EP3918260A1

EP3918260A1 - Cooling method for liquefying a feed gas

Info

Publication number: EP3918260A1
Application number: EP20701394.7A
Authority: EP
Inventors: Lutz Decker; Martin Knoche
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2019-01-30
Filing date: 2020-01-14
Publication date: 2021-12-08
Also published as: WO2020156754A1; CN113286977B; AU2020213611A1; GB201901247D0; GB2581135A; CN113286977A; CA3127832A1; US20210381756A1

Abstract

The present invention pertains to a cooling method for liquefying a feed gas, comprising the steps of providing a cooling cycle (20) with a refrigerant stream (28; dividing the refrigerant stream (28) into a first partial stream (32) and a second partial stream (36); expanding the first partial stream (32) in a first expansion device (40); and transferring cooling energy from the expanded first partial stream (42) to a feed gas stream (12) to be cooled, particularly comprising hydrogen and/or helium. Further the method comprises the steps of guiding the expanded first partial stream (42) to a suction inlet of an ejector (48); and guiding the second partial stream (36) to a propellant inlet of the ejector (48) such that, upon expanding the second partial stream (36) in the ejector (48), the expanded first partial stream (42) is compressed and merged with the expanded second partial stream.

Description

Cooling method for liquefying a feed gas

Technical Field

The invention relates to a cooling method and a cooling system for liquefying a feed gas, for example hydrogen.

Technological Background

In general, industrial hydrogen liquefaction plants are known, for example from EP 3 163 236 A1 , in which a hydrogen gas stream is cooled by means of a plurality of closed-loop cooling cycles to a temperature below a condensation point of hydrogen so as to provide a liquid hydrogen stream.

The known industrial hydrogen liquefaction plants typically comprise a hydrogen cooling and liquefaction unit, to which a hydrogen feed gas stream to be cooled is supplied with a typical feed pressure between 15 bar and 30 bar. The hydrogen feed gas stream is usually produced outside the battery-limit of the plant, for example by means of a methane steam reformer or an electrolyzer.

Upon flowing through the hydrogen cooling and liquefaction unit, the hydrogen gas stream is cooled to a temperature below its condensation point and thereby liquefied prior to being discharged into a storage tank. In order to provide cooling energy for cooling and liquefaction of the hydrogen gas stream, the hydrogen cooling and liquefaction unit is thermally coupled to several cooling cycles by means of a plurality of heat exchangers.

Specifically, in a precooling cycle, the evaporation of a liquid nitrogen stream at typically 78 K is used, which is the nitrogen saturation temperature for an ambient pressure of 1 ,1 bar, to precool the hydrogen feed stream from ambient temperature to about 80 K. This is achieved by guiding the nitrogen stream of the precooling cycle and the hydrogen feed gas stream through a heat exchanger so as to transfer cooling energy. Thereafter, the hydrogen feed is typically conducted through a purifier to remove residual impurities, mainly nitrogen, in an adsorber vessel. After the purification at 80 K, the hydrogen feed is allowed to pass through additional heat exchanger passages filled with catalyst, typically hydrous ferric oxide, for an ortho to para hydrogen conversion. In case of deuterium liquefaction, the para“isomer” is converted to ortho. The feed gas stream is then again cooled down to about 80 K by the means of liquid nitrogen of the precooling cycle.

A final cooling and liquefaction of the hydrogen feed, from about 80 K to the state of saturated or subcooled liquid, is provided by means of a closed main cooling cycle, for example a Claude loop, with typically one or more cooling strings with turbines expanding the gas from a high pressure to medium pressure to provide refrigeration at different temperature levels. Specifically, the number of cooling strings may depend on the output capacity of the plant. As a result, a medium pressure stream is generated. As soon as the expansion of hydrogen in an isenthalpic expansion will result in a significant temperature decrease, the application of ejectors or a Joule Thomson valve becomes meaningful. The last or the coldest high-pressure refrigeration stream is expanded in a Joule- Thomson valve to a low pressure and lowest temperature level. In this way, a two-phase gas liquid stream is generated to provide cooling energy capable of cooling the hydrogen gas stream below the condensation point. For heat recovery purposes, the high-pressure stream is run counter currently against the medium and low-pressure stream in series of a plurality of heat exchanger, e.g. up to ten or more heat exchangers depending on the plant size and number of turbines.

For recirculating the medium and low-pressure stream, the main cooling cycle typically comprises a low-pressure compressor which collects and compresses the low-pressure stream to medium pressure. Further, a medium pressure compressor is provided which collects the total medium pressure stream and compresses it to high pressure before being reintroduced into the closed cycle. Usually, these compressors are mechanically or electrically driven.

However, the use of mechanically or electrically driven compressors for raising the pressure level of the low-pressure stream to a medium pressure level has an impact of the operational and capital expenditures of such industrial hydrogen liquefaction plants. Summary of the invention

It is an object of the present invention to provide an optimized cooling method used for liquefying a feed gas, particularly in an industrial hydrogen liquefaction plant, which can be cost-efficiently realized. Further, it is an object of the present invention to provide a corresponding cooling system.

These objects are addressed by a cooling method having the features of claim 1 and a cooling system having the features of claim 9. A cooling method is provided for liquefying a feed gas. The cooling method comprises the steps of providing a cooling cycle with a refrigerant stream; dividing the refrigerant stream into a first partial stream and a second partial stream; expanding the first partial stream in a first expansion device and transferring cooling energy from the expanded first partial stream to a feed gas stream to be cooled. The cooling method is characterized by comprising the further steps of guiding the expanded first partial stream to a suction inlet of an ejector and guiding the second partial stream to a propellant inlet of the ejector such that, upon expanding the second partial stream in the ejector, the expanded first partial stream is compressed and merged with the expanded second partial stream.

The feed gas stream to be cooled may comprise one or more cryogenic gases. Specifically, the feed gas stream to be cooled may comprise hydrogen. Alternatively, or additionally, the feed gas stream may comprise helium. Further, the feed gas stream may comprise Oxygen and/or other cryogenic gases.

The refrigerant stream may also comprise one or more cryogenic gases. Specifically, the refrigerant stream may comprise hydrogen or helium or neon. Alternatively, or additionally, the refrigerant stream may comprise a mixture of gases, i.e. a mixture of the previously mentioned gases, e.g. a mixture of neon and helium.

The proposed method may be used in in an industrial cryogenic gas liquefaction plant, i.e. a hydrogen liquefaction plant. Further, the proposed method may be used in cooling cycles, i.e.

precooling cycles, e.g. in such a gas liquefaction plant.

According to the present disclosure, the term“ejector” refers to a pumping device, i.e. a fluid jet ejector, in which a pumping effect is generated due to an induced momentum transfer of a motive or propellant medium to a suction medium, thereby accelerating and/or compressing the suction medium. In other words, impulses are exchanged between the propellant medium, i.e. a high velocity gas jet, and the suction medium. Preferably, the ejector, i.e. the fluid jet ejector, comprises the propellant inlet for receiving a pressurized propellant fluid that is supplied to a nozzle, i.e. a laval nozzle, communicating to a suction chamber of the ejector which is configured to generate a suction pressure therein which is lower than an ejector discharge pressure. The ejector further comprises the suction inlet which opens into the suction chamber and is configured to supply a suction fluid into the suction chamber, wherein the suction fluid has a pressure lower than a pressure of the propellant fluid supplied to the propellant inlet. The suction chamber communicates to a fluid outlet of the ejector via a convergent-divergent diffuser. In operation of the ejector, the pressurized propellant fluid enters the propellant inlet of the ejector and is then accelerated to a high velocity through the nozzle which discharges a high velocity jet stream of the fluid through the suction chamber into the convergent-divergent diffuser. Acceleration of the pressurized propellant fluid through the nozzle into the suction chamber creates a reduced pressure in the chamber which feeds a suction fluid from the suction inlet into the suction chamber. The suction fluid thus entering the suction chamber is entrained by and drawn into the convergent- divergent diffuser with the high velocity fluid stream. The combined fluid is subjected to acceleration and compression as it passes through a convergent inlet portion of the diffuser and, thereafter, deceleration and expansion as it passes through the divergent outlet portion of the diffuser. In dependence on the geometrical configuration of the ejector, in particular of the convergent- divergent diffuser, a velocity and pressure of the combined fluid output by the ejector via the output line can be set.

Preferably, the second partial stream constitutes the pressurized propellant fluid supplied to the propellant inlet and the expanded first partial stream constitutes the suction fluid supplied to the suction inlet of the ejector. In this way, upon flowing through the ejector, an expanded refrigerant stream may be provided by merging the compressed first partial stream with the expanded second partial stream in the ejector. Preferably, the ejector is designed and configured such that the expanded refrigerant stream output by the ejector has a medium pressure that is higher than a low pressure prevailing in the expanded first partial stream and that is lower than an intermediate or high pressure prevailing in the second partial stream or the refrigerant stream.

Generally, in the cooling cycle, the expanded first partial stream is provided with a sufficient low temperature so as to provide sufficient cooling energy for liquefying the feed gas stream. Therefore, the first partial stream is subjected to a high pressure drop from high pressure to low pressure to sufficiently decrease the temperature thereof. For reintroducing the expanded first partial stream into the cooling cycle, i.e. the refrigerant stream, it is subjected to a compression.

According to the present invention, the compression of the expanded first partial stream, i.e. from low to medium pressure, is performed by means of the ejector. Compared to conventionally used compression devices for compressing the low-pressure refrigerant stream to a medium and high pressure, the ejector is characterized by a simple and reliable design which is free of movable parts. Specifically, in the known methods and systems for liquefying hydrogen, mechanically or electrically driven compressors are used, e.g. rotary or reciprocating driven compressors. Such compressors, however, are expensive and require costly and time-consuming maintenance. This applies in particular when hydrogen as a refrigerant medium in the cooling cycle is used which may require an oil free operation of the corresponding compressors. Further, such compressors are typically operated at ambient temperature conditions, i.e. outside a so-called cold box of gas liquefaction plants, thereby requiring additional passage-lines, such as return lines or passage-lines in the heat exchangers.

Thus, by using an ejector for compressing the low pressure expanded first partial stream, the present invention provides a cost-optimized cooling method. Specifically, as the ejector is less expansive to purchase and maintain, the present invention contributes to solving the trade-off between operational and capital expenditures when designing industrial hydrogen liquefaction plants.

Specifically, the proposed cooling method may be used for liquefying hydrogen in an industrial hydrogen liquefaction plant. Such industrial hydrogen liquefaction plant preferably comprises a hydrogen cooling and liquefaction unit, to which a hydrogen feed gas stream is supplied with a typical feed pressure between 15 bar and 30 bar. Upon flowing through the hydrogen cooling and liquefaction unit, the hydrogen feed gas stream is preferably cooled and thereby liquefied so as to generate a liquid product stream. Thereafter, the liquid product stream may be guided towards a storage tank for storing the liquefied hydrogen at a desired storage pressure, e.g. 1 ,1 bar, and a desired storage temperature, e.g. 20 K.

Further, the industrial hydrogen liquefaction plant preferably comprises a cooling system having the cooling cycle, in which the proposed cooling method is performed and which is thermally coupled to the hydrogen cooling and liquefaction unit for providing cooling energy for liquefying the feed gas stream flowing through the hydrogen cooling and liquefaction unit. This thermal coupling is preferably realized by means of at least a first heat exchanger configured to transfer cooling energy from the expanded first partial stream circulating through the cooling cycle to the feed gas stream to be cooled, which flows through the hydrogen cooling and liquefaction unit. Specifically, by transferring cooling energy from the expanded first partial stream to the feed gas stream to be cooled, particularly by means of the first heat exchanger, the cooling method is intended to cool the feed gas stream to a temperature below a critical temperature of hydrogen so as to provide the liquid product stream comprising hydrogen.

The cooling cycle for generating cooling energy for the hydrogen cooling and liquefaction unit is preferably provided in form of the cooling cycle having the refrigerant stream comprising hydrogen. The cooling cycle is preferably provided as a closed cooling cycle, in which the refrigerant circulates. For providing the closed cooling cycle, the expanded refrigerant stream, which is provided by merging the compressed first partial stream with the expanded second partial stream in the ejector, may be guided through a compressor unit so as to compress the expanded refrigerant stream to a high pressure level, thereby providing the refrigerant stream. The compressor unit may comprise one or more compressor devices, e.g. piston compressors, for compressing the expanded refrigerant stream depending on the intended pressure change. For example, the compressor unit may comprise at least one, preferably two piston compressors. However, the proposed method is not limited thereto. Rather, the cooling cycle may also be provided as an open cooling cycle.

The method may further comprise a step of guiding the expanded refrigerant stream and the first partial stream such that heat is transferred between the expanded refrigerant stream and the first partial stream. This may be achieved by a second heat exchanger configured to transfer cooling energy from the expanded refrigerant stream to the first partial stream. In a further development, the expanded refrigerant stream and the first partial stream may be guided such that cooling energy is further transferred from the expanded refrigerant stream and/or the first partial stream to the feed gas stream flowing through the hydrogen cooling and liquefaction unit. Specifically, this may be realized by thermally coupling the feed gas stream to the expanded refrigerant stream and/or the first partial stream particularly by means of the second heat exchanger. In other words, the second heat exchanger may be provided such that each of the first partial stream, the expanded refrigerant stream and the feed gas stream flow therethrough. In this way, the cooling method provides refrigeration at different temperature levels, thereby improving an overall efficiency of the cooling method as a successive cooling of the feed gas stream may be provided.

In the further development, the second partial stream may be partially expanded and thereby cooled in a second expansion device prior to being guided or supplied to the ejector, i.e. to its propellant inlet. In this way, an expanded second partial stream may be generated having an intermediate pressure that is higher than the medium pressure. Specifically, the second expansion device may comprise a Joule-Thomson-valve and/or an expansion turbine. The expansion turbine may be capable or designed to generate mechanical or electrical energy upon expansion of the second partial stream, e.g. by means of a brake wheel, in order to provide energy recovery. For example, the expansion turbine may be designed to drive the compressor unit for compressing the expanded refrigerant stream. To that end, the generated electrical energy may be supplied to a power grid or may be used elsewhere. Further, for control purposes, a bypass line may be provided through which at least a part of the second partial stream is guided, and which is configured for bypassing the second expansion device and guiding the second partial stream flowing therethrough into the ejector, i.e. directly into the ejector. Additionally, or alternatively, the refrigerant stream may be further divided into at least one third partial stream. Specifically, the refrigerant stream may be divided into the first, the second and the at least one third partial stream after passing the different heat exchanger having different temperature levels, respectively. In other words, the refrigerant forming the respective partial stream is branched off from the refrigerant stream at different positions, at which the refrigerant has different temperatures. Accordingly, the first partial stream, the second partial stream and the at least one third partial stream, respectively, comprise different temperature levels. In this way, multilevel refrigeration at different temperature levels can be provided, thereby further contributing to an improved overall efficiency of the cooling method. This may be realized by the method further comprising the steps of expanding the at least one third partial stream in at least one third expansion device, and guiding the at least one expanded third partial stream, the first partial stream and the second partial stream such that heat is transferred, particularly by means of at least one third heat exchanger, between the at least one expanded third partial stream, the first partial stream and the second partial stream.

In a further development, the first partial stream, the second partial stream and the at least one expanded third partial stream may be guided such that cooling energy is further transferred from the first partial stream, the second partial stream and/or the at least one expanded third partial stream to the feed gas stream flowing through the hydrogen cooling and liquefaction unit. Specifically, this may be realized by thermally coupling the feed gas stream to the first partial stream, the second partial stream and/or the at least one expanded third partial stream particularly by means of the at least one third heat exchanger. In other words, the at least one third heat exchanger may be provided such that each of the at least one expanded third partial stream, the first partial stream and the feed gas stream flow therethrough. Specifically, the at least one expanded third partial stream may be feed to the expanded refrigerant stream, e.g. downstream of the at least one third heat exchanger. According to the present disclosure, the terms“downstream” and“upstream” refer to a flow direction of the respective stream through the passages of the cooling cycle or hydrogen cooling and liquefaction unit.

Further, the at least one third expansion device may be provided in form of at least one further expansion turbine. According to the above described expansion turbine, also the at least one further expansion turbine may be capable or designed to generate mechanical or electrical energy upon expansion of the at least one third partial stream, e.g. by means of a brake wheel, in order to provide energy recovery. Additionally, or alternatively, the expanded first partial stream is guided into a gas liquid separator arranged downstream of the first expansion device and configured to store the refrigerant in a liquid and gaseous phase, wherein the expanded first partial stream in a liquid phase is guided from the separator to the suction inlet of the ejector.

In a further development, the cooling system of the industrial hydrogen liquefaction plant may further comprise a closed precooling cycle configured to precool the refrigerant stream and/or the feed gas stream. Accordingly, the cooling method may comprise a step of precooling the refrigerant stream by means of a closed precooling cycle having a further refrigerant stream comprising or consisting of nitrogen, wherein in particular the further refrigerant stream is expanded in a fourth expansion device prior to being supplied to a fourth heat exchanger for transferring cooling energy to the refrigerant stream and particularly to the feed gas stream.

Furthermore, a cooling system used for liquefying the feed gas stream is provided, which may be used in the above described industrial hydrogen liquefaction plant. Specifically, the cooling system may be provided to perform the above described cooling method. Thus, the technical features previously described in connection with the method may also apply to the cooling system. In other word these features are also disclosed in connection with the cooling system.

The cooling system has a cooling circuit with the refrigerant stream circulating through a refrigerant line. Specifically, the cooling circuit further comprises an expansion device configured to expand a first partial stream flowing through a first junction line which branches off from the refrigerant line and a heat exchanger for transferring cooling energy from the expanded first partial stream to the feed gas stream to be cooled. In other words, in the heat exchanger, heat is transferred from the feed gas stream to be cooled to the expanded first partial stream. The cooling system is characterized in that the cooling circuit further comprises an ejector having a suction inlet connected to the first junction line for receiving the expanded first partial stream and a propellant inlet connected to a second junction line which branches off from the refrigerant line for receiving a second partial stream, wherein the ejector is configured to, upon expanding the second partial stream in the ejector, compress the expanded first partial stream and merge it with the expanded second partial stream.

As described above, the feed gas stream to be cooled may comprise one or more cryogenic gases. Specifically, the feed gas stream to be cooled may comprise hydrogen. Alternatively, or additionally, the feed gas stream may comprise helium. Further, the feed gas stream may comprise oxygen and or other cryogenic gases. Further, the refrigerant stream may also comprise one or more cryogenic gases. Specifically, the refrigerant stream may comprise hydrogen or helium or neon. Alternatively, or additionally, the refrigerant stream may comprise a mixture of gases, i.e. a mixture of the previously mentioned gases, e.g. a mixture of neon and helium.

The heat exchanger may be configured to transfer cooling energy from the expanded first partial stream to the feed gas stream to be cooled such that the feed gas stream is cooled to a

temperature below its critical temperature so as to provide a liquid product stream. The cooling may be performed in such a way that a two-phase region is reached by isenthalpic expansion. More specifically, the cooling may be performed in such a way that the feed gas stream, after isenthalpic expansion into the product storage tank, may be provided in the form of a subcooled or at least saturated liquid. For example, in case the feed gas stream comprises hydrogen, the feed gas stream may be cooled to a temperature of at least 33 K. The temperature of 33 K may be the critical point of the feed gas stream comprising hydrogen. Thus, in order to have phase separation, the feed gas stream may be cooled to a temperature below 33 K.

The cooling system may further comprise a compressor and/or ejector unit configured to compress an expanded refrigerant stream output by the ejector and formed by merging the compressed first partial stream with the expanded second partial stream so as to provide the refrigerant stream, and wherein the compressor and/or ejector unit takes both streams back to at least one compressor device, e.g. piston compressor, in case the cooling cycle is a closed cooling cycle.

A second heat exchanger may be provided which is configured to transfer heat between the expanded refrigerant stream and the first partial stream and particularly the feed gas stream.

The cooling system may further comprise a second expansion device, particularly a Joule- Thomson-valve and/or an expansion turbine, arranged upstream of the ejector. The second expansion device may be configured to partially expand the second partial stream flowing through the second junction line. In a further development, the cooling system may comprise at least one third expansion device configured to expand at least one third partial stream flowing through at least one third junction line which branches off from the refrigerant line at different temperature levels. In addition, at least one third heat exchanger may be provided for transferring heat between the at least one expanded third partial stream and the first partial stream and particularly the feed gas stream. Further, at least one supply line may be arranged downstream of the at least one third heat exchanger for feeding the at least one expanded third partial stream to the expanded refrigerant stream. Alternatively, or additionally, the cooling system may further comprise a gas liquid separator arranged downstream of the first expansion device and configured to receive the first partial stream and to store the refrigerant of the first partial stream in a liquid and gaseous phase. An ejector supply line may be provided for guiding the expanded first partial stream in a liquid phase from the separator to the suction inlet of the ejector. Prior to being supplied to the ejector, the liquid feed gas stream may be evaporated. In the further development, the cooling system may further comprise a closed precooling cycle for precooling the refrigerant stream of the cooling cycle, wherein the closed precooling cycle has a further refrigerant stream comprising or consisting of nitrogen, a fourth expansion device for expanding the further refrigerant stream, and a fourth heat exchanger configured to transfer heat between the expanded further refrigerant stream and the refrigerant stream and particularly the feed gas stream.

Brief description of the drawings

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:

Figure 1 is a schematic thermodynamic process diagram illustrating an industrial hydrogen liquefaction plant with a cooling system which uses a cooling method according to an embodiment of the present invention: and

Figure 2 is a schematic thermodynamic process diagram illustrating a further industrial hydrogen liquefaction plant with a cooling system which uses the cooling method according to a further embodiment of the present invention.

Detailed description of preferred embodiments

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 description thereof may be omitted in order to avoid redundancies.

Figure 1 illustrates a process design for an industrial hydrogen liquefaction plant for hydrogen liquefaction on a large-scale. The depicted industrial hydrogen liquefaction plant comprises a hydrogen cooling and liquefaction unit 10, to which a feed gas stream 12 comprising hydrogen is supplied. Upon flowing through the hydrogen cooling and liquefaction unit 10, the hydrogen feed gas stream 12 is cooled and thereby liquefied so as to generate a liquid product stream 14. In order to provide cooling energy for cooling and liquefaction of the hydrogen gas stream, the industrial hydrogen liquefaction plant is thermally coupled to a cooling system 16 comprising a precooling cycle 18 and a main cooling cycle 20 in form of closed-loop refrigeration cycles. The precooling cycle 18 and the main cooling cycle 20 may be provided in one or two separate vacuum insulated cold-box vessels. In the embodiment shown in figure 1 , the cooling system comprises a precooling cold-box 22 and a main cooling cold-box 24.

At first, the main cooling cycle 20 is described in more detail. In the main cooling cycle 20, a refrigerant comprising a cryogenic suitable gas, i. e. hydrogen, circulates, thereby successively passing a compressor unit 26, the precooling cold-box 22 and the main cooling cold-box 24. Prior to entering the precooling cold-box 22, the refrigerant is compressed to high pressure, thereby providing a refrigerant stream 28 flowing through a refrigerant line 30 with a pressure typically below 30 bar, e.g. 10 bar, but may also have a pressure up to 70 bar or at least 25 bar and particularly with an ambient temperature, e.g. 303 K. In general, proper operation may be ensured as soon as the refrigerant is compressed to a level allowing for enough enthalpy removal in the further process. In some configurations, this may be achieved at a pressure level of 10 bar. The higher the pressure level of the refrigerant, the higher the heat removal in the turbine, but at the same time, heat exchangers grow in thickness, which may affect their efficiency.

Thereafter, the refrigerant stream 28 is guided through the precooling cold-box 22, where it is precooled to a lower precooling temperature of, e.g. at most 100 K and preferably 80 K. Also, the precooling temperature may be 1 15 K, for example, when the cooling energy for precooling the refrigerant stream 28 is provided by means of a liquid natural gas (LNG) as a cooling fluid. If temperature of the refrigerant is kept above 80 K and the refrigerant comprises hydrogen, then additional effort may be required for the purification of the hydrogen prior to entering into the cold- box 24, since impurities may freeze out in the heat exchanger.

Upon flowing through the main cooling cold-box 24, the refrigerant stream 28 is divided into a first partial stream 32 flowing through a first junction line 34 and a second partial stream 36 flowing through a second junction line 38. In the first junction line 34, the first partial stream 32 is expanded in a first expansion device 40, i.e. through a Joule-Thomson throttle valve, and thereby cooled. In this way, the high pressure first partial stream 32 is processed so as to generate a low pressure expanded first partial stream with a pressure particularly between 1 ,1 bar to 8 bar and a temperature sufficiently low to ensure a proper cooling of the feed gas stream 12, e.g. between 20 K and 24 K. Thereafter, the expanded first partial stream is supplied to a gas liquid separator 44 arranged downstream of the first expansion device 40 and configured to store the refrigerant in a liquid and gaseous phase. From the separator 44, a liquid expanded first partial stream 42, i.e. the expanded first partial stream 32 comprising hydrogen in a liquid phase, is guided through a first heat exchanger 46.

Specifically, the first heat exchanger 46 is provided in form of a plate-fin heat exchanger through which both the feed gas stream 12 and the expanded first partial stream 42 in its liquid phase are guided. Accordingly, the first heat exchanger 46 is configured to transfer cooling energy from the expanded first partial stream 42 to the feed gas stream 12 to be cooled. More specifically, cooling energy is transferred from the expanded first partial stream 42 to the feed gas stream 12 such that the feed gas stream 12 is cooled to a temperature below the critical temperature of hydrogen, particularly below 24 K, thereby ensuring that the liquid product stream 14 is output from the hydrogen cooling and liquefaction unit 10. At the same time, heat of reaction from the ortho para conversion is removed in preferably every heat exchanger passage of the liquefaction unit 10 following the absorber 104. In a further development, the ortho para conversion may be integrated into the absorber 104.

In the main cooling cycle 20, the cooling system 16 comprises an ejector 48 having a propellant inlet and a suction inlet. After passing the first heat exchanger 46, the expanded first partial stream 42 is guided to the suction inlet of the ejector 48. Further, the second partial stream 36, after being partially expanded in a second expansion device 50 comprising a throttle valve and an expansion turbine, is guided to the propellant inlet of the ejector 48. Accordingly, the suction inlet of the ejector 48 is connected to the first junction line 34 for receiving the expanded first partial stream 42 and the propellant inlet of the ejector 48 is connected to the second junction line 38 for receiving a partially expanded second partial stream 52. Additionally, for control purposes, the second partial stream 36 at least partially may be guided directly into the ejector 48 by bypassing the second expansion device 50. Compared to the expanded first partial stream 42, the partially expanded second partial stream 52 has an intermediate pressure level that is higher than the low-pressure level of the expanded first partial stream 42.

In this configuration, the ejector 48 functions as a pumping device which is driven by the partially expanded second partial stream 52 and configured to compress the expanded first partial stream 42. More specifically, the partially expanded second partial stream 52 constitutes a propellant medium which, upon flowing through the ejector 48 and due to a momentum transfer induced by the geometric configuration of the ejector 48, compresses the expanded first partial stream 42 which constitutes a suction medium. In the following, the configuration and operation of the ejector 48 is described in more detail. The ejector 48 comprises the propellant inlet for receiving the pressurized propellant that is supplied to a nozzle, i.e. a laval nozzle, communicating to a suction chamber of the ejector 48. The ejector further comprises the suction inlet which opens into the suction chamber and is configured to supply the suction fluid into the suction chamber, wherein the suction fluid has a pressure lower than a pressure of the propellant fluid supplied to the propellant inlet. The suction chamber communicates to a fluid outlet of the ejector 48 via a convergent-divergent diffuser.

In operation of the ejector 48, the pressurized propellant fluid, i.e. the partially expanded second partial stream 52 enters the propellant inlet of the ejector 48 and is then accelerated to a high velocity through the nozzle which discharges a high velocity jet stream of the fluid through the suction chamber into the convergent-divergent diffuser. As a result, a reduced pressure in the chamber is generated causing a draw in of the expanded first partial stream 42 which is entrained by and drawn into the convergent-divergent diffuser with the high velocity fluid stream. The thus combined fluid undergoes compression as it passes through a convergent inlet portion of the diffuser and, thereafter, deceleration and expansion as it passes through the divergent outlet portion of the diffuser.

In this way, upon expanding the partially expanded second partial stream in the ejector 48, the expanded first partial stream 42 is compressed and merged with the expanded second partial stream, thereby generating an expanded refrigerant stream 54 output by the ejector 48 into a recirculation line 56. In this configuration, the ejector 48 is provided such that the expanded refrigerant stream 54 output by the ejector 48 has a medium pressure level that is higher than the low pressure level of the expanded first partial stream 42 and lower than the intermediate pressure level of the partially expanded second partial stream 52.

Further, the expanded refrigerant stream 54, the first partial stream 32 and the feed gas stream 12 are guided through a second heat exchanger 58 such that heat is transferred therebetween.

Specifically, the cooling system 16 comprises the second heat exchanger 58 in form a plate-fin heat exchanger, through which the expanded refrigerant stream 54, the first partial stream 32 and the feed gas stream 12 are guided and which is configured to transfer cooling energy from the expanded refrigerant stream 54 to both the first partial stream 32 and the feed gas stream 12.

In the main cooling cycle 20, the refrigerant stream 28 is further divided, at different temperature levels, into a third partial stream 60 flowing through a third junction line 62 and a fourth partial stream 64 flowing through a fourth at junction line 65. In the third junction line 62, a third expansion device 66 is arranged which is configured to expand the third partial stream 60 so as to generate an expanded third partial stream 68. Specifically, the third expansion device 66 comprises, for example, two expansion turbines connected in series in the third junction line 62. In an alternative embodiment, the third expansion device may also comprise one or more expansion turbines connected in series and/or in parallel.

The expanded third partial stream 68 together with the expanded refrigerant stream 54, the first partial stream 32 together with the second partial stream 36, and the feed gas stream 12 are guided through a third heat exchanger 70 such that cooling energy is transferred from the expanded refrigerant stream 54 and the expanded first partial stream 68 to the first partial stream 32, the second partial stream 36 and the feed gas stream 12. Specifically, the expanded third gas stream 68 is supplied from the third expansion device 66 via a first supply line 72 to the recirculation line 56 downstream of the third heat exchanger 70. In other words, the first supply line 72 is configured to feed the expanded third partial stream 68 two the expanded refrigerant stream 54 downstream of the third heat exchanger 70.

In the fourth junction line 65, a fourth expansion device 74 is arranged which is configured to expand the fourth partial stream 64 so as to provide an expanded fourth partial stream 76. In an alternative embodiment, the liquefaction plant 10 may also comprise more or less than four junction lines, i.e. depending on the plant capacity. Specifically, the fourth expansion device 74 comprises, for example, two expansion turbines connected in series in the fourth junction line 65. Each of the expansion devices 50, 66, 74 is configured for or has the function of performing a gas expansion such that mechanical labor is removed from the respective gas stream. For doing so, the design of each expansion device 50, 66, 74 may be adapted to a capacity of the plant 10. Thus, of course, the configuration of these components may differ compared to the present design depending on the specific application. For example, each expansion device may comprise one or more expansion turbines or other expansion units which may be arranged in series and/or in parallel.

The expanded fourth partial stream 76, the first partial stream 32, the second partial stream 36, the third partial stream 60, the expanded refrigerant stream 54 and the feed gas stream 12 are guided through a fourth heat exchanger 78. The fourth heat exchanger 78 is configured to transfer cooling energy from the expanded fourth partial stream 76, the expanded third partial stream 68 and the expanded refrigerant stream 54 to the first to third partial streams 32, 36, 60 and the feed gas stream 12. Specifically, this is realized by supplying the expanded fourth partial stream 76 via a second supply line 80 from the fourth expansion device 74 to the recirculation line 56 downstream of the fourth heat exchanger 78. In other words, the second supply line 80 is configured to feed the expanded fourth partial stream 76 to the expanded refrigerant stream 54 downstream of the fourth heat exchanger 78.

The recirculation line 56 is configured to guide the expanded refrigerant stream 54 and the expanded third and fourth partial streams 68, 76 to the compressor unit 26. The compressor unit 26 comprises a piston compressor system 82 which is configured to, upon being flown through with the fluid stream flowing through the recirculation line 56, compress the expanded refrigerant stream together with the expanded third and fourth partial streams 68, 76, thereby providing the refrigerant stream 28. In this way, a closed cooling cycle is provided. Specifically, as depicted in Figure 1 , the piston compressor system 82 comprises two piston compressors. Alternatively, the piston compressors system 82 may comprise one or more piston compressors.

After being compressed by the piston compressors 82, the refrigerant stream 28 is guided through a fifth heat exchanger 84, which is fed with a cooling water stream 86. Specifically, the fifth heat exchanger 84 is configured to transfer cooling energy from the cooling water stream 86 to the refrigerant stream 28. Downstream of the fifth heat exchanger 84, the cooling water passes through a valve 88.

Upon flowing through the precooling cold-box 22, the refrigerant stream 28 is precooled by means of the closed precooling cycle 18 which has a further refrigerant stream 90 comprising or consisting of nitrogen or liquefied natural gas (LNG). Specifically, the further refrigerant stream 90 is expanded in a fifth expansion device 92 provided in form of a throttle valve prior to being successively supplied to a further gas liquid separator 94 and a sixth heat exchanger 96. Specifically, the sixth heat exchanger 96 is configured to transfer cooling energy from the further refrigerant stream 90 and the fluid flowing through the recirculation line 56 to the refrigerant stream 28 and the feed gas stream 12. By means of the further separator 94, the further refrigerant stream 90 is separated into a mainly gaseous phase and a many liquid phase, wherein the mainly liquid phase is separately guided through the sixth heat exchanger 96. The third to sixth heat exchangers 70, 78, 84 and 96 are provided in form plate-fin heat exchangers.

At the outlet of the sixth heat exchanger 96, the refrigerant stream 28 is guided through an adsorber 98 to remove impurities present in the refrigerant stream 28. In case the refrigerant stream 28 comprises or consist of LNG, the adsorber 104 may be located further downstream. Further, at the outlet of the fifth heat exchanger 84, a third supply line 100 is provided comprising a valve 102, via which gaseous refrigerant, e. g. hydrogen, for example from a storage tank, particularly a high pressure storage tank and/or a mobile storage tank, can be supplied into the refrigerant line 30. In the following, the configuration of the hydrogen cooling and liquefaction unit 10 is described in more detail. After entering the hydrogen cooling and liquefaction unit 10, the feed gas stream 12 is guided through the sixth heat exchanger 96 so as to be precooled to a lower precooling

temperature, e.g. 100 K, particularly by the precooling cycle 18. At the outlet of the sixth heat exchanger 96, residual impurities are removed from the precooled hydrogen feed gas 12 by means of adsorber vessels 104. After this feed gas purification by means of the adsorber vessels 104, the precooled feed gas stream 12 is routed back to the sixth heat exchanger 96 through a passage 106 filled with a catalyst. In this way, the precooled feed gas stream 12 is brought into contact with the catalyst being able to catalyze a conversion of ortho hydrogen to para hydrogen. Thereafter, the feed gas stream 12 successively passes the fourth, third and second heat exchangers 78, 70, 58 having integrated catalyst prior to being supplied to a sixth expansion device comprising a throttle valve 108 and a further ejector 1 10. After passing the sixth expansion device, the feed gas stream 12 is guided through the first heat exchanger 46 and a seventh expansion device 1 12 so as to generate the liquid product stream 14 having a storage pressure in the range of 1 to 3.5 bar. The thus generated liquid product stream 14 is guided to a storage tank configured to store hydrogen in its liquid and gaseous phase.

Specifically, the further ejector 1 10 has a propellant inlet for receiving the feed gas stream 12 and a suction inlet for receiving a gaseous hydrogen stream 1 14. Preferably, the gaseous hydrogen stream 1 14 is discharged from the storage tank and supplied to the suction inlet of the further ejector 1 10.

Furthermore, downstream of the adsorber vessels 104, a branch line 1 16 is provided having a throttle valve 1 18, via which at least a part of the feed gas stream 12 can be branched off and supplied to the recirculating line 56 of the main cooling cycle 20.

Figure 2 depicts a process design for an industrial hydrogen liquefaction plant for hydrogen liquefaction on a large-scale according to a further embodiment. The following description of the liquefaction plant particularly involves the differences compared to the previously described embodiment depicted in Figure 1 so as to omit a repeated description and to avoid redundancies.

As depicted in Figure 2, upon flowing through the main cooling cold-box 24, the refrigerant stream 28 is divided into the first partial stream 32 flowing through the first junction line 34 and the second partial stream 36 flowing through the second junction line 38. Prior to being branched off, the refrigerant stream 28 is guided through a seventh heat exchanger 120. The seventh heat exchanger 120 is provided such that the feed gas stream 12 is guided therethrough upstream of the sixth heat exchanger 96 and downstream of the fourth heat exchanger 78 so as to transfer heat from the feed gas stream 12 to the expanded refrigerant stream 56.

The first partial stream 32, after being branched off from the refrigerant stream 28, is successively guided through the fourth, the third and the second heat exchanger 78, 70, 58 and thereafter through an eighth heat exchanger 122 prior to being supplied to the separator 44. The eighth heat exchanger 122 is provided such that the feed gas stream 12 is guided therethrough upstream of the second heat exchanger 58 and downstream of the further ejector 1 10 so as to transfer heat from the feed gas stream 12 to the expanded refrigerant stream 56.

The second partial stream 36, after being partially expanded in a second expansion device 50, is guided through the third heat exchanger 70 and thereafter to the propellant inlet of the ejector 48. In a further development, for control purposes, the second partial stream 36 at least partially may be guided directly into the ejector 48 and/or the third heat exchanger 70 by bypassing the second expansion device 50.

Further, separate to a first suction line for supplying the liquid expanded first partial stream 42 from the separator 44 to the suction inlet of the ejector 48, a second suction line 124 is provided for supplying a gaseous expanded first partial stream 126, i.e. a part of the expanded first partial stream 32 comprising hydrogen in a gaseous phase, from the separator 44 to a further suction inlet of the ejector 48. Compared to the liquid expanded first partial stream 42, the gaseous expanded first partial stream 126 bypasses the first heat exchanger 46. The second suction line may also be provided in the configuration depicted in Figure 1 .

Upstream of the further ejector 1 10 and downstream of the first heat exchanger 46, a further branch line 128 is provided having a throttle valve 130, via which at least a part of the feed gas stream 12 can be branched off and supplied to the separator 44.

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 10 hydrogen cooling liquefaction unit

12 feed gas stream

14 liquid product stream

16 cooling system

18 precooling cycle

20 main cooling cycle

22 precooling cold-box

24 main cooling cold-box

26 compressor unit

28 refrigerant stream

30 refrigerant line

32 first partial stream

34 first junction line

36 second partial stream

38 second junction line

40 first expansion device

42 liquid expanded first partial stream

44 gas liquid separator

46 first heat exchanger

48 ejector

50 second expansion device

52 partially expanded second partial stream

54 expanded refrigerant stream

56 recirculation line

58 second heat exchanger

60 third partial stream

62 third junction line

64 fourth partial stream

65 fourth junction line

66 third expansion device

68 expanded third partial stream

70 third heat exchanger

72 first supply line

74 second expansion device

76 expanded fourth partial stream

78 fourth heat exchanger 80 second supply line

82 piston compressor system

84 fifth heat exchanger

86 cooling water stream

88 throttle valve

90 further refrigerant stream

92 throttle valve

94 further gas liquid separator

96 sixth heat exchanger

98 adsorber

100 third supply line

102 throttle valve

104 adsorber vessel

106 heat exchanger passage

108 throttle valve

1 10 further ejector

1 12 seventh expansion device

1 14 gaseous hydrogen stream

1 16 branch line

1 18 throttle valve

120 seventh heat exchanger

122 eighth heat exchanger

124 second suction line

126 gaseous expanded first partial stream 128 further branch line

130 further throttle valve

Claims

1 . Cooling method for liquefying a feed gas, comprising the steps of:

- providing a cooling cycle (20) with a refrigerant stream (28),

- dividing the refrigerant stream (28) into a first partial stream (32) and a second partial stream (36),

- expanding the first partial stream (32) in a first expansion device (40), and

- transferring cooling energy from the expanded first partial stream (42) to a feed gas stream (12) to be cooled, characterized in that the method further comprises the steps of:

- guiding the expanded first partial stream (42) to a suction inlet of an ejector (48), and

- guiding the second partial stream (36) to a propellant inlet of the ejector (48) such that, upon expanding the second partial stream (36) in the ejector (48), the expanded first partial stream (42) is compressed and merged with the expanded second partial stream.

2. Method according to claim 1 , wherein, by transferring cooling energy from the expanded first partial stream (42) to the feed gas stream (12) to be cooled, particularly by means of a first heat exchanger (46), the feed gas stream (12) is cooled to a temperature below the critical temperature of hydrogen, particularly below 24 K, so as to provide a liquid product stream (14) comprising hydrogen.

3. Method according to claim 1 or 2, wherein an expanded refrigerant stream (54) is provided by merging the compressed first partial stream with the expanded second partial stream in the ejector (48), and wherein

the method further comprises the step of guiding the expanded refrigerant stream (54) through a compressor unit (26), particularly comprising or consisting of at least one piston compressor (82), so as to compress the expanded refrigerant stream (54), thereby providing the refrigerant stream (28).

4. Method according to any one of claims 1 to 3, further comprising the step of guiding the expanded refrigerant stream (54) and the first partial stream (32) such that heat is transferred, particularly by means of a second heat exchanger (58), between the expanded refrigerant stream (54) and the first partial stream (32) and particularly the feed gas stream (12).

5. Method according to any one of claims 1 to 4, further comprising the step of partially expanding the second partial stream (36) in a second expansion device (50), particularly a Joule- Thomson-valve and/or an expansion turbine, prior to being guided to the ejector (48), and/or the step of guiding the second partial stream (36) into the ejector (48), particularly by bypassing the second expansion device (50).

6. Method according to any one of claims 1 to 5, wherein the refrigerant stream (28) is further separated into at least one third partial stream (60, 64), particularly at different temperature levels, and the method further comprises the steps of:

- expanding the at least one third partial stream (60, 64) in at least one third expansion device (66, 74), particularly in at least one expansion turbine, and

- guiding the at least one expanded third partial stream (68, 76) and the first partial stream (32) such that heat is transferred, particularly by means of at least one third heat exchanger (70, 78), between the at least one expanded third partial stream (60, 64) and the first partial stream (32) and particularly the feed gas stream (12), and

- feeding the at least one expanded third partial stream (60, 64) to the expanded refrigerant stream (54).

7. Method according to any one of claims 1 to 6, wherein the expanded first partial stream (42) is guided into a gas liquid separator (44) arranged downstream of the first expansion device (40) and configured to store the refrigerant in a liquid and gaseous phase, and wherein the expanded first partial stream (42) in a liquid phase is guided from the separator (44), particularly through the first heat exchanger (46) acting as an evaporator, to the suction inlet of the ejector (48).

8. Method according to any one of claims 1 to 7, wherein the refrigerant stream (28) is precooled by means of a closed precooling cycle (18) having a further refrigerant stream (90) comprising or consisting of nitrogen, wherein in particular the further refrigerant stream (90) is expanded in a fourth expansion device (92) prior to being supplied to a fourth heat exchanger (96) for transferring cooling energy to the refrigerant stream (28) and particularly to the feed gas stream (12).

9. Cooling system (16) for liquefying a feed gas, having a cooling circuit (20) with a refrigerant line (30) for circulating a refrigerant stream (28), wherein the cooling circuit (20) further comprises:

- an expansion device (40) configured to expand a first partial stream (32) flowing through a first junction line (34) branching off from the refrigerant line (30), and - a heat exchanger (46) for transferring cooling energy from the expanded first partial stream (42) to a feed gas stream (12) to be cooled, characterized in that the cooling circuit (20) further comprises an ejector (48) having a suction inlet connected to the first junction line (34) for receiving the expanded first partial stream (42) and a propellant inlet connected to a second junction line (38) branching off from the refrigerant line (30) for receiving a second partial stream (36), wherein the ejector (48) is configured to, upon expanding the second partial stream (38) in the ejector, compress the expanded first partial stream (42) and merge it with the expanded second partial stream.

10. Cooling system according to claim 9, wherein the heat exchanger (46) is configured to transfer cooling energy from the expanded first partial stream (42) to the feed gas stream (12) to be cooled such that the feed gas stream (12) is cooled to a temperature below the critical temperature of hydrogen, particularly below 24 K, so as to provide a liquid product stream (14) comprising hydrogen.

1 1 . Cooling system according to claim 9 or 10, wherein the cooling system further comprises a compressor unit (26) configured to compress an expanded refrigerant stream (28) output by the ejector and formed by merging the compressed first partial stream with the expanded second partial stream so as to provide the refrigerant stream (28), and wherein the compressor unit (26) comprises or consists of at least one piston compressor (82).

12. Cooling system according to any one of claims 9 to 1 1 , further comprising a second heat exchanger (58) configured to transfer heat between the expanded refrigerant stream (54) and the first partial stream (32) and particularly the feed gas stream (12).

13. Cooling system according to any one of claims 9 to 12, further comprising a second expansion device (50), particularly a Joule-Thomson-valve and/or an expansion turbine, arranged upstream of the ejector (48) and configured to partially expand the second partial stream (36) flowing through the second junction line (38), wherein particularly a bypass line is provided through which at least a part of the second partial stream (36) is guided and which is configured for bypassing the second expansion device (50) and guiding the second partial stream (36) flowing therethrough into the ejector (48).

14. Cooling system according to any one of claims 9 to 13, further comprising:

- at least one third expansion device (66, 74) configured to expand at least one third partial stream (60, 64) flowing through at least one third junction line (62, 65) which branches off from the refrigerant line (30) at different temperature levels,

- at least one third heat exchanger (70, 78) for transferring heat between the at least one expanded third partial stream (60, 64) and the first partial stream (32) and particularly the feed gas stream (12), and

- at least one supply line (72, 80) arranged downstream of the at least one third heat exchanger (70, 78) for feeding the at least one expanded third partial stream (60, 64) to the expanded refrigerant stream (54).

15. Cooling system according to any one of claims 9 to 14, further comprising:

- a gas liquid separator (44) arranged downstream of the first expansion device (40) and configured to receive the expanded first partial stream (42) and to store the refrigerant of the expanded first partial stream (42) in a liquid and gaseous phase,

- an ejector supply line for guiding the expanded first partial stream (42) in a liquid phase from the separator (44), particularly evaporated in the first heat exchanger (46), to the suction inlet of the ejector (48), and/or

- a closed precooling cycle (18) for precooling the refrigerant stream (28) of the cooling cycle (20), wherein the closed precooling cycle (18) has a further refrigerant stream (90), particularly comprising or consisting of nitrogen or liquid natural gas, a fourth expansion device (92) for expanding the further refrigerant stream (90), and a fourth heat exchanger (96) configured to transfer heat between the expanded further refrigerant stream and the refrigerant stream (28) and particularly the feed gas stream (12).