Liquefied hydrogen production process

Abstract

A process for liquefying hydrogen gas comprising cooling the hydrogen gas to a temperature suitable for substantially complete conversion of the ortho-hydrogen content to para-hydrogen, passing the cooled hydrogen over a catalyst that promotes substantially complete conversion of the ortho-hydrogen content to para-hydrogen and further cooling to remove the heat of reaction generated, passing the resulting stream consisting essentially of para-hydrogen, in gas or vapor form, through an expander or turbine having an outlet stream consisting of vapor and liquid, separating the outlet stream into vapor and liquid fractions, the liquid fraction constituting the liquefied hydrogen product of the process, and recycling the vapor fraction through one or more compressors having a cryogenic inlet temperature.

Description

[Technical field]

[0001] The present invention relates to a method for liquefying hydrogen gas, and in particular to a method for liquefying hydrogen gas using a partial liquefaction expander or turbine. [Background technology]

[0002] Liquefied hydrogen has the potential to replace carbon-containing fuels. In addition to its current use in space applications, larger quantities of liquid hydrogen will be needed in the future for use as a fuel for aircraft, ships and other transportation purposes. As the use of hydrogen as a fuel increases, the need for large-scale storage and transportation of liquid hydrogen will increase.

[0003] As is well known, hydrogen at ambient temperature ("normal" hydrogen) exists as a mixture of two forms: 75% ortho-hydrogen and 25% para-hydrogen, but at liquid hydrogen temperatures of around -250°C, the equilibrium composition is almost entirely para-hydrogen. For this reason, hydrogen liquefaction technologies generally involve one or more stages of catalytic conversion at low temperatures, roughly in the range of -200°C to -250°C, whereby the ortho-hydrogen content in the feed hydrogen is exothermically converted to para-hydrogen upstream of the final liquefaction step. In the absence of this catalytic conversion step, the ortho-hydrogen content in the liquefied hydrogen would be slowly converted exothermically to para-hydrogen in the storage tanks, resulting in most or all of the product being lost to evaporation.

[0004] Existing and proposed hydrogen liquefaction processes generally: converting the ortho-hydrogen content of the feed gas into para-hydrogen, followed by liquefying the resulting parahydrogen gas or vapour by indirect heat exchange with a cooler fluid.

[0005] Helium has a lower boiling point range than hydrogen (-269°C at atmospheric pressure for helium and -253°C for hydrogen), and is already in use as such a low-temperature fluid, and has been proposed for future use.

[0006] Helium is an excellent refrigerant for hydrogen liquefaction, but it is expensive and its price is expected to rise with increased use in hydrogen liquefaction and other applications. Also, there may be logistical difficulties in refilling closed-circuit helium systems at large industrial plants after a significant leak or accident.

[0007] So, to overcome such potential difficulties with the use of helium, it is conceivable to use hydrogen itself as the cold fluid in the final heat exchange stage. As proposed by U Cardella (PhD thesis, Technical University of Munich, 2018 and possibly others), "normal" hydrogen, i.e. with a content of 75% ortho-hydrogen + 25% para-hydrogen, is used in the closed cooling circuit, and only the amount of hydrogen liquefied as product can be passed over a catalyst to convert the ortho-hydrogen content to para-hydrogen.

[0008] The use of hydrogen as the cold-end refrigerant avoids the economic and practical problems mentioned above for helium, but the coldest heat exchangers require very small temperature differentials, which can be difficult to achieve when the product hydrogen is required to be transported at pressures approaching atmospheric pressure. Summary of the Invention

[0009] The present invention relates to the final stage of the hydrogen liquefaction process, and in particular to the use of hydrogen as a refrigeration fluid.

[0010] Wherever in this application pressures are referred to as "bars", they are bar absolute.

[0011] The term expander as used in this application refers to process duty only. A particular process duty may require multiple expanders or rotors connected in series.

[0012] The present invention has two aspects: The present invention aims to avoid reliance on a final condensing heat exchanger due to the near temperature approach and to facilitate the production of liquid hydrogen at near atmospheric pressure.

[0013] According to a first aspect of the invention, the final heat exchanger as described in the prior art (which typically requires a temperature approach of about 1° C. and where hydrogen in the form of parahydrogen is condensed by an indirect heat exchanger with cooler "normal" hydrogen) is replaced by an expander or turbine having an output stream consisting of vapor and liquid. The expander output stream flows to a gas-liquid separator, which may be integrated with a storage tank, where the liquid fraction is separated to form a liquefied hydrogen product of the process and the vapor fraction is recompressed and recycled.

[0014] According to a second aspect of the invention, the extent of reconversion of para-hydrogen to ortho-hydrogen during the above recompression and recycle steps is minimised by providing the recompressor to operate with one or more compression stages having cryogenic inlet temperatures.

[0015] Naturally, some back-conversion of para-hydrogen to ortho-hydrogen occurs during the recompression and recycle step, and additional catalyst is provided in the lower temperature region of the process to convert the relatively small amount of resulting ortho-hydrogen.

[0016] Applicants believe that the above-described combination of (1) production of liquid hydrogen in a partially liquefied para-hydrogen expander and (2) cryogenic recompression and recycling of the separated vapor fraction of the expander effluent stream (thereby minimizing back-conversion of para-hydrogen to ortho-hydrogen) is novel and original.

[0017] From the viewpoint of practical application in a hydrogen liquefaction plant using hydrogen as a cooling fluid, the present invention can be used to: In the expander, the heat of condensation of the product hydrogen is removed in the form of mechanical work, thereby significantly reducing or eliminating the need for low-temperature heat exchangers with small temperature approaches; and Compressing the recycled hydrogen at low temperatures to increase its density can reduce the power required for hydrogen recycle compression and facilitate the use of centrifugal hydrogen compressors.

[0018] Below is provided a description of a process for liquefying hydrogen that illustrates the main aspects of the present invention (see Figure 1 / 3 and the unit tags and stream numbers therein). The process comprises: providing a stream of pure hydrogen feed gas [1] at a pressure between 10 bar and 150 bar; cooling the stream [1] in a heat exchanger [A] having an outlet stream [2] at a temperature between -150 °C and -210 °C; introducing stream [2] into an assembly [B], the assembly [B] comprising a catalyst [C] for converting ortho-hydrogen to para-hydrogen having an outlet stream [3], and a heat exchanger [D] having an outlet stream [4], the assembly [B] comprising a plurality of catalysts [C] and heat exchangers [D], the composition of stream [4] being essentially para-hydrogen and the temperature being between -210°C and -250°C; providing a hydrogen recycle stream

[11] having a composition consisting essentially of parahydrogen and at the same pressure as stream [4]; combining stream [4] and stream

[11] to form stream [5]; introducing the stream [5] into an expander [E] having a pressure between 10 bar and 1 bar and having an outlet stream [6] containing both liquid and vapor; passing stream [6] to a vessel [F] in which a liquid fraction stream [7] comprising the liquid hydrogen product from the process is separated from a vapor fraction stream [8]; providing in vessel [F] a catalyst for converting residual ortho-hydrogen in stream [6] into para-hydrogen; reheating the stream [8] in a heat exchanger [G] to form an effluent stream [9] having a temperature between -100°C and -240°C; Introducing the stream [9] into a compressor [H]; providing an outlet stream

[10] having a pressure between 10 bar and 150 bar to a compressor [H]; cooling the stream

[10] in a heat exchanger [I] having said stream

[11] as an outlet stream.

[0019] FIG. 2 / 3 shows a version of FIG. 1 / 3, where the catalyst in the assembly [B] is integrated into the hot passages of the heat exchanger [D].

[0020] In a further embodiment of the above description, in a particular use of the present invention, if it is desired that streams [4] and

[11] have different pressures or temperatures, the expander [E] can be split into two or more stages connected in series. In such a case, one of the two said streams can be introduced into the expander [E] at an intermediate stage.

[0021] Furthermore, one or more additional heat exchangers may be introduced between stages of the expander [E]. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 / 3 shows the main aspects of the present invention. [Diagram 2] Figure 2 / 3 shows a version of Figure 1 / 3. [Diagram 3] FIG. 3 / 3 shows one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Further, a description of one embodiment of the present invention is provided (see FIG. 3 / 3 and the device tags and stream numbers therein). This embodiment includes: providing a stream of pure hydrogen feed gas

[21] at a pressure between 10 bar and 150 bar; cooling the stream

[21] in a hot passage of a heat exchanger [a] having an outlet stream

[22] at a temperature between 0°C and -150°C; further cooling the stream

[22] in a first hot passage of a heat exchanger [b] having an outlet stream

[23] at a temperature between -150°C and -210°C; passing the stream

[23] through an assembly [c] comprising a catalyst [d] for converting ortho-hydrogen into para-hydrogen having an outlet stream

[24] and a heat exchanger [e] provided with a first high temperature passage having an outlet stream

[25] , the composition of which is essentially para-hydrogen and which has a temperature between -210°C and -250°C; providing a hydrogen recycle stream

[35] having a composition consisting essentially of parahydrogen and at the same pressure as stream

[25] ; combining stream

[25] and stream

[35] to form stream

[26] ; passing the stream

[26] through a first expander [f] having a pressure between 10 bar and 1 bar and having an outlet stream

[27] containing both liquid and vapor; passing stream

[27] to a vessel [g] where a liquid fraction stream

[28] comprising the liquid hydrogen product from the process is separated from a vapor fraction stream

[29] ; providing in vessel [g] a catalyst for converting residual ortho-hydrogen in stream

[27] into para-hydrogen; continuously reheating the stream

[29] in a first cold pass of a heat exchanger [e] to form an outlet stream

[30] and continuously reheating the stream

[29] in a first cold pass of a heat exchanger [b] to form an outlet stream

[31] having a temperature between -100°C and -240°C; introducing the stream

[31] into a compressor [h] as a first low pressure inlet stream; providing a second high pressure inlet stream

[39] having a composition consisting essentially of para-hydrogen to a compressor [h]; providing an outlet stream

[32] having a pressure between 10 bar and 150 bar to a compressor [h]; cooling the stream

[32] in a second hot passage of a heat exchanger [b] having an outlet stream

[33] at the same temperature as the stream

[23] ; splitting stream

[33] into two parts, stream

[34] and stream

[36] ; cooling the stream

[34] in a second hot pass of a heat exchanger [e] having said stream

[35] as an exit stream; passing the stream

[36] through a second expander [i] having an outlet stream

[37] with a pressure between 30 bar and 2 bar; continuously reheating stream

[37] in a second cold pass of heat exchanger [e] to form an outlet stream

[38] and continuously reheating stream

[39] in a second cold pass of heat exchanger [b] to form said outlet stream

[39] ; providing a stream of cooling fluid

[40] and passing the stream

[40] through a cold passage of a heat exchanger [a] having an outlet stream

[41] ; providing a stream of cooling fluid

[42] and passing the stream

[42] through a third cold passage of the heat exchanger [b] having an outlet stream

[43] .

Claims

1. A process for liquefying hydrogen gas, comprising: - providing a stream [1] of pure hydrogen feed gas at a pressure of 10 bar to 150 bar; - cooling stream [1] in the high-temperature passage of a heat exchanger [A] having an outlet stream [2] at a temperature of -150°C to -210°C; - introducing stream [2] into assembly [B], wherein assembly [B] comprises a catalyst [C] for converting ortho-hydrogen to para-hydrogen having an outlet stream [3], and a heat exchanger [D] having an outlet stream [4], said assembly [B] including a plurality of catalysts [C] and heat exchangers [D], the composition of stream [4] being essentially para-hydrogen and the temperature being -210°C to -250°C; - providing a recycle stream [11] of hydrogen having a composition consisting essentially of para-hydrogen and having the same pressure as stream [4]; - combining stream [4] and stream [11] to form stream [5]; - introducing stream [5] into an expander [E], wherein expander [E] has a pressure of 10 bar to 1 bar and has an outlet stream [6] containing both liquid and vapor; - passing stream [6] through a vessel [F], where a liquid fraction stream [7] containing the liquid hydrogen product from the process is separated from a vapor fraction stream [8]; - providing a catalyst in vessel [F] for converting residual ortho-hydrogen in stream [6] to para-hydrogen; - reheating stream [8] in a heat exchanger [G] to form an outlet stream [9] having a temperature of -100°C to -240°C; - introducing stream [9] into a compressor [H]; - providing an outlet stream [10] having a pressure of 10 bar to 150 bar to compressor [H]; - cooling stream [10] in a heat exchanger [I] having said stream [11] as an outlet stream. A process characterized by comprising the above steps.

2. In the process according to claim 1, the catalyst in assembly [B] is incorporated into the high-temperature passage of heat exchanger [D]. A process characterized by this.

3. In the process according to claim 1 or 2, A process characterized in that the expander [E] is divided into stages in series, whereby the stream [4] and the stream [11] are introduced at different pressures.

4. In the process according to claim 3, a process characterized in that one or more additional heat exchangers are introduced between the stages of the expander [E].

5. A process for liquefying hydrogen gas, comprising: - providing a stream [21] of pure hydrogen feed gas at a pressure of 10 bar to 150 bar; - cooling the stream [21] in the high-temperature passage of a heat exchanger [a] having an outlet stream [22] at a temperature of 0 °C to -150 °C; - further cooling the stream [22] in the first high-temperature passage of a heat exchanger [b] having an outlet stream [23] at a temperature of -150 °C to -210 °C; - passing the stream [23] through an assembly [c], the assembly [c] comprising a catalyst [d] for converting ortho-hydrogen to para-hydrogen having an outlet stream [24] and a heat exchanger [e] provided with a first high-temperature passage having an outlet stream [25], the assembly [c] comprising a plurality of catalysts [d] and heat exchangers [e], the composition of the stream [25] being essentially para-hydrogen and the temperature being -210 °C to -250 °C; - providing a recycle stream [35] of hydrogen having a composition consisting essentially of para-hydrogen and having the same pressure as the stream [25]; - combining the stream [25] and the stream [35] to form a stream [26]; - passing the stream [26] through a first expander [f], the first expander [f] having a pressure of 10 bar to 1 bar and having an outlet stream [27] containing both liquid and vapor; - passing the stream [27] through a vessel [g] where a liquid fraction stream [28] containing the liquid hydrogen product from the process is separated from a vapor fraction stream [29]; - providing a catalyst in the vessel [g] for converting residual ortho-hydrogen in the stream [27] to para-hydrogen. - Continuously reheating stream [29] in the first low-temperature passage of heat exchanger [e] to form an outlet stream [30], and continuously reheating in the first low-temperature passage of heat exchanger [b] to form an outlet stream [31] having a temperature of -100°C to -240°C; - Introducing stream [31] as a first low-pressure inlet stream into compressor [h]; - Providing compressor [h] with a second high-pressure inlet stream [39] having a composition consisting essentially of parahydrogen; - Providing compressor [h] with an outlet stream [32] having a pressure of 10 bar to 150 bar; - Cooling stream [32] in the second high-temperature passage of heat exchanger [b] having an outlet stream [33] at the same temperature as stream [23]; - Dividing stream [33] into two parts, stream [34] and stream [36]; - Cooling stream [34] in the second high-temperature passage of heat exchanger [e] having said stream [35] as an outlet stream; - Passing stream [36] through a second expander [i] having an outlet stream [37] having a pressure of 30 bar to 2 bar; - Continuously reheating stream [37] in the second low-temperature passage of heat exchanger [e] to form an outlet stream [38], and continuously reheating in the second low-temperature passage of heat exchanger [b] to form said outlet stream [39]; - Providing a stream [40] of a cooling fluid and passing this stream [40] through the low-temperature passage of heat exchanger [a] having an outlet stream [41]; - Providing a stream [42] of a cooling fluid and passing this stream [42] through the third low-temperature passage of heat exchanger [b] having an outlet stream [43]. A process characterized by comprising these steps.

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