Installation and method for refrigerating a fluid flow.

Abstract

The invention relates to a refrigeration installation comprising a supply circuit (3) for the flow of fluid to be cooled, a set of heat exchanger(s) (5, 6) in heat exchange with the supply circuit (3), at least one refrigerator (2) in heat exchange with at least one of the heat exchanger(s) (5, 6), and of the type with a cycle circuit (12) comprising: at least one compressor (20), at least one cooling element (5, 6), an expansion mechanism (22) with turbine(s), and at least one heating element (5). The cycle circuit (12) includes a pressure control device (32, 42) at the inlet of the compressor (20) configured to allow lowering or raising this pressure at the inlet of the compressor (20), and a pressure control device (9, 10) at the outlet of the compressor (20) configured to allow lowering or raising this pressure at the outlet of the compressor. (20),the installation (1) comprising a device (7) for determining the thermal load of the fluid flow to be cooled in the supply circuit (3) and a control device (8) configured to control the pressure regulation devices (32, 42, 9, 10) at the inlet and outlet of the compressor (20) and to lower or raise these pressures in response to a decrease or increase in the thermal load of the fluid flow to be cooled. Abbreviated figure: Fig. 1,

Description

Title of the invention: Installation and method for refrigerating a fluid flow.

[0001] The invention relates to an installation and a method for refrigerating a fluid flow.

[0002] The invention relates more particularly to a refrigeration installation for a fluid flow, for example for the liquefaction of a fluid such as hydrogen and / or helium, the installation comprising a supply circuit for the fluid flow to be cooled having a determined thermal load which may be variable, the supply circuit having an upstream end intended to be connected to a source of gaseous fluid and a downstream end, for example intended to be connected to a collection device for the cooled and liquefied fluid, the installation comprising a set of heat exchanger(s) in heat exchange with the supply circuit, the installation comprising at least one refrigerator in heat exchange with at least part of the set of heat exchanger(s) configured to cool the supply circuit under determined thermodynamic conditions,The refrigerator being a refrigeration cycle refrigerator using a cycle gas having a cycle circuit comprising: at least one cycle gas compressor, at least one cycle gas cooling element, a cycle gas expansion mechanism having at least one turbine and at least one heating element for the expanded cycle gas, the cycle circuit comprising a pressure control device at the compressor inlet configured to allow lowering or raising this pressure at the compressor inlet and a pressure control device at the compressor outlet configured to allow lowering or raising this pressure at the compressor outlet.

[0003] It is known to combine several refrigeration cycles of different components to achieve a cold temperature, in order to cool or liquefy a feed gas stream. Each refrigeration cycle has optimal efficiency within a certain temperature range, and these cycles will be connected in series to achieve optimal efficiency.

[0004] Liquefaction plants are designed to operate at an optimized operating point. When the heat load to be cooled is lower or decreasing, energy consumption is often somewhat degraded compared to the optimum. It is not uncommon to have plants operating at approximately 80 to 85% of their reference operating point and therefore not operating at their optimal levels.

[0005] In addition, the start-ups and shutdowns of the installation can also have undesirable effects, such as increased labor requirements, product loss, and equipment aging due to temperature cycles.

[0006] Stops and restarts may therefore be less favoured than operations at low constant load.

[0007] One problem is therefore to optimize the energy efficiency of the installation in order to be able to produce a liquefied fluid efficiently over a wide range of loads without stopping the installation.

[0008] In the case of refrigeration cycles, such as Rankine or Brayton cycles, the basic principle of cold generation is compression and expansion. Most of the energy consumed for cooling or liquefaction is due to compression. In the specific case of cascade cycles, there are multiple parameters that define the actual efficiency of the entire cycle. For example, a degradation in the coldest loop will have a cascading impact on all the warmest loops (according to Carnot's theorem).

[0009] One object of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

[0010] To this end, the installation according to the invention, which also conforms to the generic definition given in the preamble above, is essentially characterized in that it comprises a device for determining the thermal load of the flow of fluid to be cooled in the supply circuit and a control device configured to control the pressure regulation devices at the inlet and outlet of the compressor and to lower or raise these pressures in response to a decrease or increase in the thermal load of the flow of fluid to be cooled in the supply circuit determined by the determining device.

[0011] Furthermore, embodiments of the invention may include one or more of the following features: - In response to a decrease in the thermal load of the fluid flow to be cooled in the supply circuit, as determined by the determining element, the control element is configured to control the pressure regulating devices at the inlet and outlet of the compressor and lower or raise these pressures without changing the compressor's compression ratio, - The control unit is configured to control the pressure regulation devices at the inlet and outlet of the compressor without affecting the volumetric flow rate of the compressed cycle fluid that feeds the turbine of the cycle gas expansion mechanism, - The pressure regulation device at the compressor inlet includes a compressor bypass line connecting the compressor inlet to the compressor outlet and a set of valve(s) configured to allow a portion of the cycle gas flow to bypass the compressor, - The pressure regulation device at the compressor outlet includes a sampling line and a set of valve(s) configured to allow the extraction of a cycle gas flow from the cycle circuit at the compressor outlet to a receiver separate from the cycle circuit, - In response to a decrease in the thermal load of the fluid flow to be cooled in the supply circuit, the control device is configured to first reduce the pressure at the compressor inlet by opening the compressor bypass line and then to extract a flow of cycle gas from the cycle circuit to the receiver by opening the sampling line. - The receiver includes one of the following: a buffer storage, the power supply circuit, - the installation includes a gas reserve of the same nature as the cycle gas and a system for injecting this gas from the reserve into the cycle circuit configured to allow gas from the reserve to be injected into the cycle circuit to increase the pressure in the cycle circuit.

[0012] The invention also relates to a method of refrigerating a fluid flow using an installation conforming to any one of the above or below characteristics, comprising a step of determining a decrease in the thermal load of the fluid flow to be cooled and a step of reducing the inlet and outlet pressures of the compressor as a function of said thermal load.

[0013] According to other possible features: - During the stage of reducing the compressor inlet and outlet pressures, the compressor compression ratio is constant and the volumetric flow rate of cycle gas feeding the turbine is constant, - the step of reducing the inlet and outlet pressures of the compressor as a function of said thermal load includes first a controlled reduction of the pressure at the inlet of the compressor via a bypass of the cycle gas flow supplying the compressor then an extraction of a cycle gas flow out of the cycle circuit to the receiver, for example a buffer storage and / or the supply circuit.

[0014] The invention also relates to a method of refrigerating a fluid flow using an installation conforming to any one of the above or below characteristics comprising a step of determining an increase in the thermal load of the fluid flow to be cooled and a step of increasing the inlet and outlet pressures of the compressor (20) as a function of said thermal load.

[0015] According to other possible features, the process includes a step of injecting gas into the cycle circuit to increase the pressure in the cycle circuit.

[0016] 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.

[0017] Other features and advantages will become apparent from the following description, given with reference to the figures in which: Brief description of the figures

[0018] The invention will be better understood upon reading the following description, given solely by way of example and made with reference to the accompanying drawings in which:

[0019] [Fig. 1] is a schematic and partial view illustrating an example of structure and operation of an installation according to the invention

[0020] [Fig.2] is a schematic and partial view illustrating an example of structure and operation of a detail of such an installation. Detailed description

[0021] In all figures, the same references refer to the same elements.

[0022] In this detailed description, the following embodiments are examples. Although the description refers to one or more embodiments, this does not mean that the features apply only to a single embodiment. Simple features from different embodiments can also be combined and / or interchanged to provide other embodiments.

[0023] The illustrated fluid flow refrigeration installation 1 is, for example, intended for the liquefaction of a fluid such as hydrogen and / or helium.

[0024] The installation 1 comprising a circuit 3 for supplying the flow of fluid to be cooled having a determined thermal load which may be variable.

[0025] The supply circuit 3 has an upstream end intended to be connected to a source of gaseous fluid and a downstream end 23. The downstream end is for example intended to be connected to a collection device 4 for the cooled and liquefied fluid, for example a cryogenic tank.

[0026] Installation 1 includes a set of heat exchanger(s) 5, 6 in thermal exchange with the supply circuit 3.

[0027] The installation 1 comprises at least one refrigerator 2 in heat exchange with at least part of the heat exchanger assembly(ies) 5, 6 and configured to cool the supply circuit 3 under predetermined thermodynamic conditions. As shown schematically, the installation may also include a pre-cooling device 13, for example a refrigerator with a cycle circuit, for example with nitrogen.

[0028] The refrigerator 2 is a cycle refrigeration refrigerator of a cycle gas having a cycle circuit 12 comprising: at least one cycle gas compressor 20, at least one cycle gas cooling element 5, 6, a cycle gas expansion mechanism 22 having at least one turbine and at least one cycle gas heating element 5.

[0029] The cycle circuit 12 includes a pressure regulation device 32, 42 at the inlet of the compressor 20 (or at least part of the compressors).

[0030] This inlet pressure regulation device 32, 42 is configured to allow lowering or raising this pressure at the inlet of the compressor 20.

[0031] The cycle circuit 12 further includes a device 9, 10 for regulating the pressure at the outlet of the compressor 20 configured to allow lowering or raising this pressure at the outlet of the compressor 20.

[0032] The installation 1 comprising a device 7 for determining the thermal load of the flow of fluid to be cooled in the supply circuit 3 and a control device 8 configured to control the pressure regulation devices at the inlet and outlet of the compressor 20 and lower or raise these pressures in response to a decrease or increase in the thermal load of the flow of fluid to be cooled in the supply circuit 3 determined by the determining device 7.

[0033] The determining element 7 may include, for example, at least one of the following: a flow sensor in the supply circuit, a temperature sensor of the supply gas.

[0034] The control unit 8 may include an electronic data storage and processing device comprising a microprocessor.

[0035] That is to say, installation 1 can adjust the pressure of the cycle circuit according to the thermal load to optimize the compression power (therefore the cooling power of the cycle). This directly optimizes the cost of producing cold.

[0036] The compression outlet pressure can be the main control parameter.

[0037] For low effective loads, the pressure cycles upstream and downstream of the compressor will fluctuate to adapt to good efficiency on rotating equipment.

[0038] The efficiency of a turbine is indeed linked to the volumetric flow rates at the inlet and outlet.

[0039] For the compressor, if a relatively constant compression ratio is maintained, the pressure at the compressor outlet will be a direct consequence of the pressure at the compressor inlet. The setpoint for the pressure control at the compressor inlet can be adjusted with the thermal load, for example, the temperature of the cold end of the hydrogen cooled in the supply circuit 3 before its transfer in the collection unit 4. The compressor's suction pressure is thus a consequence of the temperature at the cold end.

[0040] For example, at 100% load, a cycle compressor (reciprocating compressor) will compress from 6 barg to 60 barg, while at 40% of the installation's load, it will compress from 4 barg to 40 barg. The turbines will be maintained at their optimal operating points, and so will the compressors, since the volumetric flow rate is almost constant.

[0041] Thus, it is essentially the discharge pressure of the cycle compressor that is adjusted according to the thermal load of the unit. For example, for a 40% production load, the cycle pressure can, for example, be reduced to 40 barg.

[0042] A similar philosophy could be applied to other cycle compressors of any technology in the cascade process.

[0043] Thus, in response to a decrease in the thermal load of the fluid flow to be cooled in the supply circuit 3 determined by the determining element 7, the control element 8 can be configured to control the pressure regulation devices 32, 42, 9, 10 at the inlet and outlet of the compressor 20 and lower these pressures without changing the compression ratio of the compressor 20.

[0044] The control member 8 can in particular be configured to control the pressure regulation devices 32, 42, 9, 10 at the inlet and outlet of the compressor 20 without affecting the volumetric flow rate of the compressed cycle fluid that feeds the turbine of the cycle gas expansion mechanism 22

[0045] Fig. 2 schematically represents in a simplified way the cycle circuit 12 with compression 20 (compressor), cooling 5, 6 (heat exchanger(s)), expansion 22 (turbine) and reheating 5, 6.

[0046] As illustrated, pressure sensors 11 can be provided at the inlet and outlet of the compressor 20. These pressure values ​​can be transmitted to the control element 8 for the aforementioned regulation or below.

[0047] As schematically shown in [Fig.2], the pressure control device at the inlet of the compressor 20 may include a compressor bypass line 32 connecting the inlet of the compressor 20 to the outlet of the compressor 20 and a set of valve(s) 42 configured to allow a portion of the cycle gas flow to bypass the compressor 20. The discharge pressure control device of the cycle compressor includes or is the bypass (recycle) system 32, 42.

[0048] The installation may include a sampling line 9 and a set of valve(s) 10 configured to allow the extraction of a cycle gas flow from the cycle circuit 12 at the compressor outlet to a receiver separate from the cycle circuit 12. The receiver may include one of the following: a buffer storage, the supply circuit 3.

[0049] At the compressor suction (low pressure) the installation 1 preferably includes a "make up" line, i.e. a line allowing the injection of cycle gas molecules whose source can be independent (but of the same quality as the cycle fluid) or the supply circuit (after a stage of purifying impurities).

[0050] These molecules can be supplied by any suitable source (schematized by the horizontal dashed arrows pointing to the cycle circuit 12), and in particular for example by the supply circuit 3, in particular after purification (for example after pre-cooling).

[0051] At the compressor discharge (high pressure) the installation therefore preferably includes a line allowing hydrogen to be discharged for example to the supply circuit 3 and thus to lower the quantity of molecules in the cycle circuit.

[0052] Thus, in response to a decrease in the thermal load of the fluid flow to be cooled in the supply circuit 3, the control device 8 can be configured to first reduce the pressure at the inlet of the compressor 20 by opening the compressor bypass line 32, and then to extract a cycle gas flow from the cycle circuit 12 to the receiver by opening the sampling line 9. A variation in thermal load may include or be a change in the conditions of the fluid flow to be cooled in the fluid 3, but also a variable recovery of cold fluid (for example, cold gases recovered from downstream equipment: storage, loading bays, etc.) and / or a variation in the flow rate or temperature of another fluid extracted during cooling.

[0053] The compressor inlet pressure setpoint 20 can be lowered at a relatively lower thermal load because the required cooling capacity is lower. The compressor outlet pressure 20 will be lower because the machines preferably operate with a relatively constant compression ratio. The effective compression will remain the same. Less mass is compressed, therefore energy consumption is efficiently optimized.

[0054] Similarly, the installation 1 may include a gas reservoir of the same type as the cycle gas and a system for injecting this gas from the reservoir into the cycle circuit 12, configured to allow the injection of gas from the reservoir into the cycle circuit to increase the pressure in the cycle circuit 12. This addition of molecules is necessary to increase the pressure in the closed circuit. This reservoir is preferably a pure gas reservoir; for example, downstream of a cryogenic purification of the supply circuit 3, this pure gas is injected into the cycle circuit.

[0055] Thus, in the event of an increase in the thermal load of the fluid flow to be cooled, the installation 1 can increase the pressure in the cycle circuit 12 to increase the inlet and outlet pressures of the compressor 20.

[0056] As illustrated in [Fig. 1], the control unit 8 can also control the first compressor of the pre-cooling cycle 13. This leads to a cycle cascade and the overall response of the system to a change in the required thermal load. The control unit 8 can, for example, act (preferably in a differentiated manner) on the two nested refrigeration loops.

[0057] Other advantages are also related to this cycle arrangement with controlled pressure fluctuation. This is the case, for example, in a nitrogen liquefier or more generally in any refrigeration system with a first nitrogen cooling stage.

[0058] The compressor can be simplified, thereby achieving cost savings. That is to say, the compressor is controlled by a single inlet pressure and a single outlet pressure, without the withdrawal of intermediate gas.

[0059] The third advantage of such control is to ensure that the rotating elements (turbine in particular) will never enter a prohibited operating speed range, i.e. a speed range close to the critical pulsations generating resonance phenomena which would damage the machine (according to the definition for example of the Campbell diagram) since the operation of these turbines will be maintained in a very narrow speed range.

[0060] This installation and method also allow for adaptation in the case of variable recovery of cold fluid. For example, if cold vaporization gas is collected in the installation (from, for example, loading bay storage or other sources), the required thermal load may vary and, in particular, decrease. The installation can therefore adjust accordingly as described below (for example, in response to a flow rate and / or temperature measurement of a recovered vaporization gas stream).

[0061] Similarly, the invention can be applied to an installation that has two or more fluids to be cooled / liquefied (for example, in the case of a co-production of liquid nitrogen and liquid hydrogen). The installation can also be adapted to the thermal load.

Claims

1.

2. Demands Installation for refrigerating a fluid stream, for example for the liquefaction of a fluid such as hydrogen and / or helium, the installation (1) comprising a supply circuit (3) for the fluid stream to be cooled having a determined thermal load which may be variable, the supply circuit (3) having an upstream end intended to be connected to a source of gaseous fluid and a downstream end (23), for example intended to be connected to a collection device (4) for the cooled and liquefied fluid, the installation (1) comprising a set of heat exchanger(s) (5, 6) in heat exchange with the supply circuit (3), the installation (1) comprising at least one refrigerator (2) in heat exchange with at least part of the set of heat exchanger(s) (5, 6) configured to cool the supply circuit (3) under determined thermodynamic conditions,the refrigerator (2) being a cycle refrigerator using a cycle gas, having a cycle circuit (12) comprising: at least one cycle gas compressor (20), at least one cycle gas cooling element (5, 6), a cycle gas expansion mechanism (22) having at least one turbine, and at least one expanded cycle gas heating element (5), the cycle circuit (12) comprising a device (32, 42) for regulating the pressure at the inlet of the compressor (20) configured to allow lowering or raising this pressure at the inlet of the compressor (20), and a device (9, 10) for regulating the pressure at the outlet of the compressor (20) configured to allow lowering or raising this pressure at the outlet of the compressor (20), the installation (1) comprising a device (7) for determining the thermal load of the fluid flow to be cooled in the supply circuit (3) and a control device (8) configured to order the devices (32,42, 9, 10) of pressure regulation at the inlet and outlet of the compressor (20) and lowering or raising these pressures in response to a decrease or increase in the thermal load of the fluid flow to be cooled in the supply circuit (3) determined by the determining device (7). Installation according to claim 1, characterized in that, in response to a decrease in the thermal load of the fluid flow to be cooled in the supply circuit (3) determined by the component (7) In determining, the control organ (8) is configured to control the pressure regulation devices (32, 42, 9, 10) at the inlet and outlet of the compressor (20) and to lower or raise these pressures without changing the compression ratio of the compressor (20).

3. Installation according to claim 1 or 2, characterized in that the control member (8) is configured to control the pressure regulation devices (32, 42, 9, 10) at the inlet and outlet of the compressor (20) without affecting the volumetric flow rate of compressed cycle fluid that feeds the turbine of the cycle gas expansion mechanism (22).

4. Installation according to any one of claims 1 to 3, characterized in that the device (32, 42) for regulating the pressure at the inlet of the compressor (20) comprises a compressor bypass line (32) connecting the inlet of the compressor (20) to the outlet of the compressor (20) and a set of valve(s) (42) configured to allow a portion of the cycle gas flow to bypass the compressor (20).

5. Installation according to any one of claims 1 to 4, characterized in that the pressure regulation device (9, 10) at the outlet of the compressor (20) comprises a sampling line (9) and a set of valve(s) (10) configured to allow extraction of a cycle gas flow from the cycle circuit (12) at the outlet of the compressor to a receiver separate from the cycle circuit (12).

6. Installation according to any one of claims 4 and 5, characterized in that, in response to a decrease in the thermal load of the fluid flow to be cooled from the supply circuit (3), the control member (8) is configured to first reduce the pressure at the inlet of the compressor (20) by opening the compressor bypass line (32) and then to extract a cycle gas flow from the cycle circuit (12) to the receiver by opening the sampling line (9).

7. Installation according to claim 5 or 6, characterized in that the receiver comprises one of: a buffer storage, the supply circuit (3).

8. An installation according to any one of claims 1 to 6, characterized in that it comprises a gas reservoir of the same nature that the cycle gas and a system for injecting this gas from the reserve into the cycle circuit (12) configured to allow the injection of gas from the reserve into the cycle circuit to increase the pressure in the cycle circuit (12).

9. A method for refrigerating a fluid stream using an installation according to any one of claims 1 to 8, comprising a step of determining a decrease in the thermal load of the fluid stream to be cooled and a step of reducing the inlet and outlet pressures of the compressor (20) as a function of said thermal load.

10. The method according to claim 9 characterized in that during the step of reducing the inlet and outlet pressures of the compressor (20), the compression ratio of the compressor is constant and the volumetric flow rate of cycle gas feeding the turbine is constant.

11. Method according to claim 9 or 10 characterized in that the step of reducing the inlet and outlet pressures of the compressor (20) as a function of said thermal load comprises first a controlled reduction of the pressure at the inlet of the compressor (20) via a bypass of the cycle gas flow supplying the compressor (20) and then an extraction of a cycle gas flow out of the cycle circuit (12) to the receiver, for example a buffer storage and / or the supply circuit.

12. A method for refrigerating a fluid stream using an installation according to any one of claims 1 to 8, comprising a step of determining an increase in the thermal load of the fluid stream to be cooled and a step of increasing the inlet and outlet pressures of the compressor (20) as a function of said thermal load.

13. A refrigeration method according to claim 12 comprising a step of injecting gas into the cycle circuit (12) to increase the pressure in the cycle circuit (12).

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