JP2011106755A - Cryogenic refrigerator and method for operating the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cryogenic refrigerator which adjusts the pressure of coolant gas in a closed loop while reducing the usage of the coolant gas, and a method for operating the same. <P>SOLUTION: The cryogenic refrigerator includes the closed loop L1 which is provided with the main compressor 2 for compressing/circulating the coolant gas, the main heat exchanger 3 for cooling the compressed coolant gas by heat exchanging with the returned coolant gas, an expansion turbine 4 for adiabatically expanding the cooled coolant gas, and an auxiliary heat exchanger 5 for heat exchanging between cryogenic coolant gas coming out of the expansion turbine 4 and cooling liquid, and which is structured of a circulation route for circulating the coolant gas after being heat-exchanged in the auxiliary heat exchanger 5 in the main compressor 2 via the main heat exchanger 3. The cryogenic refrigerator 1 includes a buffer tank 6 communicated with the closed loop L1 on an inlet side 2a of the main compressor 2, and an auxiliary compressor 7 which compares the pressure in the closed loop L1 on the inlet side 2a of the main compressor 2 with the pressure in the buffer tank 6 for pressure-feeding the coolant gas from the low-pressure side to the high-pressure side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cryogenic refrigeration apparatus that cools a refrigerant gas to a cryogenic temperature and an operation method thereof, and more particularly, to a cryogenic refrigeration apparatus including a system that efficiently replenishes and collects refrigerant gas and an operation method thereof.

  In order to cool high-temperature superconducting equipment (for example, superconducting power transmission cables, superconducting transformers, superconducting motors, superconducting fault current limiters, superconducting power storage units, etc.) Stirling refrigerators, Brayton cycle refrigerators, etc.) are used. When cooling a high-temperature superconducting device, the cooling temperature varies depending on the type and application of the superconducting wire, but the cooling temperature is lower than the liquid nitrogen temperature (77K) at atmospheric pressure (for example, 70K, 65K, 40K). ) Is used. For such cryogenic cooling, helium, neon, hydrogen, a mixed gas thereof, or the like is used as a refrigerant gas.

  By the way, as a cryogenic refrigeration apparatus, patent document 1 and patent document 2 are known. Specifically, the cryogenic refrigeration apparatus described in Patent Document 1 is a Brayton equipped with a compressor 102, a first intermediate heat exchanger 103, an expansion turbine 104, and a cryogenic heat exchanger 105 as shown in FIG. It is a cycle refrigerator. The cryogenic refrigeration apparatus 101 is located in the middle of the bypass line L106 that connects the high-pressure part and the low-pressure part, and an air storage tank having pressure control valves 106a and 106b on the high-pressure side and the low-pressure side, respectively. 106 and a pressure control device 126 for controlling the pressure regulating valves 106a and 106b. The pressure control device 126 makes the pressure of the air storage tank 106 the same as that of the closed loop L101 at normal temperature and when stopped, so that the valve opening is opened, and the pressure of the high pressure section is set to a predetermined pressure during operation that generates extremely low temperature. The pressure control valves 106a and 106b are controlled so that

  Moreover, in the refrigeration apparatus which is the prior art described in Patent Document 2, a buffer tank connected via a path having a circulation amount adjusting valve to the discharge side and the suction side of the circulation compressor, respectively, and the discharge pressure of the circulation compressor And a pressure regulator that opens and closes the circulation amount regulating valve. Then, as a path for keeping the suction pressure of the circulation compressor constant, a path connecting the discharge side and the suction side of the circulation compressor via a bypass valve, and measuring the suction pressure of the circulation compressor, the bypass A pressure regulator for adjusting the opening of the valve is provided.

JP 2009-121786 A Japanese Patent Laid-Open No. 5-223378

  In the cryogenic refrigeration apparatus having such a configuration, when the inside of the refrigeration apparatus becomes extremely cold due to operation of the apparatus, the specific volume of the refrigerant gas becomes small, and the pressure inside the refrigeration apparatus cannot be maintained at a predetermined pressure. . For this reason, it is necessary to replenish the refrigerant gas into the refrigeration apparatus from the buffer tank (or the air storage tank). Further, the pressure of the refrigerant gas filled in the closed loop when the cryogenic refrigeration apparatus is at a normal temperature and in a stopped state is generally set higher than the atmospheric pressure. This is because the specific volume is reduced by increasing the pressure of the refrigerant gas, the refrigeration capacity of the refrigerator is increased by increasing the circulation flow rate of the refrigerant gas, and the entire apparatus is reduced in size. For example, in the cryogenic refrigeration apparatus described in Patent Document 1, the low-pressure side pressure is 0.5 to 0.6 MPa, and the high-pressure side pressure is 1.0 to 1.2 MPa.

  However, in the cryogenic refrigeration apparatus shown in Patent Document 1 and Patent Document 2, when the refrigerant gas stored in the buffer tank (or the storage tank) is supplied to the low pressure side of the closed loop, the pressure in the buffer tank is reduced. There is no problem when the pressure is higher than the low pressure side of the closed loop, but when the pressure in the buffer tank becomes the same as the low pressure side of the closed loop, there is a problem that the refrigerant gas cannot be replenished any more. That is, the cryogenic refrigeration apparatus having the above-described configuration has a problem that expensive and rare helium and neon used as a refrigerant gas are wastedly stored in a buffer tank without being used up to atmospheric pressure. It was.

  The present invention has been made in view of the above circumstances, and provides a cryogenic refrigeration apparatus capable of adjusting the pressure of refrigerant gas in a closed loop while reducing the amount of refrigerant gas used, and an operating method thereof. It is aimed.

To solve this problem,
The invention according to claim 1 is a main compressor for compressing and circulating refrigerant gas;
A main heat exchanger that cools the compressed refrigerant gas by heat exchange with the returned refrigerant gas;
An expansion turbine for adiabatically expanding the cooled refrigerant gas;
A sub heat exchanger for exchanging heat between the cryogenic refrigerant gas exiting the expansion turbine and the coolant; and
A cryogenic refrigeration apparatus comprising a closed loop consisting of a circulation path for circulating the refrigerant gas after heat exchange in the sub heat exchanger to the main compressor via the main heat exchanger,
A buffer tank in communication with the closed loop via a valve on the inlet side of the main compressor;
A sub-compressor that compares the pressure in the closed loop on the inlet side of the main compressor with the pressure in the buffer tank, and pumps the refrigerant gas from the low pressure side to the high side. It is a cryogenic refrigeration system.

The invention according to claim 2 is a replenishment path connected from the buffer tank to the inlet side of the main compressor in the closed loop via the sub compressor,
2. The cryogenic refrigeration apparatus according to claim 1, further comprising a recovery path connected to the buffer tank from the inlet side of the main compressor in the closed loop via the sub compressor.

  The invention according to claim 3 is provided with a replenishment / recovery path for connecting the inlet side of the main compressor of the closed loop and the buffer tank without passing through the sub-compressor. 2. The cryogenic refrigeration apparatus according to 2.

The invention according to claim 4 includes a bypass path communicating the inlet side and the outlet side of the main compressor in the closed loop,
The cryogenic refrigeration apparatus according to any one of claims 1 to 3, wherein the bypass path includes a bypass valve in an intermediate portion of the bypass path.

  A fifth aspect of the present invention is the cryogenic refrigeration apparatus according to any one of the first to fourth aspects, wherein a pressure reducing valve is provided on the inlet side of the sub-compressor.

  The invention according to claim 6 is the cryogenic refrigeration apparatus according to any one of claims 1 to 5, wherein the sub-compressor has a smaller processing amount than the main compressor.

  A seventh aspect of the present invention is the cryogenic refrigeration apparatus according to any one of the first to sixth aspects, wherein the main compressor is driven by an inverter.

The invention according to claim 8 is an aftercooler provided on the outlet side of the main compressor,
The cryogenic refrigeration according to any one of claims 1 to 7, further comprising: a check valve provided on an outlet side of the after cooler or between the main compressor and the after cooler. Device.

The invention according to claim 9 is a heat-insulating container that houses the object to be cooled and the coolant,
The cryogenic refrigeration apparatus according to any one of claims 1 to 5, further comprising a circulation pump that circulates the cooling liquid to the sub heat exchanger.

Invention of Claim 10 is the operating method of the cryogenic refrigeration apparatus as described in any one of Claims 1 thru | or 9, Comprising:
The pressure of the refrigerant gas in the closed loop on the inlet side of the main compressor is equal to or lower than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank is higher than the pressure in the closed loop on the inlet side of the main compressor. If low, introduce refrigerant gas from the buffer tank to the sub-compressor, replenish the refrigerant gas pumped by the sub-compressor into the closed loop,
The pressure of at least one of the inlet side and the outlet side of the main compressor of the refrigerant gas in the closed loop is equal to or higher than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank is the inlet side of the main compressor When the pressure in the closed loop is higher, refrigerant gas is introduced into the sub-compressor from the closed loop, and the refrigerant gas pumped by the sub-compressor is recovered in the buffer tank. It is the operating method of a low-temperature freezing apparatus.

  The invention according to claim 11 is characterized in that the pressure of the refrigerant gas in the closed loop is made atmospheric pressure by pumping the refrigerant gas in the closed loop by a sub-compressor and collecting it in the buffer tank. The operation method of the cryogenic refrigeration apparatus according to Item 10.

Invention of Claim 12 is the operating method of the cryogenic refrigeration apparatus as described in any one of Claims 4 thru | or 9, Comprising:
The operation method of the cryogenic refrigeration apparatus according to claim 10 or 11, wherein the bypass valve is opened when the operation of the main compressor is stopped.

Invention of Claim 13 is the operating method of the cryogenic refrigeration apparatus as described in any one of Claims 5 thru | or 9, Comprising:
The cryogenic refrigeration apparatus operating method according to any one of claims 10 to 12, wherein the pressure of the refrigerant gas is reduced to substantially atmospheric pressure before introducing the refrigerant gas into the sub-compressor. is there.

Invention of Claim 14 is the operating method of the cryogenic refrigeration apparatus as described in any one of Claims 7 thru | or 9, Comprising:
When the pressure on the outlet side of the main compressor of the refrigerant gas in the closed loop becomes higher than a predetermined pressure, the operating frequency of the main compressor is decreased by changing the output frequency of the inverter. A method for operating a cryogenic refrigeration apparatus according to any one of claims 10 to 13.

  According to the cryogenic refrigeration apparatus and the operation method thereof of the present invention, the buffer tank communicated with the closed loop on the inlet side of the main compressor via the valve, the pressure in the closed loop on the inlet side of the main compressor, and the buffer tank A sub-compressor that compares the pressure and pumps the refrigerant gas from the low pressure side to the high pressure side. Thus, if the pressure on the inlet side of the main compressor in the closed loop is equal to or lower than a predetermined pressure and the pressure of the refrigerant gas in the buffer tank is higher than the pressure on the inlet side of the main compressor in the closed loop, When the refrigerant gas is replenished directly from the tank into the closed loop and the pressure of the refrigerant gas in the buffer tank is lower than the pressure on the inlet side of the main compressor in the closed loop, the refrigerant gas in the buffer tank is pumped by the sub compressor. Can be refilled in the closed loop. In addition, the pressure of at least one of the inlet side and the outlet side of the main compressor in the closed loop is equal to or higher than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank is the pressure on the inlet side of the main compressor in the closed loop. If higher, the refrigerant gas in the closed loop can be pumped by the sub-compressor and recovered in the buffer tank. In this way, the refrigerant gas stored in the buffer tank can be boosted by the sub-compressor and sent out into the closed loop. Therefore, the refrigerant gas is effectively used until the pressure in the buffer tank reaches atmospheric pressure. Can be replenished. For this reason, expensive and rare refrigerant gas cannot be used and is not stored in the buffer tank in vain. Therefore, the pressure of the refrigerant gas in the closed loop can be adjusted while reducing the amount of refrigerant gas used. Further, the installation space can be reduced by reducing the volume of the buffer tank.

  Further, according to the operation method of the cryogenic refrigeration apparatus of the present invention, the refrigerant gas in the closed loop is pumped into the buffer tank by the sub-compressor until the pressure of the refrigerant gas in the closed loop becomes atmospheric pressure. Can be recovered in the buffer tank. This can reduce the loss of the refrigerant gas released into the atmosphere when the components are opened and inspected at the time of maintenance or device failure.

It is a systematic diagram which shows one example of the cryogenic refrigeration apparatus of this invention. It is a systematic diagram for demonstrating the filling amount of refrigerant gas from the volume of the component apparatus of FIG. 1, pressure, and temperature. It is a systematic diagram which shows an example of the conventional cryogenic refrigeration apparatus.

  Hereinafter, a cryogenic refrigeration apparatus which is an embodiment to which the present invention is applied will be described in detail with reference to the drawings together with an operation method. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

  FIG. 1 is a diagram showing a cryogenic refrigeration apparatus which is an embodiment to which the present invention is applied. As shown in FIG. 1, the cryogenic refrigeration apparatus 1 of the present embodiment includes a closed loop L1 including a circulation path provided with a main compressor 2, a main heat exchanger 3, an expansion turbine 4, and a sub heat exchanger 5, A buffer tank 6 that communicates with the closed loop L1 and a sub-compressor 7 that pumps refrigerant gas between the closed loop L1 and the buffer tank 6 are schematically configured. More specifically, the cryogenic refrigeration apparatus 1 includes a heat insulating container 8 that houses a cooled object 8a and a refrigerant liquid 8b, and a circulation pump 9 that circulates the refrigerant liquid 8b to the auxiliary heat exchanger 5. ing.

Further, as shown in FIG. 1, the cryogenic refrigeration apparatus 1 of the present embodiment compresses refrigerant gas by the main compressor 2, and converts the high-pressure side refrigerant gas to the low-pressure side return refrigerant gas in the main heat exchanger 3. The refrigerant is cooled by exchanging heat with it, and the cooled refrigerant gas is adiabatically expanded by the expansion turbine 4 to generate a cryogenic temperature. In the auxiliary heat exchanger 5, the liquid sent from the circulation pump 9 by the cryogenic refrigerant gas. The refrigerant liquid (cooling liquid) 8b such as nitrogen is cooled, and the cooled object 8a is cooled by the refrigerant liquid 8b.
As the refrigerant gas of this embodiment, helium, neon, or hydrogen having a lower boiling point than nitrogen and a mixed gas thereof, or a mixed gas obtained by slightly mixing an inert gas such as nitrogen or argon is used.

  The closed loop L1 includes a main compressor 2 that compresses and circulates refrigerant gas, a main heat exchanger 3 that cools the compressed refrigerant gas by heat exchange with the returned refrigerant gas, and an expansion turbine that adiabatically expands the cooled refrigerant gas. 4 and a sub heat exchanger 5 for exchanging heat between the cryogenic refrigerant gas exiting the expansion turbine 4 and the coolant, and the refrigerant gas after heat exchange in the sub heat exchanger 5 Is circulated through the main compressor 2 through the main heat exchanger 3.

  The main compressor 2 is a turbo compressor provided in the closed loop L1 for compressing and circulating the refrigerant gas. In the present embodiment, as shown in FIG. 1, a single-stage turbo compressor is illustrated as the main compressor 2, but the present invention is not limited to this, and the intercooler is replaced with a single-stage turbo compressor. It is good also as a two-stage turbo compressor provided with.

  The pressure on the inlet side 2a of the main compressor 2 in the closed loop L1 is preferably, for example, 0.5 to 1 MPa. The pressure on the outlet side 2b of the main compressor 2 in the closed loop L1 is preferably 1 to 2 MPa. And it is preferable that the compression ratio of the main compressor 2 shall be about 1.6-3 from the point of the cooling temperature range and the energy efficiency of a freezing apparatus.

  The main compressor 2 may be driven by an inverter. When the main compressor 2 is inverter-controlled, when the pressure on the outlet side 2b of the main compressor 2 becomes higher than a specified value, the operating frequency of the main compressor 2 is changed by changing the output frequency of the inverter. Therefore, the pressure on the outlet side 2b of the main compressor 2 can be kept below a specified value. Thereby, the maximum pressure in the closed loop L <b> 1 can be kept below the pressure resistance of the pressure vessel constituting the cryogenic refrigeration apparatus 1.

  In addition, as shown in FIG. 1, for example, a water-cooled aftercooler 10 is preferably installed on the outlet side (secondary side) 2 b of the main compressor 2. The aftercooler 10 is supplied with cooling water from an external cooling tower (not shown), and can cool the high-temperature refrigerant gas to near the atmospheric temperature.

  Furthermore, a check valve (check valve) 11 may be provided on the outlet side of the aftercooler 10. Thereby, it is possible to prevent the compressed cooling gas from flowing backward to the main compressor 2 and reversely rotating when the cryogenic refrigeration apparatus 1 is stopped during normal operation or emergency stop. The check valve 11 may be provided at an intermediate position between the main compressor 2 and the aftercooler 10.

As shown in FIG. 1, the main heat exchanger 3 is disposed in the middle of the main compressor 2 and the expansion turbine 4 in the closed loop L <b> 1, and the refrigerant gas compressed by the main compressor 2 and the auxiliary heat exchanger 5. The compressed refrigerant gas is cooled by exchanging heat with the refrigerant gas returned from the refrigerant.
As shown in FIG. 1, the expansion turbine 4 is installed on the secondary side of the main heat exchanger 3 in the closed loop L <b> 1, and a refrigerant gas cooled by the main heat exchanger 3 is adiabatically expanded to produce a cryogenic temperature. Refrigerant gas. Further, the expansion turbine 4 may be mounted on the same axis as the main compressor 2 to have an integral structure.

As shown in FIG. 1, the auxiliary heat exchanger 5 is installed on the secondary side of the expansion turbine 4 in the closed loop L <b> 1, and is a refrigerant gas that is made a cryogenic temperature by the expansion turbine 4 and a refrigerant that is a heat exchanger. The refrigerant liquid 8b is cooled by exchanging heat with the liquid 8b.
The refrigerant gas cooled to an extremely low temperature indirectly cools the cooled object 8a accommodated in the heat insulating container 8 by the refrigerant liquid 8b.
Here, the object to be cooled 8a in the present embodiment is a high-temperature superconducting device such as a superconducting power transmission cable, a superconducting transformer, a superconducting motor, a superconducting current limiter, a superconducting power storage, or the like.

  The buffer tank 6 is a storage tank for storing the refrigerant gas, and is connected to the closed loop L1 on the inlet side 2a of the main compressor 2 by a replenishment / recovery path L2, as shown in FIG. The buffer tank 6 communicates with the closed loop L1 through an on-off valve (valve) 12 provided in the replenishment / recovery path L2. Here, the replenishment / recovery path L2 is a path that connects the inlet side 2a of the main compressor 2 in the closed loop L1 and the buffer tank 6 without passing through the sub compressor 7. The buffer tank 6 is connected to a path L3 provided with an on-off valve 13 so that the refrigerant gas can be supplied into the buffer tank 6 from the path L3.

The sub-compressor 7 compares the pressure in the closed loop L1 on the inlet side 2a of the main compressor 2 with the pressure in the buffer tank 6, and pumps the refrigerant gas from the low pressure side to the high pressure side. Is provided.
The sub-compressor 7 of the present embodiment may have a smaller processing amount than the main compressor 2, and uses a small-sized compressor that can be easily obtained at low cost, such as an oil-free diaphragm type, reciprocating type, or scroll type. be able to.

By the way, in general, the above-described small compressors that are inexpensive and easily available are mainly inhaled at atmospheric pressure. When such a small compressor is used as the sub-compressor 7, when a refrigerant gas having a high pressure enters the suction side, not only the load of the small compressor increases rapidly, but also there is a problem in pressure resistance. Therefore, it is preferable to provide the pressure reducing valve 14 on the suction side (inlet side) of the sub compressor 7. Since the pressure of the refrigerant gas on the suction side of the sub compressor 7 can be reduced to near atmospheric pressure by the pressure reducing valve 14, a commercially available small-sized compressor can be used as the sub compressor 7. .
A check valve 15 is provided on the discharge side (exit side) of the sub compressor 7.
Furthermore, it is preferable to provide a buffer tank (not shown) having a small capacity, for example, several liters, between the pressure reducing valve 14 and the sub compressor 7. Thereby, the pulsation of the suction pressure of the sub compressor 7 can be prevented.

  The cryogenic refrigeration apparatus 1 of the present embodiment includes a replenishment path L4 that is connected from the buffer tank 6 to the inlet side 2a of the main compressor 2 in the closed loop L1 via the sub compressor 7, and the inlet of the main compressor 2 in the closed loop L1. A recovery path L5 connected from the side 2a to the buffer tank 6 via the sub compressor 7, and a bypass path L6 communicating the inlet side 2a and the outlet side 2b of the main compressor 2 in the closed loop L1. .

Here, the replenishment path L4 is provided with an on-off valve 16 on the connection side with the buffer tank 6 and an on-off valve 17 on the connection side with the closed loop L1.
In the recovery path L5, an opening / closing valve 18 is provided on the connection side with the closed loop L1, and an opening / closing valve 19 is provided on the connection side with the buffer tank 6.
Further, the bypass path L6 is provided with a bypass valve 20 composed of an open / close valve.

In other words, the suction side of the sub-compressor 7 is communicated with the buffer tank 6 and the on-off valve 16 at the same time as being communicated with the closed loop L 1 and the on-off valve 18 on the inlet side 2 a of the main compressor 2.
On the other hand, the discharge side of the sub-compressor 7 is communicated with the buffer tank 6 via the on-off valve 19 and at the same time with the closed loop L1 and the on-off valve 17 on the inlet side 2a of the main compressor 2.

Next, the operation method of the cryogenic refrigeration apparatus 1 of the present embodiment will be described.
First, in the closed loop L <b> 1 of the cryogenic refrigeration apparatus 1, the refrigerant gas is compressed by the main compressor 2. Since the refrigerant gas compressed by the main compressor 2 becomes high temperature, the high-temperature refrigerant gas is cooled to near atmospheric temperature by the aftercooler 10 installed on the outlet side (downstream side) of the main compressor 2.

  Next, the refrigerant gas having passed through the after cooler 10 is introduced into the main heat exchanger 3 housed in the cold box, and heat exchange with the returned refrigerant gas from the sub heat exchanger 5 is performed. Thereby, the refrigerant gas is cooled to a temperature of 65 to 75 K and introduced into the expansion turbine 4. Then, in the expansion turbine 4, the temperature of the refrigerant gas is lowered to 55 to 65K by adiabatically expanding the refrigerant gas from the high pressure side pressure (1 to 2 MPa) to the low pressure side pressure (0.5 to 1 MPa).

  Next, the refrigerant gas whose temperature has been lowered to 55 to 65 K by the expansion turbine 4 is introduced into the auxiliary heat exchanger 5. Then, in the sub heat exchanger 5, the refrigerant liquid 8b is subcooled by heat exchange between the cryogenic refrigerant gas and the refrigerant liquid 8b such as liquid nitrogen, which means that the liquid is lower than its saturation temperature. Then, the liquid nitrogen is cooled to about 65K, which is the boiling point of liquid nitrogen (about 77K) to the freezing point (about 63K). At this time, the temperature of the refrigerant gas after heat exchange with the refrigerant liquid 8b rises to 60 to 70K. The refrigerant gas that has passed through the auxiliary heat exchanger 5 then returns to the main heat exchanger 3. Here, the temperature of the low-pressure-side return refrigerant gas that has returned to the main heat exchanger 3 rises to substantially room temperature when leaving the main heat exchanger 3 by exchanging heat with the high-pressure side refrigerant gas. Then, the refrigerant gas that has reached the room temperature through the main heat exchanger 3 returns to the inlet side 2 a of the main compressor 2. In the closed loop L1 in the polar refrigeration apparatus 1 of the present embodiment, the refrigerant gas circulates as described above.

  Note that the refrigerant liquid 8b in the heat insulating container 8 that cools the object to be cooled 8a is maintained at about 70K by heat exchange in the sub heat exchanger 5 described above.

  Here, when the pressure of the refrigerant gas in the closed loop L1 on the inlet side 2a of the main compressor 2 becomes equal to or lower than a predetermined pressure, the pressure of the refrigerant gas in the buffer tank 6 becomes the inlet of the main compressor 2. When the pressure is higher than the pressure on the side 2a, the on-off valve 12 provided in the replenishment / recovery path L2 is opened to replenish the refrigerant gas from the buffer tank 6 into the closed loop L1.

  On the other hand, when the pressure of the refrigerant gas in the buffer tank 6 is lower than the pressure in the closed loop L1 on the inlet side 2a of the main compressor 2, the on-off valve 16 provided in the replenishment path L4 is opened. Then, the refrigerant gas is introduced from the buffer tank 6 to the sub compressor 7. Then, the subcompressor 7 supplies the refrigerant gas to the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1 (meaning the minimum pressure necessary for replenishing the refrigerant gas, and the inlet side of the main compressor 2). The pressure is increased to a pressure slightly higher than the pressure of 2a), and the on-off valve 17 provided in the replenishment path L4 is opened to replenish the refrigerant gas into the closed loop L1. Thus, by replenishing the closed loop L1 with the refrigerant gas pumped by the sub compressor 7, the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1 can be kept constant.

  On the other hand, the pressure of at least one of the inlet side 2a and the outlet side 2b of the main compressor 2 in the closed loop L1 is equal to or higher than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank 6 is the main compression in the closed loop L1. When the pressure is higher than the pressure on the inlet side 2 a of the machine 2, the refrigerant gas in the closed loop L <b> 1 can be pumped by the sub compressor 7 and recovered in the buffer tank 6. In addition, when the pressure of the refrigerant gas in the closed loop L1 on the outlet side 2b of the main compressor 2 is equal to or higher than a predetermined pressure, the pressure of the refrigerant gas in the buffer tank 6 is the inlet side of the main compressor 2 When the pressure is lower than the pressure of the main compressor 2, the main compression is performed by opening the bypass valve 20 provided in the bypass path L6 that connects the outlet side 2b (high pressure side) and the inlet side 2a (low pressure side) of the main compressor 2. Since the refrigerant gas is returned to the inlet side (low pressure side) 2b of the compressor 2 and the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1 becomes higher than a specified value, the opening / closing provided in the replenishment / recovery path L2 The refrigerant gas can be recovered from the closed loop L1 into the buffer tank 6 by opening the valve 12.

  On the other hand, when the pressure of the refrigerant gas in the buffer tank 6 is higher than the pressure in the closed loop L1 on the inlet side 2a of the main compressor 2, the on-off valve 18 provided in the recovery path L5 is released. Then, the refrigerant gas is introduced into the sub compressor 7 from the closed loop L1. Then, the sub-compressor 7 raises the refrigerant gas to a pressure in the buffer tank 6 (which means a minimum pressure necessary for the recovery of the refrigerant gas and is slightly higher than the pressure in the buffer tank 6). After that, the on-off valve 19 provided in the recovery path L5 is opened to recover the refrigerant gas in the buffer tank 6. In this way, by collecting the refrigerant gas pumped by the sub compressor 7 in the buffer tank 6, the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1 can be kept constant.

  Further, when the cryogenic refrigeration apparatus 1 is stopped, the main compressor 2 is stopped from the steady operation. However, in order to prevent abnormal vibration of the main compressor 2, the main compressor 2 is stopped after receiving a stop signal of the apparatus. In the meantime, by releasing the bypass valve 20 and returning the refrigerant gas from the high pressure side (outlet side 2b) to the low pressure side (inlet side 2a) of the main compressor 2, the pressure on the high pressure side of the main compressor 2 is reduced. The pressure in the closed loop L1 is equalized. As a result of this operation, the pressure on the low pressure side (inlet side 2a) of the main compressor 2 becomes higher than the specified value, so the on-off valve 12 provided in the replenishment / recovery path L2 is opened to buffer the refrigerant gas in the closed loop L1. It collects in the tank 6.

  Furthermore, when the cryogenic refrigeration apparatus 1 is maintained or broken, it is necessary to open and check each component device. In this case, the on-off valve 18 provided in the recovery path L5 is opened, and the refrigerant gas in the closed loop L1 is pumped by the sub compressor 7 and recovered in the buffer tank 6. Thereby, the pressure of the refrigerant gas in the closed loop L1 can be recovered to near atmospheric pressure.

  Next, with regard to the state where the cryogenic refrigeration apparatus 1 of the present embodiment is started from the normal temperature stop state at normal temperature, and how much refrigerant gas replenishment amount from the buffer tank 6 is required from the pressure and temperature change during the freezing operation, This will be described with reference to FIG.

  As shown in FIG. 2, the volume in the closed loop L1 of the cryogenic refrigeration apparatus 1 is divided into (A) to (E), and the volume of the buffer tank 6 is set to (F). Here, for the sake of simplicity, the volumes of (A) to (E) are all equal, and the amount of refrigerant gas that occupies each volume of (A) to (E) at atmospheric pressure (0.1 MPa) and room temperature (300 K). Let (mass) be “Wt”.

  In addition, the pressure and temperature in the closed loop L1 ((A) to (E)) when the cryogenic refrigeration apparatus 1 is at a normal temperature stop state are all equal to 0.7 MPa and 300K. At this time, the amount of refrigerant gas in each volume from (A) to (E) is 7 (Wt). Therefore, the total refrigerant gas amount in the closed loop L1 is 5 × 7 (Wt) = 35 (Wt).

  When the main compressor 2 is started from a normal temperature stop state, (B) and (C) from the main compressor 2 to the expansion turbine 4 are 1.0 MPa, and (D) from the expansion turbine 4 to the main compressor 2. , (E), (A) has a low pressure side of 0.5 MPa. Immediately after startup, the temperatures of (A) to (E) are all 300K, so the amount of refrigerant gas (A) to (E) at this time is 10 for each of (B) and (C) due to the increase or decrease of the pressure. (Wt), (D), (E), and (A) are each 5 (Wt), and the total is 2 × 10 (Wt) + 3 × 5 (Wt) = 35 (Wt).

  If the operation of the cryogenic refrigeration apparatus 1 is continued, the temperature of (C) to (E) decreases due to adiabatic expansion in the expansion turbine 4, and finally the temperature of the auxiliary heat exchanger 5 in (D) is 60K. It becomes. On the other hand, since the high-pressure side inlet and the low-pressure side outlet of the main heat exchanger 2 remain at room temperature, the temperature of (C) and (E) is a simple average of 300K and 60K, and (300 + 60) / 2 = 180K. And

  The final amount of refrigerant gas in the closed loop L1 is 10 (Wt) because (A) is 5 (Wt), (B) is 10 (Wt), and (C) is the amount of refrigerant gas that increases as the temperature decreases. ) × 300/180 = 16.67 (Wt). (D) is 5 (Wt) × 300/60 = 25 (Wt), and (E) is 5 (Wt) × 300/180 = 8.33 (Wt).

  Therefore, the sum of (A) to (E) is 5 (Wt) +10 (Wt) +16.67 (Wt) +25 (Wt) +8.33 (Wt) = 65 (Wt) as a whole. Since the refrigerant gas amount in the closed loop L1 before the operation of the cryogenic refrigeration apparatus 1 is 35 (Wt), 30 (Wt) refrigerant gas is replenished from the buffer tank 6 into the closed loop L1 by the progress of operation and cooling. Will have to.

  Here, assuming that the pressure when the buffer tank 6 is stopped at room temperature is 0.7 MPa, and the volume (F) is assumed to be 5 times the volume of (A) to (E), the buffer tank 6 has atmospheric pressure and room temperature. Thus, 5 (Wt) of refrigerant gas can be stored, and at 0.7 MPa, 7 × 5 (Wt) = 35 (Wt). When the refrigerant gas is boosted from the buffer tank 6 using the sub-compressor 7 (not shown in FIG. 2) and replenished by 30 (Wt) in the closed loop L1 according to the present invention, the remaining refrigerant gas in the buffer tank 6 is obtained. 5 (Wt). That is, the pressure in the buffer tank 6 becomes almost atmospheric pressure, and the refrigerant gas in the buffer tank 6 can be effectively used.

  According to the present invention, by providing the sub-compressor 7, the refrigerant gas in the buffer tank 6 can be replenished into the closed loop L1 up to almost atmospheric pressure. However, in the conventional technology, the refrigerant gas in the buffer tank has a minimum closed loop pressure ( In the example of Patent Document 1 described above, replenishment can only be performed up to 0.5 MPa.

  That is, in order to replenish the refrigerant gas 30 (Wt) in the closed loop from the buffer tank in the cryogenic refrigerator of the prior art, the amount that can be used for replenishment is from 0.7 MPa to 0.5 MPa, The required volume of the buffer tank is 30 (Wt) ÷ (7−5) = 15 (Wt), and a capacity for storing 15 (Wt) of refrigerant gas at atmospheric pressure and room temperature is required.

  Therefore, in the present invention, the volume of the buffer tank 6 can be reduced to 1/3, and the space occupied by the entire apparatus is reduced. Further, the amount of refrigerant gas stored in the buffer tank 6 is 7 × 15 (Wt) = 105 (Wt) in the prior art, and is reduced from 105 (Wt) to 35 (Wt) in the present invention. A small amount of refrigerant gas is also required. That is, the amount of refrigerant gas stored in the buffer tank without being used can be reduced by about 2/3 compared to the conventional case.

  As described above, according to the cryogenic refrigeration apparatus 1 and the operation method thereof according to the present embodiment, the buffer tank 6 communicating with the closed loop L1 via the valve on the inlet side 2a of the main compressor 2, and the main compressor 2 And a sub-compressor 7 that compares the pressure in the closed loop L1 on the inlet side 2a with the pressure in the buffer tank 6 and pumps the refrigerant gas from the low pressure side to the high pressure side. Thus, the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1 is equal to or lower than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank 6 is the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1. Is higher, the refrigerant gas is replenished directly from the buffer tank 6 into the closed loop L1, and the pressure of the refrigerant gas in the buffer tank 6 is lower than the pressure on the inlet side 2a of the main compressor 2 in the closed loop L1. The refrigerant gas in the buffer tank 6 can be pumped by the sub compressor 7 and replenished in the closed loop L1. Further, the pressure of at least one of the inlet side 2a and the outlet side 2b of the main compressor 2 in the closed loop L1 is equal to or higher than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank 6 is the main compression in the closed loop L1. When the pressure is higher than the pressure on the inlet side 2 a of the machine 2, the refrigerant gas in the closed loop L <b> 1 can be pumped by the sub compressor 7 and recovered in the buffer tank 6. Thus, the refrigerant gas stored in the buffer tank 6 can be pressurized by the sub compressor 7 and sent out into the closed loop L1, so that the refrigerant gas is effectively used until the pressure in the buffer tank 6 reaches atmospheric pressure. Thus, the closed loop L1 can be replenished. For this reason, it is not stored in the buffer tank 6 wastefully without using expensive and rare refrigerant gas. Therefore, the pressure of the refrigerant gas in the closed loop L1 can be adjusted while reducing the amount of refrigerant gas used. Moreover, the volume of the buffer tank 6 can be reduced and the installation space can be reduced.

  Further, according to the operation method of the cryogenic refrigeration apparatus 1 of the present embodiment, the refrigerant gas in the closed loop L1 is increased in pressure by feeding the refrigerant gas in the closed loop L1 into the buffer tank 6 by the sub compressor 7. The refrigerant gas can be collected in the buffer tank 6 until the pressure is reached. This can reduce the loss of the refrigerant gas released into the atmosphere when the components are opened and inspected at the time of maintenance or device failure.

  Further, a bypass path L6 that communicates the outlet side (high pressure side) 2b and the inlet side (low pressure side) 2a of the main compressor 2 and a bypass valve 20 is provided in the middle of the path L6, and the outlet of the main compressor 2 When the pressure on the side 2b becomes higher than the specified value, the pressure on the outlet side 2b of the main compressor 2 can be kept below the specified value by opening the bypass valve 20. Thereby, the maximum pressure in the closed loop L <b> 1 can be kept below the pressure resistance of the pressure vessel constituting the cryogenic refrigeration apparatus 1.

  Further, when the main compressor 2 is driven by an inverter and the pressure on the outlet side 2b of the main compressor 2 becomes higher than a specified value, the operating speed of the main compressor 2 is changed by changing the output frequency of the inverter. The pressure on the outlet side of the main compressor 2 can be kept below a specified value. Thereby, the maximum pressure in the closed loop L <b> 1 can be kept below the pressure resistance of the pressure vessel constituting the cryogenic refrigeration apparatus 1.

  In addition, a check valve (check valve) 11 is installed at the outlet of the aftercooler 10 installed on the secondary side (outlet side) of the main compressor 2 or at an intermediate position between the main compressor 2 and the aftercooler 10. Thus, it is possible to prevent the cooling gas compressed at the time of normal operation stop or emergency stop of the cryogenic refrigeration apparatus 1 from flowing backward to the main compressor 2 and reversely rotating.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the present embodiment, the main compressor 2 is a turbo compressor, but it may be a reciprocating compressor or a screw compressor, and has pressure control valves on the outlet side 2b and the inlet side 2a of the main compressor 2, respectively. A path may be provided and connected to the buffer tank 6.

  In the cryogenic refrigeration apparatus 1 of the present embodiment, the refrigerant liquid 8b for cooling the object to be cooled 8a is used as the heat exchanger to be heat exchanged (cooled) by the sub heat exchanger 5. Without installing the auxiliary heat exchanger 5 and the circulation pump 9, the refrigerant gas cooled to a cryogenic temperature by the cryogenic refrigeration apparatus 1 is introduced into the heat insulating container 8 to cool the refrigerant liquid 8b, or to be cooled It is good also as a structure which cools the to-be-cooled body 8a directly by supplying to 8a.

DESCRIPTION OF SYMBOLS 1 ... Cryogenic refrigeration apparatus 2 ... Main compressor 2a ... Inlet side 2b ... Outlet side 3 ... Main heat exchanger 4 ... Expansion turbine 5 ... Sub heat exchanger 6 ... Buffer tank 7 ... Sub compressor 8 ... Insulated container 8a ... Object to be cooled 8b ... Refrigerant liquid (cooling liquid)
9 ... Circulating pump 10 ... After cooler 11 ... Check valve (check valve)
12, 13, 16, 17, 18, 19 ... open / close valve (valve)
14 ... Pressure reducing valve 15 ... Check valve 20 ... Bypass valve L1 ... Closed loop L2 ... Replenishment / recovery path L3 ... Path L4 ... Refill path L5 ... Recovery path L6 ... Bypass path

Claims (14)

A main compressor that compresses and circulates refrigerant gas;
A main heat exchanger that cools the compressed refrigerant gas by heat exchange with the returned refrigerant gas;
An expansion turbine for adiabatically expanding the cooled refrigerant gas;
A sub heat exchanger for exchanging heat between the cryogenic refrigerant gas exiting the expansion turbine and the coolant; and
A cryogenic refrigeration apparatus comprising a closed loop consisting of a circulation path for circulating the refrigerant gas after heat exchange in the sub heat exchanger to the main compressor via the main heat exchanger,
A buffer tank in communication with the closed loop via a valve on the inlet side of the main compressor;
A sub-compressor that compares the pressure in the closed loop on the inlet side of the main compressor with the pressure in the buffer tank, and pumps the refrigerant gas from the low pressure side to the high side. Cryogenic refrigeration equipment. A replenishment path connected from the buffer tank to the inlet side of the main compressor in the closed loop via the sub-compressor;
The cryogenic refrigeration apparatus according to claim 1, further comprising: a recovery path connected to the buffer tank from the inlet side of the main compressor in the closed loop via the sub compressor.   3. The cryogenic refrigeration apparatus according to claim 1, further comprising a replenishment / recovery path that connects the closed-loop inlet side of the main compressor and the buffer tank without passing through the sub-compressor. 4. In the closed loop, comprising a bypass path communicating the inlet side and the outlet side of the main compressor,
The cryogenic refrigeration apparatus according to any one of claims 1 to 3, wherein the bypass path includes a bypass valve in an intermediate portion of the bypass path.   The cryogenic refrigeration apparatus according to any one of claims 1 to 4, wherein a pressure reducing valve is provided on an inlet side of the sub compressor.   The cryogenic refrigeration apparatus according to any one of claims 1 to 5, wherein the sub compressor has a smaller processing amount than the main compressor.   The cryogenic refrigeration apparatus according to any one of claims 1 to 6, wherein the main compressor is driven by an inverter. An aftercooler provided on the outlet side of the main compressor;
The cryogenic refrigeration according to any one of claims 1 to 7, further comprising: a check valve provided on an outlet side of the after cooler or between the main compressor and the after cooler. apparatus. A heat-insulating container for storing the object to be cooled and the coolant;
The cryogenic refrigeration apparatus according to any one of claims 1 to 8, further comprising a circulation pump that circulates the cooling liquid to the sub heat exchanger. An operation method of the cryogenic refrigeration apparatus according to any one of claims 1 to 9,
The pressure of the refrigerant gas in the closed loop on the inlet side of the main compressor is equal to or lower than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank is higher than the pressure in the closed loop on the inlet side of the main compressor. If low, introduce refrigerant gas from the buffer tank to the sub-compressor, replenish the refrigerant gas pumped by the sub-compressor into the closed loop,
The pressure of at least one of the inlet side and the outlet side of the main compressor of the refrigerant gas in the closed loop is equal to or higher than a predetermined pressure, and the pressure of the refrigerant gas in the buffer tank is the inlet side of the main compressor When the pressure in the closed loop is higher, refrigerant gas is introduced into the sub-compressor from the closed loop, and the refrigerant gas pumped by the sub-compressor is recovered in the buffer tank. Operation method of low-temperature refrigeration equipment.   The cryogenic refrigeration apparatus according to claim 10, wherein the pressure of the refrigerant gas in the closed loop is set to atmospheric pressure by pumping the refrigerant gas in the closed loop by a sub-compressor and collecting the refrigerant gas in the buffer tank. Driving method. An operation method of the cryogenic refrigeration apparatus according to any one of claims 4 to 9,
The operation method of the cryogenic refrigeration apparatus according to claim 10 or 11, wherein the bypass valve is opened when the operation of the main compressor is stopped. An operation method of the cryogenic refrigeration apparatus according to any one of claims 5 to 9,
The method of operating a cryogenic refrigeration apparatus according to any one of claims 10 to 12, wherein the pressure of the refrigerant gas is reduced to substantially atmospheric pressure before introducing the refrigerant gas into the sub-compressor. An operation method of the cryogenic refrigeration apparatus according to any one of claims 7 to 9,
When the pressure on the outlet side of the main compressor of the refrigerant gas in the closed loop becomes higher than a predetermined pressure, the operating frequency of the main compressor is decreased by changing the output frequency of the inverter. The operation method of the cryogenic refrigeration apparatus according to any one of claims 10 to 13.

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