The present invention relates to improved refrigerant compositions and methods for liquefying gaseous streams, particularly gaseous streams consisting of or comprising hydrogen or helium.

The demand for liquid hydrogen production for e.g. clean energy applications is rapidly increasing. Thus, a significant upscaling of industrial hydrogen liquefiers is required to step up from the current largest state-of-the-art plants with a capacity in the range of 5 tpd to 10 tpd (upscaling factor 10 to 20). New large-scale hydrogen liquefaction plants with production capacities of, for instance, up to 150 tpd will require thermodynamically and economically efficient process designs. Specific energy consumption, and thus operational costs, has to be significantly reduced compared to state-of-the art plant and prior concepts, while limiting additional capital expenditures as well as utilizing process equipment and technology available today.

In current industrial hydrogen liquefiers, the hydrogen feed stream is precooled from ambient temperature to approximately 80 K by evaporating a liquid nitrogen stream at typically about 78 K. Liquid nitrogen is supplied, for example, from an onsite air separation unit, a nitrogen reliquefier or by liquid trailers. This plant design is economically effective for small to medium scale liquefiers. However, for higher liquefaction capacities, the liquid nitrogen stream supplied as a refrigerant will significantly increase the plant operating costs, thus reducing sharply the cost effectiveness of liquid hydrogen production.

In order to increase the energy-efficiency of the hydrogen feed precooling, closed loop refrigeration cycles can be designed for medium and large-scale liquefiers. Currently known conceptual designs for precooling cycles in hydrogen liquefiers show, however, deficiencies in either energy-efficiency, capital costs and/or process complexity e.g. rotating equipment count, refrigerant make-up system. Up to now, this has been a major limiting factor for upscaling hydrogen liquefaction plants from current maximum single train production rates.

Closed-loop nitrogen expander cycles as proposed in Ohlig et al. (“Hydrogen, 4. Liquefaction” Ullmanns's Encyclopedia of Industrial Chemistry, edited by F. Ullmann, Wiley-VCH Verlag, 2013) can reach precooling temperatures around or below 80 K, but are characterized by a relatively high number of additional rotating machines and a significantly lower thermodynamic efficiency compared to mixed-refrigerant cycles.

Currently, known mixed-refrigerant cycles, (U.S. Pat. No. 4,033,735, U.S. Pat. No. 5,657,643 and Bauer (StarLNG™: a Family of Small-to-Mid-Scale LNG Processes, Conference paper, 9th Annual Global LNG Tech Summit 2014: March 2014) for large industrial gas cooling processes, such as natural gas, can increase precooling efficiency but are designed for relatively high precooling temperatures, typically above 120 K, thus shifting the generation of the required cooling duty to the colder, more inefficient refrigeration cycle in a hydrogen liquefier. Additionally, prior conceptual designs for hydrogen liquefiers, such as in the IDEALHY study (2012, http://www.idealhy.eu), have proposed precooling refrigerant mixtures with a comparatively high number of fluid components (5 or more). In contrast to natural gas processing sites, these refrigerants have to be regularly imported to potential hydrogen liquefaction plant sites for inventory make-up and typically require additional storage vessels for each component, thus increasing operational complexity and handling.

Thus, it is the objective of the present invention to provide improved refrigerant compositions and a method for efficiently and economically liquefying gas streams, particularly suitable for large scales.

This objective is attained by the refrigerant composition according to claim1and the method according to claim11.

According thereto, a refrigerant composition is provided, wherein the composition comprises an inert gas selected from nitrogen, argon, neon and a mixture thereof, and a mixture of at least two C1-C5hydrocarbons. The refrigerant composition comprises four components, wherein a first component is nitrogen or nitrogen in a mixture with neon and/or argon, a second component is methane or argon, a third component is ethane or ethylene, and a fourth component is one of n-butane, isobutane, 1-butene, propane, propylene, n-pentane and isopentane.

The refrigerant composition of the invention is particularly useful for refrigerants that are designed to cool fluid streams from ambient temperature to lower temperatures in the range of 80 K to 125 K. This is achieved by pressurizing such refrigerants and expanding under cooling of the refrigerant, particularly to the above-mentioned temperature range, thereby producing cold. Particularly, such refrigerants may advantageously be used as precooling refrigerants in processes such as the liquefactions of gases such as hydrogen.

In certain embodiments, the refrigerant composition comprises an inert gas selected from nitrogen and nitrogen in a mixture with argon and/or neon, and further comprises a mixture of at least two C1-C5hydrocarbons.

In certain embodiments, the C1-C5hydrocarbon is selected from the group comprised of methane, ethane, ethylene, n-butane, isobutane, propane, propylene, n-pentane, isopentane and 1-butene.

In certain embodiments, the refrigerant composition comprises or consists of four components, wherein a first component is nitrogen, or nitrogen in a mixture with neon and/or argon, a second component is argon or methane, a third component is ethane or ethylene, and a fourth component is n-butane, isobutane, 1-butene, propane, propylene, n-pentane or isopentane.

In certain embodiments, the refrigerant composition comprises a fifth component, wherein the fifth component is argon, neon, n-butane, isobutane, 1-butene, propane, propylene, n-pentane or isopentane, provided that the fifth component is different from the fourth component or the second component, e.g. the fifth component can be n-butane, isobutane, propane, propylene or n-pentane if the fourth component is isopentane.

In certain embodiments, the refrigerant composition comprises a sixth component, wherein the sixth component is argon, neon, n-butane, isobutane, 1-butene, propane, propylene, n-pentane or isopentane, provided that the sixth component is different from the second component, the fourth component and fifth component, e.g. the sixth component can be isobutane, propane, propylene or n-pentane if the fourth component is isopentane and the fifth component is n-butane.

The refrigerant composition of the invention can be adapted depending on the designed precooling temperatures. Also, the refrigerant composition can be monitored and regulated by the plant make-up system in order to adapt the mixture composition to changing ambient and process conditions.

In certain embodiments, the first component is nitrogen, the second component is methane, the third component is ethane or ethylene, and the fourth component is isobutane, n-butane, isopentane or n-pentane. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is in the range 100 K and 120 K, and higher.

In certain embodiments, the third component is ethane. Such composition of the refrigerant of the invention is particularly useful if the intermediate temperature to be achieved in the precooling step is below or equal to approx. 100 K (±5 K). In certain embodiments, third component is ethylene. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is above approx. 100 K (±5 K).

In certain embodiments, the fourth component, and optionally the fifth component, is isobutane, 1-butene, propane, propylene or isopentane, provided that the fifth component is different from the fourth component. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is below approx. 100 K (±5 K).

In certain embodiments, the refrigerant composition comprisesnitrogen in the range of up to 25 mol. %, and,methane in the range of up to 40 mol. %, and,ethane or ethylene in the range of up to 45 mol. %, and1-butene, n-butane, isobutane, n-pentane or isopentane in the range of up to 35 mol. %, or propane or propylene in the range of up to 45 mol. %,
provided that the sum of the above concentrations does not exceed 100 mol. %.

In certain embodiments, the refrigerant composition comprisesnitrogen in the range of 5 mol. % to 25 mol. %, and,methane in the range of 20 mol. % to 40 mol. %, and,ethane or ethylene in the range of 10 mol. % to 45 mol. %, and1-butene, n-butane, isobutane, n-pentane or isopentane in the range of 10 mol. % to 35 mol. % or propane or propylene in the range of 10 mol. % to 45 mol. %,
provided that the sum of the above concentrations does not exceed 100 mol. %.

In certain embodiments,the first component is nitrogen, particularly in the range of 5 mol. % to 25 mol. %, more particularly in the range 8 mol. % to 18 mol. %,the second component is methane, particularly in the range of 20 mol. % to 40 mol. %, more particularly in the range 30 mol. % to 36 mol. %,the third component is ethane or ethylene, particularly ethylene, particularly in the range of 20 mol. % to 45 mol. %, more particularly in the range 28 mol. % to 35 mol. %, andthe fourth component is n-butane, isobutane, propane, propylene, n-pentane or isopentane, particularly n-butane or n-pentane preferably:n-butane or isobutane in the range 10 mol. % to 35 mol. %, more particularly in the range 22 mol. % to 28 mol. %, orn-pentane or isopentane in the range 10 mol. % to 30 mol. %, more particularly 15 mol. % to 25 mol. %.

Such compositions of the refrigerant of the invention are particularly useful if the cooling temperature to be achieved with the refrigerant is between 100 K and 120 K, particularly between 100 K and 110 K.

In certain embodiments, the refrigerant composition consists of 11 mol. % nitrogen, 33 mol. % methane, 31 mol. % ethane and 25 mol. % n-butane. In certain embodiments, the refrigerant composition consists of 12 mol. % nitrogen, 32 mol. % methane, 31 mol. % ethane and 25 mol. % n-butane. In certain embodiments, the refrigerant composition consists of 14 mol. % nitrogen, 32 mol. % methane, 29 mol. % ethane and 25 mol. % isobutane. In certain embodiments, the refrigerant composition consists of 16 mol. % nitrogen, 31 mol. % methane, 27 mol. % ethane and 26 mol. % isobutane. In certain embodiments, the refrigerant composition consists of 10 mol. % nitrogen, 33 mol. % methane, 41 mol. % ethane and 16 mol. % pentane. In certain embodiments, the refrigerant composition consists of 11 mol. % nitrogen, 32 mol. % methane, 38 mol. % ethane and 19 mol. % isopentane. Such compositions of the refrigerant of the invention are particularly useful the cooling temperature to be achieved with the refrigerant is between 100 K and 120 K.

In certain embodiments,the first component is nitrogen, particularly in the range 10 mol. % to 30 mol. %, more particularly in the range 15 mol. % to 25 mol. %,the second component is methane, particularly in the range 20 mol. % to 40 mol. %, more particularly in the range 28 mol. % to 35 mol. %,the third component is ethane or ethylene, particularly in the range of 10 mol. % to 40 mol. %, more particularly in the range 23 mol. % to 36 mol. %, andthe fourth component is isobutane, 1-butene, propane, propylene or isopentane, particularly isobutane or isopentane. preferably:isobutane in the range 10 mol. % to 30 mol. %, more particularly in the range 21 mol. % to 28 mol. %, orisopentane in the range 10 mol. % to 25 mol. %, more particularly in the range 15 mol. % to 22 mol. %, orpropane in the range 20 mol. % to 40 mol. %, more particularly 30 mol. % to 40 mol. %.

In certain embodiments,the first component is nitrogen, in the range of up to 30 mol. %,the second component is methane, in the range of up to 40 mol. %,the third component is ethane or ethylene, in the range of up to 40 mol., andthe fourth component is isobutane, 1-butene, propane, propylene or isopentane, particularly isobutane or isopentane. preferably:isobutane in the range of up to 30 mol. %, orisopentane in the range of up 25 mol. %, orpropane in the range of up to 40 mol.

Such compositions of the refrigerant of the invention are particularly useful if the cooling temperature to be achieved with the refrigerant is between 90 K and 100 K

In certain embodiments, the refrigerant composition consists of 22 mol. % nitrogen, 30 mol. % methane, 24 mol. % ethane and 24 mol. % isobutane. In certain embodiments, the refrigerant composition consists of 17 mol. % nitrogen, 33 mol. % methane, 24 mol. % ethane and 26 mol. % isobutane. In certain embodiments, the refrigerant composition consists of 18 mol. % nitrogen, 29 mol. % methane, 36 mol. % ethane and 17 mol. % isopentane. In certain embodiments, the refrigerant composition consists of 18 mol. % nitrogen, 27 mol. % methane, 37 mol. % ethane and 18 mol. % isopentane. In certain embodiments, the refrigerant composition consists of 23 mol. % nitrogen, 30 mol. % methane, 12 mol. % ethane and 35 mol. % propane. Such compositions of the refrigerant of the invention are particularly useful if the cooling temperature to be achieved with the refrigerant is between 90 K and 100 K.

In certain embodiments, the refrigerant composition comprisesnitrogen, in the range of up to 35 mol. %, and,argon, in the range of up to 40 mol. %, and,ethane or ethylene, in the range of up to 40 mol. %, and,isobutane, isopentane or 1-butene in the range of up to 35 mol. %, or propane or propylene in the range of up to 45 mol. %,
provided that the sum of the above concentrations does not exceed 100 mol. %.

In certain embodiments, the refrigerant composition comprisesnitrogen, particularly in the range of 5 mol. % to 35 mol. %, and,argon, particularly in the range of 20 mol. % to 40 mol. %, and,ethane or ethylene, particularly in the range of 10 mol. % to 40 mol. %, and,isobutane, isopentane or 1-butene (preferably in the range of 10 mol. % to 35 mol. %), or propane or propylene (preferably in the range of 10 mol. % to 45 mol. %),
provided that the sum of the above concentrations does not exceed 100 mol. %.

In certain embodiments,the first component is nitrogen, particularly in the range 5 mol. % to 25 mol. %, more particularly in the range 10 mol. % to 15 mol. %,the second component is argon, particularly in the range 20 mol. % to 40 mol. %, more particularly in the range 30 mol. % to 40 mol. %,the third component is ethane or ethylene, particularly in the range 20 mol. % to 40 mol. %, more particularly in the range 30 mol. % to 40 mol. %, andthe fourth component is isobutane or isopentane, particularly in the range 10 mol. % to 30 mol. %, more particular in the range 15 mol. % to 25 mol. %.

Such compositions of the refrigerant of the invention are particularly useful if the cooling temperature to be achieved with the refrigerant is between 90 K and 100 K.

In certain embodiments,the first component is nitrogen, particularly in the range 10 mol. % to 35 mol. %, more particularly in the range 18 mol. % to 25 mol. %,the second component is methane, particularly in the range 20 mol. % to 40 mol. %, more particularly in the range 28 mol. % to 34 mol. %,the third component is ethane, particularly in the range 5 mol. % to 35 mol. %, more particularly in the range 20 mol. % to 27 mol. %, andthe fourth component is 1-butene, propane or propylene, particularly1-butene in the range 10 mol. % to 35 mol. %, more particularly in the range 20 mol. % to 28 mol. %, orpropane in the range 10 mol % to 45 mol. %, more particularly 30 mol. % to 40 mol. %.

Such compositions of the precooling refrigerant are particularly useful if the cooling temperature to be achieved with the refrigerant is between 85 K and 90 K.

In certain embodiments, the refrigerant composition consists of 20 mol. % nitrogen, 30 mol. % methane, 26 mol. % ethane and 24 mol. % 1-butene. In certain embodiments, the refrigerant composition consists of 20 mol. % nitrogen, 30 mol. % methane, 24 mol % ethane and 26 mol. % 1-butene. In certain embodiments, the refrigerant composition consists of 22 mol. % nitrogen, 29 mol. % methane, 11 mol. % ethane and 38 mol. % propane. Such compositions of the refrigerant of the invention are particularly useful if the cooling temperature to be achieved with the refrigerant is between 80 K and 90 K.

In certain embodiments,the first component is nitrogen, particularly in the range 10 mol. % to 35 mol. %, more particularly in the range 10 mol. % to 20 mol. %,the second component is argon, particularly in the range of 20 mol. % to 40 mol. %, more particularly in the range of 30 mol. % to 40 mol. %,the third component is ethane, particularly in the range 5 mol. % to 35 mol. %, more particularly in the range 20 mol. % to 27 mol. %, andthe fourth component is 1-butene, propane or propylene, particularly1-butene in the range 10 mol. % to 35 mol. %, particularly in the range 20 mol. % to 28 mol. %, orpropane in the range 10 mol. % to 45 mol. %.

Such compositions of the refrigerant of the invention are particularly useful if the cooling temperature to be achieved with the refrigerant is between 80 K and 90 K.

In certain embodiments, the refrigerant composition consists of 12.5 mol. % nitrogen, 38 mol. % argon, 25.5 mol. % ethane and 24 mol. % 1-butene. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is between 80 K and 90 K, particularly between 85 K to 90 K.

In certain embodiments, the first component is nitrogen in a mixture with neon and/or argon, the second component is methane, the third component is ethane or ethylene, and the fourth component is n-butane, isobutane, i-butene, propane, propylene, n-pentane or isopentane. Such composition of the precooling refrigerant is particularly useful if the intermediate temperature to be achieved in the precooling step is below 100 K.

In certain embodiments, the refrigerant composition comprises10 mol. % to 23 mol. % nitrogen, and,27 mol. % to 33 mol. % methane, and,11 mol. % to 38 mol. % ethane, and,16 mol. % to 30 mol. % n-butane, isobutane, isopentane, 1-butene or isobutane, or 20 mol. % to 40 mol. % propane,
provided that the sum of the concentrations of the above-mentioned components does not exceed 100 mol %.

In certain embodiments, the refrigerant composition 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, provided that the sum of the concentrations of the abovementioned components does not exceed 100 mol %. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is around 100 K.

In certain embodiments, the refrigerant composition consists of 18 mol. % nitrogen, 27 mol. % methane, 37 mol. % ethane and 18 mol. % isopentane. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is around 100 K.

In certain embodiments, the refrigerant composition consists of 23 mol. % nitrogen, 29 mol. % methane, 24 mol. % ethane and 24 mol. % isobutane. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is around 100 K.

In certain embodiments, the refrigerant composition consists of 22 mol. % nitrogen, 29 mol. % methane, 28 mol. % ethane, 12 mol. % isobutane and 9 mol. %) isopentane. Such composition of the refrigerant of the invention is particularly useful if the cooling temperature to be achieved with the refrigerant is around 100 K.

According to a further aspect of the invention, the use of the refrigerant composition of the invention, particularly as a precooling refrigerant, in the liquefaction of a gaseous substance is provided.

In certain embodiments, the gaseous substance is selected from the group comprised of hydrogen and helium.

According to another aspect of the invention, a method for liquefaction of a feed gas stream is provided. The method comprises the steps of:providing a feed gas stream comprising a gas, wherein the feed gas stream is characterized by an initial temperature,precooling the feed gas stream from the initial temperature to an intermediate temperature in a precooling step by a closed precooling cycle with a precooling refrigerant yielding a precooled feed gas stream,cooling the precooled feed gas stream in a cooling step from the intermediate temperature to a temperature equal or below the boiling temperature or the critical temperature of the gas,
wherein the precooling refrigerant stream, comprises or consists of the refrigerant composition of the invention.

The term boiling temperature refers to the temperature at which the gas liquefies or begins to liquefy. The boiling temperature is dependent on the pressure of the gas.

In certain embodiments, the feed gas is selected from hydrogen and helium. The feed gas may comprise hydrogen. The feed gas may comprise helium.

In certain embodiments, the feed gas stream consists of hydrogen or helium.

Particularly, if the gas to be liquefied is hydrogen, ortho hydrogen comprised within the feed gas stream (typically about 75%) is preferably converted to higher para hydrogen fractions preferably before liquefaction of the feed gas stream to avoid that the exothermic ortho to para reaction takes place in the liquid product possibly resulting in an undesired partial vaporization of the liquid hydrogen product during storage and transport.

In certain embodiments, the precooled feed gas stream is cooled from the intermediate temperature to a temperature below the boiling temperature or the critical temperature of the gas by at least a first closed cooling cycle with a first cooling refrigerant, particularly in a first cooling zone, wherein the first cooling refrigerant is expanded, thereby producing cold.

In certain embodiments, the first refrigerant comprises or consists of hydrogen and/or helium.

In certain embodiments, the first refrigerant is provided with a high pressure, expanded to low pressure in an expansion device. The expansion device is preferably: a turbo expander, a throttle valve or a turbo expander and a throttle valve. The expanded first refrigerant and the precooled feed gas stream may be guided such that heat can indirectly be transferred between the expanded first refrigerant and the precooled feed gas stream, thereby preferably cooling the precooled feed gas stream below the boiling temperature or the critical temperature of the gas comprised within the feed gas stream. The expanded refrigerant may be compressed to high pressure yielding the first refrigerant.

In certain embodiments, the precooled feed gas stream is cooled from the intermediate temperature to a first temperature by a second closed cooling cycle with a second cooling refrigerant, particularly in a second cooling zone, wherein the second cooling refrigerant is expanded, thereby producing cold, and the cooled feed gas stream is further cooled from the first temperature to the temperature below the boiling temperature or the critical temperature of the gas comprised within the feed gas stream by the first closed cooling cycle.

In certain embodiments, the second refrigerant comprises or consists of neon and/or hydrogen.

In certain embodiments, the second refrigerant is provided with an initial high pressure, and is then expanded to low pressure in: an expansion device, preferably: a turbo expander; a throttle valve; in two turbo expanders; or in a turbo expander and a throttle valve The expanded second refrigerant and the precooled feed gas stream may be guided such that heat can indirectly be transferred between the expanded second refrigerant and the precooled feed gas stream, (preferably cooling the precooled feed gas stream to the first temperature) yielding a cooled feed gas stream. The expanded second refrigerant may be compressed to high pressure yielding the second refrigerant. The cooled feed gas stream and the expanded first refrigerant stream may be guided such that heat can indirectly be transferred between the cooled feed gas stream and the expanded first refrigerant stream, thereby preferably cooling the cooled feed gas to a temperature equal to or below the boiling temperature or the critical temperature of the gas comprised within the feed gas stream.

In certain embodiments, the first cooling zone is arranged within a cooling heat exchanger or one or more blocks of the cooling heat exchanger. In certain embodiments, the second cooling zone is arranged within another cooling heat exchanger or within one or more another blocks of the aforementioned cooling heat exchanger. In certain embodiments, the cooling heat exchanger is a plate heat exchanger.

In certain embodiments, the intermediate (precooling) temperature is in the range of 80 K to 125 K. In certain embodiments, the intermediate temperature is in the range of 80 K to 120 K. In certain embodiments, the intermediate temperature is in the range of 85 K to 120 K. In certain embodiments, the intermediate temperature is in the range of 90 K to 120 K, particularly in the range 90 K to 110 K, most particularly 95 K to 105 K. In certain embodiments, the intermediate temperature is 100 K. In certain embodiments, the intermediate temperature is in the range of 120 K to 150 K.

In certain embodiments, the feed gas stream and other cooling down refrigerant streams (such the above mentioned first refrigerant stream and/or second refrigerant stream) are precooled to the intermediate temperature in a precooling zone. In certain embodiments, the precooling zone is located within an at least one precooling heat exchanger or in one or more other blocks of the abovementioned cooling heat exchanger. In certain embodiments, the at least one precooling heat exchanger is a plate heat exchanger or a coil-wound heat exchanger.

In certain embodiments, the feed gas stream comprises hydrogen and is precooled to an intermediate temperature in the range 80 K to 120 K, yielding the precooled feed gas stream, and the precooled feed gas stream is brought into contact with a catalyst being able to catalyse the ortho to para conversion of hydrogen. In certain embodiments, the catalyst is or comprises hydrous ferric oxide. In certain embodiments, the catalyst is arranged within a heat exchanger in which the feed gas stream is precooled. The catalyst may be arranged within the at least one precooling heat exchanger or the one or more blocks of the above-mentioned cooling heat exchanger.

In certain embodiments, residual impurities, particularly nitrogen, are removed from the precooled feed gas stream before contacting the precooled feed stream with the above-mentioned catalyst, particularly by means of an adsorber. In certain embodiments, an adiabatic or isothermal ortho-para catalytic converter vessel is placed directly downstream or within the adsorber, wherein normal hydrogen comprised within the feed gas stream is converted in a first step to a para-content near the equilibrium at the intermediate temperature, e.g. 39% at 100 K).

In certain embodiments, the precooling step comprises the steps of:providing the precooling refrigerant with a first pressure,expanding the precooling refrigerant stream in an expansion device to a second pressure levelyielding an expanded precooling refrigerant stream,guiding the expanded precooling refrigerant stream and the feed gas stream such that heat can indirectly be transferred between the expanded precooling refrigerant stream and the gas feed stream, thereby particularly cooling the feed gas stream, andcompressing the expanded precooling refrigerant to the high pressure level, particularly to the first pressure, in a first precooling compressor.

In the above described precooling step, the step of guiding the precooling stream and the feed gas stream may include guiding the expanded precooling refrigerant stream, the feed gas stream and other refrigerant streams (e.g. high pressure precooling refrigerant as well as other cold-cycle refrigerant streams such as the above mentioned first and second refrigerant) such that heat can indirectly be transferred between the expanded precooling refrigerant stream and the other streams, thereby particularly cooling the feed gas stream as well as other cooling down streams to the intermediate temperature.

The term “indirectly heat transfer” in the context of the present invention refers to the heat transfer between at least two fluid streams that are spatially separated such that the at least two fluid streams do not merge or mix but are in thermal contact, e.g. two fluid streams are guided through two cavities and both streams do not mix, but heat can be transferred via the wall or the plate, for example of a plate heat exchanger, wherein the cavities are separated from each other by a wall or plate.

In certain embodiments, the first pressure is in the range of 20 bar(a) to 80 bar(a), more particularly in the range of 30 bar(a) to 60 bar(a), most particularly in the range of 40 bar(a) to 60 bar(a).

In certain embodiments, the first pressure is in the range of 60 bar(a) to 75 bar(a). In certain embodiments, the second pressure is in the range of 1.1 bar(a) to 10 bar(a), more particularly in the range of 1.1 bar(a) to 8 bar(a), most particularly in the range of 2 bar(a) to 6 bar(a).

In certain embodiments, the expanded precooling refrigerant stream has a temperature in the range of 80 K to 150 K, preferably in the range of 80 k to 120 K, more preferably in the range of 90 K to 120 K, more preferably in the range of 90 K to 110 K, most preferably in the range of 95 K to 105 K. In certain embodiments, the expansion device is a throttle valve.

In certain embodiments, compressing the precooling refrigerant comprises the steps of:compressing the expanded precooling refrigerant stream in a first precooling compressor or a first compressor stage of the first precooling compressor to an intermediate pressure yielding an intercooled precooling refrigerant stream,separating the intercooled precooling refrigerant stream into a mainly liquid precooling refrigerant stream and a mainly gaseous precooling refrigerant stream, whereinthe mainly liquid precooling refrigerant stream is pumped to the high pressure level, preferably to the first pressure, andthe mainly gaseous precooling refrigerant stream is compressed in a second compressor or a second compressor stage of the first precooling compressor to the high pressure level, preferably to the first pressure, andmerging the compressed mainly liquid precooling refrigerant stream and the compressed mainly gaseous precooling refrigerant stream to form the precooling refrigerant stream.

In certain embodiments, the expanded precooling refrigerant stream is compressed in at least two compressor stages or compressors, optionally with intercooling. Alternatively, the precooling refrigerant is compressed in the two phase region after intercooling with a pump and a phase separator between the compressor stages or the compressor stages, wherein as described above liquid phases and vapour phases of the precooling refrigerant stream are separately compressed. Alternatively, all liquid phases are unified and compressed together.

The intermediate pressure is designed between the low level, particularly the second pressure, and high pressure level, particularly the first pressure. In certain embodiments, the intermediate pressure is designed such that a liquid-vapour two-phase flow is generated at the compressor discharge after intercooling. In certain embodiments, the intermediate pressure is in the range of 10 bar(a) and 30 bar(a).

In certain embodiments, the precooling refrigerant stream is additionally separated into a mainly gaseous phase and a mainly liquid phase. The mainly gaseous phase and the mainly liquid phase may be separately expanded, preferably at different temperatures levels. The mainly gaseous phase and the mainly liquid phase may be guided with the feed gas stream, particularly in separate heat exchangers or separate heat exchanger blocks. In certain embodiments, the mainly gaseous phase and/or the mainly liquid phase are expanded in a throttle valve. In certain embodiments, both vapour and liquid phase are separately guided against the feed gas stream in the precooling zone.

In certain embodiments, the feed gas stream is provided with a pressure above the critical pressure of the gas comprised within the feed gas stream. In certain embodiments, the feed gas stream is provided with a pressure in the range of 15 bar(a) to 75 bar(a). In certain embodiments, the feed gas stream is provided with a pressure in the range of 25 bar(a) to 50 bar(a).

In certain embodiments, the cooled feed gas stream is expanded in an expansion device, and is thereby cooled. In certain embodiments, the expansion device is a turbo-expander or a throttle valve. In certain embodiments, the expansion device is a combination of a turbo-expander and a throttle valve. In certain embodiments, the cooled feed gas stream is expanded in the expansion device to a storage pressure, wherein particularly the storage pressure is in the range of 1 bar(a) to 3.5 bar(a), more particularly in the range of 1.8 bar(a) to 2.5 bar(a), even more particularly equal or close to the ambient pressure.

