Optimization method, structure and maleic anhydride reactor for improving temperature field and flow field uniformity

Abstract

The present invention relates to the field of heat exchanger technology, specifically to an optimization method, structure and maleic anhydride reactor for improving the uniformity of temperature field and flow field. The optimization method comprises the following steps: establishing an original model of the maleic anhydride reactor; establishing multiple optimization models based on the original model; importing the original model and each optimization model into the pre-processing software for meshing, performing coupled calculation of the flow field and temperature field of the maleic anhydride reactor, and obtaining an optimized structure with the minimum radial temperature difference of the maleic anhydride reactor. The optimized structure is to add a vertical annular rectifier plate to the entire flow area above the bend on the inner side of the first, third and fifth annular baffles, and to open a guide hole on the rectifier plate; each rectifier plate is divided into three parts from top to bottom, and the aperture and porosity of the guide hole of each part are optimized and adjusted according to the specific flow conditions of the reactor. The invention can effectively improve the uniformity of the temperature field and flow field of the molten salt on the radial section of the shell side.

Description

Technical Field

[0001] The present invention relates to the technical field of maleic anhydride production equipment, in particular to an optimization method and structure for improving the uniformity of temperature field and flow field, and a maleic anhydride reactor. Background Art

[0002] Maleic anhydride is a key chemical raw material for synthetic resins, coatings, plasticizers, and pharmaceutical intermediates. Its industrial production primarily utilizes the gas-phase catalytic oxidation of benzene or n-butane. The reactor, as a core piece of equipment, requires high temperatures and a catalyst to achieve efficient and selective oxidation.

[0003] Maleic anhydride reactors are essential equipment for the production of maleic anhydride. During their operation, temperature and flow field uniformity are key factors in determining reaction efficiency, product selectivity, and energy consumption. However, maleic anhydride reactors of varying structures exhibit varying flow and temperature distributions. Even within the same maleic anhydride reactor, the flow and temperature distributions vary at different locations. These differences in flow and temperature distributions directly impact the lifespan of the reactor catalyst, and thus the operating cycle and cost of the entire unit.

[0004] Therefore, in order to improve the uniformity of the temperature and flow fields of the molten salt on the radial cross section of the shell side, the industry generally believes that through-flow holes can be set on the horizontal baffles of the maleic anhydride reactor to eliminate local flow dead zones. However, adding conventional vertical flow guide structures to the heat exchanger baffles has the following disadvantages:

[0005] (1) Destruction of flow field uniformity

[0006] Flow velocity distribution distortion: Vertical guide plates may force the main flow direction to change, resulting in excessively high or low flow velocity in local areas of the tube bundle, forming new heat transfer dead zones;

[0007] Intensified bypass flow: If the gap between the guide plate and the shell is not properly controlled, bypass flow may be induced, reducing the utilization rate of the effective heat exchange area.

[0008] (2) Flow resistance and energy loss:

[0009] Local pressure drop amplification: Vertical guide plates will directly block the flow direction of the fluid, increase the local pressure drop, and generate secondary vortices: The edges of the guide plates may induce new small-scale vortices (such as boundary layer separation), especially under high-speed flow conditions, which will in turn aggravate energy dissipation.

[0010] When installing horizontal baffles and vertical guide plates at the same time, the following problems may occur in the structural design of small heat exchangers:

[0011] (1) Installation space limitation: The gap between the baffle and the tube bundle is limited. The installation of the vertical guide plate may require changing the original compact layout, resulting in adjustment of the tube bundle spacing or increase in the shell size.

[0012] (2) Difficulty in welding and supporting: The guide plate needs to be welded to the baffle or shell. If it is arranged vertically, local stress concentration may occur due to different force directions, increasing the risk of fatigue failure.

[0013] (3) Inconvenient maintenance: The guide plate may hinder the extraction or cleaning of the tube bundle, especially in the multi-pass structure, the vertical guide plate will further limit the operating space.

[0014] In summary, how to design an alternative optimization method, optimized structure and maleic anhydride reactor to improve the uniformity of temperature field and flow field is a research field that has yet to be developed. Summary of the Invention

[0015] The present invention aims to provide an optimization method, structure, and maleic anhydride reactor for improving temperature and flow field uniformity. This paper analyzes the baffle structure of a large maleic anhydride reactor, aiming to improve the reactor's temperature and flow field uniformity through computational fluid dynamics (CFD) methods, thereby enhancing its performance. Comparison of the temperature and flow fields before and after optimization demonstrates that the optimized structure effectively reduces radial temperature differences and improves temperature uniformity across the radial cross-section of the molten salt shell.

[0016] In order to achieve the above technical effects, the present invention discloses an optimization method for improving the uniformity of temperature field and flow field, the steps of which are as follows:

[0017] S1. Establishing an original model of a maleic anhydride reactor; a quarter model of the original model of the maleic anhydride reactor, specifically, an inlet pipe at the bottom and an outlet pipe at the top; arranging five annular baffles (from the first to the fifth) in the axial direction in the maleic anhydride reactor to divide the flow area into six regions (from the first to the sixth);

[0018] S2. Multiple optimization models were established based on the original model; the maleic anhydride reactor was divided into six flow regions with five baffles as boundaries; the optimization model was to add annular rectifiers with guide holes in the vertical direction at the inner bends of the first, third, and fifth annular baffles;

[0019] S3. Import the original model and each optimized model into the simulation software for meshing and sensitivity analysis, perform coupled calculation of the flow field and temperature field of the maleic anhydride reactor, and obtain the optimized structure with the minimum radial temperature difference of the maleic anhydride reactor.

[0020] Furthermore, multiple optimization schemes are formed based on the number, position, height, thickness, guide hole diameter, hole spacing, and porosity of the rectifier plates:

[0021] Optimization Solution 1: Add a vertical annular straightening plate to the top of the flow area directly below the inner bend of the first, third, and fifth annular baffles. The straightening plate should be shorter than the overall height of the flow area, and have diversion holes distributed in a circular array. The diversion holes on the same straightening plate should have the same aperture and porosity.

[0022] Optimization Plan 2: Add a vertical annular rectifier plate to the top of the corresponding flow area directly above the inner bend of the first, third, and fifth annular baffles. The rectifier plate height is smaller than the overall height of the flow area, and the rectifier plate is provided with flow guide holes distributed in a circular array. The pore size and porosity of the rectifier holes on the same rectifier plate are the same.

[0023] Optimization Plan 3: In the flow areas directly above the inner bends of the first, third, and fifth annular baffles, a vertical annular straightening plate is added at the top and bottom, respectively. A gap for fluid flow is provided between the two straightening plates, and flow guide holes are provided in a circular array on both straightening plates. The aperture and porosity of the flow guide holes on the same straightening plate are the same.

[0024] Optimization Solution 4: Install a vertical annular rectifier plate in the flow area directly above the inner bend of the first, third, and fifth annular baffles, extending through the entire area. The rectifier plate's height is equal to the overall height of the flow area, and the rectifier plate has flow guide holes arranged in a circular array or triangular pattern. Each rectifier plate is divided into three sections from top to bottom, and the diameter and porosity of the guide holes in each section vary.

[0025] Optimization Scheme 5: Further verify the model examples that meet the verification criteria in the first four optimization schemes under different inlet flow conditions;

[0026] Verification criteria: the average radial temperature difference does not exceed ±2°C, and the difference between the highest and lowest temperatures in the same horizontal section does not exceed 4°C;

[0027] The optimization model described in S2 is formed according to the parameter combination of the rectifier plate and the guide hole in the above optimization scheme.

[0028] Furthermore, the calculation strategy in S3 is as follows: S3.1 Calculation strategy: Select the calculation model and use the Realizable ke turbulence model for steady-state calculation; S3.2 Determine the boundary conditions and physical parameters; S3.3 Allocate the guide holes on the ring plate and the rectifier plate according to the inlet and outlet flow, and set the resistance coefficient.

[0029] Furthermore, the drag coefficient formula in S3.3 is as follows:

[0030] (4)

[0031] (5)

[0032] (6)

[0033] In the above formula, Refers to the sum of the resistance coefficients generated by the fluid entering and exiting the diversion hole; Refers to the resistance coefficient of the fluid along the diversion hole and The total drag coefficient after addition; and All are dimensionless quantities; is the pressure drop, unit: Pa; ; is the friction resistance coefficient, is the thickness of the orifice plate, m; is the aperture, m; is a function; is the flow hole area, m 2 ; is the total circulation area, m 2 ; is the porosity, is the Reynolds number, is the density, kg / m 3 ; is the speed, m / s; is the hydraulic diameter, m; is the viscosity, .

[0034] The present invention also discloses an optimized structure obtained by an optimization method for improving the uniformity of the temperature field and the flow field. The optimized structure is that a vertical annular rectifier plate running through the entire area is added to the flow area corresponding to the inner bend directly above the first, third and fifth annular deflectors. The height of the rectifier plate is equal to the overall height of the flow area, and evenly distributed guide holes are provided on the rectifier plate; each rectifier plate is divided into three parts from top to bottom, and the aperture and porosity of the guide holes in each part are different.

[0035] Furthermore, the specifications of each rectifier board are as follows:

[0036] The upper part of the rectifier plate accounts for 33% to 75% of the overall height of the plate, the middle part of the rectifier plate accounts for 12.5% ​​to 33% of the overall height of the plate, and the lower part of the rectifier plate accounts for 12.5% ​​to 33% of the overall height of the plate;

[0037] The diameter of the guide holes on the upper part of the rectifier plate is 12~25mm; the diameter of the guide holes in the middle part of the rectifier plate is 12~25mm; the diameter of the guide holes on the lower part of the rectifier plate is 0~32mm; the diameter of the guide holes is 16~30mm, and the porosity is 0.2~0.775;

[0038] The diversion holes are distributed in a circular array or a triangle, with a hole spacing of 20~32.45mm.

[0039] Furthermore, the upper part of the rectifier plate accounts for 75% of the overall height of the plate, has a pore diameter of 12 mm, and a porosity of 0.125; the middle part of the rectifier plate accounts for 12.5% ​​of the overall height of the plate, has a pore diameter of 12 mm, and a porosity of 0.125; the lower part of the rectifier plate accounts for 12.5% ​​of the overall height of the plate, has a pore diameter of 12 mm, and a porosity of 0.125.

[0040] Furthermore, the maximum radial temperature difference of each cross section in the optimized flow region is 2.00°C, and the average radial temperature difference is 1.74°C.

[0041] The invention also discloses a maleic anhydride reactor, which comprises an optimized structure obtained by an optimization method for improving the uniformity of temperature field and flow field.

[0042] The beneficial effects of the present invention are:

[0043] (1) To address the numerous issues associated with installing vertical baffles in maleic anhydride reactors, the present invention opts for installing vertical baffles in large maleic anhydride reactors with diameters of 7 to 9 meters. These reactors have a large, unpiped area in the center, leaving ample space for vertical baffle installation. Large maleic anhydride reactors are fixed-bed reactors with high shell-side media cleanliness, eliminating the need for core extraction and cleaning, and eliminating maintenance issues.

[0044] (2) The rectifier plate in this application is a monolithic structure that can be welded between the reactor tube sheet and the horizontal baffle plate or between two baffle plates. For long weld lengths, a butt joint can be selected as the welding groove form, which is easy to ensure strength. After optimizing the position, number, and structure of the rectifier plate, the flow field is evenly distributed on the plate, reducing the risk of stress concentration and fatigue.

[0045] (3) The present invention establishes an original model and multiple optimization models, and uses computational fluid dynamics methods to perform coupled calculations of the flow field and temperature field. Different areas and opening rates are divided on the rectifier plate, so that the resistance coefficients of different areas of the rectifier plate are different, eliminating factors such as vortices and turbulence that change the fluid flow rate and affect heat transfer. On the basis of greatly reducing the resistance of traditional guide plates, the fluid is evenly distributed after passing through the rectifier plate, reducing the risk of stress concentration and fatigue, and improving the overall heat transfer effect of the reactor.

[0046] The present invention uses software to perform flow and heat transfer analysis before and after optimization, proving that the optimized structure can effectively reduce the radial temperature difference. After optimization, the maximum radial temperature difference of each section in the flow area is reduced from 6.08°C to 2.00°C, significantly improving the temperature field uniformity of the molten salt on the radial section on the shell side, and effectively improving the flow field in the flow area, reducing or even eliminating a large number of vortices existing below the flow area behind the deflector. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the original model area division of the present invention;

[0048] Figure 2 This is a schematic diagram of the molten salt flow path of the original model of the present invention;

[0049] Figure 3 This is the flow field distribution diagram of the original model of the present invention;

[0050] Figure 4 This is the temperature distribution diagram of the original model of the present invention;

[0051] Figure 5 This is a cross-sectional distribution diagram of the flow area of ​​the original model of the present invention;

[0052] Figure 6 This is a schematic diagram of an optimization model according to Example 1 of the present invention;

[0053] Figure 7 This is a schematic diagram of an optimization model according to Example 2 of the present invention;

[0054] Figure 8 This is a schematic diagram of an optimization model of Example 3 of the present invention;

[0055] Figure 9 This is a schematic diagram of an optimization model according to Example 4 of the present invention;

[0056] Figure 10 This is a streamline diagram under 80% flow conditions of Example 5 of the present invention;

[0057] Figure 11 This is the streamline diagram under 90% flow conditions of Example 6 of the present invention.

[0058] In the figure: 1. baffle; 11. first annular baffle; 12. second annular baffle; 13. third annular baffle; 14. fourth annular baffle; 15. fifth annular baffle; 2. inlet pipe; 3. outlet pipe; 4. first flow area; 5. second flow area; 6. third flow area; 7. fourth flow area; 8. fifth flow area; 9. sixth flow area; 10. central heat transfer tube; 11. non-tube bundle area; 12. tube bundle area; 13. first section; 14. second section; 15. third section; 16. rectifier. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0060] This invention provides an optimization method for improving temperature and flow field uniformity. This optimization method is suitable for large maleic anhydride reactors with a diameter of 7 to 9 meters. Such reactors have a large unpiped area in the center, leaving ample space for the installation of vertical rectifier plates. The specific optimization steps are as follows:

[0061] S1. Establish the original model:

[0062] The original model of maleic anhydride reactor was constructed through software;

[0063] The maleic anhydride reactor comprises a cylindrical cavity shell, in which an annular baffle 1, a central heat transfer pipe 10, an inlet flow distribution ring plate, and a guide plate are arranged in an annular chamber of the cavity shell, and a bilaterally symmetrical inlet pipe 2 and outlet pipe 3 are opened on the side wall of the cavity shell;

[0064] Due to the symmetry of the maleic anhydride reactor, all optimization designs of the present invention are carried out using a quarter model; the original model of the maleic anhydride reactor is as follows: Figure 1 As shown, the lower part is the inlet pipe and the upper part is the outlet pipe; the first to fifth annular baffles 1 are arranged axially in the maleic anhydride reactor to divide the flow area into six flow areas, namely the first to sixth flow areas; this can increase the heat exchange distance of the molten salt, thereby improving the cooling effect. Figure 2 After the molten salt passes through the inlet pipe, it Figure 2 The path shown flows across the tube bundle area, exchanges heat with the central heat transfer tube, and finally takes away the reaction heat in the tube through the outlet pipe.

[0065] S2. Establish an optimized model based on the original model:

[0066] S2.1 The maleic anhydride reactor is divided into 6 areas with the baffles as the boundaries. The present invention aims to optimize the inner structure of the baffles, which affects the flow areas above the first, third and fifth baffles. The cross-sections of the three flow areas are shown in the figure below. Figure 5 shown.

[0067] S2.2 The optimization idea of ​​the present invention is to add annular rectifying plates 16 with guide holes in the vertical direction at the inner bends of the first, third and fifth annular baffles (11, 13, 15);

[0068] The following optimization solutions are included:

[0069] Optimization Solution 1: Add a vertical annular straightening plate to the top of the flow area directly below the inner bend of the first, third, and fifth annular baffles. The straightening plate should be shorter than the overall height of the flow area, and have diversion holes distributed in a circular array. The diversion holes on the same straightening plate should have the same aperture and porosity.

[0070] Optimization Plan 2: Add a vertical annular rectifier plate to the top of the corresponding flow area directly above the inner bend of the first, third, and fifth annular baffles. The rectifier plate height is smaller than the overall height of the flow area, and the rectifier plate is provided with flow guide holes distributed in a circular array. The pore size and porosity of the rectifier holes on the same rectifier plate are the same.

[0071] Optimization Plan 3: In the flow areas directly above the inner bends of the first, third, and fifth annular baffles, a vertical annular straightening plate is added at the top and bottom, respectively. A gap for fluid flow is provided between the two straightening plates, and flow guide holes are provided in a circular array on both straightening plates. The aperture and porosity of the flow guide holes on the same straightening plate are the same.

[0072] Optimization Solution 4: Install a vertical annular rectifier plate in the flow area directly above the inner bend of the first, third, and fifth annular baffles, extending through the entire area. The rectifier plate's height is equal to the overall height of the flow area, and the rectifier plate has flow guide holes arranged in a circular array or triangular pattern. Each rectifier plate is divided into three sections from top to bottom, and the diameter and porosity of the guide holes in each section vary.

[0073] Among the above four optimization schemes, each optimization scheme can form multiple model examples based on the combination of parameters such as rectifier plate height, thickness, guide hole diameter, hole spacing, porosity, etc.

[0074] Optimization Scheme 5: The model examples that meet the verification criteria in the first four optimization schemes are further verified and calculated under different inlet flow conditions.

[0075] S3. The original model and the optimized models of each case were imported into the pre-processing software for meshing and sensitivity analysis. The coupling calculation of the flow field and temperature field of the maleic anhydride reactor was performed to obtain the optimized structure with the minimum radial temperature difference of the maleic anhydride reactor.

[0076] S3.1 Calculation strategy: Select the calculation model and use the Realizable ke turbulence model for steady-state calculation;

[0077] S3.2 Determine boundary conditions and physical parameters:

[0078] 1) This calculation uses a mass flow inlet and a pressure outlet, where the mass flow inlet flow rate is 1763.33 kg / s and the temperature is 420°C.

[0079] 2) Physical properties of molten salt: Since the flow rate of shell-side molten salt in the maleic anhydride reactor is large and the temperature change is small, the physical properties of the molten salt at 420°C are used, and its density is 1840.0 kg / m 3 , specific heat capacity 1792.0 J / kg-K, kinematic viscosity 0.00175 Pa-s, thermal conductivity 0.664 W / mK.

[0080] 3) The inlet and outlet flow distribution ring plates, tube bundle area, and baffles were simplified, retaining the outer contour of the flow area; the tube bundle area adopted distributed porous medium resistance;

[0081] 4) There is a complex chemical reaction in the central heat transfer tube that releases heat, and the heat transfer of the molten salt in the tube bundle area is simulated in the form of axial distribution.

[0082] S3.3 distributes the guide holes on the ring plate and the rectifier plate according to the inlet and outlet flow, and sets the resistance coefficient:

[0083] ;

[0084] ;

[0085] ;

[0086] In the above formula, Refers to the sum of the resistance coefficients generated by the fluid entering and exiting the diversion hole; Refers to the resistance coefficient of the fluid along the diversion hole and The total drag coefficient after addition; and All are dimensionless quantities; is the pressure drop, unit: Pa; ; is the friction resistance coefficient, is the thickness of the orifice plate, m; is the aperture, m; is a function; is the flow hole area, m 2 ; is the total circulation area, m 2 ; is the porosity, is the Reynolds number, is the density, kg / m 3 ; is the speed, m / s; is the hydraulic diameter, m; is the viscosity, .

[0087] Table 1 Value selection

[0088]

[0089] This application uses the method in S3 to analyze and calculate the original model. Figure 3 、 Figure 4 The velocity and temperature field distributions of the original model are shown in Figure 2. It can be seen that in this structure, because the fluid velocity above each flow area is higher than below, a large number of vortices appear below the flow area after passing through the baffles. These vortices form stagnation points of flow, resulting in uneven velocity distribution of the molten salt and the generation of hot spots. The maximum radial temperature difference between each cross section is 6.59°C.

[0090] In order to obtain an optimized structure that improves the uniformity of the temperature field and flow field in the maleic anhydride reactor, the following optimization schemes 1 to 6 are verified one by one:

[0091] Verification criteria: The average radial temperature difference does not exceed ±2°C (the difference between the highest and lowest temperatures on the same horizontal section does not exceed 4°C);

[0092] Example 1

[0093] like Figure 6 As shown, in this embodiment, a vertical annular rectifier plate is added to the top of the flow area below the bend on the inner side of the first, third and fifth annular deflectors (the second, fourth and sixth flow areas). The height of the rectifier plate is smaller than the height of the flow area in which it is located, and guide holes distributed in a circular array are opened on the rectifier plate. The hole spacing is 32.45 mm, and the angle between the axes of adjacent holes is 60°.

[0094] The specifications of the rectifier board in Example 1 are as follows:

[0095] 1) The height of the rectifier plates is 50% of the height of the flow area where they are located;

[0096] 2) The thickness of the rectifier plate is 16mm;

[0097] 3) The diameter of the diversion holes is 16 mm, the porosity is 0.538; the hole spacing is 32.45 mm, and the angle between the axes of adjacent holes is 60°.

[0098] A sensitivity analysis of Example 1 shows that adding a straightening plate below the inner side of the baffle has almost no effect on the flow above the baffle, and obvious vortices still exist, which cannot effectively improve the flow field in this area.

[0099] Table 2 lists the radial temperature difference, maximum temperature difference, and average temperature difference change percentage of each section of Section 1, Section 2, and Section 3. It can be seen that the radial temperature difference of the cross section in the calculation results of Example 10 is large, and the temperature field has not been significantly improved, which cannot meet the verification criteria.

[0100] Table 2

[0101]

[0102] Example 2

[0103] like Figure 7 As shown, this embodiment adds a vertical annular rectifier plate on the top of the flow area (the first, third, and fifth flow area) above the bend on the inner side of the first, third, and fifth annular deflectors. The height of the rectifier plate is smaller than the height of the flow area in which it is located, and guide holes distributed in an annular array are provided on the rectifier plate.

[0104] The specifications of the rectifier plate in this embodiment are as follows:

[0105] 1) The height of the rectifier plate is 33%, 50% and 67% of the height of the flow area respectively;

[0106] 2) The thickness of the rectifier plate is 16mm;

[0107] 3) The diameter of the diversion hole is 20 mm, the porosity is 0.345; l / d = 0.8, where l is the depth of the diversion hole and d is the diameter of the diversion hole; the hole spacing is 32.45 mm, and the angle between the axes of adjacent holes is 60°.

[0108] Table 3

[0109]

[0110] A sensitivity analysis of Examples 2-4 shows that, even with the addition of a straightening plate above the flow area, significant vortices still exist below the plate. While these vortices gradually decrease with increasing straightening plate height, they are still not completely eliminated. The flow velocity behind the straightening plate decreases significantly, but in the area below the flow area without the straightening plate, a significant axial velocity difference persists, causing vortices to form. Therefore, this structural solution cannot effectively improve the flow field in this area.

[0111] Table 4 lists the radial temperature difference, maximum temperature difference, and average temperature difference percentage change of each section of Section 1, Section 2, and Section 3. It can be seen that with the increase of the rectifier plate height, the radial temperature difference of each section in the calculated results gradually decreases, and there is a significant improvement in the temperature field compared with the prototype structure. The results of Examples 11 and 13 meet the verification criteria.

[0112] Table 4

[0113]

[0114] Example 3

[0115] like Figure 8 As shown, in this embodiment, a vertical annular rectifier plate is added to the top and bottom of the flow area (the first, third, and fifth flow areas) in the flow area above the bend on the inner side of the first, third, and fifth annular deflectors. There is a gap between the two rectifier plates for fluid to pass through, and guide holes distributed in an annular array are provided on both rectifier plates.

[0116] The specifications of the rectifier plate in this embodiment are as follows:

[0117] 1) The height of the rectifier plate is 33%, 50%, 67% and 75% of the height of the flow area respectively;

[0118] 2) The thickness of the rectifier plate is 16mm;

[0119] 3) The diameters of the diversion holes are 16mm, 20mm, 25mm and 30mm, and the porosities are 0.22, 0.345, 0.538 and 0.775; the hole spacing is 32.45mm, and the angle between the axes of adjacent holes is 60°.

[0120] 4) The radial lengths of the straightening plate from the baffle bend are 0, 200 mm, 400 mm, 520 mm, 800 mm, and 1000 mm, respectively. When the distances are 0, 200 mm, and 400 mm, the vertical plate is located in the inner non-tube bundle area 11; when the distance is 520 mm, it is located at the junction of the tube bundle area 12 and the non-tube bundle area 11; and when the distances are 800 mm and 1000 mm, it is located in the tube bundle area.

[0121] The specific data of the rectifier plate for each example are listed in Table 5.

[0122] Table 5

[0123]

[0124] A sensitivity analysis of Examples 5 to 21 shows that, after adding two straightening plates above the flow region, a large amount of fluid flows between the two straightening plates, where the highest velocity is achieved. However, due to the obstruction of the straightening plates, the velocity downstream of the lower straightening plate is extremely low. Consequently, significant vortices still exist behind the lower straightening plates, and the flow field in this area cannot be effectively improved.

[0125] Table 6 lists the radial temperature difference, maximum temperature difference, and average temperature difference percentage change of each section relative to the prototype. It can be seen that the radial temperature difference of the cross section calculated in Examples 14 to 30 is significantly reduced compared with the prototype structure, and the temperature field is significantly improved. Among them, Examples 7, 10, and 12 meet the verification criteria.

[0126] Table 6

[0127]

[0128] Example 4

[0129] like Figure 9 As shown, in this embodiment, a vertical annular rectifier plate is added to the entire flow area (the first, third, and fifth flow areas) above the bend on the inner side of the first, third, and fifth annular baffles, and runs through the entire area. The height of the rectifier plate is equal to the overall height of the flow area in which it is located. The rectifier plate is provided with evenly distributed guide holes, and the molten salt can only pass through the guide holes. Each rectifier plate is divided into three parts from top to bottom, and the aperture and porosity of the guide holes in each part are different.

[0130] The specifications of the rectifier plate in this embodiment are as follows:

[0131] 1) The upper part of the rectifier plate accounts for 33% to 75% of the overall height of the plate, the middle part of the rectifier plate accounts for 12.5% ​​to 33% of the overall height of the plate, and the lower part of the rectifier plate accounts for 12.5% ​​to 33% of the overall height of the plate;

[0132] 2) The thickness of the rectifier plate is 16mm;

[0133] 3) The diameters of the guide holes in the upper part of the rectifier are 12 mm, 14 mm, 16 mm, 20 mm, and 25 mm; the diameters of the guide holes in the middle part of the rectifier are 12 mm, 14 mm, 16 mm, 20 mm, and 25 mm; the diameters of the guide holes in the lower part of the rectifier are 0 mm, 12 mm, 14 mm, 16 mm, 20 mm, 25 mm, 30 mm, and 32 mm; the diameters of the guide holes are 16 mm, 20 mm, 25 mm, and 30 mm, and the porosity is 0.22, 0.345, 0.538, and 0.775;

[0134] The specific data of the rectifier plate for each example are listed in Table 7, forming Examples 22 to 39: In Examples 22 to 38, the guide holes are distributed in a circular array, with a hole spacing of 32.45 mm and an angle between the axes of adjacent holes of 60°; in Example 39, the guide holes are arranged in a triangular array with a hole spacing of 20 mm.

[0135] Table 7

[0136]

[0137] Through the sensitivity analysis of Examples 22 to 39, it can be concluded that after adding the entire straightening plate to the flow area above the first, third, and fifth baffles, the vortex at this location is eliminated and the flow field in this area is effectively improved.

[0138] Table 8 lists the radial temperature difference, maximum temperature difference, and percentage change in average temperature difference for each cross-section. It can be seen that the radial temperature difference for the cross-sections in Examples 22–39 is small, significantly improving the temperature field compared to the prototype structure. Some examples meet the verification criteria. Examples 26 and 27 have the smallest cross-section temperature difference, but vortices still exist in the flow field. Considering the flow field uniformity and radial temperature difference for each cross-section, Example 38 is the optimal structure: a straightening plate is added at the bend above the inner baffle, occupying the entire height of the flow area. The straightening plate also features flow guide holes with a diameter of 12 mm, a spacing of 32.45 mm, and a porosity of 0.125.

[0139] Table 8

[0140]

[0141] Example 5

[0142] In order to verify that the optimized example 38 in Example 4 can eliminate the vortex in the flow field under different flow conditions and improve the uniformity of the flow field and temperature field, different inlet flow conditions are taken for calculation, namely 80% and 90% flow. The flow area structure is to add a vertical annular rectifier plate with a porosity of 0.125 to the entire flow area cross section above the bend on the inner side of the first, third, and fifth annular baffles. The calculated streamlines under the two sets of flow are as follows Figure 10 and Figure 11 As shown in Figure 3, the calculation results show that the optimized structure effectively improves the flow field distribution in the maleic anhydride reactor and eliminates the vortex in the flow area by reducing the flow velocity downstream of the vertical plate.

[0143] The maximum radial temperature difference of the cross section decreased from 6.08°C to 2.00°C, and the average radial temperature difference of the cross section decreased from 3.41°C to 1.74°C.

[0144] In summary, the optimized structure in Example 5 can effectively reduce the vortex generated after the molten salt flows through the baffle area, avoid the generation of flow stagnation points, and then improve the local flow field, thereby reducing the hot spots in the local area, effectively improving the temperature field uniformity of the maleic anhydride reactor, and improving the heat exchange performance of the reactor.

[0145] In practice, optimized vertical rectifiers are installed by welding, either between the reactor tube sheet and the horizontal baffles or between two baffles. For longer weld lengths, butt joints can be used as the weld groove, ensuring greater strength. Optimizing the position, number, and structure of the rectifiers ensures a uniform flow distribution across the plates, reducing the risk of stress concentration and fatigue.

[0146] In addition, the optimization scheme of this application was verified in a large-scale maleic anhydride reactor, and the practical results were consistent with the software simulation.

[0147] Although the present invention has been described above with reference to exemplary embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present invention. In particular, the various features of the embodiments disclosed herein may be combined with one another in any manner, provided no structural conflicts exist. The omission of an exhaustive description of these combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. An optimization method for improving the uniformity of temperature field and flow field, which is applicable to large-scale maleic anhydride reactors, characterized in that: The optimization steps are as follows: S1. Establishing an original model of a maleic anhydride reactor; a quarter model of the original model of the maleic anhydride reactor, specifically, an inlet pipe at the bottom and an outlet pipe at the top; arranging five annular baffles (from the first to the fifth) in the axial direction in the maleic anhydride reactor to divide the flow area into six regions (from the first to the sixth); S2. Establish multiple optimization models based on the original model; The maleic anhydride reactor was divided into six flow zones by five baffles. The optimized model was based on the addition of annular rectifiers with flow guide holes along the vertical direction at the inner bends of the first, third, and fifth annular baffles. According to the number, position, spacing, guide hole diameter, hole spacing, and porosity of the rectifier plates, the following multiple parallel optimized structures are formed: Optimized structure 1: A vertical annular rectifier plate is added to the top of the corresponding flow area directly below the inner bend of the first, third, and fifth annular baffles. The height of the rectifier plate is less than the overall height of the flow area, and the rectifier plate has diversion holes distributed in a circular array. The diversion holes on the same rectifier plate have the same aperture and porosity. Optimized structure 2: A vertical annular rectifier plate is added to the top of the corresponding flow area directly above the inner bend of the first, third, and fifth annular baffles. The height of the rectifier plate is less than the overall height of the flow area, and diversion holes are arranged in a circular array on the rectifier plate. The diversion holes on the same rectifier plate have the same aperture and porosity. Optimized structure 3: In the flow areas directly above the inner bends of the first, third, and fifth annular baffles, a vertical annular rectifier plate is added at the top and bottom, respectively. A gap for fluid flow is provided between the two rectifier plates, and flow guide holes are provided in a circular array on both rectifier plates. The pore size and porosity of the flow guide holes on the same rectifier plate are the same. Optimized Structure 4: A vertical annular rectifier plate is installed in the flow area directly above the inner bend of the first, third, and fifth annular baffles, extending through the entire area. The height of the rectifier plate is equal to the overall height of the flow area, and the rectifier plate has guide holes arranged in a circular array or triangular distribution. Each rectifier plate is divided into three parts from top to bottom, and the guide holes in each part have different apertures and porosities. The model examples that meet the verification criteria in the above four optimized structures are further verified and calculated under different inlet flow conditions; the verification criteria are: the average radial temperature difference does not exceed ±2°C, and the difference between the highest and lowest temperatures in the same horizontal section does not exceed 4°C; The optimization model is formed based on the above four optimization structures and the parameter combination of the rectifier plate and the guide hole; S3. Import the original model and each optimized model into the pre-processing software for meshing, perform coupled calculation of the flow field and temperature field of the maleic anhydride reactor, and obtain the optimized structure with the minimum radial temperature difference of the maleic anhydride reactor.

2. The optimization method for improving the uniformity of temperature field and flow field according to claim 1, characterized in that: Calculation strategy in S3: S3.1 Calculation strategy: Select the calculation model and use the Realizable Ke turbulence model for steady-state calculation; S3.2 Determine the boundary conditions and physical parameters; S3.3 Allocate the guide holes on the ring plate and the rectifier plate according to the inlet and outlet flow, and set the resistance coefficient.

3. The optimization method for improving the uniformity of temperature field and flow field according to claim 2, characterized in that: The drag coefficient formula in S3.3 is as follows: ； ； ； In the above formula, Refers to the sum of the resistance coefficients generated by the fluid entering and exiting the diversion hole; Refers to the resistance coefficient of the fluid along the diversion hole and The total drag coefficient after addition; and All are dimensionless quantities; is the pressure drop, unit: Pa; ; is the friction resistance coefficient, is the thickness of the orifice plate, m; is the aperture, m; is a function; is the flow hole area, m 2 ; is the total circulation area, m 2 ; is the porosity, is the Reynolds number, is the density, kg / m 3 ; is the speed, m / s; is the hydraulic diameter, m; is the viscosity, .

4. An optimized structure obtained by using the optimization method for improving the uniformity of temperature field and flow field according to any one of claims 1 to 3, characterized in that: The optimized structure is optimized structure 4.

5. The optimized structure obtained by the optimization method for improving the uniformity of temperature field and flow field according to claim 4, characterized in that: The specifications of each rectifier board are as follows: The upper part of the rectifier plate accounts for 33% to 75% of the overall height of the plate, the middle part of the rectifier plate accounts for 12.5% ​​to 33% of the overall height of the plate, and the lower part of the rectifier plate accounts for 12.5% ​​to 33% of the overall height of the plate; The diameter of the guide holes on the upper part of the rectifier plate is 12~25mm; the diameter of the guide holes in the middle part of the rectifier plate is 12~25mm; the diameter of the guide holes on the lower part of the rectifier plate is 0~32mm; the diameter of the guide holes is 16~30mm, and the porosity is 0.2~0.775; The diversion holes are evenly distributed in a circular array with a hole spacing of 32.45 mm; or, the diversion holes are evenly distributed in a triangular array with a hole spacing of 20 mm.

6. The optimized structure obtained by the optimization method for improving the uniformity of temperature field and flow field according to claim 5, characterized in that: After optimization, the maximum radial temperature difference of all sections in the flow area is 2.00°C, and the average radial temperature difference is 1.74°C.

7. A maleic anhydride reactor, characterized in that The maleic anhydride reactor comprises the optimized structure according to any one of claims 4 to 6.

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