GB2571569A

GB2571569A - Cooling system

Info

Publication number: GB2571569A
Application number: GB1803389.4A
Authority: GB
Inventors: Alekseev Alexander; Cardella Umberto
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2018-03-02
Filing date: 2018-03-02
Publication date: 2019-09-04
Also published as: WO2019166383A1; GB2571569A8; GB201803389D0; KR20200130252A; JP2021515169A; US20200400371A1; EP3759192A1; CN111819264A

Abstract

A cooling system for use in a refrigeration plant and/or liquefier plant, the system comprising a refrigerant mixture of helium and neon extracted from air by an air separation plant 2. The mixture may comprise nitrogen and / or hydrogen. A purification device (3, fig 2) may remove impurities such as nitrogen from the mixture. The mixture may comprise a neon / helium ratio of 3:5. The cooling system may be used for cooling temperatures below 80K, below 70K, below 63K to 25K. The cooling system comprises a refrigerant circuit 1 as part of a Brayton or Claude cycle having one or more turbo-compressor(s) 11. The helium and neon may be extracted from the air in rectification columns. The refrigeration plant may be used for cooling high temperature superconductors, pre-cooling in refrigeration plants such as shield cooling in particle accelerators and helium or hydrogen liquefiers. Conventional processes (fig 1) extract helium and neon separately and are mixed together thereafter, whereas this system has one source of air for extracting the mixture of helium and neon in one process.

Description

Cooling system

Technical Field

The invention relates to a cooling system, preferably for use in or including a refrigeration plant and/or a liquefier plant, having a refrigeration circuit. The invention further relates to a method for producing a refrigerant usable in a refrigeration circuit.

Technological Background

Refrigeration plants, configured to achieve very low temperatures of 80 K or below, typically use hydrogen or helium as a refrigerant. An industrial hydrogen liquefaction plant is known from EP 3 163 236 A1, in which a hydrogen gas stream is cooled my means of a plurality of closed-loop cooling cycles to a temperature below a condensation point of hydrogen so as to provide a liquid hydrogen stream.

Refrigeration plants, adapted for temperatures below 80 K, usually apply a Brayton cycle or a Claude cycle with compression of the refrigerant at ambient temperature, heat exchange and refrigeration via expansion. The refrigerant is compressed via a screw type compressor, piston compressor or turbo-compressor. The turbo-compressor is favorable in view of efficiency, flow rate capacity and reliability.

If temperatures below 54 K need to be achieved, only hydrogen, helium, neon or mixtures thereof are applicable, because other fluids would freeze at such very low temperatures. Generally speaking, helium used in refrigeration plants is more efficient than neon. On the other hand, compression of helium and hydrogen via turbo-compressors is difficult or requires a large number of compression stages due to the low molecular weight of the hydrogen. The molar weight of neon, however, is larger than that of helium and hydrogen. Thus, neon is advantageous in view of compression when used in combination for instance with helium and/or hydrogen.

Such alternative refrigerants have been investigated, and it was found that mixtures of helium and neon, called nelium”, allow processes with higher efficiency compared to pure neon; see Hans Quack, Christoph Haberstroh, Ilka Seemann, Marcel Klaus, Nelium, a refrigerant with high potential for the temperature range between 27 and 70 K, Physics Procedia 67 (2015) 176-182.

The industrial application of neon mixtures with helium and/or hydrogen in refrigeration plants (in particular of large scale) involves a number of technical and economic challenges.

Figure 1 illustrates the conventional process to provide a mixture including helium and neon as a refrigerant for a refrigeration and/or liquefaction plant. A first process line 100 includes an air separation plant 101 configured to separate ambient air into its component parts by cryogenic rectification. A neon rich stream produced from the air separation plant 101 is fed to a neon rectification column 102 to produce a second neon rich stream with a higher concentration of neon. This second neon rich stream is then purified and thereafter stored in a neon-storage 103.

Helium is obtained from a different plant via a second process line 110 which is locally separated from the first process line 100. Usually the helium is obtained and separated from natural gas, which contains helium at a proportion of 1 % or more, within a fractionating column 111. Helium is extracted and accumulated within a subsequent process stage 112 and thereafter stored in a helium-storage 113. The pure neon stored in the neon-storage 103 and the pure helium stored in the helium-storage 113 are mixed according to a desired ratio and supplied to a refrigeration plant 120.

Helium and neon, as well as mixtures thereof are rather expensive gases. Pure neon is considerably more expensive than helium and not available everywhere. Moreover, refrigeration systems are not completely leak-proof. Considerable quantities of the product may get lost especially during maintenance work. This implies substantial initial, operating and maintenance costs. Moreover, the technology and logistics are complicated. Helium is usually extracted from natural gas. Neon is separated from air by applying a complex process. Thus, both gases are usually extracted, transported and delivered separately and only subsequently mixed to be used in a refrigeration circuit or refrigeration plant.

To maintain the required characteristics in the refrigeration circuit or refrigeration plant, the mixture, particularly the ratio of neon and helium, has to be monitored and adjusted, which additionally implies technical challenges and costs regarding the analysis and gas management system.

Summary of the invention

It is an object of the present invention to provide a cooling system and a method for producing a refrigerant which solves or reduces at least one of the above mentioned problems.

The object is solved with a cooling system having the features of claim 1 and a method having the features of claim 9. Preferred embodiments are given by the dependent claims, the description and the drawings.

According to a first aspect of the invention, there is provided a cooling system including a refrigeration circuit configured to use a refrigerant including a mixture of helium and neon; wherein the refrigerant is based on a raw mixture, preferably the refrigerant comprises the raw mixture, and wherein the raw mixture extracted from air by an air separation plant.

The cooling system is preferably adapted for use in or including a refrigeration plant and/or a liquefiers. This for instance includes refrigeration plants for cooling high-temperature superconductors, precooling in refrigeration plants (e.g. shield cooling in particle accelerators) and liquefiers, particularly helium or hydrogen liquefiers, etc.

The cooling system according to the invention has a refrigeration circuit configured to use a refrigerant including a mixture of helium and neon. Preferably, the mixture comprises helium, neon and hydrogen. The refrigerant is based on a raw mixture, preferably is the raw mixture, including helium and neon, extracted from air by an air separation plant. Preferably, the cooling system has the air separation plant configured to extract from air the raw mixture including helium and neon. In other words, both components - helium and neon - are extracted from the air.

The extraction is preferably done by the same process and/or simultaneously such that after the process the raw mixture is present without any further processing. In particular, the raw mixture to be used as the refrigerant is provided by extracting it as such from air but not by supplying it by mixing two or more gases which are provided in separate processes or extracted from different raw materials such as air and natural gas.

Preferably, the raw mixture including helium and neon is extracted from air in rectification columns of the (cryogenic) air separation plant. The air separation plant may be locally separated from the refrigeration circuit. Further, the raw mixture may be extracted at any time and stored until usage. According to the invention, the raw mixture ex is directly used as the refrigerant or forms the basis of the refrigerant. In other words, the raw mixture including helium and neon (possibly as well as other components) is used as the refrigerant with or without further treatment, such as cleaning.

Importantly, the raw mixture including helium and neon is extracted from the air via the air separation plant. This helps solving the problem of availability and reduces technical complexity and costs as compared to the conventional processes for extracting helium and neon separately and subsequently mixing the two components. The logistics for obtaining the refrigerant is simplified since the desired raw mixture is provided via one source, i.e. air as the source not for the individual components but the raw mixture itself.

Preferably the raw mixture further includes nitrogen and/or hydrogen. A certain amount of nitrogen and/or hydrogen is permitted depending on the intended cooling temperatures. Maintaining nitrogen and/or hydrogen in the raw mixture and preferably also in the refrigerant helps further reducing the technical complexity, because the extracted raw mixture may be used without further treatment, particularly without purification, for instance in an adsorber. Hydrogen, which is present in ambient air in a concentration of usually 0.4 ppm, may be present in the raw mixture and/or refrigerant corresponding to the amount of 2% or below. Thus, the raw helium-neon mixture produced from the column(s) of the air separation plant (typically consisting of neon, nitrogen, helium and hydrogen) can directly be used without any further treatment in the refrigeration circuit preferably configured for cooling temperatures below 80 K to approximately 63 K (triple point of nitrogen).

Preferably, the cooling system further includes a purification device configured to remove impurities, for example nitrogen, from the raw mixture. This provides a refrigerant suitable for lower cooling temperatures such as below 80 K, preferably below 70 K, to approximately 25 K. “Impurities” in this connotation are to be understood to refer to the components not desired in a refrigerant for a particular application but which are inherently included to the raw mixture in the process used to extract the raw mixture.

Preferably, the air separation plant is configured to extract the raw mixture from ambient air, wherein the raw mixture includes a neon/helium-ratio which is approximately equal to the neon/helium-ratio included in the ambient air, preferably of approximately 3.5. In this very preferred case of maintaining the natural ratio of neon and helium (present in a ratio of approximately 3.5 in ambient air), which is constant worldwide, there is no need for technical solutions regarding the mixture and management of the raw mixture and/or refrigerant. The logistics for obtaining the refrigerant is further simplified.

Preferably the refrigeration circuit is configured to implement a Brayton cycle or a Claude cycle which are particularly suitable for producing cryogenic refrigeration temperatures.

Preferably the refrigeration circuit includes one or more turbo-compressors. The refrigeration circuit for instance involves the compression, preferably in one or more turbo-compressors, the cooling, expansion and warming-up of the refrigerant mixture. The mixture including neon has a low freezing point and a high molar mass compared to pure helium and hydrogen. The mixture is therefore particularly advantageous with respect to turbo-compressors.

Preferably the cooling system is configured such that neither helium nor neon included in the raw mixture, preferably also in the refrigerant, is added by a source different from the air separation plant. Moreover, the helium and neon are preferably extracted from air together as if they were a single component. This further reduces technical complexity and costs and further simplifies the logistics for obtaining the refrigerant.

According to the invention, a method for producing a refrigerant usable in a refrigeration circuit, for instance as described above, is provided. The method comprises extracting a raw mixture including helium and neon from air and obtaining the refrigerant from the raw mixture.

The technical effects, preferred or optional features as well as technical contributions and advantages described with respect to the cooling system similarly apply to the method for producing the refrigerant.

A cooling method according to the invention utilizing the refrigerant as described above comprises: a process or method for producing the refrigerant according to the description above; and circulating the refrigerant in a refrigeration circuit, preferably used in or including a refrigeration plant and/or a condenser.

The technical effects, preferred or optional features as well as technical contributions and advantages described with respect to the cooling system similarly apply to the cooling method.

Brief description of the drawings

The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawing.

Figure 1 schematically illustrates a conventional process to provide mixtures of neon with helium as a refrigerant for a refrigeration and/or liquefaction plant.

Figure 2 schematically illustrates a system and process to obtain and supply a raw helium-neon mixture as a refrigerant for a refrigeration plant and/or a liquefier.

Figure 3 schematically illustrates a cooling system having an air separation plant and a refrigeration circuit.

Figure 4 schematically illustrates a cooling system according to a further embodiment.

Figure 5 schematically illustrates a cooling system according to a further embodiment.

Detailed description of preferred embodiments

In the following, preferred embodiments of the invention will be described with reference to the drawings. Elements that are identical, similar or have an identical or similar effect are provided with the same reference numerals in the figures. Repeating the description of such elements may be omitted in order to prevent redundant descriptions.

As has been discussed above, Figure 1 illustrates the conventional process to provide a mixture including helium and neon as a refrigerant for a refrigeration and/or liquefaction plant. A first process line 100 includes an air separation plant 101 configured to separate ambient air into its component parts by cryogenic rectification. A neon rich stream produced from the air separation plant 101 is fed to a neon rectification column 102 to produce a second neon rich stream with a higher concentration of neon. This second neon rich stream is then purified and thereafter stored in a neon-storage 103. Helium is obtained via a second process line 110 which is locally separated from the first process line 100. Usually the helium is obtained and separated from natural gas (petroleum gas), which contains helium at a proportion of 1% or more, within a fractionating column

111. Helium is extracted and accumulated within a subsequent process stage 112 and thereafter stored in a helium-storage 113. The pure neon stored in the neon-storage 103 and the pure helium stored in the helium-storage 113 are mixed according to a desired ratio and supplied to a refrigeration plant 120.

Figure 2 schematically illustrates a system and process according to the present disclosure to obtain and supply a raw helium-neon mixture (nelium) as a refrigerant for a refrigeration plant and/or a condenser including a refrigeration circuit 1. The raw helium-neon mixture is obtained via an air separation plant 2 which includes one or more rectification columns. Thereafter the raw helium-neon mixture may be cleaned or further treated via a purification device 3 (described further below) and is supplied to the refrigeration circuit 1.

It is proposed to use the mixture of helium and neon as a refrigerant preferably at a ratio as found in the ambient air (approximately 3.5). This advantageously implies that the mixture is provided by the air separation plant 2 without further treatment. The mixture is typically regarded as a waste product due to missing applications. The ratio between neon and helium is almost constant due to the natural occurrence in ambient air. Since an enormous technical effort is required to obtain pure neon from air, only a small number of air separation plants worldwide are operated to separate and accumulate neon from air. Thus, directly utilizing the waste helium-neon mixture supplied by the air separation plant 2 drastically reduces costs and technical equipment for obtaining the refrigerant.

The raw helium-neon mixture may be used as a refrigerant for cooling temperatures below 80 K to approximately 25 K. In this case the cooling system may be equipped with a purification device 3 or absorber stages configured to remove impurities (mainly nitrogen but also other impurities). Alternatively the raw helium-neon mixture, which is extracted from the column(s) of the air separation plant 2, i.e. typically a mixture of helium, neon, nitrogen and hydrogen, may be directly used as a refrigerant. The helium-neon mixture of neon, nitrogen, helium and hydrogen can be used in a refrigeration circuit 1 of a cooling system adapted for cooling temperatures below 80 K to 63 K (triple point of nitrogen). A small proportion of hydrogen does not interfere with the operation of the cooling system in the proposed temperature range above 25 K.

The raw mixture obtained from the rectification column(s) of the air separation plant 2 is used as a refrigerant (or basis for a refrigerant) for instance in a refrigeration circuit of a refrigeration plant and/or a liquefier. In particular, the raw mixture may be used in a low-temperature refrigeration circuit including expansion turbine(s) (Brayton circuit) and/or in a low-temperature refrigeration circuit including expansion turbine(s) and at least one further expansion stage for instance including an expansion valve or expansion device (Claude circuit).

In the following, cooling systems according to different embodiments applying the process and mixture described herein are described with respect to the Figures 3 to 5. The main components may comprise: a compressor configured to compress the mixture and/or a purification device or adsorber configured to eliminate impurities and/or a heat exchanger and/or an expansion turbine and/or expansion valve. The mixture used as a refrigerant has a low freezing point and a high molar mass compared to helium and hydrogen. The mixture is therefore particularly advantageous for use with turbo-compressors and expansion turbines. Unlike nitrogen, the helium-neon mixture used for cooling temperatures below 77 K does not have to be operated at a sub-atmospheric pressure.

Figure 3 illustrates an exemplary cooling system utilizing a direct application of the raw helium-neon mixture provided by the air separation plant 2 as a refrigerant circulated in the refrigeration circuit 1 which is configured as a Brayton cycle.

The refrigerant, preferably a mixture of helium, neon, nitrogen and hydrogen, is compressed via compressor 11, preferably configured as a turbo-compressor, and subsequently pre-cooled in a cooler 12 and heat exchanger 13a, preferably configured as a plate heat exchanger. Thereafter, the refrigerant is expanded via an expansion device 14. The expansion device 14 preferably includes a turbine or a number of turbine-stages. The work of the expansion is used to cool and/or liquefy an object 20 or fluid. The refrigerant is then heated in heat exchanger(s) 13a, 13b and supplied to the suction side of the compressor 11.

The helium-neon mixture as used in a process and refrigeration circuit 1 as illustrated in Figure 3 is applicable for cooling temperatures below 80 K to 63 K (triple point of nitrogen).

Figure 4 illustrates a further cooling system using a raw helium-neon mixture provided by the air separation plant 2 as a refrigerant for a refrigeration circuit T which is configured as a Claude cycle.

The raw helium-neon mixture is compressed via compressor 11, preferably configured as a turbocompressor, and subsequently pre-cooled in the cooler 12 and heat exchanger 13a, preferably configured as a plate heat exchanger. Thereafter, the raw helium-neon mixture is expanded via an expansion device 14a and expansion valve (Joule-Thomson valve) 14b. The refrigerant expanded in the expansion device 14a is used to further cool a partial flow of the refrigerant. Further, the raw helium-neon mixture is purified in an adsorber tank 15. In particular, nitrogen is separated from the raw helium-neon mixture. The refrigerant is cooled down in heat exchangers 13b, 13c and released in the expansion valve 14b. The work of the expansion is used to cool and/or liquefy object 20 or fluid. The refrigerant is then heated in the heat exchanger(s) 13a, 13b, 13c and supplied to the suction side of the compressor 11.

The exemplary process illustrated in Figure 4 is applicable for cooling temperatures between 80 K and 25 K. Thus, the refrigeration plant designed as a Claude circuit including the expansion valve 14b and the adsorber tank 15 allows for lower temperatures as compared to the embodiment of Figure 3.

Figure 5 illustrates a further cooling system using a raw helium-neon mixture provided by the air separation plant 2 as a refrigerant for a refrigeration circuit 1. The cooling system according to the present embodiment includes a further purification in a purification device 3 and is adapted for cooling temperatures between 80 K and 25 K.

The raw helium-neon mixture is purified in the purification device 3 by separating nitrogen. The resulting helium-neon-hydrogen mixture can then be used as a refrigerant in the refrigeration circuit 1 as illustrated in Figure 5 for very low cooling temperatures up to 25 K. After purifying the raw mixture in the purification device 3, the refrigerant is supplied to the compressor 11. Thereafter, the process essentially corresponds to the process illustrated in Figure 4.

Possible applications for the helium-neon mixture extracted from the rectification column(s) of the air separation plant 2 include refrigeration plants for cooling of high-temperature superconductors (HTS, High Temperature Superconductor cooling) regarding temperatures below 80 K. Further applications include: precooling in refrigeration plants (e.g. shield cooling in particle accelerators) and liquefiers, particularly helium or hydrogen liquefiers. The refrigerant and process may be used in refrigeration plants adapted for cooling temperatures between 25 K and 80 K, preferably between 30 K and 75 K.

According to the described embodiments, an air separation plant 2 is directly used for producing the refrigerant or a raw mixture including helium and neon. This solves the problem of availability and reduces technical complexity and costs as compared to the conventional processes which are based on separately extracting helium and neon and subsequently mixing the two components.

In the preferred case of maintaining the natural ratio of neon and helium of approximately 3.5 which is present in ambient air and which is constant worldwide, there is no need for technical solutions regarding the mixture and management of the composition. The logistics for obtaining the refrigerant is simplified since the desired mixture is provided via one source, i.e. air as the source not for the individual components but the resulting mixture. It is possible to compress the raw helium-neon mixture via a turbo-compressor including a small number of compressor stages.

Adding or maintaining a slight amount of hydrogen (usually 0.4 ppm in ambient air) corresponding to 2% or below in the helium-neon mixture is possible. Thus, the raw helium-neon mixture produced from the column(s) of the air separation plant (typically consisting of neon, nitrogen, helium and hydrogen) can directly be used without any further treatment in a refrigeration circuit configured for cooling temperatures below 80 K to approximately 63 K (triple point of nitrogen).

It will be obvious for a person skilled in the art that the 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

Refrigeration circuit

1' Refrigeration circuit

Refrigeration circuit

Air separation plant

Purification device

Compressor

Cooler

13a Heat exchanger

13b Heat exchanger

13c Heat exchanger

Expansion device

14a Expansion device

14b Expansion valve

Adsorber tank

Object to be cooled

100 First process line

101 Air separation plant

102 Neon rectification column

103 Neon-storage

110 Second process line

111 Fractionating column

112 Subsequent process stage

113 Helium-storage

120 Refrigeration plant

Claims

1. Cooling system, preferably adapted for use in or including a refrigeration plant and/or liquefier plant, the cooling system including a refrigeration circuit (1) configured to use a refrigerant including a mixture of helium and neon; wherein the refrigerant is based on a raw mixture, preferably the refrigerant comprises the raw mixture, and wherein the raw mixture extracted from air by an air separation plant (2).

2. Cooling system according to claim 1, further including an air separation plant (2) configured to extract the raw mixture including helium and neon from air, wherein the raw mixture is used as the refrigerant or forms the basis of the refrigerant.

3. Cooling system according to claim 1 or 2, wherein the raw mixture further includes nitrogen and/or hydrogen.

4. Cooling system according to any one of the previous claims, further including a purification device (3) configured to remove impurities, preferably nitrogen, from the raw mixture.

5. Cooling system according to any one of the previous claims, wherein the air separation plant (2) is configured to extract the raw mixture from ambient air and the raw mixture preferably includes a neon/helium-ratio which is approximately equal to the neon/helium-ratio present in the ambient air, preferably of approximately 3.5.

6. Cooling system according to any one of the previous claims, wherein the cooling system and the refrigerant are configured for cooling temperatures below 80 K, preferably below 70 K or 63 K, to approximately 25 K.

7. Cooling system according to any one of the previous claims, wherein the refrigeration circuit (1) is configured to implement a Brayton cycle ora Claude cycle and/or the refrigeration circuit (1) includes one or more turbo-compressors (11).

8. Cooling system according to any one of the previous claims, wherein the raw mixture including helium and neon is extracted from air in rectification columns of the cryogenic air separation plant (2).

9. Cooling system according to any one of the previous claims, wherein the cooling system is configured such that neither helium nor neon included in the raw mixture, preferably also in the refrigerant, is added by a source different from the air separation plant (2).

10. Cooling system according to any one of the previous claims, wherein the refrigeration circuit (1) is configured for cooling and/or liquefaction of gases, preferably helium and/or neon and/or hydrogen.

11. Method for producing a refrigerant usable in a refrigeration circuit (1), comprising: extracting a raw mixture including helium and neon from air, wherein the raw mixture preferably further includes nitrogen and hydrogen; and using the raw mixture as the refrigerant or obtaining the refrigerant from the raw mixture.

12. Method according to claim 10 or 11, further comprising removing impurities, preferably nitrogen, from the raw mixture.

13. Method according to any one of the claims 10 to 12, wherein the raw mixture is extracted from ambient air, and the raw mixture includes a neon/helium-ratio which is approximately equal to the neon/helium-ratio included in the ambient air, preferably of approximately 3.5.

14. Cooling method, comprising:

a method for producing a refrigerant according to any of the claims 9 to 12; and circulating the refrigerant in a refrigeration circuit (1), preferably the refrigerant circuit being used in or including a refrigeration plant and/or a liquefier plant.

15. Cooling method according to claim 14, wherein the refrigeration circuit (1) implements a Brayton cycle or a Claude cycle, and the refrigeration circuit (1) preferably includes one or more turbo-compressors (11).