Low temperature liquid transfer line dry pre-cooling system

Abstract

The application discloses a low-temperature liquid conveying pipe dry precooling system, which comprises a plurality of sealed and connected precooling pipeline subsystems; each precooling pipeline subsystem comprises a conveying pipe unit, a refrigerating machine heat conduction unit and a cold box unit; the conveying pipe unit comprises an inner metal pipe and an outer metal pipe, and a plurality of layers of heat insulation materials are arranged in the interlayer space of the inner and outer metal pipes; the refrigerating machine heat conduction unit comprises a refrigerating machine and a flexible heat bridge; the cold box unit comprises a vacuum cold box and a temperature control module; the vacuum cold box is arranged at the middle position of the inner metal pipe, and the interlayer space of the inner and outer metal pipes shares a vacuum environment with the vacuum cold box; the cold head of the refrigerating machine is arranged inside the vacuum cold box and is connected to the surface of the inner metal pipe through the flexible heat bridge to conduct heat; and the temperature control module is used for monitoring the change of sensor parameters in the vacuum cold box and completing power regulation of the refrigerating machine. The application can solve the problems of complex precooling process, unstable two-phase flow and large liquid consumption of the low-temperature liquid conveying pipe.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of precooling, and particularly relates to a dry precooling system for a low-temperature liquid delivery pipe. BACKGROUND

[0002] The delivery and filling speed of liquid rocket low-temperature propellant is the key to improving the launch frequency. The current mainstream rocket propellant includes liquid hydrogen, liquid oxygen and liquid methane, and the saturation temperatures of the liquid at normal pressure are 20.28 K, 90.19 K and 111.66 K respectively, all of which are low-temperature liquids. The launch preparation cycle of such low-temperature propellant is long, and the filling process is complex. It usually takes 3-4 days to complete the liquid-phase delivery pipe replacement precooling and rocket fuel tank filling. This is because the pipe for delivering low-temperature fluid must ensure high-purity gas-free contamination, have a strict gas purging replacement process, and avoid impurity gas contacting the low-temperature fluid to form particles and block the pipe to cause explosion. On the other hand, based on the safety design of the large low-temperature propellant storage tank, the distance between the launch pad and the tank is hundreds of meters, and the volume of the rocket fuel tank is huge. In order to avoid the occurrence of violent boiling of the low-temperature fluid when it is directly filled, the pipe and tank as a whole have large heat capacity and heat leakage. In order to reduce the consumption of low-temperature propellant, the precooling and temperature reduction need to be carried out gradually. This leads to another problem: the pipe under low-temperature fluid precooling with small flow rate is in stratified flow flow pattern, and the temperature difference between the top and bottom of the pipe is large, which will also adversely affect the performance of the pipe.

[0003] To sum up, in order to improve the high-frequency and high-efficiency launch task of low-temperature launch vehicle, it is necessary to have the ability to quickly deliver and fill low-temperature propellant. The traditional pipe and tank precooling process has a long cycle and high complexity. The launch task interval must repeat the process, and the process design using low-temperature fluid as the precooling working medium has a short board problem that cannot be made up, and cannot meet the demand. The precooling of low-temperature fluid pipe is essentially based on the forced flow of low-temperature fluid in the pipe based on convective heat transfer. Due to the large temperature difference between the fluid and the solid, the strong instability of the turbulent flow, the high intensity of boiling, and the complex structure of the pipe design, the adverse phenomena such as pipe thermal stress, vibration, water hammer and cavitation are inevitable. Heat conduction is the most stable form among the three basic forms of heat transfer, and its intensity is much lower than that of convective and radiative heat transfer. At the same time, the low-temperature liquid delivery pipe is generally made of metal alloy, which is a good conductor of heat.

[0004] The Chinese patent document with the publication number CN116928574A discloses a liquefied gas pipeline precooling system and method for a gas filling station. The self-pressurization form of the gasifier is used instead of the transfer pump to make liquid nitrogen flow into the liquid-phase pipeline, which actually belongs to the traditional wet precooling method.

[0005] The Chinese patent document with the publication number CN117419278A discloses an LNG pipeline precooling method based on a liquid nitrogen precooling device, which also belongs to the traditional wet precooling method. The liquid nitrogen circulates in the liquid phase pipeline in the form of variable flow by applying pipeline design and valve control cooperation. However, it is inevitable that the liquid nitrogen contacts the normal temperature pipeline to produce a large top and bottom temperature difference of the pipeline, uneven precooling, gas-liquid two-phase flow in the pipeline, and pressure pulsation of the pipeline. SUMMARY

[0006] The application provides a low-temperature liquid delivery pipe dry precooling system, which can fundamentally solve the problems of complex internal precooling process, unstable two-phase flow, and large loss of low-temperature liquid of the existing low-temperature liquid delivery pipe.

[0007] A low-temperature liquid delivery pipe dry precooling system, comprising a plurality of sealed precooling pipeline subsystems; each precooling pipeline subsystem comprises a delivery pipe unit, a refrigerator heat conduction unit, and a cold box unit.

[0008] The delivery pipe unit comprises an inner metal pipeline and an outer metal pipeline, and the interlayer space of the inner metal pipeline and the outer metal pipeline is provided with a plurality of layers of thermal insulation materials.

[0009] The refrigerator heat conduction unit comprises a refrigerator and a flexible heat bridge; the refrigerator is arranged on the vacuum cold box, the cold head of the refrigerator is arranged inside the vacuum cold box, and the flexible heat bridge is connected to the surface of the inner metal pipeline for heat conduction and heat transfer.

[0010] The cold box unit comprises a vacuum cold box and a temperature control module; the temperature control unit is used for monitoring the sensor parameter change in the vacuum cold box and completing power regulation of the refrigerator.

[0011] The vacuum cold box is arranged at the middle position of the inner metal pipeline and connected with the outer metal pipelines on both sides, so that the interlayer space of the inner metal pipeline and the outer metal pipeline and the vacuum cold box are in communication and share the vacuum environment.

[0012] Further, the delivery pipe units of adjacent two precooling pipeline subsystems are sealed and connected, including but not limited to the use of vacuum flanges and O-rings for sealed connection.

[0013] Preferably, the flexible heat bridge is knitted from a high-thermal-conductivity material, such as a knitted copper band, which is tightly wrapped around the surface of the inner metal pipeline in the form of spiral winding.

[0014] Preferably, the plurality of layers of thermal insulation materials are a combination of a plurality of layers of radiation layers and spacing layers, and the inner metal pipeline surface after winding the flexible heat bridge is wrapped with the plurality of layers of thermal insulation materials.

[0015] Further, the radiation layer of the multilayer thermal insulation material adopts a metal thin layer material including but not limited to an aluminum foil, a double-sided aluminum-coated film, etc., and a spacing layer is arranged between two adjacent metal thin layers and does not contact each other.

[0016] Further, the top of the vacuum cold box comprises a vacuum extraction port, an electrical interface and an emergency pressure relief valve. The vacuum extraction port is connected to a vacuum pump to extract the inside of the chamber to a vacuum, the electrical interface provides power supply for the equipment in the vacuum cold box and feeds back the real-time parameters of the sensors in the chamber to the temperature control module, and the emergency pressure relief valve is used for pressure relief in case of abnormal pressure rise in the chamber.

[0017] Further, a plurality of sensors are arranged in the vacuum cold box, including but not limited to temperature sensors, pressure sensors, vibration sensors and dryness sensors, which are connected to the temperature control module through the electrical interface.

[0018] Further, the refrigerator adopts a large-cooling-capacity refrigerator, such as a high-power pulse tube refrigerator with a primary cold head, and the lowest refrigeration temperature should match the actual use requirement.

[0019] The low-temperature liquid delivery pipe dry precooling system is used for precooling, including the following steps:

[0020] S01, a precooling pipe sub-system is formed by installing a delivery pipe unit, a refrigerator heat conduction unit and a cold box unit, and a plurality of precooling pipe sub-systems are sealed and connected to obtain a low-temperature liquid delivery pipe unit dry precooling system; a helium mass spectrometer or other leak detection equipment can be used to detect gas leakage of the system to ensure that the system has no obvious leakage point;

[0021] S02, a vacuum pump is used to extract the vacuum degree inside the vacuum cold box to 10E-3 to 10E-6 Torr (Torr);

[0022] S03, the refrigerator heat conduction unit is operated, the target temperature of the refrigerator is set by the temperature control module, the refrigerator is adjusted to the precooling mode, at this time the input power of the refrigerator matches the best refrigeration capacity curve, the sensor parameter changes in the vacuum cold box are monitored by the temperature control module until the cooling of the inner metal pipe is completed;

[0023] S04, the cold capacity of the refrigerator is adjusted to the cold preservation mode by the temperature control module, at this time the heat absorbed by the inner metal pipe and the cold capacity of the refrigerator are equivalent, and the temperature of the inner metal pipe is basically maintained unchanged;

[0024] S05, the upstream of the delivery pipe unit is opened to the stop valve and the flow regulating valve, the low-temperature liquid is controlled to flow into the precooling completed pipe, and the transfer is completed.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. In the present invention, the cold energy is transferred to the inner metal pipe in the form of solid heat conduction. The heat transfer of the refrigerator is more gentle and stable than the convection of low-temperature fluid and the boiling phase change heat transfer. It can reduce the pressure pulsation and thermal stress caused by the sudden cooling of the pipe, and avoid the resonance and stress damage of the pipe.

[0027] 2. In this invention, the flexible thermal bridge can evenly transfer cooling energy to the pipe surface. During the cold-keeping phase, the entire pipe is at essentially the same temperature, and the heat exchange with the flexible thermal bridge is very small, maintaining a thermally stable state. This prevents the large temperature difference between the upper and lower spaces of the pipe caused by the stratified flow of the low-temperature fluid in the pipe, which could lead to thermal stress damage.

[0028] 3. The present invention converts the input power of the refrigerator into the form of solid cold energy in the pipeline, replacing the low-temperature fluid cold energy that is converted into the form of solid cold energy in the pipeline, greatly reducing the mass consumption of the low-temperature fluid in the pre-cooling of the conveying pipe, and saving the consumption of expensive low-temperature liquids such as liquid hydrogen and liquid helium. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic structural diagram of a pre-cooling pipeline subsystem of the present invention;

[0030] Figure 2 Schematic diagram of the two-dimensional connection between the internal metal pipe and the flexible thermal bridge in the present invention;

[0031] Figure 3 It is a connection diagram of several pre-cooling pipeline subsystems;

[0032] Figure 4 The figure is a schematic diagram of the layout of the dry pre-cooling system for cryogenic liquid delivery pipes of the present invention when applied at a carrier rocket launch site.

[0033] In the figure: 10-inner metal pipe, 11-outer metal pipe, 12-insulation material, 13-vacuum flange, 20-refrigeration machine, 21-cold head, 22-flexible thermal bridge, 220-braided copper belt, 30-vacuum cold box, 31-temperature control module, 32-vacuum port, A-propellant storage spherical tank, B-liquid hydrogen core transport section, C-refrigeration unit control unit, D-rocket body tank. DETAILED DESCRIPTION

[0034] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0035] A dry precooling system for a cryogenic liquid delivery pipe comprises a plurality of precooling pipe subsystems which are sealed and connected.

[0036] like Figure 1As shown, each precooling pipeline subsystem includes a delivery pipe unit and a refrigerator heat conduction unit and a cold box unit arranged on the delivery pipe unit.

[0037] The delivery pipe unit includes an inner metal pipe 10 and an outer metal pipe 11, and an interlayer space of the inner metal pipe 10 and the outer metal pipe 11 is provided with thermal insulation material 12.

[0038] The refrigerator heat conduction unit includes a refrigerator 20 and a flexible heat bridge 22, and the cold box unit includes a vacuum cold box 30 and a temperature control module 31.

[0039] The vacuum cold box 30 is arranged at a middle position of the inner metal pipe 10 and is sealingly connected with the outer metal pipes 11 on both sides through vacuum flanges and O-rings, so that the interlayer space of the inner metal pipe 10 and the outer metal pipe 11 and the vacuum cold box 30 are in communication with each other and share a vacuum environment.

[0040] The refrigerator 20 is installed on the vacuum cold box 30, the cold head 21 of the refrigerator 20 is arranged inside the vacuum cold box 30, and the flexible heat bridge 22 is connected to the surface of the inner metal pipe 10 for heat transfer; the temperature control module 31 is used to monitor the sensor parameter changes in the vacuum cold box 30 and complete power regulation of the refrigerator 20.

[0041] In the embodiment, the refrigerator 20 adopts a high-power pulse tube refrigerator, the cold end heat exchanger of which transfers cold energy to a load primary cold head, and the load primary cold head transfers cold energy to the flexible heat bridge 22.

[0042] The flexible heat bridge 22 serves as a relay connecting the cold head 21 and the inner metal pipe 10, and directly contacts the surfaces of the cold head 21 and the inner metal pipe 10.

[0043] As shown, the flexible heat bridge 22 is made of high-thermal-conductivity braided copper strips 220, which are tightly wrapped around the surface of the inner metal pipe 11 in the form of spiral winding. Figure 2

[0044] The multi-layer thermal insulation material 12 adopts aluminum foil metal thin layers, and the inner metal pipe 10 after winding the braided copper strips 220 is wrapped with multiple layers of aluminum foil, and adjacent aluminum foils are separated by a spacing layer and do not contact each other.

[0045] In the present application, the vacuum cold box 30 provides a vacuum chamber accommodating the cold head 21 of the refrigerator and the flexible heat bridge 22, connecting the interlayer space of the inner metal pipe 10 and the outer metal pipe 11, and using vacuum flanges 13 and O-ring sealing connection at the sealing connection.

[0046] ​The top of the vacuum cold box 30 is provided with a vacuum port 32, an electrical interface and an emergency pressure relief valve. The vacuum port 32 is connected to a vacuum pump to evacuate the interior of the chamber to a vacuum, the electrical interface feeds real-time parameters of the sensors in the chamber to the temperature control module 31, and the emergency pressure relief valve is used for pressure relief in the case of abnormal pressure rise in the chamber.

[0047] The vacuum cold box 30 is provided with temperature sensors, pressure sensors, vibration sensors and dryness sensors and other measurement elements, and the measurement signals are externally connected to the temperature control module 31 through the electrical interface.

[0048] As shown in Figure 1 and Figure 3 , a plurality of pre-cooling pipeline subsystems are sealed and connected through the vacuum flange 13 to obtain the low-temperature liquid delivery pipe dry pre-cooling system of the application.

[0049] The application provides cold energy to the internal metal pipe of the high-vacuum delivery pipe from the outside of the pipe in the form of refrigeration and flexible heat bridge heat conduction, so that the temperature of the internal metal pipe is maintained in the ideal temperature zone. Compared with the traditional low-temperature liquid wet pre-cooling, the principle is simple and the advantages are obvious, and it is suitable for scenes of high-frequency transfer of low-temperature liquid, such as launch vehicle launch site, LNG receiving station, air separation rectification plant, etc.

[0050] As shown in Figure 4 , it is a layout schematic diagram of the low-temperature liquid delivery pipe dry pre-cooling system of the application applied in a launch vehicle launch site, mainly including a liquid hydrogen propellant storage spherical tank A, a liquid hydrogen core delivery section B, a refrigeration machine unit control unit C and a missile body storage tank D. The liquid hydrogen core delivery section B is the low-temperature liquid delivery pipe dry pre-cooling system of the application, which is connected by at least one pre-cooling pipeline subsystem as shown in Figure 1 .

[0051] Before the pre-cooling operation, first complete the overall leak detection of all pre-cooling pipeline subsystems in the liquid hydrogen core delivery section B, use a helium mass spectrometer for helium leak detection, and ensure that there is no gas leak point in the connection sealing place. Use a vacuum pump to evacuate the vacuum cold box 30 of all pre-cooling pipeline subsystems.

[0052] Start the refrigeration machine 20 to work and refrigerate, select the appropriate refrigeration temperature of the refrigeration machine according to the three-phase region temperature boundary of the low-temperature liquid, which can be higher than the three-phase point temperature to the vicinity of the boiling critical heat flux density temperature point. For liquid hydrogen transfer requirements, the temperature range can be 14.9K-85K, and the refrigeration temperature of the refrigeration machine is determined according to the economic evaluation results.

[0053] As the temperature of the cold head 21 gradually decreases to the refrigeration temperature zone, the heat imbalance causes the cold energy to be transferred to the flexible thermal bridge 22, continuously taking away the heat of the inner metal pipeline 10. The temperature of the inner metal pipeline 10 is monitored by the temperature control module 31 until it reaches the required temperature range for precooling. The cryogenic unit control unit C connects each temperature control module 31 to control the corresponding precooling pipeline subsystem to enter the refrigeration mode. At this time, the input cold energy is approximately equal to the heat leakage of the inner metal pipeline 10. The cryogenic unit control unit C controls all precooling subsystems to complete the precooling, indicating that the dry precooling of the liquid hydrogen core delivery section B is completed.

[0054] The transfer of low-temperature liquid hydrogen begins. The liquid hydrogen propellant storage tank A outlet stop valve and the flow regulating valve are opened, and the liquid hydrogen flows through the liquid hydrogen core delivery section B which is fully pre-cooled and has uniform temperature. If the refrigeration temperature of the cryogenic refrigerator 20 is higher than the liquid temperature, the liquid hydrogen will undergo nucleate boiling and then form a bubble flow. The fluid in the pipe will quickly change to a stable single-phase liquid flow after a short gas-liquid two-phase flow. If the pipeline temperature is lower than the liquid hydrogen temperature, the liquid hydrogen will be further cooled in the pipeline, and the fluid in the pipeline will always be a stable single-phase liquid flow. After the liquid level of the liquid hydrogen in the arrow tank D meets the requirements, the liquid hydrogen propellant storage tank A outlet stop valve and the flow regulating valve are closed, and the transfer is completed.

[0055] The above-described embodiments have described the technical solutions and beneficial effects of the present application in detail. It should be understood that the above-described embodiments are only specific embodiments of the present application and are not intended to limit the present application. Any modifications, supplements and equivalent replacements made within the principle range of the present application should be included in the protection range of the present application.

Claims

1. A cryogenic liquid delivery pipe dry precooling system, characterized in that: It includes several sealed pre-cooling pipe subsystems; each pre-cooling pipe subsystem includes a delivery pipe unit and a refrigerator heat conduction unit and a cold box unit arranged on the delivery pipe unit; The transport pipe unit comprises an inner metal pipe (10) and an outer metal pipe (11), wherein the interlayer space between the inner metal pipe (10) and the outer metal pipe (11) is provided with multiple layers of heat insulating material (12); The refrigerator heat conduction unit comprises a refrigerator (20) and a flexible thermal bridge (22), and the cold box unit comprises a vacuum cold box (30) and a temperature control module (31); The flexible thermal bridge (22) is made of a high thermal conductivity material and tightly surrounds the surface of the inner metal pipe (10); the multi-layer thermal insulation material (12) is a combination of a multi-layer radiation layer and a spacer layer, and the multi-layer thermal insulation material is wrapped around the surface of the inner metal pipe (10) after the flexible thermal bridge is wrapped; The vacuum cold box (30) is arranged in the middle of the inner metal pipe and is sealed with the outer metal pipes (11) on both sides, so that the interlayer space between the inner metal pipe (10) and the outer metal pipe (11) is communicated with the vacuum cold box (30) to share a vacuum environment; The refrigerator (20) is inserted into the vacuum cold box (30), and the cold head (21) of the refrigerator (20) is arranged inside the vacuum cold box (30) and is connected to the surface of the inner metal pipe (10) through a flexible thermal bridge (22) for heat transfer; the temperature control module (31) is used to monitor the changes in sensor parameters in the vacuum cold box (30) and complete the power regulation of the refrigerator (20); Precooling includes the following steps: S01: Install the delivery pipe unit, refrigerator heat transfer unit, and cold box unit, and seal and connect several pre-cooling pipe subsystems to obtain a low-temperature liquid delivery pipe dry pre-cooling system; perform gas leak detection on the system to ensure that there are no leaks in the system; S02, use a vacuum pump to pump the vacuum degree inside the vacuum cold box (30) to 10×10 -3 to 10×10 -6 Torr; S03, operating the heat transfer unit of the refrigerator, setting the target cooling temperature through the temperature control module (31), adjusting the refrigerator (20) to the pre-cooling mode, at which time the refrigerator input power matches the optimal cooling capacity curve, and monitoring the sensor parameter changes in the vacuum cold box (30) through the temperature control module (31) until the inner metal pipe (10) completes the cooling; S04, adjusting the cooling capacity of the refrigerator (20) to a cold preservation mode through the temperature control module (31), at which time the amount of heat leakage absorbed by the inner metal pipe (10) is equivalent to the cooling capacity of the refrigerator (20), and the temperature of the inner metal pipe (10) remains substantially unchanged; S05: Open the stop valve and flow regulating valve upstream of the delivery pipe unit to control the cryogenic liquid to flow into the pre-cooled delivery pipe unit until the transfer is completed.

2. The cryogenic liquid delivery pipe dry precooling system according to claim 1, characterized in that: The delivery pipe units of two adjacent pre-cooling pipeline subsystems are sealed and connected.

3. The cryogenic liquid delivery pipe dry precooling system according to claim 1, characterized in that: The top of the vacuum cold box (30) includes a vacuum port (32), an electrical interface and an emergency pressure relief valve.

4. The cryogenic liquid delivery pipe dry precooling system according to claim 3, characterized in that: The vacuum cold box (30) is provided with multiple sensors, which are connected to the temperature control module (31) via an electrical interface.

5. The cryogenic liquid delivery pipe dry precooling system according to claim 1, characterized in that: The refrigerator (20) is a large-capacity refrigerator, and the lowest refrigeration temperature matches the actual use requirements.

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