Coiled tube shell type flue gas molten salt heat exchanger and molten salt heat storage system

Abstract

The invention belongs to the technical field of heat exchangers, and discloses a coiled tube shell type flue gas molten salt heat exchanger which comprises a plurality of plane coiled tubes which are arranged at intervals from the left side to the right side of a flue. The inlet ends of the plurality of planar coiled pipes are connected to the same fused salt inlet flow dividing pipe, and the outlet ends of the plurality of planar coiled pipes are connected to the same fused salt outlet flow collecting pipe; the plane coiled pipe comprises a heat exchange pipe crossed with the flowing direction of the flue gas and a flow collecting and distributing pipe parallel to the flowing direction of the flue gas; according to the invention, heat exchange between flue gas and molten salt can be realized by arranging the plurality of plane coiled pipes in the flue, and the straight pipe type flow collecting and distributing pipes are used for replacing elbows of the traditional plane coiled pipes, so that vortexes generated by the elbows in the existing design can be obviously reduced, the local resistance of molten salt flowing is reduced, the flow speed of the molten salt is increased, and the heat exchange efficiency is improved. And the heat exchange efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat exchangers, in particular to a serpentine tube shell type flue gas molten salt heat exchanger and a molten salt heat storage system. BACKGROUND

[0002] The high-temperature flue gas (usually 600-1100 DEG C) generated in the electric furnace steelmaking process has the characteristics of high dust content, easy formation of dioxin, and large temperature fluctuation, and the traditional waste heat recovery equipment is usually a tube type boiler or a heat pipe boiler.

[0003] As an excellent medium and high temperature heat transfer and heat storage medium, molten salt has good thermal stability and wide temperature range operation capability, but its easy solidification characteristics put high requirements on the design of the heat exchanger. The existing serpentine tube shell type heat exchanger is provided with a bend at the turning part of the serpentine tube, which will cause local resistance to the flow of molten salt and affect the heat exchange effect. SUMMARY

[0004] The purpose of the present application is to provide a serpentine tube shell type flue gas molten salt heat exchanger and a molten salt heat storage system, which improves the structure of the turning part of the serpentine tube, thereby reducing the local resistance of the molten salt flow.

[0005] The application adopts the following technical scheme: a serpentine tube shell type flue gas molten salt heat exchanger, comprising a plurality of planar serpentine tubes, the plurality of planar serpentine tubes being arranged at intervals from the left side to the right side of the flue; The inlet ends of the plurality of planar serpentine tubes are connected to the same molten salt inlet manifold, and the outlet ends of the plurality of planar serpentine tubes are connected to the same molten salt outlet manifold; The planar serpentine tube comprises a heat exchange tube arranged transversely to the flue gas flow direction and a manifold arranged parallel to the flue gas flow direction; Among them, the number of heat exchange tubes of the same stroke is at least two, and the heat exchange tubes of the same stroke are arranged in parallel along the flue gas flow direction; the heat exchange tubes of the same stroke are connected to the same manifold, and the heat exchange tube and the manifold are both straight pipes; the stroke is the space for arranging the heat exchange tube between the front side and the rear side of the flue within a predetermined range in the length direction of the flue, and the length direction is the flue gas flow direction; The inner diameter of the manifold is greater than the inner diameter of the heat exchange tube; The connection part of the heat exchange tube and the manifold is an arc-shaped tube.

[0006] The application has the beneficial effects that: the application can realize heat exchange between flue gas and molten salt by arranging a plurality of planar serpentine tubes in the flue, and the manifold in the form of a straight pipe can replace the bend of the traditional planar serpentine tube, which can significantly reduce the vortex generated by the existing design of the bend, thereby reducing the local resistance of the molten salt flow, increasing the flow rate of the molten salt, and improving the heat exchange efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 Figure 1 is a structural schematic diagram of a serpentine tube shell type flue gas molten salt heat exchanger according to an embodiment of the present application; Figure 2 Figure 2 is a structural schematic diagram of the serpentine tube shell type flue gas molten salt heat exchanger according to an embodiment of the present application from another perspective; Figure 3 Figure 3 is a structural schematic diagram of a partial structure of the serpentine tube shell type flue gas molten salt heat exchanger according to an embodiment of the present application; Figure 4 Figure 4 is a structural schematic diagram of another partial structure of the serpentine tube shell type flue gas molten salt heat exchanger according to an embodiment of the present application; Figure 5 Figure 5 is a schematic diagram of the flow rate of molten salt when the inner diameter of the heat exchange tube is 50 mm and the inner diameter of the flow and distribution pipe is also 50 mm according to an embodiment of the present application; Figure 6 Figure 6 is a schematic diagram of the flow rate of molten salt when the inner diameter of the heat exchange tube is 50 mm and the inner diameter of the flow and distribution pipe is 150 mm according to an embodiment of the present application; Figure 7 Figure 7 is a schematic diagram of the change of the flue gas outlet temperature with the fin thickness according to an embodiment of the present application; Figure 8 Figure 8 is a schematic diagram of the change of the molten salt outlet temperature with the fin thickness according to an embodiment of the present application; Figure 9 Figure 9 is a schematic diagram of the change of the flue gas outlet temperature and the flue gas temperature drop rate with the fin height according to an embodiment of the present application; Figure 10 Figure 10 is a schematic diagram of the flue gas flow when the heat exchange tube is not provided with fins according to an embodiment of the present application; Figure 11 Figure 11 is a schematic diagram of the ash accumulation when the heat exchange tube is not provided with fins according to an embodiment of the present application; Figure 12 Figure 12 is a schematic diagram of the flue gas flow when the heat exchange tube is provided with fins according to an embodiment of the present application; Figure 13 Figure 13 is a schematic diagram of the ash accumulation when the heat exchange tube is provided with fins according to an embodiment of the present application.

[0008] In the drawings: 10. Molten salt inlet distribution pipe; 20. Molten salt outlet flow pipe; 30. Fixing member; 40. Flat serpentine tube; 41. Heat exchange tube; 42. Flow and distribution pipe. DETAILED DESCRIPTION

[0009] The present application will be described in detail below with reference to the drawings and specific embodiments.

[0010] The present application discloses a serpentine tube shell type flue gas molten salt heat exchanger, such as Figure 1 and Figure 2As shown, the plurality of planar serpentine tubes 40 are arranged in intervals from the left side to the right side of the flue; the inlet ends of the plurality of planar serpentine tubes 40 are connected to the same molten salt inlet manifold 10, and the outlet ends of the plurality of planar serpentine tubes 40 are connected to the same molten salt outlet manifold 20; the planar serpentine tube 40 comprises heat exchange tubes 41 arranged transversely to the flue gas flow direction and manifold tubes 42 arranged parallel to the flue gas flow direction; wherein 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 in parallel along the flue gas flow direction; the heat exchange tubes 41 in the same stroke are connected to the same manifold tube 42, and the heat exchange tubes 41 and the manifold tubes 42 are straight tubes; the stroke is the space for arranging heat exchange tubes between the front side and the rear side of the flue within a predetermined range in the length direction of the flue, and the length direction is the flue gas flow direction.

[0011] The present application can realize heat exchange between flue gas and molten salt by arranging a plurality of planar serpentine tubes 40 in the flue, and can significantly reduce the vortex generated by the elbow of the existing design by replacing the elbow of the traditional planar serpentine tube 40 with the manifold tube 42 in the form of a straight tube, thereby reducing the local resistance of the molten salt flow, increasing the flow rate of the molten salt, and improving the heat exchange efficiency.

[0012] In the prior art, the planar serpentine tube 40 refers to a tube that meanders multiple times in a plane and has a shape similar to a snake. The turning of the pipe is usually realized by arranging a 180° elbow at the meandering part, and the straight pipes at the non-meandering part are parallel to each other and are arranged horizontally or vertically, and the connection ends of the straight pipes and the elbow are coaxial.

[0013] In the present application, when the heat exchange tubes 41 are arranged, the same stroke is between the adjacent two manifold tubes 42, and a plurality of heat exchange tubes 41 can be arranged in the stroke.

[0014] In one embodiment, the molten salt inlet manifold 10 and the molten salt outlet manifold 20 are straight tubes, and both extend from the left side to the right side of the flue. By such design, the consistency of the pipe pressure of each planar serpentine tube 40 can be ensured when the molten salt is distributed and collected, and the flow of each planar serpentine tube 40 is evenly distributed.

[0015] The plurality of planar serpentine tubes 40 are evenly spaced from the left side to the right side of the flue. Preferably, the intervals of these planar serpentine tubes 40 are equal and uniformly distributed in the flue, so as to more uniformly and fully absorb the heat of the flue gas in the flue.

[0016] In one embodiment, 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 rows are symmetrically arranged relative to the perpendicular line of the axis of the manifold 42, and the included angle between the heat exchange tube 41 and the connected manifold 42 is obtuse (preferably 95°-105°). By so arranging, the smooth flow of the molten salt between the heat exchange tube 41 and the manifold 42 can be ensured, and the flow resistance is further reduced.

[0017] It should be noted that the inner diameter of the manifold 42 is greater than the inner diameter of the heat exchange tube 41. Since the same manifold 42 collects and distributes the molten salt for multiple heat exchange tubes 41, by adjusting the inner diameter ratio between the two, the flow resistance of the molten salt can also be reduced, and the flow rate of the molten salt is improved.

[0018] In the present application, the inner diameter of the manifold 42 is crucial, and when the ratio of the inner diameter of the manifold 42 to the inner diameter of the heat exchange tube 41 is within the range of 2.5-3.5, the uniformity of the flow distribution can be significantly improved.

[0019] Specifically, when the inner diameter of the heat exchange tube 41 is 50 mm and the inner diameter of the manifold 42 is also 50 mm, the flow rate of the molten salt in each heat exchange tube 41 is as shown in FIG. 1, wherein the heat exchange tube 41 is arranged horizontally, and the manifold 42 is arranged vertically. Figure 5 When the inner diameter of the heat exchange tube 41 is 50 mm and the inner diameter of the manifold 42 is 150 mm, the flow rate of the molten salt in each heat exchange tube 41 is as shown in FIG. 2. As can be seen from the figure, Figure 6 the flow rate of the molten salt in each heat exchange tube 41 in FIG. 1 is significantly higher than Figure 6 the flow rate of the molten salt in each heat exchange tube 41 in FIG. 2, which indicates that the vortex in the heat exchange tube 41 is reduced. Figure 5

[0020] Table 1 shows the flow rate of the molten salt in each heat exchange tube 41 when the inner diameter of the heat exchange tube 41 is 50 mm and the inner diameter of the manifold 42 is 150 mm and 50 mm, respectively.

[0021] Table 1

[0022] In Table 1, tube 1-tube 6 respectively refer to the heat exchange tubes 41 arranged from bottom to top in Figure 5 and Figure 6 For example, tube 1 refers to the lowermost heat exchange tube 41 in Figure 5 and Figure 6 Tube 6 refers to the uppermost heat exchange tube 41 in Figure 5 and Figure 6

[0023] ​​As shown in Table 1, when the inner diameter of the flow-collecting and flow-distributing pipe 42 is 150 mm, the maximum deviation of flow rate in the six heat exchange pipes 41 is 12.70%; when the inner diameter of the flow-collecting and flow-distributing pipe 42 is 50 mm, the maximum deviation of flow rate in the six heat exchange pipes 41 is 145.8%. The deviation refers to the ratio of the deviation value to the average flow rate of the six heat exchange pipes 41, the deviation value is the difference between the current flow rate of the molten salt in the heat exchange pipe 41 and the average flow rate, and the average flow rate refers to the average value of the flow rates of the molten salt in the six heat exchange pipes 41.

[0024] Therefore, the design effectively eliminates the severe vortex and flow separation generated when the elbow is connected, greatly reduces the local resistance, so that the deviation of flow rate is smaller, and is the key to realizing uniform distribution of flow.

[0025] As shown in Figs. 1 and 2, the heat exchange pipes 41 are connected to the flow-collecting and flow-distributing pipe 42 in the same stroke. Figure 3 and Figure 4 As shown in Figs. 1 and 2, the heat exchange pipes 41 are connected to the flow-collecting and flow-distributing pipe 42 in the same stroke. Due to the large number of heat exchange pipes 41 in the same stroke and the limitation of the inclination angle of the heat exchange pipes 41 and the length of the flow-collecting and flow-distributing pipe 42, it is difficult to connect the end of each heat exchange pipe 41 to the side of the flow-collecting and flow-distributing pipe 42, so in order to reduce the volume of the heat exchanger, the edge heat exchange pipe 41 is connected to the end of the flow-collecting and flow-distributing pipe 42. However, the length of the heat exchange pipe 41 needs to be extended and the end thereof needs to be bent to make the flow of the molten salt therein smoother. This design further increases the flowability of the molten salt.

[0026] Meanwhile, the connection part of the heat exchange pipe 41 and the flow-collecting and flow-distributing pipe 42 is an arc-shaped pipe, through the design of the arc-shaped pipe, the flow of the molten salt at the connection part of the two is smoother, further reducing the resistance of the molten salt flow.

[0027] The heat exchange pipe 41 has symmetrically arranged fins, and the extension direction of the fins is the same as the flow direction of the flue gas. Through the design of the fins, the heat transfer area can be expanded, further absorbing the heat of the flue gas, and improving the heat exchange efficiency. At the same time, by limiting the setting direction of the fins, the symmetric vortex street generated when the flue gas flows around the heat exchange pipe 41 can be destroyed, and the wake zone can be reduced, thereby effectively inhibiting the deposition and bridging of dust.

[0028] In one embodiment, the inner diameter of the heat exchange pipe 41 is 50 mm, the inner diameter of the flow-collecting and flow-distributing pipe 42 is 150 mm, and the composition of the flue gas is 3% (by volume fraction) CO2, 2% H2O, 18% O2 and 77% N2; the working absolute pressure of the flue gas is 101325 Pa, the flue gas flow is 135000 Nm 3 •h -1The flue gas temperature is 800℃ when entering the heat exchanger, and the molten salt temperature (i.e. the molten salt inlet temperature) in the low-temperature molten salt storage tank is 200℃.

[0029] In this experiment, the fins are cuboid structures and the height thereof is set to 28mm. The flue gas outlet temperature changes with the fin thickness as shown in Figure 7 The molten salt outlet temperature changes with the fin thickness as shown in Figure 8 As can be seen from the figure, when the fin thickness is 5.5mm, sufficient extended heat transfer area can be provided, and material waste and excessive increase of flue gas flow resistance caused by excessively thick fins can be avoided, and the flue gas outlet temperature is the lowest.

[0030] In another embodiment, as shown in Figure 9 The flue gas outlet temperature and the flue gas temperature drop rate change with the fin height as shown in the figure. In this experiment, the fins are cuboid structures and the fin thickness is 5.5mm. As shown in the figure, when the fin height is 21mm, the best "performance-cost" ratio is achieved. Too high fin height will cause significant decrease of fin efficiency, and increase of equipment volume and flue gas pressure drop; too low fin height will have limited heat transfer enhancement effect.

[0031] In addition, the presence of fins not only significantly increases the heat transfer area of the flue gas side (making up for the shortcoming of low heat transfer coefficient of the flue gas side), but also can destroy the symmetrical vortex street generated when the flue gas flows around the heat exchange tube 41, reduce the wake area, and thus effectively inhibit the deposition and bridging of dust. As shown in Figure 10 The figure is a schematic diagram of the flue gas flow when the heat exchange tube 41 is not provided with fins in the embodiment of the present application. As can be seen from the figure, a flow dead zone will be formed on the left side of the heat exchange tube 41 along the flue gas flow direction, and a negative pressure wake vortex zone will be formed on the right side. Figure 11 The figure is a schematic diagram of the dust deposition of the heat exchange tube 41 when the heat exchange tube 41 is not provided with fins in the embodiment of the present application. The black area in the figure is the dust deposition area. As can be seen from the figure, serious dust deposition areas are formed on the left and right sides of the heat exchange tube 41 along the flue gas flow direction, and dust is easily sucked into the wake vortex zone. Figure 12 The figure is a schematic diagram of the flue gas flow when the heat exchange tube 41 is provided with fins in the embodiment of the present application. As can be seen from the figure, the shape of the heat exchange tube 41 is closer to the streamline. By increasing the fins, the flow field characteristics can be significantly changed, the boundary layer separation point can be significantly displaced downstream, the velocity gradient in the near-wall region can be reduced, the pressure distribution can be flattened, the flow stability can be improved, and the wake vortex zone can be reduced. Figure 13 The figure is a schematic diagram of the dust deposition of the heat exchange tube 41 when the heat exchange tube 41 is provided with fins in the embodiment of the present application. As can be seen from the figure, the fins can produce a physical separation effect, the continuous vortex street can be decomposed into discrete vortex structures, the particle entrainment intensity can be reduced, and the dust deposition phenomenon can be significantly weakened.

[0032] Therefore, adding the rectangular structure fin to the heat exchange tube 41 is an effective measure to reduce the pressure resistance, strengthen the heat transfer and reduce the ash deposition of the flue gas-molten salt heat exchanger.

[0033] In one embodiment, the heat exchange effect of the heat exchange tube 41 without the fin is compared with that of the heat exchange tube 41 with the fin. As shown in Table 2, the molten salt outlet temperature of the heat exchange tube 41 with the fin is increased by 0.32K relative to that of the heat exchange tube 41 without the fin, and the flue gas outlet temperature changes significantly, which is decreased by 15.01K. If the flue gas outlet temperature is increased by 15.01K in the complete model, 820.38KW of heat will be generated, and 1.12 tons of 1.0MPa, 300℃ superheated steam can be heated per hour.

[0034] Table 2

[0035] In order to increase the stability of the heat exchanger, a plurality of fixing members 30 are arranged in the flue, and the plurality of planar serpentine tubes 40 are fixedly installed in the flue through the fixing members 30, so as to increase the stability and practicability of the heat exchanger. Preferably, a plurality of fixing plates can be arranged, a through hole for the heat exchange tube 41 to pass through is formed on each fixing plate, and a connecting member such as a pipe clamp is installed in the through hole, or the fixing plate is directly welded with the heat exchange tube 41. In other embodiments, the fixing member 30 can also be in the form of a fixed support or a fixed rod.

[0036] In one embodiment, the flue is generally prismatic, including a shell of the flue, which can be welded by a steel plate (such as a Q345R steel plate), and the inner wall is coated with refractory wear-resistant cast material, and the thickness is designed according to the requirement, such as 50mm. The outer wall is provided with a thermal insulation layer (such as a 100mm thick aluminum silicate fiber felt thermal insulation layer), and the flue gas flows in the shell.

[0037] The shell of the entire flue is supported and fixed by a steel frame. The planar serpentine tube 40 is installed inside the flue shell through a tube plate and an internal support structure, and the included angle between the heat exchange tube 41 and the flow dividing pipe 42 is designed to be 100°. The inclination angle is beneficial to completely emptying the molten salt during shutdown and preventing solidification, and can also provide a certain heat compensation capacity. The standard length of the heat exchange tube 41 is slightly smaller than the width of the flue. Eight longitudinal straight fins are uniformly arranged on the outer wall of each heat exchange tube 41 by high-frequency brazing. The fin material is T2 red copper strip, the thickness is processed to be 5.5mm, and the height is processed to be 21mm. The extension direction of all fins is strictly parallel to the designed flow direction of the flue gas.

[0038] Specifically, the heat exchange tube 41 and the flow and distribution pipe 42 in the embodiment are both selected as T2 red copper pipes, which have excellent heat conduction performance and high temperature oxidation resistance. The outer diameter of the heat exchange tube 41 is 57 mm, and the wall thickness is 3.5 mm, that is, the inner diameter is 50 mm. The axial distance of the heat exchange tube 41 in the same stroke is equal to the distance between the adjacent flat serpentine pipes 40, and is 57 mm, which takes into account the heat transfer efficiency and structural compactness. The distance also provides operating space for the ash removal tool (such as a sonic soot blower). Preferably, the number of heat exchange tubes 41 in the same stroke is 3, and of course the number can also be reselected according to different scenes and design requirements, such as 2, 5, etc.

[0039] More specifically, the heat exchange tube 41 and the flow and distribution pipe 42 can also be connected by flanges, which is convenient for maintenance and replacement.

[0040] The working process of the application is as follows: Low-temperature molten salt (for example, 200°C) enters from the molten salt inlet distribution pipe 10, and the molten salt (such as mass fraction of 53% KNO3+40% NaNO2+7% NaNO3) is distributed to different flat serpentine pipes 40 from its respective outlets. In one flat serpentine pipe 40, the molten salt first flows through several heat exchange tubes 41 arranged in parallel in the same stroke to absorb heat, and then flows to the flow and distribution pipe 42 for flow collection. In the flow and distribution pipe 42, the molten salt is redistributed to several heat exchange tubes 41 in the next stroke, and finally flows to the molten salt outlet manifold 20. High-temperature molten salt (for example, 450°C) flows out from the molten salt outlet manifold 20.

[0041] In the above process, high-temperature flue gas enters from the flue inlet, and is driven by the fan to flush the heat exchange tube 41 with or without fins, exchange heat with the molten salt in the tube, and then is discharged from the flue outlet to enter 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 adjacent heat exchange tube 41. In this way, the heat exchange tube 41 near the flue outlet exchanges with the flue gas near the flue outlet (the temperature is lower than that of the flue gas entering from the flue inlet), that is, the flow direction of the molten salt is opposite to the flow direction of the flue gas, which can gradually increase the temperature of the molten salt.

[0042] By optimizing the diameter of the flow and distribution pipe 42, the industry problem of uneven distribution of each parallel flat serpentine pipe 40 in the multi-tube-stage molten salt heat exchanger is fundamentally solved, and the risk of local overheating or solidification and blockage is avoided. The integrated fins increase the heat transfer area and optimize the flow field, significantly improving the heat transfer coefficient. The streamlined fin structure effectively disrupts the vortex generation, reducing the deposition and bridging of fly ash on the leeward side of the heat exchange tube 41.

[0043] The heat exchange tube 41 arranged obliquely has good heat compensation capacity and can effectively absorb thermal stress caused by temperature fluctuation of flue gas, and the thermal stress is caused by expansion or contraction of the metal material of the heat exchange tube 41 when the temperature of the flue gas fluctuates. If the heat exchange tube 41 is rigidly fixed, the deformation will be constrained, thereby causing great thermal stress at the connection, and long-term action will cause cracking of the weld, damage of the support or distortion of the pipeline. However, the heat exchange tube 41 and the collecting and distributing pipe 42 are designed to cooperate with each other in the structure, and when the pipeline is expanded by heat, the connection parts can be slightly stretched, compressed and bent, thereby absorbing the cumulative deformation amount of the whole tube bundle.

[0044] The heat exchanger can be directly placed in the flue, and the structure is compact. Stable operation of the molten salt side can provide a stable heat source for the rear-end energy storage or other systems, and improve the economy of the whole waste heat recovery system.

[0045] In addition, the application also discloses a molten salt heat storage system comprising a cold salt tank, a hot salt tank and the above-mentioned serpentine tube-shell type flue gas molten salt heat exchanger.

Claims

1. A serpentine tube-in-shell flue gas molten salt heat exchanger characterized by, The plurality of planar serpentine tubes (40) are arranged at intervals from the left side to the right side of the flue; The inlet ends of the plurality of planar serpentine tubes (40) are connected to the same molten salt inlet manifold (10), and the outlet ends of the plurality of planar serpentine tubes (40) are connected to the same molten salt outlet manifold (20); The planar serpentine tube (40) comprises heat exchange tubes (41) arranged transversely to the direction of flue gas flow and manifold tubes (42) arranged parallel to the direction of flue gas flow; 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 direction of flue gas flow; the heat exchange tubes (41) in the same stroke are connected to the same manifold tube (42), and the heat exchange tubes (41) and the manifold tube (42) are straight tubes; the stroke is the space for arranging the heat exchange tubes (41) between the front side and the rear side of the flue within a predetermined range in the length direction of the flue, and the length direction is the direction of flue gas flow; The inner diameter of the manifold tube (42) is greater than the inner diameter of the heat exchange tube (41); The connection part of the heat exchange tube (41) and the manifold tube (42) is an arc-shaped tube.

2. A serpentine tube-in-shell flue gas molten salt heat exchanger as claimed in claim 1, wherein, The axis of the heat exchange tube (41) is not perpendicular to the axis of the manifold tube (42); The heat exchange tubes (41) of adjacent strokes are symmetrically arranged relative to the perpendicular line of the axis of the manifold tube (42), and the included angle formed by the heat exchange tube (41) and the connected manifold tube (42) is obtuse.

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

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

5. A serpentine tube-in-shell flue gas molten salt heat exchanger as claimed in claim 4, wherein, The distance between the axis of the heat exchange tube (41) in the same stroke and the adjacent planar serpentine tube (40) is equal.

6. A serpentine tube-in-shell flue gas molten salt heat exchanger as claimed in claim 5, wherein, The molten salt inlet manifold (10) and the molten salt outlet manifold (20) are straight tubes and extend from the left side to the right side of the flue.

7. A serpentine tube-in-tube flue gas molten salt heat exchanger according to claim 5 or 6, characterised in that, The plurality of planar serpentine tubes (40) are evenly spaced from the left side to the right side of the flue.

8. A molten salt thermal storage system characterized by, The serpentine tube shell type flue gas molten salt heat exchanger comprises a cold salt tank, a hot salt tank and the serpentine tube shell type flue gas molten salt heat exchanger according to any one of claims 1-7.

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