System and Method for Cooling Fluids Containing Hydrogen or Helium

A system for cooling a feed stream including hydrogen or helium with a mixed refrigerant includes a pre-cooling heat exchanger. A compression system has an inlet in fluid communication with the pre-cooling heat exchanger and receives and increases a pressure of a refrigerant vapor stream including hydrogen and/or helium mixed with at least one other refrigerant such that the molecular weight of the mixture is greater than 6 kg/kgmol. The compression system has an outlet in fluid communication with the pre-cooling heat exchanger. A first refrigerant separation device receives fluid from the pre-cooling heat exchanger and has a liquid outlet in fluid communication with the pre-cooling heat exchanger and a vapor outlet. A refrigerant purifier has a purifier inlet in fluid communication with the vapor outlet of the first refrigerant separation device and an outlet in fluid communication with the pre-cooling heat exchanger.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to systems and methods for liquefying gases and, more particularly, to a system and method for liquefaction of fluids containing hydrogen or helium.

BACKGROUND

Industrial gases, such as natural gas or hydrogen, are advantageously stored or transported in a liquid state because they occupy a much smaller volume (natural gas for instance is 1/600ththe gaseous state, hydrogen is 1/848th). The liquefied gases are usually vaporized back to a gaseous state for use at a site or system.

Gaseous hydrogen is converted to liquefied hydrogen by cooling it to below about 20-25 K. The typical process of cooling utilizes a high amount of energy and can be very expensive regarding equipment costs. The process may include multiple refrigeration cycles and involve multiple stages of gas compression.

Prior art hydrogen liquefaction systems commonly use reciprocating compressors or screw compressors. A system and/or process that can use a dynamic compressor for hydrogen liquefaction is desirable. Dynamic compressors are more reliable than reciprocating compressors and more efficient than screw compressors. Dynamic compressors include compressors that do not require positive displacement, such as centrifugal compressors, radial compressors, or axial compressors. In prior art liquefaction systems, dynamic compressors are not a good fit for low molecular weight gases (<6 kg/kgmol), like hydrogen or helium.

An example of a prior art hydrogen liquefaction system is presented in U.S. Pat. No. 3,992,167 to Beddome, which describes a process in which propane is added to hydrogen so that the refrigerant cycle stream being compressed is 33% propane and 67% hydrogen. An additional component with higher molecular weight than propane is desirable to improve the efficiency of the process by allowing more of the compression power to be used for hydrogen or helium and to simplify separating the additional component from the hydrogen or helium. The process of the Beddome '167 patent also contains a single adsorption purification unit for the hydrogen stream going to the coldest part of the process. This results in hydrocarbon that is not condensed being emitted from the process when the adsorbent is regenerated. A process that has near-zero hydrocarbon emission is desirable and could be particularly important depending on environmental regulations.

U.S. Pat. No. 5,579,655 to Grenier describes a prior art process in which minor amounts of saturated C2, C3, optionally C4, and C5hydrocarbons are mixed with hydrogen to form a mixed refrigerant. The process includes a separate hydrogen feed stream that is liquefied and does not mix with the mixed refrigerant stream, so dual cryogenic purifiers are required at 75-80 K. Because of the inclusion of ethane in the mixed refrigerant, purification of the hydrogen from the minor mixed refrigerant components is more complicated and a liquid propane wash column is required to perform the separation, leading to the need for a continuous hydrocarbon makeup to compensate for the hydrocarbon lost to the environment. The liquid propane wash column also adds cost and complexity to the process.

U.S. Pat. No. 10,928,127 to Cardella et al. describes a process that uses a mixed refrigerant for hydrogen liquefaction. The mixed refrigerants mentioned contain nitrogen, neon, argon, and hydrocarbons, but do not contain hydrogen or helium. The mixed refrigerant of the invention described herein must contain hydrogen or helium. Furthermore, the process described in U.S. Pat. No. 10,928,127 also uses an essentially pure hydrogen stream that requires a positive displacement compressor as a separate refrigerant in addition to the mixed refrigerant. The process described in U.S. Pat. No. 10,928,127 does not provide for precooling of the hydrogen feed below 85 K. This increases the refrigeration load on the hydrogen refrigerant compared to standard processes that use liquid nitrogen for precooling or the invention described herein.

U.S. Pat. No. 3,490,245 to Muenger describes a heat exchanger that removes trace impurities including carbon dioxide, hydrogen sulfide, carbon disulfide, and carbonyl sulfide from an ammonia synthesis feed by freezing them out of the stream being purified. It is attested that this type of heat exchanger can be used instead of an adsorption system to remove impurities that would freeze in the Cold Box heat exchangers if they were not removed. A freeze-out device is defined as a device that removes an impurity or impurities from a mixed stream by selectively freezing a particular component or components. The device described in U.S. Pat. No. 3,490,245 is one example of a freeze-out device.

SUMMARY OF THE DISCLOSURE

In one aspect, a system for cooling a feed stream including hydrogen or helium with a mixed refrigerant includes a pre-cooling heat exchanger having a feed stream cooling passage, a first refrigerant cooling passage, a second refrigerant cooling passage and a refrigerant warming passage. A compression system has an inlet in fluid communication with the refrigerant warming passage and is configured to receive and increase a pressure of a refrigerant vapor stream of hydrogen and/or helium mixed with at least one other refrigerant such that the molecular weight of the mixture is greater than 6 kg/kgmol. The compression system has an outlet in fluid communication with the first refrigerant cooling passage. A first refrigerant separation device is configured to receive fluid from the first refrigerant cooling passage in the pre-cooling heat exchanger. The first refrigeration separation device has a liquid outlet in fluid communication with the refrigerant warming passage and a vapor outlet. A refrigerant purifier has a purifier inlet in fluid communication with the vapor outlet of the first refrigerant separation device and an outlet in fluid communication with the second refrigerant cooling passage. The second refrigerant cooling passage has an outlet in fluid communication with the refrigerant warming passage.

In another aspect, a method for liquefying a feed stream containing hydrogen or helium includes the steps of mixing a hydrogen or helium refrigerant with at least one additional refrigerant component having a higher molecular weight than hydrogen or helium to form a mixed refrigerant having a molecular weight of at least 6 kg/kgmol, compressing the mixed refrigerant using a dynamic compressor, separating the at least one additional refrigerant component from the hydrogen or helium refrigerant at a temperature of 75 K or warmer to obtain a remaining hydrogen or helium refrigerant, and cooling the hydrogen or helium feed stream using the remaining hydrogen or helium refrigerant to produce a liquid hydrogen or helium product from the feed stream.

In yet another aspect, a system for cooling a cryogenic fluid feed stream including hydrogen or helium with a mixed refrigerant includes a pre-cooling heat exchanger having a pre-cool feed stream cooling passage, a low-pressure refrigerant warming passage, an intermediate-pressure refrigerant warming passage, a first refrigerant cooling passage and a second refrigerant cooling passage. A mixed gas compressor is configured to receive a mixed refrigerant vapor stream from the low-pressure refrigerant warming passage. A mixed gas aftercooler is in fluid communication with the mixed gas compressor. A mixing device has a first inlet in fluid communication with the mixed gas aftercooler, a second inlet and a mixing device vapor outlet. The second inlet is configured to receive a mixed refrigerant vapor stream from the intermediate-pressure refrigerant warming passage. A first interstage compressor is in fluid communication with the mixing device vapor outlet. A first interstage aftercooler is in fluid communication with the first interstage compressor. A high-pressure accumulator is in fluid communication with the first interstage aftercooler and has a high-pressure accumulator vapor outlet and a high-pressure accumulator liquid outlet. The high-pressure accumulator vapor outlet is in fluid communication with the first refrigerant cooling passage and the high-pressure accumulator liquid outlet is in fluid communication with the intermediate-pressure refrigerant warming passage. A first refrigerant separation device is in fluid communication with the first refrigerant cooling passage and has a first refrigerant separation device liquid outlet in fluid communication with the low-pressure refrigerant warming passage and a first refrigerant separation device vapor outlet in fluid communication with the second refrigerant cooling passage. A second refrigerant separation device is in fluid communication with the second refrigerant cooling passage and has a second refrigerant separation device liquid outlet in fluid communication with the low-pressure refrigerant warming passage and a second refrigerant separation device vapor outlet. A refrigerant purifier has a purifier inlet in fluid communication with the second refrigerant separation device vapor outlet and a purifier outlet where the purifier outlet is in fluid communication with the low-pressure refrigerant warming passage and the intermediate-pressure refrigerant warming passage.

DETAILED DESCRIPTION OF EMBODIMENTS

It should be noted herein that the lines, conduits, piping, passages and similar structures and the corresponding streams are sometimes both referred to by the same element number set out in the figures.

Also, as used herein, and as known in the art, a heat exchanger is that device or an area in the device wherein indirect heat exchange occurs between two or more streams at different temperatures, or between a stream and the environment. In addition, all heat exchangers referenced herein may be incorporated into one or more heat exchanger devices or may each be individual heat exchanger devices. As used herein, the terms “communication”, “communicating”, and the like generally refer to fluid communication unless otherwise specified. And although two fluids in communication may exchange heat upon mixing, such an exchange would not be the same as heat exchange in a heat exchanger, although such an exchange can take place in a heat exchanger.

As used herein, the terms, “high”, “middle”, “warm”, “cold” and the like are relative to comparable streams, as is customary in the art.

Any column or tower referenced in the following description may, as non-limiting examples only, be a spray tower, a packed column, a trayed column, and/or any combination thereof.

Reference numerals that are introduced in the specification in association with a drawing figure may be repeated in one or more subsequent figures for shared elements or components without additional description in the specification to provide context for other features.

In the claims, letters are used to identify claimed steps (e.g., a., b. and c.). These letters are used to aid in referring to the method steps and are not intended to indicate the order in which the claimed steps are performed, unless and only to the extent that such order is specifically recited in the claims.

Embodiments of the disclosure described below provide a process and apparatus for the liquefaction of hydrogen or helium of the type using a refrigeration cycle whose cycle fluid comprises mostly hydrogen or helium and an optional closed supplemental refrigerant refrigeration cycle. The primary refrigeration cycle fluid is a mixture containing hydrogen or helium and at least one additional component with a higher molecular weight and higher boiling point that is compressed outside the Cold Box and is used to provide cooling to the hydrogen or helium feed stream in the Cold Box. The additional component or components are removed from the hydrogen-rich or helium-rich refrigerant stream in the Cold Box by a sequence of preferential partial condensation steps and adsorption and/or freeze-out and/or distillation below ambient temperature and warmer than about 75 K. The removed components provide cooling to the Cold Box as they are flashed to low pressure, reheated, and recycled back to a point in the compression train. A controlled direct heat and mass transfer processing step is included between the hydrogen or helium and the additional component or components in at least one interstage compression drum which operates as a direct contact mixing vessel, providing simultaneous heat and mass transfer that ensures vaporization of the high molecular weight components and control of the mixed refrigerant stream composition, molecular weight, and thermal properties in all scenarios. The remaining cryogenically purified hydrogen or helium is used as the primary refrigerant at temperatures below about 75-80 K.

Increasing the molecular weight of the compressed hydrogen- or helium-containing stream by mixing other components that are then removed permits dynamic compressors to be used in place of less reliable reciprocating compressors during compression of the mixed refrigerant.

In addition, use of components with higher molecular weight than the prior art in the embodiments described below improves compressor performance while maintaining a relatively high hydrogen concentration in the mixture. The use of fluorinated hydrocarbons increases the molecular weight of the added component, which reduces how much is required to increase the molecular weight of the mixture so that the hydrogen or helium concentration in the mixture can be increased.

The embodiments disclosed below reduce the power required for the supplemental refrigerant precooling cycle by leveraging the supplemental refrigeration duty provided by the higher molecular weight components. This supplemental refrigeration duty primarily occurs above about 190 K. These improvements increase the overall efficiency of the precooling process. The excess supplemental refrigeration duty supplied can exceed the requirements of the hydrogen/supplemental refrigerant precooling system and this excess duty can provide refrigeration to other processes or systems.

The embodiments disclosed below also use a refrigerant mixture that does not contain hydrocarbons that boil at temperatures lower than about 190 K. Eliminating ethane and ethylene from the mixtures proposed in the prior art significantly simplifies and improves hydrocarbon separation from the hydrogen or helium stream before it is fed to the cold end process. The description of the figures refers to the case in which hydrogen is the feed stream and the material to be liquefied. If helium is used, there is no ortho-para conversion catalyst and the final temperature is lower, but the description generally applies.

In an embodiment, as shown inFIG.1, a high-pressure hydrogen feed101at approximately 14-26 bar and near ambient temperature is cooled in a pre-cooling heat exchanger1to approximately 77-80 K and exits as a pre-cooled hydrogen feed102. As is known in the art, the pre-cooling heat exchanger1is positioned within the interior of an insulating Cold Box7. The pre-cooling heat exchanger1can be packed with an ortho-para conversion catalyst2in the hydrogen cooling pass to facilitate conversion of a portion of the high-pressure hydrogen feed101from ortho-hydrogen to para-hydrogen. The pre-cooled hydrogen feed102is sent to an adsorption-based cryogenic purifier (51, shown inFIG.2) similar to the second refrigerant purifier23, and the hydrogen liquefaction process where most of it is liquefied is well known in the art (An example is shown inFIG.2). A minor portion of the pre-cooled hydrogen feed is returned to the pre-cooling heat exchanger1as a cold hydrogen recycle stream103.

The cold hydrogen recycle stream103is warmed in the pre-cooling heat exchanger1to provide cooling for the high-pressure hydrogen feed101. The cold hydrogen recycle will be at lower pressure than the high-pressure hydrogen feed101. This stream can optionally be passed over a para-ortho conversion catalyst3to take advantage of extra cooling capability available from the conversion. The cold hydrogen recycle stream103exits the pre-cooling heat exchanger1as a warm hydrogen recycle stream104that can be compressed and returned to the process as part of the high-pressure hydrogen feed101.

In many cases, an optional high-pressure supplemental refrigerant, such as nitrogen,111is cooled in the pre-cooling heat exchanger1to form a cold high-pressure supplemental refrigerant stream112that is expanded in a supplemental refrigerant expander4to form a cold supplemental refrigerant stream113. The cold supplemental refrigerant stream113provides cooling to the pre-cooling heat exchanger1and exits as a warm low-pressure supplemental refrigerant stream114that is compressed in a supplemental refrigerant compressor5to form a hot compressed supplemental refrigerant stream115that is cooled in a supplemental refrigerant compressor aftercooler6to form the high-pressure supplemental refrigerant feed111. The supplemental refrigerant compressor5and aftercooler6can consist of more than one stage depending on the desired pressure rise. Likewise, the supplemental refrigerant expander4can also consist of more than one stage. Alternatively, the cycle can be enhanced to include a more efficient scheme, such as the one shown inFIG.3.

A low-pressure gas mixture121comprised of hydrogen and/or helium and at least one other substance with a higher molecular weight and a boiling point above 80 K is compressed in a first mixed gas compressor11and cooled in a first compressor aftercooler12to form a first intermediate-pressure mixture122that can be sent to a mixing vessel13. The first mixed gas compressor11can be a single-stage compressor, a compressor with more than one stage, or the lowest-pressure stage or stages of a multi-stage compressor. The mixing vessel13is designed to operate with or without a liquid level and contains a sparger and/or heating coil, packing, or other devices to enhance the direct contact and heat and mass transfer between the inlet streams. Examples of these other substances include hydrocarbons, halogenated hydrocarbons, perfluorocarbons, neon, and other refrigerants. A second mixture123exits the mixing vessel13and is compressed in a second mixed gas compressor14and cooled in a second compressor aftercooler15to form a second intermediate-pressure mixture124that is fed to a first phase separator or interstage separation device16designed to remove any small amount of liquid that might form. The second mixed gas compressor14can be a single-stage compressor, a compressor with more than one stage, or a stage or stages of a multi-stage compressor operating at a higher pressure than the first mixed gas compressor. The controlled operation of the mixing vessel13heat input maximizes the amount of higher molecular weight component(s) in the second mixture123by allowing the mixture to operate at or near its saturation or dew point condition. This increases the molecular weight of the second mixture and improves its ability to be compressed. A third mixture125exits the interstage separation device16and is compressed in a third mixed gas compressor17and cooled in a third compressor aftercooler18to form a high-pressure mixture126that is fed to a second phase separator or a high-pressure accumulator19. The third compressor can be a single-stage compressor, a compressor with more than one stage, or a stage or stages of a multi-stage compressor operating at a higher pressure than the second compressor. As illustrated inFIG.1, and in all of the following embodiments, first, second and third mixed gas compressors11,14and17are positioned exterior to the Cold Box7.

A first liquid160exits the bottom of the interstage separation device16and can be drained through a first phase separator valve41to form a low-pressure first liquid161. A second liquid162that contains primarily the high molecular weight component(s) in the original mixture exits the bottom of the high-pressure accumulator19and can be drained through a second phase separator valve42to form a low-pressure second liquid163and mixed with the low-pressure first liquid161to form a low-pressure mixed liquid164.

The low-pressure mixed liquid164can be distributed among four different streams, a mixing vessel recycle stream170, a mixing vessel refrigeration feed166, a low-pressure gas mixture vessel refrigeration feed167, and a low-pressure gas mixture vessel recycle stream172. The mixing vessel recycle stream170is expanded through a mixing vessel valve43to form a low-pressure mixing vessel recycle stream171that is returned to the mixing vessel13. The mixing vessel refrigeration feed166is expanded through a mixing vessel refrigeration expansion device45, such as a valve, to form a cooled mixing vessel refrigerant169that provides cooling to the pre-cooling heat exchanger1and returns to the mixing vessel13. A portion of the cooled mixing vessel refrigerant174can be sent through the pre-cooling heat exchanger1as a separate stream so that it exits the pre-cooling heat exchanger1as a two-phase stream. This can decrease the temperature difference in the heat exchanger and improve efficiency. The low-pressure gas mixture vessel refrigeration feed167is expanded through a low-pressure mixture vessel refrigeration expansion device46, such as a valve, to form a cooled low-pressure gas mixture vessel refrigerant168that provides cooling to the pre-cooling heat exchanger1and returns to a low-pressure gas mixture vessel24. The low-pressure gas mixture vessel recycle stream172is expanded through a low-pressure gas mixture vessel valve44to form a reduced pressure gas mixture vessel recycle stream173that returns to the low-pressure gas mixture vessel24. An accumulated liquid175from the mixing vessel13can be pressurized using a mixing vessel pump49to from a pressurized accumulated liquid176and mixed with the first liquid160or the second liquid162. The pump49and the mixing vessel13allow the molecular weight of the compressor feed streams to be controlled and maintained at a relatively high level. Alternatively (not shown), the accumulated liquid175can be mixed with a low-pressure gas mixture vessel feed143and fed to the low-pressure gas mixture vessel24.

A second phase separator vapor127exits the top of the high-pressure accumulator19and is cooled in the pre-cooling heat exchanger1to form a first cooled mixed refrigerant128that is fed to a first mixed refrigerant separator20. A first mixed refrigerant vapor129exits the top of the first mixed refrigerant separator20and returns to the pre-cooling heat exchanger1where it is cooled further to form a second cooled mixed refrigerant stream130that is fed to a second mixed refrigerant separator21. A second mixed refrigerant vapor131exits the top of the second mixed refrigerant separator21and is purified in a mixed refrigerant purifier22that removes essentially all the mixture components that have a boiling point above 80 K. The mixed refrigerant purifier22can be an adsorption system that preferentially removes the components of the mixture with a boiling point above 80 K. The adsorption system will generally consist of more than one adsorbent bed so that a bed or beds can be regenerated while another bed or beds are active. Freeze-out devices, distillation columns, or other purification methods can also be used as the refrigerant purifiers. Freeze-out devices will require similar regeneration. A mixed refrigerant purifier regeneration feed191is used to sweep captured impurities out of the mixed refrigerant purifier22to regenerate it for a new feed step. The purifier regeneration feed is generally comprised of nitrogen, hydrogen, helium, or mixtures thereof. The regeneration is generally done at lower pressure and higher temperature than the typical operating pressure and temperature of the purifier. When there are at least two mixed refrigerant purifiers, it is possible to selectively remove the trace heavy refrigerant components in the first purifier without removing the lighter impurities introduced with the feed, such as nitrogen or argon. An impurity-containing regeneration stream192can be recycled to the inlet of the first mixed gas compressor or the low-pressure gas mixing vessel24. This allows the system to recover the trace amounts of other substances in the mixed refrigerant that were removed in the refrigerant purifier22. In the case in which hydrocarbons are used as the other substance, this ensures essentially full recovery of the hydrocarbons and essentially zero hydrocarbon emissions, unlike processes in the prior art.

A purified hydrogen/helium stream132exits the mixed refrigerant purifier22and returns to the pre-cooling heat exchanger1where it is cooled further and exits as a cooled refrigerant133that is further purified in a second refrigerant purifier23, similar to the mixed refrigerant purifier22, except that the second refrigerant purifier is designed to remove lighter impurities, including nitrogen and argon, while the mixed refrigerant purifier is designed to remove higher molecular weight substances with boiling points above 80 K. A low-temperature refrigerant134leaves the second refrigerant purifier23and is fed to the hydrogen liquefaction process. A second refrigerant purifier regeneration feed193is used to regenerate the second refrigerant purifier23, similar to the mixed refrigerant purifier22. All or a portion of a second impurity-containing regeneration stream194can be recycled to the crude hydrogen purifier (not shown) or vented because nitrogen, argon, and other light impurities would build up to unacceptably high concentrations if they were never removed. Alternatively, a portion of the regeneration stream can be recycled to a compressor inlet, depending on its pressure. The crude hydrogen purifier is a device located upstream of the high-pressure hydrogen feed101and can be a pressure-swing adsorption system, for example, that separates hydrogen from the other components in a mixture produced by a hydrogen generation system, such as a reformer or electrolyzer. In one alternative, the two refrigerant purifiers can be combined into a single unit. In that case, the regeneration stream can be recycled to the crude hydrogen purifier or a portion of the regeneration stream can be recycled to a compressor inlet, depending on its pressure.

A first mixed refrigerant liquid181exits the bottom of the first mixed refrigerant separator20and is expanded in a first mixed refrigerant liquid expansion device47, such as a valve, to cool the stream and reduce its pressure to form a cooled low-pressure first mixed refrigerant liquid stream182. A second mixed refrigerant liquid184exits the bottom of the second mixed refrigerant separator21and is expanded in a second mixed refrigerant liquid expansion device48, such as a valve, to cool the stream and reduce its pressure to form a cooled low-pressure second mixed refrigerant liquid stream185. The cooled low-pressure first mixed refrigerant liquid stream182and the cooled low-pressure second mixed refrigerant liquid stream185combine to make a low-pressure mixed refrigerant recycle stream183that enters the pre-cooling heat exchanger1to provide cooling.

A low-pressure refrigerant141is recycled from the hydrogen liquefaction process and enters the pre-cooling heat exchanger1to provide cooling. The low-pressure refrigerant141mixes with the cooled low-pressure gas mixture vessel refrigerant168and the low-pressure mixed refrigerant recycle stream183in the pre-cooling heat exchanger1and exits as a warmed mixed refrigerant142that combines with the reduced pressure gas mixture vessel recycle stream173to produce the low-pressure gas mixture vessel feed143that enters the low-pressure gas mixture vessel24.

An intermediate-pressure refrigerant151leaves the hydrogen liquefaction process and enters the pre-cooling heat exchanger1to provide cooling. The intermediate-pressure refrigerant151mixes with the cooled mixing vessel refrigerant169in the pre-cooling heat exchanger1and exits as a mixing vessel recycle feed152that enters the mixing vessel13.

FIG.2shows an example cold end process for producing liquid hydrogen product. There are numerous variations on this configuration that are known in the art that could be appropriate for the technology of the disclosure. The example shown inFIG.2is merely one of the many possible options. The cold-end configuration selected does not have an important impact on the technology of the disclosure or its use.

The pre-cooled hydrogen feed102fromFIG.1enters a hydrogen feed purifier51, similar to the second refrigerant purifier inFIG.1. The hydrogen feed purifier removes any impurities in the hydrogen feed before the stream is cooled further. These impurities generally consist of primarily nitrogen and argon and other trace components that could freeze in the lower-temperature heat exchangers. A purified hydrogen feed201exits the hydrogen feed purifier51and enters a first cold heat exchanger53, where it is cooled and a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a first cold heat exchanger catalyst passage52, to produce a second purified hydrogen feed202.

The second purified hydrogen feed202exits the first cold heat exchanger53and enters a second cold heat exchanger55, where a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a second cold heat exchanger catalyst passage54, to produce a third purified hydrogen feed203. The third purified hydrogen feed203exits the second cold heat exchanger55and enters a third cold heat exchanger57, where a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a third cold heat exchanger catalyst passage56, to produce a fourth purified hydrogen feed204. The fourth purified hydrogen feed204exits the third cold heat exchanger57and enters a fourth cold heat exchanger59, where a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a fourth cold heat exchanger catalyst passage58, to produce a fifth purified hydrogen feed205. The cold heat exchangers can be combined into one, two, or three heat exchangers with side feeds and exits if desired. In most cases, these heat exchangers will be combined to reduce capital cost, piping, connections, and Cold Box volume. The combination of heat exchangers selected does not impact the technology of the invention or its use.

The fifth purified hydrogen feed205is expanded through an expansion device such as a hydrogen product expansion valve60, to form a two-phase hydrogen feed206that is separated in a hydrogen product separator61. A liquid hydrogen product207is removed from the bottom of the separator. A cold hydrogen vapor208is removed from the top of the separator and fed to the fourth cold heat exchanger59, the third cold heat exchanger57, the second cold heat exchanger55, and the first cold heat exchanger53where it is warmed to provide cooling for the hydrogen feed. The cold hydrogen vapor208forms a first209, second210, and third211warmed hydrogen vapor stream after exiting the fourth59, third57, and second55heat exchangers respectively and exits the heat exchangers as the cold hydrogen recycle stream103shown inFIGS.1and2.

The low-temperature refrigerant134leaves the second refrigerant purifier23shown inFIG.1, is fed to the first cold heat exchanger53ofFIG.2and exits as a first hydrogen refrigerant221that is split between a first expander feed222and a second cold heat exchanger refrigerant feed223. The first expander feed222is expanded in a first hydrogen expander62to produce a first hydrogen expander product224that is used to provide cooling in the second cold heat exchanger55, exiting as a warmed first hydrogen expander product225, and the first cold heat exchanger53before exiting as the intermediate-pressure refrigerant151shown inFIGS.1and2. The second cold heat exchanger refrigerant feed223is fed to the second cold heat exchanger55and exits as a second hydrogen refrigerant226that is split between a second expander feed227and a third cold heat exchanger refrigerant feed231. The second expander feed227is expanded in a second hydrogen expander63to produce a second hydrogen expander product228that is used to provide cooling in the third cold heat exchanger57.

The third cold heat exchanger refrigerant feed231is fed to the third cold heat exchanger57and exits as a third hydrogen refrigerant232that is fed to a hydrogen refrigerant expansion valve64to form a two-phase hydrogen refrigerant233that is separated in a refrigerant separator65. A liquid refrigerant237is removed from the bottom of the separator and provides cooling in the fourth cold heat exchanger59where it is at least partially vaporized and returned to the refrigerant separator as a second two-phase refrigerant238. A cold hydrogen refrigerant vapor234is removed from the top of the refrigerant separator65, mixed with the second hydrogen expander product228to form a cold refrigerant feed229and fed to the third cold heat exchanger57, exiting as a second cold refrigerant feed235, the second cold heat exchanger55, exiting as a third cold refrigerant feed236, and the first cold heat exchanger53where it is warmed to provide cooling for the hydrogen feed. The cold refrigerant feed229exits the cold heat exchangers as the low-pressure refrigerant141shown inFIGS.1and2. Heat exchangers53,55,57and59ofFIG.2may be positioned within the Cold Box7ofFIG.1, or they may be positioned within their own Cold Box or Cold Boxes.

Alternatives to the process shown inFIG.2include processes in which the expanders operate in series instead of parallel or in which the heat exchangers are combined in any of several possible configurations. If helium is used as the refrigerant, and the process is used to liquefy hydrogen, it is not necessary to produce liquid helium and the refrigerant separator65, is not necessary because there is no liquid refrigerant237. None of these changes impact the practice and advantage of the technology described herein.

FIG.3shows another example warm-end process with an improved supplemental refrigerant cooling system. The supplemental refrigerant can be nitrogen or another refrigerant with appropriate refrigeration properties for the desired cycle. All numbers represent essentially the same streams or equipment as shown inFIG.1and previously described. This alternative includes an improved supplemental refrigerant refrigeration loop and the pre-cooled hydrogen feed102is mixed with the cooled refrigerant133and fed to a single hydrogen purifier33to produce a combined pre-cooled hydrogen stream135. Other processes include using the improved supplemental refrigerant refrigeration loop or the mixing of the cold streams, but not the other.

Combining the pre-cooled hydrogen feed102and the purified hydrogen stream132to form a combined purifier feed135has the advantage that only one cryogenic purifier is required for the two streams and produces a combined purifier product136. The disadvantage is that both streams must be at the same pressure and the refrigerant and feed must be the same material. For example, the streams cannot be combined if helium refrigerant is being used to liquefy hydrogen. The benefit of reducing capital cost by eliminating a second purifier and subsequently shrinking the Cold Box may be compared to the cost of reduced operational flexibility to determine if mixing the streams is beneficial. In this case, a portion of the combined purifier product136is split to form the purified hydrogen feed201, as shown inFIG.2, while the remainder becomes the low-temperature refrigerant134shown inFIG.2.

The improved supplemental refrigerant refrigeration loop involves a cooled high-pressure supplemental refrigerant stream211that is fed to the pre-cooling heat exchanger1. A first supplemental refrigerant portion212is taken from the cooled high-pressure supplemental refrigerant stream211and expanded in a first supplemental refrigerant expander4to form a first supplemental refrigerant213that is returned to the pre-cooling heat exchanger1where it provides refrigeration. A second supplemental refrigerant portion214is taken from the cooled high-pressure supplemental refrigerant stream211at a lower temperature than the first portion212and expanded in a second supplemental refrigerant expander5to form a second supplemental refrigerant215that is returned to the pre-cooling heat exchanger1where it provides refrigeration. The remaining supplemental refrigerant217of the cooled high-pressure supplemental refrigerant stream211exits the pre-cooling heat exchanger1at the lowest temperature and is expanded in a supplemental refrigerant expansion valve6to form a cold supplemental refrigerant218that is returned to the pre-cooling heat exchanger1where it provides refrigeration. The cold supplemental refrigerant218is warmed in the pre-cooling heat exchanger1to produce a warmed low-pressure supplemental refrigerant recycle219that is compressed in a first supplemental refrigerant compressor7to form a compressed first supplemental refrigerant220and cooled in a first supplemental refrigerant compressor aftercooler8to produce a first intermediate-pressure supplemental refrigerant recycle221. The first supplemental refrigerant213and the second supplemental refrigerant215are combined in the pre-cooling heat exchanger1and warmed to produce a warmed intermediate-pressure supplemental refrigerant recycle216that combines with the first intermediate-pressure supplemental refrigerant recycle221to produce an intermediate-pressure supplemental refrigerant222. The intermediate-pressure supplemental refrigerant222is compressed in a second supplemental refrigerant compressor9to form a compressed intermediate-pressure supplemental refrigerant223and cooled in a second supplemental refrigerant compressor aftercooler10to produce the cooled high-pressure supplemental refrigerant stream211. The first supplemental refrigerant compressor and/or the second supplemental refrigerant compressor can be a single-stage compressor, a compressor with more than one stage, or a stage or stages of a multi-stage compressor such that the second supplemental refrigerant compressor operates at a higher pressure than the first supplemental refrigerant compressor.

In one alternative, part of the cooled, pressurized, first supplemental refrigerant portion251of the first portion212of the high-pressure supplemental refrigerant stream211is exported to an outside process31for use as a refrigerant. The supplemental refrigerant then returns to the process as a supplemental refrigerant return stream252. The outside process31can be any process that can take advantage of additional refrigeration between the temperature of the first supplemental refrigerant portion212and ambient temperature. Another alternative is that a portion of the first supplemental refrigerant213can be exported. This has the advantage of being at a lower temperature and not requiring an additional expansion device in the outside process31, but also has lower pressure and less driving force to move through the outside process31.

In the process ofFIG.4, a warm mixing vessel refrigeration feed165is fed to the pre-cooling heat exchanger1before it is expanded in the mixing vessel refrigeration expansion device45. This allows the cooled mixing vessel refrigerant169to be at a colder temperature than would otherwise be possible and provides additional cooling to the process. Another variation shown inFIG.4is that the first mixed refrigerant liquid181is split and expanded in a first mixed refrigerant liquid expansion device47B or a second mixed refrigerant liquid expansion device47A, such as a valve, to cool the stream and reduce its pressure to form a cooled low-pressure first mixed refrigerant liquid stream182or a second low-pressure mixed refrigerant recycle stream183A, which has a higher pressure than the cooled low-pressure first mixed refrigerant liquid stream182. The cooled low-pressure first mixed refrigerant liquid stream182is combined with the cooled low-pressure second mixed refrigerant liquid stream185to form a cold mixed refrigerant recycle stream183B, which is mixed with the low-pressure refrigerant141in to the pre-cooling heat exchanger1to provide refrigeration to the process.

Other potential configurations that enable practicing the disclosed technology will be evident to those skilled in the art.

Example

The following example, with reference toFIG.5, shows one possible method for practicing the invention. The process produces 15 tonnes/day (625 kg/hr) of liquid hydrogen product. Conditions and compositions for selected streams are shown in Table 1.

The mixed refrigerant selected for this example is a mixture of hydrogen, propane, and isopentane. The molecular weight of the low-pressure gas mixture121is ˜28 kg/kgmol and the molecular weight of the second mixture123is ˜11 kg/kgmol. These are high enough to use dynamic compressors, which have higher reliability than typical positive displacement compressors used for hydrogen, which has a molecular weight of ˜2 kg/kgmol. Other hydrocarbons or other refrigerants, including halogenated and partially halogenated hydrocarbons can be used. Other compositions or ratios can also be used. Because of the conditions in the example and the refrigerant composition, there is no flow in streams160,167,170,172, or175shown inFIG.4, so these streams are not shown inFIG.5.

The high-pressure hydrogen feed101is 373.5 kgmol/hr. The warm hydrogen recycle stream104flow is 35.3 kgmol/hr. This means that 338.2 kgmol/hr of hydrogen is liquefied in the process. The liquid product flow is 15 metric tonnes per day, or 310.0 kgmol/hr. Estimated losses are 7-10%, or about 8.5% from the process to the trucks going out the plant gate. Much of these losses can be recovered and recycled to the feed with appropriate equipment not described here.

The refrigeration required to produce that liquid product is provided by the low-pressure gas mixture121that contains 51.4% hydrogen, 29.4% propane, and 19.2% isopentane that is compressed in the first mixed gas compressor11from 1.2 bar to 4.0 bar. This stream is mixed with the mixing vessel recycle feed152in the mixing vessel13to form the second mixture123and compressed to 34.1 bar and separated in the second phase separator19. The second liquid162leaving the second phase separator19contains most of the isopentane and some propane with a small amount of dissolved hydrogen. This stream is cooled to 199.8 K in the pre-cooling heat exchanger1and is recycled to the mixing vessel13.

The second phase separator vapor127exits the top of the second phase separator19and is cooled to 155.3 K in the pre-cooling heat exchanger1to form the first cooled mixed refrigerant128that is fed to the first mixed refrigerant separator20. The first mixed refrigerant liquid181, containing nearly all the remaining isopentane and most of the propane exits the bottom of the first mixed refrigerant separator20and is split into streams183A, which is expanded to 4.1 bar and has a molar flow rate of 45.4 kgmol/hr and182, which is expanded to 1.3 bar and has a flow of 182.7 kgmol/hr. Both streams provide cooling in the pre-cooling heat exchanger and are recycled to the first stage (183B) and the second stage (183A) of the mixed gas compressor.

The first mixed refrigerant vapor129, containing 99.98% hydrogen, exits the top of the first mixed refrigerant separator20and returns to the pre-cooling heat exchanger1where it is cooled further to 110.9 K, forming the second cooled mixed refrigerant stream130that is fed to the second mixed refrigerant separator21. The second mixed refrigerant liquid184, which contains most of the remaining propane and has a flow of only 0.3 kgmol/hr, exits the bottom of the second mixed refrigerant separator21and is expanded in a second mixed refrigerant liquid expansion device48, such as a valve, to cool the stream and reduce its pressure before it forms part of the returning refrigerant stream183B described above.

The second mixed refrigerant vapor131exits the top of the second mixed refrigerant separator21and is purified in a mixed refrigerant purifier22to remove any remaining propane, less than 1 ppm in this example. The purified hydrogen stream132exits the mixed refrigerant purifier22and returns to the pre-cooling heat exchanger1where it is cooled to 80.1 K and exits as the cooled refrigerant133that is further purified in the second refrigerant purifier23, similar to the mixed refrigerant purifier22, except that the second refrigerant purifier removes the 1 ppm of nitrogen from the original hydrogen feed. The low-temperature refrigerant134leaves the second refrigerant purifier23and is fed to the hydrogen liquefaction process.

After cycling in a closed loop through the liquefaction process, the pure hydrogen low-temperature refrigerant returns as two separate streams: low-pressure stream141and intermediate-pressure stream151. The low-pressure refrigerant141at 1.3 bar is recycled from the hydrogen liquefaction process and enters the pre-cooling heat exchanger1to provide cooling and is returned to the first stage of the mixed gas compressor. The intermediate-pressure refrigerant151at 4.1 bar leaves the hydrogen liquefaction process and enters the pre-cooling heat exchanger1to provide cooling and is returned to the second stage of the mixed gas compressor.

While the preferred embodiments of the disclosure have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the disclosure, the scope of which is defined by the following claims.