CN116529541A

CN116529541A - Refrigerator and method for operating refrigerator during precooling

Info

Publication number: CN116529541A
Application number: CN202180080138.5A
Authority: CN
Inventors: 下田将大; 植田翔太; 町田明登; 工藤瑞生; 矢口广晴
Original assignee: Mayekawa Manufacturing Co
Current assignee: Mayekawa Manufacturing Co
Priority date: 2020-12-01
Filing date: 2021-11-25
Publication date: 2023-08-01
Also published as: JP2022087598A; US20230417465A1; WO2022118729A1

Abstract

The device is provided with: the low-stage compressor (C1) and the high-stage compressor (C3), that is, at least two compressors, an expander (T), a cooling unit (2) for cooling a cooling object (R2) by using a refrigerant (R1) expanded in the expander (T), a refrigerant circulation line (8) for circulating the refrigerant, a bypass line (31) connected to a high-pressure line and a low-pressure line of the refrigerant circulation line (8), a bypass valve (32), a first temperature sensor (33) for detecting the temperature of the refrigerant (R1) on the inlet side of the expander (T) or a second temperature sensor (34) for detecting the temperature of the refrigerant (R1) on the outlet side of the expander (T), and a controller (40), wherein the controller (40) controls the opening degree of the bypass valve (32) and the rotation speed of the refrigerator (1) based on the detection result of the first temperature sensor (33) or the second temperature sensor (34).

Description

Refrigerator and method for operating refrigerator during precooling

Technical Field

The present disclosure relates to a refrigerator and a method of operating the refrigerator during precooling.

Background

The use of the brayton cycle for a refrigeration cycle can realize extremely low temperatures, and is attracting great attention as a refrigerator that can be used for cooling superconducting devices, liquefying various gases, replacing liquid nitrogen, and the like, for example, in various technical fields such as medical treatment and foods.

As an example of such a refrigerator, there is a refrigerator comprising: a cooling unit that cools a cooling object by heat exchange with a refrigerant, a low-stage compressor that compresses the refrigerant, an expander-integrated compressor that integrates a medium-stage compressor for compressing the refrigerant and an expander for expanding the refrigerant, and a high-stage compressor that further compresses the refrigerant, and a refrigerant circulation line that feeds and circulates the refrigerant to the plurality of compressors, the expander, the cooling unit, and the like (for example, refer to patent document 1). In addition, the following structures may be used: the expander-integrated compressor is not an integrated intermediate-stage compressor and expander, but an integrated advanced compressor and expander.

In the refrigerator configured as described above, for example, the refrigerant subjected to the first-stage compression in the low-stage compressor rotationally driven by the motor is cooled in the heat exchanger, and then sent to the intermediate-stage compressor, and is further compressed in the intermediate-stage compressor rotationally driven by the motor. The refrigerant, which has been subjected to the two-stage compression in the intermediate-stage compressor, is cooled in the heat exchanger, and then is further compressed in the high-stage compressor which is rotationally driven by the motor. The refrigerant having undergone three-stage compression in the high-stage compressor is cooled in the heat exchanger, is further cooled in the heat-and-heat-recovery heat exchanger, is sent to the expander, and is subjected to adiabatic expansion by the expander to be low-pressure and low-temperature.

The low-pressure low-temperature refrigerant is sent to a cooling unit (heat exchanger) to cool a cooling object. Thereafter, the refrigerant is sent to the heat-recovery heat exchanger, where the refrigerant sent to the expander is cooled, and then returned to the low-stage compressor.

In addition, some of such refrigerators are provided with a buffer line portion composed of: a buffer line connected to a high-pressure line extending from the high-stage compressor to the expander and a low-pressure line extending from the expander to the low-stage compressor in the refrigerant circulation line; a buffer tank arranged on the buffer pipeline; and valves (on-off valves) provided on the high-pressure line side and the low-pressure line side (inlet side and outlet side) of the buffer tank, respectively (for example, refer to patent document 1).

In these refrigerators, when a thermal load fluctuation of a cooling target is detected by a thermal load detection means, the opening degree of front and rear valves of a buffer tank is controlled to control the flow rate of refrigerant in a refrigerant line, thereby adjusting the cooling capacity.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. WO2016/178272

Disclosure of Invention

First, the technical problem to be solved

In the conventional refrigeration machine including the compressor-integrated expander, the refrigerant pressure in the system of the refrigerant circulation line increases due to the increase in the refrigerant temperature in the stopped state of the refrigeration machine, and in this state, the refrigerant pressures in the high-pressure line of the refrigerant circulation line to the high-stage compressor and the expander and in the low-pressure line from the expander to the low-stage compressor are equalized (the high-pressure and the low-pressure are equalized).

Therefore, in the pressure equalizing state, when the pressure on the low-pressure line side is higher than in the normal operation and the refrigerator is started to operate in a state where the refrigerant pressure is high, the pressure on the high-pressure line side tends to rise excessively, and in particular, the compressor-integrated expander is configured to include a motor drive, and therefore, there are cases where: the motor load increases and the operating speed needs to be limited according to the motor capacity.

In addition, when the refrigerator is started up in a state where the refrigerant pressure is high, the minimum cross section of the circulation path is present in the flow path near the inlet of the expander having the highest density under the rated operation condition, and therefore the suction temperature of the expander is liable to rise (the refrigerant density is liable to decrease) at the time of pre-cooling. This may lead to: the inlet of the expander, in which the refrigerant flow amount at this portion becomes small, fluctuates due to the choke phenomenon. This fluctuation in the starting operation is also likely to occur when the compressor-integrated expander driven by the motor is provided and the pressure on the high-pressure line side is excessively increased.

Accordingly, the above-described conventional refrigerator has room for improvement in terms of: in the initial operation period from the start-up time to the pre-cooling operation time, the high-pressure is suppressed from greatly rising from the steady operation pressure, and the occurrence of excessive load and fluctuation of the motor is suppressed, so that the pre-cooling operation with high operation efficiency can be performed.

The present disclosure has been made in view of the above-described circumstances, and an object thereof is to provide a refrigerator and an operation method for the refrigerator during pre-cooling, which can suppress a large increase in high-pressure from a steady operation pressure during an initial operation from a start-up time to a pre-cooling operation, can suppress occurrence of excessive load and fluctuation of a motor, and can improve operation efficiency (cooling efficiency of a refrigerant and a cooling object).

(II) technical scheme

One embodiment of the refrigerator of the present disclosure includes: an expander-integrated compressor including a compressor that compresses a refrigerant, and an expander that is coupled to the compressor via a rotation shaft that can be driven by a motor and that expands the refrigerant compressed by the compressor; a cooling unit that cools a cooling object by using the refrigerant expanded in the expander; a refrigerant circulation line including a low pressure line from the expander to the low-stage compressor via the cooling unit, a medium pressure line from the low-stage compressor to the high-stage compressor, and a high pressure line from the high-stage compressor to the expander, for circulating the refrigerant; a bypass line having one end connected to a first connection portion provided to the high-pressure line and the other end connected to a second connection portion provided to the low-pressure line; and a bypass valve provided in the bypass line, wherein the flow rate of the refrigerant flowing through the bypass line can be adjusted by adjusting the opening degree.

Further, it is preferable that the buffer tank is also provided for recovering the refrigerant gas in the high-pressure line.

(III) beneficial effects

According to the refrigerator (and the method of operating the refrigerator during pre-cooling) of the present disclosure, the buffer tank and the bypass line can be used to effectively suppress a significant increase in high-pressure from the steady operation pressure during the initial operation from the start-up time to the pre-cooling operation. Further, instead of detecting the flow rate of the refrigerant, the opening degree and the rotation speed of the bypass line may be controlled based on the temperature detection. In this way, during the initial operation from the start-up time to the pre-cooling operation, the occurrence of excessive load and hunting of the motor can be suppressed, stable pre-cooling operation can be performed, and the operation efficiency (cooling efficiency of the refrigerant and the cooling target) can be improved.

Drawings

Fig. 1 is a diagram showing an example of a refrigerator according to an embodiment of the present disclosure.

Fig. 2 is a flowchart showing an example of an operation method during an initial operation from a start-up time to a pre-cooling operation (to a completion of the pre-cooling operation) in the operation method during pre-cooling of the refrigerator according to the embodiment of the present disclosure.

Fig. 3 is a flowchart showing an example of the control operation of the buffer line portion during the initial operation from the start-up time to the pre-cooling operation (the completion of the pre-cooling operation) in the pre-cooling operation method of the refrigerator according to the embodiment of the present disclosure.

Fig. 4 is a diagram showing an example of a relationship between an operation time and a refrigerant temperature and a relationship between an operation time and an opening degree of a bypass valve in a case where the refrigerator and the method of operating the refrigerator during precooling according to the embodiment of the present disclosure are used.

Fig. 5 is a diagram showing a bypass control operation from the start-up time to the initial operation time at the time of the pre-cooling operation in the method for operating the refrigerator at the time of pre-cooling according to the embodiment of the present disclosure, and is a diagram showing an example of a control flow in the case of performing the stepwise (stepwise) control.

Fig. 6 is a diagram showing an example of a relationship between a refrigerant temperature and an opening degree of a bypass valve in a case where bypass control operation is performed by stepwise (stepwise) control in the operation method at the time of precooling of the refrigerator according to the embodiment of the present disclosure.

Fig. 7 is a diagram showing a bypass control operation from the start-up time to the initial operation time at the time of the pre-cooling operation in the method for operating the refrigerator at the time of pre-cooling according to the embodiment of the present disclosure, and is a diagram showing an example of a control flow in the case of performing continuous (proportional) control.

Fig. 8 is a diagram showing an example of a relationship between the refrigerant temperature and the opening degree of the bypass valve in the case of performing the bypass control operation by continuous (proportional) control in the operation method at the time of precooling of the refrigerator according to the embodiment of the present disclosure.

Fig. 9 is a diagram showing an example of a state of pressure fluctuation of the high-pressure line, the low-pressure line, and the buffer tank in an initial operation period from a start-up time to a pre-cooling operation time of the refrigerator of the present disclosure.

Detailed Description

A refrigerator and a method of operating the refrigerator during precooling according to some embodiments of the present disclosure will be described below with reference to fig. 1 to 9.

However, the dimensions, materials, shapes, relative arrangements, and the like of the constituent members described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention to these examples.

For example, the expression "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial", etc. means a relative or absolute arrangement, and means not only a strict arrangement but also a state in which there is a tolerance or a state in which there is a relative displacement in an angle or distance that can achieve the same degree of function.

For example, the expression "identical", "equal", and "homogeneous" and the like means that things are equal states, and not only a strictly equal state, but also a state having a tolerance or a difference in the degree to which the same function can be obtained.

For example, the expression indicating the shape such as a quadrangular shape or a cylindrical shape indicates not only the shape such as a quadrangular shape or a cylindrical shape in a geometrically strict sense, but also the shape including the concave-convex portion, the chamfer portion, and the like within a range where the same effect can be obtained.

On the other hand, the expression "provided with", "having", "including", or "having" one component is not an exclusive expression excluding the presence of other components.

The present disclosure relates to a refrigerator and an operation method at the time of precooling of the refrigerator, which can realize extremely low temperatures by using the brayton cycle for the refrigeration cycle, and more particularly, to a refrigerator and an operation method at the time of precooling of the refrigerator, which can perform appropriate operation control during an initial operation from the time of starting to the time of precooling operation (until the completion of precooling).

(refrigerator)

Specifically, the refrigerator 1 of the present embodiment is configured to include, for example, as shown in fig. 1: a cooling unit (secondary side load heat exchanger) 2 for cooling a cooling target (in this embodiment, the cooling target side refrigerant R2) by heat exchange with the refrigerant R1, a low-stage compressor C1 for compressing the refrigerant R1, a middle-stage compressor C2 for further compressing the refrigerant R1, an expander-integrated compressor 7 integrating a high-stage compressor C3 for further compressing the refrigerant R1 and an expander T for expanding the refrigerant R1, and a refrigerant circulation line 8 for sequentially feeding and circulating the refrigerant R1 to the low-stage compressor C1, the middle-stage compressor C2, the high-stage compressor C3, the expander T, the cooling unit 2, and the like.

The expander-integrated compressor 7 includes, in addition to the high-stage compressor C3 and the expander T, a first motor 9, and both ends of an output shaft of the first motor 9 are connected to the high-stage compressor C3 and the expander T, respectively, and the first motor 9 is configured to rotationally drive the output shaft, the high-stage compressor C3, and the expander T about an axis.

In the refrigerator 1 of the present embodiment, the low-stage compressor C1 and the intermediate-stage compressor C2 are also integrally formed, and the integral compressor 10 includes a second motor 11, both ends of an output shaft of the second motor 11 are connected to the low-stage compressor C1 and the intermediate-stage compressor C2, respectively, and the second motor 11 is configured to rotationally drive the output shaft and the low-stage compressor C1 and the intermediate-stage compressor C2 about an axis.

In the refrigerator 1 of the present embodiment, the low-stage compressor C1, the intermediate-stage compressor C2, the high-stage compressor C3, and the expander T are connected in series through the refrigerant circulation line 8.

The refrigerant circulation line 8 is a low-pressure line from the expander T to the low-stage compressor C1, and a high-pressure line from the high-stage compressor C3 to the expander T. The intermediate-pressure line is set from the low-stage compressor C1 to the high-stage compressor C3.

A first heat exchanger 12 for cooling the refrigerant discharged from the low-stage compressor C1, a second heat exchanger 13 for cooling the refrigerant R1 discharged from the intermediate-stage compressor C2, and a third heat exchanger 14 for cooling the refrigerant discharged from the high-stage compressor C3 are disposed in the first intermediate-pressure line, respectively. A heat recovery heat exchanger (regeneration heat exchanger) 15 is provided between the third heat exchanger 14 of the high-pressure line and the expander T.

The first heat exchanger 12, the second heat exchanger 13, and the third heat exchanger 14 cool the refrigerant R1 using, for example, cooling water w or the like. The heat-recovery heat exchanger 15 cools the refrigerant R1 in the high-pressure line by the refrigerant R1 after the cooling unit 2 has cooled the cooling target R2.

A cooling unit 2 is provided between the expander T and the heat exchanger 15 for heat recovery in the low-pressure line. In the present embodiment, the cooling line is a part of the low-pressure line.

In the present embodiment, the cooling target to be cooled by the refrigerant R1 sent to the heat exchanger of the cooling unit 2 is the cooling target refrigerant (secondary refrigerant) R2, and the cooling target refrigerant R2 circulates through the cooling target side circulation line 16 and is sent to the cooling unit 2 in order to be cooled to a predetermined temperature.

In the refrigerator 1 of the present embodiment configured as described above, the refrigerant that has undergone the first-stage compression in the low-stage compressor C1 that is rotationally driven by the second motor 11 is cooled in the first heat exchanger 12, is then sent to the intermediate-stage compressor C2, and is further compressed in the intermediate-stage compressor C2 that is rotationally driven by the second motor 11. The refrigerant R1 subjected to the two-stage compression in the intermediate-stage compressor C2 is cooled in the second heat exchanger 13, and is further compressed in the high-stage compressor C3 rotationally driven by the first motor 9. The refrigerant R1 subjected to three-stage compression in the high-stage compressor C3 is cooled in the third heat exchanger 14, is further cooled in the heat-and-heat recovery heat exchanger 15, is sent to the expander T, and is adiabatically expanded by the expander T to generate cold and heat. That is, the refrigerant itself undergoes adiabatic expansion to be at a low pressure and a low temperature. The high-stage compressor C3 and the expander T are also connected to both ends of the output shaft of the first electric motor 9, which is a common power source, so that the power recovered by the expander T contributes to the compression power of the high-stage compressor C3, thereby improving efficiency.

The low-pressure low-temperature refrigerant R1 is sent to the heat exchanger of the cooling unit 2, and the refrigerant R2 for cooling that flows through the cooling-target-side circulation line 16 is cooled to a predetermined temperature by the refrigerant. Thereafter, the refrigerant R1 is sent to the heat-recovery heat exchanger 15, where the refrigerant R1 sent to the expander T is cooled, and then returned to the low-stage compressor C1.

In the refrigerator 1, examples of the refrigerant R1 include helium, neon, hydrogen, nitrogen, air, and hydrocarbon. The temperature of the refrigerant R1 may be set to an extremely low temperature of about-190 to-200 ℃ (83.15 to 73.15K) on the inlet side of the expander T and about-210 to-220 ℃ (63.15 to 53.15K) on the outlet side, for example.

Thus, the refrigerator 1 of the present embodiment can be used for cooling superconducting equipment, liquefying various gases, substituting liquid nitrogen, and the like, for example.

Specifically, as shown in fig. 1, as an example of a cooling target to be cooled by heat exchange with the refrigerant R1 in the cooling unit 2, liquid nitrogen (cooling target refrigerant R2) for cooling the superconducting device 20 such as a superconducting cable is given.

In this case, for example, a cooling target side circulation line (liquid nitrogen circulation line) 16 is provided, the cooling target side circulation line (liquid nitrogen circulation line) 16 circulates between the cooling unit 2, the superconducting device 20, and the tank 21, and a circulation pump 22 is provided to the cooling target side circulation line 16 to circulate the liquid nitrogen R2 cooled to a very low temperature in the cooling unit 2 to the superconducting device 20.

On the other hand, in the refrigerator 1, as described above, in the refrigerator stopped state, the refrigerant pressure increases due to the refrigerant temperature increase, and in this state, the high and low pressures are equalized. Therefore, when the refrigerator 1 is started in a state where the refrigerant pressure is high, the refrigerant pressure in the high-pressure line increases due to the high refrigerant pressure in the low-pressure line, and the load on the motor (11 (9)) increases, and the operation rotation speed may need to be limited depending on the motor capacity.

In addition, it is also considered that: when the refrigerator 1 is started in a state where the refrigerant pressure is high, a choke phenomenon occurs at the inlet of the expander T, and the compressor (C1, C2, C3) fluctuates.

(control flow of precooling Process)

In contrast, the precooling operation process (operation method during precooling of the refrigerator) of the refrigerator 1 of the present embodiment is configured by the refrigerator precooling operation control, bypass control, and buffer tank refrigerant recovery control as shown in fig. 1 and 2.

First, in the refrigerator pre-cooling operation control, the operation control of the refrigerator 1 from the start-up to the completion of pre-cooling is performed, and the control rotational speed control is performed based on the target temperature setting (T1, T2) and the measured temperature (T) of the inlet or outlet of the expander T so that the cooling rate is kept constant.

The opening degree of the opening/closing valve 32 of the bypass line 31 is controlled in accordance with the measured temperature (T) in the bypass control, including the stepwise (step control) and the continuous control. When the refrigerant R1 is cooled before reaching the target set temperature (T1), the on-off valve 32 is closed, and the bypass-free control operation is performed.

In addition, in the buffer tank refrigerant recovery control, the refrigerant R1 is recovered from the high-pressure line to the buffer tank 27, the load of the pre-cooling operation of the refrigerator 1 is reduced, and when the pressure difference becomes equal to or greater than the set pressure difference, the on-off valve 28 is opened, and the refrigerant R1 flows into the buffer tank 27 from the high-pressure line.

These controls are a combination of bypass control and buffer tank refrigerant recovery control performed in parallel with the chiller pre-cooling operation control, and are constantly monitored.

The control content is described in more detail below.

(buffer line portion)

The refrigerator 1 of the present embodiment includes, first, a buffer pipe portion 25.

The buffer pipe portion 25 includes: a buffer line 26 having one end connected to a third connection portion S3 between the third heat exchanger 14 and the heat-and-heat recovery heat exchanger 15 of the high-pressure line and the other end connected to a fourth connection portion S4 between the heat-and-heat recovery heat exchanger 15 and the low-stage compressor C1 of the low-pressure line; a buffer tank 27 provided in the buffer line 26 for temporarily storing the refrigerant R1; a first opening/closing valve (high-pressure side buffer valve) 28 provided on the inlet side of the buffer tank 27 (high-pressure line side between the buffer tank 27 and the third connection portion S3); and a second opening/closing valve (low-pressure side buffer valve) 29 provided on the outlet side of the buffer tank 27 (low-pressure line side between the buffer tank 27 and the fourth connecting portion S4).

Then, the first opening/closing valve 28 on the inlet side is opened, and the refrigerant R1 is temporarily fed from the high-pressure line to the buffer tank 27 by the pressure difference (differential pressure) according to the opening degree of the first opening/closing valve 28, whereby the amount (flow rate) of the refrigerant R1 flowing through the refrigerant circulation line 8 can be adjusted. Further, by closing the first opening/closing valve 28 and opening the outlet-side second opening/closing valve 29 and returning the refrigerant R1 to the low-pressure line from the buffer tank 27 by the pressure difference according to the opening degree of the second opening/closing valve 29, the amount of the refrigerant R1 flowing in the refrigerant circulation line 8 can be regulated.

(bypass line portion)

The refrigerator 1 of the present embodiment includes a bypass line portion 30.

The bypass line portion 30 includes: a bypass line 31 having one end connected to the first connection portion S1 between the third heat exchanger 14 and the third connection portion S3 of the high-pressure line and the other end connected to the second connection portion S2 between the fourth connection portion S4 and the low-stage compressor C1 of the low-pressure line; and a third opening/closing valve (bypass valve) 32 provided in the bypass line 31.

The connection between the buffer line portion 25 and the high-pressure line and the low-pressure line of the bypass line portion 30 may be changed in position.

(refrigerant State/Power State detection Unit)

The refrigerant circulation line 8 is provided with a first temperature sensor 33 for detecting the temperature of the refrigerant R1 flowing therein, between the high-pressure line heat recovery heat exchanger 15 and the expander T.

A second temperature sensor 34 that detects the temperature of the refrigerant R1 flowing therethrough is provided between the expander T and the cooling unit 2 of the cooling line.

A third temperature sensor (secondary refrigerant temperature sensor) 35 is provided in the cooling target side circulation line 16, and detects the temperature of the liquid nitrogen R2, which is the cooling target cooled by the cooling unit 2.

A first pressure sensor 36 for detecting the pressure of the refrigerant R1 in the high-pressure line is provided in the high-pressure line of the refrigerant circulation line 8, for example, between the third connection portion S3 and the first connection portion S1.

The buffer tank 27 is provided with a second pressure sensor 37 for detecting the internal pressure of the buffer tank 27.

The expander-integrated compressor 7 is provided with a first power meter 38 for detecting the driving state of the first motor 9 and the rotational speeds of the rotary shaft, the high-stage compressor C3, and the expander T.

The integrated compressor 10 is provided with a second power meter 39 for detecting the driving state of the second motor and the rotational speeds of the rotary shaft, the low-stage compressor C1, and the intermediate-stage compressor C2.

The refrigerator 1 of the present embodiment further includes a controller (control device) 40 that 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 dynamometer 38, and the second dynamometer 39, and controls the driving of the first motor 9 and the second motor 11 and the opening degree (opening/closing driving) of the first opening/closing valve 28, the second opening/closing valve 29, and the third opening/closing valve 32.

( Buffer tank refrigerant recovery control: operation control during initial operation using buffer pipe portion )

First, a precooling operation control for recovering the refrigerant using the buffer tank will be described.

Accordingly, the amount of the refrigerant R1 flowing into and out of the refrigerant circulation line 8 through the buffer line portion 25 can be controlled by adjusting the opening degree of the first opening/closing valve 28 and the second opening/closing valve 29 based on the controller 40. Preferably, the third on-off valve 32 including the bypass line portion 30 is an electric valve, and the first on-off valve 28 and the second on-off valve 29 are electric valves.

More specifically, in a state where the pressure in the system of the refrigerant circulation line 8 is high, when the refrigerator 1 (the motors 9 and 11) is operated, the compressor fluctuates, and it is difficult to increase the rotation speed.

In contrast, in the refrigerator 1 of the present embodiment, a buffer tank 27 is provided between the low-pressure line and the high-pressure line in order to increase the rotation speed of the refrigerator 1 at the time of starting, and the excess refrigerant R1 is recovered so as to prevent the discharge pressure of the refrigerator 1 from becoming equal to or higher than a certain pressure.

Accordingly, the controller 40 performs the opening/closing drive control and the opening degree adjustment of the first opening/closing 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 be caused to flow in by the refrigerant pressure difference between the high-pressure line and the buffer tank 27, and the excess refrigerant R1 can be recovered to the buffer tank 27 so as to prevent the discharge pressure of the refrigerator 1 from becoming equal to or higher than a predetermined pressure.

(control at the start-up time/at the start of the precooling operation)

As shown in fig. 1, 2 and 3, when the start-up/pre-cooling operation is started (Step 1) after the stop of the refrigerator 1, and when the refrigerant pressures in the high-pressure line and the low-pressure line are equalized at a high pressure as the refrigerator 1 is stopped, the recovery of the refrigerant into the buffer tank 27 is performed by the buffer line portion 25 based on the detection results (Step 3) of the first pressure sensor 36 and the second pressure sensor 37 (Step 2).

At this time, the controller 40 receives the detection results of the first pressure sensor 36 and the second pressure sensor 37, obtains the differential pressure between the high-pressure line and the refrigerant pressure in the buffer tank 27 (Step 3), and confirms whether or not the refrigerant pressure in the high-pressure line and the buffer tank 27 is equalized at a high pressure, and when the differential pressure between the refrigerant pressure is equal to or greater than a set value (threshold value) such as 10kPa (Step 4), for example, the first on-off valve 28 is controlled to be opened (Step 5), and the refrigerant recovery is performed by the buffer line portion 25 (Step 6).

That is, when the differential pressure between the pressure of the buffer tank 27 and the refrigerant pressure of the high-pressure line is obtained and exceeds a preset value (10 kPa, etc.), the controller 40 controls the opening of the first opening/closing valve 28 in a state where the second opening/closing valve 29 is closed (Step 5).

The opening control of the first opening/closing valve 28 is performed (Step 5), and the refrigerant R1 is delivered to the buffer tank 27 by the pressure difference between the buffer tank 27 and the high-pressure line, and temporarily stored (Step 6), so that the flow rate (pressure) of the refrigerant R1 flowing in the brayton cycle is reduced.

This can prevent overload operation (excessive motor loads of the first motor 9 and the second motor 11) due to a pressure increase in the refrigerant circulation line 8 in the initial stage of pre-cooling.

When the refrigerant R1 is fed to the buffer tank 27 and temporarily stored, the flow rate (pressure) of the refrigerant R1 flowing in the brayton cycle is reduced, and the difference in refrigerant pressure is lower than the set value (Step 7), the first opening/closing valve 28 is controlled to be closed (Step 8). In the above (Step 4), when the differential pressure of the refrigerant pressure is lower than the set value, the closed state of the first opening/closing valve 28 is maintained (Step 8).

(control during precooling operation)

As described above, when the differential pressure between the buffer tank 27 and the high-pressure line exceeds a set value such as 10kPa, the refrigerant is recovered from the high-pressure line to the buffer tank via the first opening/closing valve, and the differential pressure between the buffer tank and the high-pressure line becomes small (Step 6, step 7).

Therefore, when the differential pressure continues to exceed the set value at the start of the precooling operation after the stop of the refrigerator 1, the high-pressure refrigerant R1 is collected into the buffer tank 27, but if the pressure (discharge pressure) of the high-pressure line refrigerant R1 fluctuates greatly with the operation of the refrigerator 1, the differential pressure between the buffer tank 27 and the high-pressure line becomes small and this state is maintained. That is, the refrigerant R1 is not fed between the buffer tank 27 and the high-pressure line, and the refrigerant R1 in the refrigerant circulation line 8 is not increased or decreased, so that the pressure in the high-pressure line is maintained.

In contrast, when the pressure (discharge pressure) of the refrigerant R1 in the high-pressure line varies greatly in accordance with the operation of the refrigerator 1 at the start of the precooling operation after the stop of the refrigerator 1, the refrigerant R1 is continuously recovered from the high-pressure line to the capacity-adjusting buffer tank 27.

As described above, in the refrigerator 1 of the present embodiment, since the refrigerant circulation line 8 (refrigerant flow system) is of a closed structure, the excess refrigerant R1 can be stored in the buffer tank 27 at normal temperature. That is, during the pre-cooling operation, the amount of refrigerant R1 recovered can be automatically adjusted by performing the opening/closing drive control of the first opening/closing valve 28 based on the detection results of the first pressure sensor 36 and the second pressure sensor 37 alone without measuring the flow rate, and the state can be maintained without generating excessive motor load.

Further, the following embodiments are shown: when the differential pressure of the refrigerant pressure is obtained from the pressure detection results (Step 3) to (Step 6), the controller 40 opens and controls the first on-off valve 28 when the differential pressure is equal to or higher than the set value (threshold value), and the buffer pipe portion 25 recovers the refrigerant.

On the other hand, as another example, when the differential pressure is changed and the pressure in the high-pressure line is equal to or higher than the set value (threshold value), the first opening/closing valve 28 may be controlled to be opened, and the buffer line portion 25 may be used to recover the refrigerant.

(control of transition to usual (steady) operation)

When the refrigerator 1 is started, the pressure of the refrigerant R1 on the high-pressure line side is temporarily increased, excess refrigerant is stored in the buffer tank 27, and as cooling proceeds, the pressure of the refrigerant R1 in the low-pressure line, the high-pressure line, and the entire device/system of the refrigerator 1 decreases, and the pressure approaches the pressure state at the time of normal operation. In other words, the pressures of the low-pressure line and the high-pressure line are each the pressures at the time of normal operation, and the operation is performed in a state where excessive motor load is not generated. At a stage of being lower than the buffer mechanism pressure set value, the first opening/closing valve 28 is closed (Step 8).

On the other hand, the refrigerant R1 has a higher density and a lower capacity when cooled to 100K or less from normal temperature, for example. Specifically, when the temperature of the refrigerant R1 in the equipment and piping from the heat-and-heat-recovery heat exchanger 15 to the expander T, from the expander T to the cooling unit 2, and from the cooling unit 2 to the heat-and-heat-recovery heat exchanger 15 is 100K or less, the density of the refrigerant R1 increases, and the capacity is insufficient. In contrast, in operation, the refrigerant temperature is in the vicinity of the normal temperature from the outlet of the low-pressure line heat-recovery heat exchanger 15 to the inlet of the high-pressure line heat-recovery heat exchanger 15 via the compressor, and therefore the refrigerant capacity of the refrigerant R1 is unchanged.

Therefore, it is necessary to maintain the amount of the decrease in the refrigerant capacity at the low temperature side, i.e., at the high pressure line side and at the cooling line side, in the system.

Therefore, the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment store the refrigerant R1 preferentially in the buffer tank 27. For example, during the initial operation from the start-up time to the pre-cooling operation (until the pre-cooling operation is completed) immediately after the start-up, the excess refrigerant R1 may be recovered to the buffer tank 27, and the first opening/closing valve 28 for refrigerant recovery may be opened under the condition that the pressure difference detected by the first pressure sensor 36 and the second pressure sensor 37 is equal to or greater than a preset set value such as 10 kPa.

In the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment, when the pressure difference (differential pressure) detected by the first pressure sensor 36 and the second pressure sensor 37 is equal to or greater than the set value (threshold value), the first opening/closing valve 28 is controlled to be opened, and the buffer line portion 25 is used to collect the refrigerant (see fig. 9 (a diagram showing an example of a state in which the pressures of the high-pressure line, the low-pressure line, and the buffer tank 27 are varied during the stepwise control of the bypass control operation)).

( Precooling operation control/bypass control of the refrigerator: operation control during initial operation using bypass line portion )

Next, since the refrigerant R1 needs to be cooled at a large temperature difference from normal temperature to 100K or less in the refrigerator 1, a throttle portion having a smallest cross section is provided near the inlet of the expander T having the highest density in the conventional art in the refrigerant circulation line 8.

Here, during the pre-cooling operation, the suction temperature tends to increase, in other words, the refrigerant density tends to decrease, and the refrigerant flow rate in the throttle portion having the smallest cross section near the inlet of the expander T tends to decrease, so that there is a possibility that the compressors C1, C2, and C3 may fluctuate. Therefore, in order to suppress the fluctuation during the pre-cooling operation, it is necessary to ensure a sufficient refrigerant flow rate.

In this case, the refrigerator 1 of the present embodiment includes a bypass line portion 30, and the bypass line portion 30 includes a bypass line 31 capable of returning the refrigerant R1 from the high-pressure line to the low-pressure line, and a third opening/closing valve 32 serving as a bypass valve.

Accordingly, the controller 40 controls the opening of the third opening/closing valve 32 so that a part of the refrigerant R1 compressed by the high-stage compressor C3 is not supplied to the expander T, but can be returned to the low-stage compressor C1 and the high-stage compressor C3 again. The opening degree of the third opening/closing valve 32 is adjusted by the controller 40, so that the flow rate of the refrigerant returned to the compressors C1, C2, and C3 can be adjusted.

Therefore, in the refrigerator 1 of the present embodiment, the opening degree of the third opening/closing valve 32 is appropriately changed in accordance with the operation state at the time of precooling, so that fluctuation is not caused, and the refrigerant R1 not used for cooling can be reduced, and an efficient (high COP: coefficient of Performance (coefficient of performance)) operation without wasting power can be performed.

Next, as shown in fig. 2 (fig. 5, 7, and 1), the operation method at the time of precooling of the refrigerator 1 and the refrigerator 1 according to the present embodiment controls the opening degree (Step 9) of the third opening/closing valve 32 according to the temperature condition of the refrigerant R1, and performs the precooling operation control including the refrigerator precooling operation control and the bypass control using the bypass line portion 30. The precooling operation control and the bypass control of the refrigerator are performed in parallel with the bypass control described above.

(control of precooling operation of refrigerator)

First, in the refrigerator pre-cooling operation control (Step 9), for example, 10 minutes of operation is performed at a rotation speed of 60% (Step 10).

The opening degree of the third opening/closing valve 32 is adjusted and controlled based on the temperature of the refrigerant detected by the first temperature sensor 33 provided in the high-pressure line or the second temperature sensor 34 provided in the cooling line.

At this time, the cooling rate (the rate of decrease in the temperature of the refrigerant) at the time of pre-cooling is set to 60K/h or the like, and the opening degree of the third opening/closing valve 32 is reduced stepwise or continuously by the bypass control so that the opening degree of the third opening/closing valve 32 is set to 0% at the stage where the refrigerant R1 reaches the first target temperature (100K in the present embodiment) (Step 11).

Then, the bypass line portion 30 is stopped (bypass control) at a stage (Step 12) when the expander outlet temperature reaches the first target temperature (100K), and the control is performed so that the entire amount of refrigerant is supplied to the expander T (no bypass control) (Step 13).

After the bypass line portion 30 is stopped, the refrigerator rotational speed is controlled based on the refrigerant temperature on the outlet side of the expander T detected by the second temperature sensor 34 so that the refrigerant temperature is kept at or below the second target temperature (67K or less in the present embodiment) (Step 14).

That is, in the present embodiment, before the circulation of the liquid nitrogen, which is the cooling target refrigerant R2, in the liquid nitrogen circulation line, which is the cooling target circulation line 16, is started, the second temperature sensor 34 detects the temperature of the refrigerant on the outlet side of the expander T, and the temperature of the refrigerant on the outlet side of the expander T is set to 67K or higher as the temperature control point. This prevents the liquid nitrogen from freezing in the cooling unit 2.

When circulation of liquid nitrogen is started in the liquid nitrogen circulation line, the temperature control point is switched to a third temperature sensor 35 close to the superconducting cable or the like, and operation control of the refrigerator 1 is performed based on the refrigerant temperature at the outlet side of liquid nitrogen detected by the third temperature sensor 35. This completes the pre-cooling operation (Step 15) of the refrigerator 1, and can cool the liquid nitrogen, which is the cooling target, easily and with high accuracy.

Furthermore, it was confirmed that: the same operational effects can be obtained by controlling the opening degree of the third opening/closing valve 32 by using the detection result of either the first temperature sensor 33 or the second temperature sensor 34 as long as there is no thermal load fluctuation. Therefore, although the refrigerator 1 of the present embodiment includes the first temperature sensor 33 and the second temperature sensor 34, the refrigerator may be configured by only one of the temperature sensors according to circumstances, and the number of temperature monitoring points and temperature sensors may be reduced.

(bypass control)

On the other hand, in the refrigerator 1 and the operation method at the time of precooling of the refrigerator 1 according to the present embodiment, as shown in fig. 2, 5, and 7 (fig. 1), the bypass control (Step 16) is performed by controlling the opening degree (stepwise control or proportional control) of the third opening/closing valve 32 stepwise or continuously in parallel with the above-described refrigerator precooling operation control, so that the flow rate change of the flow to the expander T is reduced. That is, the variation in cooling capacity at the time of opening variation can be suppressed, and the cooling rate control can be easily performed.

Specifically, when the precooling operation control using the bypass line portion 30 is performed, the first reason for controlling the cooling rate to be constant is that: when the heat exchanger is cooled rapidly, breakage may occur due to thermal deformation.

The second reason is: if the variation in the cooling temperature is large, the opening adjustment range of the third opening/closing valve 32 and the variation in the rotation speed of the refrigerator are large, and it is difficult to perform stable operation. That is, the flow rate of the refrigerant flowing through the bypass pipe 31 also affects the operation efficiency, and therefore the cooling rate is made constant for efficient operation.

In view of the above, in the operation method at the time of precooling of the refrigerator 1 according to the present embodiment, as described above, the opening control of the bypass valve of the bypass line portion 30, that is, the third opening/closing valve 32, and the rotation speed control of the refrigerator 1 are combined to perform temperature control for keeping the cooling rate constant at the time of precooling.

In the operation method at the time of pre-cooling of the refrigerator 1 according to the present embodiment, the flow rate is adjusted by the bypass line 31 without using a flowmeter by adjusting the opening degree of the third opening/closing valve 32 of the bypass line portion 30 instead of supplying a part of the refrigerant R1 to the expander T, and the refrigerant R1 is returned from the high-pressure line to the low-pressure line, thereby suppressing occurrence of hunting.

On the other hand, when the third opening/closing valve 32 is excessively opened, an excessive flow rate is supplied to the compressor, and unnecessary power is consumed, with the result that efficient operation is not possible.

Therefore, in the operation method at the time of pre-cooling of the refrigerator 1 according to the present embodiment, the opening degree of the third opening/closing valve 32 is controlled (stepwise control or proportional control) stepwise or continuously so as to maintain the flow rate at which no fluctuation occurs, and the third opening/closing valve 32 is closed (the opening degree is 0%) at a stage close to the design flow rate of the expander T.

In addition, in the opening degree control of the third opening/closing valve 32 of the bypass line portion 30, the condition is set as: the refrigerant flows to both the expander T and the bypass line 31 are adjusted, and efficient operation is enabled. It is therefore considered that: if only the adjustment control of the refrigerant flow rate by the bypass line section 30 is performed, the control is not necessarily performed with high accuracy in consideration of the temperature control of the refrigerant R1.

In this case, in the pre-cooling operation method of the refrigerator 1 according to the present embodiment, the rotation speed of the refrigerator 1 is controlled in addition to the opening degree control of the third opening/closing valve 32 of the bypass line portion 30, as described above, so that the cooling rate is adjusted and corrected to be constant.

That is, in the operation method at the time of pre-cooling of the refrigerator 1 according to the present embodiment, the rotation speed of the refrigerator 1 is controlled so that the cooling rate is constant according to the magnitude of the difference between the set target temperature and the measured temperature of the refrigerant R1, and the refrigerant temperature can be controlled with high accuracy.

As described above, in the operation method at the time of pre-cooling of the refrigerator 1 according to the present embodiment, by using the opening degree adjustment control of the third opening/closing valve 32 of the bypass line portion 30 and the rotation speed control of the refrigerator 1 in combination, it is possible to appropriately suppress occurrence of fluctuation and to make the cooling rate constant during the initial operation from the time of starting to the time of completion of pre-cooling, and it is possible to perform efficient operation control by cooling the refrigerant R1 with high accuracy.

Here, in order to properly achieve the above-described operational effects, the operation method of the refrigerator 1 of the present embodiment adjusts the opening degree of the third opening/closing valve 32 of the bypass line portion 30 stepwise or continuously by the bypass control (Step 16).

The operation method of the refrigerator 1 according to the present embodiment will be described in detail with reference to an example of stepwise opening degree control (stepwise control) and continuous opening degree control (proportional control) using the third opening/closing valve 32 of the bypass line portion 30.

(staged operation control (step operation control) Using bypass line portion)

First, a method of stepwise controlling the opening degree of the third opening/closing valve 32, which is the bypass valve of the bypass line portion 30, will be described.

In the stepwise opening adjustment control of the third opening/closing valve 32 in the bypass line portion 30, as shown in fig. 5 and 6 (see fig. 1, 2, and 4), for example, the rotation speed (Step 10) at which the precooling operation control (Step 9) of the refrigerator reaches 60% of the maximum value is set to 40% of the opening of the third opening/closing valve 32 (Step 17). The temperature of the refrigerant R1 at the time of startup is measured by the first temperature sensor 33 or the second temperature sensor 34 (Step 18). Then, the refrigerator 1 is started, and the opening degree of the third opening/closing valve 32 is changed stepwise from the stage in which the pre-cooling operation is started, based on the temperature of the refrigerant detected by the first temperature sensor 33 or the second temperature sensor 34 (Step 19).

In the stepwise operation control using the bypass line portion 30, the opening degree of the third opening/closing valve 32 is determined at the start point and the end point of the temperature in each step (in the present embodiment, steps 1 to 6: fig. 6). For example, when the one-step temperature range is set to T01 to T02 and the opening degree of the third opening/closing valve 32 is set to V01%, the opening degree V01% of the third opening/closing valve 32 is continuously maintained in a state where the measured temperature Ta of the first temperature sensor 33 or the second temperature sensor 34 is T02 < ta++.t01.

Then, the refrigerant temperature gradually decreases, and in the stage where the measured temperature Ta becomes T02, the opening V02% (V02 < V01) of the third opening/closing valve 32 corresponding to the next step temperature range, that is, from T02 to T03 (T03 < ta+.t02) is continuously maintained.

In this way, the steps (steps 1 to 6) are sequentially changed as the cooling temperature decreases, and the opening degree of the third opening/closing valve 32 is switched to the opening degree of the next stage every time the step of the next stage is changed.

When the opening degree of the third opening/closing valve 32 is reduced stepwise by sequentially changing the steps, the flow rate of the refrigerant R1 flowing through the bypass line 31 and flowing from the high-pressure line to the low-pressure line is reduced stepwise. In response to the stepwise decrease in the flow rate of the refrigerant R1, the amount of the refrigerant flowing from the low-stage compressor C1 side to the expander T side increases stepwise, and therefore, in the refrigerator 1 of the present embodiment, the rotational speed control (refrigerator pre-cooling operation control) is used in combination so that the cooling rate is kept constant.

For example, in fig. 5 and 6, the refrigerator rotation speed at the time of starting (at the time of rotation start) is set to 60%, the opening degree of the third opening/closing valve 32 is set to 40%, 5 steps are set before the temperature of the refrigerant R1 measured by the first temperature sensor 33 or the second temperature sensor 34 reaches 100K of the first target temperature, and the temperature ranges of 225K, 190K, 155K, 120K, and 100K and the opening degree of the third opening/closing valve 32 are set.

In this way, by using both the stepwise opening control of the third opening/closing valve 32 of the bypass line portion 30 and the rotational speed control of the refrigerator 1, in the pre-cooling operation method of the refrigerator 1 according to the present embodiment, the opening of the third opening/closing valve 32 can be set in accordance with the temperature zone of each step, and the rotational speed control (for example, the rotational speed n=60 to 75%) can be performed using PID control or the like so that the cooling rate becomes a preset constant set value (60K/h or the like) in each of the different temperature zones.

As a result, according to the method for operating the refrigerator 1 during pre-cooling of the present embodiment, stable pre-cooling operation with less fluctuation in the rotation speed and pressure of the refrigerator 1 can be performed.

In the stage of reaching 100K of the first target temperature, the opening degree of the third opening/closing valve 32 is 0%, and the operation control using the bypass line portion 30 is ended, and the operation proceeds to the no-bypass control operation (Step 20). By switching to this bypass-free control operation, the entire refrigerant circulation amount flows from the compressor to the expander T.

In the precooling operation without the bypass control operation, the rotation speed control is performed to 67K which is the second target temperature which is the next target temperature. At this time, the rotational speed control (for example, rotational speed n=75 to 95%) is performed using PID control or the like so that the cooling rate becomes a preset constant set value (60K/h or the like) before 67K of the second target temperature is reached (Step 13). Further, control is performed so as to reach 67K of the second target temperature and maintain the second target temperature before the nitrogen cycle operation of the load is applied (Steps 13, 14, 15).

Further, the rotation speed control is not limited to the use of PID (Proportional-Integral-Differential) control. For example, P may of course also be used

(pro: proportional) control, PI (pro-Integral) control, and the like.

Therefore, according to the refrigerator 1 and the method of operating the refrigerator 1 during pre-cooling of the present embodiment, by using the stepwise opening adjustment control of the third opening/closing valve 32 of the bypass line portion 30 and the rotational speed control of the refrigerator 1 in combination, it is possible to appropriately suppress occurrence of fluctuation during the initial operation from the start-up time to the completion of pre-cooling, to make the cooling rate constant, to cool the refrigerant R1 with high accuracy, and to perform efficient operation control.

(continuous operation control (proportional operation control) Using bypass line portion)

Next, a method of continuously controlling the opening of the third opening/closing valve 32, which is the bypass valve of the bypass line portion 30, will be described.

In the continuous opening adjustment control of the third opening/closing valve 32 in the bypass line portion 30, as shown in fig. 7 and 8 (see fig. 1, 2, and 4), the rotation speed (Step 10) at which the maximum value is 60% is obtained by the refrigerator pre-cooling operation control (Step 9) and the opening degree of the third opening/closing valve 32 is 40% (Step 17) similarly to the stepwise opening adjustment control. The temperature of the refrigerant R1 at the time of startup is measured by the first temperature sensor 33 or the second temperature sensor 34 (Step 18). Then, the refrigerator 1 is started, and from the stage where the pre-cooling operation is started, the opening degree of the third opening/closing valve 32 is continuously changed according to the temperature of the refrigerant detected by the first temperature sensor 33 or the second temperature sensor 34 (Step 20).

In the continuous operation control using the bypass line portion 30, the opening degree of the third opening/closing valve 32 is determined at the start and end points of the temperatures in each step (steps 1 to 6: fig. 8 in the present embodiment).

However, in the initial state of operation, the operation control of the rotation speed 60% (Step 10) and the third on-off valve opening 40% (Step 17) is prioritized, and the valve opening 40% is maintained until the temperature of the refrigerant R1 is cooled to 225K in (Step 18), so that the continuous operation control is substantially started from (Step 2).

For example, in the case where the one-step temperature range is set to T01 to T02, the opening degree of the third opening/closing valve 32 is gradually reduced from V01% to V02% during the period from T01 to T02.

That is, when the temperature of the refrigerant R1 measured by the first temperature sensor 33 or the second temperature sensor 34 is set to Ta, the opening V% of the third opening/closing valve 32 is obtained by the following equation (1).

[ 1]

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

Here, T02 < Ta < T01

The third opening/closing valve 32 is continuously controlled in accordance with the opening degree thus obtained, and the steps are sequentially changed as the cooling temperature is lowered in the continuous control (steps 1 to 6: fig. 8).

When the opening degree of the third opening/closing valve 32 is continuously reduced as the steps are sequentially changed, the flow rate of the refrigerant R1 flowing through the bypass pipe 31 and from the high-pressure pipe to the low-pressure pipe is continuously reduced as the opening degree of the third opening/closing valve 32 is continuously reduced. The flow rate of the refrigerant flowing through the bypass line and flowing from the high-pressure line to the low-pressure line is continuously reduced. In response to this continuous decrease in the flow rate of the refrigerant, the amount of the refrigerant flowing from the low-stage compressor C1 side to the expander T side is continuously increased, and therefore, in the refrigerator 1 of the present embodiment, the rotational speed control (the refrigerator precooling operation control) is used in combination so that the cooling rate is kept constant.

For example, in fig. 7 and 8, the refrigerator rotation speed at the time of starting (at the time of rotation start) is set to 60%, the opening degree of the third opening/closing valve 32 is set to 40%, and the opening degree of the third opening/closing valve 32 is continuously set according to equation (1) for each temperature range at 225K, 190K, 155K, 120K, and 100K in 4 steps from step 2 to step 5 before the temperature of the refrigerant R1 measured by the first temperature sensor 33 or the second temperature sensor 34 is set to 100K which is the first target temperature.

In this way, by using the continuous opening control of the third opening/closing valve 32 of the bypass line portion 30 according to the formula (1) and the rotational speed control of the refrigerator 1 in combination, in the pre-cooling operation method of the refrigerator 1 according to the present embodiment, the opening of the third opening/closing valve 32 can be set in accordance with the temperature zone of each step, and the rotational speed control (for example, the rotational speed n=60 to 75%) can be performed using PID control or the like so that the cooling rate becomes a preset constant set value (60K/h or the like) in each of the temperature zones that are distinguished.

In addition, in the same manner as in the stepwise opening degree control, the opening degree of the third opening/closing valve 32 is 0% at the stage of reaching 100K of the first target temperature, and the operation control using the bypass line portion 30 is ended, and the operation proceeds to the no-bypass control operation (Step 13). By switching to this bypass-free control operation, the entire refrigerant circulation amount flows from the compressors C1, C2, and C3 to the expander T.

In addition, in the case of using continuous opening degree control, the rotation speed control is not limited to PID (Proportional-Integral-Differential) control. For example, P (Proportional) control, PI (Proportional)

-integrate: proportional integral) control, and the like.

Therefore, according to the refrigerator 1 and the method of operating the refrigerator 1 during pre-cooling of the present embodiment, by using the continuous opening adjustment control of the third opening/closing valve 32 of the bypass line portion 30 and the rotational speed control of the refrigerator 1 in combination, it is possible to appropriately suppress occurrence of fluctuation during the initial operation from the start-up time to the completion of pre-cooling, to make the cooling rate constant, to cool the refrigerant R1 with high accuracy, and to perform efficient operation control.

(temperature Cooling control at precooling)

The gist of the predetermined temperature cooling control (predetermined operation method) performed by the refrigerator 1 of the present embodiment including the bypass line portion 30 and the buffer line portion 25 is summarized as follows.

1) At the time of starting, the operation is started by setting the predetermined rotation speed of the refrigerator to RPM (1) (setting the rotation speed of at least the expander T among the compressors C1, C2, and C3 and the expander T to the predetermined rotation speed RPM (1)), and setting the opening of the third opening/closing valve 32, which is the bypass valve of the bypass line portion 30, to the predetermined opening V% (2) (starting operation step).

2) The first temperature sensor 33 or the second temperature sensor 34 detects the temperature of the refrigerant on the inlet side of the expander T or the temperature of the refrigerant on the outlet side of the expander T. The opening V of the third opening/closing valve 32 is gradually or continuously reduced from 190K (225K) to 100K, for example, at the inlet side refrigerant temperature of the expander T or the outlet side refrigerant temperature of the expander T, and the high-pressure line refrigerant R1 is circulated to the low-pressure line through the bypass line 31. Further, the opening V% of the third opening/closing valve 32 is controlled stepwise or continuously, and the refrigerant R1 is cooled from the temperature at the time of start to the first target temperature (bypass control operation step).

3) Next, in a stage where the opening degree of the third opening/closing 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 on the outlet side of the expander T (or the refrigerant temperature detected by the first temperature sensor 33) detected by the second temperature sensor 34 (no bypass control operation step).

4) When the bypass control operation step and the no-bypass control operation step are performed, the rotation speed of the refrigerator 1 is continuously controlled based on the refrigerant temperature of the second temperature sensor 34 so that the cooling rate is kept constant at least until the cooling target temperature (first target temperature, second target temperature) is reached (cooling rate control step).

5) In the period from the start of the pre-cooling operation of 1) to 4), when the state in which the pressure of the refrigerant in the high-pressure line is greater than the pressure of the buffer tank 27 by a predetermined set value (10 kPa) or more is detected by the first pressure sensor 36 and the second pressure sensor 37, the first opening/closing valve 28 is opened, and the refrigerant R1 is recovered to the buffer tank 27 by the pressure difference (refrigerant recovery step).

6) Then, by the control from the start to the pre-cooling operation of 1) to 5), the pre-cooling operation is completed in a stage where the cooling is the second target temperature and the refrigerant temperature is constant, and after the pre-cooling operation is completed, the circulation of liquid nitrogen is started, 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 target side circulation line 16 of the third temperature sensor 35 that detects the temperature of the cooling target refrigerant R2, and the operation is shifted to the main cooling operation (main cooling operation switching step).

By controlling the predetermined operation of the refrigerator 1 from the start-up to the main cooling operation in this way, the refrigerant R1 is cooled with a constant temperature gradient during precooling, for example, as shown in fig. 4.

Further, the opening degree adjustment of the third opening/closing valve 32 and the adjustment control of the bypass refrigerant flow rate are controlled stepwise or continuously based on the detection value of the first temperature sensor 33 or the second temperature sensor 34 provided near the inlet or the outlet of the expander T, so that the device configuration is not complicated as compared with the case of detecting the flow rate of the refrigerant R1, and the control can be performed with high accuracy.

Therefore, according to the refrigerator 1 and the method of operating the refrigerator 1 at the time of pre-cooling, the flow rate of the refrigerant R1 is not detected, and fluctuation can be avoided by the flow rate control of the refrigerant R1, so that the device configuration can be simplified, and the safety can be improved. In addition, the compressors C1, C2, C3 and the expander T can be pre-cooled at a high rotational speed, and smooth pre-cooling operation can be realized.

For example, although stepless control of the rotational speed is performed only when fluctuation is to be avoided by rotational speed control, a flowmeter that measures the flow rate of the refrigerant is used to perform stepless control of the rotational speed. This results in a complex device structure. In addition, a method of making the opening degree of the third opening/closing valve 32 constant is also conceivable, but in this case, the bypass refrigerant R1 is unnecessarily increased as cooling proceeds.

In the refrigerator 1 of the present embodiment, if the opening degree of the third opening/closing valve 32 is increased at an appropriate timing, the refrigerant R1 can be discharged from the high-pressure line to the low-pressure line without recovering the refrigerant R1 to the buffer tank 27, and the flow rate of the refrigerant R1 can be ensured. Thus, even if the buffer pipe portion 25 is not provided, the fluctuation of the compressors C1, C2, and C3 during pre-cooling can be suppressed.

Here, fig. 9 is a diagram showing an example of a state of pressure fluctuation of the high-pressure line, the low-pressure line, and the buffer tank 27 in the bypass control operation (in the stepwise control).

In fig. 9 and 4, for example, (a) shows the start of the operation of the refrigerator, (b) shows the end point of step 1 (refrigerant temperature: 225K) of the initial operation control, and (c) shows the end point of step 2 (refrigerant temperature: 190K) of the stepwise or continuous operation control

When, (d) indicates the end point of step 5 of the stepwise or continuous operation control (refrigerant temperature: 100K).

As shown in fig. 9 (and 4), the refrigerant pressure in the high-pressure line increases from (a) to (b) at the end of step 1 (corresponding to step 1) at the start of the operation of the refrigerator, and therefore, the first on-off valve 28 is controlled to be opened and the buffer line portion 25 is used to recover the refrigerant during the period from (a) to (b). That is, in the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment, the pressure of the high-pressure line is equal to or higher than the set value (threshold value) in the period from (a) to (b), and at this time, the first on-off valve 28 is controlled to be opened, and the buffer line portion 25 is used to collect the refrigerant.

In the period from (a) to (b), the fluctuation of the internal pressure of the buffer tank 27 is substantially the same as the fluctuation of the refrigerant pressure in the high-pressure line (the same operation and tendency are exhibited).

Next, during the period from the end point (b) of step 1 to the end point (c) of step 2 (corresponding to step 2), the opening degree of the third opening/closing valve (bypass valve) 32 of the bypass line portion 30 is reduced (for example, from 40% to 35%), and the bypass amount of the refrigerant is reduced. Thus, the amount of refrigerant flowing from the compressor C3 to the expander T increases until (b) to (C), and the pressure of the high-pressure line temporarily increases.

Therefore, in the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment, the pressure of the high-pressure line is equal to or higher than the set value (threshold value) in the period from (b) to (c) (corresponding to step 2), in other words, equal to or higher than the internal pressure of the buffer tank 27, and the opening of the first on-off valve 28 is controlled in the period from (b) to (c), so that the refrigerant is recovered by the buffer line portion 25. That is, the refrigerant is recovered in a region where the refrigerant pressure in the high-pressure line is higher than the internal pressure of the buffer tank 27.

Further, during the period from (a) to (b) and the period from (b) to (c), the cooling rate of the refrigerant is kept constant by performing control to increase the rotation speed so that the cooling rate is kept constant (for example, by performing rotation speed control to control the rotation speed to 60% after the opening degree of the third opening/closing valve 32 is kept constant (40%) and the rotation speed is operated at 60% (10 minutes)), and as the temperature of the refrigerant decreases, the refrigerant pressure in the high-pressure line decreases.

In the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment, the cooling operation is continued while keeping the opening degree of the third opening/closing valve 32 constant until the refrigerant temperature reaches approximately 225K from (a) to (b).

Specifically, if the 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) occur, and there is a possibility that fluctuation in the refrigerant pressure of the high-pressure line and variation in the rotational speed occur, resulting in a decrease in the operation efficiency when the cooling rate of the refrigerant is kept constant.

Therefore, in the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment, when the operation control is performed stepwise or continuously, the opening degree of the third opening/closing valve 32 is not changed and the constant opening degree is maintained in step 1 in the period from (a) to (b).

Further, in the refrigerator 1 and the operation method of the refrigerator 1 according to the present embodiment, the recovery of the refrigerant in the buffer tank 27 is performed at the initial operation (before the refrigerant temperature reaches 225K) in the period from (a) to (b), and the excess refrigerant is recovered, and after that, the refrigerant in the amount corresponding to the pressure increase can be temporarily recovered when the opening degree of the third opening/closing valve 32 is changed.

(control of adjustment of refrigerator capacity during normal operation)

In the present embodiment, in the normal operation after the transition control to the normal (steady) operation is performed, the capacity of the refrigerator is adjusted according to the state of the heat load.

When the capacity of the refrigerator 1 is increased, the second opening/closing valve 29 is controlled to be opened, and the refrigerant R1 stored in the buffer tank 27 is returned to the low-pressure line 8a.

When the capacity of the refrigerator 1 is reduced, the first opening/closing valve 28 is controlled to be opened, and the refrigerant R1 is recovered into the buffer tank 27.

At this time, in the refrigerator 1 of the present embodiment, as the determination conditions for performing the refrigerator capacity adjustment, that is, the determination conditions for the opening/closing drive control of the first opening/closing valve 28 and the second opening/closing valve 29, the set temperature of the refrigerant R1 and the rotation speed of the refrigerator 1 (the rotation speeds of the first motor 9 and the second motor 11, and the compressors C1, C2, and C3) are used. In addition, a third pressure sensor 41 is provided in the low-pressure line.

For example, with respect to the second opening/closing valve 29, when the refrigerant temperature detected by the first temperature sensor 33 (or the second temperature sensor 34) is equal to or higher than a preset set temperature (the pressure is insufficient) and the rotation speed of the refrigerator is 100% (the motor load is appropriate), the second opening/closing valve 29 is opened, and when the pressure of the buffer tank 27 is reduced by a certain pressure or the refrigerant temperature is equal to or lower than the set temperature (the refrigerant amount is excessive) and the rotation speed of the refrigerator is lower than 100% (the motor load is increased), the second opening/closing valve 29 is closed. The high-pressure line, the buffer tank 27, and the low-pressure line measure the pressure by the pressure sensors, and discharge and recovery of the refrigerant R1 are performed under conditions equal to or higher than a set differential pressure.

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 equal to or lower than a preset set temperature (the refrigerant amount is excessively large) and the refrigerant rotation speed is 98% or lower than a preset threshold (the motor load is excessively large), and the first on-off valve 28 is closed (the refrigerant amount in the refrigerant circulation line is reduced) when the pressure of the buffer tank 27 is increased by a certain pressure or when the refrigerant temperature is equal to or higher than the set temperature (the refrigerant amount is reduced) and the refrigerant rotation speed is increased (the motor load is reduced) and becomes 98% or higher than the threshold (the refrigerant recovery is stopped).

Accordingly, the capacity of the buffer tank 27 is limited, and the refrigerant recovery amount and recovery time need to be adjusted, and the opening/closing drive control of the first opening/closing valve 28 and the second opening/closing valve 29 is performed as described above, so that the refrigerant recovery amount and recovery time can be adjusted, and the capacity of the refrigerator can be adjusted to an appropriate state and maintained in the normal operation.

While the embodiments of the refrigerator and the method of operating the refrigerator during pre-cooling of the refrigerator have been described above, the refrigerator and the method of operating the refrigerator during pre-cooling of the present disclosure are not limited to the above embodiments, and may be appropriately modified within a scope not departing from the gist thereof, including modification examples.

For example, in the present embodiment, the refrigerator is configured by including three compressors, i.e., a low-stage compressor, a medium-stage compressor, and a high-stage compressor, but the number of compressors is not particularly limited as long as at least the low-stage compressor and the high-stage compressor are included.

In the present embodiment, the single controller 40 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 dynamometer 38, and the second dynamometer 39, and controls the driving of the first motor 9 and the second motor 11 and the opening degree (opening/closing driving) of the first opening/closing valve 28, the second opening/closing valve 29, and the third opening/closing valve 32, but the controller is not necessarily one. That is, the present invention may be configured to include a plurality of controllers for receiving detection results of the respective sensors and the like, and for driving and controlling the respective motors, valves, and the like.

In addition, regarding the embodiments of the refrigerator and the operation method at the time of pre-cooling of the refrigerator of the present disclosure, the refrigerator is effective not only when starting in a state of pressure equalization at normal temperature, but also when restarting immediately after stopping the refrigerator. In this case, even when the temperature of the refrigerant in the refrigerator or the temperature of the low-temperature device is not increased, the controller can perform the refrigerator pre-cooling operation control, the bypass control, and the buffer tank refrigerant recovery control based on the measured values of the various sensors, and therefore, the pre-cooling operation can be started and continued without any trouble.

Finally, the contents described in the embodiments can be grasped as follows.

(1) A refrigerator (refrigerator 1) according to one embodiment of the present disclosure includes: an expander-integrated compressor (expander-integrated compressor 7) that includes a compressor (high-stage compressor C3) that compresses a refrigerant (refrigerant R1), and an expander (expander T) that is coupled to the compressor via a rotary shaft that can be driven by a motor (first motor 9) and that expands the refrigerant compressed by the compressor; a cooling unit (cooling unit 2) for cooling a cooling object (cooling object, liquid nitrogen, secondary refrigerant R2) by using the refrigerant expanded in the cooling expander; a refrigerant circulation line (refrigerant circulation line 8) that includes a low-pressure line that extends from the expander to the low-stage compressor (low-stage compressor C1) via the cooling unit, a medium-pressure line that extends from the low-stage compressor to the high-stage compressor, and a high-pressure line that extends from the high-stage compressor to the expander, and that circulates a refrigerant; a bypass line (bypass line 31) having one end connected to a first connection portion (first connection portion S1) provided in the high-pressure line and the other end connected to a second connection portion (second connection portion S2) provided in the low-pressure line; and a bypass valve (third opening/closing valve 32) provided in the bypass line, wherein the flow rate of the refrigerant flowing through the bypass line can be adjusted by adjusting the opening degree.

In the refrigerator of (1) above, by opening the bypass valve, a part of the refrigerant compressed by the high-stage compressor is not supplied to the expander, but can be returned to the low-stage compressor and the high-stage compressor again. Further, by adjusting the opening degree of the bypass valve, the flow rate of the refrigerant returned to the compressor and the flow rate of the refrigerant flowing to the expander can be changed.

Accordingly, by appropriately changing the opening degree of the bypass valve in accordance with the operation state during the initial operation from the start-up time to the completion of the pre-cooling, it is possible to reduce the amount of refrigerant not used for cooling without causing hunting, and to perform efficient (high COP) operation without wasting power.

(2) Another aspect of the present disclosure provides the refrigerator according to (1), comprising: a temperature sensor (first temperature sensor 33) for detecting a temperature of the refrigerant flowing between the first connection portion and the expander in the high-pressure piping; and a controller (controller 40, control device) for controlling the opening degree of the bypass valve and the rotation speed of the rotation shaft based on the detection result of the temperature sensor.

In the refrigerator of the above (2), the opening degree adjustment of the bypass valve and the adjustment control of the bypass refrigerant flow rate are controlled based on the detection value of the temperature sensor that detects the temperature of the refrigerant flowing between the first connection portion and the expander, for example, in the vicinity of the inlet of the expander, so that the device configuration is not complicated as compared with the case of detecting the refrigerant flow rate, and the control can be performed with high accuracy.

Therefore, since fluctuation can be avoided by controlling the flow rate of the refrigerant without detecting the flow rate of the refrigerant, simplification of the device structure can be achieved, and safety can be improved. In addition, the compressor and the expander can be pre-cooled by rotating at a high speed, and smooth pre-cooling operation can be realized.

That is, during the initial operation, the occurrence of hunting can be appropriately suppressed, the cooling rate can be made constant, the refrigerant can be cooled with high accuracy, and efficient operation control can be performed, as compared with the conventional art.

(3) Another aspect of the present disclosure provides the refrigerator according to (1), comprising: a temperature sensor (second temperature sensor 34) for detecting the temperature of the refrigerant between the cooling portion and the expander in the low-pressure line; and a controller that controls the opening degree of the bypass valve and the rotation speed of the rotation shaft based on the detection result of the temperature sensor.

In the refrigerator of (3), the opening degree adjustment of the bypass valve and the adjustment control of the bypass refrigerant flow rate are controlled based on the detection value of the temperature sensor that detects the temperature of the refrigerant flowing between the cooling unit and the expander, such as in the vicinity of the outlet of the expander, so that the device configuration is not complicated as compared with the case of detecting the refrigerant flow rate, and the control can be performed with high accuracy.

(4) Another aspect of the present disclosure provides the refrigerator according to (2) or (3), wherein the controller controls: during an initial operation period from when the start-up of the refrigerator is started to when the pre-cooling operation is completed, the bypass valve is controlled so as to gradually decrease the opening degree before the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance, and the rotation speed is controlled so that the rate of decrease in the temperature of the refrigerant detected by the temperature sensor is kept constant.

In the refrigerator of the above (4), in addition to the opening degree control of the bypass valve, the rotation speed control of the refrigerator (compressor, expander) is performed during the initial operation from the start-up time to the completion of the pre-cooling, whereby the cooling rate is adjusted and corrected, and the cooling rate is kept constant, whereby the refrigerant temperature can be controlled with high accuracy.

Further, by using both the stepwise opening control of the bypass valve and the rotational speed control of the refrigerator, the opening of the bypass valve can be set for each step of temperature section, and rotational speed control can be performed so that the cooling rate becomes a preset constant set value in each of the different temperature sections.

This makes it possible to perform stable precooling operation with less fluctuation in the rotation speed and pressure of the refrigerator.

(5) Another aspect of the present disclosure provides the refrigerator according to (2) or (3), wherein the controller controls: during an initial operation period from when the start-up of the refrigerator is started to when the pre-cooling operation is completed, the bypass valve is controlled so as to continuously decrease the opening degree until the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance, and the rotational speed is controlled so that the rate of decrease in the temperature of the refrigerant detected by the temperature sensor is kept constant.

In the refrigerator of the above (5), in addition to the opening degree control of the bypass valve, the rotation speed control of the refrigerator (compressor, expander) is performed during the initial operation from the start-up time to the completion of the pre-cooling, whereby the cooling rate is adjusted and corrected, and the cooling rate is kept constant, whereby the refrigerant temperature can be controlled with high accuracy.

Further, by using the continuous opening control of the bypass valve and the rotational speed control of the refrigerator in combination, the opening of the bypass valve can be set for each temperature zone of each step, and rotational speed control can be performed so that the cooling rate becomes a preset constant set value in each temperature zone.

(6) Another aspect of the present disclosure provides the refrigerator according to (4) or (5), wherein the controller controls: the bypass valve is controlled so that the opening degree is 0% at the stage when the temperature of the refrigerant detected by the temperature sensor reaches the first target temperature, 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 the second target temperature set lower than the first target temperature, and the rotation speed is controlled so that the speed of decrease in the temperature of the refrigerant detected by the temperature sensor is maintained constant.

In the refrigerator of (6), the opening degree of the bypass valve is 0% at the stage of reaching the first target temperature, and the operation control using the bypass line is ended, and the operation proceeds to the bypass-free control operation in which the entire refrigerant circulation amount flows from the compressor to the expander. In the precooling operation without the bypass control operation, the rotation speed is controlled so that the cooling rate is kept constant toward the second target temperature, which is the next target temperature

Thus, the occurrence of hunting can be more effectively suppressed during the initial operation from the start-up time to the completion of the pre-cooling by using the stepwise or continuous opening degree adjustment control of the bypass valve and the rotation speed control of the refrigerator in combination, and the refrigerant can be cooled with a constant cooling rate and high accuracy, thereby enabling efficient operation control.

(7) Another aspect of the present disclosure provides the refrigerator according to (6), comprising: a heat exchanger (cooling unit, secondary-side load heat exchanger 2) for exchanging heat between a secondary refrigerant (refrigerant R2 for cooling) for cooling a cooling target and the refrigerant; and a secondary refrigerant temperature sensor (third temperature sensor 35) for detecting the temperature of the secondary refrigerant, wherein the controller controls the rotation speed based on the detection result of the secondary refrigerant temperature sensor when the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature.

In the refrigerator according to the above (7), the temperature detection point is switched from the temperature sensor to the secondary refrigerant temperature sensor at the stage of reaching the second target temperature, and the rotation speed is controlled based on the detection result of the secondary refrigerant temperature sensor, whereby the normal (stable) operation can be smoothly shifted from the pre-cooling operation during the initial operation.

(8) Another aspect of the present disclosure provides the refrigerator according to any one of (1) to (7), comprising: a heat-and-heat recovery heat exchanger (heat-and-heat recovery heat exchanger 15) that cools the refrigerant in the high-pressure line by the refrigerant that has been used to cool the cooling object in the cooling unit; a buffer line (buffer line 26) having one end connected to a third connection portion (third connection portion S3) provided between the heat recovery heat exchanger and the expander of the high-pressure line and the other end connected to a fourth connection portion (fourth connection portion S4) provided between the expander and the cooling portion of the low-pressure line; a buffer tank (buffer tank 27) provided in the buffer line and capable of storing the refrigerant sent from the high-pressure line; a high-pressure-side buffer valve (first opening/closing valve 28) provided between the buffer tank and the third connection portion in the buffer line; a low-pressure side buffer valve (second opening/closing valve 29) provided between the buffer tank and the fourth connection portion in the buffer line; a first pressure sensor (first pressure sensor 36) for detecting a pressure of the refrigerant between the first connection portion and the third connection portion in the high-pressure piping; a second pressure sensor (second pressure sensor 37) for detecting an internal pressure of the buffer tank; and a controller for controlling the opening degrees of the high-pressure side cushion valve and the low-pressure side cushion valve according to the detection results of the first pressure sensor and the second pressure sensor.

In the refrigerator according to the above (8), when the state in which the pressure of the refrigerant in the high-pressure line is greater than the pressure of the buffer tank by the first pressure sensor and the second pressure sensor by a predetermined set value or more is detected during the period from the start to the pre-cooling operation, the high-pressure side buffer valve is opened, and the refrigerant can be recovered to the buffer tank by the pressure difference.

This can more effectively suppress occurrence of excessive motor load and occurrence of hunting.

(9) The operation method at the time of precooling of a refrigerator according to one embodiment of the present disclosure is an operation method during an initial operation period from a start-up time to a completion of precooling of a refrigerator, the refrigerator including: an expander-integrated compressor including a compressor that compresses a refrigerant, and an expander that is coupled to the compressor via a rotation shaft that can be driven by a motor and that expands the refrigerant compressed by the compressor; a cooling unit that cools the cooling object by using the refrigerant expanded in the expander; a refrigerant circulation line including a low-pressure line from the expander to the low-stage compressor via the cooling unit, a medium-pressure line from the low-stage compressor to the high-stage compressor, and a high-pressure line from the high-stage compressor to the expander, for circulating the refrigerant; one end of the bypass pipeline is connected with a first connecting part arranged on the high-pressure pipeline, and the other end of the bypass pipeline is connected with a second connecting part arranged on the low-pressure pipeline; a bypass valve provided in the bypass line, the bypass valve being capable of adjusting the flow rate of the refrigerant flowing through the bypass line by adjusting the opening degree; a temperature sensor for detecting a temperature of the refrigerant flowing between the first connection portion and the expander in the high-pressure line or a temperature of the refrigerant between the cooling portion and the expander in the low-pressure line; and a controller that controls the opening degree of the bypass valve and the rotation speed of the rotation shaft based on the detection result of the temperature sensor, wherein the operation method includes: a start operation step of starting operation by setting the rotation speed of the rotation shaft to a preset rotation speed lower than that in the steady operation after the initial operation period and setting the opening of the bypass valve to a preset opening; a bypass control operation step of controlling, by a controller, the opening degree of the bypass valve to be gradually reduced before the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance; a step of cooling the refrigerant before reaching a preset second target temperature from the first target temperature by setting the opening degree of the bypass valve to 0% at the stage when the temperature of the refrigerant reaches the first target temperature; and a cooling rate control step of controlling the rotational speed by the controller so that the rate of decrease in the temperature of the refrigerant is kept constant in at least the bypass control operation step in the bypass control operation step and the non-bypass control operation step.

In the method for operating the refrigerator in precooling of (9), the bypass valve is controlled to be opened, so that a part of the refrigerant compressed in the high-stage compressor is not supplied to the expander, and the refrigerant can be returned to the low-stage compressor and the high-stage compressor again. Further, by adjusting the opening degree of the bypass valve, the flow rate of the refrigerant returned to the compressor and the flow rate of the refrigerant flowing to the expander can be changed.

Accordingly, by appropriately changing the opening degree of the bypass valve in accordance with the operation state during the initial operation from the start-up time to the completion of the pre-cooling, it is possible to reduce the amount of refrigerant not used for cooling without causing hunting, and it is possible to perform efficient (high COP) operation without wasting power.

In addition, in the initial operation period from the start-up time to the completion of the pre-cooling, the cooling rate is adjusted and corrected by performing the rotation speed control of the refrigerator (compressor, expander) in addition to the opening degree control of the bypass valve, and the cooling rate is kept constant, whereby the refrigerant temperature can be controlled with high accuracy.

Further, by controlling the opening adjustment of the bypass valve and the adjustment control of the bypass refrigerant flow rate based on the detection values of the first temperature sensor or the second temperature sensor provided near the inlet and near the outlet of the expander, the control can be performed with high accuracy without complicating the device configuration as compared with the case of detecting the refrigerant flow rate.

Therefore, fluctuation can be avoided by the flow control of the refrigerant without detecting the flow rate of the refrigerant, and therefore simplification of the device structure can be achieved and safety can be improved. In addition, the compressor and the expander can be pre-cooled by the high rotation operation, and smooth pre-cooling operation can be realized.

That is, during the initial operation, the occurrence of hunting can be appropriately suppressed, and the refrigerant can be cooled with a constant cooling rate and high accuracy, as compared with the conventional technique, and efficient operation control can be performed.

(10) In another aspect of the present disclosure, the method for operating the refrigerator during pre-cooling is the method for operating the refrigerator according to (9) above, wherein in the bypass control operation step, the controller is configured to control the opening degree of the bypass valve to be gradually reduced until the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance.

In the method for operating the refrigerator during pre-cooling of (10), in addition to the opening degree control of the bypass valve, the cooling rate is adjusted and corrected by performing the rotation speed control of the refrigerator (compressor, expander) during the initial operation period from the start-up time to the completion of pre-cooling, and the cooling rate is kept constant, whereby the refrigerant temperature can be controlled with high accuracy.

(11) In another aspect of the present disclosure, the method for operating the refrigerator during pre-cooling is the method for operating the refrigerator according to (9) above, wherein in the bypass control operation step, the controller is used to control the opening degree of the bypass valve to be continuously reduced until the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance.

In the method for operating the refrigerator during pre-cooling of (11), in addition to the opening degree control of the bypass valve, the cooling rate is adjusted and corrected by performing the rotation speed control of the refrigerator (compressor, expander) during the initial operation from the start-up time to the completion of pre-cooling, and the cooling rate is kept constant, whereby the refrigerant temperature can be controlled with high accuracy.

Further, by using the continuous opening control of the bypass valve and the rotational speed control of the refrigerator in combination, the opening of the bypass valve can be set for each step of temperature section, and rotational speed control can be performed so that the cooling rate becomes a preset constant set value in each of the different temperature sections.

(12) Another aspect of the present disclosure provides the method for operating a refrigerator during precooling, wherein the refrigerator includes: a heat exchanger for exchanging heat between a secondary refrigerant that cools a cooling target and the refrigerant; and a secondary refrigerant temperature sensor for detecting the temperature of the secondary refrigerant, wherein the operation method includes a main cooling operation switching step of: 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.

In the method for operating the refrigerator during pre-cooling in (12), the temperature detection point on the secondary refrigerant temperature sensor is switched from the temperature sensor at the stage of reaching the second target temperature, and the rotation speed is controlled based on the detection result of the secondary refrigerant temperature sensor, whereby the operation can be smoothly shifted from the pre-cooling operation during the initial operation to the normal (steady) operation.

Description of the reference numerals

1-a refrigerator; a 2-cooling unit (secondary-side load heat exchanger); 7-expander-integrated compressor; 8-refrigerant circulation lines; 9-a first motor; 10-integral compressor; 11-a second motor; 12-a first heat exchanger; 13-a second heat exchanger; 14-a third heat exchanger; 15-a heat exchanger for heat recovery (regeneration heat exchanger); 16-cooling object side circulation line; 20-superconducting devices (cooling objects); 25-buffer line section; 26-buffer line; 27-a buffer tank; 28-a first opening/closing valve (high-pressure side buffer valve); 29-a second opening/closing valve (low-pressure side buffer valve); 30-bypass line portion; 31-a bypass line; 32-a third opening/closing valve (bypass valve); 33-a first temperature sensor (temperature sensor); 34-a second temperature sensor (temperature sensor); 35-a third temperature sensor (secondary refrigerant temperature sensor); 36-a first pressure sensor; 37-a second pressure sensor; 41-a third pressure sensor; 38-a first power meter; 39-a second power meter; 40-a controller (control means); a C1-low stage compressor; c2-intermediate compressor; a C3-advanced compressor; a T-expander; r1-refrigerant; r2-refrigerant for cooling object (liquid nitrogen, secondary refrigerant, object to be cooled); s1-a first connecting part; s2-a second connecting part; s3-a third connecting part; s4-a fourth connecting part; w-cooling water.

Claims

1. A refrigerator is provided with:

an expander-integrated compressor including a compressor that compresses a refrigerant, and an expander that is coupled to the compressor via a rotation shaft that can be driven by a motor and that expands the refrigerant compressed by the compressor;

a cooling unit that cools a cooling object by using the refrigerant expanded in the expander;

a refrigerant circulation line including a low pressure line from the expander to the low-stage compressor via the cooling unit, a medium pressure line from the low-stage compressor to the high-stage compressor, and a high pressure line from the high-stage compressor to the expander, for circulating the refrigerant;

a bypass line having one end connected to a first connection portion provided to the high-pressure line and the other end connected to a second connection portion provided to the low-pressure line; and

and a bypass valve provided in the bypass line, wherein the flow rate of the refrigerant flowing through the bypass line can be adjusted by adjusting the opening degree.

2. A refrigerator according to claim 1, wherein,

the device is provided with:

a temperature sensor for detecting a temperature of the refrigerant flowing between the first connection portion and the expander in the high-pressure line; and

And a controller that controls the opening degree of the bypass valve and the rotation speed of the rotation shaft based on a detection result of the temperature sensor.

3. A refrigerator according to claim 1, wherein,

the device is provided with:

a temperature sensor for detecting a temperature of the refrigerant between the cooling portion and the expander in the low-pressure line; and

4. A refrigerator according to claim 2 or 3, characterized in that,

the controller performs the following control: during an initial operation of the refrigerator from when a start-up is started to when a pre-cooling operation is completed, the bypass valve is controlled so as to gradually decrease in opening degree before the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance, and the rotation speed is controlled so that a speed of decrease in the temperature of the refrigerant detected by the temperature sensor is kept constant.

5. A refrigerator according to claim 2 or 3, characterized in that,

the controller performs the following control: during an initial operation of the refrigerator from when a start-up is started to when a pre-cooling operation is completed, the bypass valve is controlled so as to continuously decrease in opening degree until the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance, and the rotation speed is controlled so that a rate of decrease in the temperature of the refrigerant detected by the temperature sensor is kept constant.

6. A refrigerator according to claim 4 or 5, characterized in that,

the controller performs the following control: the bypass valve is controlled so that the opening degree is 0% at a stage when the temperature of the refrigerant detected by the temperature sensor reaches the first target temperature, 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 lower than the first target temperature, and the rotation speed is controlled so that the speed of decrease in the temperature of the refrigerant detected by the temperature sensor is maintained constant.

7. A refrigerator according to claim 6, wherein,

the device is provided with:

a heat exchanger for exchanging heat between a secondary refrigerant that cools the cooling target and the refrigerant; and

a secondary refrigerant temperature sensor for detecting a temperature of the secondary refrigerant,

the controller controls the rotation speed based on a detection result of the secondary refrigerant temperature sensor in a case where the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature.

8. A refrigerator according to any one of claims 1 to 7,

the device is provided with:

a heat recovery heat exchanger that cools the refrigerant in the high-pressure line by the refrigerant that has been used to cool the cooling target in the cooling unit;

a buffer pipe having one end connected to a third connection portion provided between the heat exchanger for heat recovery and the expander of the high-pressure pipe and the other end connected to a fourth connection portion provided between the expander and the cooling portion of the low-pressure pipe;

a buffer tank provided in the buffer line and configured to store the refrigerant sent from the high-pressure line;

a high-pressure-side buffer valve provided between the buffer tank and the third connection portion in the buffer line;

a low-pressure side buffer valve provided between the buffer tank and the fourth connection portion in the buffer line;

a first pressure sensor for detecting a pressure of the refrigerant between the first connection portion and the third connection portion in the high-pressure line;

a second pressure sensor for detecting an internal pressure of the buffer tank; and

And a controller for controlling the opening degrees of the high-pressure side cushion valve and the low-pressure side cushion valve according to the detection results of the first pressure sensor and the second pressure sensor.

9. An operation method at the time of pre-cooling of a refrigerator, which is an operation method during an initial operation period from the time of starting to the time of completing pre-cooling of the refrigerator, the refrigerator comprising:

a refrigerant circulation line provided with: a low pressure line from the expander to the low-stage compressor via the cooling portion, a medium pressure line from the low-stage compressor to the high-stage compressor, and a high pressure line from the high-stage compressor to the expander for circulating the refrigerant;

a bypass line having one end connected to a first connection portion provided to the high-pressure line and the other end connected to a second connection portion provided to the low-pressure line;

A bypass valve provided in the bypass line, the bypass valve being capable of adjusting a flow rate of the refrigerant flowing through the bypass line by adjusting an opening degree;

a temperature sensor for detecting a temperature of the refrigerant flowing between the first connection portion and the expander in the high-pressure line or a temperature of the refrigerant between the cooling portion and the expander in the low-pressure line; and

a controller that controls an opening degree of the bypass valve and a rotation speed of the rotation shaft based on a detection result of the temperature sensor,

the operation method includes:

a start-up operation step of starting operation with the rotation speed of the rotation shaft set to a preset rotation speed lower than that in the steady operation after the initial operation period and with the opening of the bypass valve set to a preset opening;

a bypass control operation step of controlling, by the controller, the opening degree of the bypass valve to be reduced before the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance;

a step of cooling the refrigerant before reaching a second target temperature set in advance from the first target temperature by setting the opening degree of the bypass valve to 0% in a stage where the temperature of the refrigerant reaches the first target temperature; and

And a cooling rate control step of controlling the rotation speed by the controller so that a rate of decrease in the temperature of the refrigerant is kept constant in at least the bypass control operation step in the bypass control operation step and the non-bypass control operation step.

10. The method for operating a refrigerator during pre-cooling according to claim 9, wherein,

in the bypass control operation step, the controller controls the opening degree of the bypass valve to be gradually reduced until the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance.

11. The method for operating a refrigerator during pre-cooling according to claim 9, wherein,

in the bypass control operation step, the controller is configured to continuously reduce the opening degree of the bypass valve until the temperature of the refrigerant detected by the temperature sensor reaches a first target temperature set in advance.

12. The method for operating a refrigerator during pre-cooling according to any one of claims 9 to 11, wherein,

the refrigerator is provided with:

the operation method includes a main cooling operation switching step of: the controller controls the rotation speed based on a detection result of the secondary refrigerant temperature sensor in a case where the temperature of the refrigerant detected by the temperature sensor is lower than the second target temperature.