Process for Producing Liquefied Hydrogen

Abstract

A process for liquefying hydrogen gas including the following is disclosed: cooling the hydrogen gas to an intermediate temperature by heat exchange with a refrigerant circulating in a refrigeration loop provided with a higher temperature expander and a lower temperature expander, wherein the outlet stream from the lower temperature expander contains some condensed refrigerant; a means is provided of separating the condensate from the circulating refrigerant; and further cooling of the hydrogen gas by heat exchange with evaporation and reheating of the said condensate.

The fluid in the refrigeration loop is typically methane (such as natural gas after removal of carbon dioxide, water vapor and other impurities), or nitrogen, or a mixture thereof.

Claims

1.-13. (canceled)

14. A process for liquefying hydrogen gas, the process comprising: providing a stream of hydrogen feed gas; providing a stream of recycled hydrogen gas at a pressure of from 1 bar to 50 bar; admitting the stream of hydrogen feed gas and the stream of recycled hydrogen gas to a first hydrogen compressor, the first hydrogen compressor having a combined discharge stream with a pressure of between 10 bar and 200 bar; cooling said combined discharge stream in a first hot passage of a first heat exchanger, said first hot passage having a first outlet stream; cooling said first outlet stream in a second hot passage of a second heat exchanger, said second hot passage having a second outlet stream; cooling said second outlet stream in a third hot passage of a third heat exchanger, said third hot passage having a third outlet stream; passing the third outlet stream to a hydrogen liquefier unit comprising one or more hydrogen gas expanders, one or more further heat exchangers, and one or more stages of catalytic conversion of ortho-hydrogen to para-hydrogen; the hydrogen liquefier unit having a first liquefier outlet stream of liquid hydrogen with a temperature of between −240° C. and −255° C. and a second liquefier outlet stream of gaseous hydrogen having a pressure between 1 bar and 20 bar; reheating the stream of gaseous hydrogen in a first cold passage of the third heat exchanger to provide a first reheated outlet stream, then in a first cold passage of the second heat exchanger to provide a second reheated outlet stream, then in a first cold passage of the first heat exchanger to provide a third reheated outlet stream from the first heat exchanger to form a stream of recycled hydrogen gas; providing a stream of refrigerant gas at a pressure of from 10 bar to 150 bar; dividing the stream of refrigerant gas into first and second parts; passing said first part to a first refrigerant gas expander to provide an outlet stream from said first refrigerant gas expander having a pressure between 5 bar and 50 bar; reheating the first refrigerant gas expander outlet stream in a second cold passage of the first heat exchanger to form a reheated refrigerant gas stream; compressing the reheated refrigerant gas stream in a second compressor to a pressure of from 10 to 150 bar to form a first constituent of the refrigerant gas; passing the second part of the refrigerant gas to a second hot passage of the first heat exchanger to provide a cooled outlet stream; passing said cooled outlet stream to a second refrigerant gas expander to provide an outlet stream from said second refrigerant gas expander having a pressure of between 3 bar and 50 bar and comprising a mixture of vapor and liquid; separating the outlet stream of the second gas expander in a vapor/liquid separator to form a vapor stream and a liquid stream; depressurizing said liquid stream in valve to form a depressurized stream with a pressure of between 0.5 bar and 10 bar; evaporating and reheating said depressurized liquid stream in a second cold passage of third heat exchanger to form an outlet vapor stream; compressing the outlet vapor stream to a same pressure as the pressure of the vapor stream from the vapor liquid separator by a low pressure refrigerant compressor having a compressor outlet stream; combining the vapor stream and the compressor outlet stream to form a combined vapor stream; reheating the combined vapor stream in the second cold passage of the second heat exchanger to form a third reheated outlet stream and then in a third cold passage of the first heat exchanger to form a fourth reheated outlet stream; and, compressing the fourth reheated outlet stream in the second compressor to a pressure of from 10 to 150 bar to form a second constituent of the refrigerant gas.

15. A process according to claim 14 in which the combined discharge stream from the first compressor has a pressure of between 20 bar and 100 bar.

16. A process according to claim 14 in which the pressure of the depressurized stream is between 1 bar and 3 bar.

17. A process according to claim 14 in which the refrigerant gas is methane or a methane-rich gas.

18. A process according to claim 17 in which the pressure of the outlet stream from second gas expander is between 10 bar and 50 bar.

19. A process according to claim 14 in which the refrigerant gas is nitrogen.

20. A process according to claim 19 in which the pressure of the outlet stream from second gas expander is between 3 bar and 30 bar.

21. A process according to claim 14 in which the refrigerant gas is a mixture of methane and nitrogen.

22. A process according to claim 14 in which the refrigerant gas flowing in first refrigerant gas expander is methane or a methane-rich gas, while the cooled outlet stream flowing in the second refrigerant gas expander, in the separator, and the valve is nitrogen.

23. A process according to claim 14 in which the temperature the inlet stream of compressor is between −200° C. and 40° C.

24. A process according to claim 23, in which the inlet stream to the first compressor is taken directly from the outlet stream of the hydrogen liquefier unit or from the outlet of the first cold passage of the third heat exchanger or the second heat exchanger.

25. A process according to claim 14, further providing a stream of a second refrigerant gas at near-ambient temperature; cooling said second refrigerant gas stream in a third hot passage of the first heat exchanger to form a fourth outlet stream; cooling said fourth outlet stream in a second hot passage of the second heat exchanger to form a fifth outlet stream; cooling said fifth outlet stream in a second hot passage of the third heat exchanger to form a sixth outlet stream; passing said sixth outlet stream into the hydrogen liquefaction unit, in which the sixth outlet stream passes through one or more stages of expansion to provide refrigeration, before leaving the liquefier unit as a seventh outlet stream; reheating the seventh outlet stream in a third cold passage of the third heat exchanger to form an eighth outlet stream; further reheating the eighth outlet stream in a third cold passage of the second heat exchanger to form a ninth stream; further reheating the ninth outlet stream in a fourth cold passage of the first heat exchanger to form a tenth outlet stream; and, recompressing the tenth outlet stream in a third compressor to form said second refrigerant gas stream.

26. A process according to claim 25 in which the said second part of the refrigerant gas is hydrogen, helium, or a mixture of hydrogen or helium with neon.

Description

DESCRIPTION OF PREFERRED EMBODIMENTS

[0067] The invention will be described with reference to the accompanying drawings in which represent flow diagrams illustrating embodiments of the process in accordance with the invention.

[0068] The exact flow sheets are subject to variation, but will generally contain these basic elements.

[0069] In a first embodiment of the invention, illustrated on Drawing 1/3, the feed stream of hydrogen to be liquefied [1] with pressure 25 bar is admitted to a compressor [A]. The compressor also receives a stream of recycle hydrogen [2], described below. The combined stream of feed hydrogen and recycle hydrogen after cooling [3] is discharged from the compressor at 75 bar.

[0070] The combined stream [3] is cooled to −50 degC by passing through the first hot passage of heat exchanger [B] to form stream [4]; then further cooled to −120 degC by passing through the first hot passage of heat exchanger [C], to form stream [5]; the necessary refrigeration being provided as described below by a closed circuit of methane refrigerant.

[0071] The outlet stream [5] from heat exchanger [C] is further cooled to −158 degC by evaporation of a low pressure methane refrigerant stream to form stream [6].

[0072] Stream [6] then flows to a hydrogen liquefaction unit [E] comprising one or more hydrogen expanders, one or more heat exchangers and one or more ortho-to-para hydrogen catalytic conversion stages.

[0073] The hydrogen liquefaction unit [E] has an outlet stream of liquid hydrogen [7] with a temperature of −244 degC and a pressure of 7.5 bar, and an outlet stream of gaseous hydrogen stream [8] having at temperature of −161 degC and a pressure of 6.8 bar.

[0074] Stream [8] is reheated first in a cold passage of heat exchanger [D] to form Stream [9] with temperature −123 degC, and then is further reheated in a first cold passage of heat exchanger [C] to form Stream [10] with a temperature of −53 degC, and then is further reheated in a first cold passage of heat exchanger [B], the reheated stream at near-ambient temperature forming the above-mentioned hydrogen recycle Stream [2],

[0075] The above-mentioned closed refrigeration circuit containing methane refrigerant has stream [21] with a pressure of 90 bar at the discharge of refrigerant compressor [M].

[0076] The outlet stream [21] from compressor [M] is divided into a first part [22] and a second part [25].

[0077] The first part [22] passes to a first refrigerant gas expander [L] having outlet stream [23] with pressure 26 bar and temperature −54 degC. The second part [25] is passed through a second hot passage of heat exchanger [B], which has an outlet stream [26] having the same outlet temperature of −50 degC as the above-mentioned hydrogen stream [4].

[0078] Stream [23] is reheated to near-ambient temperature in a second cold passage of heat exchanger [B]. The reheated stream [24] flows to refrigerant compressor [M] at near-ambient temperature as a first constituent after cooling of the above-said refrigerant gas stream [21].

[0079] The outlet stream [26] from heat exchanger [B] flows to a second refrigerant gas expander [N], having outlet stream [27] with pressure 10 bar and temperature −124 degC and containing both vapour and liquid.

[0080] Stream [27] is separated in vapour/liquid separator [O] to form vapour stream [28] and liquid stream [29].

[0081] Liquid stream [29] is depressurizing in valve [P] to near-atmospheric pressure, so as to form a mixture of liquid and vapour in the outlet Stream [30] with a temperature of −158 degC.

[0082] Stream [30] is fully evaporated and reheated in a second cold passage of heat exchanger (D), so as to form outlet vapour stream [31] having the same temperature of −123 degC as above-mentioned hydrogen stream [9]. Stream [31] is compressed by refrigerant compressor [Q] which has outlet stream [32] having the same pressure of 9.7 bar as stream [28]. Streams [28] and [33] are then combined to form stream [34].

[0083] Stream [34] is reheated first in a second cold passage of heat exchanger [C] to form stream [35] having a temperature of −53 degC and then in a third cold passage of heat exchanger [B]. The reheated stream [36] flows to compressor [M] at near-ambient temperature as a second constituent after cooling of the above-said refrigerant gas stream [21].

[0084] The invention will be further described by reference to the accompanying Drawing 2/3 representing a second embodiment of the invention. This second embodiment, which is described in concept above, comprises a variant of the first embodiment, whereby the hydrogen recycle compressor [A] receives an inlet stream with a significantly sub-ambient suction temperature.

[0085] In an example of this second embodiment, the hydrogen recycle stream [9] flows directly to compressor [A) at a temperature of −123 degC and at a pressure of 6.6 bar. The temperature of the outlet stream [3] from compressor [A] is then reduced to near-ambient temperature.