A coiled tube shell type flue gas molten salt heat exchanger and a molten salt heat storage system

Abstract

This invention belongs to the field of heat exchanger technology and discloses a serpentine tube shell-and-tube flue gas molten salt heat exchanger, comprising several planar serpentine tubes arranged at intervals from the left to the right side of the flue. The inlet ends of the several planar serpentine tubes are all connected to the same molten salt inlet branch pipe, and the outlet ends of the several planar serpentine tubes are all connected to the same molten salt outlet manifold. The planar serpentine tubes include heat exchange tubes arranged intersecting the flue gas flow direction and manifolds arranged parallel to the flue gas flow direction. This invention achieves heat exchange between flue gas and molten salt by arranging several planar serpentine tubes in the flue. By replacing the bends of traditional planar serpentine tubes with straight manifolds, the eddies generated by the bends in the existing design can be significantly reduced, thereby reducing the local resistance of molten salt flow, increasing the flow velocity of molten salt, and improving heat exchange efficiency.

Description

Technical Field

[0001] This invention belongs to the field of heat exchanger technology, and in particular relates to a serpentine shell-and-tube flue gas molten salt heat exchanger and a molten salt thermal storage system. Background Technology

[0002] The high-temperature flue gas (usually 600℃~1100℃) generated during electric arc furnace steelmaking is characterized by high dust content, easy generation of dioxins, and large temperature fluctuations. Traditional waste heat recovery equipment is usually shell and tube boilers, heat pipe boilers, etc.

[0003] Molten salt, as an excellent medium- and high-temperature heat transfer and storage medium, has good thermal stability and wide temperature range operation capability. However, its easy solidification characteristics put forward high requirements for heat exchanger design. In existing serpentine tube shell-and-tube heat exchangers, elbows are set at the turning points of the serpentine tubes. These turning points will generate local resistance to the flow of molten salt and affect the heat exchange effect. Summary of the Invention

[0004] The purpose of this invention is to provide a serpentine tube shell-and-tube flue gas molten salt heat exchanger and a molten salt thermal storage system, by improving the structure at the turning point of the serpentine tube, thereby reducing the local resistance to molten salt flow.

[0005] The present invention adopts the following technical solution: a serpentine tube shell type flue gas molten salt heat exchanger, comprising a plurality of planar serpentine tubes, which are arranged at intervals from the left to the right side of the flue.

[0006] The inlet ends of several planar serpentine tubes are all connected to the same molten salt inlet branch pipe, and the outlet ends of several planar serpentine tubes are all connected to the same molten salt outlet manifold.

[0007] The planar serpentine tube includes heat exchange tubes that are arranged intersecting the flue gas flow direction and manifolds that are arranged parallel to the flue gas flow direction.

[0008] Among them, the number of heat exchange tubes in the same stroke is at least two, and the heat exchange tubes in the same stroke are arranged in parallel along the flue gas flow direction; the heat exchange tubes in the same stroke are all connected to the same manifold and branch pipe, and both the heat exchange tubes and the manifold and branch pipe are straight pipes; the stroke is the space between the front and rear sides of the flue within a predetermined range along the length of the flue for laying heat exchange tubes, and the length direction is the flue gas flow direction;

[0009] The inner diameter of the manifold and distributor pipe is larger than the inner diameter of the heat exchange pipe;

[0010] The connection between the heat exchange tube and the manifold / diverter tube is an arc-shaped tube.

[0011] The beneficial effects of this invention are: by arranging several planar serpentine tubes in the flue, this invention can realize heat exchange between flue gas and molten salt. By replacing the elbows of the traditional planar serpentine tubes with straight-tube-shaped manifolds, the eddies generated by the elbows in the existing design can be significantly reduced, thereby reducing the local resistance of molten salt flow, increasing the flow velocity of molten salt, and improving heat exchange efficiency. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a serpentine tube-shell type flue gas molten salt heat exchanger according to an embodiment of the present invention;

[0013] Figure 2 This is a schematic diagram of the structure of a serpentine tube-shell type flue gas molten salt heat exchanger from another perspective in an embodiment of the present invention;

[0014] Figure 3 This is a partial structural schematic diagram of a serpentine shell-and-tube flue gas molten salt heat exchanger according to an embodiment of the present invention;

[0015] Figure 4 This is a partial structural schematic diagram of a serpentine tube-shell type flue gas molten salt heat exchanger according to an embodiment of the present invention;

[0016] Figure 5 This is a schematic diagram of the molten salt flow rate when the inner diameter of the heat exchange tube is 50 mm and the inner diameter of the manifold and branch pipe is also 50 mm in an embodiment of the present invention.

[0017] Figure 6 This is a schematic diagram of the molten salt flow rate when the inner diameter of the heat exchange tube is 50 mm and the inner diameter of the manifold is 150 mm in an embodiment of the present invention.

[0018] Figure 7 This is a schematic diagram illustrating the variation of flue gas outlet temperature with fin thickness in an embodiment of the present invention;

[0019] Figure 8 This is a schematic diagram illustrating the variation of molten salt outlet temperature with fin thickness in an embodiment of the present invention;

[0020] Figure 9 This is a schematic diagram illustrating the variation of flue gas outlet temperature and flue gas temperature drop rate with fin height in an embodiment of the present invention;

[0021] Figure 10 This is a schematic diagram of the flue gas flow when the heat exchange tube is not equipped with fins in an embodiment of the present invention;

[0022] Figure 11 This is a schematic diagram of the dust accumulation situation when the heat exchange tube is not equipped with fins in an embodiment of the present invention;

[0023] Figure 12 This is a schematic diagram of the flue gas flow when the heat exchange tube is equipped with fins in an embodiment of the present invention;

[0024] Figure 13 This is a schematic diagram showing the dust accumulation situation when the heat exchange tube is equipped with fins in an embodiment of the present invention.

[0025] Among them: 10. Molten salt inlet manifold; 20. Molten salt outlet manifold; 30. Fixing component; 40. Planar serpentine tube; 41. Heat exchange tube; 42. Manifold and branch manifold. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] This invention discloses a serpentine shell-and-tube type flue gas molten salt heat exchanger, such as... Figure 1 and Figure 2 As shown, the system includes several planar serpentine tubes 40, which are arranged at intervals from the left to the right side of the flue. The inlet ends of the planar serpentine tubes 40 are all connected to the same molten salt inlet branch pipe 10, and the outlet ends of the planar serpentine tubes 40 are all connected to the same molten salt outlet manifold 20. Each planar serpentine tube 40 includes a heat exchange tube 41 that is arranged intersecting the flue gas flow direction and a manifold branch pipe 42 that is arranged parallel to the flue gas flow direction. The number of heat exchange tubes 41 in the same stroke is at least two, and the heat exchange tubes 41 in the same stroke are arranged parallel to the flue gas flow direction. The heat exchange tubes 41 in the same stroke are all connected to the same manifold branch pipe 42, and both the heat exchange tubes 41 and the manifold branch pipe 42 are straight pipes. The stroke is the space between the front and rear sides of the flue gas within a predetermined range along the length of the flue gas for arranging the heat exchange tubes, and the length direction is the flue gas flow direction.

[0028] This invention enables heat exchange between flue gas and molten salt by arranging several planar serpentine tubes 40 in the flue. By replacing the bends of the traditional planar serpentine tubes 40 with straight-pipe-shaped manifolds and branch pipes 42, the eddies generated by the bends in the existing design can be significantly reduced, thereby reducing the local resistance of molten salt flow, increasing the flow velocity of molten salt, and improving heat exchange efficiency.

[0029] In the prior art, a planar serpentine pipe 40 refers to a pipe that meanders multiple times in a plane and has a serpentine shape. At the bends, the pipe is usually turned by setting 180° elbows. At the non-bends, the straight pipes are parallel to each other and are laid horizontally or vertically. The connection ends of the straight pipes and the elbows are coaxial.

[0030] In this invention, when heat exchange tubes 41 are arranged, the two adjacent manifolds 42 are in the same stroke, and a number of heat exchange tubes 41 can be arranged in this stroke.

[0031] In one embodiment, both the molten salt inlet diverter pipe 10 and the molten salt outlet collector pipe 20 are straight pipes, extending from the left side to the right side of the flue. This design ensures higher pipe pressure consistency among the planar serpentine pipes 40 during molten salt diversion and collection, and more uniform flow distribution among the planar serpentine pipes 40.

[0032] Several planar serpentine tubes 40 are evenly spaced from left to right in the flue. Preferably, these planar serpentine tubes 40 are evenly spaced and evenly distributed in the flue, thereby absorbing the heat of the flue gas more evenly and fully.

[0033] In one embodiment, the axis of the heat exchange tube 41 is not perpendicular to the axis of the manifold / distribution tube 42; the heat exchange tubes 41 of adjacent strokes are symmetrically arranged with respect to the perpendicular line of the axis of the manifold / distribution tube 42, and the angle formed by the heat exchange tube 41 and the connected manifold / distribution tube 42 is an obtuse angle (preferably 95°~105°). This arrangement ensures smooth molten salt flow between the heat exchange tube 41 and the manifold / distribution tube 42, further reducing flow resistance.

[0034] It should be noted that the inner diameter of the manifold 42 is larger than that of the heat exchange tube 41. Since the same manifold 42 collects and distributes the flow for multiple heat exchange tubes 41, the flow resistance of the molten salt can be reduced and the flow rate of the molten salt can be increased by adjusting the ratio of their inner diameters.

[0035] In this invention, the inner diameter of the manifold 42 is crucial. When the ratio of the inner diameter of the manifold 42 to the inner diameter of the heat exchange tube 41 is in the range of 2.5 to 3.5, the uniformity of flow distribution can be significantly improved.

[0036] Specifically, when the inner diameter of the heat exchange tube 41 is 50 mm and the inner diameter of the manifold / distribution tube 42 is also 50 mm, the flow rate of the molten salt in each heat exchange tube 41 is as follows: Figure 5 As shown in the figure, the horizontally arranged heat exchange tubes 41 and the vertically arranged manifolds / distribution tubes 42 are heat exchange tubes 41 and 42 respectively. When the inner diameter of the heat exchange tubes 41 is 50 mm and the inner diameter of the manifolds / distribution tubes 42 is 150 mm, the flow rate of the molten salt in each heat exchange tube 41 is as follows: Figure 6 As shown in the figure. Figure 6 The molten salt flow rate in each heat exchange tube 41 is significantly higher than that in the middle. Figure 5 The flow rate of molten salt in each heat exchange tube 41 indicates that the number of vortices in the heat exchange tube 41 has decreased.

[0037] Table 1 shows the molten salt flow rate in each heat exchange tube 41 when the inner diameter of the heat exchange tube 41 is 50 mm and the inner diameters of the manifold and branch pipe 42 are 150 mm and 50 mm respectively.

[0038] Table 1

[0039]

[0040] In Table 1, pipes 1 through 6 refer to... Figure 5 and Figure 6 The heat exchange tubes 41 are arranged from bottom to top. For example, tube 1 refers to... Figure 5 and Figure 6 The bottommost heat exchange tube 41, tube 6 refers to Figure 5 and Figure 6 The uppermost heat exchange tube is 41.

[0041] As shown in Table 1, when the inner diameter of the manifold 42 is 150 mm, the maximum deviation of the flow velocity in the six heat exchange tubes 41 is 12.70%; when the inner diameter of the manifold 42 is 50 mm, the maximum deviation of the flow velocity in the six heat exchange tubes 41 is 145.8%. Here, deviation refers to the ratio of the deviation value to the average flow velocity of the six heat exchange tubes 41. The deviation value is the difference between the current flow velocity of the molten salt in the heat exchange tubes 41 and the average flow velocity, which refers to the average flow velocity of the molten salt in the six heat exchange tubes 41.

[0042] Therefore, this design effectively eliminates the severe vortex and flow separation generated during elbow connections, significantly reducing local resistance and thus allowing for smaller flow velocity deviations, which is key to achieving uniform flow distribution.

[0043] like Figure 3 and Figure 4 As shown, the heat exchange tube 41 furthest from the center of the manifold 42 in the same stroke is connected to the end of the manifold 42, while the remaining heat exchange tubes 41 are connected to the side of the manifold 42. Due to the large number of heat exchange tubes 41 in the same stroke and the limitations of the inclination angle of the heat exchange tubes 41 and the length of the manifold 42, it is difficult to connect the end of each heat exchange tube 41 to the side of the manifold 42. Therefore, to reduce the volume of the heat exchanger, the edge heat exchange tubes 41 are connected to the end of the manifold 42. However, it is necessary to extend the length of the heat exchange tube 41 and bend its end to make the molten salt flow more smoothly inside. This design also further increases the fluidity of the molten salt.

[0044] Meanwhile, the connection between the heat exchange tube 41 and the manifold 42 is an arc-shaped tube. The arc-shaped tube design allows for smoother molten salt flow at the connection point, further reducing the resistance to molten salt flow.

[0045] The heat exchange tube 41 has symmetrically arranged fins, with the fins extending in the same direction as the flue gas flow. This fin design expands the heat transfer area, further absorbing heat from the flue gas and improving heat exchange efficiency. Simultaneously, by limiting the fin orientation, the symmetrical vortex street generated when the flue gas flows around the heat exchange tube 41 is disrupted, reducing the wake region and effectively suppressing dust deposition and bridging.

[0046] In one embodiment, the inner diameter of the heat exchange tubes 41 is 50 mm, the inner diameter of the manifold and branch pipes 42 is 150 mm, and the flue gas composition is 3% (by volume fraction) CO2, 2% H2O, 18% O2, and 77% N2; the working absolute pressure of the flue gas is 101325 Pa, and the flue gas flow rate is 135000 Nm³. 3 •h -1 When the flue gas enters the heat exchanger, the temperature is 800℃, and the temperature of the molten salt in the low-temperature molten salt storage tank (i.e., the inlet temperature of the molten salt) is 200℃.

[0047] In this experiment, the fins were rectangular with a height of 28 mm. The change in flue gas outlet temperature with fin thickness was as follows: Figure 7 As shown, the molten salt outlet temperature varies with fin thickness as follows: Figure 8 As shown in the figure, when the fin thickness is 5.5mm, it can provide sufficient extended heat transfer area, while avoiding material waste and excessive increase in flue gas flow resistance caused by excessively thick fins, and the flue gas outlet temperature is the lowest.

[0048] In another embodiment, such as Figure 9 The diagram shows the variation of flue gas outlet temperature and flue gas temperature drop rate with fin height. In this experiment, the fins were cuboid in structure and 5.5 mm thick. As shown in the figure, the optimal performance-cost ratio was achieved when the fin height was 21 mm. Excessive height would significantly reduce fin efficiency and increase equipment size and flue gas pressure drop; conversely, insufficient height would limit the enhancement of heat transfer.

[0049] Furthermore, the presence of fins not only significantly increases the heat transfer area on the flue gas side (compensating for the low heat transfer coefficient on the flue gas side), but their streamlined structure also disrupts the symmetrical vortex street generated when flue gas flows around the heat exchange tube 41, reducing the wake region and thus effectively suppressing dust deposition and bridging. Figure 10 The diagram shows the flue gas flow when the heat exchange tube 41 is not equipped with fins in an embodiment of the present invention. It can be seen from the diagram that a flow dead zone forms on the left side of the heat exchange tube 41 along the flue gas flow direction, and a negative pressure vortex region forms on the right side; as shown... Figure 11The diagram shows the ash accumulation on the heat exchange tube 41 when it is not equipped with fins in an embodiment of the present invention. The black area in the diagram represents the ash accumulation area. It can be seen from the diagram that severe ash accumulation areas are formed on the left and right sides of the heat exchange tube 41 along the flue gas flow direction, especially since dust is easily drawn into the tail vortex area. Figure 12 The diagram shows the flue gas flow when the heat exchange tube 41 is finned in an embodiment of the present invention. It can be seen from the diagram that the shape of the heat exchange tube 41 is closer to a streamline. Adding fins can significantly change the flow field characteristics, causing a significant downstream displacement at the boundary layer separation point, reducing the velocity gradient near the wall, smoothing the pressure distribution, improving flow stability, and reducing the size of the wake vortex region. Figure 13 The figure shows a schematic diagram of the dust accumulation situation when the heat exchange tube 41 is equipped with fins in an embodiment of the present invention. It can be seen from the figure that the fins can produce a physical separation effect, decompose the continuous vortex street into a discrete vortex structure, reduce the particle entrainment intensity, and significantly weaken the dust accumulation phenomenon.

[0050] Therefore, adding cuboid fins to the heat exchange tube 41 is an effective measure to reduce pressure resistance, enhance heat transfer, and reduce ash accumulation in the flue gas-molten salt heat exchanger.

[0051] In one embodiment, the heat exchange effects of the heat exchange tube 41 without fins and the heat exchange tube 41 with fins were compared and analyzed. As shown in Table 2 below, compared with the heat exchange tube 41 without fins, the molten salt outlet temperature of the heat exchange tube 41 with fins increased by 0.32K, and the flue gas outlet temperature changed significantly, decreasing by 15.01K. In the complete model, if the flue gas outlet temperature increases by 15.01K, it will generate an additional 820.38KW of heat, which can heat 100°C water into 1.12 tons of superheated steam at 1.0MPa and 300°C per hour.

[0052] Table 2

[0053]

[0054] To increase the stability of the heat exchanger, several fixing members 30 are installed inside the flue. These fixing members 30 securely install several planar serpentine tubes 40 within the flue, thereby enhancing the stability and practicality of the heat exchanger. Preferably, multiple fixing plates can be provided, each with a through hole for the heat exchange tubes 41 to pass through, and pipe clamps or other connecting components can be installed in the through hole. Alternatively, the fixing plate can be directly welded to the heat exchange tubes 41. In other embodiments, the fixing members 30 can also be in the form of fixing brackets or fixing rods.

[0055] In one embodiment, the flue is typically prismatic and includes a shell, which may be welded from steel plates (such as Q345R steel plates). The inner wall is lined with a fire-resistant and wear-resistant castable, the thickness of which is designed according to requirements, such as 50 mm. An insulation layer (such as a 100 mm thick aluminum silicate fiber felt insulation layer) is provided on the outer wall, and the flue gas flows inside the shell.

[0056] The entire flue shell is supported and fixed by a steel frame. The planar serpentine tube 40 is installed inside the flue shell via a tube sheet and internal support structure. The angle between the heat exchange tube 41 and the manifold / diverter tube 42 is designed to be 100°. This angle facilitates complete venting of the molten salt during shutdown, preventing solidification, and also provides a certain degree of thermal compensation. The standard length of the heat exchange tube 41 is slightly less than the width of the flue. Eight longitudinal straight fins are evenly arranged on the outer wall of each heat exchange tube 41 using high-frequency brazing. The fin material is T2 copper strip, with a thickness of 5.5 mm and a height of 21 mm. The extension direction of all fins is strictly parallel to the designed flow direction of the flue gas.

[0057] Specifically, in this embodiment, both the heat exchange tube 41 and the manifold / diverter tube 42 are made of T2 copper tubing, which has excellent thermal conductivity and high-temperature oxidation resistance. The heat exchange tube 41 has an outer diameter of 57mm and a wall thickness of 3.5mm, i.e., an inner diameter of 50mm. The axial distance between the heat exchange tubes 41 in the same stroke is equal to the distance between adjacent planar serpentine tubes 40, and both are 57mm. This distance balances heat transfer efficiency and structural compactness. This spacing also provides operating space for cleaning tools (such as sonic soot blowers). Preferably, the number of heat exchange tubes 41 in the same stroke is 3, but this number can be reselected according to different scenarios and design requirements, such as 2, 5, etc.

[0058] More specifically, the heat exchange tube 41 and the manifold / diverter tube 42 can also be connected by flanges for easy maintenance and replacement.

[0059] The workflow of this invention is as follows:

[0060] Low-temperature molten salt (e.g., 200°C) enters from the molten salt inlet branch pipe 10, and the molten salt (e.g., mass fraction of 53% KNO3 + 40% NaNO2 + 7% NaNO3) is branched from its various outlets into different planar serpentine tubes 40. In a planar serpentine tube 40, the molten salt first flows through several parallel heat exchange tubes 41 in the same stroke to absorb heat, and then flows to the collector branch pipe 42 for collection. In the collector branch pipe 42, the molten salt is redistributed to several heat exchange tubes 41 in the next stroke, until it flows to the molten salt outlet collector pipe 20, and finally the high-temperature molten salt (e.g., 450°C) flows out from the molten salt outlet collector pipe 20.

[0061] In the above process, high-temperature flue gas enters from the flue inlet and, driven by a fan, flows over the finned or unfined heat exchange tubes 41, exchanging heat with the molten salt inside the tubes. After cooling down, it is discharged from the flue outlet and enters the downstream dust removal and purification system. It should be noted that after the high-temperature flue gas enters from the flue inlet, it first exchanges heat with the nearby heat exchange tubes 41. In this way, the heat exchange tubes 41 near the flue outlet exchange heat with the flue gas near the flue outlet (whose temperature is lower than the flue gas entering from the flue inlet). That is, the molten salt flows in the opposite direction to the flue gas, which allows the temperature of the molten salt to gradually increase.

[0062] By optimizing the diameter of the manifold and distributor tubes 42, the industry-wide problem of uneven distribution of parallel planar serpentine tubes 40 in multi-pass molten salt heat exchangers is fundamentally solved, avoiding the risk of localized overheating or solidification blockage. The integrated fins simultaneously expand the heat transfer area and optimize the flow field, significantly improving the heat transfer coefficient. The streamlined fin structure effectively disrupts vortex generation, reducing fly ash deposition and bridging on the leeward side of the heat exchange tubes 41.

[0063] The inclined heat exchange tubes 41 have excellent thermal compensation capabilities, effectively absorbing thermal stress caused by flue gas temperature fluctuations. The source of this thermal stress is that the metal material of the heat exchange tubes 41 expands or contracts when the flue gas temperature fluctuates. If the heat exchange tubes 41 are rigidly fixed, this deformation will be constrained, resulting in significant thermal stress at the joints. Over time, this can lead to weld cracking, support damage, or pipe twisting. However, this invention, through the design of a structure where the heat exchange tubes 41 and the manifold / diverter tubes 42 cooperate, allows these connecting parts to undergo slight stretching, compression, and bending deformations like springs when the pipes expand due to heat, thereby absorbing the cumulative deformation of the entire tube bundle.

[0064] This heat exchanger can be directly placed in the flue, resulting in a compact structure. Stable operation on the molten salt side can provide a stable heat source for downstream energy storage or other systems, improving the economics of the entire waste heat recovery system.

[0065] In addition, the present invention also discloses a molten salt heat storage system, including a cold salt tank, a hot salt tank, and the above-mentioned serpentine shell-and-tube flue gas molten salt heat exchanger.

Claims

1. A serpentine shell-and-tube type flue gas molten salt heat exchanger, characterized in that, It includes several planar serpentine tubes (40), which are evenly spaced from the left to the right side of the flue. The inlet ends of several planar serpentine tubes (40) are all connected to the same molten salt inlet branch pipe (10), and the outlet ends of several planar serpentine tubes (40) are all connected to the same molten salt outlet manifold (20). The planar serpentine tube (40) includes a heat exchange tube (41) that is intersected with the flue gas flow direction and a collection and distribution tube (42) that is parallel to the flue gas flow direction. The number of heat exchange tubes (41) in the same stroke is at least two, and the heat exchange tubes (41) in the same stroke are arranged parallel to each other along the flue gas flow direction; the heat exchange tubes (41) in the same stroke are all connected to the same manifold (42), and the heat exchange tubes (41) and the manifold (42) are both straight pipes; the stroke is the space between the front and rear sides of the flue within a predetermined range along the length of the flue for laying the heat exchange tubes (41), and the length direction is the flue gas flow direction; The inner diameter of the manifold (42) is larger than the inner diameter of the heat exchange tube (41); The connection between the heat exchange tube (41) and the manifold (42) is an arc-shaped tube.

2. A serpentine shell-and-tube type flue gas molten salt heat exchanger as described in claim 1, characterized in that, The axis of the heat exchange tube (41) is not perpendicular to the axis of the manifold (42); The heat exchange tubes (41) of adjacent strokes are symmetrically arranged with respect to the vertical line of the axis of the manifold (42), and the angle formed by the heat exchange tubes (41) and the connected manifold (42) is an obtuse angle.

3. A serpentine shell-and-tube type flue gas molten salt heat exchanger as described in claim 2, characterized in that, The heat exchange tube (41) furthest from the center of the manifold (42) in the same stroke is connected to the end of the manifold (42), and the remaining heat exchange tubes (41) are connected to the side of the manifold (42).

4. A serpentine shell-and-tube type flue gas molten salt heat exchanger as described in claim 3, characterized in that, The heat exchange tube (41) has symmetrically arranged fins, and the extension direction of the fins is the same as the flue gas flow direction.

5. A serpentine shell-and-tube type flue gas molten salt heat exchanger as described in claim 4, characterized in that, The axial distance between the heat exchange tubes (41) in the same stroke is equal to the distance between the adjacent planar serpentine tubes (40).

6. A serpentine shell-and-tube type molten salt heat exchanger for flue gas as described in claim 5, characterized in that, Both the molten salt inlet diversion pipe (10) and the molten salt outlet collection pipe (20) are straight pipes, and both extend from the left side of the flue to the right side.

7. A molten salt thermal storage system, characterized in that, Includes a cold salt tank, a hot salt tank, and a serpentine shell-and-tube flue gas molten salt heat exchanger as described in any one of claims 1-6.

Images