APPARATUS AND METHOD FOR GENERATING CRYOGENIC TEMPERATURES AND USE THEREOF

Abstract

The invention relates to an apparatus (112) and to a method (210) for generating cryogenic temperatures. The apparatus (112) comprises at least one cooling stage (111) which has a cold region (110) and a warm region (116), and a refrigerant mixture designed specifically for the cooling stage (111) is provided in the warm region (116), the refrigerant mixture having at least two components each having a different boiling temperature, and the cold region (110) comprises at least one cooling stage (111): - a first heat exchanger (122), which has a high-pressure side (120) to receive the refrigerant mixture at a high-pressure level from the warm region (116) of the cooling stage (111) and a low-pressure side (126) to deliver the refrigerant mixture to the warm region (116) of the cooling stage (111); - a first expansion device (136), which is designed for expansion and for cooling of the refrigerant mixture at a low-pressure level; - a second heat exchanger (148), which is designed for cooling and for partial condensation of a proportion of the refrigerant mixture located in a buffer volume (140), the buffer volume (140) being designed to limit the pressure exerted by the refrigerant mixture; and - a second expansion device (150), which is designed for separation of the buffer volume (140) from the low-pressure level of the cooling stage (111) or connection of the buffer volume (140) to said low-pressure level. The invention enables autonomous operation of the apparatus (112) and of the method (210) for generating cryogenic temperatures, in which each cooling stage (111) of the apparatus (112) can be filled with a pre-defined refrigerant mixture and can be permanently operated, and in particular in the cooling phase the refrigerating capacity can be increased, while incorrect distribution of the refrigerant of the relevant cooling stage (111) among parallel flow channels at the cold end of the first heat exchanger (122) can be prevented.

Claims

1. A device for generating cryogenic temperatures, comprising at least one cooling stagehaving a cold region and a warm region, wherein a coolant mixture configured for the respective cooling stage is provided in the warm region, wherein the coolant mixture has at least two components having different boiling temperatures, wherein the cold region of at least one cooling stage comprises: a first heat exchanger having a high pressure side for reception of the coolant mixture at a high pressure level from the warm region of the cooling stage and a low pressure side for release of the coolant mixture to the warm region of the cooling stage; a first expansion unit configured for expansion and for cooling of the coolant mixture to a low pressure level; a second heat exchanger configured for cooling and for partial condensation of a fraction of the coolant mixture located in a buffer volume, wherein the buffer volume is configured to limit the pressure exerted by the coolant mixture; and a second expansion unit configured for separation of the buffer volume from or to a connection of the buffer volume to the low pressure level of the cooling stage.

2. The device of claim 1,wherein the second heat exchanger is configured for partial condensation of at least one of the components of the fraction of the coolant mixture in the buffer volume to provide at least one condensed component.

3. The device of claim 1, wherein the buffer volume comprises a buffer vessel,wherein the buffer vessel is in the warm region and is connected via a conduit to a second volume which is present in the cold region and is thermally coupled to the second heat exchanger, or wherein the buffer vessel is in the cold region and the second heat exchanger is integrated into the buffer vessel.

4. The device of claim 1, further comprising a third expansion unit configured to release the pressure of the cooling stage into the buffer volume.

5. The device of claim 1, further comprising a third heat exchanger configured to cool an application.

6. The device claim 1, further comprising a phase separator configured to separate a biphasic coolant mixture into a liquid phase and a vaporous phase, and for separate feeding of the liquid phase to a first low-pressure stream and of the vaporous phase to a second low-pressure stream on the low pressure side of the first heat exchanger.

7. The device of claim 1, wherein the cold region is introduced into a cryostat.

8. A method for liquefying low-boiling fluids at temperatures of 15 K to 120 K or cooling high-temperature superconductors to a temperature of 15 K to 90 K comprising a step of generating cryogenic temperatures with a device of claim 1.

9. A method for generating cryogenic temperatures, comprising the following steps: a) introducing a coolant mixture configured for a cooling stage of a device for generating cryogenic temperatures at high pressure level from a warm region of the cooling stage into a high pressure side of a first heat exchanger, wherein the coolant mixture has at least two components having different boiling temperatures; b) expanding and cooling the coolant mixture at low pressure level by using a first expansion unit; c) cooling and partly condensing at least one component of a fraction of the coolant mixture located in a buffer volume by using a second heat exchanger by releasing thermal energy to the coolant mixture at low pressure level, wherein the buffer volume is configured to limit the pressure exerted by the coolant mixture; d) feeding a condensed liquid phase from the buffer volumevia a second expansion unit to the coolant mixture at low pressure level, until a steady operating state or equalization of pressure between the buffer volume and the low pressure level has been achieved; e) releasing the coolant mixture from a low pressure side of the first heat exchanger to the warm region of the cooling stage.

10. The method of claim 9, wherein the feeding of the condensed liquid phase from the buffer volume via the second expansion unit to the coolant mixture at low pressure level is executed in a manner that a change in a current concentration of the components in the coolant mixture occurs at low pressure level.

11. The method of claim 10, wherein the change in the current concentration of the components in the coolant mixture at low pressure level is effected in a manner that at least one higher-boiling component of the fraction of the coolant mixture in the buffer volume is first condensed and then fed to the coolant mixture at low pressure level, and at least one low-boiling component of the fraction of the coolant mixture in the buffer volume is increasingly condensed and then fed to the coolant mixture at low pressure level.

12. The method of claim 9, wherein the second expansion unit is closed at the start of the cooling operation until the liquid phase has formed at the base of the buffer volume, wherein the second expansion unit is opened later on in the cooling operation in order to feed the liquid phase from the buffer volume to the coolant mixture at low pressure level, wherein the second expansion unit is opened or remains closed at the end of the cooling operation when the steady operating state or the equalization of pressure between the buffer volume and the low pressure level has been attained.

13. The method of claim 9, wherein the following step is additionally executed: f) cooling an application by using a third heat exchanger.

14. The method of claim 9, wherein the following step is additionally executed: g) separating a biphasic coolant mixture at low pressure level into a liquid phase and a gaseous phase and separately feeding the separated liquid phase to a first low-pressure stream and the gaseous phase to a second low-pressure stream on the low pressure side of the first heat exchanger.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0076] Further details and features of the present invention will be apparent from the description of preferred working examples that follows, especially in conjunction with the dependent claims. It is possible here for the respective features to be implemented on their own, or two or more in combination. However, the invention is not limited to the working examples. The working examples are shown schematically in the figures that follow. In this context, identical reference numerals in the figures denote elements that are the same or have the same function, or elements that correspond to one another in terms of their function.

[0077] The individual figures show:

[0078] FIGS. 1 to 5 a schematic diagram in each case of a cold region of a preferred working example of a device of the invention for generation of cryogenic temperatures;

[0079] FIG. 6 a schematic diagram of a preferred working example of a method for the invention for generation of cryogenic temperatures.

DESCRIPTION OF THE WORKING EXAMPLES

[0080] FIGS. 1 to 5 each show a schematic diagram of a preferred working example of a cold region 110 of a cooling stage 111 of a device 112 for generation of cryogenic temperatures, which can also be referred to as “refrigeration system”. As mentioned above, the expression “cryogenic temperature” relates to a temperature of 10 K, preferably of 15 K, up to 120 K, preferably to 90 K. The cold region 110 of the cooling stage 111 has preferably been introduced into a vacuum-insulated cryostat 114.

[0081] As well as the cold region 110, the cooling stage 111 of the device 112 also comprises a warm region 116 that has a higher temperature compared to the cold region 110. The device 112 shown in each of FIGS. 1 to 5 is in a one-stage configuration and hence comprises the exactly one cooling stage 111 with the cold region 110 and the warm region 116. In the executions of FIGS. 1 to 5, the warm region 116 of the cooling stage 111 is preferably configured for ambient temperature and is typically kept at ambient temperature. Reference is made to the above definition for the term “ambient temperature”.

[0082] In the warm region 116, a coolant mixture comprising a mixture of at least two components of coolants that has been configured for the cooling stage 111 is provided, where at least two of the components have a different boiling temperature. In order to be able to achieve maximum efficiency in cooling of the coolant mixture from the ambient temperature to the cryogenic temperature, a wide-boiling coolant mixture is used that comprises both at least one higher-boiling component and at least one lower-boiling component. As mentioned above, the at least one higher-boiling component may preferably be selected from a hydrocarbon and a fluorinated hydrocarbon, while the at least one lower-boiling component may preferably be selected from oxygen, nitrogen, argon, neon, hydrogen and helium. However, other substances are possible.

[0083] The warm coolant mixture is introduced at high pressure level from the warm region 116 into the cold region 110 by using a feed 118 that opens into a high pressure side 120 of a first heat exchanger 122, which, in the illustrative diagram of FIG. 1, is executed as a countercurrent heat exchanger 124. In addition, the first heat exchanger 122 has a low pressure side 126 which is designed for release of the cold coolant mixture to the warm region 116 by using a drain 128. Thus, the warm coolant mixture fed in from the warm region 116 on the high pressure side 120 has a higher temperature compared to the coolant mixture provided for release to the warm region 116 on the low pressure side 126. Consequently, the cold coolant mixture provided on the low pressure side 126 makes a significant contribution to the cooling of the warm coolant mixture fed in from the warm region 116 on the high pressure side 120, and a transfer of thermal energy via the countercurrent heat exchanger 124 can be made more efficient in that the warm coolant mixture fed in from the warm region 116 on the high pressure side 120 flows in an opposite direction 130 from a direction 132 of the cold coolant mixture provided on the low pressure side 126.

[0084] The warm coolant mixture that has already been partly cooled in the first heat exchanger 122 on the high pressure side 120 and has originally been fed in from the warm region 116 subsequently passes via a conduit 134 into a first expansion unit 136, designed here as an expansion valve. However, an alternative execution of the expansion unit 136 as a throttle capillary, diaphragm or sinter element is possible. The first expansion unit 136 is likewise in the cold region 110 and is configured for cooling of the coolant mixture to low pressure level. The expansion valve 136 here may preferably be configured to achieve the desired cooling of the coolant mixture by using the Joule-Thomson effect, since the coolant mixture for the cooling stage 111 has been adjusted such that the Joule-Thomson coefficient .Math..sub.JT, defined according to equation (1), of the coolant mixture has a positive value at the temperature of the cold side 110 of the cooling stage 111. Thus, the first expansion valve 136 firstly brings about the reduction in the pressure to which the coolant mixture is subject from the high pressure level to low pressure level, and secondly the desired further cooling of the coolant mixture.

[0085] The further-cooled and expanded coolant mixture subsequently passes via a further conduit 138 and an inlet 147 into a second heat exchanger 148, and exits from the second heat exchanger 148 at an outlet 149. In the executions according to FIGS. 1 and 3 to 5, the second heat exchanger 148 is thermally coupled to a second volume 146. The second volume 146 is part of a buffer volume 140 configured to limit the pressure exerted by the coolant mixture. In the executions according to FIGS. 1 and 3 to 5, the buffer volume 140 comprises a buffer vessel 142 which is disposed in the warm region 116 of the device 112 and is connected to the second volume 146 via a conduit 144. By contrast, in the execution according to FIG. 2, the buffer vessel 142 is likewise disposed in the cold region 110, with the second heat exchanger 148 integrated into the buffer vessel 142 and hence introduced into the buffer vessel 142 in such a way that the buffer vessel 142 fully encompasses the second heat exchanger 148.

[0086] The second heat exchanger 148 is configured for cooling and partial condensation of the coolant mixture in the buffer volume 140, in order in this way to further increase the efficiency of the cooling by the present device. In the particularly preferred one-step execution of the device 112 shown in schematic form in FIGS. 1 to 5, the second heat exchanger 148 is configured for partial condensation of at least one of the components of a portion of the coolant mixture present in the buffer volume 140 to provide at least one condensed component. For this purpose, the second heat exchanger 148 may preferably be provided in form of a condenser, in which case the at least one condensed component is generated in the buffer volume 140 by drawing enthalpy of evaporation from the condensed component, which is supplied to the circulating coolant mixture at low pressure level between the inlet 147 and the outlet 149 of the second heat exchanger 148. In this execution, the coolant mixture cooled down in the first expansion valve 136 enters the second heat exchanger 148 in such a way that only at least one higher-boiling component condenses out of the portion of the coolant mixture present in the buffer volume 140 at first, i.e. on commencement of the cooling phase, and this forms a condensed component in the form of a liquid phase (not shown).

[0087] In the executions according to FIGS. 1 to 5, the cold region 110 of the device 112 comprises a second expansion unit 150 that serves for stepwise or continuous supply of the liquid phase formed or present in the buffer volume 140 into a further conduit 156 for circulation of the coolant mixture at low pressure level. The second expansion unit 150 is likewise executed here as an expansion valve; however, an alternative execution as a combination of a magnetic valve and a throttle capillary, diaphragm or sinter element is possible.

[0088] As shown in schematic form by FIGS. 1 to 5, the second expansion unit 150 is especially disposed at an outlet 152 from the buffer volume 140 in a conduit 154. The expansion unit 150 may be closed at the start of the cooling operation until formation of a liquid phase in the buffer volume 140. The opening of the expansion device 150 allows the liquid phase to be fed fully or partly from the buffer volume 140 via conduit 154 to the coolant mixture circulating in conduit 156. In this way, especially on commencement of the cooling phase, proceeding from the balanced concentration corresponding to the filling of the cooling stage at rest, there may be an automatic increase in the concentration of higher-boiling components in the circulating coolant mixture for the stage. It is thus possible to increase the Joule-Thomson coefficient .Math..sub.JT of the coolant mixture, which results in more significant cooling of the coolant mixture that can lead to an overall increase in refrigeration performance of the refrigeration system. It is thus possible to gradually cool units in the cold region 110 of the device 112 that follow downstream in flow direction with an elevated refrigeration performance compared to refrigeration systems known from the prior art.

[0089] The expansion unit 150 may subsequently be closed or have such dimensions that a liquid phase forms again in the buffer volume 140 upstream of the outlet 152, or a liquid phase is present continuously. In the further cooling phase, the liquid phase formed or present in the buffer volume 140 may preferably absorb the at least one further-condensed component. The liquid phase present in the buffer volume 140 may also additionally be fed fully or partly via the second expansion unit 150 stepwise or continuously to the conduit 156 for circulation of the coolant mixture at low pressure level. Later on in the cooling phase, there is a gradual drop in the concentration of higher-boiling components in the coolant mixture in the buffer volume 140 and a gradual rise in the concentration of lower-boiling components in the coolant mixture in the buffer volume 140. It is thus possible to gradually and automatically reduce the concentration of higher-boiling components in the circulating coolant mixture again later on in the cooling phase, and gradually increase the concentration of lower-boiling components in the coolant mixture again, until the cooling phase has ended. Once the cooling phase had ended, the second expansion unit 150 may be closed or remain open in order to establish steady-state operation of the device 112.

[0090] In the executions according to FIGS. 1 to 5, the buffer volume 140 may thus be configured to enable the desired autonomous operation of the device 112 in that the apparatus 112 can be filled at any time with a predefined coolant mixture and operated sustainably, where the circulating coolant mixture at the start of the cooling phase has the balanced concentration corresponding to the filling of the cooling stage, then has a higher concentration of higher-boiling components as a result of the supply of higher-boiling components from the buffer volume 140, which is reduced again gradually, i.e. during the cooling phase, in favor of the concentration of lower-boiling components.

[0091] As is also shown schematically in FIGS. 1 to 5, the device 112 may also have, in the cold region 110, a third expansion unit 160 configured to release the pressure on the low pressure side of the cooling stage 111 into the buffer volume 140. In FIGS. 1 to 5, the expansion unit 160 is preferably connected to the conduit 138; however, connection to any other suitable conduit on the low pressure side of the cooling stage 111 is possible. The third expansion unit 160 may especially be configured as a backflow preventer having an entry side 162 indicated by a dot, which opens only when the pressure on the low pressure side is greater than in the buffer volume 140. The third expansion unit 160 may especially be selected from a nonreturn valve, a nonreturn flap, an overflow valve and a safety valve; however, a different execution is possible. The third expansion unit 160 may therefore preferably be used as safety unit for pressure safeguarding of the low pressure side, for example in the case of occurrence of a quench of a superconductor application or a break in the insulation vacuum.

[0092] The coolant mixture that circulates in the conduit 156 shown in schematic form in FIGS. 1 to 5 can ultimately enter the low pressure side 126 of the first heat exchanger 122, whence it is released to the warm region 116 of the cooling stage 111.

[0093] As also shown schematically in FIGS. 3 and 5, the device 112 in the cold region 110 may also have a third heat exchanger 164 which has been introduced into the conduit 156 for circulation of the coolant mixture and which is configured for cooling of application 166, wherein the application 166 comprises a substance or a component, the temperature of which can be reduced to a cryogenic temperature by using the device 112. The third heat exchanger 164 here is preferably designed as an evaporator, wherein at least one component of the circulating coolant mixture is partly evaporated at low pressure level in that the requisite enthalpy of evaporation is drawn from the application 166 to be cooled. However, other executions of the third heat exchanger 164 are conceivable.

[0094] As also shown schematically in FIGS. 4 and 5, the device 112 may also have, in the cold region 110, a phase separator 170 configured to separate a biphasic coolant mixture which is formed by partial evaporation in the second heat exchanger 148 and/or in the third heat exchanger 164 into the liquid phase and a vaporous phase, and for separate supply of each of the liquid phase and the vaporous phase to the low pressure side 126 of the first heat exchanger 122. As shown schematically by FIGS. 4 and 5, the liquid phase is fed by using a conduit 172 to a first low-pressure stream 176, and the vaporous phase by using a separate conduit 174 to a second low-pressure stream 178 on the low pressure side 126 of the first heat exchanger 122. In this case, the first low-pressure stream 176 absorbed by the liquid phase with the higher refrigeration output by virtue of the enthalpy of evaporation from the biphasic coolant mixture is preferably run closer to the high pressure side 120 which is configured for cooling of the coolant mixture from the warm region 116 via the conduit 118 in the first heat exchanger 122 in the cold region 110. Thus, the cold region 110 of the cooling stage 111 of the device 112 is configured such that, even during the cooling phase, it is predominantly the cold liquid component of the coolant mixture that is used to cool the warm coolant mixture entering the first heat exchanger 122 from the warm region 116, as a result of which the efficiency of the cooling of the device 112 can be increased further. The cold gaseous component of the coolant mixture likewise contributes to a lesser degree, via the second low-pressure stream 178 on the low pressure side 126 of the first heat exchanger 122, to the cooling of the warm coolant mixture entering the first heat exchanger 122 from the warm region 116.

[0095] This is especially true in the case described at the outset, in which the first heat exchanger 122 is executed in the form of a microstructured heat exchanger having a multitude of parallel microstructured flow ducts, in which strands in a mutually parallel arrangement can be cooled at the same speed. This is achieved in accordance with the invention in that, during the cooling phase, a coolant mixture comprising predominantly higher-boiling components that can be liquefied at the cold end of the heat exchanger 122 is first produced and provided automatically. In this way, all parallel entry passages of the first low-pressure stream 176 on the low pressure side 126 of the heat exchanger 122 may be flooded with liquid coolant, which can prevent maldistribution of the coolant at the cold end of heat exchanger 122. With increasing cooling of the cold region 110 of the device 112, lower-boiling components are automatically added stepwise to the coolant mixture by virtue of the inventive configuration of the buffer volume 140, such that the first heat exchanger 122 can also be operated optimally at cryogenic temperatures later on without maldistribution of the coolant at the cold end of the heat exchanger 122. In a particularly advantageous manner, this enables autonomous operation of the device for generating cryogenic temperatures.

[0096] FIG. 6 shows a schematic diagram of a preferred working example of a method 210 for generating cryogenic temperatures, which can especially be conducted using the device 112 described herein.

[0097] In a provision step 212, a coolant mixture, in step a), at high pressure level from the warm region 116 of the cooling stage 111 of the device 112 for generation of cryogenic temperatures is introduced into the high pressure side 120 of the first heat exchanger 122, preferably of the countercurrent heat exchanger 124, where it is cooled down to a lower temperature compared to the warm region 116.

[0098] In an expansion step 214, in step b), the coolant mixture is expanded and cooled to low pressure level by using a first expansion unit 136, as a result of which the coolant mixture is now at low pressure and a lower temperature compared to the high-pressure outlet of the first heat exchanger 122.

[0099] In a condensation step 216, in step c), at least one component of the fraction of the coolant mixture present in the buffer volume 140 is cooled and partly condensed by using the second heat exchanger 148 by release of thermal energy to the coolant mixture at low pressure level that flows through the second heat exchanger 148 downstream of the first expansion device 136.

[0100] In a supplying step 218, in step d), a condensed liquid phase from the buffer volume 140 is fed stepwise or continuously via the second expansion unit 150 to the circulating coolant mixture at low pressure level, until a steady operating state or equalization of pressure between the buffer volume 140 and the low pressure level has been attained.

[0101] In an optional application step 220, in the additional step f), the application 166 may be cooled by using the third heat exchanger 164, the desirability of which depends on the use of the device 112. As mentioned above, the application 166 here may especially be a liquefaction of low-boiling fluids at a temperature of 15 K to 120 K, or cooling of high-temperature superconductors or of a component having at least one high-temperature superconductor to a temperature of 15 K to 90 K.

[0102] In an optional but particularly preferred separation step 222, in the additional step g), a biphasic coolant mixture at low-pressure level may be separated into the liquid phase and the gaseous phase, which can preferably be accomplished using the phase separator 170, in which case it is additionally possible to separately supply the separated liquid phase and gaseous phase in conduits 170, 174 to low-pressure streams 176, 178 on the low pressure side 126 of the first heat exchanger 122.

[0103] In a release step 224, in step e), the coolant mixture is then released from the low pressure side 126 of the first heat exchanger 122 to the warm region 116, and may be used here, as described above, to cool a further volume of coolant mixture provided in the provision step 212 for the first time by using the first heat exchanger 122, preferably the countercurrent heat exchanger 124.

[0104] In addition, the present method 210 for generating cryogenic temperatures may optionally comprise at least one further step (not shown), especially selected from: [0105] precooling and heating an additional coolant mixture from a downstream cooling stage in at least one additional high pressure stage and at least one additional low pressure stage in the first heat exchanger 122, [0106] cooling or liquefying a gas stream to be liquefied in an additional stream of matter in the first heat exchanger 122.

[0107] For further details of the present method 210, reference is made to the above description of the device 112.

TABLE-US-00001 List of reference numerals 110 cold region 149 outlet 111 cooling stage 150 second expansion unit 112 device for generating cryogenic temperatures 152 outlet 114 (vacuum-insulated) cryostat 154 conduit 116 warm region 156 conduit 118 feed 160 third expansion unit 120 high pressure side 162 entry side 122 first heat exchanger 164 third heat exchanger 124 countercurrent heat exchanger 166 application 126 low pressure side 170 phase separator 128 drain 172 conduit 130 direction 174 conduit 132 direction 176 first low-pressure stream 134 conduit 178 second low-pressure stream 136 first expansion unit 210 method for generating cryogenic temperatures 138 conduit 212 provision step 140 buffer volume 214 expansion step 142 buffer vessel 216 condensation step 144 conduit 218 supplying step 146 second conduit 220 application step 147 inlet 222 separation step 148 second heat exchanger 224 release step