Feed-effluent heat exchanger for propane dehydrogenation unit

Abstract

The utility model provides a kind of inlet and outlet heat exchanger for propane dehydrogenation device, including tube pass inlet, upper tube box, shell, lower tube box, tube pass outlet and heat exchange tube bundle, upper tube box is connected with tube pass inlet by connecting pipe, connecting pipe has annular groove and radial flange, annular groove is opened towards the end of upper tube box;Radial flange is formed in the outside of annular groove, it is bent and extends towards the direction of upper head close to upper tube box, the end surface of radial flange and the corresponding end surface of upper head are attached, and are fixedly connected by ring weld seam.The radial flange is set and makes it with upper head adopt end surface attachment butt welding structure, replace traditional corner joint weld seam, this improvement makes weld quality more optimal, more easily realizes nondestructive testing, fundamentally guarantees the connection strength and stability.Meanwhile, the annular groove set on connecting pipe can effectively release welding residual stress, significantly improves the fatigue resistance and fracture resistance of joint under high temperature working condition.

Description

Technical Field

[0001] This utility model belongs to the technical field of propane dehydrogenation equipment, specifically relating to a feed heat exchanger for a propane dehydrogenation equipment. Background Technology

[0002] In propane dehydrogenation (PDH) units, the feed and discharge heat exchangers are the core equipment for energy recovery, and their tube-side inlets need to withstand high-temperature process media of 500-700°C for extended periods. Currently, the connection between the high-temperature end of these heat exchangers and the shell head generally uses a corner joint type D weld. However, this traditional connection method presents serious reliability and safety issues under high-temperature conditions, especially under harsh conditions with temperature fluctuations, mainly in the following aspects: First, there is the issue of extreme stress concentration and thermal stress: the D-type weld structure itself has geometrical discontinuities, leading to extreme stress concentration in this area. Under high-temperature conditions, thermal stress caused by differences in material thermal expansion coefficients and structural constraints becomes the dominant load. If there are start-up / shutdown equipment or changes in medium temperature at the high-temperature end, this stress concentration area will be subjected to alternating tensile-compressive thermal stress, making it highly susceptible to fatigue crack initiation in a short period. Simultaneously, high temperatures significantly accelerate crack propagation: on the one hand, the diffusion capacity of metal atoms is enhanced, making the crack tip more prone to creep cracking under stress; on the other hand, the high-temperature environment also increases the risk of stress corrosion cracking.

[0003] Secondly, there are inherent defects in the load-bearing capacity of welds and their weakening at high temperatures: The load-bearing capacity of Class D welds mainly depends on the "throat height" of the fillet weld, but it does not participate in the main pressure bearing of the cylinder or head. At high temperatures, the material in the weld area undergoes performance degradation (such as decreased strength and reduced plasticity), further weakening its load-bearing capacity. More importantly, Class D welds are usually located in the narrow space at the corner of the pipe end and head, making welding difficult and prone to initial defects such as incomplete penetration, slag inclusions, porosity, and undercut. At room temperature, these defects may be masked by the structural design strength redundancy, but under long-term high-temperature conditions, these defects will evolve into sharp "stress concentration sources." For example, the root of incomplete penetration will form micro-cracks, which may cause crevice corrosion after the high-temperature medium penetrates. At the same time, the edge of the defect will accelerate creep under continuous high stress, causing micro-defects to rapidly expand into macro-cracks, ultimately leading to failure.

[0004] Third, non-destructive testing has blind spots, making it difficult to detect potential safety hazards: Due to the complex structure and limited space of this type D weld, conventional non-destructive testing methods such as penetrant testing (PT) and ultrasonic testing (UT) cannot achieve effective coverage. UT probes are difficult to fit well with corners and curved surfaces, resulting in the sound beam being unable to effectively detect key stress concentration areas such as the inside of the weld toe and the root of the weld; PT testing agents are also difficult to penetrate into the tiny incomplete weld gaps. Therefore, internal microcracks existing during the manufacturing stage or early fatigue cracks that initiate during use are easily missed, creating potential safety hazards.

[0005] In summary, the existing high-temperature end connection structure of feed and discharge heat exchangers using type D welds has become a weak link and bottleneck for long-term safe operation due to its inherent stress concentration characteristics, high sensitivity to welding defects, and significant reduction in load-bearing capacity under high temperatures and alternating loads. Therefore, there is an urgent need in this field for a feed and discharge heat exchanger with better operational safety and reliability under high-temperature conditions. Utility Model Content

[0006] The purpose of this invention is to provide a novel feed heat exchanger for a propane dehydrogenation unit, which has better operational safety and reliability under high-temperature conditions.

[0007] To achieve the above objectives, the technical solution adopted by this utility model is as follows: This utility model provides a feed heat exchanger for a propane dehydrogenation unit, comprising a tube-side inlet, an upper tube box, a shell, a lower tube box, and a tube-side outlet arranged sequentially, and a heat exchange tube bundle placed within the shell. The upper tube box and the lower tube box are respectively connected to the tube-side inlet and the tube-side outlet. The upper tube box includes an upper end cap and an upper tube box cylinder. The upper end cap is connected to the tube-side inlet via a connecting pipe. One end of the connecting pipe is fixedly connected to the tube-side inlet, and the other end has an annular groove and a radial flange. The annular groove opens towards the end of the upper tube box. The radial flange is formed on the outside of the annular groove and bends and extends towards the upper end cap. The end face of the radial flange fits against the corresponding end face of the upper end cap and is fixedly connected by a circumferential weld.

[0008] In some embodiments, the inner wall of the annular groove extends axially toward the upper tube box and beyond the end face of the radial flange.

[0009] In some embodiments, the cross-section of the annular groove is U-shaped. Preferably, the bottom wall of the annular groove smoothly transitions to the inner and outer side walls via circular arcs.

[0010] In some embodiments, the circumferential weld is a full penetration weld.

[0011] In some embodiments, the housing is a segmented structure comprising an upper housing and a lower housing, which are detachably connected by a flange located between the shell-side outlet and the shell-side inlet.

[0012] In some embodiments, the feed heat exchanger further includes a skirt-type support ring connected to the outside of the housing and a pad disposed between the end of the skirt-type support ring and the housing.

[0013] In some embodiments, the feed heat exchanger further includes an anti-impact distribution plate disposed within the upper tube box, the anti-impact distribution plate being located on the feed side of the heat exchange tube bundle, and having a plurality of through holes distributed thereon. Preferably, the diameter of the through holes is 16mm to 25mm.

[0014] In some embodiments, the heat exchange tube bundle includes a tube bundle body and an upper tube sheet, wherein the tube bundle body and the upper tube sheet are connected by a fully penetrated weld through an inner hole weld.

[0015] Due to the application of the above technical solution, this utility model has the following advantages compared with the prior art: This invention significantly improves the reliability, safety, and lifespan of heat exchanger tube-box connections through structural innovation. Specifically, by incorporating a radial flange and employing a butt-welded structure with end-face contact between the radial flange and the upper end cap, replacing the traditional fillet weld, the weld quality is significantly improved, making non-destructive testing easier and fundamentally ensuring connection strength and stability. Simultaneously, the annular groove design on the connecting pipe effectively releases residual welding stress, significantly enhancing the joint's fatigue and fracture resistance under high-temperature conditions. Attached Figure Description

[0016] Figure 1 A schematic diagram of the heat exchanger provided in Example 1; Figure 2 for Figure 1 An enlarged schematic diagram of part A in the middle; Figure 3 This is a schematic diagram of the welded joint structure between the tube bundle and the upper tube sheet provided in Example 1; Among them, 1. Tube-side inlet; 2. Connecting pipe; 21. Radial flange; 22. Annular groove; 23. Inner wall; 24. Outer wall; 25. Bottom wall; 3. Upper tube box; 31. Upper head; 32. Upper tube box shell; 4. Shell; 41. Upper shell; 42. Lower shell; 43. Flange; 44. Shell-side inlet; 45. Shell-side outlet; 5. Lower tube box; 51. Manhole; 6. Tube-side outlet; 71. Tube bundle; 72. Upper tube sheet; 73. Baffle; 8. Skirt support ring; 9. Anti-impact distribution plate. Detailed Implementation

[0017] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0018] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0019] In the description of the embodiments of this utility model, it should be understood that the terms "inner" and "outer" indicate the orientation or positional relationship defined by the distance relative to the center of the device or component. Inner is the position closer to the center of the device or component, and outer is the position farther away from the center of the device or component. They are only used to facilitate the description of the embodiments of this utility model and to simplify the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this utility model.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] The following disclosure provides many different implementations or examples for different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the embodiments of the present invention. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of the present invention; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed. Example 1

[0022] A feed heat exchanger for a propane dehydrogenation unit, such as Figure 1As shown, it includes a tube-side inlet 1, an upper tube box 3, a shell 4, a lower tube box 5, and a tube-side outlet 6 arranged sequentially, as well as a heat exchange tube bundle placed within the shell 4. The upper tube box 3 and lower tube box 5 are respectively connected to the tube-side inlet 1 and the tube-side outlet 6. The upper tube box 3 includes an upper end cap 31 and an upper tube box cylinder 32. The upper end cap 31 is connected to the tube-side inlet 1 via a connecting pipe 2. One end of the connecting pipe 2 is fixedly connected to the tube-side inlet 1, and the fixed connection method includes, but is not limited to, integral molding or welding; the other end has an annular groove 22 and a radial flange 21. Figure 2 As shown, the annular groove 22 opens at one end facing the upper tube box 3; the radial flange 21 is formed on the outside of the annular groove 22, which bends and extends toward the upper end cap 31, and its end face fits with the corresponding end face of the upper end cap 31, and is fixedly connected by a circumferential weld.

[0023] Typically, the weld between the upper end cap 31 and the connecting pipe 2 at the tube-side inlet 1 is a fillet weld (Class D weld). Located at a corner where the geometry abruptly changes, this weld inherently suffers from severe stress concentration. Furthermore, the PDH reaction temperature reaches approximately 600℃, meaning that the tube-side inlet 1 and the upper end cap 31 will be subjected to extremely high temperatures for extended periods, further accelerating weld crack propagation. Once a problem occurs, existing conventional inspection methods are insufficient to detect it promptly.

[0024] The radial flange 21 is designed so that its end face is welded to the corresponding end face of the upper head 31. Compared to corner joints, this joint method ensures better weld quality, connection strength, and sealing, and facilitates non-destructive testing. Furthermore, the annular groove 22 inside the radial flange 21 helps release welding stress, reduces stress concentration, and improves fatigue and fracture resistance. Simultaneously, the annular groove 22 provides a small amount of space for thermal deformation, preventing stress cracking of the weld in the connecting pipe 2 caused by excessive stress in the rigid structure. Further, the inner wall 23 of the annular groove 22 extends axially toward the upper pipe box 3 and beyond the end face of the radial flange 21. This evenly distributes the load, buffers the direct thermal impact of high-temperature gas on the radial flange 21 and the upper head 31, and extends the service life of the equipment. Preferably, the cross-section of the annular groove 22 is U-shaped, with its bottom wall 25 smoothly transitioning to the inner wall 23 and outer wall 24 via an arc. The connecting pipe 2 is a forged connecting pipe. The circumferential weld is a full penetration weld, for example, a Class A weld.

[0025] The shell 4 is a segmented structure, comprising an upper shell 41 and a lower shell 42. The upper shell 41 and the lower shell 42 are detachably connected by a flange 43, which is located between the shell-side outlet 45 and the shell-side inlet. The upper shell 41 is provided with the shell-side outlet 45, and the lower shell 42 is provided with the shell-side inlet 44.

[0026] The design life of the tube bundle is generally 3 to 5 years, while the design life of the shell is 15 to 20 years. In actual operation, it's impossible to directly remove the tube bundle from the shell 4 for cleaning its outer surface or to replace it entirely. If tube bundle blockage, tube sheet corrosion, or perforation occurs, the entire heat exchanger must be replaced or destructive repairs (such as cutting the shell 4) must be performed, resulting in extremely high maintenance costs and significantly shortening the equipment's actual lifespan. The segmented shell 4 design allows for direct removal of the flange 43 between the upper shell 41 and lower shell 42 to replace the tube bundle 71, greatly improving the utilization efficiency of the shell 4. Furthermore, from a maintenance and repair perspective, if shell-side blockage or severe scaling occurs during operation, the flange 43 can be opened, and the shell 4 can be removed for cleaning of the tube bundle's outer wall and the shell 4 itself, further extending the equipment's service life.

[0027] A skirt-type support ring 8 is connected to the outer side of the upper part of the lower shell 4, specifically the middle part of the shell 4. Existing lugs (such as type A and type B lugs) are welded to the shell 4 at 2-4 "points," concentrating the support force at the weld between the lug and the shell 4. If the equipment has a large diameter (e.g., ≥1.2m), heavy weight (e.g., ≥5t), or internal media load, this can easily lead to localized dents in the shell 4, weld cracking, or even equipment axis misalignment. The skirt-type support ring 8 is welded to the shell 4 in a full circumferential fit, extending the support force from "points" to an "annular surface," significantly dispersing the load and preventing localized overload on the shell 4. This is particularly suitable for thin-walled equipment with a thin shell 4 (such as stainless steel heat exchangers). Furthermore, a pad is placed between the end of the skirt-type support ring 8 and the shell 4 to further increase connection stability.

[0028] The heat exchanger tube bundle includes a tube bundle body 71, an upper tube sheet 72, baffles 73, and a lower tube sheet. The specific structure can be found in existing technologies. As an example, the upper tube sheet 72 is welded to the upper tube box shell 32, and the lower tube sheet is welded to the lower tube box 5. One end of the tube bundle body 71 is connected to the upper tube sheet 72, and the other end is connected to the lower tube sheet. Multiple baffles 73 are arranged axially, perpendicular to the tube bundle body 71, and can be fixed by structures such as tie rods or spacers. Unlike existing technologies, such as… Figure 3As shown, the tube bundle body 71 and the upper tube sheet 72 are connected by a fully penetrated weld through an internal hole weld. This improvement has at least the following advantages: First, the quality is significantly improved. The butt weld formed by the internal hole weld fundamentally eliminates the sharp and right-angle abrupt changes of traditional fillet welds, greatly reducing the stress concentration factor (Kt) to 1.2~1.5, effectively solving the problems of high-temperature stress concentration and creep cracking. Second, the inspection capability is fundamentally transformed. The new structure makes it possible to use RT (radiometry) for quality assessment, completely eliminating the root blind zone present in traditional fillet weld PT inspection and rod anode RT, achieving non-destructive and precise control of weld quality. Third, the service life is greatly extended. Since the weld is located on the back of the tube sheet, it avoids direct scouring by the high-temperature inlet medium, thereby greatly reducing the wear and breakage risk of the tube head and improving the service life of the weld under harsh working conditions. The internal hole welding process can use self-fusion or filler wire. The inner diameter of the tube bundle body 71 is not less than 12mm, which facilitates the insertion of the welding torch into the tube sheet for welding.

[0029] The lower pipe box 5 is equipped with a manhole 51 for easy maintenance. Its specific structure can be found in existing technology in this field.

[0030] The feed heat exchanger also includes an anti-impact distribution plate 9 located within the upper tube box shell 32. The anti-impact distribution plate 9 is situated on the feed side of the heat exchange tube bundle and has several through holes distributed on it. Preferably, the diameter of the through holes is 16mm~25mm. The anti-impact distribution plate 9 not only prevents high-temperature gas from directly impacting and damaging the tube sheet, protecting the tube sheet surface, but also optimizes the flow field through forced flow guidance and uniform flow distribution, solving the problem of uneven fluid distribution leading to inefficient equipment performance, improving heat exchange efficiency, and simultaneously preventing localized overheating, thus protecting the stability of the equipment and process.

[0031] The feed heat exchanger is vertical, and its working process is as follows: High-temperature gas enters the heat exchange tube bundle from the tube side inlet 1 through the anti-impact distribution plate 9. The cooling medium flows through the shell side, enters the shell 4 from the shell side inlet 44, and exchanges heat with the high-temperature gas inside the tube through the outer wall of the tube bundle body 71 to reduce the temperature of the high-temperature gas. Then it flows out from the shell side outlet 45, and the high-temperature gas in the tube side flows out from the tube side outlet 6. The fluid flow mode is counter-current, which can improve the heat transfer effect and reduce the heat exchange area requirement.

[0032] The present utility model has been described in detail above, with the aim of enabling those skilled in the art to understand its contents and implement it. However, this description should not be construed as limiting the scope of protection of the present utility model. All equivalent changes or modifications made in accordance with the spirit and essence of the present utility model should be included within the scope of protection of the present utility model.

Claims

1. A feed heat exchanger for a propane dehydrogenation unit, comprising a tube-side inlet (1), an upper tube box (3), a shell (4), a lower tube box (5), and a tube-side outlet (6) arranged sequentially, and a heat exchange tube bundle placed within the shell (4), wherein the upper tube box (3) and the lower tube box (5) are respectively connected to the tube-side inlet (1) and the tube-side outlet (6), the upper tube box (3) comprising an upper end cap (31) and an upper tube box cylinder (32), the upper end cap (31) being connected to the tube-side inlet (1) via a connecting pipe (2), characterized in that: One end of the connecting pipe (2) is fixedly connected to the pipe inlet (1), and the other end has an annular groove (22) and a radial flange (21). The annular groove (22) opens towards one end of the upper pipe box (3). The radial flange (21) is formed on the outside of the annular groove (22) and bends and extends toward the upper end cap (31). The end face of the radial flange (21) fits against the corresponding end face of the upper end cap (31) and is fixedly connected by a circumferential weld.

2. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 1, characterized in that: The inner wall (23) of the annular groove (22) extends axially toward the upper tube box (3) and beyond the end face of the radial flange (21).

3. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 1, characterized in that: The cross-section of the annular groove (22) is U-shaped.

4. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 3, characterized in that: The bottom wall (25) of the annular groove (22) is smoothly transitioned to the inner side wall (23) and the outer side wall (24) by a circular arc.

5. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 1, characterized in that: The circumferential weld is a full penetration weld.

6. The feed and discharge heat exchanger for a propane dehydrogenation unit according to any one of claims 1 to 5, characterized in that: The housing (4) is a segmented structure, comprising an upper housing (41) and a lower housing (42). The upper housing (41) and the lower housing (42) are detachably connected by a flange (43) located between the shell-side outlet (45) and the shell-side inlet (44).

7. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 1, characterized in that: The feed heat exchanger also includes a skirt support ring (8) connected to the outside of the shell (4) and a pad located between the end of the skirt support ring (8) and the shell (4).

8. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 1, characterized in that: The feed heat exchanger also includes an anti-impact distribution plate (9) located inside the upper tube box (32). The anti-impact distribution plate (9) is located on the feed side of the heat exchange tube bundle and has several through holes distributed on it.

9. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 8, characterized in that: The diameter of the through hole is 16mm~25mm.

10. The feed and discharge heat exchanger for a propane dehydrogenation unit according to claim 1, characterized in that: The heat exchange tube bundle includes a tube bundle body (71) and an upper tube sheet (72), and the tube bundle body (71) and the upper tube sheet (72) are connected by a fully penetrated weld through an inner hole weld.

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