CRYOGENIC REFRIGERATION OF A PROCESS MEDIUM

Abstract

The present invention pertains to a cryogenic refrigeration system and method for cryogenic refrigeration of a process medium. In particular, the invention relates to a counter flow heat exchanger configuration and pressure regulator arrangement to reduce exergetic losses in the system. Accordingly, a cryogenic refrigeration system is suggested comprising a conduit (2) configured to provide a supply flow (10) of a process medium, a counter flow heat exchanger (3), which is thermally coupled to a heat exchanger section (2A) of the conduit (2) and comprises an inlet (34) at a cold end (30) of the heat exchanger (3) and an outlet (36) at the warm end (32) of the heat exchanger (3), a first pressure regulator (4), which is in fluid communication with the conduit (2) and is arranged downstream of the heat exchanger section (2A), and a vessel (5), which is in fluid communication with the conduit (2) and is arranged downstream of the first pressure regulator (4), wherein the vessel (5) is in fluid communication with the inlet (34) of the heat exchanger (3) and is configured to provide an evaporated gas flow from the process medium to the inlet (34) of the heat exchanger (3). Furthermore, the conduit (2) is free of any evaporation heat exchanger upstream of the heat exchanger section (2A) of the conduit (2).

Claims

1. Cryogenic refrigeration system (1), comprising: a conduit (2) configured to provide a supply flow (10) of a process medium; a counter flow heat exchanger (3), which is thermally coupled to a heat exchanger section (2A) of the conduit (2) and comprises an inlet (34) at a cold end (30) of the heat exchanger (3) and an outlet (36) at the warm end (32) of the heat exchanger (3); a first pressure regulator (4), which is in fluid communication with the conduit (2) and is arranged downstream of the heat exchanger section (2A); and a vessel (5), which is in fluid communication with the conduit (2) and is arranged downstream of the first pressure regulator (4), wherein the vessel (5) is in fluid communication with the inlet (34) of the heat exchanger (3) and is configured to provide an evaporated gas flow from the process medium to the inlet (34) of the heat exchanger (3), wherein the conduit (2) is free of any evaporation heat exchanger upstream of the heat exchanger section (2A) of the conduit (2).

2. Cryogenic refrigeration system (1) according to claim 1, wherein the heat exchanger (3) is configured to provide a temperature factor of the evaporated gas at the warm end (32) of the heat exchanger (3) relative to the process medium of the supply flow (10) at the warm end (32) of the heat exchanger (3) larger than 0.9, preferably larger than 0.98, during normal operation of the cryogenic refrigeration system (1); and/or the heat exchanger (3) comprises an NTU configured to match a temperature of the evaporated gas with a temperature of the process medium at the warm end (32) of the heat exchanger (3) during normal operation of the cryogenic refrigeration system (1).

3. Cryogenic refrigeration system (1) according to claim 2, wherein the temperature factor and/or the NTU is provided by a heat transfer area of the heat exchanger (3), preferably by a length of the heat exchanger, wherein the heat exchanger (3) is preferably of a finned tube shape, coiled shape, and/or fin shape and at least partially surrounds a circumference of the conduit (2).

4. Cryogenic refrigeration system (1) according to claim 1, wherein that the outlet (36) of the heat exchanger (3) is coupled to a recuperation system, a compressor system, a vacuum pump, and/or a liquefaction system, which is configured to provide a constant pressure in the vessel (5).

5. Cryogenic refrigeration system (1) according to claim 1, wherein that the process medium provided upstream of the first pressure regulator (4) is a pressurized liquid, preferably liquid helium or liquid nitrogen, wherein the first pressure regulator (4) is configured to reduce the pressure of the process medium to provide a two-phase process medium (13) flow downstream of the first pressure regulator (4), wherein the first pressure regulator (4) preferably comprises a valve, expansion valve, and/or turbine.

6. Cryogenic refrigeration system (1) according to claim 5, wherein the vessel (5) collects the liquid phase (15), wherein the vessel (5) is thermally coupled to a load (6) or wherein a load (6) is disposed in the collected liquid phase (15) of the vessel (5) to provide an isothermal load (6).

7. Cryogenic refrigeration system (1) according to claim 6, wherein the evaporated gas from the process medium is provided by a state of the two-phase process medium (13) controlled by the pressure regulator (4), a pressure of the vessel (5), and the load (6), wherein the evaporated gas is a sub-atmospheric evaporated gas (12).

8. Cryogenic refrigeration system (1) according to claim 6, wherein the system (1) further comprises a controller (7) and at least one sensor (70, 72, 74, 76) in communication with said controller, wherein the system (1) comprises at least one temperature sensor (70) arranged upstream of the pressure regulator (4) and downstream of the heat exchanger section (2A), wherein the controller (7) is configured to control the first pressure regulator (4) based on the measured value of the at least one temperature sensor (70) to control the state of the two-phase process medium; the system (1) comprises at least one filling sensor (72) arranged in the vessel (5) and/or at least one flow sensor (76) arranged downstream of the pressure regulator (4) for measuring a mass flow of a liquid phase of the process medium to the load, wherein the controller (7) is configured to control the pressure regulator (4) to control the mass flow based on the measured value of the at least one filling sensor (72) and/or the at least one flow sensor (76); and/or the system (1) comprises at least one pressure sensor (74) arranged in communication with the vessel (5) and a compressor system coupled to the outlet (36) of the heat exchanger (3), wherein the controller (7) is configured to control the pressure in the vessel (5) by controlling the compressor system based on the measured value of the at least one pressure sensor (74).

9. Cryogenic refrigeration system (1) according to claim 8, wherein the system (1) further comprises a control valve (20) for controlling the mass flow of the supply flow (10), which is in communication with the controller (7) and is arranged in parallel to and upstream of the first pressure regulator (4), wherein the controller (7) is configured to control the mass flow of the supply flow (10) via the control valve (20) based on the measured value of the at least one temperature sensor (70), filling sensor (72) and/or flow sensor (76).

10. Cryogenic refrigeration system (1) according to claim 8, wherein the system (1) comprises at least one warm-end temperature sensor (70) in communication with the conduit (2) and the outlet (36) of the heat exchanger (3) at the warm end (32) of the heat exchanger (3), wherein the controller (7) is configured to adjust the evaporative gas flow based on a temperature difference measured by the at least one warm-end temperature sensor (70) by controlling the pressure regulator (4).

11. Cryogenic refrigeration system (1) according to claim 1, wherein the heat exchanger (3) is configured as a plurality of heat exchanging modules (3A, 3B, 3C), which are arranged in parallel and/or in series to the conduit (2), wherein preferably a second pressure regulator (4B) in fluid communication with the conduit (2) is arranged between each serially arranged heat exchanging module (3A, 3C).

12. Method for providing a cryogenic refrigeration in a cryogenic refrigeration system (1), the method comprising: providing a supply flow (10) of a process medium in a conduit; cooling the supply flow in a counter flow heat exchanger (3); reducing the pressure of the supply flow (10) by means of a pressure regulator (4); and receiving the supply flow (10) in a vessel (5), wherein an evaporated gas flow from the process medium is used by the heat exchanger (3) to cool the supply flow (10), wherein the cooling of the supply flow is provided free of any evaporating liquid phase.

13. Method according to claim 12, characterized in that a temperature factor of the evaporated gas at a warm end (32) of the heat exchanger (3) relative to the process medium of the supply flow (10) at the warm end (32) of the heat exchanger (3) is provided by the heat exchanger, which is larger than 0.9, preferably larger than 0.98, during normal operation of the cryogenic refrigeration system (1); and/or a temperature of the evaporated gas is matched to a temperature of the process medium at a warm end (32) of the heat exchanger (3) during normal operation of the cryogenic refrigeration system (1) provided by an NTU configuration of the heat exchanger (3).

14. Method according to claim 12 or 13, wherein the supply flow (10) comprises a pressurized liquid, preferably liquid helium, wherein reducing the pressure of the supply flow (10) by the pressure regulator (4) provides a two-phase process medium (13) flow downstream of the pressure regulator (4) and wherein the evaporated gas in the vessel is provided at sub-atmospheric pressure, wherein the cooling of the supply flow (10) preferably provides the process medium between the lambda point and the saturation temperature downstream of the heat exchanger section (2A) of the conduit (2), and wherein the vessel (5) preferably collects the liquid phase (15) of the process medium to refrigerate a thermally coupled load (6) or a load (6) disposed in the liquid phase (15) of the process medium in the vessel (5), to provide an isothermal load (6).

15. Method according to claim 12, wherein the cooling of the supply flow (10) occurs in series or in parallel by means of a plurality of heat exchanger modules (3A, 3B, 3C) arranged in series or in parallel, wherein preferably the pressure of the supply flow (10) is reduced between each serially arranged heat exchanger module (3A, 3C) by means of a second pressure regulator (4B).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] 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:

[0055] FIG. 1 is a schematic view of a heat exchanger, a vessel, and a pressure regulator in a cryogenic refrigeration system;

[0056] FIG. 2 is a schematic view of the embodiment according to FIG. 1 configured to provide the process medium in predefined physical states;

[0057] FIG. 3A is a schematic cross-sectional view of a tubular heat exchanger;

[0058] FIG. 3B is a schematic top view of the tubular heat exchanger according to FIG. 3A seen from the cold end of the heat exchanger;

[0059] FIG. 4 is a schematic view of a cryogenic refrigeration system having a controller and a load;

[0060] FIG. 5 is a schematic view of the cryogenic refrigeration system according to FIG. 4 with a further controller configuration;

[0061] FIG. 6A is a schematic view of a cryogenic refrigeration system having a serial heat exchanger and pressure regulator arrangement;

[0062] FIG. 6B is a schematic view of the cryogenic refrigeration system according to FIG. 6A, comprising a further parallel heat exchanger arrangement.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0063] 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 to description thereof may be omitted in order to avoid redundancies.

[0064] In FIG. 1 a cryogenic refrigeration system 1 is schematically shown in operation using a process medium. In order to provide refrigeration, a supply flow 10 of a process medium is provided in the conduit 2. Although the process media may comprise various compounds and may furthermore be provided in different physical states, the process medium in the exemplary embodiment according to FIG. 1 comprises pressurized liquid helium. The liquid helium is hence at the pressure above atmospheric pressure, preferably between 1.5 and 10 bar, more preferably between 1.5 and 8.0 bar.

[0065] All features of the system 1 and in particular the conduit 2 are thermally isolated, such that the amount of heat entering and leaving the system 1 is considered to be zero or negligible. The cryogenic refrigeration system 1 comprises a counter flow heat exchanger 3, which is thermally coupled to a heat exchanger section 2A of the conduit 2, such that the supply flow 10 is cooled by means of the counter flow heat exchanger 3. After cooling by the heat exchanger 3 the supply flow 10 arrives at a first pressure regulator 4, which is in fluid communication with the conduit 2 and is arranged downstream of heat exchanger section 2A of the conduit 2. In this context the term downstream refers to the supply flow 10 provided in the conduit 2 and in relation to the initial entry of the supply flow 10 into the system 1. Accordingly, the entry of the supply flow 10 into the system 1 occurs upstream of the heat exchanger section 2A.

[0066] The first pressure regulator 4 is provided as an expansion valve or valve arrangement. By means of the first pressure regulator 4 the pressure of the process medium in the supply flow 10 is reduced to a pressure slightly above atmospheric pressure, e.g. 1.05 to 1.2 bar. The supply flow 10 then flows into a vessel 5, which is in fluid communication with the conduit 2 and is hence arranged downstream of the first pressure regulator 4. Although the fluid communication between the first pressure regulator 4 and the vessel 5 is depicted in FIG. 12 to comprise a conduit, e.g. an outlet of the first pressure regulator 4 and/or a corresponding inlet of the vessel 5, the fluid communication may also be provided by coupling a downstream end of the first pressure regulator 4 directly to a corresponding opening or coupling element of the vessel 5.

[0067] The vessel 5 comprises a constant pressure, which is lower than the pressure upstream of the vessel 5, and is configured to collect a liquid phase and provide an evaporated gas from the process medium. The evaporated gas is generated depending on the state of the process medium downstream of the first pressure regulator 4, e.g. the specific enthalpy, any boundary activities or implementations of the vessel 5, e.g. a load (not shown), and the pressure in the vessel, which is remained constant. Due to a sudden volume increase in the vessel 5 compared to the volume of the process medium downstream of the first pressure regulator 4, the process medium is further relaxed downstream of the first pressure regulator 4. For example, the vessel 5 is sized and dimensioned to promptly expand the process medium. The sudden volume increase of the process medium in the vessel 5 results in a rapid pressure reduction of the process medium, such that a gas phase or flash gas is generated, which comprises a sub-atmospheric pressure, i.e. below 1.0 bar. In this Joule-Thomson expansion, the temperature of the sub-atmospheric evaporated gas may remain constant or is slightly reduced while the latent heat of the evaporated gas is reduced. In addition, as outlined in the above, an implementation of the vessel 5 may cause the liquid phase in the vessel also to provide an evaporated gas. Accordingly, the sub-atmospheric evaporated gas 12 is then provided to an inlet 34 of the heat exchanger 3 to serve as a coolant or refrigerant for the supply flow 10 of the process medium. The inlet 34 of the heat exchanger 3 may be either directly coupled to the vessel 5 or may be fluidly connected to an outlet of the vessel 5 by means of a conduit or tube section.

[0068] As the latent heat and temperature of the sub-atmospheric evaporated gas 12 are considered to be at its lowest in the system 1 at the inlet 34 of the heat exchanger 3, this region is considered the cold end 30 of the heat exchanger 3. During cooling of the supply flow 10 of the process medium in the heat exchanger section 2A by the sub-atmospheric evaporated gas 12 in the heat exchanger 3, the sub-atmospheric evaporated gas 12 absorbs heat from the supply flow 10 of the process medium, such that the outlet 36 of the heat exchanger 3 is considered to be a warm end 32 of the heat exchanger 3. Accordingly, the sub-atmospheric evaporated gas 12 flows from an inlet 34 at the cold end 30 of the heat exchanger 3 to an outlet 36 at a warm end 32 of the heat exchanger 3, thereby absorbing heat from the supply flow 10 of the process medium and transitioning from a cold sub-atmospheric evaporated gas 12 to a warm sub-atmospheric evaporated gas 12, and leaves the system 1 at the outlet 36 as an exhaust gas 14.

[0069] 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 of the process medium at various points or locations in the system 1 is considered to be constant and predictable during normal operation. Accordingly, the process medium in the vessel 5 may be used to provide isothermal conditions, e.g. an isothermal load (not shown).

[0070] The conduit 2 is free of any evaporation heat exchanger upstream of the heat exchanger section 2A of the conduit 2. Accordingly, by providing a cold counter flow heat exchanger 3 comprising an evaporated gas flow with low specific enthalpy, the system does not require an evaporator to precool the supply flow 10. Furthermore, the cold counter flow heat exchanger 3 may provide the supply flow 10 and the evaporated gas 12 at a higher temperature level at the warm end 32 of the heat exchanger 3 having an increased heat capacity, such that temperature differences may be minimized.

[0071] In particular, the heat exchanger 3 of the system 1 is configured such that during normal operation the temperature of the exhaust gas 14 matches the temperature of the supply flow 10 of the process medium at the warm end 32 of the heat exchanger 3. The term matches here is to be understood to also include minimal differences, e.g. up to 0.5 K, preferably between 0.05 and 0.2 K. This matching minimal difference of said temperatures is achieved by the configuration of the heat exchanger 3, wherein the corresponding NTU or the heat transfer rate is accordingly adapted. For example, the area of the heat exchanger 3, e.g. the heat transfer area or length of the heat exchanger 3 may be sized and dimensioned to provide the corresponding temperature range, wherein at least the mass flow and the heat capacity values at various temperatures of the process medium are considered to be known. For example, the heat transfer area of the heat exchanger 3 may be sized to provide the required NTU to provide a sufficient cooling of the process medium such that the process medium downstream of the heat exchanger section 2A of the conduit 2 and upstream of the first pressure regulator 4 is provided above the lambda point at a temperature of 2.14 to 2.40 K while at the same time providing a temperature of the exhaust gas 14 matching the temperature of the process medium upstream of the heat exchanger section 2A at the warm end 32 of the heat exchanger 3 between 4.5 and 20 K or even higher, preferably around 12 K. The corresponding NTU of the heat exchanger 3 may hence be optimal for said temperature ranges of liquid helium. However, the NTU may be adapted for other temperature ranges and/or compounds and may furthermore provide an excess to accommodate system fluctuations or variating needs, e.g. of a load to be cooled by the system 1.

[0072] The cryogenic refrigeration system 1 according to FIG. 2 largely corresponds to the embodiment depicted in FIG. 1. Again, the process medium is provided by a supply flow 10 in the conduit 2 and is cooled by the heat exchanger 3 as described in the above. In addition, the heat transfer area of the heat exchanger 3 is adapted to provide a heat transfer rate, which provides a cooling of the process medium resulting in a cooled process medium 11, e.g. comprising a temperature just above the lambda point and below the saturation temperature of the corresponding pressure of the supply flow 10, for example between 2.14 and 2.40 K. The pressure of the cooled process medium 11 is then reduced by the first pressure regulator 4 or expansion valve, to obtain a two-phase process medium 13. In other words, the pressurized liquid helium in the supply flow 10 is first cooled by the heat exchanger 3 to a predetermined temperature and is subsequently depressurized to provide a process medium comprising a liquid and gas phase.

[0073] The configuration of the vessel 5 is such that the liquid phase 15 of the two-phase process medium 13 is collected upon entry into the vessel 5 while at the same time the configuration, e.g. the dimensioning and the constant pressure in the vessel 5, causes the generation of sub-atmospheric evaporated gas 12, depending on the respective state of the two-phase process medium 13. The sub-atmospheric evaporated gas 12 then flows into the heat exchanger 3 via an inlet 34 at a cold end of the heat exchanger 3 to cool the supply flow 10. The sub-atmospheric evaporated gas 12 leaves the heat exchanger 3 at a warm end 32 of the heat exchanger 3 and exits the system 1 via an outlet 36 as exhaust gas 14.

[0074] Accordingly, the cryogenic refrigeration system 1 according to FIG. 2 is optimized to both provide a sufficient cooling of the supply flow 10 by the sub-atmospheric evaporated gas 12 and a sufficient amount of the liquid phase 15 of the process medium at a required temperature, e.g. for further refrigeration requirements, by means of a corresponding depressurization of the supply flow 10 to provide a two-phase process medium 13, a configuration and constant pressure of the vessel 5, and a configuration of the heat exchanger 3, e.g. by a corresponding NTU or heat transfer rate.

[0075] In FIGS. 3A and 3B the counter flow heat exchanger 3 is schematically shown in further detail. The process medium is provided by means of the supply flow 10 in the conduit 2. The heat exchanger 3 comprises a tube shape, which surrounds the circumferential area of the conduit 2 forming a heat exchanger section 2A. Although the heat exchanger 3 is depicted comprising a cylindrical form and fully surrounding the conduit 2, other shapes and configurations are possible. However, in any case the NTU of the heat exchanger 3 is predefined to accordingly cool the supply flow 10 and minimize a temperature difference of the exhaust gas 14 and the supply flow 10 at the warm end 32 of the heat exchanger 3.

[0076] As shown in FIG. 3A, the heat exchanger section 2A of the conduit 2 linearly traverses the heat exchanger 3 from the warm end 32 to the cold end 30 of the heat exchanger 3 and comprises a substantially straight configuration. However, other configurations that increase the heat transfer rate or are thermodynamically efficient are possible, for example, a meandering, sinusoidal, or coiled shape of the conduit 2. While traversing the heat exchanger 3 the supply flow 10 is cooled by the heat exchanger 3 by means of the sub-atmospheric evaporated gas 12 entering the heat exchanger 3 at the cold end 30 via an inlet 34.

[0077] The cooling of the supply flow 10 is provided by the sub-atmospheric evaporated gas 12, which is distributed through the heat exchanger 3 by means of a spirally formed heat exchanger element 38. Accordingly, the spirally formed heat exchanger element 38 traverses the heat exchanger 3 in a counter flow direction of the conduit 2, wherein the sub-atmospheric evaporated gas 12 absorbs the heat from the supply flow 10 provided in the thermally coupled heat exchanger section 2A of the conduit 2, either through direct contact or thermal coupling by means of a heat conducting material. At the warm end 32 of the heat exchanger 3 the sub-atmospheric evaporated gas 12 then exits the heat exchanger 3 via an outlet 36 as an exhaust gas 14.

[0078] The inlet 34 and the outlet 36 of the heat exchanger 3 are arranged in parallel and adjacent to the conduit 2 at the cold end 30 and the warm end 32 of the heat exchanger 3, respectively. This configuration is also shown in FIG. 3B, which shows the heat exchanger 3 from a perspective in flowing direction of the sub-atmospheric evaporated gas 12 and in counter flowing direction of the cooled process medium 11 at the cold end 30 of the heat exchanger 3. Although the conduit 2 and the inlet 34 of the heat exchanger 3 are arranged adjacently in a vertical orientation, any orientation that is perpendicular to an extending direction of the heat exchanger 3 or the spirally formed heat exchanger element 38 or a substantial lateral arrangement may be provided. By the same token, the spirally formed heat exchanger element 38 may be arranged adjacent to the conduit 2 within the heat exchanger 3 to provide a direct heat transfer between the spirally formed heat exchanger element 38 and the conduit 2. Accordingly, the heat exchanger 3 may be alternatively dimensioned to comprise a smaller size in a radial direction.

[0079] However, other configurations of the heat exchanger 3 may be provided. For example, the heat exchanger 3 may be configured as a plate fin heat exchanger, e.g. for larger systems or plants, or as a coil finned tube heat exchanger, e.g. for smaller systems or plants. In a plate fin heat exchanger, the heat exchanger comprises a plurality of compartments that are arranged adjacently and in countercurrent orientation to each other and wherein said compartments comprise either the sub-atmospheric evaporated gas or the supply flow. When implementing the heat exchanger 3 as a coil finned tube heat exchanger on the other hand, the sub-atmospheric evaporated gas may be guided along the conduit 2 comprising the supply flow 10 in a coiled fashion, wherein the coiled arrangement furthermore comprises a plurality of loop sections that extend radially outward, thereby defining a plurality of fins.

[0080] A further embodiment of the cryogenic refrigeration system 1 is shown in FIG. 4. FIG. 4 essentially corresponds to the system 1 according to FIG. 2, such that like features and functions are not discussed in further detail. The system 1 comprises a controller 7, which is in communication with the first pressure regulator 4 and is configured to control the first pressure regulator 4 in order to relax or expand the cooled process medium 11 to provide a two-phase process medium 13 downstream of the first pressure regulator 4. To appropriately adjust the pressure of the cooled process medium 11, the controller 7 is in communication with a temperature sensor 70 which is in communication with the conduit 2 and the outlet 36 of the heat exchanger 3 at the warm end 32 of the heat exchanger 3. Said sensor 70 hence provides an actual temperature of the supply flow 10 entering the system 1 and the exhaust gas 14 exiting the system 1 via the outlet 36. The measured values of the sensor 70 are provided to the controller 7, wherein the controller 7 controls the first pressure regulator 4 based at least on the measured values of the sensor 70, the state of the two-phase process medium 13, and the pressure in the vessel 5.

[0081] Although the system 1 is generally designed for specific boundary conditions and the status of the system 1 is maintained constant, the provision of the controller 7 and the temperature sensor 70 allow the system 1 to react to or prevent minor fluctuations in the system 1, e.g. by adjusting the volume flow of the sub-atmospheric evaporated gas 12. The volume flow of sub-atmospheric evaporated gas 12 is dependent on the state of the two-phase process medium 13 and the pressure in the vessel 5, which is maintained at a constant level by a compressor (not shown) in communication with the vessel 5 at a downstream end, e.g. downstream of the outlet 36. As both the temperature and the pressure of the supply flow 10 are fixed boundary conditions and the cooling efficiency of the heat exchanger 3, and therefore the state of the cooled process medium 11, is generally known, the state or specific enthalpy of the two-phase process medium may be controlled by adjusting the pressure regulator 4. For example, the controller 7 may adjust the first pressure regulator 4 to further reduce the pressure of the cooled process medium 11, when an undesirable temperature difference between the exhaust gas 14 and the supply flow 10 is measured, e.g. when the measured temperature of the exhaust gas 14 is higher than the temperature of the supply flow 10, such that the two-phase process medium 13 is relaxed and/or the gas phase is increased and hence, at a constant vessel pressure, a larger volume flow of sub-atmospheric evaporated gas 12 is provided to the heat exchanger 3. Accordingly, an improved cooling of the supply flow 10 may be provided while at the same time absorbed heat in the sub-atmospheric evaporated gas 12 levels out the temperature difference between the exhaust gas 14 and the supply flow 10 at the warm end 32 of the heat exchanger 3.

[0082] Provided in the liquid phase 15 of the process medium collected in the vessel 5 is a load 6. The load also affects the volume flow of sub-atmospheric evaporated gas 12 as, depending on the activity of the load 6, the liquid phase 15 may partially attain a temperature above the saturation temperature and hence enter the gas phase. In order to maintain an isothermal load 6, the controller 7 may hence accordingly adjust the first pressure regulator 4 to e.g. compensate for a loss of liquid phase 15. For example, the controller 7 may adjust the pressure and hence the specific enthalpy of the two-phase process medium 13 by controlling the first pressure regulator 4 to increase the liquid phase 15 of the two-phase process medium 13 to be collected in the vessel 5 and to compensate for an increased amount of sub-atmospheric evaporated gas 12 and a loss of the liquid phase 15 in the vessel 5. By the same token, the change in mass flow to the load 6 may be detected by a change in temperature, which is measured by the temperature sensor 70 and may be provided to the controller 7 as feedback.

[0083] In addition to the temperature sensor 70, the embodiment according to FIG. 5 comprises a fill sensor 72 and a pressure sensor 74 disposed in the vessel 5 that are in communication with the controller 7. Accordingly, the controller 7 controls the first pressure regulator 4by adjusting the pressure of the cooled process medium 11 based on a fill status measured by the fill sensor 72 in the vessel 5. For example, an increase in the activity of the load 6 may reduce the fluid level of the liquid phase 15 of the process medium, which is detected by the fill sensor 72 and indicates to the controller that a deficit of the liquid phase 15 is present in the system 1. The controller 7 may then control the first pressure regulator 4 to accordingly adjust the state of the two-phase process medium 13 and hence the liquid phase 15 provided to the vessel 5.

[0084] In addition, the controller 7 is in communication with a control valve 20, which is arranged in parallel to and upstream of the pressure regulator 4. The control valve 20 is configured as a three-way-valve and connects the conduit 2 to a parallel system. Should the fill sensor 72 indicate a deficit or excess of the liquid phase 15 of the process medium in the vessel 5, the controller 7 may control the control valve 20 to accordingly adjust the mass flow while retaining a constant pressure and temperature of the supply flow. Alternatively, or in addition, such indication may be provided by a flow sensor 76 in communication with the controller 7 and provided downstream of the pressure regulator 4 and indicating a mass flow to a load 6

[0085] The pressure in the vessel 5 is furthermore maintained at a constant level by a compressor (not shown) in communication with the vessel 5 at a downstream end, e.g. downstream of the outlet 36. The pressure in the vessel 5 is measured by the pressure sensor 74. Should a pressure deviation from a predefined range or threshold occur, said pressure sensor 74 provides a feedback to the controller 7, which accordingly adjusts the pressure via the downstream compressor.

[0086] Furthermore, a temperature sensor 70 is provided, which is arranged downstream of the heat exchanger section 2A and upstream of the pressure regulator 4 and is in communication with the controller 7. As the temperature and pressure of the supply flow 10 are generally regulated at a constant level and may hence be considered as fixed boundary conditions, a measured temperature deviation from a predefined temperature may be corrected by accordingly adjusting the pressure regulator 4 to control the state of the process medium, e.g. the specific enthalpy, downstream of the pressure regulator 4. As the pressure and the load 6 in the vessel 5 are considered to be constant, a change in the state of the two-phase process medium 13 hence changes the volume flow of the sub-atmospheric evaporated gas 12 entering the heat exchanger 3 at the cold end 30. Accordingly, the measured temperature deviation of the process medium downstream of the heat exchanger section 2A is reduced.

[0087] Although the load 6 may be disposed in the liquid phase 15 of the process medium in the vessel 5, the load 6 may also be provided outside of the vessel 5, as depicted in FIG. 5. The volume flow entering and exiting the vessel 5 is hence not affected by the dimensions of the load 6 while a thermal coupling between the vessel 5 and the load 6 provides a similar refrigeration of the load 6, e.g. to provide an isothermal load 6. The thermal coupling may be provided by either a direct contact between the outer surface of the vessel 5 and the load 6 or by means of e.g. a fluid coupling such as a check valve.

[0088] The heat exchanger 3 may comprise various configurations to provide the required temperature factor at the warm end of the heat exchanger, e.g. by a corresponding NTU or heat transfer rate. For example, the heat exchanger 3 may comprise a plurality of counter flow heat exchanger modules 3A, 3B, 3C, which are arranged in series and/or in parallel, as shown in the embodiments according to FIGS. 6A and 6B. In FIG. 6A the heat exchanger comprises two heat exchanging modules 3A and 3C that are arranged in series. The serial heat exchanger modules 3A, 3C are fluidly coupled to each other and thermally coupled with the conduit 2, comprising the process medium.

[0089] In operation, the sub-atmospheric evaporated gas 12 enters the second serial heat exchanger module 3C at a cold end 30 and traverses said heat exchanger module 3C, thereby absorbing heat from the process medium in the conduit 2. The sub-atmospheric evaporated gas exiting the second serial heat exchanger module 3C hence comprises a different latent heat and/or temperature compared with the sub-atmospheric evaporated gas 12 provided in the inlet 34 and is hence considered a warmed sub-atmospheric evaporated gas 17. The warmed sub-atmospheric evaporated gas 17 then enters the first serial heat exchanger module 3A and exits the system 1 as an exhaust gas 14 at the warm end 32 via an outlet 36. While the warmed sub-atmospheric evaporated gas 17 absorbs heat in the first serial heat exchanger module 3A, the process medium in the supply flow 10 is accordingly cooled, such that the process medium in the conduit 2 arriving at the second serial heat exchanger module 3C is considered to be a subcooled process medium 16. Subsequent cooling of the subcooled process medium 16 by the second serial heat exchanger module 3C then results in the cooled process medium 11 downstream of the second serial heat exchanger 3C.

[0090] The system 1 furthermore comprises a pressure regulating arrangement comprising a first pressure regulator 4A and a second pressure regulator 4B that are in fluid communication with the conduit 2. The first pressure regulator 4A is arranged downstream of the second serial heat exchanger module 3C and upstream of the first pressure regulator 4A to adjust a pressure of the process medium 11 provide a two-phase process medium 13 downstream of the first pressure regulator 4A. The second pressure regulator 4B is arranged between the first and second heat exchanger modules 3A, 3C. this arrangement provides that the pressure of the process medium or the pressurized liquid may be adjusted or reduced after subcooling of the process medium and prior to the cooling by the second heat exchanger module 3C to provide the cooled process medium 11, wherein the subcooled process medium 16 may be provided as a liquid or as a two-phase process medium. Accordingly, the system 1 is configured to optimally use the different heat capacity values of the process medium for different temperatures and pressures, thereby providing an NTU of the heat exchanger to match the temperatures of the exhaust gas 14 and the supply flow 10 at the warm end 32.

[0091] A combination of a parallel and serial arrangement of counter flow heat exchanger modules is shown in FIG. 6B. In addition to the first and second heat exchanger modules 3A, 3C, the system 1 comprises a parallel heat exchanger module 3B, such that the first serial heat exchanger module 3A and the parallel heat exchanger module 3B are arranged in parallel. In order to provide such arrangement of the cryogenic refrigeration system 1, the vessel 5 is fluidly coupled via an inlet 34 to a cold end 30 of the second heat exchanger module 3C to provide the sub-atmospheric evaporated gas 12 exiting the vessel 5. After traversing the second heat exchanger module 3C, the warmed sub-atmospheric evaporated gas is then divided or split into a first and second parallel warmed sub-atmospheric evaporated gas 17A, 17B and introduced into the first serial exchanger module 3A and the parallel heat exchanger module 3B, respectively, using parallel fluid couplings. The warmed sub-atmospheric evaporated gas 17A, 17B subsequently exits the respective first serial exchanger module 3A and the parallel heat exchanger module 3B as a first and second exhaust gas 14A, 14B, respectively, wherein the first and second exhaust gas 14A, 14B are coupled to the outlet 36 at the warm end 32 and are combined to provide exhaust gas 14 exiting the system 1 via the outlet 36.

[0092] In order to provide the parallel cooling, the conduit 2 is split into two parallel sections that are thermally coupled to the parallel exchanger modules 3A, 3B at a point just before the first serial exchanger module 3A and the parallel heat exchanger module 3B. The parallel heat exchanger modules 3A, 3B hence provide a subcooling of the process medium as described in further detail for the embodiment according to FIG. 6A. The parallel sections of the conduit 2 are then merged again downstream of the parallel heat exchanger modules 3A, 3B and prior to entry into the second pressure regulator 4B. Downstream of the second pressure regulator 4B the process medium is further cooled by the second serial heat exchanger module 3C and passes the first pressure regulator 4A prior to entry into the vessel 5, as described in relation to FIG. 6A.

[0093] According to the embodiment of FIG. 6B, the second serial heat exchanger module 3C comprises a tube shape surrounding the circumference of the conduit 2, while the parallel heat exchanger modules 3A, 3B are depicted to be thermally coupled to the parallel sections of the conduit 2 in an adjacent manner. However, configurations other than those depicted are possible, e.g. a plurality of tubular heat exchanger modules and/or heat exchanger modules only partially surrounding the circumference of the conduit 2 may be provided. Furthermore, the conduit sections and the fluid couplings are adjacently arranged to each other to both increase thermal efficiency and reduce the dimensions and size of the system 1. However, it will be understood that other configurations, wherein e.g. the conduit sections and the fluid couplings are at least partially space apart, may also be provided. In particular, further possible configurations of the heat exchanger as described in view of FIGS. 3A and 3B, i.e. plate fin heat exchanger modules or coil finned tube heat exchanger modules, may also be implemented.

[0094] 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

[0095] 1 Cryogenic refrigeration system [0096] 10 Supply flow of a process medium [0097] 11 Cooled process medium [0098] 12 Sub-atmospheric evaporated gas [0099] 13 Two-phase process medium [0100] 14 Exhaust gas [0101] 14A First parallel exhaust gas [0102] 14B Second parallel exhaust gas [0103] 15 Liquid phase of process medium [0104] 16 Subcooled process medium [0105] 17 Warmed sub-atmospheric evaporated gas [0106] 17A First parallel warmed sub-atmospheric evaporated gas [0107] 17B Second parallel warmed sub-atmospheric evaporated gas [0108] 2 Conduit [0109] 2A Heat exchanger section [0110] 20 Control valve [0111] 3 Counter flow heat exchanger [0112] 3A First serial counter flow heat exchanger module [0113] 3B Parallel counter flow heat exchanger module [0114] 3C Second serial counter flow heat exchanger module [0115] 30 Cold end of heat exchanger [0116] 32 Warm end of heat exchanger [0117] 34 Inlet [0118] 36 Outlet [0119] 38 Spirally formed heat exchanger element [0120] 4 First pressure regulator [0121] 4A First pressure regulator [0122] 4B Second pressure regulator [0123] 5 Vessel [0124] 6 Load [0125] 7 Controller [0126] 70 Temperature sensor [0127] 72 Fill sensor [0128] 74 Pressure sensor [0129] 76 Flow sensor