A shell-and-tube molten salt heat exchanger

Abstract

The utility model provides a kind of tube-shell type molten salt heat exchanger, it is related to thermal power generation field, including shell, streamline baffle and heat exchange tube bundle, shell is formed by streamline baffle and heat exchange tube bundle in shell and is supplied for the shell side of molten salt flow, it is characterized in that, still include hot material outlet pipe and hot material inlet pipe being respectively arranged in the lateral wall of shell along radial direction, streamline baffle is distributed using three-section variable pitch along shell side axial direction, guide molten salt to flow along oblique spiral path in shell side, to reduce flow dead zone, set up flow guide in the import side of tail streamline baffle, guide molten salt to flow direction inclination certain angle and flush streamline baffle area.It can reduce flow dead zone in shell side, promote molten salt and heat exchange tube effective contact, effectively improve the problem of low local heat transfer efficiency caused by high-temperature molten salt due to retention dead zone.

Description

Technical Field

[0001] This utility model relates to the field of thermal power generation, and in particular to a shell-and-tube molten salt heat exchanger. Background Technology

[0002] In thermal power generation technology, molten salt plays a core role as a heat storage medium. During off-peak hours, the system uses excess energy to heat the molten salt to achieve energy storage; during peak hours, the molten salt releases the stored heat and converts it into electrical energy. The heat exchange efficiency of the entire thermal storage system is no less than 95%, and the electrical conversion efficiency is no less than 70%.

[0003] Molten salt is a "high-temperature heat-conducting medium" composed of inorganic salts such as sodium nitrate and potassium nitrate. Its core characteristic is that it can "remain liquid at high temperatures and store a large amount of heat".

[0004] Thermal storage is essentially the storage of sensible heat by molten salt through "temperature increase". For example, when cold molten salt at about 300°C is heated to 565°C, each kilogram of molten salt can store about 300 kilojoules of heat, which is equivalent to 0.08 kilowatt-hours of electricity.

[0005] However, when high-temperature molten salt flows in the shell side of a shell-and-tube heat exchanger, it is easy to form local flow dead zones with a velocity of ≤0.3m / s in the gap between the baffle and the heat exchange tube bundle, on the back of the baffle, and near the inner wall of the shell. These dead zones cause poor flow of molten salt, and some molten salt remains here for a long time, unable to make effective contact with the heat exchange tube, thereby reducing the local heat transfer efficiency. Utility Model Content

[0006] In view of the shortcomings of the existing technology, the technical problem to be solved by this utility model is to provide a shell-and-tube molten salt heat exchanger that can reduce the flow dead zone in the shell side and promote effective contact between molten salt and heat exchange tubes, which can effectively improve the problem of low local heat transfer efficiency caused by the dead zone of high temperature molten salt.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows: This utility model provides a shell-and-tube molten salt heat exchanger, including a shell, streamlined baffles, and heat exchange tube bundles. The shell side, which allows molten salt to flow, is formed inside the shell through the streamlined baffles and heat exchange tube bundles. The feature is that it also includes a hot material outlet pipe and a hot material inlet pipe respectively arranged radially on the side wall of the shell. The streamlined baffles are distributed in three sections with variable pitch along the shell side axial direction to guide the molten salt to flow along an oblique spiral path in the shell side, thereby reducing the flow dead zone. A flow guide is provided on the inlet side of the streamlined baffles at the tail section to guide the molten salt to scour the streamlined baffle area at a certain angle along the flow direction.

[0008] In the preferred embodiment, the hot material outlet pipe is located at 1 / 4 of the axial length on the left side of the shell and extends directly upwards, with the pipe opening communicating with the shell side, forming a channel for molten salt to flow out of the shell side; The hot material inlet pipe is located at 3 / 4 of the axial length on the right side of the shell and extends directly downwards. The pipe opening is connected to the shell side, forming a channel for molten salt to flow into the shell side.

[0009] In the preferred embodiment, the streamline baffle is spiral-shaped and is divided into an inlet section, a middle section, and an outlet section along the shell side axis. The inlet section is located in the front 1 / 3 region of the shell side near the hot material inlet pipe, with a pitch of 300-400 mm; The middle section is located in the middle 1 / 3 region of the shell side axial direction, with a pitch of 150-200mm; The outlet section is located in the rear 1 / 3 region of the shell side near the hot material outlet pipe, with a pitch of 250-300 mm; Among them, the pitch of the inlet section is greater than that of the outlet section, and the pitch of the outlet section is greater than that of the middle section.

[0010] In a preferred embodiment, the flow guide includes a flow guide ring inclined along the direction of molten salt flow, and flow guide plates evenly distributed circumferentially along the inner wall edge of the flow guide ring. The flow guide ring is coaxial with the shell, the distance between the end of the flow guide and the inner wall of the shell is 3-5mm, and the tangent direction of the end of the flow guide forms a 20° angle with the shell side axis. The molten salt flows through the flow guide to guide and scour the dead zone on the back of the baffle and suppress the bypass flow.

[0011] In a preferred embodiment, the helix angle of the streamlined baffle is 15°-20°, and multiple conical protrusions are arranged in a staggered manner along the helix direction on the flow-facing surface of the streamlined baffle. The ratio of the height of the conical protrusion to its bottom diameter is 1:2.5-1:4, and the line connecting the centers of adjacent protrusions forms a 30° angle with the central helix of the streamlined baffle.

[0012] In a preferred embodiment, an elastic sealing gasket is embedded at the contact point between the streamlined baffle and the housing to reduce molten salt bypass flow, wherein the elastic sealing gasket has a metal wound structure; The skeleton of the metal winding structure is formed by spiral winding of Inconel 625 metal strips, and the filling layer is one of high-temperature resistant ceramic fiber or flexible graphite.

[0013] In the preferred embodiment, the internal channels of the heat exchanger tube bundle constitute the tube side; It also includes tube sheet assemblies for fixing the heat exchanger tube bundles and isolating the shell-side and tube-side media; The tube sheet assembly is located at both ends of the housing and is sealed to the housing.

[0014] In a preferred embodiment, the tube sheet assembly includes a tube sheet, baffles, and positioning holes; The tube sheet is a bimetallic composite tube sheet; The tube sheet has baffle holes and positioning holes along the shell side axial direction, and the streamline baffle plate has tube bundle holes that correspond to the baffle holes in the tube sheet and pass through it along the spiral trajectory. The heat exchange tube bundle is inserted through the baffle holes in the tube sheet at both ends, and the middle section passes through the tube bundle hole corresponding to the streamline baffle, so that the heat exchange tube bundle is suspended in the shell side.

[0015] In a preferred embodiment, the device also includes a fixing rod that extends through the shell and a spacer tube that is sleeved on the outside of the fixing rod. The two ends of the fixing rod are fixed to the positioning holes of the tube sheet, and the middle section passes through the positioning hole of the streamline baffle. One spacer tube is installed every 90° along the inner wall of the shell. One end abuts against the surface of the streamline baffle plate, and the other end abuts against the end face of the tube plate, so as to constrain the radial sway and axial displacement of the streamline baffle plate.

[0016] In the preferred embodiment, the baffle holes are distributed in a zoned manner along the shell-side cross-section, and are divided into a central zone, a transition zone, and an edge zone from the center of the tube sheet to the edge, with the hole spacing in each zone decreasing in a progressive manner; The central area is a circular region with a radius of 500 mm, and the center distance between adjacent baffles is 35-40 mm; The transition zone is an annular area extending outward from the outer edge of the central zone to a radius of 1200mm, with the center distance between adjacent baffles being 30-35mm. The edge zone is an annular area extending outward from the outer edge of the transition zone to a radius of 1800 mm, and the center distance between adjacent baffles is 20-25 mm. Among them, the hole spacing in the transition zone is smaller than that in the center zone, and the hole spacing in the edge zone is smaller than that in the transition zone. This utility model provides a shell-and-tube molten salt heat exchanger, which, through the combination of the above structures, has the following advantages compared with the prior art: First, it significantly reduces the range of flow dead zones. Streamlined baffles guide molten salt to flow along a continuous spiral trajectory, avoiding the flow reversal caused by structural discontinuities in traditional baffles. It also reduces the stagnation area on the back of the baffles, effectively agitating the low-velocity molten salt near the inner wall of the shell. The heat exchange tubes are densely arranged in the edge region, which can enhance the disturbance to the molten salt in the tube bundle gaps, thus significantly reducing the local low-velocity areas in the gaps between the baffles and the heat exchange tube bundles, on the back of the baffles, and near the inner wall of the shell.

[0017] Secondly, it promotes smooth flow of molten salt and reduces stagnation. The streamlined spiral flow channel makes the molten salt flow path continuous without abrupt changes, and the flow guide ring can break the local stagnation state, allowing the molten salt that was originally stagnant for a long time to participate in the mainstream flow. The elastic sealing structure at the edge of the streamlined baffle plate suppresses the ineffective bypass flow, guides more molten salt to flow through the heat exchange tube area, avoids local stagnation caused by short-circuit flow, and makes the molten salt flow more uniformly and smoothly in the shell side.

[0018] Third, the spiral flow field drives the molten salt to continuously scour the outer wall of the heat exchange tube, increasing the contact opportunities between the molten salt and the heat exchange tube. The molten salt that could not contact the heat exchange tube due to the existence of dead zones can fully exchange heat with the tube wall in the optimized flow field, significantly improving the local heat transfer effect and solving the problem of low local heat transfer efficiency caused by dead zones in traditional structures. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is the exploded view of the main structure of this utility model; Figure 2 This utility model will Figure 1 Exploded view of the structure after the heat exchanger tube bundle has been removed; Figure 3 This is a utility model Figure 2 A magnified view of part A in the middle; Figure 4 This is a structural diagram of the fluid flow direction in this utility model; Figure 5 This is a utility model Figure 2 Structural diagram of the central guide component; Figure 6 This is a utility model Figure 2 Structural diagram of the tube sheet assembly; Figure 7 This is a utility model Figure 6 Diagram showing the spacing and arrangement of the intermediate baffle holes; Figure 8 This is a utility model Figure 2 Structural diagram of the streamline baffle; Figure 9 This is a schematic diagram illustrating the working principle of the heat storage and release process of this utility model; Figure 10 This is a schematic diagram of the fluid in a simulation experiment using this utility model.

[0020] In the figure: 1. Shell; 2. Hot material outlet pipe; 3. Hot material inlet pipe; 4. Streamline baffle; 5. Sealing gasket; 6. Tube sheet assembly; 6. Tube sheet; 61. Baffle hole; 62. Positioning hole; 63. Flow guide; 7. Flow guide ring; 71. Flow guide plate; 72. Heat exchange tube bundle; 8. Fixing rod; 9. Spacing tube; 10. Inlet tube box; 11. Outlet tube box; 12. Support; 13. Detailed Implementation

[0021] To better understand the purpose, structure, and function of this utility model, the embodiments and features described herein can be combined with each other without conflict. The utility model will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] like Figures 1-10As shown in the figure, this embodiment illustrates a shell-and-tube molten salt heat exchanger, including a shell 1, a streamlined baffle 4, and a heat exchange tube bundle 8. The shell 1 is formed by the streamlined baffle 4 and the heat exchange tube bundle 8 to provide fluid flow. It also includes a hot material outlet pipe 2 and a hot material inlet pipe 3. Both the hot material outlet pipe 2 and the hot material inlet pipe 3 are cylindrical pipes that are welded to the side wall of the shell. Specifically, shell 1 refers to the outer container of the heat exchanger, which is usually a closed cylindrical pressure vessel. It is the "outer shell" of the heat exchanger and its main function is to house the internal core components such as heat exchange tube bundle 8 and streamline baffle 4, and to provide a closed space for fluid flow while bearing the pressure and temperature of the fluid.

[0023] The shell side refers to the channel or space through which the molten salt fluid flows "inside the shell 1 and outside the heat exchange tube bundle 8". In a molten salt heat exchanger, the molten salt, as a fluid, flows within the shell side, exchanging heat with the steam and other media flowing inside the heat exchange tubes. The boundary of the shell side is formed by the inner wall of the shell, the tube sheets at both ends, and the baffles in the middle. Its shape and size are determined by the shell dimensions and the tube bundle layout.

[0024] like Figure 1 , 2 As shown, the hot material outlet pipe 2 extends radially upwards along the shell 1, with the welding point located at 1 / 4 of the length on the left side of the shell 1. The pipe opening directly communicates with the shell-side space inside the shell 1, serving as a channel for high-temperature molten salt (such as 565℃ molten salt) to enter the shell side. The upper end of the hot material outlet pipe 2 is connected to an external low-temperature molten salt return pipe, leading to a low-temperature storage tank, to export the molten salt after heat exchange, completing the circulation of the shell-side molten salt. Under exothermic conditions, the hot material outlet pipe 2 forms a channel for the cooled molten salt (300℃) to flow out of the shell side after heat exchange; under regenerative conditions, the hot material outlet pipe 2 forms a channel for the heated molten salt (565℃) to flow out of the shell side after heat exchange. The hot material inlet pipe 3 extends radially downward along the shell 1, with the welding point located at 3 / 4 of the length on the right side of the shell 1. The pipe opening is also connected to the shell-side space, serving as a channel for the cooled molten salt (such as 300℃ molten salt) to flow out of the shell side after heat exchange. The lower end of the hot material inlet pipe 3 is connected to an external high-temperature molten salt transport pipe from the extraction steam heat exchanger, which receives the high-temperature molten salt to be exchanged. Under heat storage conditions, the hot material inlet pipe 3 forms a channel for the low-temperature molten salt (300℃) to flow into the shell side.

[0025] When implementing, such as Figure 4 , 9As shown, when the high-temperature molten salt tank is releasing heat: the high-temperature molten salt (565℃) in the high-temperature molten salt tank is transported to the hot material inlet pipe 3 through the external high-temperature molten salt conveying pipe (from the output pipe of the high-temperature tank), and enters the shell side interior radially downward along the shell 1 through the hot material inlet pipe 3; the high-temperature molten salt entering the shell side flows along a spiral path under the guidance of the streamline baffle 4, and exchanges heat with the tube side medium (such as cold water or low-temperature steam) in the heat exchange tube bundle 8, releasing heat and cooling down to 300℃; the cooled molten salt continues to flow to the left 1 / 4 length of the shell 1, and flows out of the shell side radially upward through the hot material outlet pipe 2, and is transported to the low-temperature molten salt tank for storage through the external low-temperature molten salt return pipe connected to the upper end of the hot material outlet pipe 2, completing the molten salt circulation of the heat release stage.

[0026] When the molten salt is stored in the cryogenic molten salt tank: the cryogenic molten salt (300℃) in the cryogenic molten salt tank is transported to the hot material inlet pipe 3 through the external cryogenic molten salt conveying pipe (from the output pipe of the cryogenic tank), and enters the shell side interior radially downward along the shell 1 through the hot material inlet pipe 3; the cryogenic molten salt entering the shell side flows along a spiral path under the guidance of the streamline baffle 4, and exchanges heat with the tube side medium (such as high-temperature steam from the extraction steam heat exchanger) in the heat exchange tube bundle 8, and rises to 565℃ after absorbing heat; the high-temperature molten salt continues to flow to the left 1 / 4 length of the shell 1, and flows out of the shell side radially upward through the hot material outlet pipe 2, and is transported to the high-temperature molten salt tank for storage through the external high-temperature molten salt conveying pipe (the input pipe leading to the high-temperature tank) connected to the upper end of the hot material outlet pipe 2, completing the molten salt circulation of the heat storage stage.

[0027] Specifically, the hot material outlet pipe 2 and the hot material inlet pipe 3 are symmetrically distributed along the axis of the shell 1, forming a spatial layout of "outlet at the top, left 1 / 4; inlet at the bottom, right 3 / 4", covering the main heat exchange area along the shell side axis.

[0028] Both the upper end of the hot material outlet pipe 2 and the lower end of the hot material inlet pipe 3 are welded with necked butt-welding flanges, and the flange sealing surfaces are machined into raised and recessed surfaces. The flanges are fastened to the external pipes with high-strength bolts. Preferably, the high-strength bolts are high-temperature alloy bolts. A metal-clad gasket is placed between the flange faces. The metal shell is Hastelloy C276, and the inner core is flexible graphite combined with ceramic fiber, which can withstand high temperatures of 300-565℃ and molten salt corrosion, ensuring long-term sealing without leakage.

[0029] Specifically, the bottom-in, top-out, and symmetrical layout utilizes the synergistic effect of axial flow velocity to create an "oblique spiral flow" of molten salt within the shell side. The flow velocity is stabilized at 0.8-1.5 m / s, avoiding stagnation due to excessively low velocity and a surge in resistance due to excessively high velocity. After flowing in from the lower opening at the right 1 / 4, the high-temperature molten salt is propelled by the spiral flow field within the shell side (i.e., guided by the spiral baffles) to flow axially upwards and to the left, fully passing through the heat exchange tube bundle 8, and finally exiting from the upper opening at the left 3 / 4. This path covers more than 90% of the shell side space, avoiding "local short-circuit flow" caused by the inlet and outlet tubes being on the same side or concentrated in position, and significantly reducing flow dead zones behind the baffles and near the inner wall of the shell.

[0030] It should be noted that the high-temperature molten salt (565℃) has a lower density, and its flow into the lower hot material inlet pipe 3 can reduce the direct impact on the bottom of the shell; the molten salt that has cooled down after heat exchange (300℃) has a higher density, and the molten salt (300℃) that can be cooled with the assistance of a molten salt pump flows out from the upper hot material outlet pipe 2.

[0031] Among them, the streamlined baffle 4 adopts a "large-small-medium" variable pitch along the shell side axis, with the inlet section pitch being 300-400mm. The inlet section is located at the front 1 / 3 length near the hot material inlet pipe 3, reducing the impact resistance when molten salt enters. The pitch of the middle section is reduced to 150-200mm, and the middle section is the middle 1 / 3 of the length. Turbulent disturbance is enhanced by compressing the flow channel to reduce dead zone; The pitch of the outlet section is adjusted to 250-300mm, and the outlet section is located at the end of the second third of the hot material outlet pipe to stabilize the flow field and ensure temperature uniformity.

[0032] Further as Figure 1 , 2 As shown in Figure 4, a flow guide 7 is provided on the inlet side of the streamline baffle 4 in the tail section to guide part of the molten salt in the shell side to flow towards the tube bundle region at an angle of 10°-20° along the flow direction, and to flush the dead zone on the back of the streamline baffle 4.

[0033] The flow guide 7 includes a flow guide ring 71 and a flow guide plate 72; The flow guide ring 71 is made of either Hastelloy C276 or nickel-based alloy Inconel 625. 18-20 flow guide vanes 72 are evenly distributed circumferentially along the inner wall edge of the flow guide ring 71. The distance between the flow guide vanes 72 and the inner wall of the shell 1 is controlled at 3-5 mm. The ends of the flow guide vanes 72 are tilted to one side at 20° along the flow direction. When molten salt flows through the flow guide vanes 72, it can disturb and generate secondary flow, enhance the heat transfer with the tube wall, guide part of the molten salt through the flow guide vanes 72 to flow to the tube bundle area, suppress bypass flow, and flush the dead zone on the back of the baffle.

[0034] Specifically, Hastelloy C276 exhibits excellent corrosion resistance to nitrate-based molten salts, can operate stably for extended periods below 565°C, and possesses good plasticity, enabling it to adapt to deformation caused by thermal expansion.

[0035] Incone L625, a nickel-based alloy, has strong oxidation resistance and high-temperature strength. Its compatibility with molten salt has been verified in projects such as solar thermal power plants, molten salt pipelines, and tank seals. It is also more suitable as a shell-side guide ring material.

[0036] The guide ring is inclined at 30° along the direction of molten salt flow, which allows for a small amount of thermal expansion space to prevent thermal stress damage caused by rigid contact, and can also guide the bypass flow back to the main flow area of ​​the tube bundle to reduce ineffective flow.

[0037] Specifically, the streamline baffle 4 is spiral-shaped, with the overall spiral angle controlled at 15°-20°, which is 5°-10° smaller than that of a traditional spiral baffle. This guides the spiral flow to avoid alternating reversals while reducing flow resistance. Furthermore, such as Figure 8 As shown, conical micro-protrusions are evenly distributed on the flow-facing surface (i.e. the side in contact with molten salt) of the streamlined baffle 4. The protrusions are 2-3 mm high, 5-8 mm in diameter at the bottom, and 15-20 mm apart. They are arranged in a staggered manner along the spiral direction, and the line connecting the centers of adjacent protrusions forms a 30° angle with the spiral line.

[0038] During implementation, as the molten salt flows through, the protrusions generate local eddies, breaking the boundary layer and enhancing heat transfer with the outer wall of the heat exchange tube; at the same time, the staggered arrangement avoids flow field interference and reduces additional resistance.

[0039] Among them, such as Figure 1 , 2 As shown, an elastic sealing gasket is embedded at the contact point between the streamlined baffle 4 and the shell 1. The sealing gasket is 2-3mm thick and the compression is controlled at 10%-15%, which effectively reduces bypass flow and enhances heat transfer efficiency.

[0040] Preferably, the elastic sealing gasket is made of metal spiral wound elastic gasket, which is formed by spirally winding Inconel 625 metal strip as the skeleton to form an elastic matrix, and filled with high temperature resistant ceramic fiber (i.e., temperature resistance > 800℃) or flexible graphite (treated with anti-oxidation). Specifically, the metal-wound elastic gasket provides structural strength and elasticity, while the filler layer enhances sealing and can withstand high temperatures of 565°C and molten salt corrosion; the linear expansion coefficient of the metal-wound elastic gasket is 15×10⁻⁶. -6 ( / ℃) is close to the shell 1 and the streamlined baffle 4, and the expansion amount is matched at high temperature to avoid excessive compression or gap generation. It can also be cut according to the gap size to adapt to the non-standard gap between the streamlined baffle 4 and the shell 1.

[0041] further, Figure 2 , 3 As shown, weld neck flanges are welded to both ends of the housing 1, the flange sealing surface is machined into a raised face, and the flange sealing surface forms an annular sealing groove. It also includes sealing gasket 5, tube sheet assembly 6, inlet tube box 11 and outlet tube box 12; The sealing gasket 5 is located between the flange face of the tube sheet assembly 6 facing the shell 1 and the flange face of the shell 1 port, serving as an "intermediate sealing layer" between the two connection surfaces. One side of the sealing gasket 5 is tightly attached to the end face of the tube sheet assembly 6 facing the shell 1, and the other side is tightly attached to the flange sealing face of the shell 1 port. The entire gasket 5 is pressed together by the flange bolt assembly of the tube sheet assembly 6 and the shell 1, forming a closed barrier against the shell-side molten salt.

[0042] Specifically, because it needs to withstand the high temperature of molten salt, i.e., high temperature of 300 to 565°C, and the oxidizing properties of sodium nitrate-based molten salt and the corrosive properties of chloride molten salt, the sealing gasket 5 is a metal spiral wound gasket with a nickel-based alloy strip as the main body. Preferably, it is made of Inconel 625 with high-temperature resistant ceramic fibers sandwiched in the middle, or a metal-coated gasket with Hastelloy C276 metal shell and flexible graphite core, to ensure that it does not age or corrode by molten salt at high temperatures.

[0043] During installation, the sealing gasket 5 is pre-placed in the annular sealing groove on the flange face of the housing 1. The groove depth is slightly less than 1 / 2 of the gasket thickness. The seal is achieved by fastening the tube sheet assembly 6 to the flange of the housing 1 with bolts. The bolts are evenly distributed along the circumference of the flange. After tightening, the gasket generates a compression of 15%-25%, and its metal layer is tightly attached to the flange face. The fiber or graphite layer fills the micro gaps, forming a leak-free seal.

[0044] Among them, the tube sheet assembly 6 is the "end cap" of the shell 1, which is directly connected to the edge of the flange face of the shell 1 port, together forming a closed shell-side space. It is used to fix the spatial position of the heat exchange tube bundle 8, prevent the heat exchange tube bundle 8 from vibrating or shifting during the high-speed flow of molten salt, and prevent collision damage with the shell 1 and the streamline baffle 4. It separates the molten salt in the shell side from the steam and other fluids in the tube side, and prevents the two media from mixing through a tight connection. That is, molten salt leakage to the tube side will contaminate the steam, and steam leakage to the shell side will cause the molten salt to be diluted.

[0045] In the preferred solution, such as Figure 6 , 7 As shown, the tube sheet assembly 6 includes a tube sheet 61, a baffle hole 62, and a positioning hole 63; A flow-through baffle 4 with a baffle hole 62 and a positioning hole 63 is provided on the tube sheet 61 along the shell side axial direction. The flow-through baffle 4 has tube bundle holes that are corresponding to the flow-through baffle holes 62 of the tube sheet along a spiral trajectory. The heat exchange tube bundle 8 passes through the tube bundle holes. The two ends of the heat exchange tube bundle 8 pass into the flow-through baffle holes 62 of the tube sheet 61, and the middle section passes through the corresponding flow-through baffle holes 62 on each flow-through baffle 4 in sequence, so that the heat exchange tube bundle 8 is suspended in the shell side. The internal channels of the heat exchange tube bundle 8 constitute the tube side, that is, the medium such as water and steam flows, forming a through-type fixed structure of "tube sheet 61-flow-through baffle 4-tube sheet 61".

[0046] The heat exchange tube bundle 8 is made of φ25×2mm nickel-based alloy tubes, which are resistant to molten salt corrosion. Preferably, Inconel625 is used. The tube length of the heat exchange tube bundle 8 is matched with the axial length of the shell side.

[0047] Specifically, the diameter of the baffle 62 is 1-2 mm larger than the outer diameter of the heat exchange tube bundle 8. Preferably, the outer diameter of the tube bundle is 25 mm and the diameter of the baffle is 26-27 mm, leaving room for thermal expansion. At high temperature, the difference in expansion between the heat exchange tube bundle 8 and the streamline baffle 4 is about 0.5-1 mm / m, avoiding stress tearing caused by rigid contact. Among them, such as Figure 1 As shown, a fixing rod 9 is inserted into the positioning hole 63, which is a baffle plate 4 that passes through the shell side axially. The fixing rod 9 is a slender rod-shaped structure. The fixing rod 9 is made of the same corrosion-resistant material as the heat exchange tube bundle 8, namely Inconel 625. The two ends of the fixing rod 9 are connected to the tube sheets 61 at both ends of the shell 1 and pass through the positioning holes 63 of the tube sheets 61. The middle section passes through the corresponding positioning holes 63 on each streamline baffle 4 along the shell side axial direction, serving as the "positioning skeleton" of the baffle. A spacer tube 10 is sleeved on the outside of the fixing rod 9. The spacer tube 10 is a hollow round tube made of the same material as the fixing rod 9. The spacer tubes 10 are evenly distributed along the inner wall of the shell 1, i.e., one is set every 90°. One end of the spacer tube 10 is in contact with the plate surface of the streamline baffle 4, and the other end is in contact with the end face of the tube sheet 61 on the shell side of the shell 1, forming a radial limit.

[0048] Specifically, the fixed rod 9, together with the spacer tube 10, forms an axial positioning structure of "tube sheet 61-fixed rod 9-spacer tube 10-streamline baffle 4-fixed rod 9-spacer tube 10-tube sheet 61".

[0049] It should be noted that the spacer tube 10 and the fixing rod 9 are clearance fit, preferably with a clearance ≤ 0.5mm, to ensure that the spacer tube 10 can be finely adjusted along the axis of the fixing rod 9, which facilitates the calibration of the baffle plate spacing during installation. The contact part between the spacer tube 10 and the streamline baffle plate 4 is not directly welded, but is axially limited through the positioning hole 63 preset in the streamline baffle plate 4, so as to avoid the thermal stress caused by welding from affecting the shape of the streamline baffle plate 4. This facilitates the pre-installation and positioning of the streamline baffle plate 4 and reduces the amount of adjustment work during on-site installation. At the same time, if the streamline baffle plate 4 needs to be replaced due to corrosion or wear, the component can be quickly removed by disassembling the nut of the fixing rod 9, reducing maintenance costs.

[0050] It should be noted that the fixing rod 9 has external threads machined at both ends, passes through the pre-set through holes in the tube sheet, and is then tightened with nuts; at the same time, the contact area between the fixing rod 9 and the tube sheet is sealed by argon arc welding to prevent molten salt from leaking from the gap.

[0051] The combination of the fixed rod 9 and the spacer tube 10 forms a rigid constraint to prevent the streamline baffle 4 from radially swaying or axially shifting when the high-temperature molten salt flows at high speed. This avoids the streamline baffle 4 from colliding with the heat exchange tube bundle 8 and the shell 1, causing wear, and at the same time reduces flow field turbulence caused by vibration.

[0052] Tube sheet 61 is a bimetallic composite tube sheet, consisting of a Q345R base layer combined with an Inconel 625 cladding. The connection between tube sheet 61 and heat exchanger tube bundle 8 employs a dual process of explosive welding combined with sealing welding. Experiments have shown that the weld leakage rate is ≤1×10⁻⁶. -9 mbar L / s; It should be noted that traditional expansion joints or fusion welding are difficult to achieve a reliable seal, while explosive welding uses instantaneous high pressure to generate micro-jets at the interface, removing the oxide layer and forming a wavy metallurgical bond; Explosive welding utilizes the energy of an explosive explosion to tightly bond the heat exchange tubes to the inner wall of the tube sheet through-holes, forming a metallurgical bonding layer to ensure the connection strength under high temperature and high pressure. Sealing welding involves performing another sealing weld on the surface of the joint to further block the leakage path between the molten salt and the pipe medium, adapting to the corrosiveness of the molten salt, such as the oxidizing properties of sodium nitrate-based molten salt.

[0053] Furthermore, such as Figure 7 , 8 As shown, the flow-deflecting holes 62 on the tube sheet 61 and the streamlined baffle 4 adopt a density distribution of "sparser at the center and denser at the edges," with the hole spacing in the edge region being 10%-15% denser than that in the center region. Because the molten salt velocity is lower at the shell-side edges, increasing the number of edge openings and reducing the hole spacing enhances the molten salt disturbance in the edge region and reduces dead zones at the edges. The specific hole spacing is as follows: The central region has a radius of 0-500 mm, occupying 30%-35% of the shell-side cross-sectional area. Preferably, the central region has a radius of 500 mm, corresponding to the core region with the highest flow velocity in the helical flow. The spacing between the baffles 62, i.e., the center-to-center distance between adjacent baffles 62, is 35-40 mm, preferably 35 mm. Because the molten salt flow velocity in the central region is high, approximately 1.5-2.0 m / s, a larger spacing between the baffles can reduce flow resistance and avoid excessive pressure drop due to excessive flow velocity. The transition zone has a radius of 500-1200 mm, accounting for 45%-50% of the total area. Preferably, the transition zone has a radius of 1200 mm and a moderate flow velocity. The hole spacing gradually decreases to 30-35 mm, preferably 30 mm. The flow velocity in the transition zone is moderate (1.0-1.5 m / s). By appropriately reducing the hole spacing, the number of heat exchange tubes is increased, thereby increasing the heat transfer area and compensating for the weakening of heat transfer caused by the decrease in flow velocity.

[0054] The edge zone has a radius of 1200-1800 mm, accounting for 15%-20% of the total flow. Preferably, the transition zone has a radius of 1800 mm, located near the inner wall of the shell, where the flow velocity is lowest. The hole spacing is further reduced to 20-25 mm, preferably 20 mm. Because this region has the lowest flow velocity (0.5-1.0 m / s) and is prone to forming flow dead zones, densely arranged heat exchange tube bundles 8 increase the contact opportunities with molten salt, thereby enhancing heat transfer in the edge zone.

[0055] like Figure 8 As shown, the streamlined baffle 4 is designed as a streamlined shape with rounded edges to reduce molten salt impact resistance. The baffle holes 62 opened in the streamlined baffle 4 are arranged along the long axis of the molten salt flow direction. The hole spacing of the baffle holes 62 has an increasing-decreasing gradient along the flow path. The hole spacing is larger in the central area, gradually increases in the transition area, and is denser in the edge area, which adapts to the changes in molten salt flow velocity and enhances turbulent disturbance.

[0056] like Figure 1 As shown, the inlet tube box 11 and the outlet tube box 12 are located at both ends of the shell 1 and are directly connected to the flanges of the corresponding tube sheet 61 to form a closed "transition space". The internal space of the inlet tube box 11 and the outlet tube box 12 is connected to the tube side of the heat exchange tube bundle 8, forming a complete flow path of the tube side medium, namely, external pipe → inlet tube box → heat exchange tube → outlet tube box → external pipe. The top of the inlet pipe box 11 is equipped with an inlet pipe for connecting to an external pipe-side medium supply pipeline, such as a water supply pipeline or a steam pipeline. The outlet pipe box 12 is equipped with an outlet pipe at the corresponding position, which is connected to an external medium discharge pipe, such as a steam condensate pipe or a high-temperature steam channel; The flanges of the inlet tube box 11 and the outlet tube box 12 are fastened to the flange of the shell 1 by bolts. High and low temperature resistant and aging resistant metal spiral wound gaskets are installed between the flange faces to ensure that the tube side medium (steam) and the shell side medium (molten salt) are completely isolated.

[0057] Furthermore, such as Figure 1 , 2 As shown, the bracket 13 is directly connected to the bottom or lower side wall of the shell 1, and is usually arranged at intervals along the axial direction of the shell 1. Preferably, a group is set every 2-3 meters to form a "multi-point support" structure. Each group of brackets contains 1-2 support legs, which are symmetrically distributed on both sides of the shell 1 to ensure that the shell is subjected to balanced forces. Among them, the support arm of bracket 13 is fixed to the lower part of shell 1 by argon arc welding. The weld material is the same as that used in shell, which is either Q345R or nickel-based alloy, to ensure that the connection strength is sufficient to withstand the weight of shell and internal medium. The bottom of the bracket 13 is provided with a base plate. Furthermore, the size of the base plate is designed according to the load. In actual applications, it is 300×300mm. It is fastened to the concrete foundation by pre-embedded bolts or welded to the pre-embedded steel plate of the steel structure platform. Preferably, for heat exchangers with large axial thermal expansion, such as shell length exceeding 6m, the supports 13 near both ends of the shell 1 adopt "sliding supports", that is, a polytetrafluoroethylene sliding plate is installed between the base plate and the foundation, with a friction coefficient ≤0.1. The middle support adopts "guide supports" to limit lateral displacement and allow axial sliding, ensuring that the shell can freely expand and contract at high temperatures and avoid generating additional stress.

[0058] In the preferred scheme, such as Figure 4 , 9 As shown in Figure 10, the high-temperature molten salt storage tank is made of J347H, which is a high-carbon niobium-containing Cr-Ni austenitic stainless steel. It contains the stabilizing element niobium, has good resistance to intergranular corrosion, and has high high-temperature strength and good resistance to high-temperature oxidation.

[0059] During the heat storage stage: store the "unused heat" from thermal power plants; When electricity demand is low (such as late at night) and thermal power generation exceeds demand, the excess heat is not wasted directly, but is used to heat molten salt: Steam is extracted from a boiler or steam turbine. The extracted steam is high-temperature steam, which exchanges heat with cold molten salt (from a low-temperature storage tank) through a "molten salt heater". After absorbing heat, the temperature of the cold molten salt rises from 300℃ to 565℃, turning it into "hot molten salt," which is then pumped into a "high-temperature storage tank" for storage. At this time, thermal power can reduce fuel consumption (or even "idle"), using only excess heat for heat storage, thus reducing energy waste.

[0060] During the heat release phase: the stored heat is "converted into electricity"; When electricity demand is high (such as during the day), thermal power plants need to operate at full capacity or even exceed their output, the molten salt in the high-temperature storage tank releases heat: Hot molten salt exchanges heat with cold water through a "steam generator". After releasing heat, the temperature drops from 565°C to 300°C, turning back into cold molten salt, which flows back to the low-temperature storage tank for recycling. Cold water absorbs heat and turns into high-temperature steam, which is then added to the steam turbine to drive it to do extra work and increase power generation. At this time, thermal power plants do not need to suddenly increase fuel combustion to avoid efficiency decline and a surge in pollutants. They can achieve flexible peak shaving by "rapidly replenishing energy" through molten salt thermal storage.

[0061] In the description of this utility model, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0062] Furthermore, the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this utility model are for distinguishing similar objects and are limited to descriptive purposes. They should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features, nor are they necessarily used to describe a specific order or sequence. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified. It should be understood that such data can be interchanged where appropriate for the embodiments of this utility model described herein.

[0063] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0064] To enable those skilled in the art to better understand the present invention, the above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be the technical solution described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A shell-and-tube molten salt heat exchanger, comprising a shell (1), streamlined baffles (4), and heat exchange tube bundles (8), wherein the shell (1) contains a shell side for molten salt flow formed by the streamlined baffles (4) and the heat exchange tube bundles (8), characterized in that, It also includes a hot material outlet pipe (2) and a hot material inlet pipe (3) respectively located on the side wall of the shell (1) in the radial direction. The streamline baffle (4) adopts a three-section variable pitch distribution along the shell side axis to guide the molten salt to flow along the oblique spiral path in the shell side to reduce the flow dead zone. A guide (7) is set on the inlet side of the streamline baffle (4) in the tail section to guide the molten salt to scour the streamline baffle (4) area at a certain angle along the flow direction.

2. The shell-and-tube molten salt heat exchanger according to claim 1, characterized in that, The hot material outlet pipe (2) is located at 1 / 4 of the axial length on the left side of the shell (1) and extends directly upward. The pipe opening is connected to the shell side, forming a channel for molten salt to flow out of the shell side. The hot material inlet pipe (3) is located at 3 / 4 of the axial length on the right side of the shell (1) and extends directly downwards. The pipe opening is connected to the shell side, forming a channel for molten salt to flow into the shell side.

3. The shell-and-tube molten salt heat exchanger according to claim 1, characterized in that, The streamline baffle (4) is spiral and is divided into an inlet section, a middle section and an outlet section along the shell side axis; The inlet section is located in the front 1 / 3 region of the shell side near the hot material inlet pipe (3), with a pitch of 300-400 mm; The middle section is located in the middle 1 / 3 region of the shell side axial direction, with a pitch of 150-200mm; The outlet section is located in the rear 1 / 3 region of the shell side near the hot material outlet pipe (2), with a pitch of 250-300 mm; Among them, the pitch of the inlet section is greater than that of the outlet section, and the pitch of the outlet section is greater than that of the middle section.

4. The shell-and-tube molten salt heat exchanger according to claim 1, characterized in that, The flow guide (7) includes a flow guide ring (71) inclined along the direction of molten salt flow, and flow guide plates (72) evenly distributed circumferentially along the inner wall edge of the flow guide ring (71). The guide ring (71) is coaxial with the shell (1). The distance between the end of the guide plate (72) and the inner wall of the shell (1) is 3-5 mm. The tangent direction of the end of the guide plate (72) forms a 20° angle with the shell side axis. The molten salt flows through the guide plate (72) to guide and scour the dead zone on the back of the baffle and suppress the bypass flow.

5. The shell-and-tube molten salt heat exchanger according to any one of claims 1 to 4, characterized in that, The streamlined baffle (4) has a helix angle of 15°-20°. Multiple conical protrusions are arranged in a staggered manner along the helix direction on the flow-facing surface of the streamlined baffle (4). The ratio of the height of the conical protrusion to its bottom diameter is 1:2.5-1:

4. The line connecting the centers of adjacent protrusions forms a 30° angle with the central helix of the streamlined baffle (4).

6. The shell-and-tube molten salt heat exchanger according to claim 5, characterized in that, An elastic sealing gasket is embedded at the contact point between the streamlined baffle (4) and the housing (1) to reduce the flow of molten salt bypass, wherein the elastic sealing gasket is a metal wound structure; The skeleton of the metal winding structure is formed by spiral winding of Inconel 625 metal strips, and the filling layer is one of high-temperature resistant ceramic fiber or flexible graphite.

7. The shell-and-tube molten salt heat exchanger according to claim 1, characterized in that, The internal channels of the heat exchange tube bundle (8) constitute the tube side; It also includes a tube sheet assembly (6) for fixing the heat exchange tube bundle (8) and isolating the shell-side and tube-side media. The tube sheet assembly (6) is located at both ends of the housing (1) and is sealed to the housing (1).

8. The shell-and-tube molten salt heat exchanger according to claim 7, characterized in that, The tube sheet assembly (6) includes a tube sheet (61), baffles (62) and positioning holes (63); Tube sheet (61) is a bimetallic composite tube sheet; A flow deflector (62) and a positioning hole (63) are provided on the tube sheet (61) along the shell side axial direction. The streamlined flow deflector (4) is provided with tube bundle holes that are corresponding to the flow deflector (62) of the tube sheet along the spiral trajectory. The heat exchange tube bundle (8) is inserted at both ends into the baffle holes (62) of the tube sheet (61), and the middle section is inserted through the corresponding tube bundle hole of the streamline baffle (4), so that the heat exchange tube bundle (8) is suspended in the shell side.

9. The shell-and-tube molten salt heat exchanger according to claim 8, characterized in that, It also includes a fixed rod (9) that runs through the shell and a spacer tube (10) that is sleeved on the outside of the fixed rod (9). The two ends of the fixed rod (9) are fixed to the positioning holes (63) of the tube sheet (61), and the middle section passes through the positioning holes (63) of the streamline baffle (4). One spacer tube (10) is set every 90° along the inner wall of the shell (1). One end abuts the surface of the streamline baffle (4) and the other end abuts the end face of the tube plate (61) to constrain the radial sway and axial displacement of the streamline baffle (4).

10. The shell-and-tube molten salt heat exchanger according to claim 8, characterized in that, The flow baffles (62) are distributed in a partitioned manner along the shell-side cross section, and are divided into a central area, a transition area and an edge area from the center of the tube sheet (61) to the edge. The spacing between the holes in each area is set in a decreasing manner. The central area is a circular region with a radius of 500 mm, and the center distance between each adjacent baffle (62) is 35-40 mm; The transition zone is an annular area extending outward from the outer edge of the central area to a radius of 1200 mm, and the center distance between each adjacent baffle (62) is 30-35 mm; The edge region is an annular area extending outward from the outer edge of the transition region to a radius of 1800 mm, and the center distance between each adjacent baffle (62) is 20-25 mm; Among them, the hole spacing in the transition zone is smaller than that in the center zone, and the hole spacing in the edge zone is smaller than that in the transition zone.

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