Stub tubes and boilers

Abstract

To extend the life of a stub tube while restraining an increase in the diameter of the stub tube in comparison with a case where the internal diameter of the stub tube is equal to that of a heat transfer tube.SOLUTION: A boiler (1) comprises a header (7) inside which a heat medium flows, a stub tube (8) of which a base end part (8a) is connected to the header (7), and a heat transfer tube (9) connected to a tip part (8b) of the stub tube (8). The thickness of the stub tube (8) is larger than that of the heat transfer tube (9). The external diameter of the stub tube (8) is larger than that of the heat transfer tube (9). The internal diameter of the stub tube (8) is smaller than that of the heat transfer tube (9).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a stub pipe that connects a pipe header and a heat transfer pipe, and a boiler provided with the stub pipe.

Background Art

[0002] In boilers for thermal power generation, industrial boilers, boilers for waste incineration power generation, etc., as a technique for arranging heat transfer pipes in a boiler to superheat exhaust gas or recover heat from the exhaust gas, the technique described in Patent Document 1 is known.

[0003] In Patent Document 1 (Japanese Patent No. 4792355), a large number of pipe headers (2) are welded between a superheater inlet pipe header manifold (1a) and a superheater outlet pipe header manifold (1b), and a stub pipe (3) and a transition piece (4) are provided on the pipe header (2). A configuration in which a leg tube (5), which is the main body of the heat transfer pipe, is connected via is described. The outer diameter of each member is the largest for the manifolds (1a, 1b), the second largest for the pipe header (2), the second largest for the stub pipe (3) and the transition piece (4), and the smallest for the leg tube (5). Further, the inner diameters of the stub pipe (3), the transition piece (4), and the leg tube (5) are the same, and as a result, the wall thickness of the stub pipe (3) and the transition piece (4) is thicker than the wall thickness of the leg tube (5).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a heat exchanger like the one described in Patent Document 1, steam, acting as a heat transfer medium, passes through the manifold (1a, 1b), header (2), stub tube (3), transition piece (4), and leg tube (5). In recent years, the above components have been subjected to higher temperatures (600°C or higher) to increase boiler efficiency, and highly durable materials are used for the header and stub tube. Examples of highly durable materials include steel containing W, Mo, Nb, and V, and containing approximately 9-12% Cr, known as 9Cr-12Cr steel.

[0006] However, in reality, it has become clear that stub pipes made of 9Cr steel and other materials often break down or fail in a shorter time than their expected lifespan. To improve the durability of stub pipes, it is common practice to increase the wall thickness of the pipes. However, increasing the wall thickness of stub pipes increases the pipe diameter and reduces the spacing between stub pipes. When the spacing between stub pipes is reduced, the space available for welding during installation or replacement becomes smaller. Consequently, welding work becomes more difficult, and welding robots may not be usable.

[0007] The present invention aims to address the technical challenge of extending the lifespan of stubble tubes while suppressing an increase in the diameter of the stubble tubes compared to the case where the inner diameter of the stubble tubes is the same as that of the heat transfer tubes. [Means for solving the problem]

[0008] The above-mentioned problem of the present invention can be achieved by adopting the following configuration. The boiler of the invention described in claim 1 is A header through which a heat transfer fluid flows, A stub pipe that branches off from the aforementioned header and whose base end is connected to the aforementioned header, A heat transfer tube is connected to the tip of the aforementioned stub tube, through which a heat transfer medium from the header flows, It has, The wall thickness of the aforementioned stub tube is thicker than that of the aforementioned heat transfer tube. The outer diameter of the stub tube is larger than that of the heat transfer tube. The inner diameter of the stub tube is smaller than that of the heat transfer tube. The stub tube has a base end made of the same material as the header and a tip end made of the same material as the heat transfer tube. The material of the base end and the material of the tip end are different. the law of nature, At the end of the tip on the heat transfer tube side, the inner diameter and outer diameter of the stub tube are the same as the inner diameter and outer diameter of the heat transfer tube. The thickness of the base end and the tip end is thicker than that of the heat transfer tube. The outer diameter of the base end and the tip end is larger than that of the heat transfer tube. The inner diameters of the base end and the tip end are smaller than those of the heat transfer tube. It is characterized by the following:

[0010] Claim 2 The invention described in the claim 1 In the boiler described, The inner diameter of the tip portion decreases as you move from the end on the heat transfer tube side towards the header side. It is characterized by the following:

[0012] To solve the aforementioned technical problems, Claim 3 The stub tube of the invention described above is A stub tube that connects a header through which a heat transfer medium flows to a heat transfer tube, It has a thicker wall than the aforementioned heat transfer tube, a larger outer diameter than the aforementioned heat transfer tube, and a smaller inner diameter than the aforementioned heat transfer tube. It has a base end made of the same material as the header and connected to the header, and a tip end made of the same material as the heat transfer tube and connected to the heat transfer tube, The material of the base end and the material of the tip end are different. the law of nature, At the end of the tip on the heat transfer tube side, the inner diameter and outer diameter of the stub tube are the same as the inner diameter and outer diameter of the heat transfer tube. The thickness of the base end and the tip end is thicker than that of the heat transfer tube. The outer diameter of the base end and the tip end is larger than that of the heat transfer tube. The inner diameters of the base end and the tip end are smaller than those of the heat transfer tube. It is characterized by the following: [Effects of the Invention]

[0013] According to the invention described in claims 1 and 5, the life of the stub tube can be prolonged while suppressing an increase in the large diameter of the stub tube as compared with the case where the inner diameter of the stub tube is the same as that of the heat transfer tube. According to the invention described in claim 2, in addition to the effects of the invention described in claim 1, breakage of the connection portion due to the difference in the coefficient of thermal expansion between the base end portion and the tube alignment or between the tip end portion and the heat transfer tube is suppressed. According to the invention described in claim 3, in addition to the effects of the invention described in claim 1 or 2, generation of vortices and turbulent flows in the flowing heat medium is suppressed as compared with the case where the inner diameter of the tip end portion changes in a stepped shape, and a decrease in heat exchange efficiency is suppressed. According to the invention described in claim 4, in addition to the effects of the invention described in any one of claims 1 to 3, non-uniformity of the flow rate as a whole of the plurality of heat transfer tubes is suppressed as compared with the case where the inner diameter of the stub tube is not set according to the flow resistance.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic explanatory view of a boiler according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of a main portion of a tube alignment portion in the heat exchanger of Example 1. [Figure 3] FIG. 3 is a cross-sectional explanatory view of a portion of the stub tube.

Mode for Carrying Out the Invention

[0015] Next, examples as specific examples of embodiments of the present invention will be described while referring to the drawings, but the present invention is not limited to the following examples. In the following description using the drawings, illustrations other than the members necessary for the description are omitted as appropriate for easy understanding.

Examples

[0016] FIG. 1 is a schematic explanatory view of a boiler according to an embodiment of the present invention. In Figure 1, the boiler 1 of Embodiment 1 of the present invention has a furnace 3 on which a plurality of burners 2 are installed. Superheaters 4 (4a-4c), as an example of a heat exchanger, are arranged in the front part 3a of the boiler above the furnace 3 and in the rear part 3b of the boiler behind the front part 3a of the tubes.

[0017] Figure 2 is an enlarged view of the main part of the header section in the heat exchanger of Example 1. In Figure 1, the superheaters 4 are connected by a manifold 6 made of large-diameter pipes, similar to Patent Document 1, and multiple medium-diameter headers 7 branch off from the manifold 6. In Figure 2, the base ends of stub tubes 8 are connected to the headers 7, and heat transfer tubes 9 are connected to the ends of the stub tubes 8. Therefore, in the superheater 4, steam, as an example of a heat transfer medium, flows through the manifold 6, headers 7, stub tubes 8, and heat transfer tubes 9, and heat exchange takes place in the heat transfer tubes 9.

[0018] Figure 3 is a cross-sectional diagram illustrating the stubble section. In Figure 3, the stub tube 8 of Embodiment 1 has a base end portion 8a on the header 7 side and a tip portion 8b on the heat transfer tube 9 side. The base end portion 8a and the tip portion 8b are connected by a welded joint 11. In Example 1, the base end portion 8a is made of the same material as the header 7, and is made of 9Cr steel as an example. Also in Example 1, the tip portion 8b is made of the same material as the heat transfer tube 9, and is made of stainless steel (SUS304) as an example.

[0019] A diameter reduction section 12 is provided at the base end side (towards the header 7) of the base end 8a, and the diameter reduction section 12 is formed so that its outer diameter decreases as it approaches the base end. In other words, the diameter of the diameter reduction section 12 is narrowed. The inner diameter of the base end 8a is formed to be the same from the tip end 8b side to the header 7 side and does not narrow. As a result, the wall thickness in the diameter reduction section 12 becomes thinner as it approaches the header 7 side. The stub tube 8 is welded to the header 7 at this diameter reduction section 12. In this specification and claims, the term "identical" is used to include cases where there are unavoidable practical variations, such as manufacturing tolerances or design tolerances.

[0020] The tip portion 8b, in the part connected to the base portion 8a, has the same inner and outer diameters as the base portion 8a. The tip side (heat transfer tube side) of the tip portion 8b has an inner diameter reduction portion 13 formed in which the inner diameter decreases as it moves from the heat transfer tube 9 side end 13a towards the header 7 side. In Embodiment 1, the outer diameter of the inner diameter reduction portion 13 is formed to increase as it moves from the heat transfer tube 9 side end 13a towards the header 7 side. Therefore, at the heat transfer tube 9 side end 13a of the tip portion 8b, the inner diameter reduction portion 13 is formed so that the inner and outer diameters of the stub tube 8 are the same as the inner and outer diameters of the heat transfer tube 9. Therefore, except for the portion of the inner diameter reduction section 13 that connects to the heat transfer tube 9, the stub tube 8 of Example 1 is formed to have a larger outer diameter, thicker walls, and a smaller inner diameter overall compared to the heat transfer tube 9.

[0021] In Example 1, the inner diameter of the stub tube 8 is set according to the flow resistance of the steam flowing through the heat transfer tube 9. That is, the longer the heat transfer tube 9, the greater the flow resistance, and the more bends the heat transfer tube 9 has or the greater the angle of the bends, the greater the flow resistance. In addition, the flow resistance changes depending on the material of the heat transfer tube 9 and whether or not the inner surface is processed. Therefore, in Example 1, according to the flow resistance of each heat transfer tube 9, the inner diameter of the stub tube 8 is increased as the flow resistance increases, and the inner diameter of the stub tube is decreased as the flow resistance decreases.

[0022] (Effect of Example 1) In the boiler 1 of Embodiment 1, which has the above configuration, the stub tubes 8 of the superheater 4 have a larger outer diameter but a smaller inner diameter compared to the heat transfer tubes 9. Here, in order to improve the durability of the stub tubes 8, if the wall thickness of the stub tubes is increased while keeping the inner diameter of the stub tubes the same as that of the heat transfer tubes, as in Patent Document 1, the outer diameter of the stub tubes will increase. Consequently, the spacing between the stub tubes becomes narrower, making it difficult to secure space for welding.

[0023] In contrast, in Example 1, the inner diameter of the stub tube 8 is also smaller, so compared to the case where the inner diameter of the stub tube is the same as the inner diameter of the heat transfer tube, it is possible to suppress the increase in outer diameter even when the wall thickness is the same. Therefore, in Example 1, the increase in the outer diameter of the stub tube 8 is suppressed, making it easier to secure welding space. Consequently, it becomes easier to use a welding robot. If a welding robot can be used, manufacturing costs and maintenance costs will be more favorable, and the construction period can be shortened. In addition, in the stub tube 8 of Example 1, it is possible to increase the wall thickness compared to when the inner diameter is not reduced, which improves the lifespan and durability of the stub tube 8.

[0024] Furthermore, while reducing the inner diameter decreases the steam flow rate toward the heat transfer tube 9, it is possible to suppress the increase of insoluble solids (so-called scale) originating from the steam, thereby reducing the frequency of maintenance such as cleaning and replacement. Furthermore, in Example 1, the inner diameter reduction section 13 is formed in the shape of an inclined surface, and the inner diameter does not change in a stepped manner. If the inner diameter changes in a stepped manner, turbulence and vortices may be generated in the steam flowing in the stepped section, which may increase flow resistance or reduce the efficiency of heat exchange. In contrast, in Example 1, the inner diameter reduction section 13 is in the shape of an inclined surface, which suppresses the generation of turbulence and vortices, and thus suppresses the decrease in the efficiency of heat exchange.

[0025] Furthermore, in Example 1, the base portion 8a is made of the same material as the header 7, and the tip portion 8b is made of the same material as the heat transfer tube 9. If the base end portion 8a is made of a different material from the header 7, the coefficients of thermal expansion will differ between the base end portion 8a and the header 7, causing thermal ductility at the weld joint, which can lead to deterioration and breakage of the weld. In contrast, in Example 1, the base end portion 8a and the header 7 are made of the same material, thus suppressing breakage at the weld joint between the header 7 and the stub pipe 8. When the tip 8b and the heat transfer tube 9 are made of different materials, the coefficients of thermal expansion differ between the tip 8b and the heat transfer tube 9, making the welded portion between the tip 8b and the heat transfer tube 9 prone to breakage. In particular, the welded portion between the heat transfer tube 9 and the stub tube 8 has a thin wall thickness, and there is less welding material than in the thicker-walled portion, making it more susceptible to breakage. In contrast, in Example 1, the tip 8b and the heat transfer tube 9 are made of the same material, suppressing breakage due to thermal expansion.

[0026] Furthermore, in the stub tube 8 of Example 1, the connection between the base end 8a and the tip end 8b, which have a thicker wall than the heat transfer tube 9, is welded, making it less prone to damage. In addition, while the stub tube 8 and the header 7 have different outer diameters and different axial directions, the base end 8a and the tip end 8b have the same inner and outer diameters and the same axial direction. Therefore, even if an extrinsing force (external force) due to heat acts on them, the direction and magnitude of the external force are easier to predict and easier to address by welding between the base end 8a and the tip end 8b of the stub tube 8 in the example compared to the connection between the stub tube 8 and the header 7.

[0027] Furthermore, in Example 1, the inner diameter of the stub tube 8 is set to an inner diameter corresponding to the flow resistance of each heat transfer tube 9. Therefore, when the flow resistance of the heat transfer tube 9 is high (when the heat transfer medium does not flow easily), the inner diameter is increased to minimize the flow resistance in the stub tube 8, and when the flow resistance of the heat transfer tube 9 is low (when the heat transfer medium flows easily), the inner diameter is increased. smallThe stubble tube 8 restricts the flow of the heat transfer medium to some extent. In the case where the inner diameter of the stubble tube 8 is the same as that of the heat transfer tube 9, as in Patent Document 1, steam flows more easily through the stubble tube 8, but there was a problem that the overall efficiency of heat exchange in the heat transfer tube 9 became uneven due to the differences in the individual flow resistance of the heat transfer tubes 9. In contrast, in Embodiment 1, the inner diameter of the stubble tube 8 is set according to the flow resistance of the heat transfer tube 9, so that the flow of the heat transfer medium in the heat transfer tube 9 is balanced overall, and the efficiency of heat exchange is made more uniform. In addition, when the balance of the flow of the heat transfer medium is maintained in each of the heat transfer tubes 9, the probability-based failure of individual heat transfer tubes 9 deteriorating by chance is reduced compared to when there is variation, and the management of multiple superheaters 4 becomes easier.

[0028] Furthermore, in Example 1, the outer diameter reduction portion 12 on the header 7 side of the base end 8a has a narrowed shape. If the outer diameter remained large, the wall thickness at the end on the header 7 side would increase, and the surface area of ​​the surface 12a at the header 7 side would increase. When the surface area of ​​the surface 12a at the header 7 side increases, the heat transfer fluid can enter the minute gap between the surface 12a and the header 7, increasing the area over which the heat transfer fluid presses against the surface 12a. In other words, the force pushing the stub tube 8 away from the header 7 increases, making the welded portion more susceptible to damage. In contrast, when the outer diameter reduction portion 12 is narrowed as in Example 1, the surface area of ​​the surface 12a decreases, and the surface area pressed by the heat transfer fluid decreases. Therefore, the welded portion is less likely to be damaged.

[0029] (Example of change) Although embodiments and modifications of the present invention have been described in detail above, the present invention is not limited to the embodiments and modifications described above, and various modifications can be made within the scope of the gist of the present invention as described in the claims. Other modifications of the present invention (H01) to (H05) are exemplified below. (H01) In the above embodiment, a superheater 4 was used as an example of a heat exchanger, but the invention is not limited to this. For example, it can also be applied to heat exchangers such as reheaters and heat recovery units.

[0030] (H02) In the above embodiment, it is desirable that the combination of materials for the base end 8a and tip end 8b of the stub tube 8 and the materials for the header 7 and heat transfer tube 9 be the example combination, but different configurations are also possible. That is, it is possible to use different materials for all of the header 7, base end 8a, tip end 8b, and heat transfer tube 9, and it is also possible to use the same material for all of the header 7, stub tube 8, and heat transfer tube 9. Furthermore, it is also possible to use the same material for the header 7 and stub tube 8, or for the same material for the stub tube 8 and heat transfer tube 9.

[0031] (H03) In the above embodiment, the stub tube 8 is shown as having a base end 8a and a tip end 8b that are welded together as separate members, but it is not limited to this. It can also be made of one member or three or more members. (H04) In the above embodiment, it is desirable that the inner diameter changes in an inclined surface shape in the inner diameter reduction section 13, but it is also possible to configure it to change in a stepped or staircase shape. (H05) In the above embodiment, it is desirable to set the inner diameter of the stub tube 8 according to the flow resistance of the heat transfer tube 9, but it is not limited to this. For example, the inner diameter of the stub tube 8 can be the same for all heat transfer tubes 9, or several inner diameters of the stub tube 8 can be prepared and the stub tube 8 with the inner diameter closest to the most appropriate according to the flow resistance of the heat transfer tube 9 can be used. [Explanation of Symbols]

[0032] 1... Boiler, 7... Pipe assembly, 8... Stub tube, 8a...Proximal end, 8b...Tip part, 9… Heat transfer tube.

Claims

1. A header through which a heat transfer fluid flows, A stub pipe that branches off from the aforementioned header and whose base end is connected to the aforementioned header, A heat transfer tube is connected to the tip of the aforementioned stub tube, through which a heat transfer medium from the header flows, It has, The wall thickness of the aforementioned stub tube is thicker than that of the aforementioned heat transfer tube. The outer diameter of the stub tube is larger than that of the heat transfer tube. The inner diameter of the stub tube is smaller than that of the heat transfer tube. The stub tube has a base end made of the same material as the header and a tip end made of the same material as the heat transfer tube. The material of the base end and the material of the tip end are different, At the end of the tip on the heat transfer tube side, the inner diameter and outer diameter of the stub tube are the same as the inner diameter and outer diameter of the heat transfer tube. The thickness of the base end and the tip end is thicker than that of the heat transfer tube. The outer diameter of the base end and the tip end is larger than that of the heat transfer tube. The inner diameters of the base end and the tip end are smaller than those of the heat transfer tube. A boiler characterized by the following features.

2. The inner diameter of the tip portion decreases as you move from the end on the heat transfer tube side towards the header side. The boiler according to feature 1.

3. A stub tube that connects a header through which a heat transfer medium flows to a heat transfer tube, It has a thicker wall than the aforementioned heat transfer tube, a larger outer diameter than the aforementioned heat transfer tube, and a smaller inner diameter than the aforementioned heat transfer tube. It has a base end made of the same material as the header and connected to the header, and a tip end made of the same material as the heat transfer tube and connected to the heat transfer tube, The material of the base end and the material of the tip end are different, At the end of the tip on the heat transfer tube side, the inner diameter and outer diameter of the stub tube are the same as the inner diameter and outer diameter of the heat transfer tube. The thickness of the base end and the tip end is thicker than that of the heat transfer tube. The outer diameter of the base end and the tip end is larger than that of the heat transfer tube. The inner diameters of the base end and the tip end are smaller than those of the heat transfer tube. A stub tube characterized by the following features.

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