A fin structure for a molten salt heat exchanger of an alkylation spent acid regeneration unit

Abstract

The utility model discloses a kind of fin structure for molten salt heat exchanger of alkylated waste acid regenerating device, and the finned tube heat exchanger of this structure has two different tube types: T1, T2.Tube bundle upstream 1~14 rows are T1 tube type, and 15~20 rows are T2 tube type.Its working principle is: by thickening fin, corrosion allowance of molten salt heat exchanger is promoted, and structural corrosion resistance is improved;Increase fin spacing, under the premise that not affecting molten salt heat exchanger heat exchange performance and fin heat dissipation capacity, make that finned tube heat exchanger is not easy to scale, conducive to cleaning, improve service life.

Description

Technical Field

[0001] This utility model relates to the field of petrochemical equipment technology, specifically to a finned structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit. Background Technology

[0002] Alkylation is a key process in petroleum processing, involving the reaction of isobutane with olefins (such as butene) to produce alkylate oils with high octane numbers. This process typically uses concentrated sulfuric acid or hydrofluoric acid as catalysts. During the alkylation reaction, some sulfuric acid loses its activity due to various reasons (such as dilution, side reactions, and impurity accumulation), becoming waste acid. This waste acid contains organic matter, metallic impurities, and unreacted sulfuric acid, requiring treatment and recycling to avoid environmental pollution and resource waste. Direct discharge of waste acid can cause serious environmental pollution, including soil acidification and water pollution. Therefore, it is essential to convert it into a reusable resource through effective treatment methods. Waste acid regeneration systems, through a series of process steps such as incineration, cracking, absorption, and purification, convert the sulfuric acid in waste acid back into high-concentration sulfuric acid for reuse in the alkylation process. This process not only reduces environmental pollution but also achieves resource recycling.

[0003] However, molten salt heat exchangers in existing alkylation waste acid regeneration units (such as equipment E-8270) face significant challenges:

[0004] 1. Corrosion problem: The heat exchange tube material is S31668 and the fin material is S32168. The resistance to sulfuric acid corrosion is insufficient. After three months of operation, the lower five rows of fins almost completely failed due to corrosion, which seriously affected the normal operation of the equipment.

[0005] 2. Scaling and clogging: The original design had a high fin density (10 fins / inch) and small spacing, which made it easy for impurities in waste acid to deposit, making cleaning difficult and further exacerbating the decline in heat exchange efficiency and shortening the equipment life.

[0006] 3. Economic losses: Given the high added value of alkylated oils, frequent equipment maintenance and downtime lead to economic losses for enterprises.

[0007] To address the aforementioned issues, existing technologies primarily improve the situation by replacing corrosion-resistant materials or adjusting structural parameters, but these methods often fail to simultaneously meet the requirements for corrosion resistance, heat exchange performance, and scale prevention.

[0008] Therefore, there is an urgent need for a new type of fin structure that can improve corrosion resistance, optimize fin layout to reduce the risk of scaling, and ensure that heat exchange efficiency is not reduced. Utility Model Content

[0009] The purpose of this invention is to provide a finned structure for a molten salt heat exchanger in an alkylation waste acid regeneration device, aiming to solve the problems of easy corrosion, scaling, and reduced heat exchange efficiency in existing heat exchangers.

[0010] To achieve the above objectives, the technical solution of this utility model is as follows:

[0011] A finned structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit, characterized in that it includes:

[0012] The tube bundle assembly consists of two different types of finned tubes arranged together. The upstream rows 1-14 use T1 type tubes, and the downstream rows 15-20 use T2 type tubes. The T1 type tubes have a fin density of 8 fins / inch, a fin thickness of 0.6-0.9 mm, a fin spacing of 2.629-4.629 mm, and a fin outer diameter of 42-46 mm. The T2 type tubes have a fin density of 6 fins / inch, a fin thickness of 0.9-1.1 mm, a fin spacing of 4.080-6.080 mm, and a fin outer diameter of 38-42 mm.

[0013] Tube sheet I and tube sheet II are respectively disposed at both ends of the tube bundle assembly;

[0014] The molten salt inlet and outlet are connected to the tube bundle assembly via a 1 / 2 semi-circular tube.

[0015] Furthermore, the base tube of the finned tube has a specification of Φ25×2mm and an effective length of 2655mm; the finned tube is fixed to the tube sheet I, the support plate, and the tube sheet II by a connection method of strength welding and expansion bonding.

[0016] Furthermore, the fins of both the T1 and T2 tubular types are made of corrosion-resistant alloy materials. The fin thickness of the T2 tubular type is greater than that of the T1 tubular type, and the fin spacing is also greater than that of the T1 tubular type.

[0017] Furthermore, the arrangement of the tube bundle assembly is determined through thermal calculation optimization to ensure that the area margin of the heat exchanger is 11.91%-14.20% and the gas pressure drop is 0.349-0.355 kPa;

[0018] Furthermore, the upstream T1 tube type adopts a higher fin density to adapt to the high-temperature flue gas environment, while the downstream T2 tube type adopts a larger fin spacing to prevent waste acid scaling.

[0019] Furthermore, the 1 / 2 semi-circular tube is connected to the molten salt inlet and molten salt outlet by welding.

[0020] An optimization method for a molten salt heat exchanger in an alkylation waste acid regeneration unit includes the following steps:

[0021] (1) Use three-dimensional modeling software to establish a heat dissipation simulation experimental model of a spiral finned tube heat exchanger;

[0022] (2) Perform finite element mesh generation on the heat dissipation simulation model, and calculate the changes in flue gas velocity, temperature and pressure in the fluid domain by combining on-site working condition data;

[0023] (3) Perform thermodynamic calculations on the structure of the molten salt heat exchanger of the original alkylation waste acid regeneration unit to obtain parameters such as the area margin and pressure drop of the heat exchanger.

[0024] (4) Keeping other parameters unchanged, change the fin density and fin thickness respectively to perform thermodynamic calculations and obtain a series of parameters such as area margin and pressure drop corresponding to different tube types;

[0025] (5) Based on the above flow field analysis and thermodynamic calculation, different tube types are selected to optimize the tube bundle structure, and the most suitable tube type and tube bundle structure are selected from them.

[0026] The specific steps (1) are as follows:

[0027] (1) Determine the structural parameters of the spiral finned tube based on its structural characteristics, determine the range of values ​​for the structure based on actual needs, and establish the geometric model of the spiral finned tube.

[0028] The structural parameters of the spiral finned tube include: finned tube diameter, fin density, fin thickness, and fin height;

[0029] (2) Establish a fluid domain in the geometric model of the spiral finned tube, where there is a fluid-structure interaction surface between the air and the finned tube;

[0030] (3) Adjust the boundaries and volume of the fluid domain to make the simulation environment conform to the actual working conditions.

[0031] Step (2) is as follows:

[0032] (1) Perform finite element mesh generation on the initial heat dissipation simulation model and verify mesh independence to determine the optimal range of mesh number;

[0033] (2) Heat dissipation simulation experiments were conducted using FLUENT software under different fin densities, fin thicknesses, and fin heights.

[0034] (3) Based on the simulation results, record the temperature and pressure distribution cloud map and velocity vector map of the fluid domain, and compare the optimization effect.

[0035] Steps (3) to (5) are as follows:

[0036] (1) Use HTRI software to perform thermodynamic calculations on the original design to obtain the gas pressure drop and area margin;

[0037] (2) Select fin densities of 10, 7, 6 and 5 fins / inch, and fin thicknesses of 0.4, 1, 1.2, 1.5 and 2 mm, respectively. The fin densities and fin thicknesses are combined in a cross-cutting manner. The heat exchanger is thermally calculated according to the original design parameters and tube bundle structure, and the area margin is compared.

[0038] (3) Select tube bundle structures with low pressure drop, large area margin and low fin density to give them good anti-fouling and anti-clogging performance.

[0039] Compared with the prior art, the present invention has the following main advantages:

[0040] The design employs a combination of two different finned tube types (T1 and T2), wherein:

[0041] T1 tube type (upstream rows 1-14): fin density is 8 fins / inch, fin thickness is 0.8 mm, fin spacing is 3.629 mm, and outer diameter is 44 mm.

[0042] T2 tube type (downstream 15-20 rows): fin density is 6 fins / inch, fin thickness is 1.0 mm, fin spacing is 5.080 mm, and outer diameter is 40 mm.

[0043] Corrosion resistance is improved by thickening the fins (thicker for the T2 tube type), while the fin spacing is increased to reduce the risk of scaling.

[0044] The improved design features thicker fins and a larger spacing compared to the original design, resulting in a greater gap between the two layers, making it less prone to scaling and easier to clean.

[0045] Thickening the fins increases the corrosion allowance of the finned tube heat exchanger, which can effectively improve the corrosion resistance of the finned tube heat exchanger without affecting its heat dissipation performance, thus improving its overall service life.

[0046] The original S31668 / S32168 was replaced with a material with better corrosion resistance (such as 825 or 904L alloy) to enhance its resistance to sulfuric acid corrosion. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the fin structure of the molten salt heat exchanger used in the alkylation waste acid regeneration device of this utility model.

[0048] Figure 2 This is a schematic diagram of the finned tube cross-section of the molten salt heat exchanger in an alkylation waste acid regeneration unit.

[0049] Figure 3 This is a side view of the finned tube T1 of the molten salt heat exchanger in the alkylation waste acid regeneration unit.

[0050] Figure 4This is a side view of the finned tube T2 of the molten salt heat exchanger in the alkylation waste acid regeneration unit.

[0051] In the diagram: 1-finned tube 1, Ⅰ2-tube sheet, 3-support plate, Ⅱ4-tube sheet, 5-1 / 2 semi-circular tube, 6-molten salt outlet, 7-molten salt inlet. Detailed Implementation

[0052] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0053] Example 1

[0054] like Figure 1 As shown, a finned structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit includes:

[0055] The tube bundle assembly consists of two different types of finned tubes arranged together. The upstream rows 1-14 use the T1 type, and the downstream rows 15-20 use the T2 type. The T1 type has a fin density of 8 fins / inch, a fin thickness of 0.8 mm, a fin spacing of 3.629 mm, and a fin outer diameter of 44 mm. The T2 type has a fin density of 6 fins / inch, a fin thickness of 1.0 mm, a fin spacing of 5.080 mm, and a fin outer diameter of 40 mm.

[0056] Tube sheet I2 and tube sheet II4 are respectively disposed at both ends of the tube bundle assembly;

[0057] The molten salt inlet 7 and the molten salt outlet 6 are connected to the tube bundle assembly via a 1 / 2 semi-circular tube 5.

[0058] Finned tube 1 is connected to tube sheet I 2, support plate 3, and tube sheet II 4 by a combination of strength welding and expansion bonding.

[0059] The specific route is as follows:

[0060] (1) Perform thermal calculations on the original design to obtain parameters such as the area margin and pressure drop of the heat exchanger.

[0061] (2) Keeping other parameters unchanged, the fin density and fin thickness are changed respectively to perform thermodynamic calculations and obtain a series of parameters such as area margin and pressure drop corresponding to different tube types.

[0062] (3) Based on the above thermal calculations, different tube types are selected to optimize the tube bundle structure, and the most suitable tube type and tube bundle structure are selected from them.

[0063] First, thermal calculations were performed on the original design. Table 1 shows the results of the thermal calculations for the original design.

[0064] Table 1

[0065]

[0066] The improved finned tube heat exchanger has two different tube types: T1 and T2, as shown in Table 2. Among them, rows 1 to 14 upstream of the tube bundle are of type T1, and rows 15 to 20 are of type T2.

[0067] Table 2

[0068]

[0069] The improved tube bundle structure uses two materials, 825 and 904L, respectively, and thermal calculations are performed on the tube bundles of both materials. The results of the thermal calculations are shown in Table 3.

[0070] Table 3

[0071]

[0072] The 1 / 2 semi-circular tube 5 is connected to the molten salt outlet 6 and the molten salt inlet 7 by welding.

[0073] Example 2

[0074] Based on Example 1, the improved finned tube heat exchanger has two different tube types: T1 and T2. Rows 1-14 upstream of the tube bundle are of type T1, and rows 15-20 are of type T2, as shown below. Figures 2-4 As shown.

[0075] The working process of this utility model is as follows: high-temperature flue gas flows from upstream through the tube bundle assembly and exchanges heat with the molten salt inside the tube; the dense fins of the T1 tube type enhance the upstream heat exchange efficiency; the T2 tube type with increased spacing effectively prevents downstream scaling; the molten salt circulates inside the tube to complete the heat transfer.

[0076] Compared with the original solution, this embodiment has thicker fins, larger spacing, and a larger gap between the two layers, making it less prone to scaling, easier to clean, and improving cleaning efficiency. The thicker fins increase the corrosion allowance of the finned tube heat exchanger, which can effectively improve the corrosion resistance of the finned tube heat exchanger. Furthermore, thermal calculations show that it will not affect its heat dissipation performance, thus improving the overall service life of the equipment.

Claims

1. A finned structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit, characterized in that, include: The tube bundle assembly consists of two different types of finned tubes arranged together. The upstream rows 1-14 use T1 type tubes, and the downstream rows 15-20 use T2 type tubes. The T1 type tubes have a fin density of 8 fins / inch, a fin thickness of 0.6-0.9 mm, a fin spacing of 2.629-4.629 mm, and a fin outer diameter of 42-46 mm. The T2 type tubes have a fin density of 6 fins / inch, a fin thickness of 0.9-1.1 mm, a fin spacing of 4.080-6.080 mm, and a fin outer diameter of 38-42 mm. Tube sheet I (2) and tube sheet II (4) are respectively disposed at both ends of the tube bundle assembly; The molten salt inlet (7) and molten salt outlet (6) are connected to the tube bundle assembly via a 1 / 2 semi-circular tube (5).

2. The fin structure for the molten salt heat exchanger of the alkylation waste acid regeneration unit according to claim 1, characterized in that, The base tube of the finned tube (1) has a specification of Φ25×2mm and an effective length of 2655mm. The finned tube (1) is fixed to the tube sheet I (2), the support plate (3), and the tube sheet II (4) by a connection method of strength welding and expansion bonding.

3. The finned structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit according to claim 1, characterized in that, The fins of both the T1 and T2 tube types are made of corrosion-resistant alloy material. The fin thickness of the T2 tube type is greater than that of the T1 tube type, and the fin spacing is also greater than that of the T1 tube type.

4. The fin structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit according to claim 1, characterized in that, The arrangement of the tube bundle assembly is determined through thermal calculation optimization to ensure that the area margin of the heat exchanger is 11.91% to 14.20% and the gas pressure drop is 0.349 to 0.355 kPa.

5. The fin structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit according to claim 1, characterized in that, The upstream T1 tube type uses a higher fin density to adapt to the high-temperature flue gas environment, while the downstream T2 tube type uses a larger fin spacing to prevent waste acid scaling.

6. The fin structure for a molten salt heat exchanger in an alkylation waste acid regeneration unit according to claim 1, characterized in that, The 1 / 2 semi-circular tube (5) is connected to the molten salt inlet (7) and the molten salt outlet (6) by welding.

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