Large-scale hydrogen liquefaction by means of a high pressure hydrogen refrigeration cycle combined to a novel single mixed-refrigerant precooling

Abstract

The present invention relates to a method for liquefying hydrogen, the method comprises the steps of: cooling a feed gas stream comprising hydrogen with a pressure of at least 15 bar(a) to a temperature below the critical temperature of hydrogen in a first cooling step yielding a liquid product stream. According to the invention, the feed gas stream is cooled by a closed first cooling cycle with a high pressure first refrigerant stream comprising hydrogen, wherein the high pressure first refrigerant stream is separated into at least two partial streams, a first partial stream is expanded to low pressure, thereby producing cold to cool the precooled feed gas below the critical pressure of hydrogen, and compressed to a medium pressure, and wherein a second partial stream is expanded at least close to the medium pressure and guided into the medium pressure first partial stream.

Claims

1. A method for liquefying hydrogen, the method comprising: providing a feed gas stream comprising hydrogen, wherein said feed gas stream has a pressure of at least 15 bar(a) and an initial temperature, precooling said feed gas stream from said initial temperature to an intermediate temperature to yield a precooled feed gas stream, wherein said intermediate temperature is in the range of 85 K to 120 K, cooling said precooled feed gas stream from said intermediate temperature to a temperature below the critical temperature of hydrogen yielding a liquid product stream comprising hydrogen; wherein said precooled feed gas stream is cooled by a closed cooling cycle with a first refrigerant stream comprising hydrogen wherein said cooling cycle comprises: providing said first refrigerant stream with a first pressure, wherein said first pressure is at least 25 bar(a), separating said first refrigerant stream at least into a first partial stream and a second partial stream, expanding said first partial stream in a first expansion device to a second pressure yielding a partially expanded first partial stream, wherein said second pressure is at least 6 bar(a), guiding said partially expanded first partial stream and said second partial stream such that heat can indirectly be transferred between said partially expanded first partial stream and said second partial stream, expanding said second partial stream in a second expansion device to a third pressure yielding an expanded second partial stream, wherein said third pressure is below said second pressure, guiding said expanded second partial stream and said precooled feed gas stream such that heat can indirectly be transferred between said expanded second partial stream and said precooled feed gas stream, compressing said expanded second partial stream from said third pressure to a pressure that differs from said second pressure by not more the 10% yielding a partially expanded second partial stream, merging said partially expanded first partial stream and said partially expanded second partial stream to form a partially expanded first refrigerant stream, and compressing said partially expanded first refrigerant stream to said first pressure yielding said first refrigerant stream; and wherein said feed gas stream is precooled in said precooling by a closed precooling cycle with a second refrigerant stream, wherein said second refrigerant comprises a mixture of C.sub.1-C.sub.5 hydrocarbons or a mixture of nitrogen and C.sub.1-C.sub.5 hydrocarbons, wherein said precooling comprises: providing said second refrigerant with a fourth pressure, expanding said second refrigerant stream in an additional expansion device to a fifth pressure yielding an expanded second refrigerant stream, guiding said expanded second refrigerant stream and said feed gas stream such that heat can indirectly be transferred between the expanded second refrigerant stream and said feed gas stream, thereby cooling said feed gas stream to said intermediate temperature, and compressing said expanded second refrigerant stream to said fourth pressure in a first precooling compressor yielding said second refrigerant stream.

2. The method according to claim 1, wherein said first refrigerant stream is further separated at least into a third partial stream, and optionally a fourth partial stream, wherein said third partial stream is expanded in a third expansion device yielding a partially expanded third partial stream, and, if present, said fourth partial stream is expanded in a fourth expansion device, yielding a partially expanded fourth partial stream, said partially expanded third partial stream and said partially expanded first partial stream, and, if present, said expanded fourth partial stream, are merged to form a combined partially expanded partial stream, and said combined partially expanded partial stream and said partially expanded second partial stream are merged to form said partially expanded first refrigerant stream.

3. The method according to claim 1, wherein said first partial stream is expanded in said first expansion device to a first intermediate pressure yielding an intermediate first partial stream, said intermediate first partial stream is expanded in said first expansion device to said partially expanded first partial stream, and, prior to expansion of said intermediate first partial stream in said first expansion device, said intermediate first partial stream and said second partial stream are guided such that heat can indirectly be transferred between said intermediate first partial stream and said second partial stream.

4. The method according to claim 1, wherein said second refrigerant stream comprises four components, wherein a first component is nitrogen, a second component is methane, a third component is ethane or ethylene, and a fourth component is n-butane, isobutane, propane, propylene, n-pentane or isopentane.

5. The method according to claim 1, wherein said precooled feed gas stream is brought into contact with a catalyst being able to catalyze conversion of ortho hydrogen to para hydrogen.

6. The method according to claim 5, wherein residual impurities are removed from said precooled feed gas stream before contacting said catalyst.

7. The method according to claim 1, wherein compressing said expanded second refrigerant stream comprises: compressing said expanded second refrigerant stream in said first precooling compressor or a first compressor stage of said first precooling compressor to yield compressed second refrigerant stream at an intermediate pressure, and subjecting the compressed second refrigerant stream to intercooling to yield an intercooled second refrigerant stream, separating said intercooled second refrigerant stream into a mainly liquid second refrigerant stream and a mainly gaseous second refrigerant stream, wherein said mainly liquid second refrigerant stream is pumped to said fourth pressure, and said mainly gaseous second refrigerant stream is compressed in a second precooling compressor or a second compressor stage of said first precooling compressor to said fourth pressure, and merging said compressed mainly liquid second refrigerant and said compressed mainly gaseous second refrigerant to form said second refrigerant stream.

8. The method according to claim 7, wherein said second refrigerant stream is additionally separated into a mainly gaseous phase and a mainly liquid phase, wherein said mainly gaseous phase and said mainly liquid phase are separately expanded, and said expanded phases and said feed gas stream are separately guided such that heat can indirectly be transferred between said expanded phases and said feed gas stream.

9. The method according to claim 1, wherein said cooled feed gas stream is expanded in a further expansion device to a storage pressure and thereby further cooled.

10. The method according to claim 9, wherein said at least one turbo-expander is designed to generate mechanical or electrical energy upon expansions of the streams expanded by the respective turbo-expander.

11. The method according to claim 1, wherein said precooled feed gas stream is further compressed to a pressure above 15 bar(a).

12. The method according to claim 1, wherein said precooled feed gas stream is cooled from said intermediate temperature to a temperature below 24 K to yield said liquid product stream comprising hydrogen.

13. The method according to claim 1, wherein in guiding said expanded second partial stream and said precooled feed gas stream such that heat can indirectly be transferred between said expanded second partial stream and said precooled feed gas stream, aid precooled feed gas stream is cooled to a temperature below the critical temperature of hydrogen.

14. The method according to claim 2, wherein said cooled feed gas stream is expanded in a further expansion device to a storage pressure and thereby further cooled.

15. The method according to claim 14, wherein at least one or all of said first expansion device, said second expansion device, said third expansion device, said fourth expansion device, and said further expansion device comprise at least one turbo-expander.

16. The method according to claim 1, wherein said second refrigerant stream consists of four components, wherein a first component is nitrogen, a second component is methane, a third component is ethane or ethylene, and a fourth component is n-butane, isobutane, propane, propylene, n-pentane or isopentane.

17. The method according to claim 1, wherein said intermediate temperature is in the range of 85 K to 110 K.

18. The method according to claim 5, wherein residual impurities are removed from said precooled feed gas stream by means of an adsorber before contacting said catalyst.

19. The method according to claim 9, wherein said storage pressure is in the range of 1.0 bar(a) to 3.5 bar(a).

20. The method according to claim 9, wherein said storage pressure is in the range of 1.0 bar(a) to 2.5 bar(a).

21. The method according to claim 11, wherein said precooled feed gas stream is further compressed to a pressure up to 90 bar(a).

22. The method according to claim 11, wherein said precooled feed gas stream is further compressed to a pressure between 25 bar(a) and 60 bar(a).

23. The method according to claim 3, wherein the first expansion device comprises at least two turbo expanders, wherein the first partial stream is expanded in a first turbo-expander of the first expansion device to the intermediate pressure and further to the second pressure in a second turbo-expander of the first expansion device, wherein the guiding of the intermediate first partial stream and the second partial stream such that heat can indirectly be transferred between said intermediate first partial stream and said second partial stream occurs after expansion in said first turbo-expander and prior to expansion in said second turbo-expander.

24. The method according to claim 1, wherein the first refrigerant stream comprises at least 80 mol. % hydrogen, and the second refrigerant comprises 18 mol. % to 23 mol. % nitrogen, and/or 27 mol. % to 29 mol. % methane, and/or 24 mol. % to 37 mol. % ethane, and/or 18 mol. % to 24 mol. % isopentane or isobutane, wherein the sum of the concentrations of the components does not exceed 100 mol %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, further features and advantages of the present invention as well as preferred embodiments are described with reference to the Figures, wherein

(2) FIG. 1 shows a schematic illustration of a method according to a first embodiment of the invention;

(3) FIG. 2 shows schematic illustration of a method according to another embodiment invention, and

(4) FIG. 3 shows a schematic illustration of a method according to a further embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

(5) The present invention particularly provides a novel process design for hydrogen liquefaction on a large-scale, combining several process features to a new technically feasible and thermodynamically efficient configuration. The hydrogen feed gas cooling and liquefaction as well as the closed-loop refrigeration cycles can be installed in one or two separate cold-box vessels. Advantageously, the hydrogen feed stream can be directly cooled and liquefied to the state of saturated or even subcooled liquid by the proposed process design, with a final para-hydrogen that can be catalytically converted in the coldest plate-fin heat exchanger to contents above 99.5% para.

(6) Particularly when using two separated cold-boxes (78, 79), a precooling cold-box 78 contains the process equipment for the hydrogen feed gas 11 cooling and part of the single-mixed refrigerant cycle, namely the aluminium-brazed plate-fin heat exchanger 81 and the feed gas purification units 76,77 (adsorber vessels). The feed gas cooling from the lower precooling temperature to liquid hydrogen state is installed in a liquefier cold-box 79.

(7) The precooling duty is provided by a newly designed highly efficient single mixed-refrigerant (MR) cycle. The MR composition in this invention has been optimized for hydrogen precooling to temperatures between 90 K and 120 K, thus differentiating itself from warmer cooling temperature applications as in natural gas liquefaction. In this preferred example the MR mixture precooling is carried out down to a temperature T-PC of about 100 K.

(8) The cooling duty in the liquefier cold-box 79 is provided by a newly designed high pressure process configuration for the hydrogen cold refrigeration cycle. Normal-hydrogen with an approximate 25% para-fraction is preferably used as a refrigerant. Hydrogen with a higher para-fraction may be used as well.

(9) With this new process configuration, the cold-cycle is optimized in pressure level and cold temperature range between the LP (low pressure) streams or partial streams and the MP (medium pressure) stream or partial streams and to allow the implementation of existing process equipment for liquefaction capacities significantly higher than the state-of-the-art. This allows an appropriate shift of the respective refrigerant cooling duty and total mass flow rate of the two cycles, in order to obtain optimal compressor and expander frame-sizes, in terms of energy-efficiency and technical feasibility.

(10) The high pressure hydrogen cold-cycle is new to hydrogen liquefaction as it is specifically designed for large-scale liquefiers, particularly in combination with the Single-Mixed Refrigerant Precooling Cycle at the precooling temperature T-PC, which are significantly lower than in conventionally mixed refrigerant cycles, e.g. 100 K. Particularly, the precooling temperature level in the range 90 to 120 K is higher than in state-of-the art liquefiers e.g. 80 K. Thus, higher cold cycle cooling mass flows are required. This can be balanced by the high-pressure cold-cycle configuration.

(11) Hydrogen Cooling and Liquefaction:

(12) A normal hydrogen (25% para) feed gas stream 11 from a hydrogen production plant is fed to the liquefaction plant 100 with a feed pressure above 15 bar(a), e.g. 25 bar(a), and a feed temperature near ambient temperature, e.g. 303 K. The feed stream 11 with a mass flow rate above 15 tpd, e.g. 100 tpd, is optionally cooled down between 283 K and 308 K, e.g. 298 K, with a cooling water system 75 or air coolers before entering the precooling cold-box 78 through plate-fin heat exchanger 81.

(13) The hydrogen feed 11 is cooled in the aforementioned heat exchanger 81 to the lower precooling temperature T-PC, e.g. 100 K, by the warming-up the low pressure streams of the single mixed-refrigerant cycle 41 and the cold hydrogen refrigeration cycle (26 and 33). At the outlet of the heat exchanger 81, residual impurities are removed from the precooled hydrogen feed gas 12 to achieve a purity of typically 99.99% in the adsorber vessels (also referred to as an adsorption unit) 76, 77 by physisorption. The feed gas 12 enters the adsorption unit 76, 77 at the temperature T-PC, e.g. 100 K, which can thus be designed at about 20 K higher than in prior known hydrogen liquefier applications. This allows the start of the catalytic ortho-para conversion to be shifted to higher temperatures, e.g. 100 K, which is thermodynamically convenient.

(14) After the feed gas purification in the adsorption unit 76, 77, the precooled feed gas stream 12 is routed back to the heat exchanger through 81 the catalyst filled passages (hatched areas in FIG. 1 or 2) of the plate-fin heat exchanger 81, where the normal hydrogen (25% para) is catalytically converted to about 39% para while being cooled to T-PC, while the exothermic heat of conversion is being removed by the warming up refrigerants 42 in the heat exchanger 81.

(15) The precooled feed stream can be further compressed by cold compression, particularly up to 90 bar, more particularly up 75 bar, even more particularly to a pressure in the range of 25 bar(a) to 60 bar(a), in compressor 65. The precooled feed gas stream 12 enters the vacuum-insulated liquefier cold-box 79 with T-PC (between 90 K and 120 K, e.g. 100 K). The precooled feed stream 12 is subsequently cooled and liquefied as well as being catalytically converted to higher hydrogen para-fractions (hatched areas in FIG. 1 or 2) in plate-fin heat exchanger (82 to 90).

(16) The hydrogen gas feed stream 11 from battery-limits may be further compressed e.g. from 25 bar(a) to higher pressures, e.g. 75 bar(a), to increase process efficiency and to reduce volumetric flows and equipment sizes by means of a one or two stage reciprocating piston compressor at ambient temperature, or a one stage reciprocating piston compressor with cold-suction temperatures after precooling in the heat exchanger 81 or an ionic liquid piston compressor.

(17) Alternatively, an adiabatic ortho-para catalytic converter vessel may be used in the precooling cold box 78 to pre-convert normal-hydrogen (25%) para to a para-fraction near equilibrium in the feed gas stream 12 at the outlet of adsorber vessels 76, 77, before routing the feed gas stream 12 back to the heat exchanger 81.

(18) Detailed Description of the Single Mixed-Refrigerant Precooling Cold Cycle

(19) A low pressure mixed refrigerant stream 42 is routed through suction drum 71 to avoid that entrained liquid droplets from the warmed-up refrigerant stream arrive to the suction side of compressor of stage one 63a of the compressor 63. The MR composition and the discharge pressure of the resulting refrigerant stream 43 (particularly in the range of 10 bar(a) to 25 bar(a)), after at least one compression stage, are optimized to produce the aforementioned stream 43 with a liquid fraction after intercooling. This reduces the mass-flow of refrigerant 43 that has to be compressed in stage two 63b of the compressor 63. The intercooled refrigerant stream 43 is separated into a liquid mixed refrigerant stream 45 that is pumped to the high pressure (particularly in the range of 30 bar(a) and 70 bar(a)) and into a vapour refrigerant stream 44, which is compressed to high pressure (particularly in the range of 25 bar(a) and 60 bar(a)) by the second stage 63b of compressor 63. Both the vapour 44 and the liquid stream 45 are mixed to form a two-phase high pressure mixed-refrigerant stream 41 after compression in the compressor 63. The first vapour stream 44 may be additionally separated into a second liquid phase and a second vapour phase, wherein preferably the first liquid phase 45 and the second liquid phase are unified, pumped together to high pressure and afterwards unified with the second vapour phase before entering the precooling cold box 78. Alternatively, the low pressure mixed refrigerant stream may be compressed by more than two stages. If compression and after-cooling results in the formation of a liquid phase, additional phase separators may be arranged between the compressor stages.

(20) The two-phase high pressure mixed-refrigerant stream 41 enters the precooling cold-box 78 passing through the heat exchanger 81, where it is precooled to the lower precooling temperature of 100 K. A Joule-Thomson valve 64 expands the precooled mixed-refrigerant stream 41 to form an expanded mixed refrigerant stream 42 that is characterized by an optimized low pressure level, particularly between 1.5 bar(a) and 8 bar(a). The refrigerant mixture of the high pressure mixed refrigerant stream 41 is designed to cool down from the temperature T-PC by at least 2.5 K, e.g. 96 K, through the Joule-Thomson expansion. The mixture temperature decrease is designed to maintain a feasible temperature difference between warming up and cooling down streams in the heat exchanger 81 as well as to assure that no component freeze-out occurs in the refrigerant mixture.

(21) Additionally, the two-phase high pressure mixed-refrigerant stream 41 may be further separated into a vapour 41a and a liquid phase 41b, wherein the liquid phase 41b may be additionally pumped to a high pressure and then unified with the vapour phase 41b before entering the precooling cold box 78. Alternatively, the vapour stream 41a of the above mentioned additional separation is guided through the heat exchanger 81 and an additional heat exchanger 81a or through two separate blocks 81, 81a of heat exchanger 81 in the precooling cold-box 78, expanded in a throttle valve 64b and guided again through both exchangers or blocks 81, 81a, whereby the liquid stream 41b of the additional separation is guided through the additional heat exchanger 81a, expanded in a throttle valve 64a and guided again through the additional exchanger 81a.

(22) Also alternatively as depicted in FIG. 3, the two-phase high pressure mixed-refrigerant stream 41 may be guided through the additional heat exchanger 81a, and thereby cooled, and separated into a vapour 41a and a liquid phase 41b in a phase separator 73. The vapour stream 41a of the above mentioned additional separation is then guided through the heat exchanger 81 and an additional heat exchanger 81a or through two separate blocks 81, 81a of heat exchanger 81 in the precooling cold-box 78, expanded in a throttle valve 64b and guided again through both exchangers or blocks 81, 81a, wherein the liquid stream 41b of the additional separation is guided through the additional heat exchanger 81a, expanded in a throttle valve 64a and guided again through the additional exchanger 81a.

(23) Particularly, the vapour stream 41a may be merged after passing the heat exchanger 81 and expansion in the throttle valve 64b with the liquid stream 41b after passing the additional heat exchanger 81a and expansion in the throttle valve 64a, wherein the so merged expanded mixed-refrigerant stream is then guided through the additional heat exchanger 81a.

(24) The MR composition can be regulated and controlled by the make-up system to adapt the mixture composition to ambient conditions and changed process conditions. The mixed-refrigerant is compressed in a two-stage MR turbo-compressor with interstage water cooling to decrease power requirement.

(25) Alternatively, in a very simplified configuration, the low pressure refrigerant stream 42 can be compressed within an at least two-stage compressor 63 with inter-stage cooling, and the refrigerant composition can be designed to avoid the appearance of a liquid fraction after the first compression stage 63a. Advantageously, no liquid pumps and no phase separator are required. However, a lower efficiency is expected.

(26) Low temperature precooling is efficiently achieved with a refrigerant mixture optimized specifically for hydrogen liquefaction, wherein the refrigerant preferably contains only four refrigerant components to maintain a manageable plant makeup system. A preferred mixture composition for a precooling temperature in the range of 90 K to 100 K consists of 18 mol. % nitrogen, 27 mol. % methane, 37 mol. % ethane and 18 mol. % isopentane. Ethylene may replace the ethane component for reasons of refrigerant availability and cost. For precooling temperatures between 90 K and 100 K, iso-butane may be replaced by 1-butene, iso-pentane, propane or propylene The mixture of the mixed-refrigerant may be adapted depending on the precooling temperatures. Accordingly, the mixture may contain nitrogen, methane, ethylene, and n-butane, isobutane, propane, propylene isopentane, iso-butane and/or n-pentane for precooling temperatures between 100 K and 120 K (or higher).

(27) For precooling temperatures above 85 K, the mixture may contain nitrogen, argon, neon, methane, ethane, propane, propylene, 1-butene.

(28) Also alternatively, the hydrogen feed stream 11 may be precooled to temperatures above 120 K, wherein in this case the mixed-refrigerant preferably contains nitrogen, methane, ethylene, n-butane.

(29) For slightly higher process efficiencies, a fifth or more refrigerant mixture component(s) can be added to the refrigerant mixture: iso-butane, iso-pentane, 1-butane, argon, neon, propane or propylene for precooling temperatures between 90 K and 100 K, or n-butane, iso-butane, iso-pentane, propane, propylene or pentane for the precooling temperature T-PC, particularly above 100 K, and additionally n-pentane, for precooling temperatures above 110 K.

(30) Additionally, conventional refrigeration units (chiller), e.g. vapour compression refrigerators, operated with e.g. propane, propylene or CO2, can be placed to cool down the high pressure lines 11, 21, 41 from ambient temperature, downstream the respective water coolers 75, to increase the overall energy-efficiency of the plant. Chiller(s) can be placed in the Single Mixed-Refrigerant stream 41 and/or the Hydrogen Cold Refrigeration cycle stream 21 and/or the Feed Hydrogen stream 11.

(31) Alternatively or additionally, a liquid nitrogen (LIN) stream at e.g. 78 K, or liquid natural gas (LNG) at e.g. 120 K, can be evaporated in the heat exchanger 81 against the high pressure cooling down streams 21, 31 to provide additional cooling duty to precool the high pressure cooling down streams. The LIN stream, for instance, can reduce the cooling duty, and thus the refrigerant mass flows, to be provided by both the SMR cycle and the HP Hydrogen cycle.

(32) Detailed Description of the Main Cooling High Pressure-Hydrogen Cycle

(33) The high pressure hydrogen stream 21 with a pressure of at least 25 bar(a), particularly 30 bar(a) to 70 bar(a) enters the precooling cold-box 78 and is precooled by the warming up streams 42, 33, 26 in the heat exchanger 81 to the precooling temperature T-PC. At the inlet of the liquefier cold-box 79, this stream 21 is further precooled by the warming up streams of the cold hydrogen refrigeration cycle (33 and 26). The high pressure stream 21 is then separated in to four partial streams 22, 23, 24, 25 at different temperature levels, to generate cooling by nearly isentropic expansions (polytropic) in min. five turbine-expanders. In the illustrated example, seven turbine-expanders are employed (51 to 57) providing in total four turbine strings for the four partial streams 22, 23, 24, 25. The turbines 51 to 57 within the high-pressure process are designed with rotational speeds and frame-sizes that are industrially feasible and allow the partial recovery of process energy e.g. by the means of turbine brakes coupled with a turbo-generator to produce electricity and thus increase the total plant energy-efficiency. Alternatively, each of the above mentioned turbine strings may comprise only one turbo-expander, respectively, wherein the each partial stream is directly expanded in a single turbo-expander to a low or a medium pressure.

(34) In the preferred invention example, the high pressure hydrogen flow 21 is first separated after being cooled in a heat exchanger 82. One fraction, or partial stream (also referred to as a fourth partial stream) 25 is routed to a first turbine string (57 and 56), in which it is expanded in two-stages from high pressure to a medium pressure to form a medium pressure (fourth partial) stream 32, particularly in the range 6 bar(a) to 12.9 bar (a), more particularly in the range of 7 bar (a) to 11 bar(a), e.g. 9 bar(a), to achieve high isentropic efficiencies with moderate turbine rotational speeds. This medium pressure stream 32 provides cooling duty to the cooling down streams 12, 21.

(35) The remaining high pressure flow fraction is subsequently cooled in heat exchanger 83 to the temperature of a second turbine string 24. A further partial stream (also referred to as a third partial stream) 24 is then separated and expanded in two-stages (55 and 54) to the above-mentioned medium pressure level to form a partially expanded stream 31. This partially expanded (third partial) stream 31 is warmed up and mixed with the above-mentioned medium pressure stream 32 in order to provide additional cooling to duty to the cooling down streams 12, 21. The turbine strings for the streams 25 and 24 can, alternatively, be designed with intermediate cooling between the two expansion stages.

(36) A further remaining high pressure flow fraction, or partial stream (also referred to as the first partial stream) 23 routed to a third turbine string after being further cooled down by the warming up streams in heat exchanger(s) 85, 86. The following process feature is special to this hydrogen liquefaction process: the first partial stream 23 is expanded in turbo-expander 53 to an intermediate pressure between medium pressure and high pressure, to produce an intermediate pressure stream 29. The resulting intermediate pressure stream 29 preferably has a temperature above the critical temperature of the refrigerant, e.g. 34 K to 42 K. The intermediate pressure stream 29 is then re-warmed slightly in a further heat exchanger 88 before being expanded again in turbo-expander 52 to the medium pressure level yielding a medium pressure (first partial) stream 30. In this way, cooling with the third turbine string is generated at two different pressures (medium and intermediate pressure) and two different temperature levels. The heat exchanger enthalpy-temperature curve between the cooling down and warming up streams in a critical temperature range, e.g. 30 K to 50 K, can, hence, be matched more closely. This can reduce exergetical losses in the heat exchanger. This new process configuration is particularly beneficial for hydrogen feed cooling since: depending on the pressure, the specific isobaric heat capacity of the hydrogen feed stream possesses steep gradients in the region close to its critical temperature (particularly between 30 K and 50 K). Alternatively in an embodiment not shown, the third turbine string for the first partial stream 23 can be designed analogous to first and second turbine strings 25 and 24, with no intermediate warming-up after the first turbine, or with a slight cooling down between the expanders.

(37) The medium pressure stream 30 provides cooling duty to the cooling down streams in the heat exchangers 86 to 89 up to the temperature of turbine outlet 54, where it is mixed with the medium pressure stream 31. The mixed stream is warmed approximately to the temperature of the turbine 56 outlet (between the precooling temperature and the temperature of cooled feed stream 13 at the cold end of the heat exchanger 89, where it is further mixed with the medium pressure stream 32. The total medium pressure hydrogen flow 33 is warmed up in the heat exchangers 84 to 81 to a temperature close to ambient temperature, thereby providing additional cooling duty to the cooling down streams 11, 21, 41.

(38) The outlet temperature and pressure of turbo-expander 52 are optimized in combination with the cold-end hydrogen cycle. The temperature of the medium pressure stream 30 at the turbine outlet is the cold-end temperature T-CE. For the newly proposed high pressure cycle, optimal cold-end temperatures T-CE for the high pressure cycle are set between 28 K and 33 K, particularly between 29 K and 32 K, for a dry-gas turbine discharge and an optimal MP1 pressure level, particularly in the range of 6 bar(a) and 12.9 bar(a), more particularly between 7 bar(a) and 11 bar(a), at the outlet of the turbo-expander 52 (medium pressure level between 7 bar(a) and 11 bar(a)). The warmed-up stream 33 is mixed with the compressed low pressure stream 26 from the compressor 61 to produce a mixed stream 34. The mixed stream 34 is compressed from medium pressure level in e.g. one or preferably two parallel running 100% reciprocating piston compressors 62, or alternatively three parallel running 50% reciprocating piston compressors to the high pressure level between 30 bar(a) and 75 bar(a). Temperature T-CE, medium and high pressure levels are optimized in function of precooling temperature TPC and liquid hydrogen production rate (feed mass flow rate). Piston compressors 61 and 62 are designed with at least two intercooled stages each (three stages preferred). Alternatively, at least one 100% multi-stage turbo-compressor can be installed in the line of the mixed stream 34 for compression from medium pressure to an intermediate pressure. This has the advantage to reduce the volumetric flow before the MP to HP compression for very large liquefaction capacities or directly for MP to HP compression (high compressor blade tip speeds required). Alternatively, for cold-compression (range 80 K to 150 K), a 100% hydrogen turbo-compressor is used for MP to HP compression.

(39) Compared to prior known technology, this high pressure configuration with significantly higher turbine outlet pressure levels (medium and high) yields moderate effective volumetric flows at the suction of compressor 62, thus enabling the design of mechanically viable frame-sizes for the hydrogen piston compressor, even for very large liquefaction capacities e.g. up to 150 tpd (with two parallel compressors).

(40) Alternatively or additionally, a hydrogen high-speed turbo-compressor is installed in the line before the reciprocating compressor 62.

(41) At the cold end, the remaining high pressure hydrogen flow fraction, or partial stream (also referred to as the second partial stream) 22 in the cold-cycle provides the cooling for the final liquefaction and ortho-para conversion of the feed stream 12, 13, 14. The high pressure hydrogen refrigerant 22 is expanded from high pressure to low pressure in at least one turbine string through at least one turbo-expander e.g. 51.

(42) If the turbo-expander 51 is to be designed with a dry-gas discharge, high pressure stream 22 is expanded from high pressure to an intermediate pressure, above the critical pressure, e.g. 13 bara, or to a pressure below, e.g. in the range of 5 bar(a) to 13 bar(a), if no two-phase is to be generated within the turbine 51 or at the outlet of the turbine 51. Subsequently, the cooled stream is expanded through a Joule-Thomson throttle valve 59 into a gas-liquid separator 74. For a turbo-expander with allowed two-phase discharge, e.g. a wet expander, the high pressure stream 22 can be expanded directly to low pressure level. Alternatively, a cold liquid piston expander can be employed to expand the high pressure stream 22 directly to low pressure level into the two-phase region. In either case, the low pressure level is fixed to provide a cooling temperature of stream 26 below the feed temperature for saturated liquid (between 20 K and 24 K). The low pressure stream 26 stream is warmed-up to near ambient temperature providing cooling duty to the cooling down streams 11, 12, 21, 41 in the precooling and liquefier cold-box. The low pressure stream 26 is then compressed in one multistage reciprocating piston compressor 61 with interstage cooling.

(43) Alternatively, the warming up low pressure stream 26 may be compressed at cold suction temperatures instead at near ambient temperature. The low pressure hydrogen stream 26 is warmed up to a cold compressor suction temperature level of e.g. 100 K. This cold stream 26 is then compressed by the means of a cold reciprocating compressor. Compressor frame-size and number of stages of compressor 61 are significantly reduced. The cold compressor can be designed without gas intercoolers and aftercoolers, further reducing equipment capital cost. The medium pressure hydrogen stream 33 is warmed up in the heat exchanger 81 close to compressor 61 discharge temperature. The medium pressure stream 33 is compressed in a cold turbo-compressor or reciprocating compressor instead that at near ambient temperature. Feasible turbo-compressor stage pressure ratio is increased and volumetric flow at suction is significantly decreased at decreased suction temperature. The required number of compressor stages and the machine frame-size (investment costs) are reduced significantly.

(44) Alternatively, the reciprocating piston compressor 61 and 62 can be installed in one-casing in a multi-service reciprocating compressor machine.

(45) The hydrogen feed stream 12 is cooled by the warming up cold low pressure stream 26 down to a temperature equal to the high pressure stream 22, e.g. 29.5 K, and is catalytically converted to a para-fraction slightly below the equilibrium para-fraction. The cooled feed stream 13 is then expanded by the means of at least one turbo-expander 58 from feed pressure to an intermediate pressure e.g. 13 bar(a) or lower. Subsequently, the expanded and cooled feed stream is further expanded through the Joule-Thomson throttle valve 60 to the low pressure level that is required for final product storage pressure e.g. 2 bar(a) and particularly further cooled by the low pressure stream 26.

(46) For turbo-expanders allowing a two-phase discharge, the high pressure feed stream 13 can be directly expanded into the two-phase region to the product storage pressure e.g. 2 bar(a). For shaft power around 50 kW or above, as in large-scale liquefiers with e.g. 100 tpd capacity, a turbo-expander with energy-recovery via a turbo-generator can be employed to raise the plant energy-efficiency. Alternatively, a cold liquid piston expander can be employed to directly expand the feed stream from the intermediate pressure level, e.g. 13 bar(a), to the low pressure level near the final product storage pressure. In either case, the two-phase hydrogen feed stream 14 is finally cooled and can be further catalytically converted in the last part of plate-fin heat exchanger 91 with the aid of the warming-up low pressure cold-cycle refrigerant stream 26.

(47) With this configuration, a liquid hydrogen product stream 15 at the outlet can be generated as saturated liquid or even subcooled liquid. A final para-fraction of the liquid product stream 15 above 99.5% can be reached if desired.

(48) The method of the invention offers the following advantages:

(49) In summary: Significant decrease in specific energy demand and specific costs for the production of liquid hydrogen on a large-scale compared to prior known technologies; New process configuration combining a highly efficient Single-Mixed Refrigerant precooling cycle (precooling cold-box 78) to an optimized High-Pressure Hydrogen Claude-Cycle (liquefier cold-box 79) for large-scale hydrogen liquefaction; The new configuration combining Single-Mixed-Refrigerant technology with a High-Pressure Hydrogen Claude-Cycle reduces the total rotating equipment count of the liquefier plant compared to known concepts for large-scale hydrogen liquefaction. The resulting moderate hydrogen refrigerant volumetric flows, even at high hydrogen liquefaction capacities, enable the use of only three highly-efficient reciprocating piston compressor machines, which are based on available compression technology. The HP Hydrogen Cycle design avoids the use of more than two very large piston compressors running in parallel (high maintenance/downtimes) or the design of not yet available hydrogen compressor technologies e.g. very high-speed hydrogen turbo-compressors at ambient temperature. New refrigerant mixture for hydrogen liquefaction enabling precooling temperatures T-PC between 90 K and 120 K e.g. 100 K, which are significantly lower than in conventional mixed-refrigerant technology applications.

(50) Temperature decrease from T-PC across Joule-Thomson expansion valve is designed to maintain safety margin to the mixture melting point to avoid component freeze out. The low precooling temperature for the mixed-refrigerant combines the benefits of a high energy-efficient single mixed-refrigerant cycle with comparatively low precooling temperatures. This is beneficial because of the decreased cooling duty to be provided by the cold-cycle, thus reducing equipment size in the colder refrigeration cycle e.g. size of heat exchanger, compressor and turbine. The size of the most critical part of the plant in respect to space requirements, the liquefier cold-box, can also be reduced. HP Hydrogen Cycle configuration providing cooling at different temperature levels: Hydrogen refrigeration cycle with at least two turbine strings for the HP-MP level and at least one turbine string for the HP-LP level. New turbine configuration for turbine string 53 and 52 to provide additional cooling duty at two different pressure levels (MP1 and MP2) to match closely the temperature-enthalpy curve of the hydrogen feed stream between, particularly between 30 K and 50 K. This is important especially for the sharp increase in specific isobaric heat of capacity of the hydrogen feed stream around the critical temperature of hydrogen. For the pressure ratios and volumetric gas flows required by conventional refrigeration cycles for large-scale hydrogen liquefaction, turbo-compressors for ambient temperature suction for 100 mol. % helium and 100 mol. % hydrogen refrigerants would require complex designs with impracticable high number of compression stages per machine or very high wheel tip speeds and thus rotational speeds that are currently not feasible. Screw compressors for helium or hydrogen have a low isentropic efficiency. Reciprocating compressors are limited in frame-size principally by the maximum practicable volumetric suction flow rates. Prior known designs for hydrogen reciprocating compressors for large-scale hydrogen liquefiers with e.g. up to 150 liquefaction capacity, would require three or more very large reciprocating piston compressors with among the largest available frame-sizes, and thus footprint, to operate in parallel e.g. 3100% or 4100%. This would be an unfavourable design in terms of investment costs, plant maintainability, reliability and availability. Industrial gas plants with reciprocating compressors that require favourable turndown capabilities as well as economically feasible investment and operating costs (plant availability), are typically designed with reciprocating compressors in a 2100% configuration. Hydrogen cycle HP-MP and HP-LP pressure and temperature levels in this new configuration are optimized for the design of mechanically feasible and highly-efficient compressor frame-sizes for hydrogen. In this way, hydrogen compressor 62 can be designed with two parallel running highly-efficient reciprocating compressors, 2100%, even for liquefaction capacities in the range of ten to thirty times the current largest plants e.g. 150 tpd. HP level of the hydrogen refrigeration cycle effectively reduces the frame-size of hydrogen turbo-expanders 51 to 56. This enables the implementation of available and highly-efficient hydrogen high-speed turbo-expanders even for liquefaction capacities >50 tpd e.g. turbines with gas bearings. The low melting point of normal-hydrogen refrigerant (14 K) allows the cooling down and liquefaction of the feed stream. Compared to prior known technologies for large-scale liquefaction, adopting neon or neon-mixtures as sole cold-cycle refrigerant, para-fractions above 99.5% and a subcooling of the liquid hydrogen feed stream can be reached. A cold-cycle compression for compressor(s) 61 and 62 can be performed at cryogenic suction temperatures alternatively to the state-of-the-art warm suction compression. This configuration would further reduce hydrogen compressor frame sizes and number of required stages. Compared to neon and helium, the cost of hydrogen refrigerant is currently significantly lower than the cost of neon or helium refrigerants. For hydrogen liquefaction, a higher thermodynamic efficiency can typically be achieved by pure hydrogen or hydrogen-rich cycles compared to refrigeration cycles based on 100 mol. % neon or 100% mol. helium refrigerant, Innovative possibility to apply new highly efficient ionic compression technology to hydrogen liquefaction e.g. for hydrogen feed compressor, alternatively to state-of-the-art hydrogen piston compressors. Start of the continuous catalytic ortho-para conversion in plate-fin heat exchanger, e.g. directly after the MR precooling, is designed at a higher temperature level, e.g. 100 K, compared to prior known technology. (80 K) Due to the removal of exothermic heat of conversion at a higher temperature level, the thermodynamic efficiency of the plant is improved. This can be realized by installing an adsorption unit at 100 K or higher. The adsorption vessel (physisorption) removes residual impurities from the hydrogen feed which can poison the catalyst and block the feed stream.

REFERENCE NUMERALS

(51) TABLE-US-00001 100 hydrogen liquefaction plant 11 hydrogen feed stream (25 bar(a), ambient temperature) 12 precooled hydrogen feed stream (100 K, 25 bar(a)) 13 cooled hydrogen feed stream (27 K to 35 K) 14 expanded cooled hydrogen feed stream (2 bar(a)) 15 Liquid hydrogen product stream 21 high pressure stream 22 high pressure second partial stream 23 high pressure first partial stream 24 high pressure third partial stream 25 high pressure fourth partial stream 26 low pressure second partial stream 27 vapour phase of low pressure first partial stream 28 liquid phase of low pressure first partial stream 29 intermediate pressure first partial stream 30 medium pressure first partial stream 31 medium pressure third partial stream 32 medium pressure fourth partial stream 33 combined medium pressure stream 34 further combined medium pressure stream 35 medium pressure second partial stream 41 high pressure mixed refrigerant stream 41a vapour phase of high pressure mixed refrigerant stream 41b Liquid phase of high pressure mixed refrigerant stream 42 low pressure mixed refrigerant stream 43 medium pressure mixed refrigerant stream 44 vapour phase of medium pressure mixed refrigerant stream 45 liquid phase of medium pressure mixed refrigerant stream 51, 52, 53, 54, turbo-expander 55, 56, 57, 58 59, 60, 64, 64a, throttle valve 64b 61 piston compressor 62 piston compressor 63a first compressor stage 63b second compressor stage 71 suction drum 72, 73, 74 phase separator 75 water cooling 76, 77 adsorber vessel 78 pre cooling cold box 79 liquefier cold box 81, 82, 83, 84, heat exchanger block or heat exchanger filled with 85, 86, 87, 88, ortho-para catalyst (hatched area) 89, 90, 91