Dividing wall heat exchange method of shell-and-tube heat exchanger

Abstract

The invention discloses a dividing wall heat exchange method of a shell-and-tube heat exchanger, and belongs to the technical field of heat exchange equipment. The shell pass of the heat exchanger is transformed into a closed space filled with magnesium oxide / water and other intermediate heat transfer media, high-temperature wet oxygen oxidation liquid and cold materials all reversely flow in the tube pass in a multi-pass mode, and the flow on the two sides is adjusted through monitoring and linkage; and a steady-state temperature difference greater than or equal to 10 DEG C is formed and maintained between the central high-temperature pipe area and the peripheral low-temperature pipe area by the medium in the shell pass, so that the medium is driven to generate natural convective circulation in the shell pass, and dividing wall heat exchange of'hot fluid-intermediate medium-cold fluid 'is realized.

Description

Technical Field

[0001] This invention relates to the field of heat exchange equipment technology, and more specifically, to a shell-and-tube heat exchanger indirect heat exchange. Background Technology

[0002] In processes such as wet oxygen oxidation leaching, wet oxygen desulfurization and denitrification, and wet oxygen oxidation organic wastewater treatment, high-temperature wet oxygen oxidation liquid usually needs to be cooled, while low-temperature materials need to be preheated. Fixed tube sheet shell-and-tube heat exchangers are commonly used in engineering for indirect heat exchange.

[0003] Existing literature 1 (Design and Optimization of Gas-to-Gas Indirect Wall Heat Exchanger for Mine Waste Heat Recovery, 2024) establishes a design and numerical calculation model for a gas-to-gas indirect wall heat exchanger for the working condition of mine return air waste heat utilization. It studies the influence of structural parameters such as baffle notch ratio and tube spacing on heat transfer coefficient, pressure drop and overall performance, and obtains a compromise design scheme using a multi-objective optimization method. However, in actual operation, the overall heat transfer coefficient is significantly lower than the design value, so it is necessary to increase the heat exchange area to ensure heat exchange, resulting in an increase in equipment volume and floor space. At the same time, during the return air flow in the shell side, condensate and ash are easily formed in areas such as the rear side of the baffle and the bottom of the shell, resulting in scaling, blockage and cleaning difficulties.

[0004] Existing published literature 2 (Application Research of Ultrasonic Enhanced Heat Transfer Technology in Shell-and-Tube Heat Exchangers, 2024) focuses on waste heat recovery from industrial wastewater. It analyzes the mechanism of fouling layer formation on the inner wall of the heat exchange tubes, near the inlet and outlet, and in dead zones during long-term flow of wastewater within a shell-and-tube heat exchanger. The literature points out that fouling significantly reduces heat transfer efficiency and can even corrode the inner wall. Figure 1 The diagram shows a traditional heat exchanger before and after scaling. It can be seen that the inner wall of the heat exchange tube is covered with a thick layer of fouling, requiring regular shutdown for inspection and mechanical or chemical cleaning. This paper proposes to use ultrasonic online anti-scaling and descaling technology to disrupt the conditions for fouling deposition and inhibit fouling growth through cavitation and pulsating pressure, and to remove fouling online during equipment operation to extend the cleaning cycle. Although ultrasonic online cleaning can alleviate the scaling problem to some extent, it is based on the premise that sewage or process media containing solids or corrosives flow directly through the shell side or tube side. It only performs "post-treatment" by applying an external physical field after scaling, which is difficult to fundamentally eliminate the hidden dangers of shell-side scaling and corrosion from the perspective of equipment structure and heat exchange method. At the same time, it increases the system complexity and investment cost.

[0005] Therefore, there is an urgent need in the field for a technical method that enables efficient and stable heat transfer between high-temperature wet oxygen oxidizing liquid and cold materials under wet oxygen conditions, while isolating the corrosive and scale-forming wet oxygen oxidizing liquid from the shell side. Summary of the Invention

[0006] To overcome the aforementioned deficiencies of the prior art, the present invention provides a shell-and-tube heat exchanger indirect heat exchange method, which involves transforming the shell side into a closed space filled with an inert intermediate heat transfer medium, and actively controlling the temperature difference between the medium in the central high-temperature tube bundle and the peripheral low-temperature tube bundle region to drive its natural convection, thereby solving the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A shell-and-tube heat exchange method is provided for a vertically arranged shell-and-tube heat exchanger. The shell has an upper tube box and a lower tube box at both ends. High-temperature oxidant tubes are arranged in the central region of the tube sheet, and cold material tubes are arranged in the outer perimeter region. An intermediate heat transfer medium, comprising at least magnesium oxide and pure water, is filled into the shell side through a shell side filling port, occupying 70%–90% of the shell side volume, and sealed through a shell side vent port. The method includes: Step 1: Before operation, complete the preparation, filling and venting of the above intermediate heat transfer medium to form a closed intermediate heat transfer space in the shell side. Step 2: Send the cold material from the lower pipe box into the cold material pipe, and let it flow from bottom to top to the upper pipe box for discharge. Adjust the flow rate so that the outlet temperature of the cold material meets the preheating requirements. Step 3: Send the high-temperature humid oxygen oxidizing liquid from the upper tube box into the high-temperature oxidizing liquid pipe, and let it flow from top to bottom to the lower tube box for discharge. Adjust the flow rate so that its outlet temperature meets the cooling requirements. Step 4: When both sides are running simultaneously, monitor the temperature of the high-temperature humid oxygen oxidizing liquid and the cold material and adjust the flow rate accordingly. This will create and maintain a temperature difference of ≥10℃ between the heat transfer medium in the shell side and the area near the high-temperature oxidizing liquid tube and the area near the cold material tube. This will allow for natural convection within the shell side, heat absorption in the central area and heat release near the cold material tube, thus achieving heat exchange between the high-temperature humid oxygen oxidizing liquid and the cold material through the wall. Step 5: When shutting down or reducing the load, gradually reduce the flow rates of the high-temperature wet oxygen oxidizing liquid and the cold material until the supply stops, keeping the heat transfer medium in the middle of the shell side sealed and retained. When restarting, re-establish the flow on both sides according to steps 2 and 3 to restore the natural convection heat transfer in the shell side.

[0008] As a further embodiment of the present invention, the intermediate heat transfer medium includes at least magnesium oxide and pure water, the mass ratio of magnesium oxide to pure water is 1:(1-5), preferably 1:(2-3), and the average particle size of the magnesium oxide particles is 10μm-200μm.

[0009] As a further embodiment of the present invention, the volume fraction of the intermediate heat transfer medium in the shell side is preferably 70% to 85% of the shell side volume, and a gas phase buffer space is reserved in the upper part of the shell side to absorb thermal expansion and pressure fluctuations during operation.

[0010] As a further embodiment of the present invention, the high-temperature humid oxygen oxidation liquid flows from top to bottom in two or more passes in the high-temperature oxidation liquid pipe, and the cold material flows from bottom to top in two or more passes in the cold material pipe. The baffles installed in the upper and lower pipe boxes divide each pipe box into several chambers to realize the multi-pass series connection of the fluids on both sides.

[0011] As a further embodiment of the present invention, the inlet temperature of the high-temperature wet oxygen oxidation liquid is 120℃~200℃ and the outlet temperature is 80℃~160℃, the inlet temperature of the cold material is 10℃~60℃ and the outlet temperature is 60℃~120℃, and the working temperature range of the intermediate heat transfer medium covers the above temperature range and maintains chemical stability.

[0012] As a further embodiment of the present invention, in step four, the steady-state temperature difference between the shell-side intermediate heat transfer medium in the high-temperature oxidizing liquid pipe region and the cold material pipe region is controlled at 10℃~40℃, preferably 15℃~25℃.

[0013] As a further aspect of the present invention, the intermediate heat transfer medium is kept sealed throughout the entire life cycle of the heat exchanger and is only replaced or replenished through the shell-side filling port and shell-side venting port during planned overhauls.

[0014] As a further embodiment of the present invention, the high-temperature wet oxygen oxidation liquid is wet oxygen oxidation leachate, wet oxygen desulfurization and denitrification oxidation liquid, or oxidizing liquid in wet oxygen oxidation organic wastewater, and the cold material is the process slurry to be heated, makeup water, or other liquid production medium.

[0015] A shell-and-tube heat exchanger for use in the above-mentioned shell-and-tube heat exchanger in a wall-to-wall heat exchanger includes: a shell; an upper large tube box disposed at the upper end of the shell; an upper small tube box fitted inside and sealed to the upper large tube box; a lower large tube box disposed at the lower end of the shell; a lower small tube box fitted inside and sealed to the lower large tube box; a tube sheet fixedly connected to the shell, the upper large tube box, and the lower large tube box respectively; high-temperature oxidant tubes connected at both ends to the upper and lower small tube boxes respectively and passing through the tube sheet and arranged in the shell side; cold material tubes connected at both ends to the upper and lower large tube boxes respectively and passing through the tube sheet and arranged in the shell side; a shell-side intermediate heat transfer medium sealed and filled in the shell-side space enclosed by the shell and the tube sheet; and a shell-side intermediate heat transfer medium disposed at the upper end of the shell. The shell includes: an upper large-tube box partition, an upper small-tube box partition, a lower large-tube box partition, and a lower small-tube box partition; support plates spaced along the shell axial direction within the shell side for the passage of high-temperature oxidizing liquid pipes and cold material pipes; inspection ports on the shell sidewalls; a cold material inlet on the lower large-tube box sidewall; a cold material outlet on the upper large-tube box sidewall; a high-temperature oxidizing liquid inlet on the upper small-tube box sidewall; a high-temperature oxidizing liquid outlet on the lower small-tube box sidewall; a shell-side filling port communicating with the shell side; a shell-side vent port communicating with the shell side; a safety valve communicating with the shell side; and a support at the bottom of the shell.

[0016] As a further embodiment of the present invention, the shell-and-tube heat exchanger has an upper large tube box and an upper small tube box, and a lower large tube box and a lower small tube box arranged coaxially to form a double-layer concentric structure of "large tube box inside small tube box". The high-temperature oxidizing liquid tubes are arranged on the tube sheet in the central region, and the cold material tubes are arranged on the tube sheet in the annular region surrounding the central region. The upper large tube box partition, the upper small tube box partition, the lower large tube box partition, and the lower small tube box partition are arranged correspondingly to each other, so that the upper small tube box, the lower small tube box and the high-temperature oxidizing liquid tubes form a high-temperature wet oxygen oxidizing liquid multi-pass tube loop, and the upper large tube box, the lower large tube box and the cold material tubes form a cold material multi-pass tube loop, providing a structural basis for the formation of natural convection circulation of the intermediate heat transfer medium in the shell side between the high-temperature oxidizing liquid tube region and the cold material tube region.

[0017] The technical effects and advantages of the shell-and-tube heat exchange method for indirect heat exchange in this invention are as follows: 1. This invention transforms the shell side into a permanently sealed space filled with an inert medium, allowing corrosive and fouling process fluids to flow entirely within the tube side. This eliminates the conditions for scaling and corrosion in the shell side, significantly improving equipment reliability and enabling efficient and long-lasting operation.

[0018] 2. The magnesium oxide-water suspension medium filling the shell side forms stable natural convection under the controllable temperature difference, avoiding the high pressure drop and flow dead zone caused by the baffle, and significantly reducing operating energy consumption while ensuring heat transfer effect.

[0019] 3. The shell-side medium of this invention can be used in a sealed manner for a long time without replacement; the shell side itself never scales, completely eliminating the need for frequent chemical or mechanical cleaning. Maintenance is only required for the tube side, making operation simple and cycle-free, and significantly reducing equipment downtime and maintenance costs. Attached Figure Description

[0020] Figure 1 This is a schematic diagram showing the scaling process before and after scaling in a conventional shell-and-tube heat exchanger in the prior art. Figure 2 This is a schematic vertical cross-sectional view of the shell-and-tube heat exchanger of the present invention. Figure 3 for Figure 2 Horizontal sectional view of the upper and middle pipe box section; Figure 4 This is a flowchart of a shell-and-tube heat exchanger heat exchange method according to the present invention.

[0021] In the diagram, 1. Shell; 2. Upper large tube box; 3. Upper small tube box; 4. Lower large tube box; 5. Lower small tube box; 6. Tube sheet; 7. High-temperature oxidizing liquid tube; 8. Cold material tube; 9. Shell-side intermediate heat transfer medium; 10. Upper large tube box partition; 11. Upper small tube box partition; 12. Lower large tube box partition; 13. Lower small tube box partition; 14. Support plate; 15. Inspection port; 16. Cold material inlet; 17. Cold material outlet; 18. High-temperature oxidizing liquid inlet; 19. High-temperature oxidizing liquid outlet; 20. Shell-side filling port; 21. Shell-side vent; 22. Safety valve; 23. Support. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 This embodiment applies the system of the present invention to a metal wet oxygen oxidation leaching production line. The wet oxygen oxidation reactor outlet produces a high-temperature wet oxygen oxidation liquid with a temperature of approximately 150°C, containing metal ions, sulfate ions, chloride ions, and a certain amount of suspended solids, exhibiting strong corrosiveness and a tendency to form scale. The cold slurry entering the reactor is at a temperature of approximately 30°C. The system utilizes the residual heat of the high-temperature wet oxygen oxidation liquid to preheat the cold slurry to approximately 80°C, while simultaneously cooling the wet oxygen oxidation liquid to approximately 90°C to facilitate subsequent solid-liquid separation and precipitation operations.

[0024] like Figure 2As shown, the heat exchanger in this embodiment is a vertical fixed tube sheet shell-and-tube structure, including a vertically arranged shell 1, an upper large tube box 2 at the upper end of the shell, a lower large tube box 4 at the lower end of the shell, and a support 23 at the bottom of the shell. An upper small tube box 3 is coaxially fitted inside the upper large tube box 2, and the upper small tube box 3 is sealed and isolated from the upper large tube box 2 by an annular partition; a lower small tube box 5 is coaxially fitted inside the lower large tube box 4, and the lower small tube box 5 is sealed and isolated from the lower large tube box 4 by an annular partition, forming a double-layer concentric structure of "large tube box inside small tube box".

[0025] Tube sheets 6 are installed between the shell 1 and the upper large tube box 2 and the lower large tube box 4, respectively. High-temperature oxidizing liquid tubes 7 are arranged in the central area of ​​the tube sheet 6, and cold material tubes 8 are arranged in the outer ring area. The two types of tube bundles are arranged in a triangular staggered manner. The high-temperature oxidizing liquid tubes 7 are made of wet oxygen corrosion resistant alloy steel pipes with an outer diameter of about 25 mm and a wall thickness of about 2 mm. The cold material tubes 8 are made of stainless steel pipes with an outer diameter of 25 mm. The effective length of the two types of tubes is about 6 m, and the total number of tubes is 96, of which there are 48 high-temperature oxidizing liquid tubes 7 and 48 cold material tubes 8.

[0026] like Figure 2 and Figure 3 As shown, the upper large tube box partition 10 divides the upper large tube box 2 into multiple chambers to achieve two-pass or multi-pass flow on the cold material side; the upper small tube box partition 11 divides the upper small tube box 3 into multiple chambers to achieve multi-pass flow of high-temperature humid oxygen oxidizing liquid; the lower large tube box partition 12 and the lower small tube box partition 13 are respectively arranged corresponding to the upper partitions 10 and 11, so that the high-temperature humid oxygen oxidizing liquid flows from top to bottom in two passes in the central tube bundle, and the cold material flows from bottom to top in two or three passes in the outer tube bundle.

[0027] The shell-side space is enclosed by the shell 1 and the upper and lower tube sheets 6. A support plate 14 is set every 1m along the axial direction in the shell-side. The support plate 14 has through holes for the high-temperature oxidizing liquid pipe 7 and the cold material pipe 8 to pass through. A certain annular gap is reserved between the outer edge of the support plate and the inner wall of the shell 1. Some of the through holes have notches at their edges, so that the heat transfer medium 9 in the middle of the shell-side can flow between different heights and radial positions, forming a natural convection channel. The side wall of the shell 1 is provided with an inspection port 15 for inspecting the shell-side and the outer surface of the tube bundle when the machine is stopped. The upper part of the shell is provided with a shell-side filling port 20, a shell-side exhaust port 21 and a safety valve 22.

[0028] A cold material inlet 16 is provided on the side wall of the lower large pipe box 4, and a cold material outlet 17 is provided on the side wall of the upper large pipe box 2; a high-temperature oxidizing liquid inlet 18 is provided on the side wall of the upper small pipe box 3, and a high-temperature oxidizing liquid outlet 19 is provided on the side wall of the lower small pipe box 5. The cold material and the high-temperature wet oxygen oxidizing liquid are connected to the external pipelines and pumps through their respective inlets and outlets.

[0029] In this embodiment, the intermediate heat transfer medium 9 is a homogeneous suspension prepared from high-purity magnesium oxide (MgO) powder and deionized purified water. The average particle size (D50) of magnesium oxide is approximately 50 μm, with a high thermal conductivity (approximately 45-60 W / (m·K)). Furthermore, it exhibits extremely stable chemical properties within the operating temperature range of 120℃ to 200℃ and does not react violently with water. Deionized water has a high specific heat capacity, low cost, and is environmentally friendly. To determine the optimal ratio, small-scale experiments were conducted: the thermal conductivity and apparent viscosity of the suspension were tested within a mass ratio range of 1:1 to 1:5. The experiments revealed that as the magnesium oxide content increased, the thermal conductivity of the suspension improved, but the viscosity also increased accordingly. Excessively high viscosity significantly weakens the natural convection driving force. When the mass ratio of magnesium oxide to purified water was 1:2, the thermal conductivity of the suspension at room temperature was approximately 35% higher than that of pure water, while its viscosity (approximately 15 mPa·s) still ensured effective natural convection circulation under the designed temperature difference (≥10℃). Therefore, in this embodiment, the preferred ratio is determined to be 1:2, which achieves a good balance between enhanced thermal conductivity and flow resistance.

[0030] The main structural dimensions of the heat exchanger in this embodiment are as follows: inner diameter of shell 1 D = 0.6m, effective length (i.e., heat exchange tube length) between upper and lower tube sheets 6 L = 6.0m. First, calculate the total shell-side volume V. total =π×(D / 2)²×L≈3.14×(0.3)²×6.0≈1.696m³. Subtracting the solid volume occupied by the tube bundle (96 tubes with an outer diameter of 25mm), tube sheet, and support plate 14 (accounting for approximately 25%-30% of the total volume), the estimated "shell-side effective working volume" V available for filling and flowing the intermediate heat transfer medium is obtained. effective ≈1.1m³. To ensure safe operation and accommodate the thermal expansion of the medium, a certain proportion of gas phase buffer space must be reserved in the upper shell side during design. Based on engineering experience and thermodynamic calculations, reserving 15%-25% of the effective working volume of the shell side as expansion space is reasonable. In this embodiment, a filling volume fraction of 80% is selected, that is, the filling volume V of the intermediate heat transfer medium. fill =1.1m³×80%≈0.88m³, correspondingly, the volume of the gas phase buffer space reserved in the upper part of the shell side is about 0.22m³ (accounting for 20% of the effective working volume), and this gas phase space is guaranteed by liquid level control during the filling process and sealing of the exhaust port 21.

[0031] The specific operation is as follows: Add a certain amount of magnesium oxide powder to the preparation tank, add pure water at a mass ratio of 1:2, turn on the stirrer and stir thoroughly until a uniform suspension is formed, open the shell-side vent 21, and slowly inject the intermediate heat transfer medium 9 from the shell-side filling port 20. Observe the gas-liquid state discharged from the vent 21. When the intermediate heat transfer medium without obvious bubbles continuously overflows from the vent and the shell-side liquid level reaches the design height, stop the injection, close the vent 21 and the filling port 20, and perform a tightness check on the shell side. After confirming that there is no leakage, a closed intermediate heat transfer space is formed in the shell side.

[0032] The cold material is the slurry before entering the wet oxygen leaching reactor, with an inlet temperature of approximately 30°C and a target outlet temperature of 75°C–85°C. The cold material circulation pump is started, introducing the cold material slurry from the lower large tube box 4 through the cold material inlet 16. It flows upwards within the cold material pipe 8, passing through a multi-pass channel formed by the baffles in the lower and upper large tube boxes 4 and 2, before being discharged from the cold material outlet 17. The cold material mass flow rate is stabilized at approximately 13 t / h (approximately 3.6 kg / s) by adjusting the circulation pump speed and pipeline valves. Temperature sensors are installed on the cold material inlet and outlet pipes to monitor the inlet and outlet temperatures in real time. By appropriately adjusting the flow rate, the cold material outlet temperature is stabilized within the preheating range of 75°C–85°C.

[0033] The high-temperature humid oxygen oxidation liquid is drawn from the outlet of the humid oxygen oxidation reactor, with an inlet temperature of approximately 150℃ and a target outlet temperature of approximately 90℃. The high-temperature humid oxygen oxidation liquid transfer pump is started, introducing the oxidant from the upper small tube box 3 through the high-temperature oxidant inlet 18. It flows downwards within the high-temperature oxidant pipe 7, undergoes two-pass flow after passing through the baffle in the lower small tube box 5, and is discharged from the high-temperature oxidant outlet 19. By adjusting the transfer pump flow rate and the inlet valve, the mass flow rate of the high-temperature humid oxygen oxidation liquid is controlled at approximately 13 t / h, basically matching the flow rate on the cold material side. Temperature sensors are installed on the inlet and outlet pipes of the high-temperature humid oxygen oxidation liquid to monitor the temperature in real time. Through linkage with the cold material side flow rate adjustment, the outlet temperature of the high-temperature humid oxygen oxidation liquid is stabilized at approximately 90℃.

[0034] Once the flow on both the cold material side and the high-temperature wet oxygen oxidizing liquid side reaches a steady state, the temperature of the intermediate heat transfer medium outside the high-temperature oxidizing liquid pipe 7 is higher, while the temperature of the intermediate heat transfer medium outside the cold material pipe 8 is lower. Because the high-temperature oxidizing liquid pipes are concentrated in the central region and the cold material pipes are arranged in the outer annular region, a radial temperature field gradually forms in the shell side, characterized by a "hotter central region and a colder outer region".

[0035] By monitoring the inlet and outlet temperatures of the fluids on both the high and low temperature sides in real time, and based on the principle of energy conservation, the average temperature difference ΔT between the heat transfer medium in the shell side and the central high-temperature region and the peripheral low-temperature region can be indirectly calculated. avg， The core of the operation control of this invention lies in the fact that the operator (or automatic control system) uses this temperature difference ΔT avgAs a key regulation target, the flow rates of the fluids on both sides are regulated in tandem. For example, when ΔT avg When the temperature is below 15℃, the flow rate of the high-temperature oxidizing liquid can be appropriately increased or the flow rate of the cold material can be slightly decreased to enhance the heating effect in the central region, thereby reducing ΔT. avg It actively enhances and stabilizes the temperature within the optimal range of 15℃ to 25℃. This method, which uses the "shell-side medium temperature difference" as an observable and controllable operating parameter to drive and maintain the intensity of natural convection, surpasses the traditional heat exchanger model that only controls the fluid outlet temperature, ensuring the stability and efficiency of the indirect heat exchange process.

[0036] During the natural convection circulation process, the intermediate heat transfer medium absorbs heat by exchanging heat with the outer wall of the high-temperature oxidizing liquid pipe in the central region, flows to the outer region through the upper flow channel, and releases heat by exchanging heat with the outer wall of the cold material pipe in the outer region. After the temperature decreases, it sinks along the inner wall of the shell and then flows back to the central region through the lower part. This cycle is repeated to realize the indirect heat exchange process of "high-temperature wet oxygen oxidizing liquid - intermediate heat transfer medium - cold material".

[0037] When the production unit needs to be shut down or its load significantly reduced, first, slowly reduce the speed of the high-temperature wet oxygen oxidizing liquid transfer pump and the valve opening to bring its flow rate down to zero smoothly; then, slowly reduce the speed of the cold material circulation pump to bring the cold material flow rate down to zero to avoid thermal stress shock caused by excessive instantaneous temperature difference. During the shutdown, keep the intermediate heat transfer medium 9 sealed in the shell side without discharge or replacement, and only release a small amount of non-condensable gas through the shell side exhaust port 21 when necessary.

[0038] Upon restart, there is no need to re-prepare and refill the intermediate heat transfer medium; simply re-establish the flow of cold material and high-temperature wet oxygen oxidizing liquid according to steps two and three in the embodiment. As the flow rate and temperature on both sides gradually stabilize, the temperature difference between the shell-side intermediate heat transfer medium in the central and peripheral regions is re-established, and the natural convection circulation is restored, thereby quickly restoring the normal shell heat exchange process.

[0039] Under the typical steady-state conditions described above, the mass flow rate of the high-temperature wet oxygen oxidizing liquid is approximately 3.6 kg / s, and the temperature drops from 150℃ to 90℃, with a temperature drop ΔT. h =60K; cold material mass flow rate is approximately 3.6 kg / s, temperature rises from 30℃ to 80℃, temperature rise ΔT c =50K. Referring to the typical physical properties of the materials in this wet oxygen oxidation leaching process, the average specific heat capacity c of both is taken. p Estimating based on ≈4.0 kJ / (kg·K); then the approximate heat release on the high-temperature side is: Q hot ≈3.6kg / s×4000J / (kg·K)×60K≈0.86×10 6 W = 0.86MW; Approximate heat absorption on the cold side is: Q cold≈3.6kg / s×4000J / (kg·K)×50K≈0.72MW. Considering system heat dissipation and heat storage during startup, the effective heat exchange can be stabilized at around 0.8MW during actual operation by fine-tuning the flow rate, thus meeting the process requirements.

[0040] In this embodiment, the heat exchanger has 96 tubes with an outer diameter of 25mm and an effective length of 6m. The heat exchange area A is approximately A≈π×0.025×6×96≈45m². The logarithmic mean temperature difference ΔT lm At approximately 65K, the overall heat transfer coefficient U is approximately: U≈Q / (A·ΔT) lm )≈0.86×10 6 / (45×65)≈294W / (m²·K), which is within the reasonable range of a typical liquid-liquid heat exchanger, indicating that the present invention can still achieve good overall heat transfer performance under the premise that only natural convection occurs in the shell side.

[0041] The device in this embodiment operated continuously and stably for over six months. During this period, regular observations through inspection port 15 showed that the shell-side inner wall and the outer surfaces of all heat exchange tubes remained clean, with only trace amounts of magnesium oxide particles settling at the bottom. No signs of scaling or corrosion caused by the process medium were observed. The shell-side pressure gauge readings remained stable, confirming the absence of flow blockage. In contrast, the traditional shell-and-tube heat exchanger originally used in this production line (with high-temperature oxidant flowing through the shell side and baffles) experienced a shell-side pressure drop of approximately 40% after about two months of operation under the same conditions, requiring shutdown for chemical cleaning. A large amount of hard scale accumulated behind the baffles and at the bottom of the shell. This invention not only eliminates the maintenance costs of frequent shell-side cleaning but also, by eliminating scaling thermal resistance, allows the heat exchanger to maintain heat transfer performance close to its design value during long-term operation. The estimated annual average overall heat transfer coefficient decay rate is less than one-tenth of that of the traditional structure, fully demonstrating the engineering superiority of this invention.

[0042] Example 2 This embodiment illustrates the application of the method of the present invention in a wet oxygen organic wastewater treatment device. In a certain wet oxygen organic wastewater treatment system, a high-temperature wet oxygen oxidizing liquid with a temperature of about 130°C is generated at the reactor outlet. The cold end medium is makeup water with an inlet temperature of about 20°C. It is desirable to use waste heat to heat the makeup water to 60°C to 70°C. A traditional heat exchanger with "wet oxygen oxidizing liquid flowing through the shell side" is used. After a period of operation, scaling and localized corrosion are easily generated in the shell side.

[0043] The structure of the heat exchanger in this embodiment is the same as that in Embodiment 1. It also adopts a vertical structure with the shell side filled with intermediate heat transfer medium 9, the central area arranged with high-temperature oxidizing liquid pipe 7, and the outer area arranged with cold material pipe 8. The arrangement of the shell side filling port 20, the shell side exhaust port 21 and the safety valve 22 is also completely the same. The ratio, filling volume fraction and magnesium oxide particle size of the intermediate heat transfer medium 9 are the same as those in Embodiment 1.

[0044] The operating method must strictly follow the following: Figure 4 The following is a process flow diagram of a shell-and-tube heat exchanger for indirect heat exchange: First, an intermediate heat transfer medium is prepared and filled to form a closed shell side; then, a bottom-up flow of makeup water is established and the outlet temperature is controlled; next, a top-down flow of high-temperature humid oxygen oxidizing liquid is established and its outlet temperature is controlled; under stable flow conditions on both sides, by monitoring the inlet and outlet temperatures and adjusting the flow rate accordingly, a temperature difference of not less than 10°C is formed and maintained between the central and peripheral regions of the intermediate heat transfer medium in the shell side, thereby establishing natural convection circulation within the shell side and achieving indirect heat exchange; when shutting down, the intermediate heat transfer medium is kept sealed, and when restarting, natural convection heat exchange can be restored simply by re-establishing the flow on both sides according to steps two and three.

[0045] During the approximately 9-month operation period, routine inspections revealed no obvious fouling or corrosion on the inner wall of the shell side and the outer surface of the tube bundle. The shell side pressure drop did not change significantly, and no blockage occurred. This indicates that the indirect heat exchange method of the present invention also has good applicability and stability under the condition of waste heat recovery from wet oxygen organic wastewater.

[0046] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0047] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for heat exchange between tubes and shells in a shell-and-tube heat exchanger, characterized in that, The method is applied to a vertically arranged shell-and-tube heat exchanger, with upper and lower tube boxes at both ends of the shell. High-temperature oxidant tubes are arranged in the central region of the tube sheet, and cold material tubes are arranged in the outer perimeter region. The shell side is filled with an intermediate heat transfer medium, comprising at least magnesium oxide and pure water, occupying 70%–90% of the shell side volume, through a shell side filling port and sealed through a shell side vent port. The method includes: Step 1: Before operation, complete the preparation, filling and venting of the above intermediate heat transfer medium to form a closed intermediate heat transfer space in the shell side. Step 2: Send the cold material from the lower pipe box into the cold material pipe, and let it flow from bottom to top to the upper pipe box for discharge. Adjust the flow rate so that the outlet temperature of the cold material meets the preheating requirements. Step 3: Send the high-temperature humid oxygen oxidizing liquid from the upper tube box into the high-temperature oxidizing liquid pipe, and let it flow from top to bottom to the lower tube box for discharge. Adjust the flow rate so that its outlet temperature meets the cooling requirements. Step 4: When both sides are running simultaneously, monitor the temperature of the high-temperature humid oxygen oxidizing liquid and the cold material and adjust the flow rate accordingly. This will create and maintain a temperature difference of ≥10℃ between the heat transfer medium in the shell side and the area near the high-temperature oxidizing liquid tube and the area near the cold material tube. This will allow for natural convection within the shell side, heat absorption in the central area and heat release near the cold material tube, thus achieving heat exchange between the high-temperature humid oxygen oxidizing liquid and the cold material through the wall. Step 5: When shutting down or reducing the load, gradually reduce the flow rates of the high-temperature wet oxygen oxidizing liquid and the cold material until the supply stops, keeping the heat transfer medium in the middle of the shell side sealed and retained. When restarting, re-establish the flow on both sides according to steps 2 and 3 to restore the natural convection heat transfer in the shell side.

2. The indirect heat exchange method for a shell-and-tube heat exchanger according to claim 1, characterized in that... The intermediate heat transfer medium includes at least magnesium oxide and pure water, with a mass ratio of magnesium oxide to pure water of 1:(1-5), and the average particle size of the magnesium oxide particles is 10μm-200μm.

3. The method for heat exchange between tubes and shells in a shell-and-tube heat exchanger according to claim 1, characterized in that... The intermediate heat transfer medium is filled in the shell side with a volume fraction of 70% to 85% of the shell side volume. A gas phase buffer space is reserved in the upper part of the shell side to absorb thermal expansion and pressure fluctuations during operation.

4. The method for heat exchange between tubes and shells in a shell-and-tube heat exchanger according to claim 1, characterized in that, The high-temperature humid oxygen oxidizing liquid flows from top to bottom in two or more passes within the high-temperature oxidizing liquid pipe, while the cold material flows from bottom to top in two or more passes within the cold material pipe. The baffles installed in the upper and lower pipe boxes divide each pipe box into several chambers to realize multi-pass series connection of the fluids on both sides.

5. The method for heat exchange between tubes and shells in a shell-and-tube heat exchanger according to claim 1, characterized in that, The inlet temperature of the high-temperature wet oxygen oxidation liquid is 120℃~200℃, and the outlet temperature is 80℃~160℃. The inlet temperature of the cold material is 10℃~60℃, and the outlet temperature is 60℃~120℃. The working temperature range of the intermediate heat transfer medium covers the above temperature range and maintains chemical stability.

6. The method for heat exchange between tubes and shells in a shell-and-tube heat exchanger according to claim 1, characterized in that, In step four, the steady-state temperature difference between the shell-side intermediate heat transfer medium in the high-temperature oxidant tube region and the cold material tube region is controlled between 10°C and 40°C.

7. The method for heat exchange between tubes and shells in a shell-and-tube heat exchanger according to claim 1, characterized in that, The intermediate heat transfer medium is kept sealed throughout the entire life cycle of the heat exchanger and is only replaced or replenished through the shell-side filling port and shell-side venting port during planned overhauls.

8. A shell-and-tube heat exchanger heat transfer method according to claim 1, characterized in that, The high-temperature wet oxygen oxidation liquid is wet oxygen oxidation leachate, wet oxygen desulfurization and denitrification oxidation liquid, or wet oxygen oxidation organic wastewater oxidation liquid, and the cold material is the process slurry to be heated, makeup water, or other liquid production medium.

9. A shell-and-tube heat exchanger for implementing a shell-and-tube heat exchanger according to any one of claims 1 to 8, characterized in that, include: Shell (1); upper large tube box (2) disposed at the upper end of shell (1); upper small tube box (3) fitted inside and sealed to the upper large tube box (2); lower large tube box (4) disposed at the lower end of shell (1); lower small tube box (5) fitted inside and sealed to the lower large tube box (4); tube sheet (6) fixedly connected to shell (1), upper large tube box (2), and lower large tube box (4) respectively; both ends connected to the upper small tube box (3) respectively. High-temperature oxidizing liquid pipe (7) connected to the lower small tube box (5) and passing through the tube sheet (6) and arranged in the shell side; cold material pipe (8) connected to the upper large tube box (2) and the lower large tube box (4) at both ends and passing through the tube sheet (6) and arranged in the shell side; shell-side intermediate heat transfer medium (9) sealed and filled in the shell-side space enclosed by the shell (1) and the tube sheet (6); upper large tube box partition (10) set in the upper large tube box (2); and upper small tube box partition (10) set in the upper small tube box (5). 3) The upper small tube box partition (11), the lower large tube box partition (12) set in the lower large tube box (4), and the lower small tube box partition (13) set in the lower small tube box (5); the support plate (14) is arranged axially along the shell (1) in the shell side and opened to allow the high temperature oxidizing liquid pipe (7) and the cold material pipe (8) to pass through; the inspection port (15) is opened on the side wall of the shell (1); the cold material inlet is set on the side wall of the lower large tube box (4). The container includes: a port (16); a cold material outlet (17) located on the side wall of the upper large tube box (2); a high-temperature oxidizing liquid inlet (18) located on the side wall of the upper small tube box (3); a high-temperature oxidizing liquid outlet (19) located on the side wall of the lower small tube box (5); a shell-side filling port (20) connected to the shell side; a shell-side exhaust port (21) connected to the shell side; a safety valve (22) connected to the shell side; and a support (23) located at the bottom of the shell (1).

10. The shell-and-tube heat exchanger according to claim 9, characterized in that, The upper large tube box (2) and the upper small tube box (3), the lower large tube box (4) and the lower small tube box (5) are arranged coaxially to form a double-layer concentric structure of "large tube box inside small tube box". The high-temperature oxidizing liquid tube (7) is arranged on the tube sheet (6) in the central area, and the cold material tube (8) is arranged on the tube sheet (6) in the annular area surrounding the central area. The upper large tube box partition (10), the upper small tube box partition (11), the lower large tube box partition (12) and the lower small tube box partition (13) are arranged correspondingly to each other, so that the upper small tube box (3), the lower small tube box (5) and the high-temperature oxidizing liquid tube (7) constitute a high-temperature wet oxygen oxidizing liquid multi-pass tube loop, and the upper large tube box (2), the lower large tube box (4) and the cold material tube (8) constitute a cold material multi-pass tube loop, providing a structural basis for the formation of natural convection circulation of the shell-side intermediate heat transfer medium between the high-temperature oxidizing liquid tube area and the cold material tube area.

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