JP7303781B2 - reflux tube - Google Patents

Description

The present invention relates to a reflux tube used as a riser or a downcomer in a vacuum degassing apparatus for molten steel processing.

As a vacuum degassing device for degassing molten steel, an upper tank equipped with an inlet and an exhaust port for charging alloys, auxiliary raw materials, slag forming materials, etc., and two reflux pipes at the bottom were installed. Vacuum degassers of the RH or KTB type are known, consisting of a lower tank and a dip tube connected by flanges to the lower ends of two reflux tubes. When performing degassing using such a vacuum degassing apparatus, two immersion tubes are immersed in molten steel contained in a ladle, and Ar gas is introduced into one reflux tube and immersion tube functioning as a riser tube. is supplied, accompanied by the ascending current of Ar gas, the molten steel is introduced into the vacuum region of the lower tank and degassed, and then discharged into the ladle through the other reflux pipe and the immersion pipe, which function as downcomers. The molten steel is circulated by

The reflux pipe installed in the lower tank of the vacuum degassing apparatus as described above is significantly damaged by the molten steel flow during the degassing process, so it must be replaced periodically. Therefore, as in Patent Document 1, a step (joint) is provided between a cylindrical body made of refractory bricks in the upper stage and a cylindrical body made of refractory bricks in the lower stage so that the horizontal joint is damaged by the heat of molten steel. Circulation pipes have also been developed to improve durability by preventing the molten steel from penetrating through the joints from penetrating to the outside.

Japanese Utility Model Laid-Open No. 7-31850

In the vacuum degassing apparatus as described above, due to the circulation of molten steel from the ascending pipe to the descending pipe during the degassing process, a higher pressure is applied to the inside of the reflux pipe (the side close to the other reflux pipe) than the outside. It will be. However, in the conventional reflux tube such as the above-mentioned Patent Document 1, since the reflux tube has the same physical and chemical properties over the entire circumference, the inner portion is eroded faster than the outer portion. In many cases, spalling occurs earlier in the inner portion than in the outer portion, and as a result, it has been difficult to use for a long period of time.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of conventional circulation tubes, and to provide a circulation tube which is excellent in corrosion resistance and spalling resistance, has a long service life, and can be used for a long period of time. It is in.

Among the present inventions, the invention described in claim 1 is provided in the lower part of the vacuum degassing device for degassing and circulating the molten metal, and two are installed side by side in a state of being connected to the immersion pipe. A reflux pipe used as a downcomer pipe . The radial thickness of the refractory brick located on the side closer to the other circulation pipe) is the outside at the time of installation (the side farther from the other circulation pipe when installing two side by side while connected to the immersion pipe) It is characterized by being thicker than the radial thickness of the refractory bricks located at .

The invention recited in claim 2 is the invention recited in claim 1, wherein the circumferential width of the refractory bricks positioned inside when installed is greater than the circumferential width of the refractory bricks positioned outside when installed. It is characterized by being wide.

The invention recited in claim 3 is the invention recited in claim 1 or 2, wherein the refractory bricks positioned inside when installed are made of a refractory material having higher corrosion resistance than the refractory bricks positioned outside when installed. It is characterized by being formed.

When two reflux pipes according to claim 1 are installed side by side in the lower part of the vacuum degassing device, the side on which the refractory bricks having a thick radial thickness are arranged is close to the other reflux pipe. , excellent erosion resistance and spalling resistance can be expressed, so that it has a long service life and can be used for a long period of time.

In the immersion pipe according to claim 2, the refractory bricks located inside when installed are wider than the refractory bricks located outside when installed and have fewer vertical joints. When installing the thick (thick in the radial direction) refractory bricks are installed so that the side on which the refractory bricks are arranged is close to the other circulation pipe, thereby achieving higher corrosion resistance and spalling resistance. Therefore, it can be used for a very long period of time.

In the immersion pipe according to claim 3, since the refractory bricks located inside when installed are made of a refractory material with higher corrosion resistance than the refractory bricks located outside when installed , At the time of installation, by placing the thick (thick in the radial direction) refractory brick side close to the other circulation pipe, extremely high corrosion resistance and spalling resistance can be achieved. Therefore, it can be used for a very long period of time.

It is an explanatory view (plan view) showing a circulation pipe. It is an explanatory view (front view) showing a reflux pipe. It is an explanatory view (right side view) showing a circulation pipe. It is an explanatory view (left side view) showing a circulation pipe. FIG. 2 is an explanatory view (an AA line cut end view in FIG. 1) showing a circulation tube; It is explanatory drawing (perspective view) which shows an upper side 1st refractory brick. It is explanatory drawing (vertical sectional view) which shows the usage condition of a circulation tube. FIG. 8 is an explanatory diagram (cross-sectional view taken along the line BB in FIG. 7) showing a reflux pipe installation portion of the lower tank of the vacuum degassing apparatus; It is explanatory drawing (perspective view) which shows the example of a change of a firebrick.

An embodiment of a reflux tube according to the present invention will be described in detail below with reference to the drawings.

[First embodiment]
<Structure of circulation pipe>
1 to 5 show an example of a reflux tube according to the first embodiment. The circulation pipe 1 is made by assembling a plurality (62 pieces) of refractory bricks 3, 3 . It is formed by winding at each position, and has a size of outer diameter = about 1,100 mm x height = about 900 mm. In addition, the reflux pipe 1 is composed of two flat cylindrical bodies (an upper cylindrical body 2a and a lower cylindrical body 2b) having the same horizontal cross-sectional shape at approximately the center in the height direction. is in a state of

The upper cylindrical body 2a is formed by assembling 30 firebricks 3, 3, . . . having different radial widths, circumferential widths, heights, and materials. That is, the upper cylindrical body 2a includes an upper first refractory brick 3a, two upper second refractory bricks 3b, 3b, two upper third refractory bricks 3c, 3c, 14 upper fourth refractory bricks 3d, 3d... and 11 upper fifth refractory bricks 3e, 3e... are assembled.

FIG. 6 shows the first upper refractory brick 3a (center on the right side in FIG. 1). It has a fan shape with a sharp horizontal cross section. And compared with other refractory bricks, the thickness of the radial direction is the thickest, and the lateral width of the circumferential direction is also the widest.

In addition, the upper second refractory brick 3b, the upper third refractory brick 3c, the upper fourth refractory brick 3d, and the upper fifth refractory brick 3e have a trapezoidal horizontal cross section, and have a width in the circumferential direction, a thickness in the radial direction, and a height. etc. are different from the upper first refractory bricks 3a. Furthermore, the upper second refractory brick 3b, the upper third refractory brick 3c, the upper fourth refractory brick 3d, and the upper fifth refractory brick 3e have a width in the circumferential direction (the inner hole side is the upper base, and the outer hole side is the lower base). The width of the lower base in the case where the upper first refractory brick 3a is formed is the same (approximately 1/3 of the lateral width in the circumferential direction of the upper first refractory brick 3a). In addition, the thickness of the upper second refractory brick 3b in the radial direction is the same as that of the upper first refractory brick 3a, and the upper third refractory brick 3c, the upper fourth refractory brick 3d, and the upper fifth refractory brick 3e are arranged in this order. The thickness in the radial direction is reduced by 20 to 30 mm.

In addition, the refractory bricks 3, 3 ... (that is, the upper first refractory brick 3a, the upper second refractory brick 3b, 3b, the upper third refractory brick 3c, 3c, the upper fourth refractory brick 3c, 3c) The refractory bricks 3d, 3d... and the upper fifth refractory bricks 3e, 3e...) are all made of magnesia-chromium refractories.

In the upper cylindrical body 2a, upper second refractory bricks 3b, 3b are arranged on both sides of the upper first refractory brick 3a, respectively, and the outer sides of the upper second refractory bricks 3b, 3b are arranged. Upper third refractory bricks 3c, 3c are respectively arranged (on the side opposite to the side adjacent to the upper first refractory brick 3a). Further, seven upper fourth refractory bricks 3d, 3d, . , and eleven upper fifth refractory bricks 3e, 3e, . . . are arranged so as to be sandwiched between the upper fourth refractory bricks 3d, 3d, . In the upper cylindrical body 2a, the center one of the upper fifth refractory bricks 3e, 3e .

Further, in the upper cylindrical body 2a, as shown in FIG. 2, the positions of the upper edges of the upper fifth refractory bricks 3e, 3e, . . . The positions of the upper edges of the upper fourth refractory bricks 3d, 3d, ... arranged on both sides of the upper 5th refractory bricks 3e, 3e ... are gradually lowered (lowering by 50 mm there). Furthermore, the positions of the upper edges of the upper second refractory bricks 3b, 3b and the upper third refractory bricks 3c, 3c are the upper fourth refractory bricks 3d, 3d, . is the same as the position of the upper edge of the In addition, the position of the upper edge of the upper first refractory brick 3a is lower (50 mm lower than the upper edge of the upper second refractory bricks 3b, 3b and the upper third refractory bricks 3c, 3c). ).

In the upper cylindrical body 2a, as shown in FIG. 3, the positions of the lower edges of the upper first refractory bricks 3a and the upper second refractory bricks 3b disposed outside thereof are substantially the same, The positions of the lower edges of the upper third refractory bricks 3c, 3c arranged outside of them are higher than that (by 40 mm). and positions of the lower edges of the upper fourth refractory bricks 3d, 3d, . The positions of the lower edges of the upper fifth refractory bricks 3e, 3e, .

On the other hand, the lower cylindrical body 2b is formed by assembling 32 firebricks 3, 3, . . . having different radial widths, heights, and materials. That is, the lower cylindrical body 2b includes five lower first refractory bricks 3α, 3α, two lower third refractory bricks 3γ, 3γ, and fourteen lower fourth refractory bricks 3δ, 3δ. . . and 11 lower fifth refractory bricks 3ε, 3ε .

Lower first refractory bricks 3α, 3α..., lower third refractory bricks 3γ, 3γ, lower fourth refractory bricks 3δ, 3δ..., and lower fifth refractory bricks 3ε, 3ε... The horizontal cross section has a trapezoidal shape, like the refractory bricks 3b, 3c, . . . of the cylindrical body 2a. Further, the lower first refractory bricks 3α, 3α . . , the third refractory bricks 3γ, 3γ, the lower fourth refractory bricks 3δ, 3δ . Also, the lower edge of the outer side is notched in a slanted shape.

Further, the lower first refractory bricks 3α, 3α . . , the lower third refractory bricks 3γ, 3γ, the lower fourth refractory bricks 3δ, 3δ . , the width in the circumferential direction is the same, and the thickness in the radial direction decreases in the order of the lower third refractory brick 3γ, the lower fourth refractory brick 3δ, and the lower fifth refractory brick 3ε (every 20 to 30 mm thinner). In addition, lower first refractory bricks 3α, 3α..., lower third refractory bricks 3γ, 3γ, lower fourth refractory bricks 3δ, 3δ..., and lower fifth refractory bricks 3ε, 3ε... are the radial thicknesses of the upper first refractory brick 3a, the upper second refractory brick 3b, the upper third refractory brick 3c, the upper fourth refractory brick 3d, and the upper fifth refractory brick 3e, respectively. is identical to

In addition, the refractory bricks 3, 3, which constitute the lower cylindrical body 2b (that is, the lower first refractory bricks 3α, 3α . The bricks 3[delta], 3[delta]... and the lower fifth refractory bricks 3[epsilon], 3[epsilon]...) are all made of magnesia-chromium refractories.

In the lower cylindrical body 2b, five lower first refractory bricks 3α, 3α, . ing. In addition, lower third refractory bricks 3γ, 3γ are arranged outside the first refractory bricks 3α, 3α, respectively, and the outer sides of the lower third refractory bricks 3γ, 3γ ( Seven lower fourth refractory bricks 3[delta], 3[delta], . Eleven lower fifth refractory bricks 3ε, 3ε are arranged so as to be sandwiched between the fourth lower refractory bricks 3δ, 3δ, . Then, the central one of the lower fifth refractory bricks 3ε, 3ε . . . faced the central one of the lower first refractory bricks 3α, 3α . state.

In addition, the positions of the upper edges of the lower first refractory bricks 3α, 3α, . However, the upper edges of the other refractory bricks (lower third refractory bricks 3γ, 3γ, lower fourth refractory bricks 3δ, 3δ, and lower fifth refractory bricks 3ε, 3ε) is aligned with the lower edge of each refractory brick (upper third refractory bricks 3c, 3c, upper fourth refractory bricks 3d, 3d, and upper fifth refractory bricks 3e, 3e, . . . ) in the upper cylindrical body 2a. In addition, it is in a state of alternately moving up and down (a state of moving up and down by 50 mm).

The reflux pipe 1 is formed by stacking the above-described upper cylindrical body 2a and lower cylindrical body 2b in two stages at approximately the center in the height direction. The thickness in the radial direction (radial direction from the central axis C) of the first upper refractory brick 3a and the second upper refractory brick 3b, and the first lower refractory brick 3α located on the side (right side in FIG. 1) is the central axis It is thicker (about 70 mm thicker) than the radial thickness of the upper fifth refractory brick 3e and the lower fifth refractory brick 3ε located on the opposite side (left side in FIG. 1) to the one direction side with respect to C. there).

<How to use the reflux tube>
7 and 8 show an example of how to use the reflux tube 1 constructed as described above. Circulation pipes 1 are installed vertically in a state where two are arranged side by side inside a portion near the lower end of the lower tank 13 of the vacuum degassing device M (in the following description, the circulation pipe 1 on the left side in FIGS. 7 and 8 is The tube 1 is referred to as a reflux tube 1a, and the right reflux tube 1 is referred to as a reflux tube 1b). Also, at that time, the thick portions of the circulation pipes 1a and 1b (installed portions of the upper first refractory bricks 3a and the lower first refractory bricks 3α) are arranged side by side (see FIG. 8).

In addition, when the two reflux pipes 1a and 1b are arranged side by side inside the portion near the lower end of the lower tank 13 of the vacuum degassing device M, the floor bricks 15 (the lower part of the vacuum degassing device M The portion F located between the circulation pipes 1a and 1b in the refractory bricks laid on the bottom surface of the tank 13 is replaced by the thick portion of each circulation pipe 1a and 1b (the upper first refractory brick 3a and the lower first refractory brick 3a). It is preferable to form a recessed groove in accordance with the shape of the upper edge of the portion where the firebricks 3α are installed (stepped recessed shape, see FIG. 3, etc.). Each of the circulation pipes 1a and 1b is connected to the lower end of each of the cylindrical dip pipes 11 and 11, and the portion near the lower end of the dip pipes 11 and 11 is melted in the ladle 14. One side (reflux tube 1a) functions as an ascending tube together with the immersion tube 1, and the other (reflux tube 1b) functions together with the immersion tube 1 as a descending tube.

Then, in the vacuum degassing device M, the upper tank 12 and the lower tank 13 are evacuated, and an inert gas (such as argon gas) is supplied to the ascending pipes (circulating pipe 1a and immersion pipe 11) through pipes (not shown). is blown into the ladle 14, the molten metal in the ladle 14 is drawn into the lower tank 13 side and rises through the molten metal passage of the rising pipe (inside the circulating pipe 1a and the immersion pipe 11), and then flows into the descending pipe (circulating pipe 1b and immersion pipe Descending the molten metal passage in tube 11) back to ladle 14 for reflux. During the circulation process, the molten metal is degassed and discharged to the outside of the vacuum degassing device M.

When performing degassing in the vacuum degassing apparatus M as described above, a higher pressure is applied to the inside of the ascending pipe and the descending pipe (the side closer to the other pipe, the side closer to the center of the lower tank 13) than the outside. However, in the reflux pipes 1a and 1b, the inner portions are thicker than the outer portions. That is, in the circulation pipes 1a and 1b, the radial thickness of the upper first refractory bricks 3a, the upper second refractory bricks 3b, and the lower first refractory bricks 3α located inside the circulation pipes 1a and 1b is located outside the circulation pipe 1a. It is thicker than the radial thickness of the upper fifth refractory brick 3e and the lower first refractory brick 3ε. Therefore, even if the inner portion continues to be subjected to a higher pressure than the outer portion, the reflux pipes 1a and 1b can be used for a long period of time because the allowable amount of erosion of the inner portion is large. can be done.

On the other hand, in the reflux pipes 1a and 1b, the outer portions are thinner than the other portions (the inner portion and the intermediate portion). That is, the radial thicknesses of the upper fifth refractory bricks 3e and the lower fifth refractory bricks 3ε positioned on the outside are equal to the upper first refractory bricks 3a and the upper second refractory bricks 3b, and the lower first refractory bricks 3α and , upper third refractory bricks 3c and lower third refractory bricks 3γ, upper fourth refractory bricks 3d and lower fourth refractory bricks 3δ, and the like. Therefore, since the circulation pipes 1a and 1b have substantially the same horizontal cross-sectional area of the molten metal passage as that of a conventional constant-thickness cylindrical circulation pipe, efficient degassing can be achieved without causing a change in circulation efficiency. can be implemented.

<Effect of circulating pipe>
As described above, the circulation pipe 1 is formed in a cylindrical shape by assembling a plurality of refractory bricks 3, 3 . The radial thickness of the upper first refractory brick 3a and the lower first refractory brick 3α is equal to the diameter of the upper fifth refractory brick 3e and the lower fifth refractory brick 3ε positioned on the opposite side (left side in FIG. 1). It is thicker than the thickness in the direction. Therefore, according to the reflux pipe 1, when two are installed side by side in the lower part of the vacuum degassing device M, the side on which the upper first refractory brick 3a and the lower first refractory brick 3α having a thick radial thickness are arranged is By installing it so as to be close to the other reflux pipe (that is, by installing it as shown in FIG. 8), excellent corrosion resistance and spalling resistance can be exhibited, so the service life is long and long. can be used over

In addition, the circulation pipe 1 is arranged such that the width in the circumferential direction of the upper first refractory brick 3a located on the one side (right side in FIG. 1) with respect to the central axis C is the upper side located on the opposite side (left side in FIG. 1). It is wider than the width of the fifth refractory brick 3e in the circumferential direction and has fewer vertical joints. Therefore, according to the reflux pipe 1, when installing it in the lower part of the vacuum degassing device M, it is installed so that the side on which the upper first refractory brick 3a is arranged is close to the other reflux pipe (that is, the figure 8), higher erosion resistance and spalling resistance can be exhibited, so that it can be used for a very long period of time.

In addition, in the circulation pipe 1, the height of the upper first refractory brick 3a located on the one side (right side in FIG. 1) with respect to the central axis C is the height of the upper side first refractory brick 3a located on the opposite side (left side in FIG. 1). It is lower than the height of the fifth refractory brick 3e. Therefore, according to the reflux pipe 1, the portion F located between the two reflux pipes 1a and 1b in the laying bricks 15 of the lower tank 13 of the vacuum degassing device M is replaced with the thick portion of the reflux pipe 1 ( A large amount of molten steel flows into the groove by forming a concave groove that matches the shape of the upper edge (stepped concave shape) of the installation portion of the upper first refractory brick 3a and the lower first refractory brick 3α. This prevents an increase in the flow velocity, and equalizes the flow velocity of the molten steel on the bottom surface of the lower tank 12, thereby improving the degassing speed and shortening the degassing time.

[Second embodiment]
<Structure of circulation pipe>
The circulation pipe 1' according to the second embodiment has the same structure as the circulation pipe 1 according to the first embodiment, but the material for forming the refractory bricks 3, 3... It is different from that of tube 1. That is, the upper first refractory bricks 3a and the upper second refractory bricks 3b, 3b of the reflux tube 1' according to the second embodiment are formed of magnesia-carbon refractories, and the reflux tube 1 according to the second embodiment ', the upper third refractory bricks 3c, 3c, the upper fourth refractory bricks 3d, 3d, . . . and the upper fifth refractory bricks 3e, 3e, . That is, the upper first refractory bricks 3a and the upper second refractory bricks 3b, 3b of the circulation pipe 1' according to the second embodiment are the upper third refractory bricks 3c, 3c, the upper fourth refractory bricks 3d, 3d, . It is formed of a refractory material having higher corrosion resistance than the upper fifth refractory bricks 3e, 3e.

Moreover, the lower first refractory bricks 3α, 3α, . The third refractory bricks 3γ, 3γ, the fourth lower refractory bricks 3δ, 3δ . . . and the fifth lower refractory bricks 3ε, 3ε . That is, the lower first refractory bricks 3α, 3α of the circulation pipe 1' according to the second embodiment are the lower third refractory bricks 3γ, 3γ, the lower fourth refractory bricks 3δ, 3δ, and the lower side. It is formed of a refractory material having higher corrosion resistance than the fifth refractory bricks 3ε, 3ε .

<Effect of circulating pipe>
As described above, the circulation tube 1' according to the second embodiment includes the upper first refractory brick 3a and the upper second refractory brick 3b located on one side (right side in FIG. 1) with respect to the central axis C, and the lower The side first refractory brick 3α is a refractory with higher corrosion resistance than the forming material (magnesia-chromium refractory) of the upper fifth refractory brick 3e and the lower fifth refractory brick 3ε located on the opposite side (left side in FIG. 1). It is made of material (magnesia-carbon refractory). Therefore, according to the reflux pipe 1' according to the second embodiment, when it is installed in the lower part of the vacuum degassing device M, the side on which the upper first refractory brick 3a is arranged is installed so as to be close to the other reflux pipe. By doing so (that is, by installing as shown in FIG. 8), very high corrosion resistance and spalling resistance can be exhibited, so that it can be used for a very long period of time.

<Example of changing circulation pipe>
The circulation tube according to the present invention is not limited to the above-described embodiment, and the configuration such as the material, shape, size, etc. of the refractory bricks and steel wheels can be changed within the scope of the present invention. can be changed as appropriate. In addition, the configuration of the vacuum degassing device in which the reflux tube according to the present invention is installed and the configuration of the immersion tube connected to the lower end of the reflux tube according to the present invention are not limited to the aspects of the above-described embodiment, and if necessary, It can be changed as appropriate.

For example, the circulation tube according to the present invention is not limited to a cylindrical assembly of 62 refractory bricks (fixed with mortar) as in the above embodiment, and the number of refractory bricks as a constituent unit is You can change it if you want. Further, in the circulation tube according to the present invention, as in the above-described embodiment, the refractory bricks that are relatively thick in the radial direction are made of magnesia carbonaceous refractories, and the refractory bricks that are relatively thin in the radial direction are made of magnesia. The material of the refractory brick, which is a structural unit, is not limited to the chromium refractory material, and can be appropriately changed as necessary. Furthermore, the reflux tube according to the present invention is not limited to having a structure in which two cylindrical bodies are stacked vertically as in the above embodiment, but a structure in which three or more cylindrical bodies are stacked vertically. or the like may be used.

Further, the circulation pipe according to the present invention may be a plurality of refractory bricks fixed with mortar, a plurality of refractory bricks fixed with a bond, or a plurality of bricks may be fixed with mortar or bond. It is also possible to use an open joint type that maintains the assembled shape by restraining it with a band iron. In addition, the circulation pipe according to the present invention is not limited to the assembly of a plurality of refractory bricks having a trapezoidal horizontal cross section as in the above-described embodiment, but as shown in FIG. It is also possible to change it to one in which refractory bricks or the like are assembled.

In addition, in the circulation pipe according to the present invention, as in the above embodiment, the circumferential width of the refractory bricks (the first upper refractory brick and the first lower refractory brick) positioned on one side with respect to the central axis is The refractory bricks are not limited to those wider than the refractory bricks located on the opposite side (the upper fifth refractory brick and the lower fifth refractory brick), but the refractory bricks having the same circumferential width are assembled. Anything is fine. Furthermore, in the circulation tube according to the present invention, as in the above embodiment, the refractory bricks (the first upper refractory brick and the first lower refractory brick) positioned on one side with respect to the central axis are placed on the opposite side. It is not limited to the one that is lower than the positioned refractory bricks (the upper fifth refractory brick and the lower fifth refractory brick), and it is also possible to assemble refractory bricks of the same height.

INDUSTRIAL APPLICABILITY The reflux tube according to the present invention exhibits the excellent effects as described above, and can be suitably used as a member installed in the lower tank of a vacuum degassing apparatus to function as an ascending tube or a descending tube.

1, 1'... Circulation pipe 2a... Upper cylindrical body 2b... Upper cylindrical body 3 (3a to 3e and 3α to 3ε)... Refractory bricks 5... Iron wheel 11... Dip pipe 12... Upper tank 13 Lower tank 14 Ladle 15 Laying brick 16 Steel shell M Vacuum degassing device

Claims (3)

At the bottom of a vacuum degassing device that degasses and circulates the molten metal, two reflux tubes are installed side by side in a state of being connected to the immersion tube and used as an ascending pipe or a descending pipe,
It is formed in a cylindrical shape by assembling a plurality of refractory bricks in a circumferential shape,
A circulation pipe characterized in that the radial thickness of the refractory bricks positioned inside when installed is greater than the radial thickness of the refractory bricks positioned outside when installed . 2. The circulation pipe according to claim 1, wherein the circumferential width of the refractory bricks positioned inside when installed is wider than the circumferential width of the refractory bricks positioned outside when installed . 3. The circulation pipe according to claim 1 or 2, wherein the refractory bricks positioned inside when installed are made of a refractory material having higher corrosion resistance than the refractory bricks positioned outside when installed .

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