Outer baffling shell-and-tube heat exchanger

Abstract

The invention discloses an external baffling shell-and-tube heat exchanger which comprises a shell, two tube plates, two end sockets, a plurality of heat exchange tubes, a shell side inlet, a shell side outlet, a tube side inlet and a tube side outlet, wherein the two tube plates and the end sockets are fixedly connected with the shell; the heat exchanger is characterized in that a plurality of partition plates are fixedly arranged in the shell to form a plurality of independent heat exchange chambers, and the heat exchange pipes penetrate through the partition plates; every two adjacent heat exchange chambers are connected through a drainage pipe fixedly connected to the outer side wall of the shell, and the drainage pipes are sequentially and fixedly connected to the outer side walls of the two opposite sides of the shell at intervals. The shell side can be effectively prevented from forming a flowing dead zone, the effective heat exchange area is increased, the heat exchange efficiency is improved, the temperature over-limit risk is effectively reduced, manufacturing is easy, the cost is low, the shell volume utilization rate is high, the overall economical efficiency of equipment is improved, and a large heat exchanger is easy to manufacture.

Description

Technical Field

[0001] The invention relates to a shell and tube heat exchanger, in particular to an external baffle shell and tube heat exchanger. Background Art

[0002] Heat exchanger, also known as heat exchanger, is a key equipment widely used in chemical, petroleum, power, food and many other industrial production. Its basic function is to achieve heat transfer between fluids of different temperatures, that is, to effectively transfer part of the heat of hot fluid to cold fluid to achieve the purpose of heating, cooling, evaporation or condensation. Heat exchanger plays an indispensable role in improving production efficiency, optimizing energy utilization and ensuring product quality.

[0003] The shell and tube heat exchanger is a partition-type heat exchanger that uses the wall of the tube bundle enclosed in the shell as the heat transfer surface. The shell and tube heat exchanger has become the most widely used heat exchanger at present due to its significant advantages such as simple structure, reliable operation, low cost, wide flow cross-section and easy cleaning of scale. Its structure is mainly composed of shell, tube sheet, head, heat exchange tube, baffle (or baffle rod) and other components. Among them, the baffle or baffle rod makes the medium in the shell baffle, which is an important factor affecting heat transfer. In the actual operation of the shell and tube heat exchanger, a common problem is the existence of flow and heat transfer dead zone on the shell side. The heat transfer dead zone refers to the area where the heat transfer efficiency is significantly reduced due to poor fluid flow or structural design defects. These areas not only affect the overall performance of the heat exchanger, but may also accelerate scaling, further reduce heat transfer efficiency and increase maintenance costs.

[0004] Although different forms of baffles or baffle rods are widely used in heat exchangers, each form may cause different degrees of dead zone problems; Single segment baffle: The dead zone produced by this baffle is usually located on the leeward side of the baffle, because when the fluid bypasses the baffle, a low-speed zone is formed behind it, causing the fluid to stagnate; Double-segment baffles: Compared with the single-segment design, double-segment baffles can reduce (but not eliminate) the dead zone on the leeward side by directing the flow in two directions. At the same time, dead zones may appear in some areas between the two segment baffles, especially when the baffle spacing is large; Disk annular baffle: The disk annular baffle guides the fluid in the circumferential direction and has a smaller leeward dead zone than the bow baffle. However, due to the disk-shaped baffle structure, a dead zone will appear in the central area of ​​this design, because when the fluid flows around the disk, the flow velocity in the central part is low, which is easy to form a stagnant area.

[0005] Spiral baffle: This is a new baffle design that allows the fluid to flow in a spiral shape in the heat exchanger. In principle, it can avoid the fluid short-circuit and dead zone problems existing in traditional baffles, and make the fluid evenly distributed between the tube bundles, thereby improving the heat transfer efficiency of the heat exchanger and reducing the local temperature gradient in the heat exchanger. It has the advantages of uniform flow, low pressure drop, low vibration and noise. However, in actual engineering, there is still a risk of dead zone on the leeward side of the junction of the discontinuous structure of the discontinuous spiral baffle; the continuous spiral baffle has a spiral angle of 90 degrees in the center, and the spiral surface cannot be drilled. The baffle cannot cover the center area of ​​the shell side, and a short circuit will form in the center area, affecting the heat exchange effect, which relatively reduces the effective heat exchange area of ​​the heat exchanger, and the diameter of the invalid center area increases with the increase of the baffle pitch. On the other hand, the three-dimensional structure of the spiral baffle is complex, making the manufacturing process of this design more difficult than that of the traditional baffle. Especially in the production of large-scale industrial equipment, the processing accuracy of the spiral baffle is required to be high, which leads to manufacturing difficulties and increased costs; Baffle rods: Baffle rods are usually designed to guide the fluid to form local small-scale velocity fluctuations (turbulence, coherent structures) between the tube bundles, thereby improving the heat transfer efficiency. Although the dead zone of the baffle rod is significantly smaller than that of the traditional baffle plate, when the fluid flows through the baffle rod, the change in the fluid path forms a dead zone with lower flow velocity upstream or downstream of the baffle rod. On the other hand, the baffle rod has a limited disturbing effect on the fluid, resulting in a lower heat exchange efficiency than the baffle plate, resulting in an increase in the overall size of the equipment, an increase in cost, and the possibility of failing to meet the design requirements under extreme conditions.

[0006] The application of the above-mentioned different forms of baffle structures in heat exchangers has its own advantages and disadvantages, but all of them have different degrees of dead zone problems. Although some dead zones can be reduced by optimizing the shape, spacing and guide structure of the baffles, this problem cannot be completely solved. Although the existing technology can barely meet the established functional requirements, its performance is often accompanied by a certain degree of compromise. In the face of increasingly complex and changing working environments and emerging application requirements, a typical technical challenge for heat exchanger applications is the energy storage peak-shaving heat exchange equipment using HITEC molten salt (KNO3-NaNO2-NaNO3 (53%-40%-7%)) as the medium. HITEC molten salt is a low-melting-point molten salt widely used in the industrial field. Due to its excellent energy storage characteristics, it has recently been used as a heat storage and heat transfer medium for energy storage peak-shaving in thermal power plants. Energy storage peak-shaving is to extract steam as a heat source to heat and store the molten salt medium when there is surplus steam for power generation, and release the heat stored in the molten salt during the peak period of power generation to provide heat and generate electricity. Energy storage peak regulation can significantly improve the economy of power stations and further meet the load fluctuations of the power grid and the external heating needs. The solidification temperature and decomposition temperature of HITEC molten salt are low, so there are strict restrictions on its use temperature. The crystallization temperature of HITEC molten salt is 142℃ and the decomposition temperature is 454℃. Since the NaNO2 in its composition is easily oxidized, its solidification point will further increase. Therefore, the usual use temperature of this molten salt medium in engineering is 190℃-450℃. Once it exceeds 450℃, there is a risk of chemical decomposition to generate nitrogen oxides and nitrogen. When using HITEC molten salt as a heat storage and exchange medium, precise temperature control of the molten salt medium is an important guarantee for system safety. In the energy storage peak regulation project of coal-fired power plants, the steam parameters of the mainstream supercritical units are higher than 550℃, while the steam parameters of the newly built ultra-supercritical units are higher than 600℃. From the perspectives of heat exchanger design, equipment safety, etc., the low-temperature and low-pressure molten salt medium should go through the shell of the heat exchanger to reduce equipment cost and ensure equipment safety. However, in existing heat exchangers, molten salt is prone to form flow dead zones when it is deflected on the shell side, the local flow velocity is low or recirculation occurs, and the local heat exchange performance outside the tube is reduced, causing the wall temperature of the heat exchange tube to be closer to the steam temperature inside the tube. The local temperature of the heat exchange tube surface in contact with the molten salt medium exceeds the limit, and the molten salt decomposes. Its heat exchange efficiency, durability, and safety show limitations. Summary of the invention

[0007] The object of the present invention is to provide an external baffle shell and tube heat exchanger in view of the above-mentioned deficiencies in the prior art, which can effectively avoid the formation of flow dead zones on the shell side and increase the effective heat exchange area, thereby improving the heat exchange efficiency and effectively reducing the risk of temperature over-limit. It is also easy to manufacture, has low cost, and high shell volume utilization, thereby improving the overall economy of the equipment and facilitating the manufacture of large-scale heat exchangers.

[0008] In order to achieve the above-mentioned purpose, an external baffle shell and tube heat exchanger of the present invention comprises a shell, two tube sheets and a head fixedly connected to the shell, a plurality of heat exchange tubes, a shell side inlet, a shell side outlet, a tube side inlet, and a tube side outlet; characterized in that: a plurality of partitions are fixedly arranged in the shell to form a plurality of independent heat exchange chambers, and the heat exchange tubes all pass through each partition; two adjacent heat exchange chambers are connected by a drainage tube fixedly connected to the outer side wall of the shell, and each drainage tube is fixedly connected to the outer side walls of the shell on opposite sides at intervals in sequence.

[0009] The present invention fixes several partitions in the shell and arranges several drainage pipes outside the shell. The medium in the shell flows through each heat exchange chamber in turn, and the deflection area of ​​the dead zone generated by the original baffle is transferred to the outside of the shell, so that a through-flow flow area is formed in the shell. On the one hand, the problem of dead zone generated on the leeward side of the baffle area of ​​the traditional baffle is avoided. On the other hand, all the tube bundles in the shell are placed in the through-flow area, which not only increases the effective heat exchange area and the volume utilization rate of the shell, but also improves the convective heat exchange efficiency outside the tube, so that the surface temperature of the heat exchange tube is closer to the shell side medium, and the risk of temperature over-limit is effectively reduced. The drainage pipe is easy to manufacture and has a low cost, which improves the overall economy of the equipment. The manufacturing difficulty is independent of the equipment size, and it is easy to manufacture a large heat exchanger. As a further improvement of the present invention, the axes of the shell-side inlet, shell-side outlet and each drainage pipe are in the same plane on both sides of the shell; this can ensure that the medium forms a pure through-flow in the shell, further improving the heat exchange efficiency; As a further improvement of the present invention, the inner diameter of the drainage pipe is greater than 20% of the distance between the two partitions of the heat exchange chamber to which it is connected; so as to ensure that the medium is more evenly distributed along the axial direction of the equipment after entering the heat exchange chamber through the drainage pipe, and the surface temperature of the heat exchange tube is closer to the shell side medium, effectively reducing the risk of temperature over-limit; As a further improvement of the present invention, the axial distance between the axis of the shell side inlet, shell side outlet and the inlet and outlet of each drainage pipe and the axial partitions on both sides thereof is less than 70% of the spacing between the partitions on both sides thereof; thus preventing the inlet and outlet from being relatively offset in the axial direction of their respective heat exchange chambers, and ensuring that the medium is relatively evenly distributed in the axial direction after entering the heat exchange chamber; As a further improvement of the present invention, the maximum spacing between the baffles on both sides of each heat exchange chamber is not greater than 50% of the minimum spacing; when the spacing between the baffles on both sides of each heat exchange chamber is independently adjusted according to the thermal performance requirements, it can prevent the medium pressure in each heat exchange chamber from fluctuating too much, ensure the uniformity of heat exchange, and prevent the temperature from exceeding the limit; In summary, the present invention can effectively avoid the formation of flow dead zones on the shell side and increase the effective heat exchange area, thereby improving the heat exchange efficiency and effectively reducing the risk of temperature over-limit. It is also easy to manufacture, has low cost, and high shell volume utilization, thereby improving the overall economy of the equipment and facilitating the manufacture of large-scale heat exchangers. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1This is a front view of the first embodiment of the present invention.

[0011] Figure 2 This is a partial view of another drainage tube structure used in Example 1.

[0012] Figure 3 This is a partial view of another drainage tube structure used in Example 1.

[0013] Figure 4 This is a front view of the second embodiment of the present invention.

[0014] Figure 5 This is a front view of the third embodiment of the present invention.

[0015] Figure 6 for Figure 5 Top view of the . DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with the accompanying drawings.

[0017] Embodiment 1 like Figure 1 As shown, an external baffle shell and tube heat exchanger of this embodiment comprises a shell 1, two tube sheets 2 and a head 3 fixedly connected to both ends of the shell, a plurality of heat exchange tubes 4, a shell side inlet 5, a shell side outlet 6, a tube side inlet 7, and a tube side outlet 8; a plurality of partitions 9 are fixedly arranged in the shell 1 to form a plurality of independent heat exchange chambers, and the heat exchange tubes 4 all pass through the partitions 9, and the partitions 9 on both sides of all the heat exchange chambers are arranged at equal intervals, and two adjacent heat exchange chambers are connected by a drainage pipe 10 fixedly connected to the outer wall of the shell by welding, and the drainage pipe 10 is 1 80-degree elbow, each drainage pipe 10 is fixedly connected to the outer side walls of the shell 1 on opposite sides in sequence; the shell side inlet 5, the shell side outlet 6 and the axis of each drainage pipe 10 are in the same plane on both sides of the shell 1; the inner diameter of each drainage pipe 10 is greater than 20% of the distance between the two partitions 9 of each heat exchange chamber connected to it; the axial distance between the axis of the shell side inlet 5, the shell side outlet 6 and the inlet and outlet of each drainage pipe 19 and the axial partitions 9 on both sides thereof is less than 70% of the distance between the partitions 9 on both sides thereof (or the partition 9 and the tube sheet 2).

[0018] This embodiment is a straight tube BEM type heat exchanger and is used for high-temperature steam to heat molten salt. The molten salt flows through the shell side and the high-temperature steam flows through the tube side, and a pure countercurrent heat exchange method is adopted; the steam inlet is 550°C and the molten salt outlet is 390°C; by fixing several partitions 9 in the shell 1 and several drainage pipes 10 outside the shell, the medium in the shell flows through each heat exchange chamber in turn, and the baffle area where the dead zone of the original baffle is generated is transferred to the outside of the shell 1. In addition, the shell side inlet 5, the shell side outlet 6 and the axes of each drainage pipe 10 are in the same plane on both sides of the shell 1, so that a pure through-flow flow area is formed in the shell 1, which avoids the baffle area of ​​the traditional baffle. The dead zone problem on the leeward side. On the other hand, all the heat exchange tubes 4 in the shell 1 are flow-through areas, and all the heat exchange tubes are effectively utilized. The flow velocity and heat transfer performance in the flow-through area are much greater than those in the baffle area, which not only increases the effective heat exchange area and the shell volume utilization rate, thereby improving the convective heat exchange efficiency outside the tube, but also makes the surface temperature of the heat exchange tube 4 closer to the shell side medium. Even if the steam inlet temperature is significantly higher than the molten salt limit temperature of 450°C, the risk of temperature over-limit can be effectively reduced. The draft tube 10 is easy to manufacture and has a low cost, which improves the overall economy of the equipment. The manufacturing difficulty is independent of the equipment size, and it is easy to manufacture a large heat exchanger. The larger inner diameter of the drainage pipe and the prevention of large axial offset of the inlets and outlets in the heat exchange chamber can ensure that the medium is more evenly distributed in the axial direction after entering the heat exchange chamber through the drainage pipe 10. The surface temperature of the heat exchange tube 4 is closer to the shell side medium, further reducing the risk of temperature over-limit. It has been proved by use that the average wall temperature of the heat exchange tube 4 is lower than 420 degrees, and the local maximum temperature is 449 degrees. At the same time, the temperature of the high-temperature steam has dropped below the molten salt limit temperature when leaving the flow zone, and there will be no risk of overtemperature in the subsequent heat exchange process.

[0019] This embodiment is not limited to the described implementation mode. Figure 2 , Figure 3 As shown, the drainage pipe may also adopt a structure of two straight pipes clamping double 90-degree elbows 12 or two straight pipes clamping a header 13; the spacing between the baffles 9 on both sides of each heat exchange chamber can be adjusted according to the thermal performance requirements, but the maximum spacing between the baffles 9 on both sides of each heat exchange chamber is not greater than 50% of the minimum spacing, so as to prevent excessive fluctuations in the medium pressure in each heat exchange chamber, ensure the uniformity of heat exchange, and prevent temperature from exceeding the limit; The present invention can control the flow velocity through the partition spacing, thereby controlling the shell side heat transfer performance and pressure loss; the partition spacing design method is consistent with the simplex baffle. For the thermal calculation of the shell-out baffle scheme, the single-bow baffle can be referred to, and the 20% notch simplex single-bow baffle is used as the benchmark. For the case where the shell side Reynolds number (indicating the liquid flow state: laminar or turbulent) is lower than 4000, the shell side heat transfer coefficient is increased by +35%; for the case where the shell side Reynolds number is between 4000 and 8000, the shell side heat transfer coefficient is increased by +20%; for the case where the shell side Reynolds number is greater than 8000, the shell side heat transfer coefficient is increased by +30%. It has been verified by experiments that the average shell side heat transfer coefficient (W / m^2K) of the shell-out baffle scheme is 20%-40%, 30%-80% higher than that of the single-bow / double-bow / disc annular baffles, respectively. and 35%-75%; compared with the baffle rod scheme, although the baffle rod has a more uniform flow than the traditional baffle, the shell-outside baffle scheme can still provide better heat transfer performance and more uniform flow. The average heat transfer coefficient (W / m^2K) on the shell side of the shell-outside baffle scheme is 100%-180% higher than that of the baffle rod. This is because the baffle rod can provide limited disturbance, and there is a significant difference in heat transfer performance between the shell-outside baffle scheme and the flow zone of the traditional bow baffle; compared with the spiral baffle, from the heat transfer performance comparison, according to the different configurations of the spiral baffles, the average heat transfer coefficient on the shell side of the shell-outside baffle scheme is The heat transfer coefficient (W / m^2K) is 5%-160% higher than that of spiral baffles (helix angle 5 degrees-30 degrees). This is because the shell-outside baffle scheme is a full through-flow scheme, and the heat transfer effect is stronger than the oblique through-flow of the spiral baffles. On the other hand, due to the large rotation angle in the central area of ​​the spiral baffles, the drilling process cannot be completed, and heat exchange tubes or baffles are usually not set in this area, resulting in considerable volume waste. Under the same shell diameter, the shell-outside baffle scheme has a larger effective heat transfer area than the spiral baffles, and the shell volume utilization rate is high, which improves the overall economy of the equipment and makes it easy to manufacture large heat exchangers.

[0020] Embodiment 2 like Figure 4 As shown, this embodiment is an external baffle BFU shell and tube heat exchanger 16, whose heat exchange tube 17 is U-shaped, and two tube sheets and a head are connected to the same end of the shell and isolated by a baffle 18; similarly, a plurality of partitions 9 are fixedly arranged in the shell to form a plurality of independent heat exchange chambers, and two adjacent heat exchange chambers are connected by a drainage pipe 10 fixedly welded to the outer wall of the shell.

[0021] Embodiment 3 like Figure 5 , Figure 6 As shown, this embodiment is an external baffle hairpin heat exchanger 19, the shell and heat exchange tubes are both U-shaped, and according to working conditions, a few partitions 9 are fixedly provided in the high-temperature section shell at the steam inlet, and two adjacent heat exchange chambers are connected by a drainage pipe 10 fixedly connected to the outer wall of the shell.

[0022] The above embodiments have been used for illustration, but it should be understood that the above embodiments are only used for the purpose of examples and explanations, and are not intended to limit the present invention to the scope of the described embodiments. The purpose of the present invention is to provide an external baffle shell and tube heat exchanger in view of the above-mentioned deficiencies in the prior art, which can effectively avoid the formation of flow dead zones on the shell side and increase the effective heat exchange area, thereby improving the heat exchange efficiency and effectively reducing the risk of temperature over-limit, and is easy to manufacture, low in cost, and has a high shell volume utilization rate, thereby improving the overall economy of the equipment and facilitating the manufacture of large-scale heat exchangers.

Claims

1. An external baffle shell and tube heat exchanger, comprising a shell, two tube sheets and a head fixedly connected to the shell, a plurality of heat exchange tubes, a shell side inlet, a shell side outlet, a tube side inlet, and a tube side outlet; characterized in that: Several partitions are fixed inside the shell to form several independent heat exchange chambers, and the heat exchange tubes pass through each partition; two adjacent heat exchange chambers are connected by a drainage tube fixedly connected to the outer side wall of the shell, and each drainage tube is fixedly connected to the outer side walls of the shell on opposite sides at intervals.

2. The external baffle shell and tube heat exchanger according to claim 1, characterized in that: The axes of the shell-side inlet, the shell-side outlet and each drainage pipe are located in the same plane on both sides of the shell.

3. An external baffle shell and tube heat exchanger according to claim 1 or 2, characterized in that: The inner diameter of the drainage pipe is greater than 20% of the distance between the two partitions of the heat exchange chamber to which it is connected.

4. The external baffle shell and tube heat exchanger according to claim 3, characterized in that :: The axial distance between the axis of the shell side inlet, shell side outlet and the inlet and outlet of each drainage pipe and the axial partitions on both sides thereof is less than 70% of the spacing between the partitions on both sides thereof.

5. The external baffle shell and tube heat exchanger according to claim 4, characterized in that: The maximum spacing between the partitions on both sides of each heat exchange chamber shall not be greater than 50% of the minimum spacing.

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