Device and method for refrigeration or liquefaction of a fluid

Abstract

Disclosed is a device for refrigerating or liquefying a fluid such as natural gas or hydrogen, comprising a circuit (3) for fluid that is to be cooled and has an upstream end for connection to a source (2) of gaseous fluid and a downstream end (23) for connection to a member for collecting the cooled or liquefied fluid, the device (1) comprising a heat exchanger assembly (6, 10) in heat exchange with the circuit (3) of fluid to be cooled, the device (1) comprising a refrigerator (20) in heat exchange with at least a portion of the heat exchanger assembly (6, 10), the refrigerator (20) being of the type that has a cycle for refrigerating a cycle gas containing at least one of: helium, hydrogen, nitrogen or neon; said refrigerator (20) comprising, arranged in series in a cycle circuit (14): a mechanism (15) for compressing the cycle gas, at least one member (7, 6, 10) for cooling the cycle gas, a mechanism (17) for expanding the cycle gas, and at least one member (6, 10) for reheating the expanded cycle gas, wherein the compression mechanism comprises a plurality of compression stages (15) in series composed of a centrifugal compressor assembly, the compression stages (15) being mounted on a set of shafts rotated by an assembly of one or more motors (18), the at least one member (7, 6, 10) for cooling the cycle gas comprising at least one heat exchanger (7) arranged at the outlet of at least one compression stage (15) in heat exchange with the cycle circuit (14), said heat exchanger (7) being cooled by a heat-transfer fluid, characterised in that the compression mechanism comprises at least two compression stages (15) that are arranged successively in series and do not include any member for cooling the cycle gas such as a heat exchanger (7) therebetween.

Description

[0001] The invention relates to a device and a method for refrigerating or liquefying a fluid.

[0002] The invention relates more particularly to a device for refrigerating or liquefying a fluid such as natural gas or hydrogen, comprising a circuit for the fluid to be cooled having an upstream end intended to be connected to a source of gaseous fluid and a downstream end intended to be connected to a collection device for the cooled or liquefied fluid, the device comprising a set of heat exchanger(s) in heat exchange with the circuit for the fluid to be cooled, the device comprising a refrigerator in heat exchange with at least a part of the set of heat exchanger(s), the refrigerator being of the type with a cycle refrigeration system for a cycle gas comprising at least one of: helium, hydrogen, nitrogen or neon, said refrigerator comprising, arranged in series in a cycle circuit: a cycle gas compression mechanism, at least one cycle gas cooling device,a cycle gas expansion mechanism and at least one expanded cycle gas heating device, wherein the compression mechanism comprises several compression stages in series consisting of a set of centrifugal compressor(s), the compression stages being mounted on a set of shafts driven in rotation by a set of motor(s), and at least one cycle gas cooling device comprising at least one heat exchanger disposed at the outlet of at least one compression stage in heat exchange with the cycle circuit, said heat exchanger being cooled by a heat transfer fluid.

[0003] Increasing the capacity of a cryogenic refrigerator / liquefier (i.e., the delivered refrigeration / liquefaction power) generally requires a significant modification of the refrigeration cycle architecture and the addition of supplementary equipment (additional compressors with outlet coolers). One aim is to limit the complexity and cost of such an installation without significantly impacting the overall efficiency of the system, and in particular its compression system. One objective of the present invention is to overcome all or part of the drawbacks of the prior art noted above.

[0004] Document EP2211124A1 and the article by N. Saji ET AL: "Design of oil-free simple turbo type 65 K / 6 KW helium and neon mixture gas refrigerator for high temperature superconducting power cable cooling", May 15, 2002 (2002-05-15), pages 893-900, XP055598218, describe refrigeration devices according to the prior art, in which the article by N. Saji ET AL discloses an apparatus conforming to the preamble of claim 1 and a method conforming to the preamble of claim 10.

[0005] To this end, the invention provides an apparatus according to claim 1, which is characterized in that either the compression mechanism comprises four compression stages in series, the cycle gas cooling element comprising three cooling heat exchangers disposed respectively between the first and second compression stages, between the second and third compression stages and at the outlet of the fourth compression stage, or the device comprises cooling heat exchangers disposed only every two compression stages in series.

[0006] Furthermore, embodiments of the invention may include one or more of the following characteristics: The engine assembly includes several drive motors for the compression stages; the engine assembly includes a separate motor for each compression stage; at least one of the motors is cooled by a cycle gas flow via at least one bypass line for a fraction of the cycle gas flow supplying the compression mechanism; the bypass line includes an upstream end connected to the outlet of at least one of the compression stages to draw a fraction of the cycle gas flow; a downstream end of at least one bypass line is connected to the inlet of a compression stage after its passage and heat exchange with at least one motor; the at least one bypass line includes, between its upstream and downstream ends, a subdivision into at least two separate branches supplying separate motors respectively for their cooling.The at least two distinct branches formed by the subdivision of a bypass line have a downstream junction within the same portion of the line; at least one bypass line includes at least one cycle gas cooling device; at least one bypass line includes a cooling heat exchanger.

[0007] Moreover : the cycle gas may consist of helium or a mixture comprising at least 50% helium, the cycle gas may consist of hydrogen or a mixture comprising at least 50% hydrogen, the cycle gas may consist of nitrogen or a mixture comprising at least 50% nitrogen, the compression mechanism may consist solely of centrifugal type compressors, the fluid to be cooled may consist of at least one of the following: hydrogen, natural gas, biogas, methane, helium.

[0008] The invention also relates to a method of refrigerating or liquefying a fluid using a refrigeration device according to claim 1 and comprising a step of circulating a fluid in the circuit of fluid to be cooled and a step of cooling said fluid via the cold produced by the refrigerator.

[0009] According to other possible features: the process includes a step of controlling the rotation speed of the compression stages according to independent speeds in which, during at least one determined operating phase, the rotation speed of the series compression stages without a cycle gas cooling device such as a heat exchanger between them is maintained at a speed lower than the rotation speed of the compression stages equipped at their outlet with a cycle gas cooling device.

[0010] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0011] Other features and advantages will become apparent upon reading the description below, made with reference to the figures in which: [ Fig. 1 ] is a schematic and partial representation illustrating an example of the structure and operation of a device according to the invention.

[0012] Device 1 is configured for the cryogenic refrigeration and / or liquefaction of a fluid (such as natural gas, biomethane, or hydrogen, for example, but this is not limited to such fluids). Device 1 comprises a circuit 3 for the fluid to be cooled / liquefied, having an upstream end intended to be connected to a fluid source 2 (gaseous, for example) and a downstream end 23 intended to be connected to a collection device for the cooled or liquefied fluid (a storage unit, for example).

[0013] Device 1 includes a set of heat exchanger(s) 6, 10 in thermal exchange with the circuit 3 of fluid to be cooled.

[0014] Device 1 includes a cold source comprising a refrigerator 20 in heat exchange with at least part of the heat exchanger assembly(ies) 6, 10.

[0015] Refrigerator 20 is cryogenic and of the refrigeration cycle type of a cycle gas comprising predominantly helium and / or hydrogen and / or nitrogen and / or neon.

[0016] For example, the cycle gas consists of pure helium or a mixture comprising at least 50% helium.

[0017] Similarly, the cycle gas can consist of pure hydrogen or a mixture comprising at least 50% hydrogen.

[0018] Similarly, the cycle gas can consist of nitrogen or a mixture comprising at least 50% nitrogen.

[0019] Alternatively, the cycle gas can consist of neon or a mixture comprising at least 50% neon.

[0020] Of course any other suitable cycle gas or mixture can be considered, for example including at least one of: helium, hydrogen, nitrogen, neon, methane.

[0021] Typically, the refrigerator 20 comprises, arranged in series in a cycle circuit 14: a cycle gas compression mechanism 15, at least one cycle gas cooling device 7, 6, 10, a cycle gas expansion mechanism 17 and at least one cycle gas reheating device 6, 10.

[0022] The compression mechanism comprises several compression stages 15 in series consisting of a set of centrifugal compressor(s), the compression stages being mounted on a set of shafts driven in rotation by a set of motor(s) 18.

[0023] At least one cycle gas cooling unit comprises at least one heat exchanger 7 located at the outlet of at least one compression stage 15 in heat exchange with the cycle circuit 14. This at least one heat exchanger 7 may be cooled by a heat transfer fluid, for example water or air.

[0024] The heat exchanger assembly may comprise one or more heat exchangers 6, 10 arranged in series, in which two distinct portions of the cycle circuit 14 circulate simultaneously in counter-current flow, respectively for cooling and heating the cycle gas. The plurality of heat exchangers can therefore form both a cycle gas cooling element and a cycle gas heating element.

[0025] According to an advantageous feature, the compression mechanism comprises at least two compression stages 15 arranged successively in series and lacking a cycle gas cooling device such as a heat exchanger 7 between them. That is to say, two compression stages can follow one another without interstage cooling.

[0026] More specifically, at least one compression stage 15 does not have an aftercooler at its outlet of a heat exchanger 7 cooled by a heat transfer fluid separate from the cycle gas (no "aftercooler"). On the other hand, the cycle gas at the outlet of this compression stage may, if necessary, enter directly into a counter-flow heat exchanger 6, 10 cooled by a cooler flow of cycle gas.

[0027] This can be advantageous for modifying, for example, an existing device of a given capacity to increase its refrigeration power.

[0028] In the case of a relatively "heavy" cycle gas (i.e., one that heats up significantly under centrifugal compression), such as the one commonly used (typically a helium-nitrogen mixture), prior art involves adding an additional cooling exchanger ("intercooler") to prevent the cycle gas from entering the next compression stage at an excessively high temperature. This is done to avoid reaching excessively high temperatures.

[0029] For lighter gases such as helium or hydrogen, volumetric compressors are conventionally used where a single compression stage is followed by a cooling exchanger.

[0030] The invention challenges conventional wisdom, as the overall compression efficiency may be lower compared to known systems (the final compression stage operating at a higher temperature). However, particularly in the case of very light cycle gases (molar mass less than 30 g / mol, and especially less than 20 g / mol or 10 g / mol), the performance loss of the less isothermal compression according to the invention is more than compensated by the reduction in pressure losses (due to the reduced number of cooling exchangers).

[0031] Furthermore, the savings in equipment are significant (especially cooling exchanger(s) and associated circuitry).

[0032] This is particularly advantageous when adding a compressor downstream to an existing device (only one piece of equipment added, module: compressor + motor), which can be identical to the previous compression module. This requires little to no modification to the design.

[0033] The final compression stage, added without outlet cooling, can be easily integrated. The advantage lies in the improved competitiveness of the new system and greater versatility through the cost-effective addition of an extra compression stage on-site, particularly useful for increasing plant output after several years of operation. In a first illustrated embodiment, the compression mechanism comprises four compression stages (impellers) 15 in series, with cooling 7 only at the outlet of three of these four compression stages, preferably at the outlet of the first, second, and fourth compression stages. This means that the cycle gas is not cooled between the third and fourth compression stages.

[0034] Thus, the device maintains a (relatively) low temperature increase due to centrifugal compression, eliminating the need for an intercooler between each compression stage. This results in cost and compactness gains while limiting the impact on the overall efficiency of the compression system. In an alternative configuration, a cooling heat exchanger 7 is located only every two (or every three) series compression stages 15. In other possible configurations, for example, a device with three series compression stages where the first two stages have a cooling heat exchanger at their outlet, the cycle gas can then enter directly into a counter-current heat exchanger of the refrigeration unit at the outlet of the third compression stage and subsequently into an expansion stage (for example, a single turbine).At the outlet of the expansion stage, the cycle gas can then be used for heat exchange with the gas circuit to be cooled (typically in a heat exchanger). Following this exchange with the fluid to be cooled, the cycle gas can then pass into a counter-current heat exchanger where it is heated, cooling the flow exiting the aforementioned compression stage. This heated cycle gas can then re-enter the first compression stage to begin the cycle again.

[0035] Preferably, the set of motor(s) 18 includes several drive motors for the compression stages.

[0036] In the illustrated example, a respective motor 18 is provided for each compression stage. Of course, a single motor 18 could drive several compression stages (mounted on the same output shaft, for example). Similarly, one or more turbines 17 could be mounted on the shaft of a motor 18 that drives one or more compression stages.

[0037] At least one of the 18 engines can be cooled by a cycle gas flow.

[0038] As illustrated, at least one bypass line 4, 5, 9 may be provided to draw off a fraction of the cycle gas flow feeding the compression mechanism. The bypass line 4 may include an upstream end connected to the outlet of at least one of the compression stages 15 (for example, downstream of the first compression stage 15, particularly after cooling 7) to draw off a fraction of the cycle gas flow.

[0039] The downstream end of the bypass pipe can be connected to the inlet of another compression stage after it has passed through and exchanged heat with at least one motor 18 (for example upstream of the first compression stage 15 in this example).

[0040] The bypass conduit 4 may include, between its upstream and downstream ends, at least one subdivision into at least two separate branches 5, 9, supplying separate motors 18 respectively for cooling. That is to say, a cooling circuit may thus be provided to cool all or part of the motors 18.

[0041] Thus, all or part of the engines 18 can be cooled by cycle gas drawn from different pressure levels in the circuit. As illustrated, the at least two separate branches 5, 9 formed by subdividing a bypass line 4 can include a downstream junction within the same portion of the line.

[0042] At least one bypass line may include at least one cycle gas cooling device 8, for example, at least one cooling heat exchanger 8 to cool the flow after heat exchange with at least one motor 18. Advantageously, the rotational speed of the last two compression stages (compression wheels) may be reduced relative to the other stages to limit their compression ratio and the heating of the cycle fluid. This prevents excessively high temperatures that could damage the equipment.

[0043] This invention is particularly suited to refrigerators where the cycle gas is a light gas, i.e., having a molar mass between 2 and 30 g / mol, and preferably between 2 and 20 g / mol. Indeed, in this case, the decrease in compression performance resulting from the absence of interstage compression cooling is largely compensated by the structural gains, cost reductions, and ease of implementation.

[0044] Of course, the invention can be used with a heavier cycle gas (in this case the compression ratios of each compression stage are preferably reduced to limit heating but still remain higher than that which would be obtained with helium and / or h2 alone).

[0045] As illustrated, the cycle gas cooling system may include a heat exchanger, disposed at the outlet of at least some of the turbines 17 excluding the last turbine 17 in series according to the direction of cycle gas flow.

[0046] Device 1 can have more compression stages 15 than turbines 17.

[0047] Device 1 may have a number of compression stages equal to five or more.

Claims

1. A device for refrigeration or liquefaction of a fluid such as natural gas or hydrogen, comprising a fluid circuit (3) to be cooled having an upstream end intended to be connected to a source (2) of gaseous fluid and a downstream end (23) intended to be connected to a collecting member for the cooled or liquefied fluid, the device (1) comprising an assembly of heat exchanger(s) (6, 10) in thermal exchange with the fluid circuit (3) to be cooled, the device (1) comprising a refrigerator (20) in thermal exchange with at least a part of the heat exchanger(s) assembly (6, 10), the refrigerator (20) being of the refrigeration cycle type for a cycle gas comprising at least one of: helium, hydrogen, nitrogen or neon, said refrigerator (20) comprising, arranged in series in a cycle circuit (14): a compression mechanism (15) for the cycle gas, at least one cooling member (7, 6, 10) for the cycle gas, an expansion mechanism (17) for the cycle gas and at least one reheating member (6, 10) for the expanded cycle gas, wherein the compression mechanism comprises at least three compression stages (15) in series composed of an assembly of centrifugal type compressor(s), the compression stages (15) being mounted on an assembly of shafts rotated by an assembly of motor(s) (18), the at least one cooling member (7, 6, 10) for the cycle gas comprising at least one heat exchanger (7) disposed at the outlet of at least one compression stage (15) in thermal exchange with the cycle circuit (14), said heat exchanger (7) being cooled by a cooling fluid, characterized in that the compression mechanism comprises at least two compression stages (15) arranged successively in series and devoid of a cycle gas cooling member such as a heat exchanger (7) between them, and in that, either the compression mechanism comprises four compression stages (15) in series, the cycle gas cooling member comprising three cooling heat exchangers (7) disposed respectively at the outlet of three of these four compression stages (15), for example between the first and the second compression stage (15), between the second and the third compression stage (15) and at the outlet of the fourth compression stage (15), or the device comprises cooling heat exchangers (7) disposed only every two compression stages (15) in series.

2. The device according to claim 1, characterized in that the motor(s) assembly (18) comprises several motors for driving the compression stages.

3. The device according to claim 2, characterized in that the motor(s) assembly (18) comprises a respective distinct motor (18) for each compression stage (15).

4. The device according to claim 2 or 3, characterized in that at least one of the motors of the motor(s) assembly (18) is cooled by a flow of cycle gas via at least one bypass line (4, 5, 9) diverting a fraction of the cycle gas flow supplying the compression mechanism, the bypass line (4, 5, 9) comprising an upstream end connected to the outlet of at least one of the compression stages (15) to draw off a fraction of the cycle gas flow.

5. The device according to claim 4, characterized in that a downstream end of at least one bypass line (4, 5, 9) is connected to the inlet of a compression stage after its passage and heat exchange with at least one motor of the motor(s) assembly (18).

6. The device according to claim 5, characterized in that the at least one bypass line (4, 5) comprises, between its upstream end and its downstream end, a subdivision into at least two distinct branches (5, 9) supplying respective distinct motors of the motor(s) assembly (18) for their cooling.

7. The device according to claim 6, characterized in that the at least two distinct branches (5, 9) formed by the subdivision of a bypass line (4) include a downstream junction within the same portion of the line.

8. The device according to any one of claims 4 to 7, characterized in that the at least one bypass line (4, 5, 9) comprises at least one cooling member (8) for the cycle gas.

9. The device according to claim 8, characterized in that the at least one cycle gas cooling member (8) of the at least one bypass line (4, 5, 9) comprises a cooling heat exchanger (8).

10. A method for refrigeration or liquefaction of a fluid using a refrigeration device according to any one of claims 1 to 9, characterized in that it comprises a step of circulating a fluid in the fluid circuit (3) to be cooled and a step of cooling said fluid via the cold produced by the refrigerator (20).

11. The method according to claim 10, characterized in that it comprises a step of controlling the rotational speed of the compression stages according to independent speeds, wherein, during at least one determined operating phase, the rotational speed of the compression stages (15) arranged in series and devoid of a cycle gas cooling member such as a heat exchanger (7) between them is maintained at a speed lower than the rotational speed of the compression stages (15) provided at their outlet with a cycle gas cooling member.

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