Refrigerator and operation method of refrigerator at precooling time

Abstract

Provided are: a low-stage compressor (C1) and a high-stage compressor (C3), that is, at least two compressors; an expander (T); a cooling unit (2) that cools a cooling target (R2) using refrigerant (R1) expanded in the expander (T); a refrigerant circulation line (8) that circulates the refrigerant; a bypass line (31) that connects a high-pressure line and a low-pressure line of the refrigerant circulation line (8); a bypass valve (32); a first temperature sensor (33) that detects the temperature of the refrigerant (R1) on the inlet side of the expander (T) or a second temperature sensor (34) that detects the temperature of the refrigerant (R1) on the outlet side of the expander (T); and a controller (40) that controls the opening degree of the bypass valve (32) and the rotation speed of the refrigerant circulator (1) based on the detection result of the first temperature sensor (33) or the second temperature sensor (34).

Description

Technical Field

[0001] This disclosure relates to a refrigeration machine and a method of operating the refrigeration machine during precooling. Background Technology

[0002] Extremely low temperatures can be achieved by using the Brayton cycle for refrigeration. For example, it can be used as a refrigerator in various fields such as medical and food for cooling superconducting devices, liquefying various gases, and replacing liquid nitrogen. It has been put into practical use and has attracted much attention.

[0003] As an example of such a refrigeration unit, one configuration includes: a cooling section, a low-stage compressor, an integrated expander compressor, a high-stage compressor, and a refrigerant circulation pipeline. The cooling section cools the object being cooled through heat exchange with the refrigerant. The low-stage compressor compresses the refrigerant. The integrated expander compressor integrates a mid-stage compressor for compressing the refrigerant and an expander for expanding the refrigerant. The high-stage compressor further compresses the refrigerant. The refrigerant circulation pipeline supplies and circulates the refrigerant to the aforementioned compressors, expander, cooling section, etc. (see, for example, Patent Document 1). Furthermore, there are configurations where the integrated expander compressor integrates the high-stage compressor and expander instead of the mid-stage compressor and expander.

[0004] In a refrigeration machine configured as described above, for example, the refrigerant, after undergoing primary compression in a low-stage compressor driven by a rotary electric motor, is cooled in a heat exchanger and then sent to an intermediate compressor, where it is further compressed. The refrigerant, after undergoing secondary compression in the intermediate compressor, is cooled in a heat exchanger and then further compressed in a high-stage compressor driven by a rotary electric motor. The refrigerant, after undergoing tertiary compression in the high-stage compressor, is cooled in a heat exchanger, further cooled in a heat recovery heat exchanger, and then sent to an expander, where it undergoes adiabatic expansion to become low-pressure and low-temperature refrigerant.

[0005] The refrigerant, now at low pressure and low temperature, is sent to the cooling section (heat exchanger) to cool the object being cooled. Afterward, the refrigerant is sent to the heat recovery heat exchanger, where it is cooled before being supplied to the expander, and then returned to the lower-stage compressor.

[0006] In addition, some of these refrigeration machines are configured to include a buffer piping section, which consists of the following components: a buffer piping that is connected to the high-pressure piping of the refrigerant circulation piping leading to the high-pressure compressor and the expander, and the low-pressure piping from the expander to the low-pressure compressor; a buffer box installed on the buffer piping; and valves (on / off valves) installed on the high-pressure piping side and the low-pressure piping side (inlet side and outlet side) of the buffer box respectively (for example, see Patent Document 1).

[0007] For these refrigeration units, when the heat load of the object being cooled is detected by the heat load detection unit, the refrigerant flow in the refrigerant pipeline is controlled by controlling the opening degree of the valves before and after the buffer tank, thereby adjusting the refrigeration capacity.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Publication No. WO2016 / 178272 Summary of the Invention

[0011] (a) Technical problems to be solved

[0012] Here, for the aforementioned existing refrigeration unit with an integrated compressor and expander, when the refrigeration unit is stopped, the refrigerant pressure in the refrigerant circulation system increases due to the rise in refrigerant temperature. In this state, the refrigerant pressure in the high-pressure line from the expander to the high-pressure compressor and the high-pressure line from the expander to the low-pressure compressor reaches equilibrium (high and low pressures are equalized).

[0013] Therefore, under equal pressure conditions, when the pressure on the low-pressure side of the pipeline is higher than during normal operation and the refrigeration unit is started under this high refrigerant pressure, the pressure on the high-pressure side of the pipeline is prone to rise excessively. In particular, since it is an integrated expander with a motor-driven compressor, the following situation may occur: the motor load increases and the operating speed needs to be limited according to the motor capacity.

[0014] Furthermore, when the refrigeration unit is started under high refrigerant pressure, the smallest cross-section in the circulation path exists near the inlet of the expander, which has the highest density under rated operating conditions. Therefore, the expander's suction temperature tends to rise during precooling (reserve density tends to decrease). This can lead to compressor fluctuations at the expander inlet, where refrigerant flow is reduced, due to obstruction. These startup fluctuations are also more likely to occur in cases involving an integrated compressor-expander type with an electric motor drive and excessive pressure rise on the high-pressure side.

[0015] Therefore, for the existing refrigeration unit mentioned above, there is room for improvement in the following aspects: during the initial operation period from startup to pre-cooling operation, the situation where the high pressure rises significantly compared to the stable operating pressure is suppressed, and the excessive load and fluctuation of the motor are suppressed, so as to achieve a pre-cooling operation with better operating efficiency.

[0016] This disclosure addresses the above-mentioned situation and aims to provide a refrigeration machine and a method for operating the refrigeration machine during pre-cooling, which can suppress a significant increase in high pressure from stable operating pressure during the initial operation period from startup to pre-cooling operation, suppress excessive load and fluctuations in the motor, and improve operating efficiency (cooling efficiency of refrigerant and object being cooled).

[0017] (II) Technical Solution

[0018] One embodiment of the refrigeration machine disclosed herein includes: an integrated expander compressor comprising a compressor for compressing refrigerant and an expander connected to the compressor via a rotating shaft capable of being driven by an electric motor, and for expanding the refrigerant compressed by the compressor; a cooling section for cooling an object using the refrigerant expanded in the expander; a refrigerant circulation line comprising a low-pressure line from the expander through the cooling section to the low-pressure compressor, a medium-pressure line from the low-pressure compressor to the high-pressure compressor, and a high-pressure line from the high-pressure compressor to the expander, for circulating the refrigerant; a bypass line having one end connected to a first connection portion provided in the high-pressure line and the other end connected to a second connection portion provided in the low-pressure line; and a bypass valve provided in the bypass line, capable of adjusting the flow rate of the refrigerant flowing in the bypass line by adjusting its opening degree.

[0019] In addition, a buffer tank that also recovers refrigerant gas from high-pressure pipelines is preferred.

[0020] (III) Beneficial Effects

[0021] According to the refrigeration unit disclosed herein (and its pre-cooling operation method), during the initial operation period from startup to pre-cooling operation, a buffer tank and bypass pipeline can effectively suppress a significant increase in high pressure from the stable operating pressure. Furthermore, the opening degree and rotational speed of the bypass pipeline can be controlled based on temperature detection, replacing refrigerant flow detection. Therefore, during the initial operation period from startup to pre-cooling operation, excessive load and fluctuations in the motor can be suppressed, stable pre-cooling operation can be achieved, and operating efficiency (cooling efficiency of the refrigerant and the object being cooled) can be improved. Attached Figure Description

[0022] Figure 1This is a diagram illustrating an example of a refrigeration machine according to one embodiment of the present disclosure.

[0023] Figure 2 This is a flowchart illustrating an example of an operation method during the pre-cooling operation of a refrigerator according to one embodiment of this disclosure, showing the initial operation period from startup to pre-cooling operation (until the pre-cooling operation is completed).

[0024] Figure 3 This is a flowchart illustrating an example of the control operation of the buffer piping section during the initial operation period from startup to pre-cooling operation (completion of pre-cooling operation) in a pre-cooling operation method of a refrigerator according to one embodiment of this disclosure.

[0025] Figure 4 This is a figure illustrating an example of the relationship between operating time and refrigerant temperature, and the relationship between operating time and bypass valve opening, when using a refrigeration machine according to an embodiment of the present disclosure and the operating method of the refrigeration machine during precooling.

[0026] Figure 5 This diagram illustrates the bypass control operation during the initial operation period from startup to pre-cooling operation in a refrigeration machine operation method according to one embodiment of this disclosure. It is an example of a control flow diagram showing a case where staged (step-by-step) control is performed.

[0027] Figure 6 This is a diagram illustrating an example of the relationship between refrigerant temperature and bypass valve opening during the precooling operation of a refrigeration unit according to one embodiment of this disclosure, in the case of bypass control operation using phased (step-by-step) control.

[0028] Figure 7 This diagram illustrates the bypass control operation during the initial operation period from startup to pre-cooling operation in a pre-cooling operation method of a refrigerator according to one embodiment of this disclosure. It is also a diagram illustrating an example of the control flow under continuous (proportional) control.

[0029] Figure 8 This is a graph illustrating an example of the relationship between refrigerant temperature and bypass valve opening during the precooling operation of a refrigeration unit according to one embodiment of this disclosure, in the case of bypass control operation using continuous (proportional) control.

[0030] Figure 9 This is a diagram illustrating an example of the pressure variations in the high-pressure lines, low-pressure lines, and buffer tank of the refrigeration unit disclosed herein during the initial operation period from startup to pre-cooling operation. Detailed Implementation

[0031] The following is for reference Figures 1 to 9The present disclosure describes some embodiments of the refrigeration machine and the operation method of the refrigeration machine during precooling.

[0032] However, the dimensions, materials, shapes, relative arrangements, etc. of the constituent components described in these embodiments or shown in the accompanying drawings are not intended to limit the scope of the invention, but are merely illustrative examples.

[0033] For example, expressions such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" that indicate relative or absolute configuration do not only indicate configuration in a strict sense, but also indicate a state of relative displacement with tolerance or at an angle or distance that can achieve the same level of functionality.

[0034] For example, expressions such as "same," "equal," and "homogeneous" that indicate that things are in an equal state do not only mean that they are strictly equal, but also that there is a difference in the degree to which they can achieve the same function.

[0035] For example, expressions representing shapes such as quadrilaterals and cylinders do not only refer to quadrilaterals and cylinders in a strictly geometric sense, but also include shapes with concave and convex parts, chamfers, etc., within the range that can achieve the same effect.

[0036] On the other hand, expressions that "have", "possess", "have", "include", or "have" a constituent element are not exclusive expressions that exclude the existence of other constituent elements.

[0037] Furthermore, this disclosure relates to a refrigerator capable of achieving extremely low temperatures by using the Brayton cycle in the refrigeration cycle, and a method of operating the refrigerator during precooling. In particular, it relates to a refrigerator capable of performing appropriate operation control during the initial operation period from startup to precooling operation (until precooling is completed), and a method of operating the refrigerator during precooling.

[0038] (Refrigeration unit)

[0039] Specifically, the refrigeration unit 1 in this embodiment is, for example, as follows: Figure 1As shown, the system is configured to include: a cooling section (secondary-side load heat exchanger) 2, a low-stage compressor C1, a medium-stage compressor C2, an integrated expander compressor 7, and a refrigerant circulation line 8. The cooling section (secondary-side load heat exchanger) 2 is used to cool the object being cooled (in this embodiment, the refrigerant R2 on the object side) through heat exchange with the refrigerant R1. The low-stage compressor C1 is used to compress the refrigerant R1, and the medium-stage compressor C2 is used to further compress the refrigerant R1. The integrated expander compressor 7 integrates an advanced compressor C3 for further compressing the refrigerant R1 and an expander T for expanding the refrigerant R1. The refrigerant circulation line 8 sequentially supplies and circulates the refrigerant R1 to the low-stage compressor C1, the medium-stage compressor C2, the advanced compressor C3, the expander T, and the cooling section 2.

[0040] In addition to the advanced compressor C3 and the expander T, the integrated expander compressor 7 also has a first motor 9. The two ends of the output shaft of the first motor 9 are respectively connected to the advanced compressor C3 and the expander T. The first motor 9 is used to drive the output shaft and the advanced compressor C3 and the expander T to rotate around the axis.

[0041] In addition, in the refrigeration machine 1 of this embodiment, the low-stage compressor C1 and the intermediate compressor C2 are also configured as a single unit. The single-unit compressor 10 has a second motor 11. The two ends of the output shaft of the second motor 11 are respectively connected to the low-stage compressor C1 and the intermediate compressor C2. The second motor 11 is used to drive the output shaft and the low-stage compressor C1 and the intermediate compressor C2 to rotate around the axis.

[0042] Furthermore, in the refrigeration unit 1 of this embodiment, the low-stage compressor C1, the intermediate compressor C2, the high-stage compressor C3, and the expander T are connected in series via the refrigerant circulation pipeline 8.

[0043] Regarding refrigerant circulation line 8, the section from expander T to low-pressure compressor C1 is designated as a low-pressure line, and the section from high-pressure compressor C3 to expander T is designated as a high-pressure line. The section from low-pressure compressor C1 to high-pressure compressor C3 is designated as a medium-pressure line.

[0044] A first heat exchanger 12 for cooling the refrigerant discharged from the low-stage compressor C1 and a second heat exchanger 13 for cooling the refrigerant R1 discharged from the intermediate compressor C2 are respectively installed on the first medium-pressure pipeline. A third heat exchanger 14 for cooling the refrigerant discharged from the high-stage compressor C3 is installed on the high-pressure pipeline. In addition, a heat recovery heat exchanger (regenerative heat exchanger) 15 is installed between the third heat exchanger 14 on the high-pressure pipeline and the expander T.

[0045] The first heat exchanger 12, the second heat exchanger 13, and the third heat exchanger 14 use cooling water w, for example, to cool the refrigerant R1. The heat recovery heat exchanger 15 uses the refrigerant R1 in the cooling section 2, after cooling the object R2, to cool the refrigerant R1 in the high-pressure pipeline.

[0046] Additionally, a cooling section 2 is provided between the expander T and the heat recovery heat exchanger 15 in the low-pressure pipeline. Furthermore, in this embodiment, the cooling pipeline is part of the low-pressure pipeline.

[0047] In this embodiment, the object to be cooled by the refrigerant R1 sent to the heat exchanger of the cooling section 2 is the refrigerant (secondary refrigerant) R2 for the object to be cooled. The refrigerant R2 for the object to be cooled circulates in the circulation pipe 16 on the object side and is sent to the cooling section 2 in sequence to be cooled to a specified temperature.

[0048] In the refrigerator 1 of this embodiment, which is constructed with the above-described structure, the refrigerant that has undergone first-stage compression in the low-stage compressor C1, driven by the second electric motor 11, is cooled in the first heat exchanger 12 and then sent to the intermediate compressor C2, where it is further compressed. The refrigerant R1 that has undergone second-stage compression in the intermediate compressor C2 is cooled in the second heat exchanger 13 and then further compressed in the advanced compressor C3, driven by the first electric motor 9. The refrigerant R1 that has undergone third-stage compression in the advanced compressor C3 is cooled in the third heat exchanger 14 and then further cooled in the heat recovery heat exchanger 15 before being sent to the expander T, where it undergoes adiabatic expansion and generates heat. That is, the refrigerant itself undergoes adiabatic expansion to become low-pressure and low-temperature. The advanced compressor C3 and the expander T are also connected to the two ends of a common power source, namely the output shaft of the first electric motor 9, so that the power recovered through the expander T contributes to the compression power of the advanced compressor C3, thereby improving efficiency.

[0049] Additionally, the low-pressure, low-temperature refrigerant R1 is sent to the heat exchanger of the cooling section 2, where it is used to cool the object flowing in the cooling object circulation pipe 16 to a specified temperature using refrigerant R2. Afterwards, the refrigerant R1 is sent to the heat recovery heat exchanger 15, where it is cooled before being supplied to the expander T, and then returned to the low-stage compressor C1.

[0050] Furthermore, in this refrigerator 1, refrigerant R1 can be, for example, helium, neon, hydrogen, nitrogen, air, hydrocarbons, etc. Moreover, the temperature of refrigerant R1 can be set to an extremely low temperature, for example, approximately -190 to -200°C (83.15 to 73.15 K) at the inlet side of the expander T and approximately -210 to -220°C (63.15 to 53.15 K) at the outlet side.

[0051] Therefore, the refrigerator 1 of this embodiment can be used, for example, for cooling superconducting devices, liquefying various gases, and replacing liquid nitrogen.

[0052] Specifically, such as Figure 1 As shown, regarding the object being cooled by heat exchange with refrigerant R1 in the cooling section 2, liquid nitrogen (refrigerant R2 for cooling the object) used to cool superconducting equipment 20 such as superconducting cables can be cited as an example.

[0053] In this case, for example, a cooling target-side circulation pipeline (liquid nitrogen circulation pipeline) 16 is provided, which circulates between the cooling section 2, the superconducting device 20 and the storage tank 21, and a circulation pump 22 is provided on the cooling target-side circulation pipeline 16 to circulate the liquid nitrogen R2, which is cooled to an extremely low temperature in the cooling section 2, to the superconducting device 20.

[0054] On the other hand, in the refrigerator 1, as described above, when the refrigerator is stopped, the refrigerant pressure will increase due to the rise in refrigerant temperature, and the high and low pressures will be equalized in this state. Therefore, when the refrigerator 1 is started and operated under high refrigerant pressure, the refrigerant pressure in the high-pressure line will increase due to the higher refrigerant pressure in the low-pressure line, and the load on the motor (11(9)) will increase. Depending on the capacity of the motor, it may be necessary to limit the operating speed.

[0055] In addition, it is also considered that when the refrigeration unit 1 is started and operated under high refrigerant pressure, a blocking phenomenon will occur at the inlet of the expander T, and fluctuations will occur in the compressors (C1, C2, C3).

[0056] (Control process for the pre-cooling step)

[0057] In this embodiment, the pre-cooling operation process of the refrigeration unit 1 (the operation method of the refrigeration unit during pre-cooling) is as follows: Figure 1 and Figure 2 As shown, it consists of refrigeration unit pre-cooling operation control, bypass control, and buffer tank refrigerant recovery control.

[0058] First, in the pre-cooling operation control of the refrigerator, the operation control of the refrigerator 1 from start-up to pre-cooling completion is carried out, and the speed control is performed based on the target set temperature (T1, T2) and the measured temperature (T) of the inlet or outlet of the expander T in a way that keeps the cooling rate constant.

[0059] In bypass control, the opening degree of the on / off valve 32 of the bypass line 31 is controlled according to the measured temperature (T), including staged (step-by-step control) and continuous control. If the refrigerant R1 is cooled before the target set temperature (T1) is reached, the on / off valve 32 closes, resulting in operation without bypass control.

[0060] In addition, in the refrigerant recovery control of the buffer tank, refrigerant R1 is recovered from the high-pressure pipeline to the buffer tank 27 to reduce the load of the pre-cooling operation of the refrigeration unit 1. When the set pressure difference is reached, the on-off valve 28 opens, and refrigerant R1 flows from the high-pressure pipeline to the buffer tank 27.

[0061] Regarding these controls, in parallel with the pre-cooling operation control of the refrigeration unit, bypass control and buffer tank refrigerant recovery control are performed, forming a combination that is constantly monitored.

[0062] The following provides a more detailed explanation of the control content.

[0063] (Buffer piping section)

[0064] Regarding the refrigeration unit 1 of this embodiment, firstly, it includes a buffer piping section 25.

[0065] The buffer piping section 25 is configured to include: a buffer piping 26, one end of which is connected to the third connection S3 between the third heat exchanger 14 and the cold and heat recovery heat exchanger 15 of the high-pressure piping, and the other end of which is connected to the fourth connection S4 between the cold and heat recovery heat exchanger 15 and the low-stage compressor C1 of the low-pressure piping; a buffer tank 27 disposed on the buffer piping 26 for temporarily storing refrigerant R1; a first on / off valve (high-pressure side buffer valve) 28 disposed on the inlet side of the buffer tank 27 (the high-pressure piping side between the buffer tank 27 and the third connection S3); and a second on / off valve (low-pressure side buffer valve) 29 disposed on the outlet side of the buffer tank 27 (the low-pressure piping side between the buffer tank 27 and the fourth connection S4).

[0066] Furthermore, by opening the first on / off valve 28 on the inlet side and temporarily supplying and storing refrigerant R1 from the high-pressure line to the buffer tank 27 using the pressure difference (differential pressure) according to the opening degree of the first on / off valve 28, the amount (flow rate) of refrigerant R1 flowing in the refrigerant circulation line 8 can be regulated. Additionally, by closing the first on / off valve 28 and opening the second on / off valve 29 on the outlet side, and by returning refrigerant R1 from the buffer tank 27 to the low-pressure line using the pressure difference according to the opening degree of the second on / off valve 29, the amount of refrigerant R1 flowing in the refrigerant circulation line 8 can be regulated.

[0067] (Bypass Piping Department)

[0068] Furthermore, the refrigerator 1 in this embodiment includes a bypass pipe section 30.

[0069] The bypass pipeline section 30 is configured to include: a bypass pipeline 31, one end of which is connected to the first connection S1 between the third heat exchanger 14 and the third connection S3 of the high-pressure pipeline, and the other end of which is connected to the second connection S2 between the fourth connection S4 and the low-pressure compressor C1 of the low-pressure pipeline; and a third on / off valve (bypass valve) 32, which is provided in the bypass pipeline 31.

[0070] Furthermore, the connection points of the high-pressure and low-pressure pipelines of the buffer pipeline section 25 and the bypass pipeline section 30 can be interchanged.

[0071] (Refrigerant Status / Power Status Detection Unit)

[0072] On the refrigerant circulation line 8, a first temperature sensor 33 is provided between the heat recovery heat exchanger 15 of the high-pressure line and the expander T, which is used to detect the temperature of the refrigerant R1 flowing here.

[0073] A second temperature sensor 34 is installed between the expander T and the cooling section 2 in the cooling pipeline to detect the temperature of the refrigerant R1 flowing here.

[0074] A third temperature sensor (secondary refrigerant temperature sensor) 35 is installed on the circulation pipe 16 on the cooling object side, which detects the temperature of the cooling object, i.e., liquid nitrogen R2, which is being cooled by the cooling unit 2.

[0075] On the high-pressure line of the refrigerant circulation line 8, for example, a first pressure sensor 36 is provided between the third connection part S3 and the first connection part S1, which is used to detect the pressure of the refrigerant R1 in the high-pressure line.

[0076] A second pressure sensor 37 is provided on the buffer tank 27 for detecting the internal pressure of the buffer tank 27.

[0077] A first power meter 38 is installed on the integrated expander compressor 7, which is used to detect the driving status of the first electric motor 9 and the rotation speed of the rotating shaft, the advanced compressor C3, and the expander T.

[0078] A second power meter 39 is provided on the integrated compressor 10, which is used to detect the driving status of the second electric motor and the rotation speed of the rotating shaft, the low-stage compressor C1, and the intermediate compressor C2.

[0079] Furthermore, the refrigerator 1 in this embodiment includes a controller (control device) 40, which receives the detection results of the first temperature sensor 33, the second temperature sensor 34, the third temperature sensor 35, the first pressure sensor 36, the second pressure sensor 37, the first power meter 38, and the second power meter 39, and controls the driving of the first motor 9 and the second motor 11, as well as the opening degree (opening and closing drive) of the first opening and closing valve 28, the second opening and closing valve 29, and the third opening and closing valve 32.

[0080] (Buffer tank refrigerant recovery control: Operation control during the initial operation of the buffer piping section was used)

[0081] First, the pre-cooling operation control for refrigerant recovery using a buffer tank will be explained.

[0082] Therefore, the amount of refrigerant R1 flowing into and out of the refrigerant circulation line 8 through the buffer line section 25 can be controlled by adjusting the opening degree of the first on / off valve 28 and the second on / off valve 29 based on the controller 40. Furthermore, it is preferable that the third on / off valve 32, which includes the bypass line section 30, and the first on / off valve 28 and the second on / off valve 29 are electric valves.

[0083] More specifically, when the pressure in the system of refrigerant circulation line 8 is high, fluctuations will occur in the compressor when the refrigeration unit 1 (motor 9, 11) is running, making it difficult to increase the speed.

[0084] In contrast, in the refrigerator 1 of this embodiment, a buffer tank 27 is provided between the low-pressure pipeline and the high-pressure pipeline in order to increase the speed of the refrigerator 1 during startup, and excess refrigerant R1 is recovered in a way that prevents the discharge pressure of the refrigerator 1 from exceeding a certain pressure.

[0085] Therefore, the controller 40 performs opening and closing drive control and opening degree adjustment of the first on-off valve 28 based on the detection results of the first pressure sensor 36 and the second pressure sensor 37, so that the refrigerant R1 can flow in by utilizing the refrigerant pressure difference between the high-pressure pipeline and the buffer tank 27, and can recover excess refrigerant R1 to the buffer tank 27 in a way that prevents the discharge pressure of the refrigerator 1 from exceeding a certain pressure.

[0086] (Control during startup / pre-cooling operation)

[0087] And, as Figure 1 , Figure 2 and Figure 3 As shown, after the refrigerator 1 stops, when the start-up / pre-cooling operation begins (Step 1), when the refrigerant pressure in the high-pressure line and the low-pressure line is equalized under high pressure as the refrigerator 1 stops, the refrigerant is recovered to the buffer tank 27 using the buffer line section 25 based on the detection results of the first pressure sensor 36 and the second pressure sensor 37 (Step 3) (Step 2).

[0088] At this time, the controller 40 receives the detection results of the first pressure sensor 36 and the second pressure sensor 37, and calculates the pressure difference between the high-pressure pipeline and the buffer tank 27 (Step 3). It confirms whether the refrigerant pressure between the high-pressure pipeline and the buffer tank 27 is balanced under high pressure. For example, when the pressure difference of the refrigerant pressure is above a set value (threshold) such as 10 kPa (Step 4), it controls the opening of the first on / off valve 28 (Step 5) and uses the buffer pipeline section 25 to implement refrigerant recovery (Step 6).

[0089] In other words, the pressure difference between the buffer tank 27 and the refrigerant pressure in the high-pressure pipeline is calculated. When the pressure difference exceeds the preset value (10 kPa, etc.), the controller 40 controls the opening of the first on-off valve 28 while the second on-off valve 29 is closed (Step 5).

[0090] Step 5: The first on / off valve 28 is opened and controlled (Step 6): the refrigerant R1 is delivered to the buffer tank 27 and temporarily stored using the pressure difference between the buffer tank 27 and the high-pressure pipeline, thereby reducing the flow rate (pressure) of the refrigerant R1 flowing in the Brayton cycle.

[0091] Therefore, it is possible to prevent overload operation (excessive motor load of the first motor 9 and the second motor 11) caused by the pressure rise in the refrigerant circulation pipeline 8 during the initial stage of precooling.

[0092] Furthermore, when refrigerant R1 is supplied to buffer tank 27 and temporarily stored, the flow rate (pressure) of refrigerant R1 flowing in the Brayton cycle decreases, and the differential pressure of the refrigerant is lower than the set value (Step 7), the first on / off valve 28 is closed (Step 8). Additionally, in Step 4, when the differential pressure of the refrigerant is lower than the set value, the first on / off valve 28 remains closed (Step 8).

[0093] (Control during precooling operation)

[0094] As described above, when the differential pressure between the buffer tank 27 and the high-pressure pipeline exceeds a set value such as 10 kPa, refrigerant is recovered from the high-pressure pipeline to the buffer tank through the first on / off valve, and the differential pressure between the buffer tank and the high-pressure pipeline decreases (Step 6, Step 7).

[0095] Therefore, when the pre-cooling operation begins after the refrigerator 1 stops, if the differential pressure continuously exceeds the set value, the high-pressure refrigerant R1 is recovered into the buffer tank 27. However, if the pressure (discharge pressure) of the refrigerant R1 in the high-pressure pipeline fluctuates significantly due to the operation of the refrigerator 1, the differential pressure between the buffer tank 27 and the high-pressure pipeline decreases and remains in this state. That is, there is no transfer of refrigerant R1 between the buffer tank 27 and the high-pressure pipeline, and no increase or decrease in refrigerant R1 in the refrigerant circulation pipeline 8 occurs, maintaining the pressure of the high-pressure pipeline.

[0096] Conversely, when the pre-cooling operation begins after the refrigerator 1 stops, and the pressure (discharge pressure) of the refrigerant R1 in the high-pressure line changes significantly due to the operation of the refrigerator 1, refrigerant R1 is continuously recovered from the high-pressure line to the buffer tank 27 for capacity adjustment.

[0097] Thus, in the refrigeration unit 1 of this embodiment, since the refrigerant circulation pipeline 8 (refrigerant flow path system) is a closed structure, excess refrigerant R1 can be stored in the buffer tank 27 at room temperature. That is, during pre-cooling operation, as described above, by controlling the opening and closing of the first on / off valve 28 solely based on the detection results of the first pressure sensor 36 and the second pressure sensor 37 without measuring the flow rate, the amount of refrigerant R1 recovered can be automatically adjusted, achieving an appropriate state that does not generate excessive motor load, and maintaining this state.

[0098] Furthermore, the following embodiment is shown: when the differential pressure of the refrigerant pressure is determined based on the pressure detection results of (Step 3) to (Step 6), the controller 40 controls the opening of the first on / off valve 28 when the differential pressure is above the set value (threshold), and the buffer pipeline section 25 is used for refrigerant recovery.

[0099] On the other hand, as another embodiment, when the differential pressure changes and the pressure in the high-pressure pipeline is above a set value (threshold), the first on / off valve 28 can be opened, and the refrigerant can be recovered using the buffer pipeline section 25.

[0100] (Transfer control to normal (stable) operation)

[0101] Furthermore, when the refrigerator 1 starts, the refrigerant R1 on the high-pressure side temporarily increases in pressure, storing excess refrigerant in the buffer tank 27. As cooling proceeds, the pressure of refrigerant R1 in the low-pressure line, high-pressure line, and the refrigerator 1 as a whole decreases, approaching the pressure state during normal operation. In other words, the pressures of the low-pressure line and high-pressure line become the pressures during normal operation, and operation proceeds without generating excessive motor load. When the pressure reaches a level below the buffer mechanism's pressure setting value, the first on / off valve 28 is closed (Step 8).

[0102] On the other hand, for refrigerant R1, for example, when cooled from room temperature to below 100K, its density increases and its capacity decreases. Specifically, in the equipment and piping from the heat recovery heat exchanger 15 to the expander T, from the expander T to the cooling section 2, and from the cooling section 2 to the heat recovery heat exchanger 15, the temperature of refrigerant R1 is below 100K, and the density of refrigerant R1 increases, resulting in insufficient capacity. Conversely, during operation, the refrigerant temperature is near room temperature from the outlet of the heat recovery heat exchanger 15 in the low-pressure line through the compressor to the inlet of the heat recovery heat exchanger 15 in the high-pressure line, so the refrigerant capacity of refrigerant R1 remains unchanged.

[0103] Therefore, it is necessary to maintain a refrigerant capacity within the system that corresponds to the reduction in refrigerant capacity on the low-temperature side (i.e., the high-pressure pipeline side) and the cooling pipeline side.

[0104] Therefore, for the refrigerator 1 and its operation method in this embodiment, refrigerant R1 is preferentially stored in the buffer tank 27. For example, excess refrigerant R1 can be recovered to the buffer tank 27 during the initial operation period from startup to pre-cooling operation (until pre-cooling is completed), and the first on / off valve 28 for refrigerant recovery can be opened when the pressure difference detected by the first pressure sensor 36 and the second pressure sensor 37 is 10 kPa or higher, which is a preset set value.

[0105] Alternatively, regarding the refrigeration unit 1 and its operation method in this embodiment, when the pressure difference (differential pressure) detected by the first pressure sensor 36 and the second pressure sensor 37 reaches or exceeds a set value (threshold), the first on / off valve 28 is opened, and refrigerant is recovered using the buffer pipeline section 25 (see reference). Figure 9 (A diagram illustrating an example of pressure changes in the high-pressure pipeline, low-pressure pipeline, and buffer tank 27 during the phased control of bypass control operation)

[0106] (Refrigeration unit pre-cooling operation control / bypass control: Operation control during the initial operation period using the bypass piping section)

[0107] Next, for the refrigeration unit 1, for example, it is necessary to cool the refrigerant R1 under a large temperature difference from room temperature to below 100K. Therefore, for the refrigerant circulation pipeline 8, the prior art is to set a throttling section with the smallest cross-section near the inlet of the expander T with the highest density.

[0108] Here, during pre-cooling operation, the suction temperature tends to rise, meaning the refrigerant density tends to decrease. This reduces the refrigerant flow rate at the minimum cross-section throttling section near the inlet of the expander T, potentially causing fluctuations in compressors C1, C2, and C3. Therefore, sufficient refrigerant flow rate needs to be ensured during pre-cooling operation to suppress these fluctuations.

[0109] In response to this situation, the refrigerator 1 in this embodiment includes a bypass pipeline section 30, which consists of a bypass pipeline 31 that allows refrigerant R1 to return from the high-pressure pipeline to the low-pressure pipeline and a third on / off valve 32 that serves as a bypass valve.

[0110] Therefore, by using the controller 40 to control the opening of the third on / off valve 32, instead of supplying a portion of the refrigerant R1 compressed by the high-grade compressor C3 to the expander T, it is possible to return it to the low-grade compressor C1 and the high-grade compressor C3. Furthermore, by adjusting the opening degree of the third on / off valve 32 using the controller 40, the refrigerant flow rate returning to compressors C1, C2, and C3 can be adjusted.

[0111] Therefore, in the refrigerator 1 of this embodiment, when precooling, the opening degree of the third on / off valve 32 is appropriately changed according to the operating state, so as not to cause fluctuations, and the amount of refrigerant R1 not used for cooling can be reduced, and efficient (high COP: Coefficient of Performance) operation can be carried out without wasting power.

[0112] Next, regarding the operation method of the refrigerator 1 and its pre-cooling process in this embodiment, as follows: Figure 2 ( Figure 5 , Figure 7 , Figure 1 As shown in the diagram, the opening degree of the third on / off valve 32 is controlled according to the temperature condition of the refrigerant R1 (Step 9), and pre-cooling operation control is performed by the refrigeration unit pre-cooling operation control and bypass control using the bypass pipeline section 30. In addition, the refrigeration unit pre-cooling operation control and bypass control are performed in parallel with the aforementioned bypass control.

[0113] (Refrigeration unit pre-cooling operation control)

[0114] First, in the pre-cooling operation control of the refrigeration unit (Step 9), for example, it is run at 60% speed for 10 minutes (Step 10).

[0115] In addition, the opening degree of the third on / off valve 32 is adjusted and controlled based on the refrigerant temperature detected by the first temperature sensor 33 installed in the high-pressure pipeline or the second temperature sensor 34 installed in the cooling pipeline.

[0116] At this time, the cooling rate (the rate at which the temperature of the refrigerant decreases) during precooling is set to 60K / h, etc., and the cooling rate is kept constant as preset. The opening of the third on / off valve 32 is reduced in stages or continuously using bypass control, so that the opening of the third on / off valve 32 is 0% when the refrigerant R1 reaches the first target temperature (100K in this embodiment) (Step 11).

[0117] Furthermore, when the expander outlet temperature reaches the first target temperature (100K) (Step 12), the bypass line section 30 is stopped (bypass control), and the system is controlled to supply the full amount of refrigerant to the expander T (no bypass control) (Step 13).

[0118] In addition, after the bypass pipeline section 30 is stopped, the speed of the refrigerator is controlled based on the refrigerant temperature at the outlet side of the expander T detected by the second temperature sensor 34 in order to keep the refrigerant temperature below the second target temperature (below 67K in this embodiment) (Step 14).

[0119] In other words, in this embodiment, before the circulation of the refrigerant R2 (liquid nitrogen) for cooling the target begins in the circulation pipe 16 (liquid nitrogen circulation pipe) on the cooling target side, the refrigerant temperature at the outlet side of the expander T is detected using the second temperature sensor 34, and the refrigerant temperature at the outlet side of the expander T is used as the temperature control point, and the second target temperature is set to 67K or higher. This prevents the liquid nitrogen from freezing in the cooling section 2.

[0120] Once liquid nitrogen circulation begins in the liquid nitrogen circulation pipeline, the temperature control point is switched to a third temperature sensor 35 located near the superconducting cable, and the operation of the refrigerator 1 is controlled based on the refrigerant temperature at the outlet side of the liquid nitrogen detected by the third temperature sensor 35. This completes the pre-cooling operation of the refrigerator 1 (Step 15), enabling easy and precise cooling of the object being cooled, i.e., liquid nitrogen.

[0121] Furthermore, it was confirmed that as long as there is no change in heat load, controlling the opening degree of the third on / off valve 32 using the detection results of either the first temperature sensor 33 or the second temperature sensor 34 can achieve the same effect. Therefore, although the refrigerator 1 in this embodiment includes both the first temperature sensor 33 and the second temperature sensor 34, it can also be configured using only one of the temperature sensors, depending on the situation, thereby reducing the number of temperature monitoring points and temperature sensors.

[0122] (Bypass control)

[0123] On the other hand, regarding the refrigerator 1 and the operation method of the refrigerator 1 during precooling in this embodiment, such as Figure 2 , Figure 5 , Figure 7 ( Figure 1 As shown in the diagram, by controlling the opening degree of the third on / off valve 32 in parallel with the pre-cooling operation control of the refrigeration unit (step control or proportional control), bypass control is performed (Step 16), thereby reducing the flow rate variation to the expander T. That is, the variation in cooling capacity when the opening degree changes can be suppressed, and cooling rate control is easier.

[0124] Specifically, when performing pre-cooling operation control using the bypass piping section 30, the primary reason for keeping the cooling rate constant is that when the heat exchanger is cooled rapidly, it may break due to thermal deformation.

[0125] The second reason is that if the cooling temperature changes significantly, the adjustment range of the opening of the third on / off valve 32 and the variation of the refrigeration unit speed will be large, making stable operation difficult. That is, the refrigerant flow rate in the bypass pipe 31 also affects the operating efficiency, so the cooling rate must be kept constant in order to achieve efficient operation.

[0126] Furthermore, based on the above situation, regarding the operation method of the refrigerator 1 during precooling in this embodiment, as described above, during precooling, the opening degree control of the bypass valve (i.e., the third on / off valve 32) of the bypass pipeline section 30 and the speed control of the refrigerator 1 are combined to perform temperature control that keeps the cooling rate constant.

[0127] Furthermore, regarding the pre-cooling operation method of the refrigerator 1 in this embodiment, instead of supplying a portion of the refrigerant R1 to the expander T, the opening degree of the third on / off valve 32 of the bypass pipeline section 30 is adjusted. Thus, without using a flow meter, the flow rate is adjusted through the bypass pipeline 31, and the refrigerant R1 is returned from the high-pressure pipeline to the low-pressure pipeline, suppressing fluctuations.

[0128] On the other hand, when the third on / off valve 32 is over-opened, it will supply the compressor with more flow than needed, consuming unnecessary power, resulting in inefficient operation.

[0129] Therefore, in order to maintain a stable flow rate, the opening degree of the third on-off valve 32 is adjusted and controlled in stages or continuously (step control or proportional control) and the third on-off valve 32 is closed (opening degree is 0%) when the flow rate approaches the design flow rate of the expander T.

[0130] Furthermore, in the opening control of the third on / off valve 32 of the bypass pipeline section 30, the condition is set to allow for efficient operation by adjusting the refrigerant flow rate to both the expander T and the bypass pipeline 31. Therefore, it is believed that if only the refrigerant flow rate is adjusted and controlled using the bypass pipeline section 30, high-precision control may not be possible considering the temperature control of the refrigerant R1.

[0131] Based on this situation, for the pre-cooling operation method of the refrigerator 1 in this embodiment, as described above, in addition to controlling the opening degree of the third on / off valve 32 of the bypass pipeline section 30, the speed control of the refrigerator 1 is also performed, thereby adjusting / correcting the cooling speed to keep the cooling speed constant.

[0132] That is, for the pre-cooling operation method of the refrigerator 1 in this embodiment, the rotation speed of the refrigerator 1 is controlled in a constant manner according to the difference between the set target temperature and the actual temperature of the refrigerant R1, so that the refrigerant temperature can be controlled with high precision.

[0133] Thus, for the pre-cooling operation method of the refrigerator 1 in this embodiment, by using the opening degree adjustment control of the third on / off valve 32 of the bypass pipeline section 30 and the speed control of the refrigerator 1, fluctuations can be appropriately suppressed during the initial operation period from startup to the completion of pre-cooling, and the cooling rate can be kept constant. This enables high-precision cooling of the refrigerant R1 and efficient operation control.

[0134] Here, for the operation method of the refrigerator 1 during precooling in this embodiment, in order to properly achieve the above-mentioned effect, the opening degree of the third on / off valve 32 of the bypass pipeline section 30 is adjusted in stages or continuously using bypass control (Step 16).

[0135] The operation method of the refrigerator 1 in this embodiment will be described in detail by giving examples of both the phased opening control (step control) and the continuous opening control (proportional control) of the third on / off valve 32 using these bypass pipe sections 30.

[0136] (The bypass pipeline section uses phased operation control (step-by-step operation control))

[0137] First, the method for controlling the opening degree of the bypass valve, namely the third on / off valve 32, of the bypass pipeline section 30 in stages will be explained.

[0138] In the phased opening adjustment control of the third on / off valve 32 of the bypass pipeline section 30, such as Figure 5 , Figure 6 (Refer to Figure 1 , Figure 2 , Figure 4As shown, for example, the refrigeration unit is controlled to operate at 60% of its maximum speed (Step 10) via pre-cooling operation control (Step 9), and the opening degree of the third on / off valve 32 is set to 40% (Step 17). Additionally, the temperature of the refrigerant R1 at startup is measured using either the first temperature sensor 33 or the second temperature sensor 34 (Step 18). Furthermore, the refrigeration unit 1 is started, and from the start of the pre-cooling operation, the opening degree of the third on / off valve 32 is changed in stages based on the refrigerant temperature detected by the first temperature sensor 33 or the second temperature sensor 34 (Step 19).

[0139] In the phased operation control using the bypass pipeline section 30, the steps for determining the opening degree of the third on / off valve 32 by the start and end points of the temperature at each step (in this embodiment, steps 1 to 6) are: Figure 6 For example, when the temperature range of a step is set to T01 to T02 and the opening degree of the third on / off valve 32 is set to V01%, the opening degree of the third on / off valve 32 is maintained at V01 when the measured temperature Ta of the first temperature sensor 33 or the second temperature sensor 34 is T02 < Ta ≦ T01.

[0140] Furthermore, as the refrigerant temperature gradually decreases, during the stage when the measured temperature Ta becomes T02, the opening degree V02% (V02 < V01) of the third on-off valve 32, which corresponds to the temperature range of the next step from T02 to T03 (T03 < Ta ≦ T02), is maintained.

[0141] In this way, as the cooling temperature decreases, the steps (steps 1 to 6) are changed sequentially. Each time the steps are changed to the next stage, the opening degree of the third on / off valve 32 is switched to the opening degree of the next stage.

[0142] When the opening degree of the third on / off valve 32 is gradually reduced by changing the steps in sequence, the flow rate of refrigerant R1 flowing in the bypass line 31 and from the high-pressure line to the low-pressure line is gradually reduced. Corresponding to this gradual reduction in the flow rate of refrigerant R1, the amount of refrigerant flowing from the low-stage compressor C1 side to the expander T side will gradually increase. Therefore, in the refrigerator 1 of this embodiment, the cooling rate is kept constant and controlled by the rotation speed (refrigerator pre-cooling operation control).

[0143] For example, in Figure 5 , Figure 6In this process, the refrigeration unit speed at startup (when rotation begins) is set to 60%, the opening degree of the third on / off valve 32 is set to 40%, and five steps are set before the temperature of refrigerant R1 measured by the first temperature sensor 33 or the second temperature sensor 34 below it reaches the first target temperature of 100K. The temperature ranges of 225K, 190K, 155K, 120K, and 100K and the opening degree of the third on / off valve 32 are set.

[0144] In this way, by using the phased opening control of the third on / off valve 32 of the bypass pipe section 30 and the speed control of the refrigerator 1, the opening of the third on / off valve 32 can be set according to the temperature range of each step in the pre-cooling operation method of the refrigerator 1 in this embodiment, and the speed control (e.g., speed N = 60 to 75%) can be performed using PID control or the like in each of the respective temperature ranges so that the cooling rate becomes a preset constant set value (60 K / h, etc.).

[0145] Therefore, according to the pre-cooling operation method of the refrigerator 1 in this embodiment, stable pre-cooling operation with minimal fluctuations in the rotational speed and pressure of the refrigerator 1 can be performed.

[0146] Furthermore, when the first target temperature of 100K is reached, the opening degree of the third on / off valve 32 is 0%, and the operation control of the bypass pipeline section 30 ends, switching to non-bypass control operation (Step 20). By switching to non-bypass control operation, the entire refrigerant circulation volume flows from the compressor to the expander T.

[0147] Furthermore, during the pre-cooling operation without bypass control, the engine speed is controlled at the next target temperature, namely the second target temperature of 67K. At this time, before reaching the second target temperature of 67K, the engine speed is controlled using PID control or similar methods (e.g., engine speed N = 75-95%) to maintain the cooling rate at a preset constant setpoint (60K / h, etc.) (Step 13). Additionally, control is performed to maintain the second target temperature of 67K until the nitrogen cycle operation under load is completed (Steps 13, 14, 15).

[0148] Furthermore, speed control is not limited to using PID (Proportional-Integral-Differential) control. For example, P...

[0149] (Proportional) control, PI (Proportional-Integral) control, etc.

[0150] Therefore, according to the refrigeration unit 1 and the pre-cooling operation method of the refrigeration unit 1 in this embodiment, by using the phased opening adjustment control of the third on / off valve 32 of the bypass pipeline section 30 and the speed control of the refrigeration unit 1, it is possible to appropriately suppress fluctuations during the initial operation period from startup to the completion of pre-cooling, and to keep the cooling rate constant, thereby achieving high-precision cooling of the refrigerant R1 and enabling efficient operation control.

[0151] (Continuous operation control (proportional operation control) was used in the bypass pipeline section)

[0152] Next, the method for continuously controlling the opening degree of the bypass valve, namely the third on / off valve 32, of the bypass pipeline section 30 will be explained.

[0153] In the continuous opening adjustment control of the third on / off valve 32 of the bypass pipeline section 30, such as Figure 7 , Figure 8 (Refer to Figure 1 , Figure 2 , Figure 4 As shown, similar to the phased opening adjustment control, for example, the refrigerator pre-cooling operation control (Step 9) sets the speed to 60% of the maximum value (Step 10), and the opening of the third on / off valve 32 to 40% (Step 17). Additionally, the temperature of the refrigerant R1 at startup is measured using either the first temperature sensor 33 or the second temperature sensor 34 (Step 18). Furthermore, the refrigerator 1 is started, and from the start of the pre-cooling operation phase, the opening of the third on / off valve 32 is continuously changed based on the refrigerant temperature detected by the first temperature sensor 33 or the second temperature sensor 34 (Step 20).

[0154] In the continuous operation control using the bypass pipeline section 30, the starting and ending points of the temperature at each step determine the opening degree of the third on / off valve 32 (in this embodiment, steps 1 to 6). Figure 8 ).

[0155] However, regarding the initial operating state, the operation is controlled with a priority speed of 60% (Step 10) and the third on / off valve opening of 40% (Step 17), and the valve opening is maintained at 40% until the temperature of refrigerant R1 is cooled to 225K in (Step 18). Therefore, the continuous operation control actually starts from (Step 2).

[0156] For example, when the temperature range of a step is set to T01 to T02, during the period from T01 to T02, the opening degree of the third on / off valve 32 is gradually reduced from V01% to V02.

[0157] That is, when the temperature of refrigerant R1 measured by the first temperature sensor 33 or the second temperature sensor 34 is set to Ta, the opening degree V% of the third on / off valve 32 is calculated using the following formula (1).

[0158] [Formula 1]

[0159] V%=V01-((V01-V02) / (T01-T02))×(T01-Ta)····(1)

[0160] Here, T02 < Ta < T01

[0161] The opening degree is calculated in this way to continuously control the third on / off valve 32, and the steps (steps 1 to 6) are changed sequentially as the cooling temperature decreases in this continuous control. Figure 8 ).

[0162] As the steps are changed sequentially and the opening degree of the third on-off valve 32 is continuously reduced, the flow rate of refrigerant R1 flowing in the bypass line 31 and from the high-pressure line to the low-pressure line continuously decreases. Corresponding to this continuous decrease in refrigerant flow rate, the amount of refrigerant flowing from the low-stage compressor C1 side to the expander T side continuously increases. Therefore, in the refrigerator 1 of this embodiment, the cooling rate is kept constant and controlled by the rotational speed (refrigerator pre-cooling operation control).

[0163] For example, in Figure 7 , Figure 8 In the process, the speed of the refrigeration unit at startup (when rotation begins) is set to 60%, the opening degree of the third on / off valve 32 is set to 40%, and the temperature of the refrigerant R1 measured by the first temperature sensor 33 or the second temperature sensor 34 below it is set to reach the first target temperature of 100K. In the four steps from step 2 to step 5, the opening degree of the third on / off valve 32 is continuously set according to formula (1) at 225K, 190K, 155K, 120K and 100K, corresponding to each temperature range.

[0164] In this way, by using the continuous opening degree control of the third on / off valve 32 of the bypass pipe section 30 according to formula (1) and the speed control of the refrigerator 1, the opening degree of the third on / off valve 32 can be set according to the temperature range of each step in the pre-cooling operation method of the refrigerator 1 in this embodiment, and the speed control (e.g., speed N = 60 to 75%) can be performed by using PID control or the like in the respective temperature range so that the cooling rate becomes a preset constant set value (60 K / h, etc.).

[0165] Therefore, according to the pre-cooling operation method of the refrigerator 1 in this embodiment, stable pre-cooling operation with minimal fluctuations in the rotational speed and pressure of the refrigerator 1 can be performed.

[0166] In addition, similar to the phased opening control, when the first target temperature of 100K is reached, the opening of the third on / off valve 32 is 0%, the operation control of the bypass pipeline section 30 ends, and the operation switches to non-bypass control (Step 13). By switching to non-bypass control operation, the entire refrigerant circulation volume flows from the compressors C1, C2, and C3 to the expander T.

[0167] Furthermore, during the pre-cooling operation without bypass control, the engine speed is controlled at the next target temperature, namely the second target temperature of 67K. At this time, before reaching the second target temperature of 67K, the engine speed is controlled using PID control or similar methods (e.g., engine speed N = 75-95%) to maintain the cooling rate at a preset constant setpoint (60K / h, etc.) (Step 13). Additionally, control is performed to maintain the second target temperature of 67K until the nitrogen cycle operation under load is completed (Steps 13, 14, 15).

[0168] Furthermore, when using continuous opening control, speed control is not limited to PID (Proportional-Integral-Differential) control. For example, P (Proportional) control and PI (Proportional-Integral-Derivative) control can also be used.

[0169] - Integral (proportional-integral) control, etc.

[0170] Therefore, according to the refrigeration unit 1 and the pre-cooling operation method of the refrigeration unit 1 in this embodiment, by using the continuous opening adjustment control of the third on / off valve 32 of the bypass pipeline section 30 and the speed control of the refrigeration unit 1, it is possible to appropriately suppress fluctuations during the initial operation period from startup to the completion of pre-cooling, and to keep the cooling rate constant, thereby achieving high-precision cooling of the refrigerant R1 and enabling efficient operation control.

[0171] (Temperature control during pre-cooling)

[0172] The key points of the predetermined temperature cooling control (predetermined operation method) performed by the refrigerator 1 of this embodiment, which has a bypass pipeline section 30 and a buffer pipeline section 25, are summarized as follows.

[0173] 1) When starting, set the specified speed of the refrigeration unit to RPM (1) (set the speed of at least the expander T among the compressors C1, C2, C3 and expander T to the specified speed RPM (1)), and set the opening degree of the bypass valve of the bypass section 30, i.e. the third on / off valve 32, to the specified opening degree V% (2) and start operation (start-up operation procedure).

[0174] 2) Additionally, the refrigerant temperature at the inlet side or the outlet side of the expander T is detected using either the first temperature sensor 33 or the second temperature sensor 34. Furthermore, as the refrigerant temperature at the inlet side or the outlet side of the expander T decreases from, for example, 190K (225K) to 100K (the first target temperature), the opening degree V% of the third on-off valve 32 is reduced in stages or continuously, allowing the refrigerant R1 in the high-pressure line to flow to the low-pressure line through the bypass line 31. Furthermore, the staged or continuous control of the opening degree V% of the third on-off valve 32 is performed, cooling the refrigerant R1 from its startup temperature to the first target temperature (bypass control operation).

[0175] 3) Next, when the opening degree of the third on / off valve 32 is 0% (closed) and the refrigerant temperature is the first target temperature, the refrigerant temperature is cooled from the first target temperature to the second target temperature based on the refrigerant temperature at the outlet side of the expander T detected by the second temperature sensor 34 (or the refrigerant temperature detected by the first temperature sensor 33) (no bypass control operation process).

[0176] 4) In addition, when performing bypass control operation and non-bypass control operation, the speed of the refrigerator 1 is continuously adjusted and controlled based on the refrigerant temperature of the second temperature sensor 34 in a manner that keeps the cooling rate constant at least until the cooling target temperature (first target temperature, second target temperature) is reached (cooling rate control operation).

[0177] 5) In addition, during the pre-cooling operation from startup in steps 1) to 4) above, when the first pressure sensor 36 and the second pressure sensor 37 detect that the refrigerant pressure in the high-pressure line is greater than a preset value (10 kPa) or more than the pressure in the buffer tank 27, the first on / off valve 28 is opened, and the refrigerant R1 is recovered to the buffer tank 27 by using the pressure difference (refrigerant recovery process).

[0178] 6) Furthermore, through the control from start-up to pre-cooling operation in steps 1) to 5) above, the pre-cooling operation is completed in the stage where the temperature is cooled to the second target temperature and the refrigerant temperature is constant. After the pre-cooling operation is completed, the liquid nitrogen circulation begins, and the refrigerant temperature detection point of the first temperature sensor 33 or the second temperature sensor 34 is switched to the refrigerant temperature detection point of the cooling object side circulation pipe 16 of the third temperature sensor 35, which detects the temperature of the refrigerant R2 used for cooling, and the operation is switched to formal cooling operation (formal cooling operation switching process).

[0179] By controlling the refrigeration unit 1 in this way from startup to the predetermined operation of formal cooling, it is possible, for example, to achieve... Figure 4 As shown, refrigerant R1 is cooled with a constant temperature gradient during precooling.

[0180] Furthermore, based on the detection values ​​of the first temperature sensor 33 or the second temperature sensor 34 installed near the inlet or outlet of the expander T, the opening degree of the third on / off valve 32 and the bypass refrigerant flow rate are adjusted in stages or continuously. Therefore, compared with the case of detecting the flow rate of refrigerant R1, it does not lead to a more complex device structure and can perform control with high precision.

[0181] Therefore, according to the refrigeration unit 1 and its pre-cooling operation method in this embodiment, the flow rate of refrigerant R1 is not detected, and fluctuations can be avoided by controlling the flow rate of refrigerant R1. This simplifies the device structure and improves safety. Furthermore, pre-cooling can be performed by operating compressors C1, C2, C3, and expander T at high speeds, enabling smooth pre-cooling operation.

[0182] Furthermore, if stepless speed control is to be used to avoid fluctuations solely through speed control, then a flow meter for measuring refrigerant flow would be required to implement this stepless speed control. This would result in a complex device structure. Additionally, a method to keep the opening of the third on / off valve 32 constant has been considered, but in this case, the bypass refrigerant R1 would unnecessarily increase as cooling proceeds.

[0183] Furthermore, in the refrigeration unit 1 of this embodiment, if the opening degree of the third on / off valve 32 is increased at an appropriate time, refrigerant R1 can be released from the high-pressure line to the low-pressure line without recovering refrigerant R1 into the buffer tank 27, thus ensuring the flow rate of refrigerant R1. Therefore, even without the buffer line section 25, fluctuations in the compressor C1, C2, and C3 during precooling can be suppressed.

[0184] Here, Figure 9 This diagram illustrates an example of the pressure fluctuations in the high-pressure pipeline, low-pressure pipeline, and buffer tank 27 during bypass control operation (in phased control).

[0185] Additionally, for example, in Figure 9 and Figure 4 In the diagram, (a) indicates the start of the refrigeration unit's operation, (b) indicates the end point of step 1 of the initial operation control (refrigerant temperature: 225K), and (c) indicates the end point of step 2 of the phased or continuous operation control (refrigerant temperature: 190K).

[0186] (d) indicates the end point of step 5 of the phased or continuous operation control (when the refrigerant temperature is 100K).

[0187] And, as Figure 9 (and Figure 4 As shown, during the period from (a) at the start of the refrigerator's operation to (b) at the end of step 1 (equivalent to step 1), the refrigerant pressure in the high-pressure line increases. Therefore, during this period from (a) to (b), the first on / off valve 28 is opened, and refrigerant is recovered using the buffer line section 25. That is, for the refrigerator 1 and its operation method in this embodiment, during the period from (a) to (b), the pressure in the high-pressure line is above a set value (threshold). At this time, the first on / off valve 28 is opened, and refrigerant is recovered using the buffer line section 25.

[0188] Furthermore, during the period from (a) to (b), the internal pressure variation of the buffer tank 27 is substantially the same as the refrigerant pressure variation in the high-pressure line (manifesting the same action / tendency).

[0189] Next, during the period from the end point (b) of step 1 to the end point (c) of step 2 (equivalent to step 2), the opening degree of the third on / off valve (bypass valve) 32 of the bypass line section 30 is reduced (for example, from 40% to 35%), and the bypass amount of refrigerant is reduced. As a result, during the period from (b) to (c), the amount of refrigerant flowing from the compressor C3 toward the expander T increases, and the pressure in the high-pressure line temporarily increases.

[0190] Therefore, for the refrigerator 1 and its operation method in this embodiment, during the period from (b) to (c) (equivalent to step 2), the pressure in the high-pressure pipeline is above a set value (threshold), in other words, above the internal pressure of the buffer tank 27. During this period from (b) to (c), the first on / off valve 28 is opened, and refrigerant is recovered using the buffer pipeline section 25. That is, refrigerant recovery is performed in the region where the refrigerant pressure in the high-pressure pipeline is higher than the internal pressure of the buffer tank 27.

[0191] Furthermore, during the period from (a) to (b) and from (b) to (c), the speed is increased in a way that keeps the cooling rate constant (for example, keeping the opening of the third on / off valve 32 constant (40%), running at 60% speed for 10 minutes, and then controlling the speed to 60-75%), thereby keeping the cooling rate of the refrigerant constant, and as the temperature of the refrigerant decreases, the refrigerant pressure in the high-pressure line decreases.

[0192] Furthermore, regarding the refrigerator 1 and its operation method in this embodiment, during the period from (a) to (b), that is, before the refrigerant temperature reaches approximately 225K, the opening degree of the third on / off valve 32 is kept constant, and cooling operation is continuously performed.

[0193] Specifically, if valve control of the third on / off valve 32 is performed during the period from (a) to (b), external disturbances visible during the period from (b) to (c) will occur, resulting in changes in refrigerant pressure in the high-pressure line and changes in rotation speed, which may lead to a decrease in operating efficiency when the refrigerant cooling rate is kept constant.

[0194] Therefore, for the refrigerator 1 and the operation method of the refrigerator 1 in this embodiment, when the operation control is performed in stages or continuously, in step 1 from (a) to (b), the opening degree of the third on / off valve 32 is not changed and a constant opening degree is maintained.

[0195] Furthermore, regarding the refrigeration unit 1 and its operation method in this embodiment, the refrigerant recovery of the buffer tank 27 is carried out firstly during the initial operation from (a) to (b) (before the refrigerant temperature reaches 225K) to recover excess refrigerant. Secondly, thereafter, the amount of refrigerant corresponding to the pressure increase can be temporarily recovered when the opening degree of the third on / off valve 32 changes.

[0196] (Adjustment and control of the refrigeration unit's capacity during normal operation)

[0197] Furthermore, in this embodiment, during normal operation after the transfer control to normal (stable) operation is performed, the capacity of the refrigeration unit is adjusted according to the heat load condition.

[0198] When the capacity of the refrigeration unit 1 is increased, the second on / off valve 29 is opened to allow the refrigerant R1 stored in the buffer tank 27 to return to the low-pressure pipeline 8a.

[0199] When the capacity of the refrigeration unit 1 is reduced, the first on / off valve 28 is opened to recover refrigerant R1 into the buffer tank 27.

[0200] At this time, in the refrigerator 1 of this embodiment, the set temperature of the refrigerant R1 and the rotational speed of the refrigerator 1 (the rotational speeds of the first motor 9, the second motor 11, and each compressor C1, C2, and C3) are used as the judgment conditions for adjusting the refrigerator capacity, that is, as the judgment conditions for controlling the opening and closing of the first on / off valve 28 and the second on / off valve 29. In addition, a third pressure sensor 41 is installed on the low-pressure line.

[0201] For example, regarding the second on / off valve 29, it is opened when the refrigerant temperature detected by the first temperature sensor 33 (or the second temperature sensor 34) is above the preset set temperature (insufficient pressure) and the refrigerator speed is 100% (appropriate motor load). It is closed when the pressure in the buffer tank 27 decreases by a certain amount, or when the refrigerant temperature is below the set temperature (excessive refrigerant charge) and the refrigerator speed is below 100% (increased motor load). The high-pressure line, buffer tank 27, and low-pressure line utilize pressure sensors to measure pressure, and refrigerant R1 is released and recovered under conditions exceeding the set differential pressure.

[0202] Regarding the first on / off valve 28, the first on / off valve 28 is opened when the refrigerant temperature detected by the first temperature sensor 33 (or the second temperature sensor 34) is below the preset set temperature (excessive refrigerant charge) and the chiller speed is 98%, which is below the preset threshold (excessive motor load). The first on / off valve 28 is closed when the pressure in the buffer tank 27 increases by a certain amount, or when the refrigerant temperature is above the set temperature (reduced refrigerant charge) and the chiller speed increases (reduced motor load) to 98%, which is above the threshold (refrigerant recovery stops).

[0203] Therefore, the capacity of the buffer tank 27 is limited, and the amount and time of refrigerant recovery need to be adjusted. By controlling the opening and closing of the first on / off valve 28 and the second on / off valve 29 as described above, the amount and time of refrigerant recovery can be adjusted, and the refrigeration capacity can be adjusted to an appropriate state and maintained during normal operation.

[0204] The above describes the embodiments of the refrigeration machine and the operating method of the refrigeration machine during precooling according to the present disclosure. However, the refrigeration machine and the operating method of the refrigeration machine during precooling according to the present disclosure are not limited to the above embodiments, and include variations, etc., and can be appropriately modified within the scope of the spirit of the disclosure.

[0205] For example, in this embodiment, a refrigeration machine is constituted by having three compressors: a low-level compressor, a medium-level compressor, and a high-level compressor. However, as long as at least a low-level compressor and a high-level compressor are present, the number of compressors is not particularly limited.

[0206] In this embodiment, a controller 40 receives the detection results from the first temperature sensor 33, the second temperature sensor 34, the third temperature sensor 35, the first pressure sensor 36, the second pressure sensor 37, the first kinetic meter 38, and the second kinetic meter 39, and controls the driving of the first motor 9 and the second motor 11, as well as the opening degree (opening and closing drive) of the first on / off valve 28, the second on / off valve 29, and the third on / off valve 32. However, the controller is not necessarily a single controller. That is, it can also be configured to have multiple controllers, which are used to receive the detection results from each sensor, etc., and to drive and control each motor, valve, etc., respectively.

[0207] Furthermore, regarding the embodiments of the refrigeration unit and its pre-cooling operation method disclosed herein, the refrigeration unit is effective not only when starting up under equal pressure at room temperature, but also when restarting after the refrigeration unit has just stopped. In this case, even when the refrigerant temperature of the refrigeration unit and the temperature of the cryogenic equipment have not risen, the refrigeration unit's pre-cooling operation control, bypass control, and buffer tank refrigerant recovery control can be performed based on the measurements of various sensors and using a controller, thus enabling unimpeded initiation and continuous pre-cooling operation.

[0208] Finally, the content described in the implementation method can be understood, for example, as follows.

[0209] (1) One aspect of the refrigeration machine (refrigeration machine 1) of this disclosure includes: an integrated expander compressor (integrated expander compressor 7) comprising a compressor (advanced compressor C3) for compressing refrigerant (refrigerant R1), and an expander (expander T) connected to the compressor via a rotating shaft that can be driven by an electric motor (first electric motor 9), and used to expand the refrigerant compressed by the compressor; a cooling section (cooling section 2) which uses the refrigerant expanded in the cooling expander to cool the object to be cooled (the object to be cooled, liquid nitrogen, secondary refrigerant R2); and a refrigerant circulation line (refrigerant circulation line). 8) It includes a low-pressure pipeline from the expander through the cooling section to the low-level compressor (low-level compressor C1), a medium-pressure pipeline from the low-level compressor to the high-level compressor, and a high-pressure pipeline from the high-level compressor to the expander for circulating refrigerant; a bypass pipeline (bypass pipeline 31), one end of which is connected to a first connection part (first connection part S1) provided on the high-pressure pipeline, and the other end of which is connected to a second connection part (second connection part S2) provided on the low-pressure pipeline; and a bypass valve (third on / off valve 32), which is provided on the bypass pipeline and can adjust the flow rate of refrigerant flowing in the bypass pipeline by adjusting the opening degree.

[0210] In the refrigeration unit described in (1) above, by controlling the opening of the bypass valve, a portion of the refrigerant compressed by the high-level compressor is instead supplied to the expander and returned to both the low-level and high-level compressors. Furthermore, by adjusting the opening degree of the bypass valve, the flow rate of refrigerant returning to the compressor and the flow rate of refrigerant flowing to the expander can be varied.

[0211] Therefore, during the initial operation period from startup to precooling completion, by appropriately changing the opening of the bypass valve according to the operating conditions, fluctuations can be avoided, and the amount of refrigerant not used for cooling can be reduced, enabling efficient (high COP) operation without wasting power.

[0212] (2) Another aspect of the refrigerator disclosed herein is the refrigerator described in (1) above, comprising: a temperature sensor (first temperature sensor 33) for detecting the temperature of the refrigerant flowing between the first connection and the expander in the high-pressure pipeline; and a controller (controller 40, control device) for controlling the opening degree of the bypass valve and the rotational speed of the rotating shaft based on the detection result of the temperature sensor.

[0213] In the refrigeration unit described in (2) above, the opening of the bypass valve and the flow rate of the bypass refrigerant are adjusted by using the detection value of a temperature sensor that detects the temperature of the refrigerant flowing between the first connection and the expander near the inlet of the expander. This does not lead to a more complex device structure compared to the case where the flow rate of the refrigerant is detected, and allows for high-precision control.

[0214] Therefore, by not detecting the refrigerant flow rate, fluctuations can be avoided through refrigerant flow control, thus simplifying the device structure and improving safety. Furthermore, pre-cooling can be performed by rotating the compressor and expander at high speed, enabling smooth pre-cooling operation.

[0215] That is, during initial operation, compared with existing technologies, it can appropriately suppress fluctuations, maintain a constant cooling rate, cool the refrigerant with high precision, and perform efficient operation control.

[0216] (3) Another aspect of the refrigerator disclosed herein is the refrigerator described in (1) above, comprising: a temperature sensor (second temperature sensor 34) for detecting the temperature of the refrigerant between the cooling section and the expander in the low-pressure pipeline; and a controller for controlling the opening degree of the bypass valve and the rotational speed of the rotating shaft based on the detection result of the temperature sensor.

[0217] In the refrigeration unit described in (3) above, the opening of the bypass valve and the flow rate of the bypass refrigerant are adjusted by using the temperature sensor that detects the temperature of the refrigerant flowing between the cooling section and the expander near the outlet of the expander. This does not complicate the device structure compared to the case where the flow rate of the refrigerant is detected, and high-precision control can be performed.

[0218] Therefore, by not detecting the refrigerant flow rate, fluctuations can be avoided through refrigerant flow control, thus simplifying the device structure and improving safety. Furthermore, pre-cooling can be performed by rotating the compressor and expander at high speed, enabling smooth pre-cooling operation.

[0219] That is, during initial operation, compared with existing technologies, it can appropriately suppress fluctuations, maintain a constant cooling rate, cool the refrigerant with high precision, and perform efficient operation control.

[0220] (4) Another aspect of the refrigerator disclosed herein is the refrigerator described in (2) or (3) above. The controller performs the following control: during the initial operation of the refrigerator from the start of startup to the completion of pre-cooling operation, the bypass valve is controlled to reduce its opening in stages before the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature, and the rotation speed is controlled to keep the rate of decrease of the temperature of the refrigerant detected by the temperature sensor constant.

[0221] In the refrigeration machine described above (4), during the initial operation period from startup to the completion of precooling, in addition to controlling the opening degree of the bypass valve, the speed of the refrigeration machine (compressor, expander) is controlled to adjust / correct the cooling rate and keep the cooling rate constant, thereby enabling high-precision control of the refrigerant temperature.

[0222] Furthermore, by using the phased opening control of the bypass valve and the speed control of the chiller, the opening of the bypass valve can be set according to the temperature range of each step, and the speed control can be performed in such a way that the cooling rate is a preset constant set value in each of the respective temperature ranges.

[0223] Therefore, it is possible to perform stable pre-cooling operation with minimal fluctuations in the speed and pressure of the refrigeration unit.

[0224] (5) Another aspect of the refrigerator disclosed herein is the refrigerator described in (2) or (3) above. The controller performs the following control: during the initial operation of the refrigerator from the start of startup to the completion of pre-cooling operation, the bypass valve is controlled to continuously reduce its opening before the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature, and the rotation speed is controlled to keep the rate of decrease of the temperature of the refrigerant detected by the temperature sensor constant.

[0225] In the refrigeration machine described above (5), during the initial operation period from startup to the completion of precooling, in addition to controlling the opening degree of the bypass valve, the speed of the refrigeration machine (compressor, expander) is controlled to adjust / correct the cooling rate and keep the cooling rate constant, thereby enabling high-precision control of the refrigerant temperature.

[0226] Furthermore, by using continuous opening control of the bypass valve and speed control of the chiller, the opening of the bypass valve can be set according to the temperature range of each step, and the speed can be controlled in such a way that the cooling rate becomes a preset constant set value in each distinguished temperature range.

[0227] Therefore, it is possible to perform stable pre-cooling operation with minimal fluctuations in the speed and pressure of the refrigeration unit.

[0228] (6) Another aspect of the refrigerator of this disclosure is the refrigerator of (4) or (5) above, wherein the controller performs the following control: when the temperature of the refrigerant detected by the temperature sensor reaches the first target temperature, the bypass valve is controlled such that the opening degree is 0%; the opening degree is kept at 0% until the temperature of the refrigerant detected by the temperature sensor is lower than the first target temperature and reaches the second target temperature set to be lower than the first target temperature; and the rotation speed is controlled such that the rate of decrease of the temperature of the refrigerant detected by the temperature sensor is kept constant.

[0229] In the refrigeration unit described in (6) above, when the first target temperature is reached, the bypass valve opening is 0%, ending the operation control using the bypass pipeline and switching to non-bypass control operation where the entire refrigerant circulation volume flows from the compressor to the expander. Furthermore, during the pre-cooling operation without bypass control, the speed is controlled to maintain a constant cooling rate towards the next target temperature, i.e., the second target temperature.

[0230] Therefore, by using the phased or continuous opening adjustment control of the bypass valve and the speed control of the refrigeration unit, and during the initial operation period from startup to the completion of precooling, fluctuations can be more effectively suppressed, and the refrigerant can be cooled at a constant and high precision, enabling efficient operation control.

[0231] (7) Another aspect of the refrigerator disclosed herein is the refrigerator described in (6) above, comprising: a heat exchanger (cooling section, secondary load heat exchanger 2) for exchanging heat between a secondary refrigerant (refrigerant R2 for cooling the object) and a refrigerant; and a secondary refrigerant temperature sensor (third temperature sensor 35) for detecting the temperature of the secondary refrigerant, wherein if the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature, the controller controls the rotation speed based on the detection result of the secondary refrigerant temperature sensor.

[0232] In the refrigeration unit described above (7), the temperature detection point is switched from the temperature sensor to the secondary refrigerant temperature sensor when the second target temperature is reached. The rotation speed is controlled based on the detection result of the secondary refrigerant temperature sensor, so that the unit can smoothly transition from the pre-cooling operation during the initial operation to normal (stable) operation.

[0233] (8) Another aspect of the refrigerator disclosed herein is any one of the refrigerators described in (1) to (7) above, comprising: a heat recovery heat exchanger (heat recovery heat exchanger 15) which uses refrigerant in the cooling section to cool the refrigerant in the high-pressure pipeline after cooling the object being cooled; a buffer pipeline (buffer pipeline 26) one end of which is connected to a third connection (third connection S3) provided between the heat recovery heat exchanger and the expander in the high-pressure pipeline, and the other end of which is connected to a fourth connection (fourth connection S4) provided between the expander and the cooling section in the low-pressure pipeline; and a buffer tank (buffer tank 27) provided in the buffer pipeline, capable of storing refrigerant sent from the high-pressure pipeline. The system includes: a refrigerant; a high-pressure side buffer valve (first on / off valve 28), which is located between the buffer tank and the third connection in the buffer pipeline; a low-pressure side buffer valve (second on / off valve 29), which is located between the buffer tank and the fourth connection in the buffer pipeline; a first pressure sensor (first pressure sensor 36), which is used to detect the pressure of the refrigerant between the first connection and the third connection in the high-pressure pipeline; a second pressure sensor (second pressure sensor 37), which is used to detect the internal pressure of the buffer tank; and a controller, which is used to control the opening degree of the high-pressure side buffer valve and the low-pressure side buffer valve according to the detection results of the first pressure sensor and the second pressure sensor.

[0234] In the refrigeration unit described above (8), during the period from startup to pre-cooling operation, if the first pressure sensor and the second pressure sensor detect that the refrigerant pressure in the high-pressure pipeline is greater than a preset value than the pressure in the buffer tank, the high-pressure side buffer valve is opened, and the refrigerant can be recovered to the buffer tank by utilizing the pressure difference.

[0235] Therefore, it is possible to more effectively suppress excessive motor load and fluctuations.

[0236] (9) A method for operating a refrigeration machine during precooling according to one aspect of this disclosure is a method for operating the refrigeration machine during the initial operation period from startup to the completion of precooling, said refrigeration machine comprising: an integrated expander compressor including a compressor for compressing refrigerant and an expander connected to the compressor via a rotating shaft capable of being driven by an electric motor, and used to expand the refrigerant compressed by the compressor; a cooling section that uses the refrigerant expanded in the expander to cool the object being cooled; and a refrigerant circulation line including a low-pressure line from the expander through the cooling section to a lower-level compressor, and from... The system includes: a medium-pressure line from the low-pressure compressor to the high-pressure compressor, and a high-pressure line from the high-pressure compressor to the expander, for circulating refrigerant; a bypass line, one end of which is connected to a first connection on the high-pressure line and the other end of which is connected to a second connection on the low-pressure line; a bypass valve, located on the bypass line, for adjusting the flow rate of refrigerant in the bypass line by adjusting its opening; and a temperature sensor for detecting the temperature of the refrigerant flowing between the first connection and the expander in the high-pressure line, or the temperature of the refrigerant between the cooling section and the expander in the low-pressure line.

[0237] The method includes: a controller that controls the opening of a bypass valve and the rotational speed of a rotating shaft based on the detection results of a temperature sensor; an operation method comprising: a start-up operation step in which the rotational speed of the rotating shaft is set to a preset speed lower than that during stable operation after the initial operation period, and the opening of the bypass valve is set to a preset opening; a bypass control operation step in which the controller controls the bypass valve opening in stages before the refrigerant temperature detected by the temperature sensor reaches a preset first target temperature; a non-bypass control operation step in which the bypass valve opening is set to 0% during the stage when the refrigerant temperature reaches the first target temperature, and the refrigerant is cooled before reaching a preset second target temperature from the first target temperature; and a cooling rate control step in which the controller controls the rotational speed in a way that keeps the rate of temperature decrease of the refrigerant constant during at least the bypass control operation step and the non-bypass control operation step.

[0238] In the pre-cooling operation method of the refrigeration unit described in (9) above, by controlling the opening of the bypass valve, a portion of the refrigerant compressed in the high-stage compressor is not supplied to the expander, and it can return to both the low-stage and high-stage compressors. Furthermore, by adjusting the opening degree of the bypass valve, the flow rate of refrigerant returning to the compressor and the flow rate of refrigerant flowing to the expander can be varied.

[0239] Therefore, during the initial operation period from startup to precooling completion, by appropriately changing the opening of the bypass valve according to the operating conditions, fluctuations can be avoided and the amount of refrigerant not used for cooling can be reduced, enabling efficient (high COP) operation without wasting power.

[0240] In addition, during the initial operation period from startup to precooling completion, in addition to controlling the opening of the bypass valve, the cooling rate is adjusted / corrected by controlling the speed of the refrigeration unit (compressor, expander) and kept constant, thereby enabling high-precision control of the refrigerant temperature.

[0241] Furthermore, by controlling the opening of the bypass valve and the bypass refrigerant flow rate based on the detection values ​​of the first or second temperature sensor located near the inlet and outlet of the expander, high-precision control can be achieved without complicating the device structure compared to detecting the refrigerant flow rate.

[0242] Therefore, refrigerant flow control can be used to avoid fluctuations without detecting the refrigerant flow rate, thus simplifying the device structure and improving safety. Furthermore, it enables pre-cooling of the compressor and expander operating at high speeds, achieving smooth pre-cooling operation.

[0243] That is, during initial operation, compared with existing technologies, it can appropriately suppress fluctuations, maintain a constant cooling rate to cool the refrigerant with high precision, and enable efficient operation control.

[0244] (10) Another method of operation of the refrigerator during precooling is the refrigerator operation method described in (9) above. In the bypass control operation process, the controller is used to control the bypass valve opening in stages before the temperature of the refrigerant detected by the temperature sensor reaches the preset first target temperature.

[0245] In the above-mentioned (10) method of operating the refrigeration machine during precooling, during the initial operation period from startup to precooling completion, in addition to controlling the opening degree of the bypass valve, the cooling speed is adjusted / corrected by controlling the speed of the refrigeration machine (compressor, expander). By keeping the cooling speed constant, the refrigerant temperature can be controlled with high precision.

[0246] Furthermore, by using the phased opening control of the bypass valve and the speed control of the chiller, the opening of the bypass valve can be set according to the temperature range of each step, and the speed can be controlled in such a way that the cooling rate becomes a preset constant value in each of the respective temperature ranges.

[0247] Therefore, it is possible to perform stable pre-cooling operation with minimal fluctuations in the speed and pressure of the refrigeration unit.

[0248] (11) Another method of operation of the refrigerator during precooling is the refrigerator operation method of (9) above. In the bypass control operation process, the controller is used to control the bypass valve opening by continuously reducing it before the temperature of the refrigerant detected by the temperature sensor reaches the preset first target temperature.

[0249] In the pre-cooling operation method of the refrigeration machine described in (11) above, during the initial operation period from startup until pre-cooling is completed, in addition to controlling the opening degree of the bypass valve, the cooling speed is adjusted / corrected by controlling the rotational speed of the refrigeration machine (compressor, expander). By keeping the cooling speed constant, the refrigerant temperature can be controlled with high precision.

[0250] Furthermore, by using continuous opening control of the bypass valve and speed control of the chiller, the opening of the bypass valve can be set according to the temperature range of each step, and the speed can be controlled in such a way that the cooling rate becomes a preset constant value in each distinguished temperature range.

[0251] Therefore, it is possible to perform stable pre-cooling operation with minimal fluctuations in the speed and pressure of the refrigeration unit.

[0252] (12) Another method of operation of the refrigerator during precooling is the operation method of any of (9) to (11) above, wherein the refrigerator includes: a heat exchanger for exchanging heat between a secondary refrigerant and a refrigerant that cools the object being cooled; and a secondary refrigerant temperature sensor for detecting the temperature of the secondary refrigerant. The operation method includes a formal cooling operation switching process, namely: when the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature, the controller controls the rotation speed based on the detection result of the secondary refrigerant temperature sensor.

[0253] In the pre-cooling operation method of the refrigeration machine described in (12) above, when the second target temperature is reached, the temperature detection point on the secondary refrigerant temperature sensor is switched from the temperature sensor, and the speed is controlled based on the detection result of the secondary refrigerant temperature sensor, so that the pre-cooling operation during the initial operation can be smoothly switched to normal (stable) operation.

[0254] Explanation of reference numerals in the attached figures

[0255] 1-Refrigeration unit; 2-Cooling section (secondary load heat exchanger); 7-Expander integrated compressor; 8-Refrigerant circulation pipeline; 9-First motor; 10-Integrated compressor; 11-Second motor; 12-First heat exchanger; 13-Second heat exchanger; 14-Third heat exchanger; 15-Heat recovery heat exchanger (regenerating heat exchanger); 16-Cooling object side circulation pipeline; 20-Superconducting equipment (cooling object); 25-Buffer pipeline section; 26-Buffer pipeline; 27-Buffer tank; 28-First on / off valve (high pressure side buffer valve); 29-Second on / off valve (low pressure side buffer valve); 30-Bypass pipeline section; 31-Bypass pipeline; 32-Third on / off valve (bypass) 33-First temperature sensor (temperature sensor); 34-Second temperature sensor (temperature sensor); 35-Third temperature sensor (secondary refrigerant temperature sensor); 36-First pressure sensor; 37-Second pressure sensor; 41-Third pressure sensor; 38-First power meter; 39-Second power meter; 40-Controller (control device); C1-Low-stage compressor; C2-Medium-stage compressor; C3-High-stage compressor; T-Expander; R1-Refrigerant; R2-Refrigerant for cooling object (liquid nitrogen, secondary refrigerant, cooling object); S1-First connection part; S2-Second connection part; S3-Third connection part; S4-Fourth connection part; w-Cooling water.

Claims

1. A refrigeration unit, comprising: A low-level compressor used to compress refrigerant; An integrated expander compressor includes an advanced compressor for further compressing the refrigerant and an expander connected to the advanced compressor via a rotating shaft that can be driven by an electric motor, and for expanding the refrigerant compressed by the advanced compressor. The cooling section uses the refrigerant expanded in the expander to cool the object being cooled. A refrigerant circulation line includes a low-pressure line from the expander via the cooling section to the low-level compressor, a medium-pressure line from the low-level compressor to the high-level compressor, and a high-pressure line from the high-level compressor to the expander, for circulating the refrigerant; A bypass pipeline, one end of which is connected to a first connection part provided in the high-pressure pipeline, and the other end of which is connected to a second connection part provided in the low-pressure pipeline; A bypass valve, which is provided in the bypass line, can adjust the flow rate of the refrigerant flowing in the bypass line by adjusting its opening degree; A heat recovery heat exchanger is installed in the high-pressure pipeline and uses the refrigerant in the low-pressure pipeline after passing through the cooling section to cool the refrigerant flowing in the high-pressure pipeline. A temperature sensor for detecting the temperature of the refrigerant flowing between the heat recovery heat exchanger and the expander in the high-pressure pipeline; as well as The controller, based on the detection results of the temperature sensor, controls the opening degree of the bypass valve and the rotational speed of the rotating shaft. The controller performs the following control: during the initial operation of the refrigerator from startup to the completion of precooling operation, the bypass valve is controlled to reduce its opening in stages or continuously before the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature, and the rotation speed is controlled to keep the rate of decrease of the temperature of the refrigerant detected by the temperature sensor constant.

2. A refrigeration unit, comprising: A low-level compressor used to compress refrigerant; An integrated expander compressor includes an advanced compressor for further compressing the refrigerant and an expander connected to the advanced compressor via a rotating shaft that can be driven by an electric motor, and for expanding the refrigerant compressed by the advanced compressor. The cooling section uses the refrigerant expanded in the expander to cool the object being cooled. A refrigerant circulation line includes a low-pressure line from the expander via the cooling section to the low-level compressor, a medium-pressure line from the low-level compressor to the high-level compressor, and a high-pressure line from the high-level compressor to the expander, for circulating the refrigerant; A bypass pipeline, one end of which is connected to a first connection part provided in the high-pressure pipeline, and the other end of which is connected to a second connection part provided in the low-pressure pipeline; A bypass valve, which is provided in the bypass line, can adjust the flow rate of the refrigerant flowing in the bypass line by adjusting its opening degree; A temperature sensor is used to detect the temperature of the refrigerant between the cooling section and the expander in the low-pressure pipeline; as well as The controller, based on the detection results of the temperature sensor, controls the opening degree of the bypass valve and the rotational speed of the rotating shaft. The controller performs the following control: during the initial operation of the refrigerator from startup to the completion of precooling operation, the bypass valve is controlled to reduce its opening in stages or continuously before the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature, and the rotation speed is controlled to keep the rate of decrease of the temperature of the refrigerant detected by the temperature sensor constant.

3. The refrigeration unit according to claim 1 or 2, characterized in that, The controller performs the following control operations: when the temperature of the refrigerant detected by the temperature sensor reaches the first target temperature, the bypass valve is controlled such that the opening degree is 0%; the opening degree is maintained at 0% until the temperature of the refrigerant detected by the temperature sensor is lower than the first target temperature and reaches a second target temperature set to be lower than the first target temperature; and the rotational speed is controlled such that the rate of decrease of the temperature of the refrigerant detected by the temperature sensor remains constant.

4. The refrigeration machine according to claim 3, characterized in that, have: A heat exchanger for exchanging heat between a secondary refrigerant used to cool the object being cooled and the refrigerant itself; and A secondary refrigerant temperature sensor, used to detect the temperature of the secondary refrigerant. If the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature, the controller controls the rotation speed based on the detection result of the secondary refrigerant temperature sensor.

5. The refrigeration unit according to claim 1 or 2, characterized in that, have: A heat recovery heat exchanger that uses the refrigerant used to cool the object being cooled in the cooling section to cool the refrigerant in the high-pressure pipeline; A buffer line, one end of which is connected to a third connection between the heat recovery heat exchanger and the high-pressure compressor in the high-pressure line, and the other end of which is connected to a fourth connection between the low-pressure compressor and the heat recovery heat exchanger in the low-pressure line. A buffer tank, which is disposed in the buffer pipeline, is capable of storing the refrigerant delivered from the high-pressure pipeline; A high-pressure side buffer valve is disposed between the buffer tank and the third connection part in the buffer pipeline; A low-pressure side buffer valve is disposed between the buffer tank and the fourth connection part in the buffer pipeline; A first pressure sensor is used to detect the pressure of the refrigerant between the first connection and the third connection in the high-pressure pipeline; The second pressure sensor is used to detect the internal pressure of the buffer tank; as well as The controller is used to control the opening degree of the high-pressure side buffer valve and the low-pressure side buffer valve based on the detection results of the first pressure sensor and the second pressure sensor.

6. A method for operating a refrigeration machine during precooling, comprising the method for operating the refrigeration machine during the initial operation period from startup to completion of precooling, wherein the refrigeration machine comprises: A low-level compressor used to compress refrigerant; An integrated expander compressor includes an advanced compressor for further compressing the refrigerant and an expander connected to the advanced compressor via a rotating shaft that can be driven by an electric motor, and for expanding the refrigerant compressed by the advanced compressor. The cooling section uses the refrigerant expanded in the expander to cool the object being cooled. A refrigerant circulation line includes: a low-pressure line from the expander via the cooling section to the low-level compressor, a medium-pressure line from the low-level compressor to the high-level compressor, and a high-pressure line from the high-level compressor to the expander, for circulating the refrigerant; A bypass pipeline, one end of which is connected to a first connection part provided in the high-pressure pipeline, and the other end of which is connected to a second connection part provided in the low-pressure pipeline; A bypass valve, which is provided in the bypass line, can adjust the flow rate of the refrigerant flowing in the bypass line by adjusting its opening degree; A temperature sensor is used to detect the temperature of the refrigerant flowing between the first connection and the expander in the high-pressure pipeline, or the temperature of the refrigerant between the cooling section and the expander in the low-pressure pipeline; as well as The controller, based on the detection results of the temperature sensor, controls the opening degree of the bypass valve and the rotational speed of the rotating shaft. The operation method includes: The start-up process involves setting the rotational speed of the rotating shaft to a preset speed lower than the stable operating speed after the initial operation period, and setting the opening of the bypass valve to a preset opening to begin operation. The bypass control operation process utilizes the controller to reduce the opening of the bypass valve before the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature; In the bypass control operation process, when the refrigerant temperature reaches the first target temperature, the opening degree of the bypass valve is set to 0%, and the refrigerant is cooled before it reaches the preset second target temperature from the first target temperature. as well as The cooling rate control process utilizes the controller to control the rotational speed in such a way that the rate at which the temperature of the refrigerant decreases remains constant during at least the bypass control operation process, in both the bypass control operation process and the non-bypass control operation process.

7. The operating method of the refrigeration machine during precooling according to claim 6, characterized in that, In the bypass control operation, the controller is used to control the bypass valve opening in stages before the refrigerant temperature detected by the temperature sensor reaches a preset first target temperature.

8. The method for operating a refrigeration unit during pre-cooling according to claim 6, characterized in that, In the bypass control operation, the controller is used to continuously reduce the opening of the bypass valve before the temperature of the refrigerant detected by the temperature sensor reaches a preset first target temperature.

9. The method of operating the refrigeration machine during precooling according to any one of claims 6 to 8, characterized in that, The refrigeration unit includes: A heat exchanger for exchanging heat between a secondary refrigerant used to cool the object being cooled and the refrigerant itself; and A secondary refrigerant temperature sensor, used to detect the temperature of the secondary refrigerant. The operation method includes a formal cooling operation switching procedure, namely: when the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature, the controller controls the rotation speed based on the detection result of the secondary refrigerant temperature sensor.

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