter of the pin 34 is determined so that the pin does not bend and deform even when the deformation of the second bend 6 is restricted. The size of the pin hole into which each pin is inserted is determined in consideration of the thermal expansion of the pin diameter.
[0021]
In addition, the pins 27, 28, 29, 34 must not fall off or shift laterally significantly. In particular, the pin 29 needs to be securely inserted into the slit 15 on the furnace wall side fixing jig 14 from the furnace wall 13 when the radiant tube is installed, so that a large lateral displacement of the pin 29 does not occur. For example, as shown in FIG. 2C, a pin weld fixing portion 35 at the first bend tip, a pin weld fixing portion 36 at the fixed support portion from the furnace wall, and a pin weld fixing portion 37 at the third bend tip are As shown in FIG. 3 (c), between the pin holes 20 and 27, between the pin holes 21 and 29, between the pin holes 25 and 28, and as shown in FIG. The space between the pin 33 and the pin 34 is fixed by welding.
[0022]
The cross-sectional area of the rod 19 connecting the first bend 4 and the furnace wall side fixing jig 14 projecting from the furnace wall 13 is determined by the compressive force generated when the pin 29 reaches the innermost part of the slit 15 and the deformation is locked. , And a size capable of withstanding creep buckling against the weight of the first straight pipe 3 to the second straight pipe 5. The cross-sectional area of the rod 24 connecting the third bend 8 and the furnace wall side fixing jig 14 projecting from the furnace wall 13 is creeped in consideration of the weight of the tubes from the third straight pipe 7 to the fourth straight pipe 9. Decide not to deform.
[0023]
According to the in-furnace supporting structure of the present invention, the first bend 4 and the third bend 8 are connected via the rod 19 and the rod 24 and the pin 29 and the pin 29 is , The first bend 4 is supported from below, and the third bend 8 is suspended from above. At the time of temperature rise, the temperature of the first straight pipe 3 and the fourth straight pipe 9 rapidly rises, so that thermal expansion occurs in the axial direction as a whole. At this time, the pin 29 moves on the slit 15 via the rod 19 and the rod 24, so that the movement of the first bend 4 and the third bend 8 is not restricted. Also, during normal operation, the pin 29 moves to the innermost part of the slit 15 and the rod 19 is in a state of being stretched, supporting the first bend 4, so that drooping due to creep due to its own weight can be prevented. Further, the third bend 8 is always in a state of being lifted via the rod 24, so that drooping due to creep can be prevented.
[0024]
Further, the second bend 6 is movable on the slit 31 via the pin 34 and is free in the axial direction, but is restrained in the vertical direction, so that the rigidity of the entire tube due to the vertical movement of the second bend 6 is reduced. It is possible to prevent dripping due to its own weight.
[0025]
【Example】
FIG. 1 shows an embodiment of the present invention. The radiant tube 1 is used for a continuous annealing furnace. The length of the first straight tube 3 and the fourth straight tube 9 is 2500 mm, and the length of the second straight tube 5 and the third straight tube 7 is 1450 mm and 1650 mm, respectively. The axial center distance of each straight pipe is 300 mm. The outer diameter and the inner diameter are 194 mm and 177 mm, respectively, and the material is SCH22 described in JIS G 5122.
[0026]
The diameter of the pins 27 and 28 was 30 mm, the diameter of the pin 29 was 45 mm, and the diameter of the pin 34 was 30 mm. The pin holes 20 and 27, the pin holes 21 and 29, the pin holes 25 and 28, and the pin holes 33 and 34 were fixed by welding. The diameter of the pin hole 18 on the rotating receiving jig 17 and the diameter of the pin hole 23 on the receiving jig 22 are 31 mm in consideration of the thermal expansion of the pin 27 and the pin 28, respectively. The diameter was 46 mm in consideration of the thermal expansion of the pin 29.
[0027]
The width of the slit 15 was 46 mm in consideration of the thermal expansion of the pin 29. The width of the slit 31 on the fixing jig 30 projecting from the burner bank 11 was set to 31 mm in consideration of the thermal expansion of the pin 34. The depth L1 of the slit 15 is 42 mm in consideration of the maximum thermal deformation of the first bend 4 or the third bend 8 in the axial direction, and the depth L2 of the slit 31 is 23 mm in consideration of the maximum thermal deformation of the second bend 6. did.
[0028]
The cross-sectional area of the rod 19 connecting the first bend 4 and the furnace wall side fixing jig 14 projecting from the furnace wall 13 is determined by the compressive force generated when the pin 29 reaches the innermost part of the slit 15 and the deformation is locked. The rod 24 for connecting the third bend 8 and the furnace wall side fixing jig 14 projecting from the furnace wall 13 to 60 cm ² in consideration of creep buckling of the first straight pipe 3 to the second straight pipe 5 with respect to its own weight. The cross-sectional area was set to 30 cm ² in consideration of creep deformation due to the weight of the third straight pipe 7 to the fourth straight pipe 9 and subsequent tubes.
[0029]
A radiant tube supported in the furnace according to the present invention was manufactured together with a radiant tube having a conventional support structure shown in FIG. 6, and a combustion test was performed. After confirming that there was no difference between the two temperature distributions, the deformation of the tube (only the vertical deformation of the first straight pipe) was actually measured.
[0030]
FIG. 4 is a result verified by the finite element method simulation using the actual measurement result of the deformation and the temperature distribution at the time of the combustion test. As shown in FIG. 4, the deformation of the tube supported in the furnace according to the present invention is 1/3 or less of that of the conventional supporting structure, and it can be seen that the bending deformation is small.
[0031]
FIG. 5 is a graph showing a trial calculation of a stress distribution by the finite element method simulation. Accordingly, in the radiant tube supported in the furnace according to the present invention, the stress of the first and fourth straight pipes, which is the most thermally severe, is about half that of the conventional support structure, and the stress of the bend portion is also the conventional one. It is about 1/2 of the case of the support structure, and it can be seen that it is greatly reduced.
[0032]
【The invention's effect】
According to the present invention, the support structure is vertically symmetric, that is, the thermal deformation is vertically symmetric, the rigidity of the entire tube is increased by the vertical restraint of the second bend, there is no support between the tubes, and the bend tip is a rotary joint. Since it is connected by the, it does not restrict the thermal deformation in the height direction and the axial direction of the tube, so it is possible to reduce the thermal stress and reduce the creep deformation and reduce the buckling of the tube. The service life of the heat storage alternating combustion radiant tube is prolonged without causing it.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a partially detailed explanatory view of an embodiment of the present invention.
FIG. 3 is a detailed explanatory view of another portion of the embodiment of the present invention.
FIG. 4 is a diagram showing a displacement measurement result and a calculation result of a first straight pipe in a combustion test.
FIG. 5 is a diagram showing a trial calculation result of a stress distribution of a radiant tube.
FIG. 6 is an explanatory view of a W-shaped radiant tube having a conventional support structure.
FIG. 7 is an explanatory view of a deformation and damage mode of a W-type radiant tube by a conventional support structure in an early stage of normal operation.
FIG. 8 is an explanatory diagram of a deformation and damage form of a W-type radiant tube having a conventional support structure at the end of normal operation.
FIG. 9 is an explanatory view of a deformation and damage mode when a temperature of a W-shaped radiant tube is increased by a conventional support structure.
[Explanation of symbols]
1 Radiant tube 2 Burner side end (upper part)
3 1st straight pipe 4 1st bend 5 2nd straight pipe 6 2nd bend 7 3rd straight pipe 8 3rd bend 9 4th straight pipe 10 Burner side end (lower part)
DESCRIPTION OF SYMBOLS 11 Burner bank 12 Refractory 13 Furnace wall 14 Furnace wall side fixing jig 15 Slit on furnace wall side fixing jig 16 Vertical axis of radiant tube 17 First bend tip receiving jig 18 Pin hole 19 First bend support rod 20 First bend side pin hole 21 Furnace wall side fixing jig side pin hole 22 Third bend tip receiving jig 23 Pin hole 24 Third bend hanging rod 25 Third bend side pin hole 26 Furnace wall side fixing jig side pin hole 27 First bend tip pin 28 Third bend tip pin 29 Furnace wall side fixing jig pin 30 Burner bank side fixing jig 31 Slit on burner bank side fixing jig 32 Second bend tip receiving jig 33 Pin hole 34 Second Bend tip pin 35 Pin weld fixing part at first bend tip 36 Pin weld fixing part at fixed support from furnace wall 37 Pin weld fixing part at third bend tip 38 Second bend Pin welding fixing part 39 at the pointed end Saddle between radiant tubes 40 Saddle between radiant tubes 41 Third bend tip support receiving part 42 Furnace wall support jig 43 Upper burner 44 Lower burner 45 Upper burner storage 46 Lower burner storage 47 Height Direction (vertical direction)
48 First straight pipe bending moment (during normal operation)
49 1st bending moment (during normal operation)
50 Vertical load near the saddle 51 Bending moment of the third bend tip support receiving part 52 Vertical load 53 near the saddle 53 Buckling of the saddle upper straight pipe 55 Buckling of the saddle lower straight pipe 56 Buckling of the upper saddle pipe 56 Buckling of the saddle lower straight pipe 57 2 straight pipe sag 58 third bend tip support receiving part rotating deformation 59 fourth straight pipe sag 60 first straight pipe axial force (at temperature rise)
61 1st straight pipe bending moment (at elevated temperature)
62 First bend bending moment (at elevated temperature)
63 First straight pipe burner side crack 64 First bend side crack

Claims (1)

In a furnace supporting structure of a W-type heat storage alternate combustion type radiant tube arranged so that a mounting position on a burner bank is vertically, a fixing jig having a horizontal slit is disposed at a vertical center of the radiant tube. Between the pin provided on the furnace wall opposite to the burner bank so as to be located on the shaft and movable on the slit, and a pin provided on a receiving jig provided at the tip of the first bend. The first bend is supported while connecting both ends by a rod so that both ends become a rotary joint, and the pin movable on the slit and a pin provided on a receiving jig protruding from the third bend end. The third bend is suspended while connecting the both ends with a rod so that both ends become a rotary joint. Further, a fixing jig having a horizontal slit is provided by a radiant slit. The slit protrudes from the burner bank so as to be located on the vertical center axis of the tube, and the slit and a receiving jig protruding from the tip of the second bend are connected via a pin movable on the slit. A support structure for a heat storage alternating combustion radiant tube in a furnace, wherein the support structure is vertically symmetrical as a structure for supporting the second bend while forming a rotary joint.

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