HIGH TEMPERATURE SUPERCONDUCTOR REFRIGERATION SYSTEM

Abstract

A cryogenic refrigeration system and a corresponding method for increasing the cooling efficiency of the system, preferably the cooling of a thermally coupled load. Accordingly, the system comprises a supply means for providing a supply flow of a cryogenic refrigerant, a compressor fluidly coupled to said supply means and configured to compress the supplied cryogenic refrigerant, and a cold box fluidly coupled to the compressor, said cold box comprising a first expansion device and a first heat exchanger, wherein the first expansion device is configured to receive the compressed cryogenic refrigerant from the compressor and expand it and provide the expanded refrigerant to the first heat exchanger, and wherein the first heat exchanger is configured to be thermally coupled to a load. The system furthermore comprises a second heat exchanger arranged in the cold box comprising at least a first and second heat exchanging section.

Claims

1. Cryogenic refrigeration system (1), comprising: a supply means (2) for providing a supply flow of a cryogenic refrigerant; a compressor (3) fluidly coupled to said supply means (2) and configured to compress the supplied cryogenic refrigerant; and a cold box (10) fluidly coupled to the compressor (3), said cold box (10) comprising a first expansion device (4) and a first heat exchanger (5), wherein the first expansion device (4) is configured to receive the compressed cryogenic refrigerant (20) from the compressor (3) and expanded and provide the expanded refrigerant to the first heat exchanger (5), and wherein the first heat exchanger (5) is configured to be thermally coupled to a load (7), wherein the system (1) comprises a second heat exchanger (6) arranged in the cold box (10) comprising at least a first heat exchanging section (6A) and a second heat exchanging section (6B), wherein the first heat exchanging section (6A) is configured to receive the expanded refrigerant (22) from the expansion device (4) and to subsequently provide the expanded refrigerant (22) to the first heat exchanger (5); wherein the second heat exchanging section (6B) is configured to receive the expanded refrigerant (24) from the first heat exchanger (5) and to subsequently provide the received expanded refrigerant (24) to the first heat exchanger (5), wherein the first and second heat exchanger sections (6A, 6B) are thermally coupled, and wherein the first heat exchanger (5) is configured to provide the received expanded refrigerant (24) to the supply means (2) and/or the compressor (3).

2. Cryogenic refrigeration system (1) according to claim 1, wherein the cold box (10) further comprises a second expansion device (40) and the second heat exchanger (6) comprises a third and a fourth heat exchanging section (6C, 6D), wherein the second expansion device (40) is fluidly coupled to the first heat exchanger (5) and the second heat exchanger (6) and is configured to receive the expanded refrigerant (24) received by the first heat exchanger (5) from the second heat exchanging section (6B), provide a secondary expansion of said refrigerant (24), and subsequently provide the secondary expanded refrigerant (26) to the first heat exchanger (5) via the third heat exchanging section (6C), and the fourth heat exchanging section (6D) is configured to receive the secondary expanded refrigerant (28) from the first heat exchanger (5) and to subsequently provide the received secondary expanded refrigerant (28) to the first heat exchanger (5), wherein at least the third and fourth heat exchanger sections (6C, 6D) are thermally coupled.

3. Cryogenic refrigeration system (1) according to claim 1, wherein the compressor (3) is a screw compressor or turbo compressor, said turbo compressor preferably comprising magnetic couplings and/or comprising a serial compressor, and/or wherein the compressor is configured to compress the refrigerant at ambient temperature.

4. Cryogenic refrigeration system (1) according to claim 1, wherein the first heat exchanger (5) is thermally coupled to a load (7), said load (7) preferably comprising a refrigeration circuit (70) for a high temperature superconductor.

5. Cryogenic refrigeration system (1) according to claim 4, said load (7) comprising a second cryogenic refrigerant, wherein said second cryogenic refrigerant preferably comprises liquid nitrogen.

6. Cryogenic refrigeration system (1) according to claim 1, wherein at least the first and second heat exchanging sections (6A, 6B) and/or the third and fourth heat exchanging sections (6C, 6D) are arranged with respect to each other such that they provide counter flow, cross flow, or equal flow heat exchanging sections.

7. Cryogenic refrigeration system (1) according to claim 1, wherein the compressor (3) and/or the supply means (2) are configured to provide the refrigerant to the first expansion device (4) is a liquid refrigerant, preferably also to the second expansion device (40).

8. Cryogenic refrigeration system (1) according to claim 1, wherein the first expansion device (4) is configured to provide a two-phase or gas phase refrigerant; and wherein the first heat exchanger (5) is configured as a cold gas heat exchanger and wherein the first heat exchanger (5) is configured is to receive a gas phase from the cooled refrigerant (22).

9. Cryogenic refrigeration system (1) according to claim 1, wherein the cryogenic refrigerant comprises helium and/or neon.

10. Cryogenic refrigeration system (1) according to claim 1, wherein the system further comprises in evaporating heat exchanger (8A) arranged outside of the cold box (10) and upstream of the first expansion device (4), which is thermally coupled to the provided compressed cryogenic refrigerant supply flow to pre-cool said refrigerant, wherein the evaporating heat exchanger (8A) preferably comprises a liquid water circuit (80) as a refrigerant to be evaporated.

11. Cryogenic refrigeration system (1) according to claim 1, wherein the system further comprises in evaporating heat exchanger (8B) arranged in the cold box (10) and upstream of the first expansion device (4), which is thermally coupled to the provided compressed cryogenic refrigerant supply flow to pre-cool said refrigerant, wherein the evaporating heat exchanger (8B) preferably comprises a liquid nitrogen circuit (82) as a refrigerant to be evaporated.

12. Method for providing a cryogenic refrigeration, comprising the steps of: providing a supply flow of a cryogenic refrigerant with a supply means (2); compressing the supplied cryogenic refrigerant with a compressor (3); expanding the compressed cryogenic refrigerant (20) in a first expansion device (4) provided in a cold box (10), wherein the cold box is configured to be thermally coupled to a load (7); and providing the expanded refrigerant (22) to a first heat exchanger (5) in the cold box (10) wherein the expanded refrigerant (22) is received from the expansion device (4) by a first heat exchanging section (6A) of a second heat exchanger (6) in the cold box (10) and is subsequently provided to the first heat exchanger (5); the expanded refrigerant (24) from the first heat exchanger (5) is received by a second heat exchanging section (6B) of the second heat exchanger (6) and is subsequently provided to the first heat exchanger (5); and wherein heat is exchanged between the first and second heat exchanger section (6A, 6B) and wherein the expanded refrigerant (24) received by the first heat exchanger (5) from the second heat exchanging section (6B) is provided to the supply means (2) and/or the compressor (3).

13. Method according to claim 12, wherein the expanded refrigerant (24) received by the first heat exchanger (5) from the second heat exchanging section (6B) is received and expanded by a second expansion device (40), wherein the secondary expanded refrigerant (26) is provided to the first heat exchanger (5) via a third heat exchanging section (6C) of the second heat exchanger (6), the secondary expanded refrigerant (28) from the first heat exchanger (5) is received by a fourth heat exchanging section (6D) of the second heat exchanger (6) and subsequently provided via the fourth heat exchanging section (6D) to the first heat exchanger (5), and heat is exchanged between at least the third and fourth heat exchanger section (6C, 6D).

14. Method according to claim 12, wherein the supplied cryogenic refrigerant is compressed by a screw compressor, a turbo compressor, and/or at ambient temperature, wherein the cryogenic refrigerant preferably comprises helium and/or neon.

15. Method according to claim 12, wherein the first heat exchanger (5) provides a cryogenic refrigeration of a thermally coupled load (7), said load (7) preferably comprising a refrigeration circuit (70) for a high-temperature superconductor, wherein preferably the load (7) comprises liquid nitrogen as a second cryogenic refrigerant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which:

[0048] FIG. 1 is a schematic view of a first and second heat exchanger in a cryogenic system with a single recycling of the first cryogenic refrigerant;

[0049] FIG. 2 is a schematic view of the embodiment according to FIG. 1 with a double recycling of the first cryogenic refrigerant;

[0050] FIG. 3 is a schematic view of a first and second heat exchanger in a cryogenic system with a double recycling of the first cryogenic refrigerant and additional evaporating heat exchangers; and

[0051] FIG. 4 is a schematic view of a first and second heat exchanger in a further cryogenic system with a double recycling of the first cryogenic refrigerant and additional evaporating heat exchangers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0052] In the following, the invention will be explained in more detail with reference to the accompanying Figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

[0053] In FIG. 1 a cryogenic refrigeration system 1 is schematically shown in operation using liquid helium as a cryogenic refrigerant and thermally coupled to a load 7. Accordingly, a supply flow of the liquid helium is provided by a supply means 2, which is fluidly coupled to a compressor 3. The supply means 2 according to the embodiment of FIG. 1 is configured as a coupling to a refrigeration plant, which provides a continuous supply flow of liquid helium. However, the supply means 2 may also comprise e.g. a larger vessel providing the required amount and flow of liquid helium to the system 1.

[0054] The supply means 2 provides the supply flow of liquid helium as a cryogenic refrigerant to the fluidly coupled compressor 3, which is arranged downstream thereof and is configured as a screw compressor. Accordingly, the liquid helium is pressurized and provided as a compressed cryogenic refrigerant 20. The use of a screw compressor may require the implementation of a downstream oil removal system (not shown), depending on the used refrigerant and specifications of the compressor. The compressed cryogenic refrigerant 20, i.e. the pressurized liquid helium, is then provided to the cold box 10 by means of a fluid coupling or valve at the junction of the cold box 10. This configuration ensures that the cold box 10 is essentially thermally isolated and only connected to the outside components via a said fluid coupling.

[0055] Within the cold box 10, the compressed cryogenic refrigerant 20 is received by a first expansion device 4, which is depicted as a pressure regulator and an expansion valve. However, other configurations, including only an expansion valve, an expansion turbine, or a combined expansion valve and pressure regulator may be provided. Although the cryogenic refrigeration system 1 requires a normalization and stabilization of the temperatures in the system 1 during start up or an initial phase of operation, the temperature and pressure of the cryogenic refrigerant at various points or locations in the system 1 is considered to be constant and predictable during normal operation. In this regard, the expansion device 4 comprises a constant pressure, which is lower than the pressure upstream of the expansion device 4, and is configured to provide a gas phase from the compressed cryogenic refrigerant 20. Due to a sudden pressure drop in the expansion device 4, the compressed cryogenic refrigerant 20 is hence expanded, such that a relaxation of the pressurized liquid helium occurs, thereby increasing the volume of the first cryogenic refrigerant. Accordingly, the latent heat of the compressed cryogenic refrigerant 20 is reduced, thereby allowing the liquid helium to further absorb heat. The expansion device 4 hence provides an expanded refrigerant 22, which may have a lower temperature compared with the compressed cryogenic refrigerant 20 and which is received by a first heat exchanging section 6A of a second heat exchanger 6.

[0056] After traversing the first heat exchanger section 6A, the expanded refrigerant 22 is then passed to a first heat exchanger 5 via a respective inlet. Although the expansion device 4 may be configured to provide the expanded refrigerant 22 as a liquid or two-phase refrigerant, the expansion device 4 according to FIG. 1 is configured to provide the expanded refrigerant 22 in a gaseous state, such that the first heat exchanger 5 is configured as a cold gas heat exchanger. Within the first heat exchanger 5, the cooled helium absorbs heat from the thermally coupled load 7, such that the cooled helium exits the first heat exchanger 5 via a respective outlet as an expanded refrigerant 24, which may be a heated refrigerant compared with the expanded refrigerant 22 exiting the expansion device. Simultaneously, the load 7 is provided with cryogenic refrigeration, such that e.g. a high temperature superconductor may be accordingly cooled.

[0057] Instead of returning the expanded refrigerant 24 from the first heat exchanger 5 directly to the supply means 2, the expanded refrigerant 24 from the first heat exchanger is provided to a second heat exchanger section 6B of the second heat exchanger 6, which is thermally coupled to the first heat exchanging section 6A. The received expanded refrigerant 24 hence traverses the second heat exchanging section 6B and is then passed to the first heat exchanger 5 via a respective inlet. Again, the expanded refrigerant 24 received from the second heat exchanging section 6B absorbs heat within the first heat exchanger 5. The received expanded refrigerant 24 then exits the first heat exchanger 5 via a respective outlet and returns the expanded refrigerant 24 to the supply means 2, such that it can be re-used in the system 1.

[0058] Accordingly, the cryogenic refrigerant is recycled once before being returned to the compressor 3. Since the first and second heat exchanging sections 6A, 6B are thermally coupled, the expanded refrigerant 22 is provided to the first heat exchanger 5 in a relatively warmed state compared with the expanded refrigerant 22 exiting the expansion device 4 while at the same time the expanded refrigerant 24 from the first heat exchanger 5 exiting the second heat exchanger 6 is provided to the first heat exchanger 5. Not only does this allow a further expansion and the provision of a corresponding lower temperature of the compressed first cryogenic refrigerant 20, this also provides a doubling of the cooling capacity of the first heat exchanger 5 without increasing the mass flow.

[0059] Accordingly, the isentropic efficiency is improved by this configuration. Furthermore, the compressor 3 and the expansion device 4 may be controlled separately and independently without requiring complex control systems or a mechanical coupling, i.e. without having the output of the compressor linked to the expansion device and vice versa.

[0060] Although the embodiment according to FIG. 1 schematically depicts that he first heat exchanger 5 is configured to provide all of the expanded refrigerant 24 received from the first heat exchanging section 6A to the second heat exchanging section 6B, it may also be provided that only a branch of the expanded refrigerant 24 is provided to the second heat exchanging section 6B, while the rest of the expanded refrigerant 24 is returned to the supply means 2.

[0061] Furthermore, although the embodiment according to FIG. 1 is described with respect to liquid helium as a first cryogenic refrigerant, other refrigerants, such as e.g. neon, may be used. Furthermore, FIG. 1 schematically depicts the first and second heat exchanger 5, 6 as equal flow heat exchangers. However, other configurations, such as a counter flow or cross flow heat exchanger may be provided instead of or in addition to an equal flow heat exchanger.

[0062] The embodiment according to FIG. 2 generally resembles the embodiment according to FIG. 1. In addition, the embodiment according to FIG. 2 comprises a double recycling of the cryogenic refrigerant, as depicted by the additional return loop of the expanded refrigerant 24 from the first heat exchanger 5. To provide the double recycling, the cryogenic refrigeration system 1 comprises a second expansion device 40 in the cold box 10 and the second heat exchanger 6 comprises an additional third and fourth heat exchanging section 6C, 6D. Accordingly, the second expansion device 40 is fluidly coupled to an outlet of the first heat exchanger 5 to accordingly receive the expanded refrigerant 24 received by the first heat exchanger 5 to expand said refrigerant 24 for providing a secondary expanded refrigerant 26 to the first heat exchanger 5 via the third heat exchanging section 6C. Furthermore, the fourth heat exchanging section 6D is configured to receive a secondary expanded refrigerant 28 from a respective outlet of the first heat exchanger 5 and to provide the received secondary expanded refrigerant 28 to the first heat exchanger 5.

[0063] According to the embodiment, the third and fourth heat exchanger sections 6C, 6D are thermally coupled, such that heat is exchanged between said sections and the secondary expanded refrigerant 26 may hence be warmed by the secondary expanded refrigerant 28 before entering the first heat exchanger 5. Therefore, the expanded refrigerant 22 may be provided at an even lower temperature. By the same token, the received secondary expanded refrigerant 28 from the first heat exchanger may be pre-cooled before entering the first heat exchanger 5, such that the overall cooling capacity is quadrupled without increasing the mass flow.

[0064] In addition, the compressor 3 according to the embodiment is provided as a turbo compressor having magnetic couplings. Hence, no oil removal system is required and the energetic efficiency is even further increased. Alternatively, however, a screw compressor and, optionally, an oil removal system, may also be used. Furthermore, the first and second expansion devices 4, 40 are configured to provide a gas phase of the liquid helium, such that the first and second heat exchangers 5, 6 are configured as cold gas heat exchangers. However, the heat exchangers may also be configured to receive both a gas phase and a liquid phase, e.g. from a two-phase expanded refrigerant 22 and/or secondary expanded refrigerant 26, for example, by means of a phase separator or a vessel.

[0065] As outlined in the above for FIG. 1, it may also be provided that instead of providing all of the expanded refrigerant 24 received from the second heat exchanging section 6B and/or the expanded refrigerant 28 received from the third heat exchanging section 6C to the second expansion device 40 and the fourth heat exchanging section 6D, respectively, it may also be provided that only a branch of said expanded refrigerants 24, 28 is provided while the rest of the expanded refrigerant 24, 28 is returned to the supply means 2.

[0066] In FIG. 3 an embodiment of the system 1 is schematically depicted, which generally corresponds to the embodiment according to FIG. 2. In addition to the second expansion device 40 and the third and fourth heat exchanging sections 6C, 6D, the thermally coupled load 7 is configured as a refrigeration circuit 70 for a high temperature superconductor, e.g. a cable. The refrigeration circuit 70 enters the cold box 10 and is configured in a counter flow arrangement with respect to the first heat exchanger 5. Accordingly, the refrigeration circuit 70 is configured to enter the first heat exchanger 5 at a warm end and to exit the first heat exchanger 5 at a respective cold end, such that a second cryogenic refrigerant in the refrigeration circuit 70 may be efficiently cooled by the first heat exchanger 5. The second cryogenic refrigerant, e.g. liquid nitrogen, then leaves the cold box 10 and is provided to e.g. a cable to provide the required cooling.

[0067] In addition, the cold box 10 comprises an evaporating heat exchanger 8B, which is arranged upstream of the expansion device 4 and ensures that the compressed cryogenic refrigerant 20 is cooled down before being expanded by the expansion device 4. The evaporating heat exchanger 8B comprises a liquid nitrogen circuit 82, which enters the evaporating heat exchanger at a warm end of the evaporating heat exchanger 8B and is thermally coupled to the provided compressed cryogenic refrigerant 20, such that heat from the compressed cryogenic refrigerant 20 may be absorbed by the liquid nitrogen. The liquid nitrogen thereby evaporates into a gas phase, which exits the evaporating heat exchanger 8B and may be either released into the atmosphere or be received by e.g. a liquefaction plant. Although the liquid nitrogen circuit 82 is depicted in the embodiment to be provided within the cold box 10, e.g. by a respective branch of the refrigeration circuit 70, the liquid nitrogen circuit 82, may also be partly provided outside of the cold box 10 via a respective coupling. By the same token, the evaporated liquid nitrogen may also be retained within the cold box 10 instead of being released outside of the cold box 10, e.g. into the atmosphere.

[0068] To further pre-cool the compressed cryogenic refrigerant 20, the system 1 furthermore comprises an evaporating heat exchanger 8A, which is arranged outside of the cold box 10, upstream of the evaporating heat exchanger 8B, and downstream of the compressor 3. The evaporating heat exchanger 8A comprises a water circuit 80 and is thermally coupled to the supplied compressed cryogenic refrigerant 20, such that heat may be exchanged between the compressed cryogenic refrigerant 20 and the water of the water circuit 80. Accordingly, the water absorbs heat and is evaporated, such that the water exits the evaporating heat exchanger 8A in a gas phase. The evaporated water may be released into the atmosphere or may be e.g. re-used after a corresponding condensation or be used for other purposes, such as gas or steam turbines.

[0069] Although the refrigeration circuit 70, the water circuit 80, and the liquid nitrogen circuit 82 are schematically depicted in a counter flow arrangement, other configurations, such as equal flow or cross flow arrangements may also be provided.

[0070] The embodiment according to FIG. 4 generally corresponds to the embodiment according to FIG. 3, such that like features are denoted by identical reference numerals and repeated description thereof is omitted in order to avoid redundancies. In addition, the cold box 10 according to the embodiment of FIG. 4 comprises further cold gas heat exchangers 8C, 8D, which are arranged upstream of the expansion device 4. The cold gas heat exchanger 8C is arranged upstream of the evaporating heat exchanger 8B, wherein the compressed cryogenic refrigerant 20 is thermally coupled both with the liquid nitrogen circuit 82 and the secondary expanded refrigerant 28 being returned to the supply means 2 from the first heat exchanger 5. Hence, the compressed cryogenic refrigerant 20 is pre-cooled by the evaporating gas from the liquid nitrogen exiting the evaporating heat exchanger 8B and the returning gas in the secondary expanded refrigerant 28. By the same token, the returning gas in the secondary expanded refrigerant 28 may be pre-cooled due to the evaporating heat exchanger 8A, depending on the system conditions.

[0071] The cold gas heat exchanger 8D is arranged upstream of the first expansion device 4 and downstream of both the evaporating heat exchanger 8B and the cold gas heat exchanger 8C. Again, the compressed cryogenic refrigerant 20 is thermally coupled to the secondary expanded refrigerant 28 from the first heat exchanger 5, such that the compressed cryogenic refrigerant 20 is further cooled due to heat exchange with the returning gas in the secondary expanded refrigerant 28. Hence, the implementation of further evaporating heat exchangers 8A, 8B and cold gas heat exchangers 8C, 8D provides a system with an even further improved energetic efficiency.

[0072] In order to increase the cooling capacity of the first heat exchanger 5, the refrigeration circuit 70 may comprise a compressor 72 upstream of the first heat exchanger 5. Although the compressor 72 is schematically depicted in the cold box 10, a compressor 72 may also be arranged outside of the cold box 10, depending on the requirements of the system 1. In any case, the liquid nitrogen being returned to the first heat exchanger 5 may be compressed before being cooled by the first heat exchanger 5 and before being returned to e.g. a cable. The refrigeration circuit 70 may furthermore comprise an expansion device arranged downstream of the first heat exchanger 5 (not shown) to further improve the cryogenic refrigeration capacity of the load 7.

[0073] As outlined in the above, the compressor 3 and the first expansion device 4 are controlled separately and independently. Accordingly, the system 1 comprises control units 9A, 9C 2, respectively control the compressor 3 and the first expansion device 4. Both control units 9A, 9C are connected to a main controller 9, which is generally configured to monitor the respective control units 9A, 9C. In order to provide a feedback mechanism, the system 1 may furthermore comprise one or more sensors, e.g., temperature and/or pressure sensors, which provide measurement signals to the respective control unit. In addition, the system 1 comprises further control units 9B, 9D to respectively control the second expansion device 40 and the compressor 72 of the refrigeration circuit 70. Said control units 9B, 9D are furthermore in communication with the main controller 9, such that these may also be monitored by the controller 9. The provision of the independent control units 9A, 9B, 9C, 9D and the controller 9 generally improves the controllability, predictability, and stability of the system 1. However, depending on the configuration of the system 1, said one or more control units 9A, 9B, 9C, 9D may also be merely optional. For example, the second expansion device 40 and/or the compressor 72 may be e.g. not adjustable in a dynamic range and hence be configured to provide a constant pressure independently of a measured system parameter, which may be unproblematic with constant system conditions, e.g. a constant supply flow of the cryogenic refrigerant and a constant load 7.

[0074] It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention.

LIST OF REFERENCE NUMERALS

[0075] 1 Cryogenic refrigeration system

[0076] 10 Cold box

[0077] 2 Supply means

[0078] 20 Compressed cryogenic refrigerant

[0079] 22 Expanded refrigerant

[0080] 24 Expanded refrigerant from first heat exchanger

[0081] 26 Secondary expanded refrigerant

[0082] 28 Secondary expanded refrigerant from first heat exchanger

[0083] 3 Compressor

[0084] 4 First expansion device

[0085] 40 Second expansion device

[0086] 5 First heat exchanger

[0087] 6 Second heat exchanger

[0088] 6A First heat exchanging section

[0089] 6B Second heat exchanging section

[0090] 6C Third heat exchanging section

[0091] 6D Fourth heat exchanging section

[0092] 7 Load

[0093] 70 Refrigeration circuit

[0094] 72 Compressor

[0095] 8A-8B Evaporating heat exchanger

[0096] 8C-8D Cold gas heat exchanger

[0097] 80 Water circuit

[0098] 82 Liquid nitrogen circuit

[0099] 9 Controller

[0100] 9A-9D Control unit