A double-pipe fixed-tube-sheet heat exchanger and a manufacturing method thereof

Abstract

The application discloses a double-shell fixed-tube-sheet heat exchanger and a manufacturing method thereof. The heat exchanger comprises a shell-side cylinder, a left tube plate and a right tube plate arranged at two ends of the shell-side cylinder, a heat exchange tube bundle connected with the left tube plate and the right tube plate, and a longitudinal partition plate arranged in the heat exchange tube bundle. The heat exchange tube bundle comprises a plurality of heat exchange tubes, and two ends of the heat exchange tubes are fixedly connected with the left tube plate and the right tube plate respectively. The longitudinal partition plate divides the space in the shell-side cylinder into two independent flow channels. The back surfaces of the left tube plate and the right tube plate are provided with positioning grooves, the end portions of the longitudinal partition plate are inserted into the positioning grooves, and the longitudinal partition plate is fixedly connected with the left tube plate and the right tube plate through a sealing welding layer. The inner wall of the shell-side cylinder is provided with a sealing groove, and the edge of the longitudinal partition plate is precisely matched with the sealing groove through finishing.

Description

Technical Field

[0001] This invention relates to a double-shell-pass fixed tubesheet heat exchanger and its manufacturing method, belonging to the field of heat exchanger technology. Background Technology

[0002] Fixed tube sheet heat exchangers are widely used heat exchange equipment in chemical, energy and other fields. Among them, the double shell-side fixed tube sheet heat exchanger divides the shell side into two independent flow channels by setting longitudinal baffles in the shell side, allowing the shell-side fluid to flow back and forth, thereby improving the flow rate and heat exchange efficiency, and is widely used in petrochemical, power and other industries.

[0003] In existing double-shell fixed tubesheet heat exchangers, the longitudinal baffles are typically connected to the tubesheet using a rest-to-rest structure. Specifically, the longitudinal baffles rest directly against the tubesheet surface, with the gap between them controlled by machining precision. Although the design drawings specify clear dimensional requirements for the rest-to-rest gap, in actual manufacturing, due to machining errors and assembly deviations, the gap is difficult to control precisely, and it's impossible to effectively check whether the gap meets design requirements after assembly. This leads to the shell-side fluid potentially short-circuiting through the gap between the tubesheet and the longitudinal baffles during actual operation, reducing heat exchange efficiency.

[0004] Furthermore, existing sealing structures between the longitudinal diaphragm and the shell-side cylinder also suffer from several technical defects. One common sealing method uses elastic sealing sheets, which achieve a seal between the longitudinal diaphragm and the inner wall of the shell-side cylinder through deformation. However, elastic sealing sheets are easily damaged during installation and prone to aging or fatigue failure after long-term operation, leading to a decline in sealing performance. Another sealing method uses fillet welds, where the longitudinal diaphragm and shell-side cylinder are internally welded during manufacturing. While this method is structurally simple, it places high demands on the equipment diameter, typically requiring a diameter of at least DN2000. Otherwise, internal welding operations become difficult, post-weld cleaning is inconvenient, and the assembly precision of the tube bundle is extremely high.

[0005] Currently, the most widely used sealing method is the welded insertion structure of the sealing strip, which involves pre-cutting grooves in the inner wall of the shell-side cylinder, inserting longitudinal partitions into the grooves, and then welding them in place. However, in actual manufacturing, the fit clearance between the longitudinal partitions and the grooves is difficult to control precisely, and the thermal deformation generated during welding can further expand the leakage channels, causing short circuits in the shell-side fluid and significantly reducing heat exchange efficiency. In addition, there is also a sealing method using an integral welded structure, but this method has limited applicability, is only suitable for simple operating conditions, and suffers from difficulty in ensuring welding quality and lower reliability.

[0006] Therefore, there is a need for a double-shell fixed tube sheet heat exchanger structure and its manufacturing method that has good sealing performance, strong manufacturing feasibility, and wide applicability, in order to solve the technical problems of easy leakage, difficult assembly, and poor applicability in the existing technology between the longitudinal baffle and the tube sheet, and between the longitudinal baffle and the shell shell. Summary of the Invention

[0007] The purpose of this invention is to provide a double-shell-pass fixed tubesheet heat exchanger and its manufacturing method, so as to solve the following technical problems existing in the prior art: (1) The tube sheet and longitudinal partition are connected by a push-fit method, and the assembly gap is difficult to detect and control, which cannot guarantee that the shell-side fluid will not short-circuit; (2) The sealing structure between the longitudinal partition and the shell has a number of defects, including the elastic sealing sheet is prone to aging and failure, the fillet weld connection has high requirements for the equipment diameter and is difficult to clean after welding, the gap and welding deformation of the sealing strip welded into the structure are difficult to control, leading to leakage, and the overall welded structure has a limited scope of application and low reliability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a double-shell-pass fixed tubesheet heat exchanger, comprising a shell-side shell, a left tubesheet and a right tubesheet disposed at both ends of the shell-side shell, a heat exchange tube bundle connecting the left tubesheet and the right tubesheet, and a longitudinal partition disposed within the heat exchange tube bundle. The heat exchange tube bundle includes multiple heat exchange tubes, with both ends of each tube fixedly connected to the left tubesheet and the right tubesheet, respectively. The longitudinal partition divides the space within the shell-side shell into two independent flow channels. Positioning grooves are provided on the back surfaces of the left tubesheet and the right tubesheet. The end of the longitudinal partition is inserted into the positioning groove and then fixedly connected to the left tubesheet and the right tubesheet via a sealing weld layer. A sealing groove is provided on the inner wall of the shell-side shell, and the edge of the longitudinal partition and the sealing groove are precision-machined to form a precise fit.

[0009] By setting positioning grooves on the back of the tube sheet and inserting the longitudinal baffles into the positioning grooves, and then fixing them with a sealed weld layer, the assembly gap between the baffles and the tube sheet is completely eliminated, fundamentally preventing shell-side fluid leakage at this point. Simultaneously, by precision machining the sealing grooves on the inner wall of the shell-side cylinder and the edges of the longitudinal baffles, a precise fit is achieved, minimizing the leakage path between the baffles along their length and the groove wall, effectively suppressing short-circuiting of the fluid between the shell and side sides, and significantly improving heat exchange efficiency.

[0010] Furthermore, near the left and right tube sheets, the longitudinal partition has locally widened portions on both sides. These widened portions are located at the weld between the tube sheet and the shell-side cylinder, which further reduces the gap between the longitudinal partition and the shell-side cylinder, minimizing shell-side fluid short-circuiting and improving sealing performance.

[0011] Furthermore, the positioning groove is a rectangular groove. Rectangular grooves are simple to manufacture, facilitate the insertion and positioning of longitudinal partitions, and ensure assembly accuracy.

[0012] Furthermore, the sealing weld layer is a full penetration weld layer. Full penetration welding can ensure the strength and sealing performance of the weld, ensure a reliable connection between the longitudinal diaphragm and the tube sheet, and eliminate the risk of leakage.

[0013] Furthermore, the sealing groove is a rectangular groove. Rectangular grooves have a simple structure, are easy to manufacture, and facilitate the insertion and fit of the longitudinal partition edges.

[0014] Furthermore, the precision fit is achieved by precision machining the edges of the longitudinal partition and the sealing groove. This precision machining ensures that the fit clearance is controlled within 1mm, guaranteeing smooth installation of the longitudinal partition while minimizing leakage paths and effectively suppressing short-circuiting of fluid between the shell and the surrounding area.

[0015] Furthermore, the system also includes baffles disposed within the heat exchange tube bundle, the baffles being fixedly connected to the longitudinal partitions. The baffles guide the shell-side fluid to flow laterally back and forth between the heat exchange tubes, enhancing the heat transfer effect, and their fixed connection with the longitudinal partitions improves the stability of the tube bundle structure.

[0016] This invention also provides a method for manufacturing a double-shell-pass fixed tubesheet heat exchanger, the double-shell-pass fixed tubesheet heat exchanger comprising a shell-side shell, a left tubesheet, a right tubesheet, a heat exchange tube bundle, and longitudinal partitions, comprising the following steps: Step 1: Machining a sealing groove on the inner wall of the shell-side cylinder, machining positioning grooves on the back of the left and right tube sheets, and precision machining the edges of the longitudinal partitions and the sealing grooves. This precision machining ensures the accuracy of the mating clearances, laying the foundation for subsequent high-precision assembly.

[0017] Step 2: Install the positioning fixture at both ends of the sealing groove using a positioning fixture with high flatness. The positioning fixture ensures that the sealing groove openings are on the same plane, ensuring that the longitudinal partition can be smoothly installed and reducing reliance on operator skills.

[0018] Step 3: Insert the end of the longitudinal partition into the positioning groove on the back of the left tube sheet, and spot weld the left tube sheet to the longitudinal partition. Spot welding temporarily fixes the longitudinal partition, ensuring the stability of the structure during subsequent assembly.

[0019] Step 4: Assemble the tie rod, spacer tube, and baffle plate in sequence, inserting a portion of the heat exchange tubes to stabilize the structure, and spot weld the baffle plate to the longitudinal partition plate. Inserting a portion of the heat exchange tubes enhances the overall rigidity of the tube bundle, facilitating the subsequent insertion of the shell-side cylinder.

[0020] Step 5: Push the assembled tube bundle into the shell-side cylinder, leaving a predetermined distance before pushing it in. After sealing and welding the longitudinal partition to the left tube sheet, push it in completely. Leaving a predetermined distance (usually more than 1 meter) is to facilitate the sealing and welding operation. Pushing it in completely after the sealing and welding is completed avoids the impact of welding deformation on the fitting accuracy of the sealing groove.

[0021] Step 6: Install the right tube sheet and insert the remaining heat exchange tubes to complete the tube bundle assembly. Finally, install the right tube sheet and insert the remaining heat exchange tubes to complete the assembly of the entire heat exchanger.

[0022] Furthermore, the positioning fixture includes a positioning plate and a connecting plate, with the outer edge of the positioning plate fitting against the inner wall of the shell-side cylinder. The fitting of the positioning plate against the inner wall of the shell-side cylinder ensures accurate positioning of the positioning fixture within the shell-side cylinder, guaranteeing the flatness of the sealing groove.

[0023] Furthermore, in step 2, if the shell-side cylinder is long, a positioning fixture is added in the middle section. For long heat exchangers, adding a positioning fixture in the middle section can ensure that the longitudinal baffles remain straight and accurately centered along the entire length, preventing them from bending or tilting during installation.

[0024] Furthermore, in step 5, the sealing weld is a full penetration weld. Full penetration welding ensures the strength and sealing of the weld, guaranteeing a reliable connection between the longitudinal diaphragm and the tube sheet.

[0025] Furthermore, after step 6, the process further includes: connecting the shell-side cylinder to the left tube sheet and the right tube sheet via fillet welds, and connecting the heat exchange tubes to the left tube sheet and the right tube sheet via expansion joints or welding. Once these connection steps are completed, the manufacturing of the entire heat exchanger is finished.

[0026] The present invention has at least the following advantages: (1) Excellent sealing performance: The double sealing structure with positioning grooves on the back of the tube sheet and fixed connection by sealing welding layer, as well as the precision fit formed by the sealing groove on the inner wall of the shell and the edge of the longitudinal partition, fundamentally eliminates the risk of shell fluid leakage and significantly improves heat exchange efficiency.

[0027] (2) High feasibility of manufacturing process: The precision machining requirements of the sealing groove and the edge of the partition are moderate and can be achieved by ordinary manufacturers. The special positioning fixture ensures accurate installation of the sealing groove, reduces the dependence on the skills of the operators, and improves the feasibility of manufacturing.

[0028] (3) Easy installation and controllable quality: The positioning tooling facilitates assembly, and the welding of the sealing groove will not affect the fluid sealing between the shell and the shell, thus improving assembly efficiency and quality consistency.

[0029] (4) Wide range of applications: This structure has no strict limitations on equipment size (diameter, length) and operating conditions (pressure, temperature), and can be widely used in the design and manufacture of various double shell fixed tube sheet heat exchangers. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a partial schematic diagram of the internal structure of the present invention; Figure 3 This is a schematic diagram of the longitudinal partition installation in this invention; Figure 4 This is a schematic diagram of the sealed connection between the longitudinal partition and the tube sheet in this invention; Figure 5 This is a schematic diagram of the locally widened portion of the longitudinal partition in this invention; Figure 6 This is a schematic diagram of the sealed connection between the longitudinal partition shell and the cylindrical body in this invention; Figure 7 This is a schematic diagram of the positioning fixture in this invention; Figure 8 This is the usage state of the positioning tooling in this invention. Figure 1 ; Figure 9 This is the usage state of the positioning tooling in this invention. Figure 2 . Detailed Implementation

[0031] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] Reference Figure 1-6 A double-shell fixed tubesheet heat exchanger includes a shell-side cylindrical body 1, a left tubesheet 2 and a right tubesheet 3 disposed at both ends of the shell-side cylindrical body 1, a heat exchange tube bundle 4 connecting the left tubesheet 2 and the right tubesheet 3, and a longitudinal baffle 5 disposed within the heat exchange tube bundle 4. The shell-side cylindrical body 1 is cylindrical and forms the main outer shell structure of the heat exchanger. The left tubesheet 2 and the right tubesheet 3 are circular plates, fixedly connected to both ends of the shell-side cylindrical body 1 by fillet welds. The heat exchange tube bundle 4 includes multiple heat exchange tubes, which are slender tubes fixedly connected to the left tubesheet 2 and the right tubesheet 3 at both ends, and arranged parallel to the axis of the shell-side cylindrical body 1. The longitudinal baffle 5 is a long strip plate, arranged along the axial direction of the heat exchange tube bundle 4, dividing the space within the shell-side cylindrical body 1 into two independent flow channels. Through the separation effect of the longitudinal baffle 5, the shell-side fluid can flow back and forth in the two independent flow channels, thereby improving the flow velocity and heat exchange efficiency.

[0033] The left tube sheet 2 and the right tube sheet 3 have positioning grooves 6 on their back sides. These grooves are rectangular, 20mm deep, and their width matches the thickness of the longitudinal partition 5. After the end of the longitudinal partition 5 is inserted into the positioning groove 6, it is fixedly connected to the left tube sheet 2 and the right tube sheet 3 via a sealing weld layer 7. The sealing weld layer 7 is a full-penetration weld layer with a weld width of 10mm, ensuring weld strength and sealing performance. The positioning grooves 6 allow for precise positioning of the longitudinal partition 5 during insertion, preventing assembly deviations. The fixed connection via the sealing weld layer 7 completely eliminates the assembly gap between the longitudinal partition 5 and the left and right tube sheets 2 and 3, fundamentally preventing shell-side fluid leakage at this point and significantly improving sealing performance.

[0034] The inner wall of the shell-side cylinder 1 is provided with a sealing groove 8. The sealing groove 8 is rectangular, with a depth of 15 mm and a width equal to the thickness of the longitudinal partition 5 plus 2 mm. The edge of the longitudinal partition 5 and the sealing groove 8 are precision-machined to form a tight fit, with a clearance of 0.5 mm to 1 mm. The precision machining is achieved by machining the edge of the longitudinal partition 5 and the sealing groove 8 with a machining accuracy of ±0.1 mm. Through this precision fit, the longitudinal partition 5 can be smoothly installed into the sealing groove 8 while minimizing the leakage path between the longitudinal partition 5 and the wall of the sealing groove 8 along its length, effectively suppressing fluid short-circuiting between the shell and side sides, and significantly improving heat exchange efficiency.

[0035] Near the left tube sheet 2 and right tube sheet 3, the longitudinal baffle 5 has locally widened portions 9 on both sides. The width of the locally widened portion 9 is 1.5 times the thickness of the longitudinal baffle 5, and the length is 100 mm. It is located at the weld points between the left tube sheet 2 and right tube sheet 3 and the shell-side cylinder 1. By setting the locally widened portions 9, the gap between the longitudinal baffle 5 and the shell-side cylinder 1 is further reduced, reducing the possibility of short-circuiting of the shell-side fluid at this point, and further improving the sealing performance and heat exchange efficiency.

[0036] The heat exchanger tube bundle 4 also includes baffles 10, tie rods 11, and spacer tubes 12. The baffles 10 are circular plates with perforations, arranged perpendicular to the heat exchanger tube bundle 4 and spaced axially to guide the shell-side fluid in transverse reciprocating flow between the heat exchanger tubes, enhancing heat transfer. The baffles 10 are fixedly connected to the longitudinal partitions 5 by spot welding, with a spot weld spacing of 100 mm and a weld diameter of 5 mm. The tie rods 11 and spacer tubes 12 are used to fix the distance between the baffles 10 and support the entire tube bundle structure, improving the overall rigidity and stability of the tube bundle.

[0037] Implementation Principle: The shell-side fluid enters through the inlet of the shell-side tube bundle 1 and is divided into two independent flow channels by the longitudinal baffle 5. The shell-side fluid flows outside the heat exchange tube bundle 4, reciprocating laterally under the guidance of the baffle 10, and fully exchanging heat with the fluid inside the tubes. The longitudinal baffle 5 is sealed to the left tube sheet 2 and right tube sheet 3 through the positioning groove 6 and the sealing weld layer 7, and precisely fitted to the shell-side tube bundle 1 through the sealing groove 8, effectively preventing short-circuiting of the fluid between the shell and side, ensuring that the shell-side fluid flows according to the designed flow channel, and significantly improving heat exchange efficiency. The locally widened section 9 further reduces the gap between the longitudinal baffle 5 and the shell-side tube bundle 1, further improving the sealing performance. The fixed connection between the baffle 10 and the longitudinal baffle 5 improves the stability of the tube bundle structure and ensures the reliability of the equipment during long-term operation.

[0038] Reference Figure 7-9 This application also provides a method for manufacturing a double-shell-pass fixed tubesheet heat exchanger, comprising the following steps: Step 1: Machining a sealing groove 8 on the inner wall of the shell-side cylinder 1, and machining positioning grooves 6 on the back of the left tube sheet 2 and right tube sheet 3. Finish machining the edges of the longitudinal partition 5 and the sealing groove 8. The sealing groove 8 has a machining depth of 15mm and a width equal to the thickness of the longitudinal partition 5 plus 2mm. The positioning groove 6 has a machining depth of 20mm, and its width matches the thickness of the longitudinal partition 5. Precision machining is used, with machining accuracy controlled within ±0.1mm, ensuring a fit clearance of 0.5mm to 1mm between the edge of the longitudinal partition 5 and the sealing groove 8. This precision machining ensures the required fit clearance accuracy, laying the foundation for subsequent high-precision assembly.

[0039] Step 2: Install the positioning fixture 13 at both ends of the sealing groove 8. (Refer to...) Figure 6 The positioning fixture 13 includes a positioning plate 14 and a connecting plate 15. The positioning plate 14 is square or rectangular, with its outer edge fitting against the inner wall of the shell-side cylinder 1. The connecting plate 15 consists of two parallel plates used to connect the positioning plates 14 at both ends, forming a rigid frame structure. The flatness deviation of the positioning fixture 13 is less than 1mm, ensuring that the openings of the sealing groove 8 are on the same plane. (Refer to...) Figure 7 After the positioning fixture 13 is installed inside the shell-side cylinder 1, the outer edge of the positioning plate 14 fits tightly against the inner wall of the shell-side cylinder 1, ensuring accurate positioning of the positioning fixture 13 within the shell-side cylinder 1. If the shell-side cylinder 1 is long, a positioning fixture 13 is added in the middle section to ensure that the longitudinal partition 5 remains straight and accurately centered along its entire length, preventing bending or skewing during installation. The positioning fixture 13 reduces the reliance on operator skills and ensures that the longitudinal partition 5 can be smoothly installed.

[0040] Step 3: Insert the end of the longitudinal partition 5 into the positioning groove 6 on the back of the left tube sheet 2, and spot weld the left tube sheet 2 to the longitudinal partition 5. Spot welding is performed using manual electric arc welding or argon arc welding, with a spot welding spacing of 100mm and a weld diameter of 5mm. Spot welding temporarily fixes the longitudinal partition 5, ensuring structural stability during subsequent assembly and preventing displacement or skewing of the longitudinal partition 5 during assembly.

[0041] Step 4: Assemble the tie rod 11, spacer tube 12, and baffle 10 sequentially, inserting a portion of the heat exchange tubes to stabilize the structure. Spot weld the baffle 10 to the longitudinal partition 5. The tie rod 11 and spacer tube 12 are connected in series to fix the baffle 10, which is arranged perpendicular to the heat exchange tube bundle 4. Inserting a portion of the heat exchange tubes enhances the overall rigidity of the tube bundle, facilitating the subsequent insertion of the shell-side cylinder 1. The spot welding of the baffle 10 to the longitudinal partition 5, with a spot weld spacing of 100mm and a weld diameter of 5mm, improves the stability of the tube bundle structure.

[0042] Step 5: Push the assembled tube bundle into the shell-side cylinder 1, leaving a predetermined distance before pushing it in. After sealing and welding the longitudinal diaphragm 5 to the left tube sheet 2, push it in completely. The predetermined distance is usually 1000mm to 1200mm, left to facilitate the sealing welding operation. The sealing welding adopts full penetration welding, with a weld width of 10mm, which can ensure the strength and sealing performance of the weld. After the sealing welding is completed, the tube bundle is fully pushed into the shell-side cylinder 1 to avoid the influence of welding deformation on the fitting accuracy of the sealing groove 8, and to ensure the precise fit between the edge of the longitudinal diaphragm 5 and the sealing groove 8.

[0043] Step 6: Install the right tube sheet 3 and insert the remaining heat exchange tubes to complete the tube bundle assembly. The right tube sheet 3 is fixedly connected to the right end of the shell-side shell 1 by fillet welds. The heat exchange tubes are fixedly connected to the left tube sheet 2 and the right tube sheet 3 by expansion joints or welding. The shell-side shell 1 is connected to the left tube sheet 2 and the right tube sheet 3 by fillet welds, and the heat exchange tubes are connected to the left tube sheet 2 and the right tube sheet 3 by expansion joints or welding, completing the manufacturing of the entire heat exchanger.

[0044] The above manufacturing method achieves high-precision assembly of the double-shell fixed tubesheet heat exchanger, ensuring a sealed connection between the longitudinal partition 5 and the left tubesheet 2 and right tubesheet 3, as well as a precise fit between the longitudinal partition 5 and the shell-side shell 1. This effectively prevents short-circuiting of the fluid between the shell and side, significantly improving heat exchange efficiency. The use of positioning fixture 13 reduces reliance on operator skills and improves assembly efficiency and quality consistency. This manufacturing method has a wide range of applications, with no strict limitations on equipment size and operating conditions, and can be widely used in the manufacture of various types of double-shell fixed tubesheet heat exchangers.

[0045] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A double-shell-side fixed tubesheet heat exchanger, comprising a shell-side shell (1), a left tubesheet (2) and a right tubesheet (3) disposed at both ends of the shell-side shell, a heat exchange tube bundle (4) connecting the left tubesheet and the right tubesheet, and a longitudinal partition (5) disposed within the heat exchange tube bundle, characterized in that, The heat exchange tube bundle (4) includes multiple heat exchange tubes, and the two ends of the heat exchange tubes are respectively fixedly connected to the left tube sheet and the right tube sheet; The longitudinal baffle divides the space inside the shell-side cylinder into two independent flow channels; The left tube sheet and the right tube sheet are provided with positioning grooves (6) on their back sides. After the end of the longitudinal partition is inserted into the positioning groove, it is fixedly connected to the left tube sheet and the right tube sheet through the sealing welding layer (7). The inner wall of the shell-side cylinder is provided with a sealing groove (8), and the edge of the longitudinal partition plate and the sealing groove are precisely fitted by precision machining.

2. The double-shell-pass fixed tubesheet heat exchanger according to claim 1, characterized in that: The longitudinal partition has locally widened portions (9) on both sides near the left tube sheet (1) and the right tube sheet (2).

3. The double-shell-pass fixed tubesheet heat exchanger according to claim 1, characterized in that: It also includes a baffle plate (10) disposed in the heat exchange tube bundle, the baffle plate being fixedly connected to the longitudinal partition plate.

4. The double-shell-pass fixed tubesheet heat exchanger according to claim 3, characterized in that: The heat exchange tube bundle (4) also includes a tie rod (11) and a spacer tube (12), which are used to fix the distance between the baffles (10).

5. A method for manufacturing a double-shell-pass fixed tubesheet heat exchanger, the double-shell-pass fixed tubesheet heat exchanger comprising a shell-side shell, a left tubesheet, a right tubesheet, a heat exchange tube bundle, and longitudinal partitions, characterized in that, Includes the following steps: Step 1: Machining a sealing groove on the inner wall of the shell-side cylinder, machining a positioning groove on the back of the left tube sheet and the right tube sheet, and finishing the edge of the longitudinal partition and the sealing groove; Step 2: Install the positioning fixture at both ends of the sealing groove using a positioning fixture with high flatness; Step 3: Insert the end of the longitudinal partition into the positioning groove on the back of the left tube plate, and spot weld the left tube plate to the longitudinal partition; Step 4: Assemble the tie rod (11), the spacer tube (12), and the baffle (10) in sequence, insert part of the heat exchange tube to stabilize the structure, and spot weld the baffle to the longitudinal partition plate; Step 5: Push the assembled tube bundle into the shell-side cylinder, leaving a predetermined distance before pushing it in. After sealing and welding the longitudinal partition to the left tube sheet, push it in completely. Step 6: Install the right tube sheet and insert the remaining heat exchange tubes to complete the tube bundle assembly.

6. The manufacturing method according to claim 4, characterized in that: The positioning fixture includes a positioning plate and a connecting plate, with the outer edge of the positioning plate fitting against the inner wall of the shell-side cylinder.

7. The manufacturing method according to claim 4, characterized in that: In step 2, if the shell-side cylinder is long, a positioning fixture is added to the middle section.

8. The manufacturing method according to claim 4, characterized in that: In step 5, the sealing weld is a full penetration weld.

9. The manufacturing method according to claim 4, characterized in that: After step 6, the process further includes: connecting the shell-side cylinder to the left tube sheet (2) and the right tube sheet (3) by fillet weld, and connecting the heat exchange tube to the left tube sheet and the right tube sheet by expansion joint or welding.

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