A tube head connection structure with a spiral sleeve between a heat exchange tube and a tube hole of a tube sheet

Abstract

The present application relates to a kind of tube head connecting structure of spiral sleeve between heat exchange pipe and tube hole of tube sheet, spiral sleeve is assembled between the outer wall surface of heat exchange pipe and tube hole of tube sheet, inner helical channel groove is processed on the inner cylindrical surface of spiral sleeve, outer helical channel groove is processed on the outer cylindrical surface, radial through hole is provided at the end of helical channel groove close to positioning connection end, with the end face of spiral sleeve as weld bottom, welding connection is formed between the outer wall of heat exchange pipe and tube hole of tube sheet.Spiral channel groove changes the micro gap between heat exchange pipe and tube sheet into local thermosyphon flow channel, for cooling the connecting weld seam between heat exchange pipe and tube sheet on the side of tube pass, eliminates the hidden trouble of heat exchange pipe head gap corrosion, forms pipe head cooling channel, reduces the temperature of pipe head weld seam metal, improves the reliability of pipe head connection.

Description

Technical Field

[0001] This invention belongs to the fields of energy equipment and thermal energy and power engineering, and relates to a new structure of the connection tube head between the heat exchange tube and the tube sheet in a shell-and-tube waste heat boiler. Background Technology

[0002] In process industry plants such as oil refining, chemical engineering, and metallurgy, the high-temperature waste heat from large quantities of process gases needs to be recovered and utilized by waste heat boilers to produce steam. Waste heat boilers for recovering high-temperature waste heat from pressure media in industrial plants typically employ fixed tube sheet heat exchangers with thin tube sheets. The high-temperature process gas is arranged on the tube side, and saturated water on the shell side. This arrangement offers significant technical advantages: a simple overall structure and easy implementation of tube-side insulation. The shell-side medium flows transversely, with a short flow path, and a steam drum establishes natural circulation with the shell side, resulting in good shell-side flow and steam-water separation. For this widely used equipment, the national standard GB / T 151 Appendix provides design methods and technical rules, while the industry standard SH / T 3158 provides complete design methods and technical quality rules, providing strong technical support for relevant industrial applications.

[0003] In engineering practice, numerous typical cases of equipment failure have been exposed, mainly concentrated in the cracking failure of the welded connection between the heat exchange tubes and the tube sheet, and the tube sheet overheating failure caused by the cracking of the tube-side lining. Failure of waste heat boilers often has serious secondary consequences, with rapid failure propagation and difficulty in repair after failure. Therefore, industry, academia, and research institutions have invested a great deal of effort in product innovation, technical research, and operational protection of shell-and-tube waste heat boilers. Currently, the heat exchange tube and tube sheet connection structure of shell-and-tube waste heat boilers typically adopts three types: 1) strength welding + expansion joint structure; 2) full-thickness, full-section welded joint structure; 3) internal hole welded joint structure.

[0004] The core function of the tube head design connecting the heat exchanger tubes and tube sheet in a shell-and-tube waste heat boiler is to prevent the shell-side medium from entering the gap between the heat exchanger tubes and the tube sheet orifices. Poor flow would lead to repeated evaporation and concentration cycles, ultimately causing crevice corrosion and penetration cracking. Options 2) and 3) structurally eliminate the gap between the heat exchanger tubes and the tube sheet orifices, resulting in high connection reliability. However, Option 2) requires a huge amount of welding work at the tube head, with significant welding deformation and strict control requirements during the welding process. Option 3 requires high precision machining of the tube sheet orifices at the tube head, resulting in a large machining workload, welding difficulty, and a heavy inspection workload. The manufacturing costs of these two options are too high, and the risk of manufacturing quality assurance remains. Repairing even a low-probability failure is extremely difficult. While Option 1 has the risk of failure due to incomplete expansion joints and crevice corrosion, it is easier to process, weld, and manufacture, and is therefore more widely used.

[0005] Addressing the advantages and disadvantages of commonly used tube heads in shell-and-tube waste heat boilers, and considering the high reliability requirements of waste heat boilers, constructing a tube head that is easy to manufacture, easy to guarantee in quality, and safe and reliable in use is one of the key breakthroughs in waste heat boiler product innovation. Summary of the Invention

[0006] The purpose of this invention is to propose a tube head connection structure with a spiral sleeve between the heat exchange tube and the tube hole of the tube sheet.

[0007] The technical solution of this invention is as follows: A tube head connection structure with a spiral sleeve between a heat exchange tube and a tube sheet bore. The spiral sleeve is assembled between the outer wall of the heat exchange tube and the tube sheet bore. An inner spiral groove is machined on the inner cylindrical surface of the spiral sleeve, and an outer spiral groove is machined on the outer cylindrical surface. The spiral directions of the inner and outer spiral grooves are opposite. One end of the spiral sleeve is a positioning connection end. The inner and outer walls of the positioning connection end are smooth cylindrical surfaces of a certain length. A radial through hole is provided at the end of the spiral groove near the positioning connection end, which connects the inner and outer spiral grooves. The non-connecting end of the spiral sleeve extends a certain length beyond the end face of the tube sheet. The groove depth and pitch of the outer spiral groove are greater than those of the inner spiral groove. The end face of the spiral sleeve is the bottom of the weld. The end face of the spiral sleeve, the inner surface of the tube sheet bore, and the outer surface of the heat exchange tube form an annular cavity. Welding material is added into the annular cavity to form a weld.

[0008] Preferably, the length of the non-connecting end of the spiral sleeve extending beyond the end face of the tube sheet is 5-8 mm.

[0009] Preferably, the cross-sectional shape of the inner spiral groove and the outer spiral groove is T-shaped, rectangular, or arc-shaped.

[0010] The diameter of the radial through hole is smaller than the width of the spiral channel groove.

[0011] The tube sheet is a weldable metal plate of a certain thickness. Tube holes are regularly opened on the metal plate along the thickness direction. The tube holes in the thickness direction of the tube sheet have two cylindrical surfaces with different diameters. Taking the outer end face of the tube sheet as a reference, the tube hole is first a large-diameter hole of a certain length, and then becomes a small-diameter hole, forming an annular step between the large-diameter hole and the small-diameter hole.

[0012] The depth of the large-diameter hole is 1.2 to 1.5 times the wall thickness of the heat exchange tube, and the diameter of the large-diameter hole is 1.02 to 1.05 times the outer diameter of the cylindrical surface of the positioning connection end.

[0013] The heat exchange tube is a weldable metal tube of a certain thickness and length. The heat exchange tube has smooth inner and outer walls, or a non-smooth surface is set in the area outside the spiral sleeve (the inner and outer surfaces of the section in contact with the spiral sleeve are cylindrical) to enhance heat transfer.

[0014] The principle of this technology is as follows: the flow areas of the spiral grooves on the inner and outer surfaces of the spiral sleeve are different, with the outer spiral groove having a larger flow area than the inner spiral groove. The metal wall temperature of the heat exchange tubes, tube sheet, and spiral sleeve is higher than that of the shell-side saturated water. The saturated water entering the grooves on the inner and outer surfaces of the spiral sleeve undergoes convective heat transfer with the wall, generating water vapor. Due to the different flow areas of the grooves on the inner and outer surfaces, the flow resistance within the spiral grooves on the inner and outer sides of the sleeve is different, thus creating a forward spiral flow. The higher metal wall temperature of the heat exchange tubes, tube sheet, and spiral sleeve provides a continuous heat source and flow driving force for heat transfer and flow, increasing the proportion of vapor phase in the flowing steam-water mixture. With the increased vapor phase, the density of the fluid within the spiral grooves decreases, further creating a flow driving force where the inlet density is greater than the outlet density. This creates a continuous spiral flow, resulting in a thermosiphon flow in the space between the outer wall of the heat exchange tube and the tube hole in the tube sheet. The continuous flow in the spiral grooves on the inner and outer surfaces of the bushing prevents adverse thermal processes such as dry steaming and concentration from occurring in this microspace, thus avoiding crevice corrosion and improving the environmental adaptability and safety reliability of the tube head connection.

[0015] The beneficial effects of this invention are as follows: Based on the principles of engineering thermodynamics and thermodynamics, this invention introduces a spiral sleeve. The spiral groove transforms the microscopic gap between the heat exchange tube and the tube sheet into a local thermosiphon flow channel, forming a thermosiphon effect between the tube hole and the outer wall of the heat exchange tube. This guides local microflow, cools the connection weld between the heat exchange tube and the tube sheet on the tube side, eliminates the risk of corrosion in the gap of the heat exchange tube head, forms a tube head cooling channel, reduces the metal temperature of the tube head weld, and improves the reliability of the tube head connection.

[0016] This patent has the advantages of compact structure, easy machining, convenient assembly, and easy welding, thus making it easier to ensure quality. This structure forms a siphon flow between the heat exchange tube and the tube sheet holes, ensuring safe use. Attached Figure Description

[0017] Figure 1 This is a structural assembly diagram of the present invention; Figure 2 This is an axial cross-sectional view of the spiral sleeve; Figure 3 This is a view of the outer wall of the spiral sleeve; Figure 4 This is a cross-sectional diagram of the tube holes in the tube sheet. Figure 5 It is a trace diagram of the fluid velocity distribution inside the spiral groove on the outside of the spiral sleeve; Figure 6 It is a trace diagram of the fluid velocity distribution inside the spiral channel groove of the spiral sleeve; Figure 7 It is a vector diagram of the velocity distribution inside the spiral groove on the outside of the spiral sleeve; Figure 8 It is a vector diagram of the velocity distribution within the spiral grooves inside the spiral sleeve; Figure 9 This is a velocity contour plot of the central section of the spiral sleeve; Figure 10 It is a three-dimensional model diagram used by numerical simulation software. Detailed Implementation

[0018] In shell-and-tube waste heat boilers, high-temperature gas is arranged in the tubes, while boiler feedwater is arranged in the shell. Generally, unless the process gas contains solid impurities, shell-and-tube waste heat boilers are horizontally arranged. This horizontal arrangement ensures smooth gas-liquid two-phase flow in the shell side, resulting in good overall equipment safety and widespread use. High-temperature gas flows through the heat exchange tubes, where it undergoes convective heat transfer. The heat is then transferred through the metal walls of the heat exchange tubes to their outer surface, and finally released to the boiler feedwater in the shell side, causing it to vaporize and produce steam.

[0019] To improve the safety and reliability of pipe head connections, based on summarizing the failure phenomena and analyzing the failure mechanisms of existing pipe head structures, we innovatively construct a pipe head connection structure that is easy to implement, safe, and easy to use, by applying engineering thermophysics knowledge.

[0020] A tube-end connection structure with a spiral sleeve between a heat exchange tube 2 and a tube hole in a tube sheet 3 is disclosed. The spiral sleeve 1 is assembled between the outer wall of the heat exchange tube 2 and the tube hole in the tube sheet 3. An inner spiral groove 1-1 is machined on the inner cylindrical surface of the spiral sleeve 1, and an outer spiral groove 1-2 is machined on the outer cylindrical surface. The spiral directions of the inner spiral groove 1-1 and the outer spiral groove 1-2 are opposite. One end of the spiral sleeve 1 is a positioning connection end 1-3, and the inner and outer walls of the positioning connection end 1-3 are smooth cylindrical surfaces 1-4 of a certain length, approximately 3-5 mm, used for positioning the spiral sleeve 1 and the tube hole. A radial through hole 1-5 is provided at the end of the spiral groove near the positioning connection end 1-3. The diameter of the radial through hole 1-5 is smaller than the width of the spiral groove. The radial through hole 1-5 connects the inner spiral groove 1-1 and the outer spiral groove 1-2. The non-connecting end of the spiral sleeve 1 extends a certain length beyond the tube sheet end face, typically 5-8 mm. The outer diameter of the outer spiral groove 1-2 is smaller than the diameter of the cylindrical surface of the positioning connection end 1-3, while the inner diameter of the inner spiral groove 1-1 is larger than the outer diameter of the heat exchange tube. With the end face of the spiral sleeve 1 as the bottom of the weld, the end face of the spiral sleeve 1, the inner surface of the tube sheet bore, and the outer surface of the heat exchange tube form an annular cavity. Welding material is added into the annular cavity to form weld 4.

[0021] The groove depth and pitch of the outer spiral groove 1-2 are greater than those of the inner spiral groove 1-1. The cross-sectional shapes of the inner spiral groove 1-1 and the outer spiral groove 1-2 can be T-shaped, rectangular, or arc-shaped.

[0022] The tube sheet 3 is a weldable metal plate of a certain thickness. Regularly spaced tube holes are formed along the thickness direction of the metal plate. Each tube hole has two cylindrical sections of different diameters along the thickness direction. Using the outer end face 3-1 of the tube sheet as a reference, the tube hole first forms a large-diameter hole 3-2 of a certain length, then transitions to a small-diameter hole 3-3, forming an annular step 3-4 between the large-diameter hole 3-2 and the small-diameter hole 3-3. Optimal data are as follows: the depth of the large-diameter hole 3-2 is 1.2 to 1.5 times the wall thickness of the heat exchange tube, and the diameter of the large-diameter hole 3-2 is 1.02 to 1.05 times the outer diameter of the cylindrical surface of the positioning connection end 1-3. The optimized design dimension of the spiral sleeve in the thickness radius direction is 2.5-3.5 mm.

[0023] The heat exchange tube 2 is a weldable metal tube of a certain thickness and length. It is a tube with smooth inner and outer walls, or a non-smooth surface (such as fins, ridges, etc.) is set in the area outside the spiral sleeve 1 to enhance heat transfer.

[0024] Assembly Process: A spiral sleeve 1 is installed in each tube hole of the tube sheet. Then, a heat exchange tube 2 is assembled inside the spiral sleeve 1, making the end face of the heat exchange tube 2 flush with the end face of the tube sheet 3. At this point, the end face of the spiral sleeve 1 is reduced inward by approximately half the wall thickness of the heat exchange tube relative to the end face of the heat exchange tube 2. After checking that the assembly shape and positional accuracy meet the requirements and cleaning the surface, the annular cavity formed by the end face of the spiral sleeve 1, the inner surface of the tube hole in the tube sheet, and the outer surface of the heat exchange tube is welded. Using the end face of the spiral sleeve 1 as the base surface for welding melting, a connecting weld is formed within the annular cavity using argon arc welding and electric arc welding methods with filler welding material. The connecting weld serves to withstand mechanical loads and separate the shell-side medium.

[0025] During operation, a stable water circulation is generally established in the shell side first, and then high-temperature gas is slowly introduced into the tube side. Three types of tube heads are currently widely used in waste heat boilers: ① strength weld + expansion joint, ② full-section weld, and ③ internal bore weld. Compared to ② and ③, this innovative invention intentionally sets up a spiral flow channel between the heat exchange tube and the tube sheet bore. Utilizing the thermosiphon principle, a micro-flow is formed, guiding the shell-side fluid to flow to the area near the tube sheet end face to cool the tube sheet end face and the tube head weld metal. The temperature gradient along the thickness direction of the tube sheet is small, and the temperature stress is low. Although an additional component is added, the welding difficulty is significantly reduced, and the reliability of the tube head quality is easily guaranteed. Compared to ①, the inherent risk of poor gap elimination in traditional expansion joint connections between heat exchange tubes and tube sheet bores is transformed into a beneficial spiral flow channel for cooling the tube head weld metal, significantly improving the reliability of the tube head connection quality.

[0026] Calculation of whether fluid can flow into the spiral channel: According to the principle of heat transfer, the heat transfer intensity depends on the heat transfer temperature difference and the heat transfer capacity, q=(tt-tf)h, where: q is the heat transfer intensity, tt is the metal temperature, tf is the fluid temperature, and h is the convective heat transfer coefficient, with units of W / (m²). 2 According to the heat transfer principle and simulation analysis, in a waste heat boiler, the metal surface temperature of the heating surface is approximately 50°C higher than the saturated water temperature, and the convective evaporation intensity of the saturated water is greater than 5000 W / (m²). 2 (℃), calculated accordingly, q=250000w / m 2 If the heat exchanger tube diameter is 45mm, the tube sheet orifice diameter is 48mm, and the tube sheet thickness is 30mm, then the heat transfer area of ​​the outer wall of the heat exchanger tube is 4239mm². 2 The heat transfer area of ​​the tube sheet orifices is 4521.6 m². 2 Total heat transfer area: 8760.6 m² 2 Based on this calculation, the heat transfer is 2190.15 W. The latent heat of vaporization of water is approximately 2500 kJ / kg. According to the law of conservation of energy, the vaporization rate is 0.00876 kg / s. The density of water is 950 kg / m³. 3 The volumetric flow rate of water is 9.22 x 10⁻⁶. -7 m 3 / s. If the radial depth of the groove on the surface of the spiral sleeve is 1mm and the axial length is 3mm, then the area of ​​the spiral channel is 3mm². 2 The inlet velocity of the water is 0.3 m / s, which is the velocity of water that is 100% vaporized.

[0027] The following simulation calculations demonstrate the feasibility and effectiveness of the proposed solution: A 3D model was created, and numerical simulation software was used for simulation. Boundary conditions were set: an unstructured mesh was used for the simulation, with mesh refinement applied to the helical sleeve section. The thickness of the inner and outer helical channels was relatively small, and the boundary layer was set to two layers, resulting in a total mesh element count of approximately three million. The energy equation was initiated, and the k-omega SST turbulence model and the Lee thermal phase change model were selected, with water as the medium. The tube sheet wall temperature and the heat exchange tube inner wall temperature were set to 80℃ and 130℃, respectively, with a velocity inlet of 2 m / s and a pressure outlet.

[0028] Figure 5 , Figure 6 The diagram shows the velocity distribution traces of the fluid within the spiral grooves on the outside and inside of the spiral sleeve. The diagram fully reflects the flow trajectory of the fluid within the spiral grooves on the inside and outside of the spiral sleeve.

[0029] Figure 7 , Figure 8These are vector diagrams showing the velocity distribution within the spiral grooves on the outside and inside of the spiral sleeve. These two diagrams clearly show the velocity distribution of the fluid within the spiral sleeve's internal and external threaded flow channels. As can be seen from the diagrams, the fluid travels along the pre-defined flow channels, but at a relatively low speed.

[0030] Figure 8 This is a velocity cloud diagram of the central section of the spiral sleeve. Under this set operating condition, the fluid velocity inside the spiral sleeve is between 0.2 and 0.5 m / s. It continuously enters from the flow channel between the spiral groove inside the spiral sleeve and the outer wall of the heat exchange tube, and flows out from the flow channel between the spiral groove outside the spiral sleeve and the tube sheet, and merges into the mainstream.

Claims

1. A tube head connection structure with a spiral sleeve between the heat exchange tube and the tube hole of the tube sheet, characterized in that: The spiral sleeve (1) is assembled between the outer wall of the heat exchange tube (2) and the tube hole of the tube sheet (3). The inner cylindrical surface of the spiral sleeve (1) is machined with an inner spiral groove (1-1), and the outer cylindrical surface is machined with an outer spiral groove (1-2). The spiral directions of the inner spiral groove (1-1) and the outer spiral groove (1-2) are opposite. One end of the spiral sleeve (1) is a positioning connection end (1-3). The inner and outer walls of the positioning connection end (1-3) are smooth cylindrical surfaces (1-4) of a certain length. Near the positioning connection end (1-3) The end of the spiral groove is provided with a radial through hole (1-5). The radial through hole (1-5) connects the inner spiral groove (1-1) and the outer spiral groove (1-2). The non-connecting end of the spiral sleeve (1) extends a certain length from the end face of the tube sheet. The groove depth and pitch of the outer spiral groove (1-2) are greater than those of the inner spiral groove (1-1). The end face of the spiral sleeve (1) is the bottom of the weld. The end face of the spiral sleeve (1), the inner surface of the tube hole of the tube sheet, and the outer surface of the heat exchange tube form an annular cavity. Welding material is added to the annular cavity to form a weld (4).

2. The tube head connection structure with a spiral sleeve between the heat exchange tube and the tube sheet hole as described in claim 1, characterized in that: The length of the non-connecting end of the spiral sleeve (1) extending out of the tube sheet end face is 5-8mm.

3. The tube head connection structure with a spiral sleeve between the heat exchange tube and the tube sheet hole as described in claim 1, characterized in that: [The internal...] The cross-sectional shape of the spiral channel (1-1) and the outer spiral channel (1-2) is T-shaped, rectangular, or arc-shaped.

4. The tube head connection structure with a spiral sleeve between the heat exchange tube and the tube sheet hole as described in claim 1, characterized in that: The diameter of the radial through hole (1-5) is smaller than the width of the spiral channel groove.

5. The tube head connection structure with a spiral sleeve between the heat exchange tube and the tube sheet hole as described in claim 1, characterized in that: The tube sheet (3) is a weldable metal plate of a certain thickness. Tube holes are regularly opened on the metal plate along the thickness direction. The tube holes in the thickness direction of the tube sheet have two cylindrical surfaces with different diameters. Taking the outer end face (3-1) of the tube sheet as the reference, the tube hole is first a large diameter hole (3-2) of a certain length, and then becomes a small diameter hole (3-3). An annular step (3-4) is formed between the large diameter hole (3-2) and the small diameter hole (3-3).

6. The tube head connection structure with a spiral sleeve between the heat exchange tube and the tube sheet hole as described in claim 5, characterized in that: The depth of the large-diameter hole (3-2) is 1.2 to 1.5 times the wall thickness of the heat exchange tube, and the diameter of the large-diameter hole (3-2) is 1.02 to 1.05 times the outer diameter of the cylindrical surface of the positioning connection end (1-3).

7. The tube head connection structure with a spiral sleeve between the heat exchange tube and the tube sheet hole as described in claim 5, characterized in that: The heat exchange tube (2) is a weldable metal tube of a certain thickness and length. The heat exchange tube is a tube with smooth inner and outer walls, or a non-smooth surface is set in the area outside the spiral sleeve (1) to enhance heat transfer.

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