Wound tube type heat exchanger based on three-cycle liquefaction process

Abstract

The coiled tube type heat exchanger comprises a heat exchanger body, a central tube is fixedly arranged in the middle of the heat exchanger body, and a spontaneous cooling tube bundle is arranged in the heat exchanger body and used for running triple-cycle refrigerants to progressively cool natural gas. A first pipe opening, a second pipe opening, a third pipe opening, a fourth pipe opening, a fifth pipe opening and a sixth pipe opening which communicate with one another are sequentially formed in the right side of the heat exchanger from bottom to top. The problems that in the prior art, a traditional heat exchanger is not provided with a refrigerant distribution structure or only internally provided with a traditional distribution structure internal part to treat a large amount of gas-liquid two-phase refrigerants, the heat exchange performance and efficiency cannot be guaranteed, and the effect is poor when quantitative distribution is conducted on a heat exchange pipe group are effectively solved.

Description

Technical Field

[0001] This invention belongs to the technical field of nitrogen- and helium-containing natural gas liquefaction equipment based on a three-cycle process, and relates to a coiled tube heat exchanger based on a three-cycle liquefaction process. Background Technology

[0002] A coiled tube heat exchanger based on refrigerant circulation process for material liquefaction refers to a heat exchanger in which the high-pressure refrigerant discharged from each stage of the circulating compressor is sent into the tube side of the heat exchanger. The heat exchange tube group shares the flow of circulating refrigerant and cools it. When the refrigerant to be throttled condenses into a subcooled liquid, the refrigerant in the tube side is collected and sent out of the heat exchanger. Through a throttling valve or a turbine expander, the refrigerant is brought to a lower temperature, forming a temperature difference driving force to transfer the refrigeration load. The low-temperature refrigerant is then sent back to the heat exchanger and distributed to the heat exchange tubes in the tube group in a certain amount. After releasing the corresponding refrigeration load to the circulating refrigerant and natural gas in these heat exchange tubes, it turns into a gaseous state, leaves the heat exchanger, and returns to the compressor of the same stage, completing the cycle of that stage.

[0003] Chinese patent CN102538387A discloses a three-stage refrigeration spiral wound tube heat exchanger for LNG cryogenic liquefaction. It analyzes the problem that traditional integrated main heat exchangers in mixed refrigerant natural gas liquefaction systems are difficult to detect when leaks occur, easily leading to production shutdowns. The patent addresses this by dividing the refrigeration into three stages, each using three independent wound tube heat exchangers, to reduce the risk of internal leaks. While segmented independent refrigeration heat exchangers have advantages, the implementation of "throttling the refrigerant into the heat exchanger cylinder and flowing downwards to cool the natural gas tube bundle and pre-cool the mixed refrigerant tube bundle" lacks a refrigerant distribution structure after throttling. As is well known, the refrigerant returning to the heat exchanger after throttling is a two-phase flow of gas and liquid. In practice, it is impossible to spontaneously and orderly distribute the two-phase flow and its carried cooling capacity to the large number of heat exchange tubes inside the heat exchanger. Therefore, traditional liquefaction processes and wound tube heat exchangers, without a refrigerant distribution structure, cannot guarantee heat exchange performance and efficiency.

[0004] Chinese patent CN110186251B discloses a three-cycle natural gas liquefaction device and method suitable for ultra-large scale. The refrigeration load of each stage is shared by three cycles, and each stage corresponds to one heat exchanger. Natural gas is cooled sequentially through one plate-fin heat exchanger and two coiled tube heat exchangers until it is liquefied and subcooled. A total of three plate-fin and coiled tube heat exchangers are involved, all of which are of conventional type. A hydraulic turbine expander is also used in the refrigerant cycle.

[0005] The complexity of the coupling between liquefaction processes and equipment technologies leads to several issues with coiled-tube heat exchangers used in refrigerant circulation processes for material liquefaction. These include throttling valves or expanders for large-scale processing, low-temperature refrigerant distribution in gas-liquid two-phase systems, multi-stream synchronous heat exchange, difficulty in detecting internal leaks that can cause production shutdowns, and natural gas denitrification. Existing technologies have not provided detailed explanations or comprehensive solutions for these issues. While the material design of small domestic throttling valves meets low-temperature requirements, the pressure-bearing and sealing performance of key components still needs improvement. As for throttling valves in large-scale liquefaction plants, factors such as marine salt spray environments, low temperatures, explosiveness, large flow rates, high pressure reduction ratios, and large diameters affect the performance and reliability of throttling valves, presenting even more design, development, and manufacturing challenges. Moreover, the product development and application technology of low-temperature circulating refrigerant throttling valves for such demanding operating conditions is currently monopolized by foreign companies. Domestically, large expander units with high power may be used. High-efficiency centripetal turbine expansion stage with liquid and high-flow-rate low-pressure-ratio compression stage can improve the efficiency of expander units to a certain extent and recover a small amount of electrical energy by performing external work. However, the use of expander motors also requires consideration of the inherent problems of fatigue safety of high-power impellers, stability under multiple variable operating conditions such as axial thrust balance and high torque transmission of large machines, and the economy of auxiliary systems such as oil-gas separation. In any case, after the large-scale expansion valve or expander discharges gas-liquid two-phase cryogenic refrigerant, a large amount of it needs to be quantitatively distributed to a large number of heat exchange tube groups after entering the heat exchanger. The gas-liquid two-phase distribution structure also needs to be compatible with multiple streams of flowing tube bundles to complete the synchronous heat exchange of multiple materials. Since there are a large number of natural gas pipe heads and refrigerant pipe heads in the heat exchange tube group, it is inconvenient to detect pipe head leaks, thus affecting the safe operation of the heat exchanger. For nitrogen-containing natural gas, the problem of denitrification also needs to be solved during the liquefaction process. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a coiled tube heat exchanger based on a three-cycle liquefaction process. This effectively solves the problems in existing technologies where traditional heat exchangers either lack a refrigerant distribution structure or only have a single built-in traditional distribution structure to handle large quantities of gas-liquid two-phase refrigerant, resulting in poor heat exchange performance and efficiency, and ineffective quantitative distribution to the heat exchange tube group.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A coiled tube heat exchanger based on a three-cycle liquefaction process includes a heat exchanger, a central tube fixedly installed in the middle of the heat exchanger, and a self-cooling tube bundle installed inside the heat exchanger for running a three-cycle refrigerant progressively cooling natural gas. The right side of the heat exchanger has a first port, a second port, a third port, a fourth port, a fifth port, and a sixth port connected from bottom to top.

[0009] The self-cooling tube bundle includes several natural gas pipes A, refrigerant pipes B, C, D1, D2, D3, and D4. Refrigerant pipes B, C, D1, D2, D3, and D4 are arranged in combination and wound into a self-diffusion combined tube element. This self-diffusion combined tube element, together with several natural gas pipes A, is wound layer by layer around a central tube to form a single self-cooling tube bundle. The lower side of the heat exchanger is fixedly connected to a seventh, eighth, ninth, tenth, eleventh, twelfth, and thirteenth port. Natural gas pipes A, B, C, D1, D2, D3, and D4 are fixedly connected to the seventh, eighth, ninth, tenth, eleventh, twelfth, and thirteenth ports, respectively.

[0010] The self-cooling tube bundle is vertical and divided into three continuous temperature decreasing zones from bottom to top: the first cooling zone, the second cooling zone, and the third cooling zone. In the first cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipes D1, D2, D3, and D4, gradually cooling the natural gas temperature from 40°C to -35°C. In the second cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipe C after throttling, gradually cooling the natural gas temperature from -35°C to -100°C. In the third cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipe B after throttling, gradually cooling the natural gas temperature from -100°C to -160°C.

[0011] Preferably, the self-cooling tube bundle is marked from bottom to top as height position 0, height position 1, height position 2, height position 3, height position 4, height position 5, and height position 6, with sealing gaskets installed at each pair of adjacent positions. Several natural gas pipes A and refrigerant pipes B, C, D1, D2, D3, and D4 are wound side-by-side on the central tube in the same spiral diameter direction, with the winding order from bottom to top as follows: Natural gas pipe A, refrigerant pipe B, refrigerant pipe C, refrigerant pipe D1, refrigerant pipe D2, refrigerant pipe D3, and refrigerant pipe D4 are connected, and the center distance between them is the same. The lengths of refrigerant pipes B, C, D1, D2, D3, and D4 decrease sequentially. The ends of refrigerant pipes B, C, D1, and D2 are sealed.

[0012] Preferably, refrigerant pipes D4, D3, D2, and D1 each have several radiating holes on both sides of their top generatrix along their spiral circumference. The radiating hole of refrigerant pipe D4 is located below the first height position, and the pressure of the refrigerant emitted from the radiating hole of refrigerant pipe D4 is 900 kPa and the temperature is 26.4°C. The radiating hole of refrigerant pipe D3 is located below the second height position and above the first height position, and the pressure of the refrigerant emitted from the radiating hole of refrigerant pipe D3 is 500 kPa and the temperature is 5.3°C. The radiating hole of refrigerant pipe D2 is located below the third height position and above the second height position, and the pressure of the refrigerant emitted from the radiating hole of refrigerant pipe D2 is 300 kPa and the temperature is -10.8°C. The radiating hole of refrigerant pipe D1 is located below the fourth height position and above the third height position, and the pressure of the refrigerant emitted from the radiating hole of refrigerant pipe D1 is 105 kPa and the temperature is -38.3°C.

[0013] The refrigerant pipes B and C are equipped with self-throttling and diverging sections at their outlet ends. These sections are located at the fifth height position and emit refrigerant at a pressure of 440 kPa and a temperature of -112.2 °C.

[0014] Preferably, the self-throttling and diverging section comprises at least one throttling pipe section and a diverging pipe section connected together. An upstream fixed core, an upstream throttling core, a middle throttling core, a downstream throttling core, and a downstream fixed core are sequentially connected inside the self-throttling and diverging section. An upstream fixed core channel is opened in the middle of the upstream fixed core, and a downstream fixed core channel is opened in the middle of the downstream fixed core. An axially penetrating first throttling hole is opened at the axis of the middle throttling core. At least one axially penetrating second throttling hole is opened at the axis of the upstream throttling core, and an axially penetrating third throttling hole is opened at the axis of the downstream throttling core. It also has several axially penetrating overflow holes for refrigerant overflow. The end of the diverging pipe section is closed, and several small through holes are uniformly opened along both sides of the top generatrix of the diverging pipe section.

[0015] Preferably, the first cooling zone is located between the 0th and 4th height positions, the second cooling zone is located between the 5th and 6th height positions, and the third cooling zone is located between the 4th and 5th height positions.

[0016] Preferably, an isolated upper inspection chamber and a lower inspection chamber are provided above and below the self-cooling tube bundle, and the upper inspection chamber and the lower inspection chamber are respectively provided with an upper inspection port and a lower inspection port.

[0017] Preferably, sealing gaskets are provided at both the fifth and fourth height positions, and the sealing gaskets are long strips arranged in a circumferential direction.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention operates a triple refrigerant cycle with three progressive self-cooling temperature zones in a single-unit coiled tube bundle, which has better adaptability to liquefaction processes.

[0020] 2. The coiled tube heat exchanger of the present invention adopts a new technology route of refrigerant throttling and distribution. In a single coiled tube bundle, a large amount of refrigerant is distributed and throttled to handle the refrigerant, eliminating the traditional distribution structure internals, reducing the height of the heat exchanger, optimizing the structure of the coiled tube heat exchanger, and having better efficiency and economy.

[0021] 3. This invention uses a self-diffusion combined tube as the heat transfer unit to enable quantitative distribution of refrigerant and simultaneous heat exchange of multiple materials, thus optimizing the structure of the coiled tube heat exchanger and achieving better performance and efficiency.

[0022] 4. This invention optimizes the natural gas process and the structure of the coiled tube heat exchanger by connecting the natural gas pipeline to the central tube and implementing liquefied natural gas denitrification in the central tube.

[0023] 5. This invention has two inspection chambers, optimizes the structure of the coiled tube heat exchanger, and sets pressure sensors and helium leak detection probes in the upper and lower inspection chambers to monitor helium concentration and leakage level, ensuring the continued safe operation of the liquefaction unit. Inspection is carried out through the lower and upper inspection ports, which has better safety and advanced features. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the three-cycle liquefaction process structure of the present invention.

[0025] Figure 2 This is a schematic diagram of the isometric structure of the present invention.

[0026] Figure 3 This is a schematic diagram of the self-divergent combined pipe structure of the present invention.

[0027] Figure 4 This is a schematic diagram of the self-cooling tube bundle and nozzle structure of the present invention.

[0028] Figure 5 This is a schematic diagram of the self-divergent combined tube winding structure of the present invention.

[0029] Figure 6 This is a schematic diagram of the self-throttling divergence section structure of the present invention.

[0030] Figure 7 For the present invention Figure 1 Enlarged schematic diagram of section A in the middle.

[0031] In the diagram: 011, First-stage pressurization inlet; 012, Second-stage pressurization inlet; 013, Third-stage pressurization inlet; 014, Fourth-stage pressurization inlet; 031, Fourth-stage separator; 032, Third-stage separator; 033, Second-stage separator; 034, First-stage separator; 072, Third-stage throttle valve; 073, Second-stage throttle valve; 074, First-stage throttle valve; 11, Seventh port; 12, Eighth port; 13, Ninth port; 21, Tenth port; 22, Eleventh port; 23, Twelfth port; 24, Thirteenth port; 40, 0th height position; 41, First height position; 42, Second height position; 43, Third height position; 44, Fourth height position; 45, Fifth height position; 46, Sixth height position; 51, First port; 52, Second... 53. Third port; 54. Fourth port; 55. Fifth port; 56. Sixth port; 61. Upper port; 62. Lower port; 100. Heat exchanger; 110. Central tube; 120. Self-cooling tube bundle; 130. Sealing gasket; 131. Lower inspection chamber; 132. Upper inspection chamber; 140. Jacket; 200. Self-diffusion combined tube element; 302. Throttling section; 303. Diverging section; 311. Upstream core; 312. Upstream core channel; 313. Second throttling orifice; 314. Upstream throttling core; 315. First throttling orifice; 316. Middle throttling core; 317. Overflow orifice; 318. Downstream throttling core; 319. Third throttling orifice; 320. Downstream core; 321. Downstream core channel; 322. Micro-through hole. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Please see Figure 1-7 The present invention provides a technical solution: a coiled tube heat exchanger based on a three-cycle liquefaction process, including a heat exchanger 100, a central tube 110 fixedly installed in the middle of the heat exchanger 100, and a self-cooling tube bundle 120 installed inside the heat exchanger 100 for running a three-cycle refrigerant progressively cooling natural gas. The heat exchanger 100 has a first pipe port 51, a second pipe port 52, a third pipe port 53, a fourth pipe port 54, a fifth pipe port 55, and a sixth pipe port 56 connected sequentially from bottom to top on the right side.

[0034] The self-cooling tube bundle 120 includes several natural gas tubes A, refrigerant tubes B, C, D1, D2, D3, and D4. The refrigerant tubes B, C, D1, D2, D3, and D4 are arranged in combination and wound into a self-diffusion combined tube element 200. This self-diffusion combined tube element 200, together with several natural gas tubes A, is wound layer by layer around the central tube 110 to form a single self-cooling tube bundle 120. The heat exchanger 100 has a fixed connection to the seventh port 11, the eighth port 12, the ninth port 13, the tenth port 21, the eleventh port 22, the twelfth port 23, and the thirteenth port 24 on its lower side. Natural gas pipe A, refrigerant pipe B, refrigerant pipe C, refrigerant pipe D1, refrigerant pipe D2, refrigerant pipe D3, and refrigerant pipe D4 are fixedly connected to the seventh port 11, the eighth port 12, the ninth port 13, the tenth port 21, the eleventh port 22, the twelfth port 23, and the thirteenth port 24, respectively.

[0035] The self-cooling tube bundle 120 is vertical and divided into three continuous temperature decreasing zones from bottom to top: the first cooling zone, the second cooling zone, and the third cooling zone. In the first cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipes D1, D2, D3, and D4, gradually cooling the natural gas temperature from 40°C to -35°C. In the second cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipe C after throttling, gradually cooling the natural gas temperature from -35°C to -100°C. In the third cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipe B after throttling, gradually cooling the natural gas temperature from -100°C to -160°C.

[0036] The refrigerant in the first cooling zone, after being pressurized four times by the first compressor unit, enters the first-stage separator 034 after being throttled by the first-stage throttling valve 074. The separated gas phase returns to the fourth-stage pressurization inlet 014 of the first compressor unit, while the liquid phase splits into two streams. One stream flows into the first port 51 of the coiled tube heat exchanger 100, provides cooling to the central tube 110 through the refrigerant pipe D1, and then returns to the fourth-stage pressurization inlet 014 from the first port 51. The other stream is throttled by the second-stage throttling valve 073 and enters the second-stage separator 033. The gas phase separated in the second-stage separator 033 returns to the third-stage pressurization inlet 013 of the first compressor unit, while the liquid phase splits into two streams. One stream flows into the second port 52 of the coiled tube heat exchanger 100, provides cooling to the central tube 110 through the refrigerant pipe D2, and then returns to the fourth-stage pressurization inlet 034 from the second port 52. One stream enters the third-stage pressurization inlet 013, and the other stream, after being throttled by the third-stage throttling valve 072, enters the third-stage separator 032. After passing through the third-stage separator 032, the separated gas phase returns to the second-stage pressurization inlet 012 of the first compressor unit, while the liquid phase splits into two streams. One stream flows into the third port 53 of the heat exchanger 100, and after being cooled by the refrigerant pipe D3, it returns to the second-stage pressurization inlet 012 from the third port 53. The other stream, after being throttled by the fourth-stage throttling valve 071, enters the fourth-stage separator 031. After passing through the fourth-stage separator 031, the separated gas phase returns to the first-stage pressurization inlet 011 of the first compressor unit, while the liquid phase flows into the fourth port 54 of the heat exchanger 100, and after being cooled by the refrigerant pipe D4, it returns to the first-stage pressurization inlet 011 from the fourth port 54, completing the first cycle.

[0037] The first compressor unit provides refrigerant at a pressure of 900 kPa and a temperature of 26.4°C, which is introduced into the fourth port 54 of the heat exchanger 100 and sent to refrigerant pipe D4; the first compressor unit provides refrigerant at a pressure of 500 kPa and a temperature of 5.3°C, which is introduced into the third port 53 and sent to refrigerant pipe D3; the first compressor unit provides refrigerant at a pressure of 300 kPa and a temperature of -10.8°C, which is introduced into the second port 52 and sent to refrigerant pipe D2; the first compressor unit provides refrigerant at a pressure of 105 kPa and a temperature of -38.3°C, which is introduced into the first port 51 and sent to refrigerant pipe D1; the refrigerant in the central pipe 110 is efficiently cooled by the refrigerant in the above refrigerant pipes D1, D2, D3, and D4, and the refrigerant in the refrigerant pipes D1, D2, D3, and D4 is allowed to carry out their respective matching cooling cycles.

[0038] The refrigerant in the second cooling zone, after being pressurized in two stages by the second compressor unit, flows into the ninth port 13 of the heat exchanger 100. After providing cooling through the refrigerant pipe C, it returns to the second compressor unit through the fifth port 55, completing the second cycle. The second compressor unit provides gaseous refrigerant with a pressure of 4200 kPa and a temperature of 40°C.

[0039] The refrigerant in the third cooling zone, after being pressurized in two stages by the third compressor unit, flows into the eighth port 12 of the heat exchanger 100. After providing cooling through the refrigerant pipe B, it returns to the third compressor unit through the sixth port 56, completing the third cycle. The third compressor unit provides gaseous refrigerant with a pressure of 4200 kPa and a temperature of 40°C.

[0040] The self-cooling tube bundle 120 is marked from bottom to top as height position 0 40, height position 41, height position 42, height position 43, height position 44, height position 45, and height position 46, with sealing gaskets 130 installed at each pair of adjacent positions. Natural gas pipe A is wound side-by-side with refrigerant pipes B, C, D1, D2, D3, and D4 on the central pipe 110 in the same spiral diameter direction. The order from bottom to top is: natural gas pipe A, refrigerant pipe B, refrigerant pipe C, refrigerant pipe D1, refrigerant pipe D2, refrigerant pipe D3, and refrigerant pipe D4. Natural gas pipe A, refrigerant pipe B, refrigerant pipe C, refrigerant pipe D1, refrigerant pipe D2, refrigerant pipe D3, and refrigerant pipe D4 maintain the same center-to-center distance. The lengths of refrigerant pipes B, C, D1, D2, D3, and D4 decrease sequentially. The ends of refrigerant pipes B, C, D1, and D2 are sealed.

[0041] Natural gas pipe A, refrigerant pipe B, refrigerant pipe C, refrigerant pipe D1, refrigerant pipe D2, refrigerant pipe D3, and refrigerant pipe D4 are brazed together with the same center-to-center distance.

[0042] When the self-cooling tube bundle 120 is being wound, natural gas tube A is wound alongside refrigerant tubes B, C, D1, D2, D3, and D4 in the same spiral diameter direction on the central tube 110. After the length of refrigerant tube D4 is exhausted, its end is sealed. The process continues with natural gas tube A wound together with refrigerant tubes B, C, D1, D2, and D3. After the length of refrigerant tube D3 is exhausted, its end is sealed. The process continues with natural gas tube A wound together with refrigerant tubes B, C, D1, D2, and D3. After the length of refrigerant pipe D2 is exhausted, the end of refrigerant pipe D2 is sealed. Then, natural gas pipe A is wound with refrigerant pipes B, C, and D1. After the length of refrigerant pipe D1 is exhausted, the end of refrigerant pipe D1 is sealed. Natural gas pipe A is wound with refrigerant pipes B and C. After the length of refrigerant pipe C is exhausted, the end of refrigerant pipe C is sealed. Natural gas pipe A and refrigerant pipe B are continued to be wound. After the length of refrigerant pipe B is exhausted, the end of refrigerant pipe B is sealed. The end of natural gas pipe A is gathered to the central pipe 110. The starting end of natural gas pipe A is connected to the seventh port 11 of heat exchanger 100.

[0043] The raw material natural gas flows into the seventh port 11 of the coiled tube heat exchanger 100, is liquefied and subcooled through the natural gas pipe A, and is denitrified through the central tube 110. The upper and lower ends of the central tube are connected to the upper port 61 and the lower port 62, respectively. The liquefied natural gas is discharged from the lower port 62 of the central tube, and the nitrogen is discharged from the upper port 61 of the central tube. Since the temperature of the liquefied natural gas inside the central tube 110 is lower than that of the refrigerant outside, the temperature of the refrigerant is lower at the upper part of the central tube 110 and higher at the lower part, and the temperature changes. The liquefied natural gas continuously decreases in the central tube 110, and the nitrogen continuously precipitates from the liquefied natural gas along the way and rises along the central tube 110.

[0044] Refrigerant pipes D4, D3, D2, and D1 all have several radiating holes on both sides of their top spiral circumference. The radiating hole of refrigerant pipe D4 is located below the first height position 41, and the pressure of the refrigerant emitted from this hole is 900 kPa, with a temperature of 26.4℃. The radiating hole of refrigerant pipe D3 is located below the second height position 42 and above the first height position 41, and the pressure of the refrigerant emitted from this hole is 5... The refrigerant pipe D2 has a pressure of 300 kPa and a temperature of -10.8℃. The refrigerant pipe D1 has a pressure of 105 kPa and a temperature of -38.3℃. The refrigerant pipe D2 has a vent hole located below the third height position 43 and above the second height position 42. The refrigerant pipe D2 has a pressure of 300 kPa and a temperature of -10.8℃. The refrigerant pipe D1 has a vent hole located below the fourth height position 44 and above the third height position 43.

[0045] The refrigerant pipes B and C are equipped with self-throttling and diverging sections at their outlet ends. These sections are located at the fifth height position 45°. The refrigerant emitted from these sections has a pressure of 440 kPa and a temperature of -112.2°C.

[0046] Refrigerant is released from refrigerant pipes D4, D3, D2, and D1 through tiny through-holes 322. The released liquid refrigerant phase forms a descending liquid film on the outer surface of refrigerant pipes D4, D3, D2, and D1. The liquid film contains the cooling energy generated by the refrigerant's own pressure drop and the driving force of the temperature difference. This not only continuously cools the refrigerant in its own refrigerant pipes arranged below, but also continuously cools the other refrigerant pipes and natural gas pipes arranged below. The released gaseous refrigerant phase returns to the circulating refrigerant compressor unit. The refrigerant discharged from the circulating refrigerant compressor unit is processed and then sent back to refrigerant pipes D4, D3, D2, and D1, thus forming a refrigerant cycle.

[0047] The self-throttling and diverging section comprises at least one throttling pipe section 302 and a diverging pipe section 303 connected together. An upstream throttling core 311, an upstream throttling core 314, a middle throttling core 316, a downstream throttling core 318, and a downstream throttling core 320 are sequentially connected inside the self-throttling and diverging section. An upstream throttling core 311 has an upstream throttling channel 312 in its middle, and a downstream throttling core 320 has a downstream throttling channel 321 in its middle. The middle throttling core 316 has an axially penetrating first throttling hole 315 at its axis, the upstream throttling core 314 has at least one axially penetrating second throttling hole 313 at its axis, and the downstream throttling core 318 has an axially penetrating third throttling hole 319 at its axis, and several axially penetrating overflow holes 317 for refrigerant overflow. The end of the diverging pipe section 303 is closed, and several small through holes 322 are evenly distributed along both sides of the top generatrix of the diverging pipe section 303.

[0048] At the sixth altitude position, the refrigerant dissipates through the tiny through-hole 322 of refrigerant pipe B radiator section 303 at a pressure of 450 kPa and a temperature of -165.2℃.

[0049] The first cooling zone is located between the 0th altitude position 40 and the fourth altitude position 44, the second cooling zone is located between the fifth altitude position 45 and the sixth altitude position 46, and the third cooling zone is located between the fourth altitude position 44 and the fifth altitude position 45.

[0050] The first, second, and third cooling zones are all connected to radially guided jackets 140. Each jacket 140 has multiple through holes in the radial direction, allowing the gas phase that releases refrigerant to flow along the gas guide gap between the natural gas pipe A and the self-diffusion combined pipe element 200, thereby facilitating the circulation of refrigerant.

[0051] The self-cooling tube bundle 120 is provided with an isolated upper maintenance chamber 132 and a lower maintenance chamber 131 above and below it, respectively. The upper maintenance chamber 132 and the lower maintenance chamber 131 are respectively provided with an upper maintenance port 32 and a lower maintenance port 31.

[0052] By using a sealing gasket 130 installed at the lower end of the self-cooling tube bundle 120 at the 0th height position 40, the lower side of the inner wall of the heat exchanger 100 is constructed into a sealed lower maintenance chamber 131. By using a sealing gasket 130 installed at the upper end of the self-cooling tube bundle 120 at the sixth height position 46, the upper side of the inner wall of the heat exchanger 100 is constructed into a sealed upper maintenance chamber 132. Pressure sensors and helium leak detectors are installed in the upper maintenance chamber 132 and the lower maintenance chamber 131. When the pipe head of the natural gas pipe A connecting to the central pipe 110 leaks, or the refrigerant inlet pipe head leaks, the pressure in the upper maintenance chamber 132 or the lower maintenance chamber 131 increases. Since the pressure sensor is connected to an external terminal, the pressure information is transmitted to the terminal. By monitoring the pressure in the upper maintenance chamber 132 or the lower maintenance chamber 131, it is determined whether maintenance is required. When the machine is shut down, the staff enters the chamber for maintenance through the lower maintenance port 31 and the upper maintenance port 32, respectively.

[0053] Both the fifth height position 45 and the fourth height position 44 are provided with sealing gaskets 130, which are long strips arranged in a circumferential direction.

[0054] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wound-tube heat exchanger based on a three-circulation liquefaction process, characterized in that: It includes a heat exchanger, a central tube fixedly installed in the middle of the heat exchanger, and a self-cooling tube bundle installed inside the heat exchanger for running a triple-circulation refrigerant progressively cooling natural gas. The right side of the heat exchanger has a first, second, third, fourth, fifth, and sixth interconnected pipe openings from bottom to top. The self-cooling tube bundle includes several natural gas pipes A, refrigerant pipes B, C, D1, D2, D3, and D4. Refrigerant pipes B, C, D1, D2, D3, and D4 are arranged in combination and wound into a self-diffusion combined tube element. This self-diffusion combined tube element, together with several natural gas pipes A, is wound layer by layer around a central tube to form a single self-cooling tube bundle. The lower side of the heat exchanger is fixedly connected to a seventh, eighth, ninth, tenth, eleventh, twelfth, and thirteenth port. Natural gas pipes A, B, C, D1, D2, D3, and D4 are fixedly connected to the seventh, eighth, ninth, tenth, eleventh, twelfth, and thirteenth ports, respectively. The self-cooling tube bundle is vertical and divided into three continuous temperature decreasing zones from bottom to top: the first cooling zone, the second cooling zone, and the third cooling zone. In the first cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipes D1, D2, D3, and D4, gradually cooling the natural gas temperature from 40°C to -35°C. In the second cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipe C after throttling, gradually cooling the natural gas temperature from -35°C to -100°C. In the third cooling zone, the material in natural gas pipe A absorbs the cold energy emitted by refrigerant pipe B after throttling, gradually cooling the natural gas temperature from -100°C to -160°C.

2. The wound-tube heat exchanger based on a three-cycle liquefaction process according to claim 1, characterized in that: The self-cooling tube bundle is marked from bottom to top as height position 0, height position 1, height position 2, height position 3, height position 4, height position 5, and height position 6, with sealing gaskets installed at each pair of adjacent positions. Several natural gas pipes A and refrigerant pipes B, C, D1, D2, D3, and D4 are wound side by side on the central tube with the same spiral diameter direction. The winding order from bottom to top is natural gas... Refrigerant pipes A, B, C, D1, D2, D3, and D4 are connected together. The natural gas pipes A, B, C, D1, D2, D3, and D4 maintain the same center-to-center distance. The lengths of refrigerant pipes B, C, D1, D2, D3, and D4 decrease sequentially. The ends of refrigerant pipes B, C, D1, and D2 are sealed.

3. The wound-tube heat exchanger based on a three-cycle liquefaction process according to claim 2, characterized in that: Several radiating holes are opened on both sides of the top of refrigerant pipes D4, D3, D2, and D1 along the spiral circumference. The radiating hole of refrigerant pipe D4 is located below the first height position, and the pressure of the refrigerant emitted by the radiating hole of refrigerant pipe D4 is 900 kPa and the temperature is 26.4℃. The radiating hole of refrigerant pipe D3 is located in the section below the second height position and above the first height position, and the pressure of the refrigerant emitted by the radiating hole of refrigerant pipe D3 is 500 kPa and the temperature is 5.3℃. The radiating hole of refrigerant pipe D2 is located below the third height position and above the second height position, and the pressure of the refrigerant emitted by the radiating hole of refrigerant pipe D2 is 300 kPa and the temperature is -10.8℃. The radiating hole of refrigerant pipe D1 is located below the fourth height position and above the third height position, and the pressure of the refrigerant emitted by the radiating hole of refrigerant pipe D1 is 105 kPa and the temperature is -38.3℃. The refrigerant pipes B and C are equipped with self-throttling and diverging sections at their outlet ends. These sections are located at the fifth height position and emit refrigerant at a pressure of 440 kPa and a temperature of -112.2 °C.

4. The wound-tube heat exchanger based on a three-cycle liquefaction process according to claim 3, characterized in that: The self-throttling and diverging section comprises at least one throttling pipe section and a diverging pipe section connected together. An upstream fixed core, an upstream throttling flow core, a middle throttling fixed core, a downstream throttling flow core, and a downstream fixed core are sequentially connected inside the self-throttling and diverging section. An upstream fixed core channel is opened in the middle of the upstream fixed core, and a downstream fixed core channel is opened in the middle of the downstream fixed core. An axially penetrating first throttling hole is opened at the axis of the middle throttling fixed core. At least one axially penetrating second throttling hole is opened at the axis of the upstream throttling flow core, and an axially penetrating third throttling hole is opened at the axis of the downstream throttling flow core. It also has several axially penetrating overflow holes for refrigerant overflow. The end of the diverging pipe section is closed, and several small through holes are evenly opened along both sides of the top generatrix of the diverging pipe section.

5. The wound-tube heat exchanger based on a three-cycle liquefaction process according to claim 2, characterized in that: The first cooling zone is located between the 0th and 4th altitude positions, the second cooling zone is located between the 5th and 6th altitude positions, and the third cooling zone is located between the 4th and 5th altitude positions.

6. The wound-tube heat exchanger based on a three-cycle liquefaction process according to claim 1, characterized in that: The self-cooling tube bundle is provided with an isolated upper inspection chamber and a lower inspection chamber, which are respectively provided with an upper inspection port and a lower inspection port.

7. The wound-tube heat exchanger based on a three-cycle liquefaction process according to claim 4, characterized in that: Sealing gaskets are provided at both the fifth and fourth height positions. These sealing gaskets are long strips arranged in a circumferential direction.

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