A single-stage mixed refrigerant hydrogen liquefaction system

Abstract

This invention discloses a single-stage mixed refrigerant refrigeration hydrogen liquefaction system, belonging to the field of refrigeration and cryogenic engineering technology. The hydrogen liquefaction system includes a compressor unit, a vacuum cold box, a heat exchanger unit, an expander unit, a gas-liquid separator unit, an ejector, and a liquid hydrogen storage tank, all connected by pipelines. Pentane, propane, ethane, ethylene, neon, hydrogen, and helium are mixed in a certain proportion as the mixed refrigerant according to the refrigeration temperature range and cooling capacity. The multi-stage gas-liquid separator can redistribute the mixed refrigerant, thereby achieving a single-stage mixed refrigerant refrigeration cycle while avoiding the risk of freezing and blockage. This system can produce 13-25 tons of liquid hydrogen per day, with a hydrogen liquefaction rate of over 97% and a secondary hydrogen content of over 98% in the liquid hydrogen product. Due to its simple process and fewer equipment, the system can significantly reduce the size of the cold box, thereby reducing equipment manufacturing and investment costs. Furthermore, the system can reduce the specific energy consumption to 10 kWh / kg liquid hydrogen, effectively improving the economic efficiency of the hydrogen liquefaction plant.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration and cryogenic engineering technology, and specifically relates to a hydrogen liquefaction system for single-stage mixed refrigerant refrigeration. Background Technology

[0002] Aside from nuclear fuel, hydrogen has the highest calorific value per unit mass among all fossil fuels, chemical fuels, and biofuels, and its combustion product is only water. Therefore, hydrogen energy is an important pathway to achieving efficient energy utilization and zero carbon emissions.

[0003] Currently, hydrogen energy storage mainly takes two forms: high-pressure hydrogen and liquid hydrogen. For the same volume, the energy density of liquid hydrogen is 1.8 times that of 70MPa high-pressure hydrogen, indicating that liquid hydrogen has economic advantages in storage and long-distance transportation. Therefore, liquid hydrogen is an important way to promote the large-scale application of hydrogen energy.

[0004] Since hydrogen liquefies at atmospheric pressure at a temperature as low as around 20K, cooling it from room temperature and pressure to its liquefaction temperature requires an industrial refrigeration system. Currently, most industrial systems use hydrogen refrigeration based on liquid nitrogen precooling via the Claude cycle or the Brayton cycle. These systems are complex, involve numerous pieces of equipment, and have high energy consumption, with a specific energy consumption of approximately 15 kWh / kg of liquid hydrogen. Therefore, there is an urgent need to design a hydrogen liquefaction system with a simple process and low energy consumption. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of complex processes and high energy consumption in existing hydrogen liquefaction systems, and to provide a single-stage mixed refrigerant cooling hydrogen liquefaction system. On the one hand, it can reduce the specific energy consumption of the system to 10 kWh / kg liquid hydrogen, and on the other hand, it simplifies the process flow, reduces equipment investment, and helps to promote the large-scale use of liquid hydrogen.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] This invention provides a single-stage hydrogen liquefaction system using a mixed refrigerant, comprising a compressor unit, a vacuum cold box, a heat exchanger unit, an expander unit, a gas-liquid separator unit, an ejector, and a liquid hydrogen storage tank, all interconnected by pipelines. The vacuum cold box houses the heat exchanger unit, the expander unit, the gas-liquid separator unit, and the ejector. The refrigerant used in this hydrogen liquefaction system is a mixed refrigerant.

[0008] The hydrogen compressor inlet receives feedstock hydrogen through the first channel, and its outlet connects to the gas phase inlet of the first-stage heat exchanger through the second channel. The gas phase outlet of the first-stage heat exchanger connects to the gas phase inlet of the second-stage heat exchanger through the third channel. The gas phase outlet of the second-stage heat exchanger connects to the gas phase inlet of the third-stage heat exchanger through the fourth channel. The gas phase outlet of the third-stage heat exchanger connects to the gas phase inlet of the fourth-stage heat exchanger through the fifth channel. The gas phase outlet of the fourth-stage heat exchanger connects to the gas phase inlet of the fifth-stage heat exchanger through the sixth channel. The gas phase outlet of the fifth-stage heat exchanger connects to the ejector inlet through the seventh channel. The ejector outlet connects to the gas phase inlet of the sixth-stage heat exchanger through the eighth channel. The gas phase outlet of the sixth-stage heat exchanger connects sequentially to the inlet of the hydrogen separator in the gas-liquid separator group through the ninth and tenth channels. The liquid phase outlet of the hydrogen separator connects to the liquid hydrogen storage tank through the eleventh channel, forming a flow pipeline from feedstock hydrogen to liquid hydrogen.

[0009] The mixed refrigerant is delivered and driven by the refrigerant compressor within the system to complete a single-stage mixed refrigerant refrigeration cycle.

[0010] As a preferred embodiment, the specific structure of the above-mentioned single-stage mixed refrigerant refrigeration cycle is as follows:

[0011] The gas-liquid separator assembly further includes a primary separator, a secondary separator, a tertiary separator, and a quaternary separator. The outlet of the refrigerant compressor is connected to the first refrigerant inlet of the primary heat exchanger via a second refrigerant channel. The first refrigerant outlet of the primary heat exchanger is connected to the inlet of the primary separator via a third refrigerant channel. The gas phase outlet of the primary separator is connected to the first refrigerant inlet of the secondary heat exchanger via a fourth refrigerant channel. The liquid phase outlet of the primary separator is sequentially provided with a fifth refrigerant channel and a sixth refrigerant channel.

[0012] The first refrigerant outlet of the secondary heat exchanger is connected to the inlet of the secondary separator through the seventh refrigerant channel. The gas phase outlet of the secondary separator is connected to the first refrigerant inlet of the tertiary heat exchanger through the eighth refrigerant channel. The liquid phase outlet of the secondary separator is provided with the ninth and tenth refrigerant channels in sequence.

[0013] The first refrigerant outlet of the three-stage heat exchanger is connected to the inlet of the three-stage separator through the eleventh refrigerant channel. The gas phase outlet of the three-stage separator is connected to the first refrigerant inlet of the four-stage heat exchanger through the twelfth refrigerant channel. The liquid phase outlet of the three-stage separator is provided with the thirteenth and fourteenth refrigerant channels in sequence.

[0014] The first refrigerant outlet of the fourth-stage heat exchanger is connected to the inlet of the fourth-stage separator via the fifteenth refrigerant channel. The gas phase outlet of the fourth-stage separator is connected to the first refrigerant inlet of the fifth-stage heat exchanger via the sixteenth refrigerant channel. The liquid phase outlet of the fourth-stage separator is sequentially provided with the seventeenth and eighteenth refrigerant channels. The first refrigerant outlet of the fifth-stage heat exchanger is divided into two pipelines, the twentieth and twenty-second refrigerant channels, via the nineteenth refrigerant channel.

[0015] The outlet of the 20th refrigerant channel connects to the inlet of the first-stage expander, and the outlet of the first-stage expander connects to the inlet of the 21st refrigerant channel. The outlet of the 22nd refrigerant channel connects to the first refrigerant inlet of the sixth-stage heat exchanger. The first refrigerant outlet of the sixth-stage heat exchanger connects to the inlet of the second-stage expander via the 23rd refrigerant channel for cooling. The outlet of the second-stage expander connects to the second refrigerant inlet of the sixth-stage heat exchanger via the 24th refrigerant channel, and the second refrigerant outlet of the sixth-stage heat exchanger connects to the inlet of the 25th refrigerant channel. The outlets of the 21st and 25th refrigerant channels merge and then connect to the second refrigerant inlet of the fifth-stage heat exchanger via the 26th refrigerant channel. The second refrigerant outlet of the fifth-stage heat exchanger merges with the 18th refrigerant channel and then connects to the second refrigerant inlet of the fourth-stage heat exchanger via the 27th refrigerant channel. The second refrigerant outlet of the fourth-stage heat exchanger merges with the 14th refrigerant channel and then connects to the second refrigerant inlet of the third-stage heat exchanger via the 28th refrigerant channel. The second refrigerant outlet of the third-stage heat exchanger merges with the tenth refrigerant channel and then connects to the second refrigerant inlet of the second-stage heat exchanger via the twenty-ninth refrigerant channel. The second refrigerant outlet of the second-stage heat exchanger merges with the sixth refrigerant channel and then connects to the second refrigerant inlet of the first-stage heat exchanger via the thirtieth refrigerant channel. The second refrigerant outlet of the first-stage heat exchanger connects to the inlet of the refrigerant compressor via the first refrigerant channel, thus forming a single-stage mixed refrigerant refrigeration cycle.

[0016] Furthermore, a primary throttling valve is installed between the fifth and sixth refrigerant passages. A secondary throttling valve is installed between the ninth and tenth refrigerant passages. A tertiary throttling valve is installed between the thirteenth and fourteenth refrigerant passages. A quaternary throttling valve is installed between the seventeenth and eighteenth refrigerant passages.

[0017] Preferably, the above-mentioned mixed refrigerant is composed of pentane, propane, ethane, ethylene, neon, hydrogen and helium.

[0018] Preferably, the molar ratios of the components in the above-mentioned single-stage mixed refrigerant are as follows: 2.1% pentane, 4.0% propane, 5.0% ethane, 12.8% ethylene, 2.4% neon, 61.5% hydrogen and 12.2% helium.

[0019] Preferably, a hydrogen throttling valve is provided between the ninth and tenth channels.

[0020] Preferably, the hydrogen flowing out of the gas phase outlet of the hydrogen separator and the hydrogen evaporated in the liquid hydrogen storage tank are introduced into the ejector through the twelfth channel as an entrainer to recover hydrogen.

[0021] Preferably, the first-stage, second-stage, third-stage, fourth-stage, fifth-stage, and sixth-stage heat exchangers mentioned above are all aluminum plate-fin heat exchangers.

[0022] Preferably, the feed hydrogen channels of the aforementioned three-stage, four-stage, five-stage, and six-stage heat exchangers are filled with ortho- and para-hydrogen conversion catalysts with corresponding catalytic performance according to the temperature zone.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention provides a hydrogen liquefaction system for single-stage mixed refrigerant refrigeration, wherein pentane, propane, ethane, ethylene, neon, hydrogen and helium are selected according to the refrigeration temperature range and cooling capacity and mixed in a certain proportion as mixed refrigerant to realize a hydrogen liquefaction system for single-stage mixed refrigerant refrigeration cycle.

[0025] (2) The hydrogen liquefaction system for single-stage mixed refrigerant refrigeration provided by the present invention can achieve the design requirements with the lowest mixed refrigerant flow rate and the purpose of preventing freezing and blockage by optimizing process parameters and redistributing the mixed refrigerant composition through multi-stage gas-liquid separation.

[0026] (3) The hydrogen liquefaction system provided by this invention can produce 13-25 tons of liquefied hydrogen per day, with a hydrogen liquefaction rate of over 97% and a secondary hydrogen content of over 98% in the liquid hydrogen product. Due to its simple process and fewer equipment requirements, the system can significantly reduce the size of the cold box, thereby reducing equipment manufacturing and investment costs. Furthermore, the system can reduce the specific energy consumption to 10 kWh / kg of liquid hydrogen, effectively improving the economic efficiency of the hydrogen liquefaction plant. Attached Figure Description

[0027] Figure 1 This embodiment provides a schematic diagram of a hydrogen liquefaction system for single-stage mixed refrigerant refrigeration.

[0028] In the diagram: HE1—First-stage heat exchanger, HE2—Second-stage heat exchanger, HE3—Third-stage heat exchanger, HE4—Fourth-stage heat exchanger, HE5—Fifth-stage heat exchanger, HE6—Sixth-stage heat exchanger, C1—Hydrogen compressor, C2—Refrigerant compressor, D1—First-stage separator, D2—Second-stage separator, D3—Third-stage separator, D4—Fourth-stage separator, D5—Hydrogen separator, E1—First-stage expander, E2—Second-stage expander, V1—First-stage throttling valve, V2—Second-stage throttling valve, V3—Third-stage throttling valve Valve, V4—Four-stage throttle valve, V5—Hydrogen throttle valve, J—Ejector, H1—First channel, H2—Second channel, H3—Third channel, H4—Fourth channel, H5—Fifth channel, H6—Sixth channel, H7—Seventh channel, H8—Eighth channel, H9—Ninth channel, H10—Tenth channel, H11—Eleventh channel, H12—Twelfth channel, M1—First refrigerant channel, M2—Second refrigerant channel, M3—Third refrigerant channel, M4—Fourth refrigerant channel M5—Fifth refrigerant channel, M6—Sixth refrigerant channel, M7—Seventh refrigerant channel, M8—Eighth refrigerant channel, M9—Ninth refrigerant channel, M10—Tenth refrigerant channel, M11—Eleventh refrigerant channel, M12—Twelfth refrigerant channel, M13—Thirteenth refrigerant channel, M14—Fourteenth refrigerant channel, M15—Fifteenth refrigerant channel, M16—Sixteenth refrigerant channel, M17—Seventeenth refrigerant channel, M18—Eighteenth refrigerant channel Refrigerant passages: M19—19th refrigerant passage, M20—20th refrigerant passage, M21—21st refrigerant passage, M22—22nd refrigerant passage, M23—23rd refrigerant passage, M24—24th refrigerant passage, M25—25th refrigerant passage, M26—26th refrigerant passage, M27—27th refrigerant passage, M28—28th refrigerant passage, M29—29th refrigerant passage, M30—30th refrigerant passage. Detailed Implementation

[0029] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0030] like Figure 1As shown, this embodiment provides a single-stage mixed refrigerant refrigeration hydrogen liquefaction system, including a compressor unit, a vacuum cold box, a heat exchanger unit, an expander unit, a gas-liquid separator, a throttling valve, an ejector, and a liquid hydrogen storage tank. The vacuum cold box contains a first-stage heat exchanger HE1, a second-stage heat exchanger HE2, a third-stage heat exchanger HE3, a fourth-stage heat exchanger HE4, a fifth-stage heat exchanger HE5, a sixth-stage heat exchanger HE6, a first-stage expander E1, a second-stage expander E2, a first-stage separator D1, a second-stage separator D2, a third-stage separator D3, a fourth-stage separator D4, a hydrogen separator D5, a first-stage throttling valve V1, a second-stage throttling valve V2, a third-stage throttling valve V3, a fourth-stage throttling valve V4, a hydrogen throttling valve V5, and an ejector J.

[0031] The inlet of hydrogen compressor C1 receives feedstock hydrogen through the first channel H1, and its outlet is connected to the gas phase inlet of the first-stage heat exchanger HE1 through the second channel H2. The gas phase outlet of the first-stage heat exchanger HE1 is connected to the gas phase inlet of the second-stage heat exchanger HE2 through the third channel H3. The gas phase outlet of the second-stage heat exchanger HE2 is connected to the gas phase inlet of the third-stage heat exchanger HE3 through the fourth channel H4. The gas phase outlet of the third-stage heat exchanger HE3 is connected to the gas phase inlet of the fourth-stage heat exchanger HE4 through the fifth channel H5. The gas phase outlet of the fourth-stage heat exchanger HE4 is connected to the gas phase inlet of the fifth-stage heat exchanger HE5 through the sixth channel H6. The gas phase outlet of the fifth-stage heat exchanger HE5 is connected to the inlet of ejector J through the seventh channel H7. The outlet of ejector J is connected to the gas phase inlet of the sixth-stage heat exchanger HE6 through the eighth channel H8. The gas phase outlet of the sixth-stage heat exchanger HE6 is connected to the inlet of hydrogen separator D5 through the ninth channel H9 and the tenth channel H10 in sequence. A hydrogen throttling valve V5 is installed between the ninth channel H9 and the tenth channel H10 to control the flow of hydrogen. The liquid phase outlet of the hydrogen separator D5 is connected to the liquid hydrogen storage tank through the eleventh channel H11, forming a flow pipeline from raw hydrogen to liquid hydrogen.

[0032] As a preferred embodiment, the hydrogen gas flowing out of the gas phase outlet of the hydrogen separator D5 and the hydrogen gas evaporated in the liquid hydrogen storage tank enter the ejector J through the twelfth channel H12 as an ejector flow in order to recover the hydrogen gas.

[0033] The refrigerant in this hydrogen liquefaction system is a mixed refrigerant, which is transported and driven within the system by the refrigerant compressor C2 to complete a single-stage mixed refrigerant refrigeration cycle, as detailed below:

[0034] The outlet of refrigerant compressor C2 is connected to the first refrigerant inlet of primary heat exchanger HE1 via the second refrigerant passage M2. After cooling, the first refrigerant outlet of primary heat exchanger HE1 is connected to the inlet of primary separator D1 via the third refrigerant passage M3. The gas phase outlet of primary separator D1 is connected to the first refrigerant inlet of secondary heat exchanger HE2 via the fourth refrigerant passage M4. The liquid phase outlet of primary separator D1 is sequentially provided with a fifth refrigerant passage M5 and a sixth refrigerant passage M6. A primary throttling valve V1 for flow control is installed between the fifth refrigerant passage M5 and the sixth refrigerant passage M6.

[0035] The first refrigerant outlet of the secondary heat exchanger HE2 is connected to the inlet of the secondary separator D2 via the seventh refrigerant channel M7. After cooling, the gas phase outlet of the secondary separator D2 is connected to the first refrigerant inlet of the tertiary heat exchanger HE3 via the eighth refrigerant channel M8. The liquid phase outlet of the secondary separator D2 is sequentially provided with a ninth refrigerant channel M9 and a tenth refrigerant channel M10. A secondary throttling valve V2 for flow control is installed between the ninth refrigerant channel M9 and the tenth refrigerant channel M10.

[0036] The first refrigerant outlet of the three-stage heat exchanger HE3 is connected to the inlet of the three-stage separator D3 via the eleventh refrigerant channel M11. After cooling, the gas phase outlet of the three-stage separator D3 is connected to the first refrigerant inlet of the four-stage heat exchanger HE4 via the twelfth refrigerant channel M12. The liquid phase outlet of the three-stage separator D3 is sequentially provided with the thirteenth refrigerant channel M13 and the fourteenth refrigerant channel M14. A three-stage throttling valve V3 for flow control is installed between the thirteenth refrigerant channel M13 and the fourteenth refrigerant channel M14.

[0037] The first refrigerant outlet of the fourth-stage heat exchanger HE4 is connected to the inlet of the fourth-stage separator D4 via the fifteenth refrigerant channel M15. After cooling, the gas phase outlet of the fourth-stage separator D4 is connected to the first refrigerant inlet of the fifth-stage heat exchanger HE5 via the sixteenth refrigerant channel M16. The liquid phase outlet of the fourth-stage separator D4 is sequentially provided with the seventeenth refrigerant channel M17 and the eighteenth refrigerant channel M18. A fourth-stage throttling valve V4 for throttling is installed between the seventeenth refrigerant channel M17 and the eighteenth refrigerant channel M18.

[0038] The first refrigerant outlet of the five-stage heat exchanger HE5 is divided into two pipelines: the twentieth refrigerant channel M20 and the twenty-second refrigerant channel M22, through the nineteenth refrigerant channel M19.

[0039] The outlet of the twentieth refrigerant channel M20 is connected to the inlet of the first-stage expander E1, and the outlet of the first-stage expander E1 is connected to the inlet of the twenty-first refrigerant channel M21. The outlet of the twenty-second refrigerant channel M22 is connected to the first refrigerant inlet of the sixth-stage heat exchanger HE6, and the first refrigerant outlet of the sixth-stage heat exchanger HE6 is connected to the inlet of the second-stage expander E2 through the twenty-third refrigerant channel M23 to achieve cooling.

[0040] The outlet of the second-stage expander E2 is connected to the second refrigerant inlet of the sixth-stage heat exchanger HE6 via the twenty-fourth refrigerant channel M24, providing cooling capacity. After reheating in the sixth-stage heat exchanger HE6, it connects to the inlet of the twenty-fifth refrigerant channel M25 via the second refrigerant outlet. The outlets of the twenty-first and twenty-fifth refrigerant channels M21 and M25 merge and then connect to the second refrigerant inlet of the fifth-stage heat exchanger HE5 via the twenty-sixth refrigerant channel M26, providing cooling capacity. After reheating in the fifth-stage heat exchanger HE5, it exits through the second refrigerant outlet, merges with the eighteenth refrigerant channel M18, and then connects to the second refrigerant inlet of the fourth-stage heat exchanger HE4 via the twenty-seventh refrigerant channel M27, providing cooling capacity. After reheating in the fourth-stage heat exchanger HE4, it merges with the fourteenth refrigerant channel M14 via the second refrigerant outlet and then connects to the second refrigerant inlet of the third-stage heat exchanger HE3 via the twenty-eighth refrigerant channel M28, providing cooling capacity. After reheating in the third-stage heat exchanger HE3, the refrigerant flows through the second refrigerant outlet and merges with the tenth refrigerant channel M10, then connects to the second refrigerant inlet of the second-stage heat exchanger HE2 via the twenty-ninth refrigerant channel M29. The second refrigerant outlet of the second-stage heat exchanger HE2 merges with the sixth refrigerant channel M6, then connects to the second refrigerant inlet of the first-stage heat exchanger HE1 via the thirtieth refrigerant channel M30, providing cooling capacity. After reheating in the first-stage heat exchanger HE1, the refrigerant flows through the second refrigerant outlet and connects to the first refrigerant channel M1, subsequently connecting to the inlet of the refrigerant compressor C2, thus forming a single-stage mixed refrigerant refrigeration cycle.

[0041] The mixed refrigerant is composed of seven components: pentane, propane, ethane, ethylene, neon, hydrogen, and helium, mixed in a certain proportion. In this embodiment, the molar ratios of each component in the mixed refrigerant are as follows: 2.1% pentane, 4.0% propane, 5.0% ethane, 12.8% ethylene, 2.4% neon, 61.5% hydrogen, and 12.2% helium.

[0042] In a preferred embodiment, the primary heat exchanger HE1, secondary heat exchanger HE2, tertiary heat exchanger HE3, quaternary heat exchanger HE4, quinary heat exchanger HE5, and sixth heat exchanger HE6 all employ aluminum plate-fin heat exchangers. The feed hydrogen channels of the tertiary heat exchanger HE3, quaternary heat exchanger HE4, quinary heat exchanger HE5, and sixth heat exchanger HE6 are filled with ortho- and para-hydrogen conversion catalysts with corresponding catalytic performance according to the cooling temperature zone.

[0043] This embodiment also provides a specific method for using a hydrogen liquefaction system with a single-stage mixed refrigerant refrigeration, as follows:

[0044] (1) On the product hydrogen side, after the raw material hydrogen enters the hydrogen liquefaction system, it is first compressed to 2.1 MPa in the hydrogen compressor C1, and then passed through the pipeline sequentially through the first-stage heat exchanger HE1, the second-stage heat exchanger HE2, the third-stage heat exchanger HE3, the fourth-stage heat exchanger HE4, the fifth-stage heat exchanger HE5, and the sixth-stage heat exchanger HE6, gradually cooling to 20.15 K, while increasing the secondary hydrogen content from 25% to over 98%. After exiting the gas phase outlet of the sixth-stage heat exchanger HE6, it is throttled to 0.12 MPa by the hydrogen throttling valve V5, while the temperature drops to 19.35 K. The resulting gas-liquid mixture is separated in the hydrogen separator D5, and the liquid hydrogen enters the liquid hydrogen storage tank. The gas phase merges with the hydrogen evaporated from the liquid hydrogen storage tank and returns to the ejector J as an ejector stream.

[0045] (2) On the mixed refrigerant side, the mixed refrigerant composition in the first refrigerant channel M1 is 2.1% pentane, 4.0% propane, 5.0% ethane, 12.8% ethylene, 2.4% neon, 61.5% hydrogen and 12.2% helium. The refrigerant flowing back is first compressed to 2.1 MPa in refrigerant compressor C2, and after water cooling, it enters the first-stage heat exchanger HE1 as a hot stream for cooling. The gas-liquid mixture at the outlet is separated in the first-stage separator D1. The gas phase enters the second-stage heat exchanger HE2 as a hot stream, and the liquid phase is throttled and cooled, then mixes with the refrigerant flowing back in the second-stage heat exchanger HE2 and serves as a cold stream to provide cooling for the first-stage heat exchanger HE1. The processes of the first-stage heat exchanger HE1, the second-stage heat exchanger HE2, the third-stage heat exchanger HE3, and the fourth-stage heat exchanger HE4 are the same. The mixed refrigerant flowing out of the fifth-stage heat exchanger HE5 is in a gaseous state, with neon, hydrogen, and helium as its main components. A stream of this gas is expanded and cooled by the first-stage expander E1 and then mixes with the refrigerant flowing back in the sixth-stage heat exchanger HE6 and serves as a cold stream to provide cooling for the fifth-stage heat exchanger HE5. The processes of the fifth-stage heat exchanger HE5 and the sixth-stage heat exchanger HE6 are the same.

[0046] Through this method, the hydrogen liquefaction rate reaches over 97%, and the secondary hydrogen content in the liquid hydrogen product reaches over 98%.

[0047] The hydrogen liquefaction system provided by this invention can produce 13-25 tons of liquid hydrogen per day, with a hydrogen liquefaction rate of over 97% and a secondary hydrogen content of over 98% in the liquid hydrogen product. The multi-stage gas-liquid separator in this system enables the redistribution of the mixed refrigerant, thereby achieving single-stage mixed refrigerant refrigeration for hydrogen liquefaction production while avoiding the risk of freezing and blockage. Due to its simple process and fewer equipment components, this system can significantly reduce the size of the cold box, thereby reducing equipment manufacturing and investment costs. Furthermore, this system can reduce the system's specific energy consumption to 10 kWh / kg liquid hydrogen, effectively improving the economic efficiency of the hydrogen liquefaction plant.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A hydrogen liquefaction system with single-stage mixed refrigerant refrigeration, characterized in that, The system includes a compressor unit, a vacuum cold box, a heat exchanger unit, an expander unit, a gas-liquid separator unit, an ejector, and a liquid hydrogen storage tank, all connected to each other via pipelines. The vacuum cold box contains the heat exchanger unit, the expander unit, the gas-liquid separator unit, and the ejector. The refrigerant in this hydrogen liquefaction system is a mixed refrigerant. The hydrogen compressor (C1) receives feedstock hydrogen through the first channel (H1) and its outlet is connected to the gas phase inlet of the first-stage heat exchanger (HE1) through the second channel (H2). The gas phase outlet of the first-stage heat exchanger (HE1) is connected to the gas phase inlet of the second-stage heat exchanger (HE2) through the third channel (H3). The gas phase outlet of the second-stage heat exchanger (HE2) is connected to the gas phase inlet of the third-stage heat exchanger (HE3) through the fourth channel (H4). The gas phase outlet of the third-stage heat exchanger (HE3) is connected to the gas phase inlet of the fourth-stage heat exchanger (HE4) through the fifth channel (H5). The gas phase outlet of the fourth-stage heat exchanger (HE4) is connected to the gas phase inlet of the fourth-stage heat exchanger (HE4) through the fifth channel (H5). The sixth channel (H6) is connected to the gas phase inlet of the fifth-stage heat exchanger (HE5); the gas phase outlet of the fifth-stage heat exchanger (HE5) is connected to the inlet of the ejector (J) through the seventh channel (H7); the outlet of the ejector (J) is connected to the gas phase inlet of the sixth-stage heat exchanger (HE6) through the eighth channel (H8); the gas phase outlet of the sixth-stage heat exchanger (HE6) is connected to the inlet of the hydrogen separator (D5) in the gas-liquid separator group through the ninth channel (H9) and the tenth channel (H10) in sequence; the liquid phase outlet of the hydrogen separator (D5) is connected to the liquid hydrogen storage tank through the eleventh channel (H11), forming a flow pipeline from raw material hydrogen to liquid hydrogen; The gas-liquid separator assembly further includes a primary separator (D1), a secondary separator (D2), a tertiary separator (D3), and a quaternary separator (D4); the first refrigerant outlet of the primary heat exchanger (HE1) is connected to the inlet of the primary separator (D1) via a third refrigerant channel (M3); the gas phase outlet of the primary separator (D1) is connected to the first refrigerant inlet of the secondary heat exchanger (HE2) via a fourth refrigerant channel (M4); the first refrigerant outlet of the secondary heat exchanger (HE2) is connected to the inlet of the secondary separator (D2) via a seventh refrigerant channel (M7), and the gas phase outlet of the secondary separator (D2) is connected to the inlet of the secondary separator (D2) via an eighth refrigerant channel (M8). The first refrigerant inlet of the three-stage heat exchanger (HE3) is connected; the first refrigerant outlet of the three-stage heat exchanger (HE3) is connected to the inlet of the three-stage separator (D3) through the eleventh refrigerant channel (M11); the gas phase outlet of the three-stage separator (D3) is connected to the first refrigerant inlet of the four-stage heat exchanger (HE4) through the twelfth refrigerant channel (M12); the first refrigerant outlet of the four-stage heat exchanger (HE4) is connected to the inlet of the four-stage separator (D4) through the fifteenth refrigerant channel (M15); the gas phase outlet of the four-stage separator (D4) is connected to the first refrigerant inlet of the five-stage heat exchanger (HE5) through the sixteenth refrigerant channel (M16). The mixed refrigerant is composed of pentane, propane, ethane, ethylene, neon, hydrogen, and helium; The molar proportions of each component in the single-stage mixed refrigerant are as follows: 2.1% pentane, 4.0% propane, 5.0% ethane, 12.8% ethylene, 2.4% neon, 61.5% hydrogen, and 12.2% helium; The mixed refrigerant is delivered and driven within the system by the refrigerant compressor (C2) to complete a single-stage mixed refrigerant refrigeration cycle.

2. The hydrogen liquefaction system with single-stage mixed refrigerant refrigeration according to claim 1, characterized in that, The specific structure of the single-stage mixed refrigerant refrigeration cycle is as follows: The outlet of the refrigerant compressor (C2) is connected to the first refrigerant inlet of the first-stage heat exchanger (HE1) through the second refrigerant passage (M2), and the liquid phase outlet of the first-stage separator (D1) is provided with the fifth refrigerant passage (M5) and the sixth refrigerant passage (M6) in sequence. The liquid phase outlet of the secondary separator (D2) is provided with a ninth refrigerant channel (M9) and a tenth refrigerant channel (M10) in sequence; The liquid phase outlet of the three-stage separator (D3) is provided with a thirteenth refrigerant channel (M13) and a fourteenth refrigerant channel (M14) in sequence; The liquid outlet of the four-stage separator (D4) is provided with the seventeenth refrigerant channel (M17) and the eighteenth refrigerant channel (M18) in sequence; the first refrigerant outlet of the five-stage heat exchanger (HE5) is divided into two pipelines, the twentieth refrigerant channel (M20) and the twenty-second refrigerant channel (M22), through the nineteenth refrigerant channel (M19). The outlet of the 20th refrigerant channel (M20) is connected to the inlet of the first-stage expander (E1), and the outlet of the first-stage expander (E1) is connected to the inlet of the 21st refrigerant channel (M21). The outlet of the 22nd refrigerant channel (M22) is connected to the first refrigerant inlet of the sixth-stage heat exchanger (HE6). The first refrigerant outlet of the sixth-stage heat exchanger (HE6) is connected to the inlet of the second-stage expander (E2) via the 23rd refrigerant channel (M23) for cooling. The outlet of the second-stage expander (E2) is connected to the second refrigerant inlet of the sixth-stage heat exchanger (HE6) via the 24th refrigerant channel (M24), and the second refrigerant outlet of the sixth-stage heat exchanger (HE6) is connected to the inlet of the 25th refrigerant channel (M25). The outlets of the 21st and 25th refrigerant channels (M25) merge and then connect to the second refrigerant inlet of the fifth-stage heat exchanger (HE5) via the 26th refrigerant channel (M26). The second refrigerant outlet of the fifth-stage heat exchanger (HE5)... The refrigerant outlet merges with the eighteenth refrigerant channel (M18) and then connects to the second refrigerant inlet of the fourth-stage heat exchanger (HE4) via the twenty-seventh refrigerant channel (M27). The second refrigerant outlet of the fourth-stage heat exchanger (HE4) merges with the fourteenth refrigerant channel (M14) and then connects to the second refrigerant inlet of the third-stage heat exchanger (HE3) via the twenty-eighth refrigerant channel (M28). The second refrigerant outlet of the third-stage heat exchanger (HE3) merges with the tenth refrigerant channel (M10) and then connects to the second refrigerant inlet of the second-stage heat exchanger (HE2) via the twenty-ninth refrigerant channel (M29). The second refrigerant outlet of the second-stage heat exchanger (HE2) merges with the sixth refrigerant channel (M6) and then connects to the second refrigerant inlet of the first-stage heat exchanger (HE1) via the thirtieth refrigerant channel (M30). The second refrigerant outlet of the first-stage heat exchanger (HE1) connects to the inlet of the refrigerant compressor (C2) via the first refrigerant channel (M1), thus forming a single-stage mixed refrigerant refrigeration cycle.

3. The hydrogen liquefaction system with single-stage mixed refrigerant refrigeration according to claim 2, characterized in that, A primary throttling valve (V1) is provided between the fifth refrigerant passage (M5) and the sixth refrigerant passage (M6); a secondary throttling valve (V2) is provided between the ninth refrigerant passage (M9) and the tenth refrigerant passage (M10); a tertiary throttling valve (V3) is provided between the thirteenth refrigerant passage (M13) and the fourteenth refrigerant passage (M14); and a quaternary throttling valve (V4) is provided between the seventeenth refrigerant passage (M17) and the eighteenth refrigerant passage (M18).

4. The hydrogen liquefaction system with single-stage mixed refrigerant refrigeration according to claim 1, characterized in that, A hydrogen throttling valve (V5) is provided between the ninth channel (H9) and the tenth channel (H10).

5. The hydrogen liquefaction system with single-stage mixed refrigerant refrigeration according to claim 1, characterized in that, The hydrogen gas flowing out of the gas phase outlet of the hydrogen separator (D5) and the hydrogen gas evaporated in the liquid hydrogen storage tank enter the ejector (J) through the twelfth channel (H12) as an induction flow to recover hydrogen gas.

6. The hydrogen liquefaction system with single-stage mixed refrigerant refrigeration according to claim 1, characterized in that, The primary heat exchanger (HE1), secondary heat exchanger (HE2), tertiary heat exchanger (HE3), quaternary heat exchanger (HE4), quinary heat exchanger (HE5), and sixth heat exchanger (HE6) are all aluminum plate-fin heat exchangers.

7. The hydrogen liquefaction system with single-stage mixed refrigerant cooling according to claim 1, characterized in that, The feed hydrogen channels of the three-stage heat exchanger (HE3), four-stage heat exchanger (HE4), five-stage heat exchanger (HE5), and six-stage heat exchanger (HE6) are filled with corresponding catalytic performance of ortho-parahydrogen conversion catalysts according to the temperature zone.

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