DEVICE AND METHOD FOR REFRIGERATING OR LIQUEFYING A FLUID

Abstract

Disclosed is a device for refrigerating or liquefying a fluid such as natural gas or hydrogen, comprising a fluid circuit that is to be cooled and has an upstream end for connection to a source of gaseous fluid as well as a downstream end for connection to a member for collecting the cooled or liquefied fluid, the device comprising a heat exchanger assembly in heat exchange with the fluid circuit to be cooled, the device comprising a refrigerator in heat exchange with at least a portion of the exchanger assembly, the refrigerator 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 comprising in series in a cycle circuit: a mechanism for compressing the cycle gas, at least one member for cooling the cycle gas, a mechanism for expanding the cycle gas, and at least one member for reheating the expanded cycle gas, wherein the compression mechanism comprises a plurality of compression stages in series composed of a centrifugal compressor assembly, the compression stages being mounted on a set of shafts that are rotationally driven by a motor assembly, the at least one member for cooling the cycle gas comprising at least one heat exchanger 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, characterized in that the compression mechanism comprises at least two compression stages that are arranged successively in series and do not include any member for cooling the cycle gas such as a heat exchanger therebetween.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a § 371 of International PCT Application PCT/EP2022/050978, filed Jan. 18, 2022, which claims the benefit of FR2101244, filed Feb. 10, 2021, both of which are herein incorporated by reference in their entireties.

FIELD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

Increasing the capacity of a cryogenic refrigerator/liquefier (that is to say the refrigeration/liquefaction power supplied) generally requires significant modification of the architecture of the refrigeration cycle and the provision of additional equipment (additional compressors with coolers at the outlet).

SUMMARY OF THE INVENTION

The invention relates more particularly to a device for refrigerating or liquefying a fluid such as natural gas or hydrogen, comprising a circuit for 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 member for collecting the cooled or liquefied fluid, the device comprising a set of heat exchanger(s) in heat exchange with the circuit for fluid to be cooled, the device comprising a refrigerator in heat exchange with at least part of the set of heat exchanger(s), the refrigerator being of the type performing a refrigeration cycle on a cycle gas comprising at least one of the following: helium, hydrogen, nitrogen or neon, said refrigerator comprising the following, disposed in series in a cycle circuit: a mechanism for compressing the cycle gas, at least one member for cooling the cycle gas, a mechanism for expanding the cycle gas and at least one member for heating the expanded cycle gas, wherein the compression mechanism comprises a plurality of compression stages in series that are composed of a set of compressor(s) of centrifugal type, the compression stages being mounted on a set of shafts driven in rotation by a set of motor(s), the at least one member for cooling the cycle gas 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.

An aim is to limit the complexity and the cost of such an installation without significantly affecting the overall efficiency of the system and notably of its compression system.

An aim of the present invention is to overcome all or some of the drawbacks of the prior art outlined above.

To that end, the device according to the invention, which is otherwise in accordance with the generic definition thereof given in the above preamble, is essentially characterized in that the compression mechanism comprises at least two compression stages that are disposed successively in series and that do not have a member for cooling the cycle gas such as a heat exchanger between them.

Furthermore, embodiments of the invention may comprise one or more of the following features:

• • the compression mechanism comprises four compression stages in series, the member for cooling the cycle gas comprising three cooling heat exchangers disposed respectively between the first and the second compression stage, between the second and the third compression stage, and at the outlet of the fourth compression stage,
  • the device comprises cooling heat exchangers that are disposed solely every two compression stages in series,
  • the set of motor(s) comprises a plurality of motors for driving the compression stages,
  • the set of motor(s) comprises a separate respective motor for each compression stage,
  • at least one of the motors is cooled by a flow of cycle gas via at least one bypass line for a fraction of the flow of cycle gas supplying the compression mechanism, the bypass line comprising an upstream end attached to the outlet of at least one of the compression stages so as to draw off a fraction of the flow of cycle gas,
  • a downstream end of at least one bypass line is attached to the inlet of a compression stage after it passes and exchanges heat with at least one motor,
  • the at least one bypass line comprises, between its upstream end and its downstream end, a subdivision into at least two separate branches respectively supplying separate motors in order to cool them,
  • the at least two separate branches formed by the subdivision of a bypass line have a downstream junction within one and the same line portion,
  • the at least one bypass line comprises at least one member for cooling the cycle gas,
  • the at least one member for cooling the cycle gas of the at least one bypass line comprises a cooling heat exchanger.

In addition:

• • the cycle gas may be made up of helium or a mixture comprising at least 50% helium,
  • the cycle gas may be made up of hydrogen or a mixture comprising at least 50% hydrogen,
  • the cycle gas may be made up of nitrogen or a mixture comprising at least 50% nitrogen,
  • the compression mechanism may comprise solely compressors of centrifugal type,
  • the fluid to be cooled may comprise at least one of the following: hydrogen, natural gas, biogas, methane, helium.

The invention also relates to a method for refrigerating or liquefying a fluid using a refrigeration device according to any one of the features above or below and comprising a step of circulating a fluid in the circuit for fluid to be cooled and a step of cooling said fluid via the cold produced by the refrigerator.

According to further possible particular features: the method 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 in series that do not have a member for cooling the cycle gas such as a heat exchanger between them is kept at a speed lower than the rotational speed of the compression stages that are provided, at their outlet, with a member for cooling the cycle gas.

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

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments. [FIG. 1] is a schematic and partial depiction illustrating one example of the structure and operation of a device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The device 1 is configured for the cryogenic refrigeration and/or liquefaction of a fluid (such as natural gas, biomethane or hydrogen, for example, but without this being limiting). The device 1 comprises a circuit 3 for fluid to be cooled/liquefied having an upstream end intended to be connected to a source 2 of (for example gaseous) fluid and a downstream end 23 intended to be connected to a member for collecting the cooled or liquefied fluid (a store, for example).

The device 1 comprises a set of heat exchanger(s) 6, 10 in heat exchange with the circuit 3 for fluid to be cooled.

The device 1 comprises a cold source comprising a refrigerator 20 in heat exchange with at least part of the set of heat exchanger(s) 6, 10.

The refrigerator 20 is cryogenic and of the type performing a refrigeration cycle on a cycle gas predominantly comprising helium and/or hydrogen and/or nitrogen and/or neon.

For example, the cycle gas is made up of pure helium or a mixture comprising at least 50% helium.

Similarly, the cycle gas may be made up of pure hydrogen or a mixture comprising at least 50% hydrogen.

Similarly, the cycle gas may be made up of nitrogen or a mixture comprising at least 50% nitrogen.

As an alternative, the cycle gas may be made up of neon or a mixture comprising at least 50% neon.

Of course, any other suitable mixture or cycle gas can be envisaged, for example comprising at least one of the following: helium, hydrogen, nitrogen, neon, methane.

Typically, the refrigerator 20 comprises the following, disposed 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 heating the expanded cycle gas.

The compression mechanism comprises a plurality of compression stages 15 in series that are composed of a set of compressor(s) of centrifugal type, the compression stages being mounted on a set of shafts driven in rotation by a set of motor(s) 18.

The at least one member for cooling the cycle gas comprises at least one heat exchanger 7 disposed 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.

The set of heat exchanger(s) may comprise one or a plurality of heat exchangers 6, 10 which are disposed in series and in which two separate portions of the cycle circuit 14 perform circulation simultaneously in countercurrent operation for the cooling and the heating of the cycle gas, respectively. The plurality of heat exchangers may therefore form both a member for cooling the cycle gas and a member for heating the cycle gas.

According to an advantageous particular feature, the compression mechanism comprises at least two compression stages 15 that are disposed successively in series and that do not have a member for cooling the cycle gas such as a heat exchanger 7 between them. That is to say that two compression stages may follow one another without inter-stage cooling.

More specifically, at least one compression stage 15 does not comprise, at its outlet, a cooling exchanger 7 cooled by a heat transfer fluid separate from the cycle gas (no “aftercooler”). Conversely, the cycle gas at the outlet of this compression stage may, where appropriate, directly enter a countercurrent cooling exchanger 6, 10 cooled by a colder flow of cycle gas.

This can be advantageous for modifying for example an existing device of given capacity so as to increase its refrigeration power.

In the case of a relatively “heavy” cycle gas (that is to say one which heats up significantly by centrifugal compression), such as the one conventionally used (typically a mixture of helium and nitrogen), the prior art makes provision for addition of an additional cooling exchanger (“intercooler”) so that the cycle gas is not too hot when it enters the subsequent compression stage. This is done in such a way as to not reach excessively high temperatures.

For lighter gases such as helium or hydrogen, use is conventionally made of positive-displacement compressors in which a single compression stage is followed by a cooling exchanger.

The invention is counter-intuitive because the overall compression efficiency may decline with respect to the known systems (since the last compression stage works at higher temperature). However, notably in the case of very light cycle gases (molar mass less than 30 g/mol and notably less than 20 g/mol or less than 10 g/mol), the loss of performance of the less isothermal compression according to the invention is more than compensated by the reduction in pressure drops (on account of the lower number of cooling exchangers).

In addition, the saving on hardware is significant (cooling exchanger(s) and associated circuitry in particular).

This is particularly advantageous when adding a downstream compressor to an existing device (a single added item of equipment, module: compressor+motor), which may be identical to the preceding compression module. This requires few modifications, if any, to the design.

The last added compression stage without cooling at the outlet can be easily integrated. The advantage is better competitiveness of the new system and a certain degree of versatility via addition of an additional compression stage on site at lower cost, notably if there is a desire to increase the production of an installation after several years of operation.

In the non-limiting example illustrated, the compression mechanism comprises four compression stages (wheels) 15 in series and cooling means 7 solely at the outlet of three of these four compression stages, preferably at the outlet of the first, second and fourth compression stages. That is to say that the cycle gas is not cooled between the third and fourth compression stages.

Thus, the device maintains a temperature increase due to the (relatively) low centrifugal compression so as to not need an intercooler between each compression stage. This makes it possible to decrease the cost and increase compactness while limiting the impact on the overall efficiency of the compression system.

Of course, any other configuration is possible in terms of the number of compression stages and of the one or more stages that do not have cooling at the outlet, for example it is possible to envisage an architecture with a cooling heat exchanger 7 disposed solely every two compression stages 15 in series (or every three compression stages in series). In other possible configurations, for example a device with three compression stages in series, of which the two first stages are provided, at their outlet, with a cooling heat exchanger, at the outlet of the third compression stage the cycle gas may then directly enter a countercurrent exchanger of the refrigeration device and then subsequently enter an expansion stage (for example a single turbine). At the outlet of the expansion stage, the cycle gas may then be placed in heat exchange with the circuit for gas to be cooled (typically in a heat exchanger). Then, after this exchange with the fluid to be cooled, the cycle gas can pass into a countercurrent exchanger in which it heats up by cooling the flow exiting the aforementioned compression stage. This heated cycle gas may then re-enter the first compression stage to restart a cycle.

Preferably, the set of motor(s) 18 comprises a plurality of motors for driving the compression stages.

In the example illustrated, a respective motor 18 is provided for each compression stage. Of course, a motor 18 could drive a plurality of compression stages (mounted on one and the same output shaft, for example). Similarly, one or more turbines 17 could be mounted on the shaft of a motor 18 which drives one or more compression stage(s).

At least one of the motors 18 may be cooled by a flow of cycle gas.

As illustrated, at least one bypass line 4, 5, 9 may be provided to draw off a fraction of the flow of cycle gas supplying the compression mechanism. The bypass line 4 may comprise an upstream end attached to the outlet of at least one of the compression stages 15 (for example downstream of the first compression stage 15, notably after cooling means 7) so as to draw off a fraction of the flow of cycle gas.

The downstream end of the bypass line may be attached to the inlet of another compression stage after it passes and exchanges heat with at least one motor 18 (for example upstream of the first compression stage 15 in this example).

The bypass line 4 may comprise, between its upstream end and its downstream end, at least one subdivision into at least two separate branches 5, 9 respectively supplying separate motors 18 in order to cool them. That is to say that a cooling circuit may thus be provided to cool all or some of the motors 18.

Thus, all or some of the motors 18 may be cooled by the cycle gas tapped off at different pressure levels from the circuit.

As illustrated, the at least two separate branches 5, 9 formed by the subdivision of a bypass line 4 may have a downstream junction within one and the same line portion.

The at least one bypass line may comprise at least one member 8 for cooling the cycle gas, for example at least one cooling heat exchanger 8 for cooling the flow after heat exchange with at least one motor 18.

Advantageously, the rotational speed of the (two) last compression stages (compression wheels) may be reduced in relation to the other stages in order to limit their compression rate and the heating of the cycle fluid. This makes it possible to avoid reaching excessively high temperatures that are liable to damage the equipment.

This invention is particularly suitable for refrigerators whose cycle gas is a light gas, that is to say having a molar mass comprised between 2 and 30 g/mol and preferably between 2 and 20 g/mol. Specifically, in this case, the decline in compression performance resulting from the absence of cooling between compression stages is largely compensated by the structural benefit, the decrease in cost and by the simplicity of implementation.

Of course, the invention can be used with a heavier cycle gas (in this case, the compression rates of each compression stage are preferably reduced so as to limit the heating, hut while still remaining greater than that which would be obtained with helium and/or h2 alone).

As illustrated, the system for cooling the cycle gas may comprise a heat exchanger, disposed at the outlet of at least some of the turbines 17 except for the last turbine 17 in series along the direction of circulation of the cycle gas.

The device 1 may comprise more compression stages 15 than turbines 17.

The device 1 may have a number of compression stages equal to three, four, five or more.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

Claims

1-12. (canceled)

13. A method for refrigerating or liquefying a fluid using a device for refrigerating or liquefying a fluid such as natural gas or hydrogen, the method comprising the steps of:

providing the device that is comprised of: a circuit for fluid to be cooled having an upstream end configured to be connected to a source of gaseous fluid and a downstream end configured to be connected to a member for collecting the cooled or liquefied fluid, a set of heat exchanger(s) in heat exchange with the circuit for fluid to be cooled, a refrigerator in heat exchange with at least part of the set of heat exchanger(s), the refrigerator configured to perform a refrigeration cycle on a cycle gas selected from the group consisting of: helium, hydrogen, nitrogen, neon, and combinations thereof, said refrigerator comprising the following, disposed in series in a cycle circuit: a compression mechanism configured to compress the cycle gas, at least one cooling member configured to cool the cycle gas, an expanding mechanism configured to expand the cycle gas, and at least one heating member configured to heat the expanded cycle gas, wherein the compression mechanism comprises a plurality of compression stages in series that are composed of a set of compressor(s) of centrifugal type, the compression stages being mounted on a set of shafts driven in rotation by a set of motor(s), the at least one cooling member comprises 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, wherein the compression mechanism comprises at least two compression stages that are disposed successively in series and do not have a member for cooling the cycle gas such as a heat exchanger between them,

circulating a fluid in the circuit for fluid to be cooled and a step of cooling said fluid via the cold produced by the refrigerator; and

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 in series that do not have a member for cooling the cycle gas such as a heat exchanger between them is kept at a speed lower than the rotational speed of the compression stages that are provided, at their outlet, with a member for cooling the cycle gas.

14. The method as claimed in claim 13, wherein the compression mechanism comprises four compression stages in series, the member for cooling the cycle gas comprising three cooling heat exchangers that are disposed respectively at the outlet of three of these four compression stages, for example between the first and the second compression stage, between the second and the third compression stage, and at the outlet of the fourth compression stage.

15. The method as claimed in claim 13, further comprising cooling heat exchangers disposed solely every two compression stages in series.

16. The method as claimed in claim 13, wherein the set of motor(s) comprises a plurality of motors for driving the compression stages.

17. The method as claimed in claim 16, wherein the set of motor(s) comprises a separate respective motor for each compression stage.

18. The method as claimed in claim 16, wherein at least one of the motors is cooled by a flow of cycle gas via at least one bypass line for a fraction of the flow of cycle gas supplying the compression mechanism, the bypass line comprising an upstream end attached to the outlet of at least one of the compression stages so as to draw off a fraction of the flow of cycle gas.

19. The method as claimed in claim 18, wherein a downstream end of at least one bypass line is attached to the inlet of a compression stage after it passes and exchanges heat with at least one motor.

20. The method as claimed in claim 19, wherein the at least one bypass line comprises, between its upstream end and its downstream end, a subdivision into at least two separate branches respectively supplying separate motors in order to cool them.

21. The method as claimed in claim 20, wherein the at least two separate branches formed by the subdivision of a bypass line have a downstream junction within one and the same line portion.

22. The method as claimed in claim 18, wherein the at least one bypass line comprises at least one member for cooling the cycle gas.

23. The method as claimed in claim 22, wherein the at least one member for cooling the cycle gas of the at least one bypass line comprises a cooling heat exchanger.

24. A device for refrigerating or liquefying a fluid, the device comprising:

a circuit for 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 member for collecting the cooled or liquefied fluid,

a set of heat exchanger(s) in heat exchange with the circuit for fluid to be cooled,

a refrigerator in heat exchange with at least part of the set of heat exchanger(s), the refrigerator being of the type performing a refrigeration cycle on a cycle gas selected from the group consisting of: helium, hydrogen, nitrogen, neon, and combinations thereof,

said refrigerator comprising the following, disposed in series in a cycle circuit: a compression mechanism configured to compress the cycle gas, at least one cooling member configured to cool the cycle gas, an expanding mechanism configured to expand the cycle gas, and at least one heating member configured to heat the expanded cycle gas,

wherein the compression mechanism comprises a plurality of compression stages in series that are composed of a set of compressor(s) of centrifugal type,

wherein the compression stages is mounted on a set of shafts driven in rotation by a set of motor(s),

wherein the at least one cooling member comprises at least one heat exchanger disposed at the outlet of at least one compression stage in heat exchange with the cycle circuit,

wherein said heat exchanger is cooled by a heat transfer fluid,

wherein the compression mechanism comprises at least two compression stages that are disposed successively in series and that do not have a member for cooling the cycle gas such as a heat exchanger between them,

an electronic monitoring and control member configured to control a 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 in series that do not have a member for cooling the cycle gas such as a heat exchanger between them is kept at a speed lower than the rotational speed of the compression stages that are provided, at their outlet, with a member for cooling the cycle gas.