JP7585010B2 - Refrigeration System - Google Patents

Description

This disclosure relates to a refrigeration system that utilizes the Brayton refrigeration cycle.

A refrigeration system that uses the Brayton refrigeration cycle is known as a refrigeration cycle. The Brayton refrigeration cycle is a thermodynamic cycle consisting of an adiabatic compression process, an isobaric heating process, an adiabatic expansion process, and an isobaric cooling process, and is configured by arranging elements corresponding to each process on the refrigerant line through which the refrigerant circulates. These elements that make up the refrigeration cycle are designed according to the refrigeration capacity required of the refrigerator.

Patent Document 1 discloses an example of a refrigeration system that uses the Brayton refrigeration cycle. In Patent Document 1, a compressor unit corresponding to an adiabatic compression process is provided with multiple compressor stages connected in series on a refrigerant line to achieve an appropriate compression ratio and meet the required refrigeration capacity. In addition, some of the multiple compressor stages are configured as an expander-compressor integrated with an expander that shares a common rotating shaft with an expander that corresponds to an adiabatic expansion process, and the power generated by the expander is used as part of the power that drives the compressor, improving efficiency. Furthermore, in Patent Document 1, the compressors that make up the compressor unit are arranged in parallel to increase the amount of refrigerant circulating in the refrigeration cycle, improving refrigeration capacity.

JP 2014-219125 A

When trying to develop variations in product specifications with different refrigeration capacities for this type of refrigeration system, each component of the refrigeration system is generally designed from scratch, and reducing the cost and time required for development is an issue. For example, the compressors and expanders that make up the refrigeration system must be prepared in different models depending on the product specifications of the refrigeration system, and if existing models are not sufficient, a new model must be developed, which requires a lot of cost and time for development.

As a method for reducing the cost and time required for such new development, for example when developing a refrigerator with a higher refrigeration capacity than existing refrigerators, it is possible to consider parallelizing the existing configuration of the refrigeration cycle, as in the above-mentioned Patent Document 1. However, this inevitably increases the number of parts required and the occupied floor space, and is not sufficient.

At least one embodiment of the present disclosure has been made in consideration of the above circumstances, and aims to provide a refrigeration system that allows for flexible design changes while minimizing development costs and time, and the floor space required for installation, depending on the required refrigeration capacity.

In order to solve the above problems, a refrigeration system according to at least one embodiment of the present disclosure includes:
A refrigeration system using a Brayton cycle that generates cold heat using a refrigerant compressed by a compressor unit arranged on a refrigerant path,
The compressor unit includes:
A plurality of compressors arranged in parallel with each other with respect to the refrigerant path;
a plurality of first motors for driving the plurality of compressors, respectively;
an expander-integrated compressor that is integrated with an expander capable of expanding the refrigerant compressed by the compressor unit;
A second motor for driving the expander-compressor unit;
Including,
The number of the plurality of compressors is greater than the number of the expander-compressor units.

At least one embodiment of the present disclosure provides a refrigeration system that allows for flexible design changes while minimizing development costs and time, and the space required for installation, depending on the required refrigeration capacity.

1 is a diagram illustrating an overall configuration of a refrigeration system according to an embodiment of the present invention; FIG. 2 is a diagram illustrating a cross-sectional structure of the coaxial compressor of FIG. 1 . FIG. 2 is a diagram illustrating a cross-sectional structure of the expander-compressor unit of FIG. 1 . 2 is a flowchart showing a method for starting up the refrigeration system of FIG. 1 . FIG. 1 is a schematic diagram showing an embodiment of a refrigeration system including two coaxial compressors and one expander-compressor. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including two coaxial compressors and one expander-compressor. FIG. 1 is a schematic diagram illustrating an embodiment of a refrigeration system including three coaxial compressors and one expander-compressor. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including three coaxial compressors and one expander-compressor. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including three coaxial compressors and one expander-compressor. FIG. 1 is a schematic diagram illustrating an embodiment of a refrigeration system including three coaxial compressors and two expander-compressor combinations. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including three coaxial compressors and two expander-compressor combinations. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including three coaxial compressors and two expander-compressor combinations. FIG. 1 is a schematic diagram illustrating an embodiment of a refrigeration system including four coaxial compressors and two expander-compressor combinations. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including four coaxial compressors and two expander-compressor combinations. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including four coaxial compressors and two expander-compressor combinations. FIG. 1 is a schematic diagram showing another embodiment of a refrigeration system including four coaxial compressors and two expander-compressor combinations.

Hereinafter, refrigeration systems according to several embodiments of the present disclosure will be described with reference to the drawings.
However, the dimensions, materials, shapes and relative arrangements of the components described in these embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.
For example, expressions expressing relative or absolute configuration, such as "in a certain direction,""along a certain direction,""parallel,""orthogonal,""center,""concentric," or "coaxial," not only strictly express such a configuration, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained.
For example, expressions indicating that things are in an equal state, such as "identical,""equal," and "homogeneous," not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained.
For example, expressions describing shapes such as a rectangular shape or a cylindrical shape do not only refer to rectangular shapes, cylindrical shapes, etc. in the strict geometric sense, but also refer to shapes that include uneven portions, chamfered portions, etc., to the extent that the same effect is obtained.
On the other hand, the expressions "comprise,""include,""have,""includes," or "have" of one element are not exclusive expressions excluding the presence of other elements.

First, the overall configuration of a refrigeration system 100 according to one embodiment will be described with reference to FIG. 1. FIG. 1 is a diagram showing a schematic diagram of the overall configuration of a refrigeration system 100 according to one embodiment.

The refrigeration system 100 is provided with a compressor unit 102 (110A, 110B, 110C) for compressing the refrigerant, an expander 103 for expanding the refrigerant, a cooling section 104 consisting of a heat exchanger for exchanging heat between the refrigerant and the object to be cooled, and a cold heat recovery heat exchanger 105 for recovering the cold remaining in the refrigerant after it has passed through the cooling section 104, in that order on a refrigerant path 101 through which the refrigerant flows, forming a counterflow type heat exchanger type Brayton cycle with a steady circulation flow refrigeration cycle.

The refrigeration system 100 has a superconducting device 106 that uses a superconductor capable of exhibiting superconductivity at a cryogenic temperature as a cooling target. The superconducting device 106 is, for example, a superconducting cable. The refrigeration system 100 has a refrigerant path 107 through which liquid nitrogen cooled by a cooling unit 104 circulates in order to maintain the cryogenic state of the superconducting device 106. The refrigerant path 107 is configured to be able to exchange heat with the refrigerant flowing through the refrigerant path 101 of the refrigeration system 100 via the cooling unit 104, and is provided with a pump 108 for circulating the liquid nitrogen. As a result, the liquid nitrogen flowing through the refrigerant path 107 that has been heated by the thermal load of the superconducting device 106 is cooled by heat exchange with the refrigerant flowing through the refrigerant path 101 that has been cooled by the refrigeration system 100.

Note that, although neon or the like is used as a refrigerant in the refrigeration system 100 refrigeration path 101, this is not limited thereto, and the type of gas can be changed as appropriate depending on the cooling temperature, etc.

In the refrigeration system 100, an expander 103 through which a relatively low-temperature refrigerant flows, a cooling section 104, and a cold heat recovery heat exchanger 105 are housed in a cold box 109 that can be insulated from the outside.
The cold box 109 has, for example, a vacuum insulation layer between the inner and outer surfaces, thereby preventing heat from entering from the outside and reducing heat loss in the expander 103, the cooling section 104, and the cold heat recovery heat exchanger 105 housed in the cold box 109. On the other hand, the compressor unit 102 of the refrigeration system 100 is disposed outside the above-mentioned cold box 109 because a relatively high-temperature refrigerant flows through the compressor unit 102.

The cold box 109 is placed closer to the superconducting equipment 106, which is the object to be cooled, than the compressor unit 102. This allows the cold generated in the cold box 109 to be supplied to the object to be cooled with little loss, achieving good refrigeration efficiency. Because the compressor unit 102 is configured separately from the cold box 109, there is more freedom in layout, and for example, by placing it above the cold box, the installation space for the refrigeration system can be reduced.

The compressor unit 102 includes a plurality of compressors 110 connected in series to the refrigerant path 101. In the present embodiment, the compressor unit 102 includes a low-stage compressor 110A capable of compressing a fluid, a middle-stage compressor 110B capable of further compressing the fluid compressed by the low-stage compressor 110A, and a high-stage compressor 110C capable of further compressing the fluid compressed by the middle-stage compressor 110B, all of which are connected in series to the refrigerant path 101, and is configured to be capable of multi-stage compression over three stages.
The compressor unit 102 may have any number of compression stages.

In addition, downstream of each of the multiple compressors 110 in the compressor unit 102, a heat exchanger 112 is provided to cool the refrigerant heated by adiabatic compression by exchanging heat with cooling water. Specifically, heat exchanger 112A is disposed downstream of low-stage compressor 110A, heat exchanger 112B is disposed downstream of middle-stage compressor 110B, and heat exchanger 112C is disposed downstream of high-stage compressor 110C.

The refrigerant flowing through the refrigerant path 101 is first adiabatically compressed by the low-stage compressor 110A located at the most upstream side, causing the temperature to rise, and then cooled by heat exchange with cooling water in the heat exchanger 112A located downstream. The refrigerant is then adiabatically compressed again by the middle-stage compressor 110B, causing the temperature to rise, and then cooled by heat exchange with cooling water in the heat exchanger 112B located downstream. The refrigerant is then adiabatically compressed again by the high-stage compressor 110C, causing the temperature to rise, and then cooled by heat exchange with cooling water in the heat exchanger 112C located downstream.

In this way, the compressor unit 102 improves efficiency by repeating adiabatic compression by the compressor 110 and cooling by the heat exchanger 112 over multiple stages. In other words, by repeating adiabatic compression and cooling over multiple stages, the compression process of the Brayton cycle approaches ideal isothermal compression. The more stages there are, the closer it is to isothermal compression, but the number of stages should be determined taking into consideration factors such as the selection of compression ratio that comes with an increased number of stages, the complexity of the device configuration, and ease of operation.

The refrigerant compressed by the compressor unit 102 is cooled by the cold heat recovery heat exchanger 105, and then adiabatically expanded by the expander 103 to generate cold. The refrigerant discharged from the expander 103 is heat exchanged with liquid nitrogen flowing through the refrigerant path 107 on the side to be cooled in the cooling section 104, and the temperature rises due to the thermal load.

The refrigerant heated in the cooling section 104 is introduced into the cold heat recovery heat exchanger 105, where it exchanges heat with the high-temperature compressed refrigerant that has passed through the heat exchanger 112C in the compressor unit 102, recovering the remaining cold. This reduces the temperature of the refrigerant introduced into the expander 103, making it possible to obtain cold at a lower temperature.

In this way, in the refrigeration system 100, a Brayton cycle is configured using multiple rotating machines such as multiple compressors 110 and expanders 103 included in the compressor unit 102. Here, the low-stage compressor 110A and the high-stage compressor 110C are configured as coaxial compressors 118 connected to both ends of the output shaft 116A (see FIG. 2) of the first motor 114A, which is a common power source, thereby reducing the number of parts and making it possible to install them in a small installation space. The middle-stage compressor 110B and the expander 103 are also configured as an expander-integrated compressor 120 connected to both ends of the output shaft 116B (see FIG. 3) of the second motor 114B, which is a common power source, thereby reducing the number of parts and making it possible to install them in a small installation space. Furthermore, the power generated by the expander 103 contributes to the compression power of the middle-stage compressor 110B, thereby improving efficiency.

In addition, which of the multiple compressors 110 included in the compressor unit 102 are configured as coaxial compressors 118 and which are configured as expander-integrated compressors 120 can be arbitrarily changed.

Here, the configurations of the coaxial compressor 118 and the expander-integrated compressor 120 will be described with reference to Figures 2 and 3. Figure 2 is a diagram that shows a schematic cross-sectional structure of the coaxial compressor 118 in Figure 1, and Figure 3 is a diagram that shows a schematic cross-sectional structure of the expander-integrated compressor 120 in Figure 1.

As shown in FIG. 2, the coaxial compressor 118 is configured by connecting the low-stage compressor 110A and the high-stage compressor 110C to both sides of the output shaft 116A of the first motor 114A. In this embodiment, the first motor 114A is disposed between the low-stage compressor 110A and the high-stage compressor 110C, but in other embodiments, it may be disposed outside the low-stage compressor 110A and the high-stage compressor 110C (for example, the first motor 114A, the low-stage compressor 110A, and the high-stage compressor 110C may be disposed in this order in the axial direction of the output shaft 116A).

The output shaft 116A of the first motor 114A is supported rotatably without contact with the motor casing 130-1 by radial magnetic bearings 122-1 and thrust magnetic bearings 126-1 arranged between the low-stage compressor 110A and the high-stage compressor 110C. The radial magnetic bearings 122-1 are provided on both sides of the first motor 114A in the axial direction of the output shaft 116A, and bear the radial load by floating the output shaft 116A by magnetic force. The thrust magnetic bearing 126-1 is provided on one side of the first motor 114A in the axial direction of the output shaft 116A (between the first motor 114A and the low-stage compressor 110A in the embodiment shown in FIG. 2), and bears the thrust load of the output shaft 116A by magnetic force so that a gap is formed between the axial rotor disk 127-1 provided on the output shaft 116A.
The thrust magnetic bearing 126-1 and the axial rotor disk 127-1 may be provided between the high-stage compressor 110C and the first motor 114A. In this embodiment, the axial rotor disk 127-1 is provided on one side of the first motor 114A mainly to suppress fluid friction loss, but if the outer diameter of the output shaft 116A of the first motor 114A is large, the axial rotor disk 127-1 may be provided on both sides for assembly reasons or the like.

The casing 128-1 of the coaxial compressor 118 is configured by connecting a motor casing 130-1, a low-stage compressor impeller casing 132-1, and a high-stage compressor impeller casing 132-3 to each other along the axial direction of the output shaft 116A. The motor casing 130-1 is a casing that defines the outer shell of the first motor 114A, and houses a rotor 136A that is integrally configured with the output shaft 116A inside, and a stator 138A that is arranged around the rotor 136A (the rotor 136A is integrally configured with the output shaft 116A). The low-stage compressor impeller casing 132-1 is attached to one end side of the output shaft 116A and houses the impeller 140A of the low-stage compressor 110A. The high-stage compressor impeller casing 132-3 houses the impeller 140C of the high-stage compressor 110C, which is attached to the other end of the output shaft 116A.

As shown in FIG. 3, the expander-integrated compressor 120 is configured by connecting the middle stage compressor 110B and the expander 103 to both sides of the output shaft 116B of the second motor 114B. In this embodiment, the second motor 114B is disposed between the middle stage compressor 110B and the expander 103, but in other embodiments, it may be disposed outside the middle stage compressor 110B and the expander 103 (for example, the second motor 114B, the middle stage compressor 110B, and the expander 103 may be disposed in this order in the axial direction of the output shaft 116B).

The output shaft 116B of the second motor 114B is supported rotatably without contact with the motor casing 130-2 by radial magnetic bearings 122-2 and thrust magnetic bearings 126-2 arranged between the middle stage compressor 110B and the expander 103. The radial magnetic bearings 122-2 are provided on both sides of the second motor 114B in the axial direction of the output shaft 116B, and bear the radial load by floating the output shaft 116B by magnetic force. The thrust magnetic bearing 126-2 is provided on one side of the second motor 114B in the axial direction of the output shaft 116B (between the second motor 114B and the middle stage compressor 110B in the embodiment shown in FIG. 3), and bears the thrust load of the output shaft 116B by magnetic force so that a gap is formed between the axial rotor disk 127-2 provided on the output shaft 116B.
The thrust magnetic bearing 126-2 and the axial rotor disk 127-2 may be provided between the expander 103 and the second motor 114B. In this embodiment, the axial rotor disk 127-2 is provided on one side of the second motor 114B mainly to suppress fluid friction loss, but if the outer diameter of the output shaft 116B of the second motor 114B is large, the axial rotor disk 127-2 may be provided on both sides for assembly reasons or the like.

The casing 128-2 of the expander-integrated compressor 120 is configured by connecting the motor casing 130-2, the intermediate compressor impeller casing 132-2, and the expander impeller casing 134-1 together along the axial direction of the output shaft 116B. The motor casing 130-2 is a casing that defines the outer shell of the second motor 114B, and houses the rotor 136B (the rotor 136B is formed integrally with the output shaft 116B) and the stator 138B arranged around the rotor 136B. The intermediate compressor impeller casing 132-2 houses the impeller 140B of the intermediate compressor 110B attached to one end of the output shaft 116B. The expander impeller casing 134-1 houses the impeller 142 of the expander 103 attached to the other end of the output shaft 116B.

Returning to FIG. 1, the compressor unit 102 includes a plurality of coaxial compressors 118 arranged in parallel with each other in the refrigerant path 101. The coaxial compressors 118 included in the compressor unit 102 are common (same specifications), and the number of them is greater than the expander-integrated compressor 120 included in the compressor unit 102, and is set according to the refrigeration capacity required for the refrigeration system 100. In this embodiment, the compressor unit 102 includes two coaxial compressors 118A and 118B for one expander-integrated compressor 120, but it is also possible to accommodate even greater refrigeration capacity by including three or more coaxial compressors 118. Furthermore, when there are two expander-integrated compressors 120, three or more coaxial compressors 118 can also be included.

The number of coaxial compressors 118 included in the compressor unit 102 is set according to the refrigeration capacity required for the refrigeration system 100. For example, when the refrigeration capacity required for the refrigeration system 100 is increased, the flow rate of the refrigerant flowing through the refrigerant path 101 increases, so this can be accommodated by increasing the number of coaxial compressors 118. Therefore, the refrigeration system 100 can realize specifications with different refrigeration capacities with little development burden by adjusting the number of coaxial compressors 118 included in the compressor unit 102. Since the expansion machine-integrated compressor 120 can be accommodated by changing the design of only the impeller 140B of the middle stage compressor 110B and the parts related to the expansion machine impeller 142 (impeller casings 132-2 and 134-1), the development period and cost of the coaxial compressor according to the type of parts required for the refrigeration system 100 and the refrigeration capacity can be effectively reduced. In addition, the dedicated area can be reduced compared to the case where multiple refrigeration systems 100 are arranged in parallel to accommodate the required refrigeration capacity.

In addition, in the refrigeration system 100, the first motor 114A of the coaxial compressor 118 and the second motor 114B of the expander-integrated compressor 120 are common. In this way, by making the drive motor common specifications between the coaxial compressor 118 and the expander-integrated compressor 120, it is possible to realize refrigeration systems 100 with different refrigeration capacities while reducing the development burden.

When multiple first motors and second motors are "common," this means that they have at least some of the same specifications. Having at least some of the same specifications may mean, for example, that at least some of the motors' output, rotation speed, dimensions, etc. are the same, that they are interchangeable, or that their designs are the same to the extent that they do not affect the assembly of parts other than the motors.

To explain with an example, for example, if the refrigeration capacity required for the refrigeration system 100 is 5 kW, the required output for the first motor used in the coaxial compressor 118 is assumed to be 45 kW, and the required output for the second motor used in the expander-integrated compressor 120 is assumed to be 15 kW. Based on such preconditions, if a refrigeration system 100 with double the refrigeration capacity of 10 kW is developed, the amount of refrigerant flowing through the refrigerant path 101 will double, so the required output for the first motor will be 90 kW (= 45 kW x 2), and the required output for the second motor will be 30 kW (= 15 kW x 2). In the refrigeration system 100 of this embodiment, such a requirement can be met without the need for a new design of the coaxial compressor by providing two coaxial compressors 118 having a first motor with an output of 45 kW, which is the same specification as the base design, in parallel with the refrigerant path 101, as shown in FIG. In this case, the expander-compressor 120 can meet the required output of 30 kW by using an output specification of 45 kW for the second motor 114B, similar to the first motor 114A.

By adopting a common (same specification) motor as the first motor 114A and the second motor 114B in this way, it is possible to promote commonality of the peripheral configuration of the first motor 114A and the second motor 114B. For example, by making the first motor 114A and the second motor 114B common (same specification), the output shaft 116A and the output shaft 116B have the same shaft diameter, and as a result, the bearings (radial magnetic bearing 122-1, thrust magnetic bearing 126-1) that support the output shaft 116A in the coaxial compressor 118 and the bearings (radial magnetic bearing 122-2, thrust magnetic bearing 126-2) that support the output shaft 116B in the expander-integrated compressor 120 can be made common (same specification). In addition, the motor casing 130-1 of the first motor 114A and the motor casing 130-2 of the second motor 114B can also be made common (same specification).

The bearings and motor casing are "common" to each other, meaning that they share at least some of their specifications. "Shared specifications" may mean that they are substitutable for each other, or that their designs are the same to the extent that they do not affect the assembly of parts other than the motor.

The low-stage compressor impeller casing 132-1 and high-stage compressor impeller casing 132-3 of the first motor 114A and the middle-stage compressor impeller casing 132-2 and expander impeller casing 134-1 of the second motor 114B may be designed differently depending on the shape of the impellers housed in each.

In this way, in the refrigeration system 100, the first motor 114A and the second motor 114B included in the compressor unit 102, and their peripheral configurations, are made common (with the same specifications), so that even if the refrigeration capacity required for the refrigeration system 100 changes, it can be designed efficiently with little development burden.

1 illustrates an example in which the compressor unit 102 includes two coaxial compressors 118. The two coaxial compressors 118 are arranged in parallel with each other in the refrigerant path 101. The refrigerant path 101 includes a first line 144 through which a refrigerant is supplied from the cold heat recovery heat exchanger 105 to the compressor unit 102, second lines 146A and 146B that branch off from the downstream side of the first line 144 to the low-stage compressors 110A of the two coaxial compressors 118, third lines 148A and 148B through which the refrigerants compressed by the two low-stage compressors 110A flow, and a fourth line 150 through which the third lines 148A and 148B join downstream and are connected to the middle-stage compressor 110B. , a fifth line 152 through which the refrigerant compressed by the intermediate stage compressor 110B flows, sixth lines 154A, 154B that branch off from the downstream side of the fifth line 152 to the high stage compressors 110C of the two coaxial compressors 118, seventh lines 156A, 156B through which the refrigerant compressed by the high stage compressors 110C flows, and an eighth line 158 where the seventh lines 156A, 156B join downstream and are connected to the cold heat recovery heat exchanger 105 on the cold box 109 side.

A first valve 160 is provided in one of the second lines 146A, 146B (the second line 146B in FIG. 1), thereby making it possible to adjust the distribution ratio of the refrigerant to the low-stage compressor 110A of the two coaxial compressors 118. In addition, a second valve 162 is provided in one of the third lines 148A, 148B (the third line 148B in FIG. 1), through which the refrigerant compressed by the two low-stage compressors 110A flows, thereby making it possible to adjust the discharge ratio of the refrigerant from the two low-stage compressors 110A.
The third lines 148A and 148B are each provided with the above-mentioned heat exchanger 112A.

A third valve 164 is provided in one of the seventh lines 156A, 156B (in FIG. 1, the seventh line 156B), so that the discharge ratio of the refrigerant from the high-stage compressor 110C of the two coaxial compressors 118 can be adjusted.
The seventh lines 156A and 156B are each provided with the above-mentioned heat exchanger 112C.

The refrigeration system 100 also includes a first bypass line 166 that connects the upstream and downstream sides of the low-stage compressor 110A of the two coaxial compressors 118. A first bypass valve 168 is provided on the first bypass line 166. A second bypass line 170 that connects the upstream and downstream sides of the middle-stage compressor 110B is provided. A second bypass valve 172 is provided on the second bypass line 170. A third bypass line 174 that connects the upstream and downstream sides of the high-stage compressor 110C of the two coaxial compressors 118 is provided. A third bypass valve 176 is provided on the third bypass line 174.

A fourth bypass line 182 is provided to communicate between a high-pressure refrigerant line 178 between the downstream side of the high-stage compressor 110C and the cold heat recovery heat exchanger 105 in the refrigerant path 101 and a low-pressure refrigerant line 180 between the cold heat recovery heat exchanger 105 and the low-stage compressor 110A. A buffer tank 184 capable of storing refrigerant, and a fourth valve 186 and a fifth valve 188 provided on the upstream and downstream sides of the buffer tank 184, respectively, are arranged on the fourth bypass line 182.

These valves are configured so that the opening degree is controlled based on a control signal from the control device 200, which is the control unit of the refrigeration system 100, so that the flow path of the refrigerant in the refrigerant path 101 can be appropriately switched. The control device 200 is configured by installing a program for executing a predetermined control on a hardware configuration consisting of an electronic computing device such as a computer.

The arrangement of each valve and bypass valve in the refrigeration system 100 described above can be changed as appropriate within the range in which equivalent control can be achieved.

Next, a method for starting up the refrigeration system 100 having the above configuration will be described. Figure 4 is a flowchart showing a method for starting up the refrigeration system 100 of Figure 1.

First, assume that the refrigerant temperature at the inlet of the expander 103 is at room temperature (approximately 300K) as the initial state of the refrigeration system 100. In the refrigeration system 100 that was in a stopped state, the temperature of the refrigerant remaining in the refrigerant path 101 rises to near room temperature (approximately 300K), causing the refrigerant pressure to increase in the refrigerant path 101. In this state, the refrigerant pressure in the high-pressure refrigerant line 178 from the high-stage compressor 110C to the expander 103 and the low-pressure refrigerant line 180 from the expander 103 to the low-stage compressor 110A in the refrigerant path 101 is balanced (high and low pressures are equalized). In this state, the pressure on the low-pressure refrigerant line 180 side is higher than during normal operation, and if the refrigeration system 100 is started up in this high refrigerant pressure state, the pressure on the high-pressure refrigerant line 178 side is likely to rise excessively, and there is a risk of a high motor load, especially since the refrigeration system 100 is configured with a motor-driven expander-integrated compressor 120.

Therefore, when the pressure difference ΔP between the pressure of the high-pressure refrigerant line 178 and the pressure inside the buffer tank 184 exceeds a predetermined threshold ΔP1 (e.g., 10 kPa) (step S1: YES), the control device 200 controls the fourth valve 186 to open (step S2) and recovers a part of the refrigerant flowing through the refrigerant path 101 to the buffer tank 184 (step S3). This reduces the pressure difference ΔP, preventing the pressure of the high-pressure refrigerant line 178 from increasing excessively, and as a result, it is possible to preferably avoid the occurrence of an excessive motor load. After that, when the pressure difference ΔP becomes equal to or less than the threshold ΔP1 (step S4: YES), the control device 200 controls the fourth valve 186 to close (step S5).
When the pressure difference ΔP is greater than the threshold value ΔP1 (step S4: NO), the control device 200 returns the control to step S2.

The pressure difference ΔP can be obtained, for example, from the difference between the detection values of a pressure sensor installed in the high-pressure refrigerant line 178 and a pressure sensor installed in the buffer tank 184.

Here, the refrigerant path 101 has a minimum cross section in the flow path near the inlet of the expander 103, where the density is highest under rated operating conditions. During pre-cooling, the suction temperature of the expander 103 is higher than that under rated conditions (the refrigerant density is low), so there is a risk of compressor surging occurring due to the choke phenomenon of the expander 103, which reduces the refrigerant flow rate at that location. In the following step S6, in order to solve this problem, only one of the two coaxial compressors 118 included in the compressor unit 102 (coaxial compressor 118A) is started together with the expander-integrated compressor 120 (i.e., only one of the two coaxial compressors 118 is operated together with the expander-integrated compressor 120, so-called number control operation is started). This allows the expander 103 to be started with a reduced flow rate of refrigerant, effectively preventing surging in the compressor.

Next, the control device 200 controls the opening degree of the second bypass valve 172 based on the refrigerant temperature _Tin at the inlet of the expander 103 (step S7). In step S7, the opening degree of the second bypass valve 172 is controlled based on the refrigerant temperature _Tin at the inlet of the expander 103, so that a portion of the refrigerant flowing through the refrigerant path 101 bypasses the middle stage compressor 110B via the second bypass line 170. As a result, the flow rate of the refrigerant supplied to the middle stage compressor 110B increases, and surging in the compressor as described above can be more effectively prevented.

Furthermore, the control of the opening degree of the second bypass valve 172 in step S7 may be performed continuously or stepwise (in a stepped manner) based on the refrigerant temperature _Tin at the inlet of the expander 103. At this time, the rotation speed of at least one of the coaxial compressor 118 and the expander-integrated compressor 120 started in step S6 may be coordinated and controlled so that the cooling rate of the refrigerant in the cold heat recovery heat exchanger 105 becomes approximately constant (for example, 60 K/h).

The temperature T _in of the refrigerant at the inlet of the expander 103 can be obtained by a temperature sensor (not shown) installed at the inlet of the expander 103 .

In addition, in step S7, the first valve 160, the second valve 162, the third valve 164, the first bypass valve 168, and the third bypass valve 176 are controlled to be in a closed state.

Subsequently, when the temperature T _in at the inlet of the expander 103 becomes equal to or lower than the first target value T1 (e.g., 180 to 200 K) (step S8: YES), the control device 200 controls the first bypass valve 168, the third bypass valve 176 and the first valve 160 to open (step S9).

Next, the control device 200 determines whether or not surging occurs (step S10). If it is determined that surging occurs (step S10: YES), the control device 200 controls the one coaxial compressor 118A started in step S6 to reduce its rotation speed (step S11). The rotation speed of the one coaxial compressor 118A controlled in step S11 is controlled to reduce to a rotation speed at which surging does not occur in each compressor if both of the two coaxial compressors 118 included in the compressor unit 102 are started.
In step S11, the rotation speed of one of the coaxial compressors 118A may be reduced and then temporarily stopped. If it is determined that there is no surging (step S10: NO), the rotation speed reduction control in step S11 is not performed. For example, when the rotation speed is relatively low (for example, when the rotation speed during pre-cooling is low due to restrictions such as the cooling speed of the heat exchanger), surging tends not to occur easily, so depending on the operating conditions, the rotation speed reduction control in step S11 may not be necessary.

Then, the control device 200 controls the first bypass valve 168 and the third bypass valve 176 to open (step S12), and starts the other coaxial compressor 118B included in the compressor unit 102 (step S13). At this time, the rotation speed of the other coaxial compressor 118B is controlled to be equal to that of the one coaxial compressor 118A whose rotation speed has been reduced in step S6. Then, when the pressure conditions of the two coaxial compressors 118 become equal (step S14: YES), the control device controls the first bypass valve 168 and the third bypass valve 176 to close (step S15).

Then, the control device 200 controls the second valve 162 and the third valve 164 to open, thereby completing the connection of the other coaxial compressor 118B to the refrigerant path 101 (step S16). In this way, by temporarily reducing the rotation speed of one of the coaxial compressors 118A that was started earlier in step S3, and then starting the other coaxial compressor 118B, it is possible to smoothly transition from one-sided operation with one coaxial compressor 118A to two-sided operation with two coaxial compressors 118A and 118B while preventing surging in each compressor.

The control device 200 continues to proceed with the pre-cooling operation while controlling the opening degree of the second bypass valve 172 and the rotation speed of at least one of the coaxial compressor 118 and the expander-integrated compressor 120 based on the refrigerant temperature _Tin at the inlet of the expander 103 and the cooling rate of the refrigerant in the cold heat recovery heat exchanger 105. Then, when the temperature _Tin at the inlet of the expander 103 becomes equal to or lower than the second target temperature T2 (e.g., 100 to 120 K) (step S17: YES), the control device 200 controls to close the second bypass valve 172 (step S18), completes the pre-cooling and transitions to normal operation, thereby completing the series of startup control of the refrigeration system 100 (step S19).

In addition, when the refrigeration system 100 includes three or more coaxial compressors 118, the temperature T _in can be set to a desired value by controlling the number of coaxial compressors 118 in an activated state to increase in sequence in accordance with the above control.

As described above, in the start-up method of the refrigeration system 100, in the initial start-up stage, some of the coaxial compressors 118 included in the compressor unit 102 are started, and as pre-cooling progresses (as the temperature _Tin at the inlet of the expander 103 decreases), the number of coaxial compressors 118 to be started is controlled to increase. The number of coaxial compressors 118 to be started in each stage may be controlled as follows, for example, according to the temperature _Tin at the inlet of the expander 103.

ここで、Ａは膨張機１０３のノズルスロート面積でありＰ_ｉｎ，Ｐ_ｅｘはそれぞれ膨張機１０３の入口及び出口における圧力であり、κは冷媒の比熱比であり、Ｒは理想気体のガス定数である。式（１）より、膨張機１０３の入口における温度Ｔ_ｉｎに対する冷媒流量Ｇを概算することができる。そのため、同軸圧縮機１１８の１台当たりの吐出流量をＲとすると、起動すべき同軸圧縮機１１８の台数Ｄは次式により得られる（端数は切り上げ）。
Ｄ＝Ｇ／Ｒ （２） From the relationship between the speed of sound, Mach number, and adiabatic flow, the mass flow rate G of the refrigerant passing through the expander 103 is expressed as a function of the refrigerant temperature _Tin at the inlet of the expander 103 as follows (here, it is assumed that the refrigerant passing through the expander 103 is not in a critical state, i.e., the nozzle outlet flow velocity of the expander 103 does not reach the speed of sound, and the refrigerant is an ideal gas).

Here, A is the nozzle throat area of the expander 103, P _in and P _ex are the pressures at the inlet and outlet of the expander 103, respectively, κ is the specific heat ratio of the refrigerant, and R is the gas constant of an ideal gas. From equation (1), it is possible to roughly calculate the refrigerant flow rate G for the temperature T _in at the inlet of the expander 103. Therefore, if the discharge flow rate per coaxial compressor 118 is R, the number D of coaxial compressors 118 to be started can be obtained by the following equation (fractions are rounded up).
D = G / R (2)

1, when the compressor unit 102 includes two coaxial compressors 118, efficient pre-cooling can be achieved by starting only one of the coaxial compressors 118 until the temperature T _in at the inlet of the expander 103 reaches a first target value T1 (e.g., 180 to 200 K), but since the efficiency decreases at a second target value T2 (e.g., 120 to 200 K), it is preferable to start the other coaxial compressor 118 and operate the two compressors together. In this way, when the number of operating coaxial compressors 118 is changed according to the temperature range, the rotation speed of the started coaxial compressor 1 is temporarily reduced as described above under operating conditions where surging is a concern, so that the number of operating compressors can be smoothly shifted while preventing surging.

In the above embodiment, the refrigeration system 100 is described that includes one expander-integrated compressor and two coaxial compressors 118, but the number of expander-integrated compressors 120 and coaxial compressors 118 included in the refrigeration system 100 may be any number. Below, several variations of the refrigeration system 100 will be specifically described with reference to Figures 5 to 8.
In addition, in Figures 5 to 8, the coaxial compressor 118, the expander-integrated compressor 120, the first motor 114A, and the second motor 114B of the refrigeration system 100 are extracted and shown in a simplified manner, and detailed description of the other configurations is omitted as they follow the above embodiment.

Figures 5A and 5B are schematic diagrams showing refrigeration systems 100A-1 and 100A-2 equipped with two coaxial compressors 118A and 118B and one expander-integrated compressor 120. In the refrigeration system 100A-1 shown in Figure 5A, as in the above-mentioned embodiment, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, and the second motor 114B for driving the expander-integrated compressor 120 are all common. In this case, by making all the first motors 114A and second motors 114B common, the types of motors used in the refrigeration system 100A can be minimized, and the cost and time required for development can be effectively reduced.

In the refrigeration system 100A-2 shown in FIG. 5B, the first motor 114A-1 for driving the coaxial compressor 118A and the second motor 114B for driving the expander-integrated compressor 120 are common, but the first motor 114A-2 for driving the coaxial compressor 118B is different (has different specifications). In this way, by standardizing the first motor 114A and the second motor 114B used in the refrigeration system 100 as much as possible while making only some of the motors different specifications, it is possible to flexibly respond to the specifications required for the refrigeration system 100.

Next, Figs. 6A to 6C are schematic diagrams showing refrigeration systems 100B-1 to 100B-3 equipped with three coaxial compressors 118A, 118B, and 118C and one expander-integrated compressor 120. In the refrigeration system 100B-1 shown in Fig. 6A, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, the first motor 114A-3 for driving the coaxial compressor 118C, and the second motor 114B for driving the expander-integrated compressor 120 are all common. In this case, by making all the first motors 114A and second motors 114B common, the types of motors used in the refrigeration system 100A can be minimized, and the cost and time required for development can be effectively reduced.

In the refrigeration system 100B-2 shown in FIG. 6B, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, and the second motor 114B for driving the expander-integrated compressor 120 are common, while the first motor 114A-3 for driving the coaxial compressor 118C is different (has a different specification). In this way, by standardizing the first motor 114A and the second motor 114B used in the refrigeration system 100 as much as possible while making only some of the motors different specifications, it is possible to flexibly respond to the specifications required for the refrigeration system 100.

In the refrigeration system 100B-3 shown in FIG. 6C, the first motor 114A-1 for driving the coaxial compressor 118A and the second motor 114B for driving the expander-integrated compressor 120 are common to each other, while the first motor 114A-2 for driving the coaxial compressor 118B and the first motor 114A-3 for driving the coaxial compressor 118C are common to each other. In this way, by standardizing the multiple different specifications of each motor used in the refrigeration system 100, it is possible to flexibly respond to the specifications required for the refrigeration system 100.

7A to 7C are schematic diagrams showing refrigeration systems 100C-1 to 100C-3 equipped with three coaxial compressors 118A, 118B, and 118C and two expander-integrated compressors 120A and 120B. In the refrigeration system 100C-1 shown in FIG. 7A, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, the first motor 114A-3 for driving the coaxial compressor 118C, the second motor 114B-1 for driving the expander-integrated compressor 120A, and the second motor 114B-2 for driving the expander-integrated compressor 120B are all common. In this case, by making all of the first motors 114A and second motors 114B common, the types of motors used in the refrigeration system 100A can be minimized, effectively reducing the cost and time required for development.

In the refrigeration system 100C-2 shown in FIG. 7B, a first motor 114A-1 for driving the coaxial compressor 118A, a first motor 114A-2 for driving the coaxial compressor 118B, a second motor 114B-1 for driving the expander-compressor 120A, and
While the second motor 114B-2 for driving the expander-integrated compressor 120B is common, the first motor 114A-3 for driving the coaxial compressor 118C is different (has different specifications). In this way, by standardizing the first motor 114A and the second motor 114B used in the refrigeration system 100 as much as possible while making only some of the motors different specifications, it is possible to flexibly respond to the specifications required for the refrigeration system 100.

In the refrigeration system 100C-3 shown in FIG. 7C, the first motor 114A-1 for driving the coaxial compressor 118A, the second motor 114B-1 for driving the expander-integrated compressor 120A, and the second motor 114B-2 for driving the expander-integrated compressor 120B are common to each other, while the first motor 114A-2 for driving the coaxial compressor 118B and the first motor 114A-3 for driving the coaxial compressor 118C are common to each other. In this way, by standardizing the multiple different specifications of each motor used in the refrigeration system 100, it is also possible to flexibly respond to the specifications required for the refrigeration system 100.

Figures 8A to 8D are schematic diagrams showing refrigeration systems 100D-1 to 100D-4 equipped with four coaxial compressors 118A, 118B, 118C, and 118D and two expander-integrated compressors 120A and 120B. In the refrigeration system 100D-1 shown in Figure 8A, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, the first motor 114A-3 for driving the coaxial compressor 118C, the first motor 114A-4 for driving the coaxial compressor 118D, the second motor 114B-1 for driving the expander-integrated compressor 120A, and the second motor 114B-2 for driving the expander-integrated compressor 120B are all common. In this case, by making all of the first motors 114A and second motors 114B common, the types of motors used in the refrigeration system 100A can be minimized, effectively reducing the cost and time required for development.

In the refrigeration system 100D-2 shown in FIG. 8B, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, the first motor 114A-3 for driving the coaxial compressor 118C, the second motor 114B-1 for driving the expander-integrated compressor 120A, and the second motor 114B-2 for driving the expander-integrated compressor 120B are common, while the first motor 114A-4 for driving the coaxial compressor 118D is different (has a different specification). In this way, by making the first motor 114A and the second motor 114B used in the refrigeration system 100 as common as possible while making only some of the motors different specifications, it is possible to flexibly respond to the specifications required for the refrigeration system 100.

In the refrigeration system 100D-3 shown in FIG. 8C, the first motor 114A-1 for driving the coaxial compressor 118A, the first motor 114A-2 for driving the coaxial compressor 118B, the second motor 114B-1 for driving the expander-integrated compressor 120A, and the second motor 114B-2 for driving the expander-integrated compressor 120B are common to each other, while the first motor 114A-3 for driving the coaxial compressor 118C and the first motor 114A-4 for driving the coaxial compressor 118D are common to each other. In this way, by promoting commonality of the multiple different specifications of each motor used in the refrigeration system 100, it is also possible to flexibly respond to the specifications required for the refrigeration system 100.

In the refrigeration system 100D-4 shown in FIG. 8D, the first motor 114A-1 for driving the coaxial compressor 118A, the second motor 114B-1 for driving the expander-integrated compressor 120A, and the second motor 114B-2 for driving the expander-integrated compressor 120B are common to each other, while the first motor 114A-2 for driving the coaxial compressor 118B, the first motor 114A-3 for driving the coaxial compressor 118C, and the first motor 114A-4 for driving the coaxial compressor 118D are common to each other. In this way, by promoting commonality of the multiple different specifications of each motor used in the refrigeration system 100, it is also possible to flexibly respond to the specifications required for the refrigeration system 100.

The contents described in the above embodiment can be understood, for example, as follows:

(1) A refrigeration system according to one aspect includes:
A refrigeration system (e.g., the refrigeration system 100 of the above embodiment) using a Brayton cycle to generate cold heat using a refrigerant compressed by a compressor unit (e.g., the compressor unit 102 of the above embodiment) arranged on a refrigerant path (e.g., the refrigerant path 101 of the above embodiment),
The compressor unit includes:
A plurality of compressors (e.g., the plurality of coaxial compressors 118 in the above embodiment) arranged in parallel with each other with respect to the refrigerant path;
A plurality of first motors (e.g., the plurality of first motors 114A in the above embodiment) for driving the plurality of compressors, respectively;
An expander-integrated compressor (e.g., the expander 103 in the above embodiment) that is integrated with an expander capable of expanding the refrigerant compressed by the compressor unit (e.g., the expander-integrated compressor 120 in the above embodiment);
A second motor (for example, the second motor 114B in the above embodiment) for driving the expander-compressor unit;
Including,
The number of the plurality of compressors is greater than the number of the expander-compressor units.

According to the above aspect (1), even when developing a refrigeration system with a different refrigeration capacity, it is possible to respond by changing the number of compressors, which are part of the compressor unit, and therefore it is possible to effectively prevent an increase in the number of parts and the occupied floor space due to design changes.

(2) In another embodiment, in the above embodiment (1),
The plurality of first motors and the second motor are common.

According to the above aspect (2), the first motors for driving the compressors included in the compressor unit and the second motor for driving the expander-compressor are common. This reduces the number of types of motors used in the refrigeration system, and effectively reduces the cost and time required for development.

In this specification, when multiple first motors and second motors are "common," it means that the multiple first motors and second motors are separate motors and have at least some of their specifications in common. For example, having common specifications may mean that at least some of the motors' output, rotation speed, and dimensions are the same, that they are interchangeable, or that their designs are the same to the extent that they do not affect the assembly of parts other than the motors.

(3) In another aspect, in the above (1) or (2),
A control device (e.g., the control device 200 of the above embodiment) for controlling the plurality of compressors,
The control device controls the plurality of compressors so as to operate some of the plurality of compressors based on the temperature of the refrigerant at the inlet of the expander when the refrigeration system is started up.

According to the above aspect (3), by operating some of the multiple compressors when the refrigeration system is started, it is possible to effectively prevent surging from occurring in the coaxial compressor.

(4) In another embodiment, in the above embodiment (3),
The control device controls the rotation speed of the compressor in an activated state to be reduced, and then controls the number of activated compressors of the plurality of compressors to be changed.

According to the above aspect (4), when changing the number of compressors to be started, the rotation speed of the compressor that was started first is reduced, so that the number of compressors to be started can be changed smoothly while preventing surging in each compressor.

(5) In another aspect, in any one of the above (1) to (4),
The refrigerant path includes a bypass line (e.g., the second bypass line 170 in the above embodiment) configured to bypass the upstream side and downstream side of a compressor (e.g., the middle stage compressor 110B in the above embodiment) of the expander-integrated compressor;
and a bypass valve (for example, the second bypass valve 172 in the above embodiment) provided on the bypass line.

According to the above aspect (5), surging in each compressor can be effectively prevented by adjusting the opening of the bypass valve provided in the bypass line.

(6) In another embodiment, in the above embodiment (5),
The bypass valve is controlled based on the temperature of the refrigerant at the inlet of the expander so that the flow rate of the refrigerant in the compressor of the expander-integrated compressor becomes equal to or greater than a predetermined value.

According to the above aspect (6), when there is a risk of surging occurring due to an increase in the refrigerant temperature at the inlet of the expander, the opening of the bypass valve is controlled to ensure that the refrigerant flow rate in the compressor of the expander-integrated compressor is equal to or greater than a predetermined value, thereby preventing surging from occurring.

(7) In another embodiment, in the above embodiment (6),
The rotation speed of the compressor or the expander-compressor combination is controlled in coordination with the opening of the bypass valve so that the cooling rate of the refrigerant becomes approximately constant.

According to the above aspect (7), the cooling speed of the refrigerant flowing through the refrigerant path is kept substantially constant by controlling the opening of the bypass valve and the rotation speed of the compressor or the compressor with an integrated expander in a coordinated manner. This makes it possible to adjust/correct the cooling speed during the pre-cooling period from start-up to normal operation, and to precisely control the refrigerant temperature.

(8) In another aspect, in any one of the above (1) to (7),
Each of the plurality of compressors is a coaxial compressor (for example, the coaxial compressor 118 in the above embodiment) including a plurality of compressors connected in series to the refrigerant path.

According to the above aspect (8), by using coaxial compressors (multi-stage compressors) as multiple compressors, it is possible to obtain a larger compression ratio and achieve higher efficiency compared to single-stage compressors.

100 Refrigeration system 101 Refrigerant path 102 Compressor unit (110A, 110B, 110C)
103 Expander 104 Cooling section 105 Cold heat recovery heat exchanger 106 Superconducting device 107 Refrigerant path 108 Pump 109 Cold box 110 Compressor 110A Low stage compressor 110B Middle stage compressor 110C High stage compressor 112 (112A, 112B, 112C) Heat exchanger 114A First motor 114B Second motor 116A, 116B Output shaft 118 (118A, 118B) Coaxial compressor 120 Expander-integrated compressor 122-1, 122-2 Radial magnetic bearing 126 Thrust magnetic bearing 127-1, 127-2 Axial rotor disk 128 Casing 130 Motor casing 132-1 Low stage compressor impeller casing 132-2 Intermediate stage compressor impeller casing 132-3 High stage compressor impeller casing 134-1 Expander impeller casing 136A, 136B Rotor 138A, 138B Stator 140A, 140B, 140C, 142 Impeller 144 First line 146A, 146B Second line 148A, 148B Third line 150 Fourth line 152 Fifth line 154A, 154B Sixth line 156A, 156B Seventh line 158 Eighth line 160 First valve 162 Second valve 164 Third valve 166 First bypass line 168 First bypass valve 170 Second bypass line 172 Second bypass valve 174 Third bypass line 176 Third bypass valve 178 High pressure refrigerant line 180 Low pressure refrigerant line 182 Fourth bypass line 184 Buffer tank 186 Fourth valve 188 Fifth valve 200 Control device

Claims (8)

A refrigeration system using a Brayton cycle that generates cold heat using a refrigerant compressed by a compressor unit arranged on a refrigerant path,
The compressor unit includes:
A plurality of compressors arranged in parallel with each other with respect to the refrigerant path;
a plurality of first motors for driving the plurality of compressors, respectively;
an expander-integrated compressor that is integrated with an expander capable of expanding the refrigerant compressed by the compressor unit;
A second motor for driving the expander-compressor unit;
Including,
The number of the compressors is greater than the number of the expander-compressor integrated units,
A control device for controlling the plurality of compressors,
The control device controls the plurality of compressors to operate some of the plurality of compressors based on the temperature of the refrigerant at the inlet of the expander when the refrigeration system is started . The refrigeration system of claim 1, wherein the first motors and the second motor are common. The refrigeration system according to claim 1 or 2 , wherein the control device controls the number of activated compressors of the plurality of compressors to be changed after controlling the number of rotations of the compressor in an activated state to be reduced. The refrigerant path includes a bypass line configured to bypass an upstream side and a downstream side of a compressor of the expander-compressor unit;
The refrigeration system according to claim 1 , further comprising a bypass valve provided on the bypass line. The refrigeration system according to claim 4 , wherein the bypass valve controls a flow rate of the refrigerant in the compressor of the expander-integrated compressor to be equal to or greater than a predetermined value based on a temperature of the refrigerant at an inlet of the expander. The refrigeration system according to claim 5 , wherein a rotation speed of the compressor or the expander-compressor combination is controlled in coordination with an opening degree of the bypass valve so that a cooling rate of the refrigerant becomes approximately constant. The refrigeration system according to claim 1 , wherein each of the plurality of compressors is a coaxial compressor including a plurality of compressors connected in series to the refrigerant path. A refrigeration system using a Brayton cycle that generates cold heat using a refrigerant compressed by a compressor unit arranged on a refrigerant path,
The compressor unit includes:
A plurality of compressors arranged in parallel with each other with respect to the refrigerant path;
a plurality of first motors for driving the plurality of compressors, respectively;
an expander-integrated compressor that is integrated with an expander capable of expanding the refrigerant compressed by the compressor unit;
A second motor for driving the expander-compressor unit;
Including,
The number of the compressors is greater than the number of the expander-compressor integrated units,
The refrigerant path includes a bypass line configured to bypass an upstream side and a downstream side of a compressor of the expander-compressor unit;
a bypass valve provided on the bypass line;
Equipped with
A refrigeration system, wherein a rotation speed of the compressor or the expander-compressor integrated compressor is controlled in coordination with an opening degree of the bypass valve so that a cooling rate of the refrigerant becomes approximately constant.

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