Refrigerating system and refrigerating method

Abstract

The invention discloses a refrigeration system and a refrigeration method, and belongs to the technical field of gas refrigeration, the refrigeration system comprises an expansion compression mechanism, a secondary compression mechanism, a heat exchange mechanism and a plurality of cooling mechanisms, the expansion compression mechanism is integrated equipment and integrates an expansion part, a compression part and a transmission shaft, and the expansion part, the compression part and the transmission shaft are coaxial; the transmission shaft is connected with the expansion part and the compression part; the outlet end of an expansion part is connected with the inlet end of a compression part through a first pipeline, the outlet end of the compression part is connected with the inlet end of a secondary compression mechanism through a second pipeline, and the outlet end of the secondary compression mechanism is connected with the inlet end of the expansion part through a third pipeline to form a working medium circulation loop. The expansion impeller is used for acting energy to directly supply energy to the compression impeller, a motor for driving the compression impeller in a traditional system is omitted, at least one set of motor and a corresponding control system are omitted, the system complexity is effectively simplified, and meanwhile the occupied space of equipment is reduced.

Description

Technical Field

[0001] This application relates to the field of gas refrigeration technology, and in particular to a refrigeration system and refrigeration method. Background Technology

[0002] Currently, the main components of refrigeration based on the reverse Brayton principle include a compressor, an expander, and a heat exchanger. Traditional systems use a separate compressor to supply gas to the expander, which makes the entire system relatively complex and large. Summary of the Invention

[0003] This application provides a refrigeration system that simplifies system complexity; another objective of this application is to provide a refrigeration method.

[0004] To achieve the above objectives, according to a first aspect of this application, a refrigeration system is provided, comprising: An expansion and compression mechanism includes an expansion section, a compression section, and a drive shaft. The drive shaft is connected to both the expansion section and the compression section. The outlet end of the expansion section is connected to the inlet end of the compression section through a first pipeline. The expansion section performs work to drive the compression section to work. The secondary compression mechanism has its inlet end connected to the outlet end of the compression section via a second pipeline, and its outlet end connected to the inlet end of the expansion section via a third pipeline. A heat exchange mechanism is disposed between the expansion section and the secondary compression mechanism, and both the first pipeline and the third pipeline pass through the heat exchange mechanism; Multiple cooling mechanisms are provided, with one cooling mechanism installed on each of the second and third pipelines.

[0005] In some embodiments, the refrigeration system further includes: A fourth pipeline, the inlet end of which is connected to the outlet end of the secondary compression mechanism, and the outlet end of the fourth pipeline is connected to the inlet end of the secondary compression mechanism. A first valve is disposed on the fourth pipeline to control the connection between the outlet end of the secondary compression mechanism and the inlet end of the secondary compression mechanism.

[0006] In some embodiments, the refrigeration system further includes: The fifth pipeline has its inlet end connected to the outlet end of the secondary compression mechanism, and its outlet end connected to the inlet end of the compression section. The second valve, which is located on the fifth pipeline, controls the connection between the outlet end of the secondary compression mechanism and the inlet end of the compression section.

[0007] In some embodiments, the expansion and compression mechanism further includes a magnetic levitation bearing, which is sleeved outside the drive shaft.

[0008] In some embodiments, the secondary compression mechanism includes a plurality of compression units, which are connected in series along the working fluid flow direction through a plurality of sixth pipelines. The compression unit located at the inlet end of the secondary compression mechanism is connected to the outlet end of the compression section through the second pipeline, and the compression unit located at the outlet end of the secondary compression mechanism is connected to the input end of the expansion section through the third pipeline.

[0009] In some embodiments, the compression unit includes a compressor and a drive unit, the drive unit being drivenly connected to the compressor, the compressor being used to pressurize and compress the working fluid flowing into it.

[0010] In some embodiments, the compression unit includes a plurality of compressors and a plurality of drive units, each compressor being drively connected to one of the drive units; The inlet ends of all the compressors within the same compression unit are connected in parallel, and the outlet ends of all the compressors are connected in parallel.

[0011] In some embodiments, the drive unit is a motor.

[0012] In some embodiments, each of the sixth pipes is provided with one of the cooling mechanisms.

[0013] In some embodiments, the working fluid includes at least one of N2, He, H2, Ar, and Ne.

[0014] According to a second aspect of this application, a refrigeration method is provided, which employs the refrigeration system described in any of the above claims for refrigeration, and the specific steps of the refrigeration method are as follows: The expansion section of the expansion and compression mechanism is controlled to perform work, thereby driving the compression section of the expansion and compression mechanism to perform primary compression of the working medium and output primary compressed working medium. The primary compression working fluid is cooled, and the cooled primary compression working fluid is sent to the secondary compression mechanism for secondary compression to output the secondary compression working fluid; The secondary compression working fluid is cooled, and the cooled secondary compression working fluid flows through the heat exchange mechanism and is transported to the expansion section for expansion, and the expanded working fluid is output. The expanded working fluid is transported to the heat exchange mechanism for heat exchange, and the heat-exchanged working fluid is output. The heat-exchanged working fluid is transported to the inlet end of the compression section to form a circulation of the working fluid.

[0015] In some embodiments, the cooling method further includes the following steps: If the work done in the expansion section is greater than that required by the compression section, a portion of the cooled secondary compression medium is transported to the inlet of the compression section for further secondary compression. If the work done by the expansion section is less than that required by the compression section, a portion of the cooled secondary compression medium is transported to the inlet of the secondary compression mechanism for further primary compression.

[0016] Several embodiments of this application have one of the following beneficial effects: The refrigeration system in this embodiment includes an expansion and compression mechanism, a secondary compression mechanism, a heat exchange mechanism, and multiple cooling mechanisms. The expansion and compression mechanism integrates an expansion section, a compression section, and a drive shaft into a single unit. The drive shaft is connected to both the expansion section and the compression section, meaning they are coaxial. The expansion section directly drives the compression section. The outlet of the expansion section is connected to the inlet of the compression section via a first pipe. The inlet of the secondary compression mechanism is connected to the outlet of the compression section via a second pipe, and the outlet of the secondary compression mechanism is connected to the inlet of the expansion section via a third pipe, forming a working fluid circulation loop. The heat exchange mechanism is located between the expansion section and the secondary compression mechanism, with both the first and third pipes passing through it. In this embodiment, the energy generated by the expansion impeller directly powers the compression impeller, eliminating the need for a motor to drive the compression impeller in traditional refrigeration systems. This reduces the number of motors and their corresponding control systems in the entire refrigeration system by at least one, effectively simplifying the system's complexity and reducing the space occupied by the equipment.

[0017] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0020] Figure 1 This is a schematic diagram of the structure of a refrigeration system provided in an exemplary embodiment of this disclosure; Figure 2 This is a schematic diagram of another refrigeration system provided in an exemplary embodiment of this disclosure; Figure 3This is a schematic diagram of the structure of another refrigeration system provided in an exemplary embodiment of this disclosure.

[0021] Explanation of reference numerals in the attached figures: 100 - Expansion and compression mechanism; 110 - Expansion section; 120 - Compression section; 130 - Drive shaft; 140 - Magnetic levitation bearing; 200 - Secondary compression mechanism; 210 - Compression unit; 211 - Compressor; 212 - Drive unit; 300 - Heat exchange mechanism; 400 - Cooling mechanism; 510 - First pipeline; 520 - Second pipeline; 530 - Third pipeline; 540 - Fourth pipeline; 550 - Fifth pipeline; 560 - Sixth pipeline; 570 - First valve; 580 - Second valve. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] In the description of this application, it should be understood that the terms "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application 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, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a connection that allows communication; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two elements or an interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances. Furthermore, although the terms "first," "second," etc., may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Therefore, the first component discussed below may be referred to as the second component without departing from the teachings of this application. As used herein, the term "and / or" includes all combinations of any one and more of the associated listed items.

[0024] In the description of this application, "multiple" means two or more, and "at least one" means one, two, or more, unless otherwise explicitly specified. In the description of this application, "perpendicular" means completely perpendicular to 90° or nearly completely perpendicular, for example, an angle of 80° to 100° is considered perpendicular. Similarly, "parallel" means completely parallel or nearly completely parallel, for example, a perfectly parallel angle of 10° is considered parallel.

[0025] The following disclosure provides many different implementations or examples for carrying out different structures of this application. To simplify the disclosure of this application, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0026] In the process of global energy structure transformation, energy consumption demand continues to rise, while environmental requirements become increasingly stringent. These two factors have jointly driven the marketization of clean energy natural gas, thereby creating an urgent need for efficient natural gas transportation methods. As the core carrier for inter-regional natural gas transportation, maritime LNG (Liquefied Natural Gas) transportation has seen its market activity continue to rise due to its flexible scheduling advantages. LNG needs to remain liquid in an ultra-low temperature environment of -162℃. Its special low-temperature physicochemical properties, combined with the violent sloshing of LNG in the tank caused by changes in the ship's attitude during navigation, easily lead to some of the liquid LNG absorbing heat and evaporating, producing BOG (Boil-Off Gas). How to achieve efficient BOG treatment is directly related to transportation safety, energy utilization, and environmental benefits. Among these methods, BOG reliquefaction and recycling is recognized as the core solution with high technological maturity, excellent economics, and compliance with environmental requirements.

[0027] Constrained by ship space layout, load limits, and power supply, BOG reliquefaction units suitable for marine applications must meet the core requirements of compactness, high efficiency, and strong stability. Against this backdrop, reliquefaction units based on the reverse Brayton cycle principle have become the mainstream choice for marine BOG handling systems due to their outstanding advantages.

[0028] From a technical perspective, current refrigeration systems based on the reverse Brayton cycle typically consist of three core components: a compressor, an expander, and a heat exchanger. In traditional designs, the expander's gas supply is provided by a separately configured compressor. This discrete structure not only increases the overall complexity of the system but also results in a large space requirement for the equipment, making it difficult to fully adapt to the limited installation and layout space on ships.

[0029] In view of this, embodiments of this application provide a refrigeration system to solve at least part of the above-mentioned technical problems.

[0030] According to the first aspect of this application, please refer to Figure 1 In this embodiment, the refrigeration system includes an expansion and compression mechanism 100, a secondary compression mechanism 200, a heat exchange mechanism 300, and multiple cooling mechanisms 400. The expansion and compression mechanism 100 includes an expansion section 110, a compression section 120, and a drive shaft 130. The drive shaft 130 is connected to both the expansion section 110 and the compression section 120, meaning the expansion section 110 and the compression section 120 are coaxial. The work done by the expansion section 110 directly drives the compression section 120. It should be noted that in this embodiment, the expansion section 110 can be an expansion impeller, the compression section 120 can be a compression impeller, and the drive shaft 130 is fixedly connected to both the expansion impeller and the compression impeller, integrating all three into a single unit. In this embodiment, the energy generated by the work done by the expansion impeller directly powers the compression impeller, eliminating the need for a motor to drive the compression impeller in traditional refrigeration systems. This reduces the number of motors and their corresponding control systems in the entire refrigeration system by at least one, effectively simplifying the complexity of the refrigeration system and reducing the space occupied by the equipment.

[0031] The outlet of the expansion section 110 is connected to the inlet of the compression section 120 via a first pipe 510. The inlet of the secondary compression mechanism 200 is connected to the outlet of the compression section 120 via a second pipe 520, and the outlet of the secondary compression mechanism 200 is connected to the inlet of the expansion section 110 via a third pipe 530, thus forming a working fluid circulation loop. Additionally, a cooling mechanism 400 is installed on both the second pipe 520 and the third pipe 530. After the working fluid is compressed by the compression section 120, its pressure and temperature increase. During its transport from the second pipe 520 to the secondary compression mechanism 200, it needs to be cooled by the cooling mechanism 400 on the second pipe 520. Subsequently, the working fluid enters the secondary compression mechanism 200 for further pressurization, and then is cooled again by the cooling mechanism 400 on the third pipe 530 before being transported to the expansion section 110 for expansion and cooling. It should be noted that the cooling mechanism 400 can be a cooler.

[0032] The heat exchange mechanism 300 is located between the expansion section 110 and the secondary compression mechanism 200. Both the first pipe 510 and the third pipe 530 pass through the heat exchange mechanism 300. It should be noted that the heat exchange mechanism 300 can be composed of a regenerative heat exchanger and a user heat exchanger, which work together to achieve cold energy recovery and target refrigeration functions. The regenerative heat exchanger has two independent medium flow channels: one channel for the working fluid in the third pipe 530, and the other channel for the working fluid in the first pipe 510 after expansion through the expansion section 110. The user heat exchanger also has two medium flow channels, one of which is shared with the regenerative heat exchanger. The medium flowing through this shared channel is the working fluid in the first pipe 510 after expansion through the expansion section 110. The other medium flow channel of the user heat exchanger is used to flow the fluid medium that needs to be cooled. The specific heat exchange logic is as follows: the working fluid after expansion in expansion section 110 flows through both the regenerator and the user heat exchanger; the working fluid output from secondary compression mechanism 200, after cooling, flows only through the regenerator and exchanges heat with the working fluid after expansion in expansion section 110, achieving a heat recovery effect; while the working fluid after expansion in expansion section 110, when flowing through the user heat exchanger, can exchange heat with the fluid medium to be cooled in the user heat exchanger, completing the target refrigeration process.

[0033] In marine LNG reliquefaction units, where the fluid medium is LNG, the inlet temperature of the fluid medium to be cooled in the system is approximately -160°C, and the outlet temperature is approximately -170°C. By recovering the cold energy through a regenerative heat exchanger, the waste of cold energy caused by the low-temperature working fluid directly entering the compression section 120 can be avoided. Simultaneously, the compression section 120 (i.e., primary compression) and the secondary compression mechanism 200 (i.e., secondary compression) are ensured to focus solely on increasing the working fluid pressure, unaffected by low-temperature conduction, thereby improving the overall refrigeration efficiency and operational stability of the system. Specifically, the expansion section 110 converts the pressure energy of the working fluid into kinetic energy and lowers its temperature to obtain refrigeration capacity; the compression section 120 (primary compression) and the secondary compression mechanism 200 (secondary compression) focus on increasing the working fluid pressure, providing the necessary pressure conditions for the subsequent expansion and refrigeration process. It is important to emphasize that the aforementioned marine LNG reliquefaction unit is only one application scenario for this refrigeration system. This refrigeration system is applicable to all liquefaction units, including cryogenic reliquefaction units and nitrogen expansion reliquefaction units, as well as all systems based on the reverse Brayton cycle that cool or / and liquefy user fluid flows. Systems based on the reverse Brayton cycle that cool or / and liquefy user fluid flows include, but are not limited to, heat pump energy storage systems, industrial processing, and heat pumps.

[0034] It should be noted that the working fluid in this embodiment is a gaseous working fluid, which can be at least one of N2 (nitrogen), He (helium), H2 (hydrogen), Ar (argon), and Ne (neon). That is, the gaseous working fluid can be any one of N2, He, H2, Ar, and Ne; a mixture of any two of N2, He, H2, Ar, and Ne; a mixture of any three of N2, He, H2, Ar, and Ne; a mixture of any four of N2, He, H2, Ar, and Ne; or a mixture of N2, He, H2, Ar, and Ne. Using these gases as working fluids offers advantages such as excellent low-temperature performance, chemical stability and low reactivity, high safety, and the wide availability and controllable cost of some gases (such as N2). Furthermore, the thermodynamic properties of the mixed gas can be flexibly adjusted according to the system's cooling requirements, adapting to the requirements of reverse Brayton cycle cooling conditions and marine applications.

[0035] In some embodiments, please refer to Figure 2 The inherent differences in the operating characteristics of the expansion impeller and the compression impeller lead to mismatch issues in coaxial designs. Specifically, the expansion impeller outputs mechanical work through the expansion of the working fluid, relying on high-speed rotation, typically reaching thousands to tens of thousands of revolutions per minute, and its output power is directly related to the expansion amount of the working fluid and the pressure difference between the inlet and outlet. The compression impeller, on the other hand, consumes mechanical work to pressurize the working fluid, and its demands for speed and torque are not constant, dynamically changing with system conditions (such as working fluid inlet pressure, flow rate, and target pressure ratio). Because the coaxial design requires both impellers to maintain synchronized speeds, fluctuations in system conditions can easily cause either the expansion impeller or the compression impeller to deviate from its optimal operating condition, thus affecting the system's cooling efficiency and operational stability. In practical operating scenarios, two main mismatch situations exist: first, the power output of the expansion section 110 is less than the power required for the compression section 120; second, the power output of the expansion section 110 is greater than the power required for the compression section 120.

[0036] Regarding the mismatch between the expansion section 110 and the compression section 120 under the condition that the work done by the expansion section 110 is less than the work required by the compression section 120, this refrigeration system establishes a bypass regulation loop by adding a fourth pipe 540 and a first valve 570 to achieve power supply and demand balance. Specifically, the inlet end of the fourth pipe 540 is connected to the outlet end of the secondary compression mechanism 200, and the outlet end of the fourth pipe 540 is connected to the inlet end of the secondary compression mechanism 200, forming a working fluid return channel for the secondary compression mechanism 200; the first valve 570 is installed on the fourth pipe 540. The first valve 570 can be a flow regulating valve, and the on / off state of the loop and the return working fluid flow rate are controlled by adjusting the opening degree of the first valve 570. When insufficient output power of expansion unit 110 is detected, the first valve 570 is opened and adjusted to a suitable opening degree, so that part of the working fluid after being compressed by secondary compression mechanism 200 and cooled by cooling mechanism 400 flows back to the inlet end of secondary compression mechanism 200 through fourth pipeline 540. This can reduce the amount of working fluid actually processed by secondary compression mechanism 200, thereby reducing its power demand on compression unit 120, so that the power required by compression unit 120 is matched with the output power of expansion unit 110, ensuring that expansion impeller and compression impeller are always in a synchronous and stable operating state, and avoiding system efficiency reduction or failure due to insufficient power.

[0037] Regarding the mismatch between the expansion section 110 and the compression section 120 when the work done by the expansion section 110 exceeds the work required by the compression section 120, this refrigeration system establishes a flow-dividing regulation loop by adding a fifth pipe 550 and a second valve 580 to release the excess output power of the expansion section 110. Specifically, the inlet end of the fifth pipe 550 is connected to the outlet end of the secondary compression mechanism 200, and the outlet end of the fifth pipe 550 is connected to the inlet end of the compression section 120, forming a flow-dividing channel from the outlet of the secondary compression mechanism 200 to the inlet of the compression section 120; the second valve 580 is installed on the fifth pipe 550 to control the opening and closing of this flow-dividing channel and the flow rate of the diverted working fluid. When the output power of the expansion section 110 is excessive, the second valve 580 is opened and its opening degree is adjusted so that part of the working fluid after being compressed by the secondary compression mechanism 200 and cooled by the cooling mechanism 400 is directly transported to the inlet end of the compression section 120 through the fifth pipe 550, increasing the intake flow rate of the compression section 120. After the intake flow of the compression section 120 increases, the power required for its boost will increase accordingly, thereby consuming the excess power output of the expansion section 110. This achieves a dynamic balance between the power output of the expansion section 110 and the power required by the compression section 120, effectively avoiding problems such as abnormal impeller speed and increased equipment vibration caused by excessive power, and ensuring stable system operation.

[0038] In some embodiments, please refer to Figure 1 and Figure 2The expansion and compression mechanism 100 also includes a magnetic levitation bearing 140, which is sleeved on the outside of the drive shaft 130 for non-contact support. Since the expansion impeller needs to maintain a high-speed rotation of thousands to tens of thousands of revolutions per minute, traditional mechanical bearings are prone to frictional losses, wear, and vibration. The magnetic levitation bearing 140, however, levitates the drive shaft 130 using electromagnetic force, effectively eliminating frictional resistance from mechanical contact, reducing energy loss, and decreasing vibration and noise. This improves the stability and precision of the drive shaft 130's operation, thereby ensuring the coaxiality of the expansion and compression impellers during synchronous high-speed operation, improving their matching performance, and extending the equipment's service life.

[0039] In some embodiments, please refer to Figure 2 The secondary compression mechanism 200 adopts a multi-stage series structure, comprising multiple compression units 210 arranged sequentially along the working fluid flow direction. Each compression unit 210 is connected to the others via a corresponding sixth pipe 560, forming a continuous working fluid pressurization channel. It should be noted that each sixth pipe 560 is equipped with a cooling mechanism 400. Since the working fluid's temperature rises after being pressurized by the upper-stage compression unit 210, the cooling mechanism 400 on the sixth pipe 560 between adjacent compression units 210 can promptly cool the pressurized working fluid, preventing the high-temperature working fluid from directly entering the lower-stage compression unit 210. This design not only reduces the workload of the lower-stage compression unit 210 and improves compression efficiency but also effectively prevents abnormal operating conditions caused by excessively high working fluid temperatures, ensuring the stability of the multi-stage compression process.

[0040] The primary compression unit 210, located at the inlet of the secondary compression mechanism 200, is connected to the outlet of the compression section 120 via a second pipeline 520, receiving the working fluid after initial pressurization by the compression section 120. The final compression unit 210, located at the outlet of the secondary compression mechanism 200, is connected to the input of the expansion section 110 via a third pipeline 530, delivering the working fluid, which has reached the target pressure parameters after multi-stage progressive pressurization and segmented cooling, to the expansion section 110. This multi-stage series design with segmented cooling effectively reduces the compression ratio of a single-stage compression unit 210, preventing a sharp rise in working fluid temperature during single-stage compression. This not only reduces the cooling load on the subsequent cooling mechanism 400 but also improves overall compression efficiency and operational stability, better meeting the system's pressure requirements for the working fluid and the core requirements of compactness and high efficiency in marine applications.

[0041] In some embodiments, please refer to Figure 2The compression unit 210 is arranged in series and includes a compressor 211 and a drive unit 212. The drive unit 212 is connected to the compressor 211 and provides power support for the operation of the compressor 211. The compressor 211 is used to pressurize and compress the working fluid flowing into it. Specifically, the working fluid flows into the compressor 211 through a single channel. The compressor 211 operates under the drive of the drive unit 212, performing step-by-step pressurization and compression of the incoming working fluid, which can achieve a steady increase in the working fluid pressure. This scheme has a compact structure, simple flow channel, is easy to install and maintain, and can effectively ensure the stability of the working fluid compression process.

[0042] In some embodiments, please refer to Figure 3 The compression unit 210 is configured in parallel, comprising multiple compressors 211 and multiple drive units 212, with each drive unit 212 corresponding to a compressor 211. Each compressor 211 receives power through its corresponding drive unit 212 (i.e., each compressor 211 is connected to one drive unit 212). The inlet ends of all compressors 211 within the same compression unit 210 are connected in parallel via manifolds, and the outlet ends of all compressors 211 are also connected in parallel via manifolds, forming a multi-branch parallel pressurization structure. This scheme can flexibly adapt to different working fluid flow requirements by adjusting the number of compressors 211 in operation. When the system flow fluctuates significantly, it can effectively improve operational flexibility. Simultaneously, the parallel connection of multiple compressors 211 provides redundancy backup; if a single compressor 211 fails, the remaining compressors 211 can still operate normally, ensuring the reliability of the compression unit 210. This is suitable for scenarios with unstable working fluid flow or where operational redundancy is required.

[0043] In some examples, please refer to Figure 3The refrigeration unit has two compression units 210, namely a first-stage compression unit 210 and a last-stage compression unit 210 arranged sequentially along the working fluid flow direction. Each of the first-stage compression unit 210 and the last-stage compression unit 210 has two compressors 211 and two drive units 212. Specifically, the inlet ends of the two compressors 211 in the first-stage compression unit 210 are connected to a second pipeline 520 through independent pipelines; the outlet ends of the two compressors 211 in the first-stage compression unit 210 are connected to a sixth pipeline 560 through independent pipelines. This sixth pipeline 560 connects the first-stage compression unit 210 and the last-stage compression unit 210. The inlet ends of the two compressors 211 in the final stage compression unit 210 are each connected to a sixth pipeline 560 via independent pipes. This sixth pipeline 560 connects the first stage compression unit 210 and the final stage compression unit 210. The outlet ends of the two compressors 211 in the final stage compression unit 210 are each connected to a third pipeline 530 via independent pipes. Furthermore, the drive unit 212 within each compression unit 210 can be an electric motor to provide power to the corresponding compressor 211.

[0044] In some examples, please refer to Figure 1 , Figure 2 and Figure 3 The drive unit 212 can be an electric motor, which has advantages such as convenient speed adjustment, stable operation and suitability for marine power supply environment, and can better meet the power requirements of the compressor 211.

[0045] Accordingly, the refrigeration method provided in this application includes the refrigeration system of any of the above embodiments, and thus can have all the technical features and effects of the above refrigeration system, which will not be repeated here.

[0046] Specifically, please refer to Figure 1 The specific steps of the above refrigeration method are as follows: The expansion section 110 of the expansion and compression mechanism 100 performs work by expanding the working fluid, and the compression section 120 driven by the transmission shaft 130 operates synchronously. It should be noted that when the machine is initially started, the power of the compression section 120 comes from the secondary compression mechanism. Once the compression section 120 can perform work by expanding the expansion section 110, the secondary compression mechanism 200 no longer needs to supply power to the compression section 120.

[0047] The expansion section 110 of the expansion and compression mechanism 100 is controlled to do work, thereby driving the compression section 120 of the expansion and compression mechanism 100 to perform primary compression of the working medium and output the primary compressed working medium; specifically, the compression section 120 performs operations by using the mechanical energy generated by the work done by the expansion section 110 to perform primary compression of the incoming gas working medium.

[0048] The cooling mechanism 400 on the second pipeline 520 cools down the primary compressed working fluid and then transports the cooled primary compressed working fluid to the secondary compression mechanism 200 for secondary compression, outputting the secondary compressed working fluid. Specifically, the primary compressed working fluid cooled by the cooling mechanism 400 on the second pipeline 520 is pressurized by each compression unit 210 in the secondary compression mechanism 200 in sequence, and adjacent compression units 210 are cooled in stages by the cooling mechanism 400 on the sixth pipeline 560, and finally the secondary compressed working fluid is output from the outlet end of the secondary compression mechanism 200.

[0049] The cooling mechanism 400 on the third pipeline 530 cools down the secondary compressed working fluid. The cooled secondary compressed working fluid flows through the heat exchange mechanism 300 and is then transported to the expansion section 110 for expansion, outputting the expanded working fluid. Specifically, the secondary compressed working fluid cooled by the cooling mechanism 400 on the third pipeline 530 flows through the heat recovery channel of the heat exchange mechanism 300 and enters the expansion section 110 for expansion, outputting the expanded working fluid.

[0050] The expanding working fluid is transported to the heat exchange mechanism 300 through the first pipeline 510 to exchange heat with the cooling fluid that needs to be cooled. Simultaneously, the expanding working fluid in the first pipeline 510 also exchanges heat with the secondary compression working fluid in the third pipeline 530 to recover its temperature, and the heat-exchanged working fluid is output. The heat-exchanged working fluid is then transported to the inlet end of the compression section 120, forming a working fluid circulation loop. Specifically, after the gaseous working fluid completes expansion and cooling in the expansion section 110, it flows through the heat exchange mechanism 300 via the first pipeline 510, sequentially passing through the heat recovery channel and the user channel, achieving cold energy recovery and cooling of the target cooling fluid during this process. It is then transported to the inlet end of the compression section 120, forming a complete working fluid circulation loop. In other words, after the working fluid completes expansion and cooling in the expansion section 110, it flows through the heat exchange mechanism 300 via the first pipeline 510, achieving cold energy recovery and cooling of the target cooling fluid during this process, and is then transported to the inlet end of the compression section 120, forming a complete working fluid circulation loop. The working fluid cooled by the third pipeline 530 exchanges heat with the low-temperature working fluid expanded by the expansion section 110 in the heat exchange mechanism 300 (i.e., heat recovery) to achieve efficient recovery of cold energy; the low-temperature working fluid expanded by the expansion section 110 also exchanges heat with the fluid medium to be cooled (refrigeration fluid) in the heat exchange mechanism 300 to complete the target refrigeration process.

[0051] It should be noted that the cooling fluid is the target that the cooling system needs to cool, and the cooling fluid can be at least one of BOG, LNG, carbon dioxide, hydrogen, and helium. That is, the cooling fluid can be any one of BOG, LNG, carbon dioxide, hydrogen, and helium; it can be a mixture of any two of BOG, LNG, carbon dioxide, hydrogen, and helium; it can be a mixture of any three of BOG, LNG, carbon dioxide, hydrogen, and helium; it can be a mixture of any four of BOG, LNG, carbon dioxide, hydrogen, and helium; or it can be a mixture of BOG, LNG, carbon dioxide, hydrogen, and helium.

[0052] In some embodiments, the cooling method further includes an operating condition adaptation adjustment step: When the work done by the expansion section 110 exceeds the work required by the compression section 120, a portion of the cooled secondary compression working fluid is transported to the inlet of the compression section 120 for further secondary compression. Specifically, when the work done by the expansion section 110 exceeds the work required by the compression section 120, the second valve 580 on the fifth pipeline 550 is opened, and a portion of the secondary compression working fluid, cooled by the cooling mechanism 400, is transported through the fifth pipeline 550 to the inlet of the compression section 120. This consumes the excess power output by the expansion section 110, solves the matching problem between the expansion section 110 and the compression section 120 under this condition, and ensures stable coaxial operation of the two.

[0053] When the work done by the expansion section 110 is less than that required by the compression section 120, a portion of the cooled secondary compression working fluid is transported to the inlet of the secondary compression mechanism 200 for further primary compression. Specifically, when the work done by the expansion section 110 is less than that required by the compression section 120, the first valve 570 on the fourth pipeline 540 is opened, allowing a portion of the cooled secondary compression working fluid from the outlet of the secondary compression mechanism 200 to flow back to the inlet of the secondary compression mechanism 200 through the fourth pipeline 540. This reduces the power demand of the secondary compression mechanism 200 on the compression section 120, specifically addressing the mismatch between the expansion section 110 and the compression section 120 under corresponding operating conditions, and ensuring stable system cooling efficiency.

[0054] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0055] The above provides a detailed description of a refrigeration system and refrigeration method provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A refrigeration system, characterized in that, include: An expansion and compression mechanism (100) includes an expansion section (110), a compression section (120), and a drive shaft (130). The drive shaft (130) is connected to the expansion section (110) and the compression section (120) respectively. The outlet end of the expansion section (110) is connected to the inlet end of the compression section (120) through a first pipeline (510). The expansion section (110) performs work to drive the compression section (120) to work. The secondary compression mechanism (200) has its inlet end connected to the outlet end of the compression section (120) via a second pipe (520), and its outlet end connected to the inlet end of the expansion section (110) via a third pipe (530). A heat exchange mechanism (300) is disposed between the expansion section (110) and the secondary compression mechanism (200), and the first pipeline (510) and the third pipeline (530) both pass through the heat exchange mechanism (300). Multiple cooling mechanisms (400) are provided, with one cooling mechanism (400) respectively installed on the second pipeline (520) and the third pipeline (530).

2. The refrigeration system according to claim 1, characterized in that, The refrigeration system also includes: The fourth pipeline (540) has its inlet end connected to the outlet end of the secondary compression mechanism (200), and its outlet end is connected to the inlet end of the secondary compression mechanism (200). A first valve (570) is disposed on the fourth pipeline (540) to control the connection between the outlet end of the secondary compression mechanism (200) and the inlet end of the secondary compression mechanism (200).

3. The refrigeration system according to claim 1, characterized in that, The refrigeration system also includes: The fifth pipeline (550) has its inlet end connected to the outlet end of the secondary compression mechanism (200), and its outlet end connected to the inlet end of the compression section (120). The second valve (580) is disposed on the fifth pipeline (550) to control the connection between the outlet end of the secondary compression mechanism (200) and the inlet end of the compression section (120).

4. The refrigeration system according to claim 1, characterized in that, The expansion and compression mechanism (100) also includes a magnetic levitation bearing (140), which is sleeved on the outside of the transmission shaft (130).

5. The refrigeration system according to claim 1, characterized in that, The secondary compression mechanism (200) includes multiple compression units (210), which are connected in series along the working fluid flow direction through multiple sixth pipes (560). The compression unit (210) located at the inlet end of the secondary compression mechanism (200) is connected to the outlet end of the compression section (120) through the second pipe (520), and the compression unit (210) located at the outlet end of the secondary compression mechanism (200) is connected to the input end of the expansion section (110) through the third pipe (530).

6. The refrigeration system according to claim 5, characterized in that, The compression unit (210) includes a compressor (211) and a drive unit (212), the drive unit (212) being connected to the compressor (211) in a transmission manner, and the compressor (211) being used to compress the working fluid flowing into it.

7. The refrigeration system according to claim 5, characterized in that, The compression unit (210) includes a plurality of compressors (211) and a plurality of drive units (212), each compressor (211) being drivenly connected to one of the drive units (212); The inlet ends of all the compressors (211) within the same compression unit (210) are connected in parallel, and the outlet ends of all the compressors (211) are connected in parallel.

8. The refrigeration system according to claim 6 or 7, characterized in that, The drive unit (212) is a motor.

9. The refrigeration system according to claim 6 or 7, characterized in that, Each of the sixth pipes (560) is provided with a cooling mechanism (400).

10. The refrigeration system according to claim 6 or 7, characterized in that, The working medium includes at least one of N2, He, H2, Ar and Ne.

11. A refrigeration method, characterized in that, The refrigeration system according to any one of claims 1 to 10 is used for refrigeration, and the specific steps of the refrigeration method are as follows: The expansion section (110) of the expansion and compression mechanism (100) is controlled to do work, so as to drive the compression section (120) of the expansion and compression mechanism (100) to perform primary compression of the working medium and output primary compressed working medium; The primary compression working fluid is cooled down, and the cooled primary compression working fluid is sent to the secondary compression mechanism (200) for secondary compression to output the secondary compression working fluid; The secondary compression working fluid is cooled down, and the cooled secondary compression working fluid flows through the heat exchange mechanism (300) and is transported to the expansion section (110) for expansion, and the expanded working fluid is output. The expanded working fluid is transported to the heat exchange mechanism (300) for heat exchange, and the heat-exchanged working fluid is output. The heat-exchanged working fluid is transported to the inlet end of the compression section (120) to form a circulation of the working fluid.

12. The refrigeration method according to claim 11, characterized in that, The refrigeration method further includes the following steps: If the work done by the expansion section (110) is greater than that required by the compression section (120), a portion of the cooled secondary compression medium is transported to the inlet end of the compression section (120) for secondary compression. If the work done by the expansion section (110) is less than that required by the compression section (120), a portion of the cooled secondary compression medium is transported to the inlet end of the secondary compression mechanism (200) for further primary compression.

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