Patent Application
20230366620
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.
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 1/600th the 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 C5 hydrocarbons 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.
There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.
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.
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 in
The cold hydrogen recycle stream 103 is warmed in the pre-cooling heat exchanger 1 to provide cooling for the high-pressure hydrogen feed 101. The cold hydrogen recycle will be at lower pressure than the high-pressure hydrogen feed 101. This stream can optionally be passed over a para-ortho conversion catalyst 3 to take advantage of extra cooling capability available from the conversion. The cold hydrogen recycle stream 103 exits the pre-cooling heat exchanger 1 as a warm hydrogen recycle stream 104 that can be compressed and returned to the process as part of the high-pressure hydrogen feed 101.
In many cases, an optional high-pressure supplemental refrigerant, such as nitrogen, 111 is cooled in the pre-cooling heat exchanger 1 to form a cold high-pressure supplemental refrigerant stream 112 that is expanded in a supplemental refrigerant expander 4 to form a cold supplemental refrigerant stream 113. The cold supplemental refrigerant stream 113 provides cooling to the pre-cooling heat exchanger 1 and exits as a warm low-pressure supplemental refrigerant stream 114 that is compressed in a supplemental refrigerant compressor 5 to form a hot compressed supplemental refrigerant stream 115 that is cooled in a supplemental refrigerant compressor aftercooler 6 to form the high-pressure supplemental refrigerant feed 111. The supplemental refrigerant compressor 5 and aftercooler 6 can consist of more than one stage depending on the desired pressure rise. Likewise, the supplemental refrigerant expander 4 can also consist of more than one stage. Alternatively, the cycle can be enhanced to include a more efficient scheme, such as the one shown in
A low-pressure gas mixture 121 comprised 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 compressor 11 and cooled in a first compressor aftercooler 12 to form a first intermediate-pressure mixture 122 that can be sent to a mixing vessel 13. The first mixed gas compressor 11 can 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 vessel 13 is 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 mixture 123 exits the mixing vessel 13 and is compressed in a second mixed gas compressor 14 and cooled in a second compressor aftercooler 15 to form a second intermediate-pressure mixture 124 that is fed to a first phase separator or interstage separation device 16 designed to remove any small amount of liquid that might form. The second mixed gas compressor 14 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 first mixed gas compressor. The controlled operation of the mixing vessel 13 heat input maximizes the amount of higher molecular weight component(s) in the second mixture 123 by 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 mixture 125 exits the interstage separation device 16 and is compressed in a third mixed gas compressor 17 and cooled in a third compressor aftercooler 18 to form a high-pressure mixture 126 that is fed to a second phase separator or a high-pressure accumulator 19. 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 in
A first liquid 160 exits the bottom of the interstage separation device 16 and can be drained through a first phase separator valve 41 to form a low-pressure first liquid 161. A second liquid 162 that contains primarily the high molecular weight component(s) in the original mixture exits the bottom of the high-pressure accumulator 19 and can be drained through a second phase separator valve 42 to form a low-pressure second liquid 163 and mixed with the low-pressure first liquid 161 to form a low-pressure mixed liquid 164.
The low-pressure mixed liquid 164 can be distributed among four different streams, a mixing vessel recycle stream 170, a mixing vessel refrigeration feed 166, a low-pressure gas mixture vessel refrigeration feed 167, and a low-pressure gas mixture vessel recycle stream 172. The mixing vessel recycle stream 170 is expanded through a mixing vessel valve 43 to form a low-pressure mixing vessel recycle stream 171 that is returned to the mixing vessel 13. The mixing vessel refrigeration feed 166 is expanded through a mixing vessel refrigeration expansion device 45, such as a valve, to form a cooled mixing vessel refrigerant 169 that provides cooling to the pre-cooling heat exchanger 1 and returns to the mixing vessel 13. A portion of the cooled mixing vessel refrigerant 174 can be sent through the pre-cooling heat exchanger 1 as a separate stream so that it exits the pre-cooling heat exchanger 1 as a two-phase stream. This can decrease the temperature difference in the heat exchanger and improve efficiency. The low-pressure gas mixture vessel refrigeration feed 167 is expanded through a low-pressure mixture vessel refrigeration expansion device 46, such as a valve, to form a cooled low-pressure gas mixture vessel refrigerant 168 that provides cooling to the pre-cooling heat exchanger 1 and returns to a low-pressure gas mixture vessel 24. The low-pressure gas mixture vessel recycle stream 172 is expanded through a low-pressure gas mixture vessel valve 44 to form a reduced pressure gas mixture vessel recycle stream 173 that returns to the low-pressure gas mixture vessel 24. An accumulated liquid 175 from the mixing vessel 13 can be pressurized using a mixing vessel pump 49 to from a pressurized accumulated liquid 176 and mixed with the first liquid 160 or the second liquid 162. The pump 49 and the mixing vessel 13 allow the molecular weight of the compressor feed streams to be controlled and maintained at a relatively high level. Alternatively (not shown), the accumulated liquid 175 can be mixed with a low-pressure gas mixture vessel feed 143 and fed to the low-pressure gas mixture vessel 24.
A second phase separator vapor 127 exits the top of the high-pressure accumulator 19 and is cooled in the pre-cooling heat exchanger 1 to form a first cooled mixed refrigerant 128 that is fed to a first mixed refrigerant separator 20. A first mixed refrigerant vapor 129 exits the top of the first mixed refrigerant separator 20 and returns to the pre-cooling heat exchanger 1 where it is cooled further to form a second cooled mixed refrigerant stream 130 that is fed to a second mixed refrigerant separator 21. A second mixed refrigerant vapor 131 exits the top of the second mixed refrigerant separator 21 and is purified in a mixed refrigerant purifier 22 that removes essentially all the mixture components that have a boiling point above 80 K. The mixed refrigerant purifier 22 can 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 feed 191 is used to sweep captured impurities out of the mixed refrigerant purifier 22 to 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 stream 192 can be recycled to the inlet of the first mixed gas compressor or the low-pressure gas mixing vessel 24. This allows the system to recover the trace amounts of other substances in the mixed refrigerant that were removed in the refrigerant purifier 22. 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 stream 132 exits the mixed refrigerant purifier 22 and returns to the pre-cooling heat exchanger 1 where it is cooled further and exits as a cooled refrigerant 133 that is further purified in a second refrigerant purifier 23, similar to the mixed refrigerant purifier 22, 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 refrigerant 134 leaves the second refrigerant purifier 23 and is fed to the hydrogen liquefaction process. A second refrigerant purifier regeneration feed 193 is used to regenerate the second refrigerant purifier 23, similar to the mixed refrigerant purifier 22. All or a portion of a second impurity-containing regeneration stream 194 can 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 feed 101 and 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 liquid 181 exits the bottom of the first mixed refrigerant separator 20 and is expanded in a first mixed refrigerant liquid expansion device 47, such as a valve, to cool the stream and reduce its pressure to form a cooled low-pressure first mixed refrigerant liquid stream 182. A second mixed refrigerant liquid 184 exits the bottom of the second mixed refrigerant separator 21 and is expanded in a second mixed refrigerant liquid expansion device 48, such as a valve, to cool the stream and reduce its pressure to form a cooled low-pressure second mixed refrigerant liquid stream 185. The cooled low-pressure first mixed refrigerant liquid stream 182 and the cooled low-pressure second mixed refrigerant liquid stream 185 combine to make a low-pressure mixed refrigerant recycle stream 183 that enters the pre-cooling heat exchanger 1 to provide cooling.
A low-pressure refrigerant 141 is recycled from the hydrogen liquefaction process and enters the pre-cooling heat exchanger 1 to provide cooling. The low-pressure refrigerant 141 mixes with the cooled low-pressure gas mixture vessel refrigerant 168 and the low-pressure mixed refrigerant recycle stream 183 in the pre-cooling heat exchanger 1 and exits as a warmed mixed refrigerant 142 that combines with the reduced pressure gas mixture vessel recycle stream 173 to produce the low-pressure gas mixture vessel feed 143 that enters the low-pressure gas mixture vessel 24.
An intermediate-pressure refrigerant 151 leaves the hydrogen liquefaction process and enters the pre-cooling heat exchanger 1 to provide cooling. The intermediate-pressure refrigerant 151 mixes with the cooled mixing vessel refrigerant 169 in the pre-cooling heat exchanger 1 and exits as a mixing vessel recycle feed 152 that enters the mixing vessel 13.
The pre-cooled hydrogen feed 102 from
The second purified hydrogen feed 202 exits the first cold heat exchanger 53 and enters a second cold heat exchanger 55, where a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a second cold heat exchanger catalyst passage 54, to produce a third purified hydrogen feed 203. The third purified hydrogen feed 203 exits the second cold heat exchanger 55 and enters a third cold heat exchanger 57, where a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a third cold heat exchanger catalyst passage 56, to produce a fourth purified hydrogen feed 204. The fourth purified hydrogen feed 204 exits the third cold heat exchanger 57 and enters a fourth cold heat exchanger 59, where a portion of the ortho hydrogen is converted to para hydrogen over a conversion catalyst located in a fourth cold heat exchanger catalyst passage 58, to produce a fifth purified hydrogen feed 205. 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 feed 205 is expanded through an expansion device such as a hydrogen product expansion valve 60, to form a two-phase hydrogen feed 206 that is separated in a hydrogen product separator 61. A liquid hydrogen product 207 is removed from the bottom of the separator. A cold hydrogen vapor 208 is removed from the top of the separator and fed to the fourth cold heat exchanger 59, the third cold heat exchanger 57, the second cold heat exchanger 55, and the first cold heat exchanger 53 where it is warmed to provide cooling for the hydrogen feed. The cold hydrogen vapor 208 forms a first 209, second 210, and third 211 warmed hydrogen vapor stream after exiting the fourth 59, third 57, and second 55 heat exchangers respectively and exits the heat exchangers as the cold hydrogen recycle stream 103 shown in
The low-temperature refrigerant 134 leaves the second refrigerant purifier 23 shown in
The third cold heat exchanger refrigerant feed 231 is fed to the third cold heat exchanger 57 and exits as a third hydrogen refrigerant 232 that is fed to a hydrogen refrigerant expansion valve 64 to form a two-phase hydrogen refrigerant 233 that is separated in a refrigerant separator 65. A liquid refrigerant 237 is removed from the bottom of the separator and provides cooling in the fourth cold heat exchanger 59 where it is at least partially vaporized and returned to the refrigerant separator as a second two-phase refrigerant 238. A cold hydrogen refrigerant vapor 234 is removed from the top of the refrigerant separator 65, mixed with the second hydrogen expander product 228 to form a cold refrigerant feed 229 and fed to the third cold heat exchanger 57, exiting as a second cold refrigerant feed 235, the second cold heat exchanger 55, exiting as a third cold refrigerant feed 236, and the first cold heat exchanger 53 where it is warmed to provide cooling for the hydrogen feed. The cold refrigerant feed 229 exits the cold heat exchangers as the low-pressure refrigerant 141 shown in
Alternatives to the process shown in
Combining the pre-cooled hydrogen feed 102 and the purified hydrogen stream 132 to form a combined purifier feed 135 has the advantage that only one cryogenic purifier is required for the two streams and produces a combined purifier product 136. 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 product 136 is split to form the purified hydrogen feed 201, as shown in
The improved supplemental refrigerant refrigeration loop involves a cooled high-pressure supplemental refrigerant stream 211 that is fed to the pre-cooling heat exchanger 1. A first supplemental refrigerant portion 212 is taken from the cooled high-pressure supplemental refrigerant stream 211 and expanded in a first supplemental refrigerant expander 4 to form a first supplemental refrigerant 213 that is returned to the pre-cooling heat exchanger 1 where it provides refrigeration. A second supplemental refrigerant portion 214 is taken from the cooled high-pressure supplemental refrigerant stream 211 at a lower temperature than the first portion 212 and expanded in a second supplemental refrigerant expander 5 to form a second supplemental refrigerant 215 that is returned to the pre-cooling heat exchanger 1 where it provides refrigeration. The remaining supplemental refrigerant 217 of the cooled high-pressure supplemental refrigerant stream 211 exits the pre-cooling heat exchanger 1 at the lowest temperature and is expanded in a supplemental refrigerant expansion valve 6 to form a cold supplemental refrigerant 218 that is returned to the pre-cooling heat exchanger 1 where it provides refrigeration. The cold supplemental refrigerant 218 is warmed in the pre-cooling heat exchanger 1 to produce a warmed low-pressure supplemental refrigerant recycle 219 that is compressed in a first supplemental refrigerant compressor 7 to form a compressed first supplemental refrigerant 220 and cooled in a first supplemental refrigerant compressor aftercooler 8 to produce a first intermediate-pressure supplemental refrigerant recycle 221. The first supplemental refrigerant 213 and the second supplemental refrigerant 215 are combined in the pre-cooling heat exchanger 1 and warmed to produce a warmed intermediate-pressure supplemental refrigerant recycle 216 that combines with the first intermediate-pressure supplemental refrigerant recycle 221 to produce an intermediate-pressure supplemental refrigerant 222. The intermediate-pressure supplemental refrigerant 222 is compressed in a second supplemental refrigerant compressor 9 to form a compressed intermediate-pressure supplemental refrigerant 223 and cooled in a second supplemental refrigerant compressor aftercooler 10 to produce the cooled high-pressure supplemental refrigerant stream 211. 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 portion 251 of the first portion 212 of the high-pressure supplemental refrigerant stream 211 is exported to an outside process 31 for use as a refrigerant. The supplemental refrigerant then returns to the process as a supplemental refrigerant return stream 252. The outside process 31 can be any process that can take advantage of additional refrigeration between the temperature of the first supplemental refrigerant portion 212 and ambient temperature. Another alternative is that a portion of the first supplemental refrigerant 213 can be exported. This has the advantage of being at a lower temperature and not requiring an additional expansion device in the outside process 31, but also has lower pressure and less driving force to move through the outside process 31.
In the process of
Other potential configurations that enable practicing the disclosed technology will be evident to those skilled in the art.
The following example, with reference to
The mixed refrigerant selected for this example is a mixture of hydrogen, propane, and isopentane. The molecular weight of the low-pressure gas mixture 121 is ˜28 kg/kgmol and the molecular weight of the second mixture 123 is ˜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 streams 160, 167, 170, 172, or 175 shown in
The high-pressure hydrogen feed 101 is 373.5 kgmol/hr. The warm hydrogen recycle stream 104 flow 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 mixture 121 that contains 51.4% hydrogen, 29.4% propane, and 19.2% isopentane that is compressed in the first mixed gas compressor 11 from 1.2 bar to 4.0 bar. This stream is mixed with the mixing vessel recycle feed 152 in the mixing vessel 13 to form the second mixture 123 and compressed to 34.1 bar and separated in the second phase separator 19. The second liquid 162 leaving the second phase separator 19 contains 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 exchanger 1 and is recycled to the mixing vessel 13.
The second phase separator vapor 127 exits the top of the second phase separator 19 and is cooled to 155.3 K in the pre-cooling heat exchanger 1 to form the first cooled mixed refrigerant 128 that is fed to the first mixed refrigerant separator 20. The first mixed refrigerant liquid 181, containing nearly all the remaining isopentane and most of the propane exits the bottom of the first mixed refrigerant separator 20 and is split into streams 183A, which is expanded to 4.1 bar and has a molar flow rate of 45.4 kgmol/hr and 182, 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 vapor 129, containing 99.98% hydrogen, exits the top of the first mixed refrigerant separator 20 and returns to the pre-cooling heat exchanger 1 where it is cooled further to 110.9 K, forming the second cooled mixed refrigerant stream 130 that is fed to the second mixed refrigerant separator 21. The second mixed refrigerant liquid 184, 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 separator 21 and is expanded in a second mixed refrigerant liquid expansion device 48, such as a valve, to cool the stream and reduce its pressure before it forms part of the returning refrigerant stream 183B described above.
The second mixed refrigerant vapor 131 exits the top of the second mixed refrigerant separator 21 and is purified in a mixed refrigerant purifier 22 to remove any remaining propane, less than 1 ppm in this example. The purified hydrogen stream 132 exits the mixed refrigerant purifier 22 and returns to the pre-cooling heat exchanger 1 where it is cooled to 80.1 K and exits as the cooled refrigerant 133 that is further purified in the second refrigerant purifier 23, similar to the mixed refrigerant purifier 22, except that the second refrigerant purifier removes the 1 ppm of nitrogen from the original hydrogen feed. The low-temperature refrigerant 134 leaves the second refrigerant purifier 23 and 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 stream 141 and intermediate-pressure stream 151. The low-pressure refrigerant 141 at 1.3 bar is recycled from the hydrogen liquefaction process and enters the pre-cooling heat exchanger 1 to provide cooling and is returned to the first stage of the mixed gas compressor. The intermediate-pressure refrigerant 151 at 4.1 bar leaves the hydrogen liquefaction process and enters the pre-cooling heat exchanger 1 to 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.
This application claims the benefit of U.S. Provisional Application No. 63/342,338, filed May 16, 2022, the contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63342338 | May 2022 | US |
