Cryogenic cooling system and cryogenic cooling method

Abstract

The present invention makes it possible to improve energy efficiency when cooling objects by circulating a heating medium cooled using cooling sources.　This cryogenic cooling system comprises: a storage container (12) for storing a cryogenic liquid refrigerant (12A) and a gaseous refrigerant (12B); a liquid-phase heat exchanger (13) that is in contact with the liquid refrigerant in the storage container; a gas-phase heat exchanger (14) that is in contact with the liquid refrigerant in the storage container and is connected to the liquid-phase heat exchanger; and a circulation system (15) for circulating a heating medium (15H), the circulation system (15) including a supply-side pipe (16) for guiding the heating medium from the liquid-phase heat exchanger to a superconducting coil (1) and a return-side pipe (17) for guiding the heating medium from the superconducting coil to the gas-phase heat exchanger. A heat shield (2) at a higher temperature than the superconducting coil is in thermal contact with the return-side pipe of the circulation system. The heating medium sequentially cooled through heat exchange with the refrigerants using the gas-phase heat exchanger and the liquid-phase heat exchanger is supplied to the supply-side pipe to cool the superconducting coil to a cryogenic temperature, and is guided to the return-side pipe to cool the heat shield to a cryogenic temperature.

Description

Cryogenic cooling system and cryogenic cooling method

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to cryogenic cooling systems and methods.

[0002] Generally, superconducting coils are used by cooling them to extremely low temperatures using a cryogen such as liquid helium or a cooling source such as a cryogenic refrigerator. There are two methods for transferring heat between the superconducting coil and the cooling source: conduction cooling and refrigerant circulation. Conduction cooling is used in many superconducting devices due to its simple configuration. However, this conduction cooling method poses a problem in high-magnetic-field devices and large devices, where the distance between the cooling source and the superconducting coil becomes long, resulting in a large temperature difference between the two. For such superconducting devices, a refrigerant circulation method is used.

[0003] Meanwhile, in recent years, there has been active development of devices that use hydrogen energy as a measure against global warming, and development of liquid hydrogen and high-temperature superconducting equipment that uses it is progressing. Liquid hydrogen has the advantage of being smaller in volume than gaseous hydrogen, which is useful for automobiles, aircraft, etc. Furthermore, by using high-temperature superconducting motors cooled with this liquid hydrogen, it is possible to make motors smaller and lighter.

[0004] Japanese Patent Application Laid-Open No. 2003-148844 Japanese Patent Application Laid-Open No. 2004-119966 Japanese Patent Publication No. 5-51836

[0005] One of the challenges of conventional cryogenic cooling systems is reducing the amount of liquid hydrogen consumed. To achieve this, it is necessary to reduce the amount of heat entering the superconducting coils. One known method for reducing this amount of heat entry is to provide a heat shield. However, cooling the heat shield requires an additional cooling source, which is not necessarily effective when considering overall energy efficiency.

[0006] The embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide a cryogenic cooling system and a cryogenic cooling method that can improve energy efficiency when cooling an object to be cooled by circulating a heat medium cooled by a cooling source.

[0007] 1 is a schematic piping diagram showing the configuration of a cryogenic cooling system according to a first embodiment; FIG. 2 is a schematic piping diagram showing the configuration of a cryogenic cooling system according to a second embodiment; FIG. 3 is a schematic piping diagram showing the configuration of a cryogenic cooling system according to a third embodiment.

[0008] The cryogenic cooling system 10 according to the embodiment of the present invention is for cooling a first object to be cooled (such as a superconducting coil 1 and a cooling stage 11) and a second object to be cooled (such as a heat shield 2) to cryogenic temperatures, and includes a storage container 12 for storing both a cryogenic liquid refrigerant 12A and a gaseous refrigerant 12B formed by evaporation of the refrigerant 12A, a liquid-phase heat exchanger 13 provided in the storage container 12 and in contact with the liquid refrigerant 12A, a gas-phase heat exchanger 14 provided in the storage container 12 and in contact with the gaseous refrigerant 12B and connected to the liquid-phase heat exchanger 13, and a supply side heat exchanger 15H for introducing a heat medium 15H from the liquid-phase heat exchanger 13 to the first object to be cooled. The cooling system has a circulation system 15 for circulating the heat medium 15H, which includes a piping 16 and a return side piping 17 that guides the heat medium 15H from the first cooled material to the gas-phase heat exchanger 14, and the second cooled material is set to a higher temperature than the first cooled material and is provided in thermal contact with the return side piping 17 of the circulation system 15, and the heat medium 15H is sequentially cooled by heat exchange with the refrigerant 12A in the gas-phase heat exchanger 14 and the liquid-phase heat exchanger 13, and is supplied to the supply side piping 16 to cool the first cooled material to an extremely low temperature, and is also guided to the return side piping 17 to cool the second cooled material to an extremely low temperature.

[0009] [A] First Embodiment (FIG. 1) FIG. 1 is a schematic piping diagram showing the configuration of a cryogenic refrigeration system according to a first embodiment. The cryogenic refrigeration system 10 shown in FIG. 1 cools a superconducting coil 1 and a cooling stage 11, which serve as first objects to be cooled, to a cryogenic temperature (e.g., 20 K), and a thermal shield 2, which serves as a second object to be cooled, to a cryogenic temperature (e.g., 50 K to 40 K). In addition to the cooling stage 11 and the thermal shield 2, the cryogenic refrigeration system 10 includes a storage container 12 for storing refrigerants 12A and 12B, which serve as cooling sources, a liquid-phase heat exchanger 13, a gas-phase heat exchanger 14, a circulation system 15 including a supply-side pipe 16, a return-side pipe 17, and a low-temperature fan 18, which circulates a heat medium 15H, and a first vacuum vessel 21 and a second vacuum vessel 22.

[0010] The cooling stage 11 is made of, for example, a high-purity aluminum sheet and is in thermal contact with the superconducting coil 1, and the superconducting coil 1 is placed on the cooling stage 11. The cooling stage 11 is also fixed to the supply-side pipe 16 of the circulation system 15 using, for example, silver solder, and is in thermal contact with the supply-side pipe 16.

[0011] The storage container 12 stores both a cryogenic liquid refrigerant 12A and a gaseous refrigerant 12B formed by evaporation of the liquid refrigerant 12A. Liquid hydrogen is used as the liquid refrigerant 12A, but liquid neon, liquid nitrogen, liquid argon, or the like may also be used.

[0012] The liquid-phase heat exchanger 13 is installed in the storage container 12 and is in contact with the liquid refrigerant 12A, and cools the heat medium 15H in the circulation system 15 to a cryogenic temperature by heat exchange with the liquid refrigerant 12A. The gas-phase heat exchanger 14 is installed in the storage container 12 and is in contact with the gas refrigerant 12B, and is connected to the liquid-phase heat exchanger 13. The gas-phase heat exchanger 14 exchanges heat between the gas refrigerant 12B and the heat medium 15H in the circulation system 15, and cools the heat medium 15H to a cryogenic temperature.

[0013] Helium gas is used as the heat medium 15H circulating through the circulation system 15, but hydrogen gas, nitrogen gas, neon gas, argon gas, or other gases having a melting point lower than the boiling point of the refrigerant 12A may also be used. The supply side piping 16 guides the heat medium 15H from the liquid-phase heat exchanger 13 to the cooling stage 11. The return side piping 17 guides the heat medium 15H from the cooling stage 11 to the gas-phase heat exchanger 14. A low-temperature fan 18 is disposed in the return side piping 17 to pressurize the heat medium 15H and circulates the heat medium 15H among the supply side piping 16, the return side piping 17, the gas-phase heat exchanger 14, and the liquid-phase heat exchanger 13.

[0014] The first vacuum vessel 21 houses the superconducting coil 1 and the cooling stage 11, and uses vacuum insulation to reduce the amount of heat entering the superconducting coil 1 and the cooling stage 11. The second vacuum vessel 22 houses the storage vessel 12 and the low-temperature fan 18, and uses vacuum insulation to reduce the amount of heat entering the storage vessel 12 and the low-temperature fan 18. The first vacuum vessel 21 and the second vacuum vessel 22 are connected and coupled by a thermal insulation pipe section 23, and the supply side piping 16 and the return side piping 17 are housed within this thermal insulation pipe section 23.

[0015] The heat shield 2 includes a coil-side heat shield 2X that covers and encloses the superconducting coil 1 and the cooling stage 11, a vessel-side heat shield 2Y that covers and encloses a storage area in the storage container 12 where the mainly liquid refrigerant 12A is stored, and a pipe-side heat shield 2Z that covers and encloses the supply-side piping 16 within the thermal insulation pipe section 23. The coil-side heat shield 2X is provided in the first vacuum container 21 and reduces the amount of heat leaking into the superconducting coil 1 and the cooling stage 11. The vessel-side heat shield 2Y is provided in the second vacuum container 22 and reduces the amount of heat leaking into the storage container 12. The pipe-side heat shield 2Z is ​​provided in the thermal insulation pipe section 23 and reduces the amount of heat leaking into the supply-side piping 16. Of these, the coil-side heat shield 2X and the vessel-side heat shield 2Y are thermally connected by the pipe-side heat shield 2Z. Note that at least one of the coil-side heat shield 2X, the vessel-side heat shield 2Y, and the pipe-side heat shield 2Z may be provided as appropriate.

[0016] The coil-side heat shield 2X, vessel-side heat shield 2Y, and piping-side heat shield 2Z are in thermal contact with the return-side pipe 17 of the circulation system 15, and are cooled to an extremely low temperature (e.g., 50 K to 40 K) by the heat medium 15H flowing in the return-side pipe 17. On the other hand, the superconducting coil 1 is cooled to an extremely low temperature (e.g., 20 K) by the cooling stage 11 being in thermal contact with the supply-side pipe 16 of the circulation system 15 and being cooled to an extremely low temperature by the heat medium 15H flowing in the supply-side pipe 16. Therefore, the coil-side heat shield 2X, vessel-side heat shield 2Y, and piping-side heat shield 2Z are set to a higher temperature than the superconducting coil 1.

[0017] That is, by operation of low-temperature fan 18 of circulation system 15, heat medium 15H is cooled by heat exchange with gas refrigerant 12B in gas-phase heat exchanger 14, and then further cooled by heat exchange with liquid refrigerant 13H in liquid-phase heat exchanger 13. Heat medium 15H cooled sequentially by gas-phase heat exchanger 14 and liquid-phase heat exchanger 13 is guided to supply-side piping 16 to cooling stage 11, where it cools superconducting coil 1 to an extremely low temperature (e.g., 20 K). After cooling superconducting coil 1, heat medium 15H is guided to return-side piping 17, where it sequentially cools coil-side heat shield 2X, piping-side heat shield 2Z, and vessel-side heat shield 2Y, which are in thermal contact with return-side piping 17, to an extremely low temperature (e.g., 50 K to 40 K), and then returns to low-temperature fan 18.

[0018] Here, a support material 24 for supporting the cooling stage 11 by the first vacuum vessel 21 penetrates the coil side thermal shield 2X. This support material 24 is thermally connected to the coil side thermal shield 2X by a thermal anchor 25, and is cooled to a cryogenic temperature (e.g., 50 K to 40 K) similar to the coil side thermal shield 2X. Therefore, the support material 24 is also a second cooled object that is cooled by the heat medium 15H flowing in the return side piping 17 via the thermal anchor 25 and the coil side thermal shield 2X. By cooling the support material 24 to a cryogenic temperature as described above, the amount of heat that penetrates into the superconducting coil 1 and the cooling stage 11 by this support material 24 is reduced.

[0019] Furthermore, since the heat medium 15H circulating through the circulation system 15 cools the heat shields 2 (coil-side heat shield 2X, vessel-side heat shield 2Y, and piping-side heat shield 2Z) to extremely low temperatures in addition to the superconducting coil 1, the temperature of the gaseous refrigerant 12B discharged from the storage container 12 increases compared to when the heat medium 15H cools only the superconducting coil 1. However, when the liquid refrigerant 12A is liquid hydrogen, the gaseous refrigerant 12B discharged from the storage container 12 is further heated at room temperature and used in a fuel cell or the like, so as described above, there is no problem even if the temperature of the gaseous refrigerant 12B discharged from the storage container 12 increases.

[0020] As configured as described above, the first embodiment provides the following advantages (1) and (2). (1) By covering the superconducting coil 1 with the coil-side thermal shield 2X and the storage container 12 with the container-side thermal shield 2Y, the coil-side thermal shield 2X can reduce the amount of heat leaking from the outside into the superconducting coil 1 and the cooling stage 11. The container-side thermal shield 2Y can also reduce the amount of heat leaking from the outside into the storage container 12. Furthermore, by thermally connecting the support member 24 to the coil-side thermal shield 2X with the thermal anchors 25 and cooling it in the same manner as the coil-side thermal shield 2X, the thermal anchors 25 can reduce the amount of heat leaking from the outside into the superconducting coil 1 and the cooling stage 11. By reducing the amount of heat leaking into the superconducting coil 1, the cooling stage 11, and the storage container 12 as described above, the consumption (evaporation) of the liquid refrigerant 12A in the storage container 12 for cooling the heat medium 15H in the circulation system 15 can be reduced.

[0021] (2) The heat medium 15H in the circulation system 15 is cooled by heat exchange in the liquid-phase heat exchanger 13 and the gas-phase heat exchanger 14, respectively, not only by the liquid refrigerant 12A but also by the gas refrigerant 12B formed when the liquid refrigerant 12A evaporates. The heat medium 15H cools the superconducting coil 1 to an extremely low temperature (e.g., 20 K) via the cooling stage 11. After cooling the superconducting coil 1, the heat medium 15H cools the heat shields 2 (coil-side heat shield 2X, vessel-side heat shield 2Y, and piping-side heat shield 2Z), which are set to a higher temperature than the superconducting coil 1, to an extremely low temperature (e.g., 50 K to 40 K).

[0022] In particular, to cool the thermal shields 2 (coil-side thermal shield 2X, vessel-side thermal shield 2Y, and piping-side thermal shield 2Z) to cryogenic temperatures, the gas-phase heat exchanger 14 cools the heat medium 15H in the circulation system 15 through heat exchange with the gaseous refrigerant 12B. Therefore, an additional cooling source (refrigerant) for cooling the heat medium 15H is not required to cool the thermal shields 2 to cryogenic temperatures. Moreover, compared to the case where the heat medium 15H is cooled through heat exchange with only the liquid refrigerant 12A in the liquid-phase heat exchanger 13, and the superconducting coil 1 and the thermal shields 2 (coil-side thermal shield 2X, vessel-side thermal shield 2Y, and piping-side thermal shield 2Z) are cooled to cryogenic temperatures, an increase in the amount of evaporation of the liquid refrigerant 12A can be suppressed. As a result, the energy efficiency of the cryogenic cooling system 10 can be improved.

[0023] [B] Second Embodiment (FIG. 2) Fig. 2 is a schematic piping diagram showing the configuration of a cryogenic cooling system according to a second embodiment. In this second embodiment, parts similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and descriptions thereof will be simplified or omitted.

[0024] The cryogenic cooling system 27 of the second embodiment differs from the first embodiment in that the second cooled object, which is set to a higher temperature than the superconducting coil 1, is a current lead 3 that passes current through the superconducting coil 1, and this current lead 3 is provided in thermal contact with the return pipe 17 of the circulation system 15, and is cooled to a cryogenic temperature by the heat medium 15H flowing within the return pipe 17 (for example, to a cryogenic temperature of 25 K near the superconducting coil 1, with a temperature gradient down to 300 K as the temperature increases away from the superconducting coil 1).

[0025] In this cryogenic cooling system 27, most of the return piping 17 of the circulation system 15, except for the portion in thermal contact with the current lead 3, is arranged in a room temperature region outside the first vacuum vessel 21 and the second vacuum vessel 22. A compressor 28 at room temperature is disposed in the portion of the return piping 17 arranged in the room temperature region, i.e., the portion of the piping through which the heat medium 15H flows after cooling the current lead 3. The heat medium 15H in the supply piping 16 and the return piping 17 of the circulation system 15 is pressurized by the compressor 28 to circulate within the circulation system 15.

[0026] As configured as described above, the second embodiment provides the following advantages (3) to (5): (3) The current lead 3 is provided in thermal contact with the return pipe 17 of the circulation system 15, and is cooled to, for example, 300 K to 25 K by the heat medium 15H flowing in the return pipe 17. This reduces the amount of heat that enters the superconducting coil 1 from the outside through the current lead 3.

[0027] (4) The heat medium 15H in the circulation system 15 is cooled by heat exchange in the liquid-phase heat exchanger 13 and the gas-phase heat exchanger 14, respectively, not only by the liquid refrigerant 12A but also by the gas refrigerant 12B formed when the liquid refrigerant 12A evaporates. The heat medium 15H cools the superconducting coil 1 to an extremely low temperature (e.g., 20K) via the cooling stage 11, and the heat medium 15H after cooling the superconducting coil 1 cools the current lead 3, which is set to a higher temperature than the superconducting coil 1, to, for example, 300K to 25K.

[0028] In particular, in order to cool the current leads 3, the gas-phase heat exchanger 14 cools the heat medium 15H in the circulation system 15 by heat exchange with the gaseous refrigerant 12B, so no additional cooling source (refrigerant) is required to cool the heat medium 15H in order to cool the current leads 3. Moreover, an increase in the amount of evaporation of the liquid refrigerant 12A can be suppressed compared to when the heat medium 15H is cooled by heat exchange with only the liquid refrigerant 12A in the liquid-phase heat exchanger 13 to cool the superconducting coil 1 and the current leads 3. As a result, the energy efficiency of the cryogenic cooling system 27 can be improved.

[0029] (5) Most of the piping section of the return piping 17 of the circulation system 15 is located in the room temperature region outside the first vacuum vessel 21 and the second vacuum vessel 22, and the compressor 28, which is at room temperature, is disposed in this room temperature region piping section to circulate the heat medium 15H in the circulation system 15. This compressor 28 is less expensive and more reliable than the low-temperature fan 18, and therefore the equipment cost of the cryogenic cooling system 27 can be reduced and reliability can be improved.

[0030] [C] Third Embodiment (FIG. 3) Fig. 3 is a schematic piping diagram showing the configuration of a cryogenic cooling system according to a third embodiment. In this third embodiment, parts similar to those in the first and second embodiments are denoted by the same reference numerals as those in the first and second embodiments, and descriptions thereof will be simplified or omitted.

[0031] The cryogenic cooling system 30 of the third embodiment differs from the first and second embodiments in that the second cooled object is the heat shield 2 (coil side heat shield 2X, vessel side heat shield 2Y, piping side heat shield 2Z) and support material 24 of the first embodiment, and the current lead 3 of the second embodiment, and these heat shields 2, support material 24, and current lead 3 are cooled by a heat medium 15H flowing through branch pipes 31, 32 (both described later) in the return side pipe 17 of the circulation system 15. In addition, the gas-phase heat exchanger 14 includes a first-stage gas-phase heat exchanger 14M and a second-stage gas-phase heat exchanger 14N, and the second-stage gas-phase heat exchanger 14N is connected to the liquid-phase heat exchanger 13.

[0032] The return pipe 17 branches off near the downstream side of the cooling stage 11, and one branch pipe 31 is installed inside the first vacuum vessel 21, the thermal insulation pipe section 23, and the second vacuum vessel 22, and connected to the second-stage gas-phase heat exchanger 14N. A low-temperature fan 18 is disposed in this branch pipe 31, and the coil-side heat shield 2X, the piping-side heat shield 2Z, and the vessel-side heat shield 2Y are provided in thermal contact with this branch pipe 31. The heat medium 15H flowing through the branch pipe 31 by operation of the low-temperature fan 18 cools the heat shields 2 (the coil-side heat shield 2X, the vessel-side heat shield 2Y, and the piping-side heat shield 2Z) to a cryogenic temperature (50 K to 40 K) before flowing into the second-stage gas-phase heat exchanger 14N.

[0033] The other branch pipe 32 extends from inside the first vacuum vessel 21 to outside the first vacuum vessel 21 and is connected to the first-stage gas-phase heat exchanger 14M. The current lead 3 is provided in thermal contact with this branch pipe 32 inside the first vacuum vessel 21, and a compressor 28, which is at room temperature, is disposed outside the first vacuum vessel 21. The heat medium 15H flowing inside the branch pipe 32 due to the operation of the compressor 28 cools the current lead 3 to 300 K to 25 K before flowing into the first-stage gas-phase heat exchanger 14M.

[0034] As configured as above, the third embodiment achieves the effects (1) to (5) of the first and second embodiments.

[0035] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, such substitutions, changes, and combinations are included in the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims.

[0036] For example, the second cooled object that is in thermal contact with the return side piping 17 of the circulation system 15 is not limited to the heat shield 2 (coil side heat shield 2X, container side heat shield 2Y, piping side heat shield 2Z) and support material 24 of the first and third embodiments, and the current lead 3 of the second and third embodiments, but may also be, for example, an electronic circuit in a control device that controls the superconducting coil 1, and the cryogenic cooling systems 10, 27, 30 may be configured by combining a cooling system that cools this electronic circuit, etc.

Claims

1. A cryogenic cooling system for cooling a first object to be cooled and a second object to be cooled to a cryogenic temperature, comprising: a storage container for storing both a cryogenic liquid refrigerant and the gaseous refrigerant resulting from evaporation of the refrigerant; a liquid-phase heat exchanger provided within the storage container and in contact with the liquid refrigerant; a gas-phase heat exchanger provided within the storage container and in contact with the gaseous refrigerant and connected to the liquid-phase heat exchanger; and a circulation system for circulating the heat medium, the circulation system comprising a supply-side pipe for conducting the heat medium from the liquid-phase heat exchanger to the first object to be cooled, and a return-side pipe for conducting the heat medium from the first object to the gaseous heat exchanger, wherein the second object to be cooled, which is set to a higher temperature than the first object to be cooled, is provided in thermal contact with the return-side pipe of the circulation system, The heat medium cooled successively by heat exchange with the refrigerant in the gas phase heat exchanger and the liquid phase heat exchanger is supplied to the supply side piping to cool the first cooled object to a cryogenic temperature, and is guided to the return side piping to cool the second cooled object to a cryogenic temperature.

2. The cryogenic cooling system according to claim 1, characterized in that the second object to be cooled is a thermal shield containing at least one of a storage container and the first object to be cooled.

3. A cryogenic cooling system as claimed in claim 1 or 2, characterized in that the second object to be cooled is a current lead which passes electricity through the superconducting coil which is the first object to be cooled.

4. A cryogenic cooling system as described in any one of claims 1 to 3, characterized in that the second cooled object is a heat shield containing at least one of a storage container and the first cooled object being a superconducting coil, and a current lead passing current through the superconducting coil, and the return side piping is branched in the vicinity of the superconducting coil, with one branch piping being thermally contacted with the heat shield and the other branch piping being thermally contacted with the current lead.

5. A cryogenic cooling system as claimed in claim 3 or 4, characterized in that a room temperature compressor is provided in the return piping in the piping section through which the heat transfer medium flows after cooling the current leads.

6. A cryogenic cooling system according to any one of claims 1 to 5, characterized in that the refrigerant is hydrogen, neon, nitrogen or argon.

7. A method for cooling a first object to be cooled and a second object to be cooled to a cryogenic temperature, comprising: a storage container for storing both a cryogenic liquid refrigerant and the gaseous refrigerant resulting from evaporation of the refrigerant; a liquid-phase heat exchanger provided within the storage container and in contact with the liquid refrigerant; a gas-phase heat exchanger provided within the storage container and in contact with the gaseous refrigerant and connected to the liquid-phase heat exchanger; and a circulation system for circulating the heat medium, the circulation system comprising a supply-side pipe for conducting the heat medium from the liquid-phase heat exchanger to the first object to be cooled, and a return-side pipe for conducting the heat medium from the first object to the gaseous heat exchanger; and providing the second object to be cooled, which is set to a higher temperature than the first object to be cooled, in thermal contact with the return-side pipe of the circulation system; The heat medium, which has been sequentially cooled by heat exchange with the refrigerant in the gas-phase heat exchanger and the liquid-phase heat exchanger, is supplied to the supply side piping to cool the first object to a cryogenic temperature, and then is guided to the return side piping to cool the second object to a cryogenic temperature.

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