Two-stage pressure swing adsorption hydrogen purification system and process

Abstract

The application discloses a two-stage pressure swing adsorption hydrogen purification system and process, and belongs to the technical field of gas separation. The process comprises the following steps: continuously preparing product hydrogen by pressure swing adsorption of raw gas through a first-stage pressure swing adsorption device; sending desorption gas of the first-stage pressure swing adsorption device into a second-stage pressure swing adsorption device after compression to further concentrate and obtain product gas crude hydrogen; and mixing the crude hydrogen with the raw gas and sending them into the first-stage pressure swing adsorption device together. The product gas purity of the second-stage pressure swing adsorption device is set as low-purity crude hydrogen, the separation requirement is greatly reduced, the hydrogen recovery rate of the second stage is increased by 2-10%, the hydrogen recovery rate of the two-stage pressure swing adsorption hydrogen purification process can reach 99.8% at most, and the technical bottleneck of low recovery rate in the prior art is effectively overcome.

Description

Technical Field

[0001] This invention belongs to the field of gas separation technology, specifically relating to a two-stage pressure swing adsorption system and process for purifying hydrogen. Background Technology

[0002] Hydrogen, as an important industrial raw material and clean energy source, has broad application prospects in various fields such as petrochemicals, electronics, metallurgy, and new energy. In industrial production processes such as oil refining, chlor-alkali production, methanol synthesis, and ammonia synthesis, large quantities of hydrogen-rich industrial waste gases are generated. The hydrogen in these waste gases is a resource with significant recycling value. Effectively recovering and purifying hydrogen from these industrial waste gases can not only reduce raw material costs in industrial production but also improve resource utilization efficiency and reduce carbon emissions, thus possessing significant economic and environmental benefits.

[0003] Currently, the main technologies for extracting hydrogen from industrial waste gas include cryogenic separation, membrane separation, and pressure swing adsorption (PSA). Among them, pressure swing adsorption technology has become the mainstream technology in the field of hydrogen purification due to its outstanding advantages such as simple operation, low energy consumption, high product purity, and strong process flexibility, and is widely used in hydrogen recovery from various industrial waste gases.

[0004] Pressure swing adsorption (PSA) hydrogen extraction typically employs a multi-tower circulating process. Through the coordinated circulation of multiple adsorption towers, adsorption, pressure equalization, forward and reverse release, rinsing, and pressurization are sequentially completed. Utilizing the preferential adsorption characteristics of the adsorbent for impurities in the tail gas, impurities are adsorbed and retained under high pressure conditions, thereby obtaining high-purity hydrogen. Under low pressure conditions, the adsorbed impurities are desorbed from the adsorbent, regenerating the adsorbent and ensuring continuous and stable operation of the process.

[0005] With the increasing demands for hydrogen product quality and resource recovery efficiency in industrial production, traditional single-stage pressure swing adsorption (PSA) processes are no longer sufficient to meet the requirements for higher product gas purity and hydrogen recovery rates. Therefore, two-stage PSA processes have emerged and gradually developed. Two-stage PSA processes are mainly divided into two types: one is as shown in the attached... Figure 1 The diagram shows a "one-stage concentration, two-stage hydrogen production" process. The first stage, a pressure swing adsorption (PSA) unit, removes most impurities from the feed gas and concentrates the hydrogen. This concentrated hydrogen serves as the feed gas for the second stage PSA unit, where it is further purified to obtain the final qualified product hydrogen. This model is primarily suitable for situations where the hydrogen content in the feed gas is low. Another method is shown in the attached diagram. Figure 2 and Figure 3The diagram illustrates a two-stage hydrogen production process. The feed gas passes through a first-stage pressure swing adsorption (PSA) unit to produce hydrogen. The desorbed gas is then compressed and enters a second-stage PSA unit for further separation, purification, and hydrogen production. This method is primarily suitable for situations where the feed gas has a relatively high hydrogen content. However, this two-stage PSA process has significant technical drawbacks. Because the hydrogen content in the feed gas (i.e., the desorbed gas from the first stage) of the second-stage PSA unit is significantly lower than the initial feed gas, while the quality standard of the product hydrogen must remain consistent with that of the first-stage unit, the hydrogen recovery rate of the second-stage unit is generally low. This negatively impacts the overall efficiency of the two-stage PSA process, reduces the economic viability of the equipment, and limits its widespread application in demanding hydrogen recovery scenarios.

[0006] Therefore, providing an optimized two-stage pressure swing adsorption (PSA) process for hydrogen purification, which has a higher second-stage hydrogen recovery rate and overall process efficiency, can improve the economics of the equipment and solve the problems of low second-stage hydrogen recovery rate, poor process efficiency and poor equipment economics in the existing two-stage PSA process where both stages produce hydrogen. This has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a two-stage pressure swing adsorption system and process for purifying hydrogen, which can further improve the hydrogen recovery rate and reduce equipment investment.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention discloses a two-stage pressure swing adsorption (PSA) system for purifying hydrogen, comprising a first PSA unit, a first compression unit, and a second PSA unit connected in sequence. The first stage of the pressure swing adsorption unit is used to produce product hydrogen. It is connected to a feed gas delivery line and outputs to a product hydrogen delivery line and a PSA1 desorption gas delivery line. The PSA1 desorption gas delivery line is connected to the first compression unit, and the outlet of the first compression unit is then connected via pipeline to the inlet of the second stage pressure swing adsorption unit. The second stage pressure swing adsorption unit is used to produce crude hydrogen, and its product gas outlet is connected to the raw material gas conveying line via the crude hydrogen conveying line.

[0009] In some embodiments of the present invention, a second compression device is provided on the crude hydrogen delivery line. In some embodiments of the present invention, a PSA2 desorption gas delivery line is connected to the second stage of the pressure swing adsorption device.

[0010] In some embodiments of the present invention, both the first-stage pressure swing adsorption device and the second-stage pressure swing adsorption device include multiple adsorption towers, preferably 4 to 18 adsorption towers.

[0011] In some embodiments of the present invention, an online hydrogen analyzer and a trace impurity analyzer are installed on the product hydrogen delivery line to monitor the hydrogen purity and trace impurity content online.

[0012] In some embodiments of the present invention, an online hydrogen analyzer is installed on the crude hydrogen conveying line to detect the hydrogen content in the crude hydrogen.

[0013] A second aspect of this invention discloses a two-stage pressure swing adsorption process for purifying hydrogen using the above-described system, comprising the following steps: The feed gas is continuously processed by the first stage pressure swing adsorption unit to produce product hydrogen. The desorbed gas from the first stage pressure swing adsorption unit is compressed and sent to the second stage pressure swing adsorption unit for further concentration to obtain crude product hydrogen. The crude hydrogen is mixed with the feed gas and sent to the first stage pressure swing adsorption unit.

[0014] In some embodiments of the present invention, the hydrogen content in the crude hydrogen gas is not lower than the hydrogen content in the raw material gas.

[0015] Preferably, the volume content of hydrogen in the crude hydrogen gas is greater than 90%, more preferably greater than 95%.

[0016] In some embodiments of the present invention, the pressure of the crude hydrogen gas is the same as that of the raw material gas.

[0017] In some embodiments of the present invention, the crude hydrogen gas is pressurized to the same pressure as the raw material gas by a second compression device.

[0018] In some embodiments of the present invention, by adjusting the adsorption time of the second-stage pressure swing adsorption device, the recovery rate can be increased while appropriately reducing the hydrogen purity. Those skilled in the art can make corresponding adjustments based on the real-time detection results of an online hydrogen analyzer, which is prior art in this field. Compared with the prior art, the present invention has the following beneficial effects: This invention is scientifically and rationally designed and has significant effects. By setting the purity of the product gas in the second stage pressure swing adsorption device to low-purity crude hydrogen, the separation requirements are greatly reduced, and the hydrogen recovery rate of the second stage is increased by 2-10%. The hydrogen recovery rate of the two-stage pressure swing adsorption purification process can reach up to 99.8%, effectively overcoming the technical bottleneck of low recovery rate in existing technologies.

[0019] The crude hydrogen produced by the second-stage pressure swing adsorption (PSA) unit has a low impurity content. When introduced as feed gas for the first stage, it will not significantly increase the impurity load or the amount of adsorbent required in the first stage. Therefore, while the overall recovery rate is significantly improved, the investment scale of the first-stage PSA unit remains basically unchanged, avoiding the problem of excessive increase in equipment investment in order to improve the recovery rate.

[0020] Furthermore, in existing technologies, to ensure that the second-stage product gas meets high purity standards, it is usually necessary to configure online analytical instruments for detecting trace impurities. This invention, by adjusting the second-stage product gas to crude hydrogen, eliminates the need for real-time, high-precision monitoring of trace impurities, thus eliminating the need for such online analytical instruments and reducing the costs of instrument purchase, installation, and subsequent maintenance. Attached Figure Description

[0021] Figure 1 This is a flow chart of a traditional two-stage hydrogen extraction process, in which the first stage PSA produces crude hydrogen, and the second stage PSA produces finished hydrogen.

[0022] Figure 2 This is a flow chart of a traditional two-stage hydrogen extraction process, in which both the first and second stages of PSA produce hydrogen.

[0023] Figure 3 This is a flow chart of a traditional two-stage hydrogen extraction process, in which both the first and second stage PSA processes produce hydrogen, and the hydrogen produced by the second stage PSA process needs to be pressurized.

[0024] Figure 4 The structure of the two-stage pressure swing adsorption system for purifying hydrogen according to the present invention. Figure 1 .

[0025] Figure 5 The structure of the two-stage pressure swing adsorption system for purifying hydrogen according to the present invention. Figure 2 .

[0026] The names corresponding to the reference numerals in the attached figures are: PSA1 - First stage pressure swing adsorption unit, PSA2 - Second stage pressure swing adsorption unit, 101 - Feed gas conveying line, 102 - Product hydrogen conveying line, 103 - PSA1 desorption gas conveying line, 104 - Crude hydrogen conveying line, 105 - PSA2 desorption gas conveying line. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] The present invention will be described in detail below through specific examples, but should not be construed as the subject matter of the present invention.

[0029] Example 1 As attached Figure 4As shown in the figure, this embodiment discloses a two-stage pressure swing adsorption (PSA) hydrogen purification system of the present invention, which includes a first-stage PSA1, a first compression device, and a second-stage PSA2 connected in sequence. The first stage, Pressure Swing Adsorption Unit (PSA1), is used to produce product hydrogen. It is connected to a feed gas delivery line 101 and outputs to a product hydrogen delivery line 102 and a PSA1 desorption gas delivery line 103. The PSA1 desorption gas delivery line 103 is connected to the first compression unit, and the outlet of the first compression unit is then connected via a pipeline to the inlet of the second stage pressure swing adsorption unit PSA2. The second stage pressure swing adsorption unit PSA2 is used to produce crude hydrogen. Its product gas outlet is connected to the raw material gas conveying line 101 via the crude hydrogen conveying line 104. The second stage pressure swing adsorption unit PSA2 is connected to the PSA2 desorption gas conveying line 105.

[0030] The first-stage pressure swing adsorption unit PSA1 and the second-stage pressure swing adsorption unit PSA2 both contain multiple adsorption towers, preferably 4 to 18.

[0031] The product hydrogen delivery line 102 is equipped with an online hydrogen analyzer and a trace impurity analyzer. Figure 4 (Not shown in the image) is used for online monitoring of hydrogen purity and trace impurity content. The trace impurities include CO, CO2, H2O, CH4, etc. Each trace impurity can be detected separately using a single-component analyzer or centrally using a multi-component analyzer. This is existing technology, and those skilled in the art can choose according to actual needs.

[0032] An online hydrogen analyzer is installed on the crude hydrogen conveying line 104. Figure 4 (not shown in the image) to detect the hydrogen content in crude hydrogen gas.

[0033] Example 2 As attached Figure 5 As shown in the figure, this embodiment discloses a two-stage pressure swing adsorption (PSA) hydrogen purification system of the present invention, which includes a first-stage PSA1, a first compression device, and a second-stage PSA2 connected in sequence. The first stage, Pressure Swing Adsorption Unit (PSA1), is used to produce product hydrogen. It is connected to a feed gas delivery line 101 and outputs to a product hydrogen delivery line 102 and a PSA1 desorption gas delivery line 103. The PSA1 desorption gas delivery line 103 is connected to the first compression unit, and the outlet of the first compression unit is then connected via a pipeline to the inlet of the second stage pressure swing adsorption unit PSA2. The second stage pressure swing adsorption unit PSA2 is used to produce crude hydrogen. Its product gas outlet is connected to the raw material gas conveying line 101 via the crude hydrogen conveying line 104. The second stage pressure swing adsorption unit PSA2 is connected to the PSA2 desorption gas conveying line 105.

[0034] The first-stage pressure swing adsorption unit PSA1 and the second-stage pressure swing adsorption unit PSA2 both contain multiple adsorption towers, preferably 4 to 18.

[0035] The product hydrogen delivery line 102 is equipped with an online hydrogen analyzer and an online CO analyzer. Figure 5 (Not shown in the image), used for online monitoring of hydrogen purity and impurity content.

[0036] An online hydrogen analyzer is installed on the crude hydrogen conveying line 104. Figure 5 (not shown in the image) to detect the hydrogen content in crude hydrogen gas.

[0037] A second compression device is installed on the crude hydrogen conveying line 104.

[0038] Example 3 This embodiment discloses a two-stage pressure swing adsorption process for purifying hydrogen, which is implemented using the two-stage pressure swing adsorption hydrogen purification system of Example 1.

[0039] The feed gas is industrial hydrogen with a hydrogen content of 99.9%. Other impurities are: N2: 0.04%, CH4: 0.0577%, CO: 0.001%, CO2: 0.001%, H2O: 0.0003%. The feed gas pressure is 2.5 MPa, and the feed gas flow rate is 10000 Nm³. 3 / h.

[0040] The specific process in this embodiment is as follows: S1: First stage pressure swing adsorption: The feed gas is continuously produced by pressure swing adsorption in the first stage pressure swing adsorption device to produce product hydrogen, and its quality meets the high purity hydrogen standard (GB / T3634.2-2011-high purity hydrogen).

[0041] In this embodiment, the first stage of the pressure swing adsorption (PSA) unit adopts an 8-1-4 / P rinsing process, with the timing shown in Table 1. Each adsorption tower sequentially undergoes an adsorption step, four pressure equalization and depressurization steps, a forward adsorption step, a reverse adsorption step, a rinsing step, four pressure equalization steps, and a final charging step. The adsorption pressure is 2.5 MPa, and the regeneration pressure is 0.02 MPa. The product hydrogen is equipped with an online hydrogen analyzer, an online trace moisture analyzer, and online trace CO, CO2, and CH4 analyzers to monitor hydrogen purity and impurity content online.

[0042] S2. Compression: The desorbed gas from the first stage pressure swing adsorption unit is compressed and pressurized to 2.55 MPa before being sent to the second stage pressure swing adsorption unit.

[0043] S3. Second stage pressure swing adsorption: The desorbed gas from the first stage pressure swing adsorption unit after compression is further concentrated in the second stage pressure swing adsorption unit to obtain crude hydrogen product gas with a hydrogen content of 99.9%. In this embodiment, the second stage of the pressure swing adsorption (PSA) unit adopts a 7-1-4 / P rinsing process, with the timing shown in Table 2. Each adsorption tower sequentially undergoes an adsorption step, four pressure equalization and depressurization steps, a forward release step, a reverse release step, a rinsing step, four pressure equalization steps, and a final charging step. The adsorption pressure is 2.55 MPa, and the regeneration pressure is 0.02 MPa. An online hydrogen analyzer is installed for the crude hydrogen product.

[0044] S4. Circulation: The product gas of the second stage pressure swing adsorption unit is crude hydrogen, which is mixed with the raw material gas and then sent to the first stage pressure swing adsorption unit for repurification.

[0045] In this embodiment, both the first-stage pressure swing adsorption device and the second-stage pressure swing adsorption device adsorption tower adopt a composite adsorption bed of two adsorbents: activated alumina and molecular sieve, wherein the volume ratio of activated alumina to molecular sieve is 1:10.

[0046] In this embodiment, the first stage pressure swing adsorption (PSA) unit produces high-purity hydrogen with a hydrogen recovery rate of 86%; the second stage PSA unit produces 99.9% crude hydrogen with a hydrogen recovery rate of 91.5%; the overall hydrogen recovery rate is 98.49%, and the total high-purity hydrogen production is 9839 Nm³. 3 / h.

[0047] The traditional two-stage method, specifically the second-stage pressure swing adsorption (PSA) unit, produces 99.999% high-purity hydrogen with a hydrogen recovery rate of only 84%, an overall hydrogen recovery rate of 97.6%, and a total high-purity hydrogen yield of 9750 Nm³. 3 / h.

[0048] Table 1 8-1-4 / P Process Timing Table

[0049] In Table 1: A: Adsorption step, 1D: First equalization and depressurization step, 2D: Second equalization and depressurization step, 3D: Third equalization and depressurization step, 4D: Fourth equalization and depressurization step, PP: Forward release step, D: Reverse release step, P: Rinsing step, 4R: Fourth equalization and pressurization step, 3R: Third equalization and pressurization step, 2R: Second equalization and pressurization step, 1R: First equalization and pressurization step, FR: Final pressurization step.

[0050] Table 2 7-1-4 / P Process Timing Table

[0051] In Table 2: A: Adsorption step, 1D: First pressure equalization and depressurization step, 2D: Second pressure equalization and depressurization step, 3D: Third pressure equalization and depressurization step, 4D: Fourth pressure equalization and depressurization step, PP: Forward release step, D: Reverse release step, P: Rinsing step, 4R: Fourth pressure equalization and pressurization step, 3R: Third pressure equalization and pressurization step, 2R: Second pressure equalization and pressurization step, 1R: First pressure equalization and pressurization step, FR: Final pressure increase step, IS: Isolation step.

[0052] Example 4 This embodiment discloses a two-stage pressure swing adsorption process for purifying hydrogen, which is implemented using the two-stage pressure swing adsorption hydrogen purification system of Example 2.

[0053] The feed gas composition in this embodiment is: H2:N2:CO = 84.5:3.2:12.3, the feed gas pressure is 2.5 MPa, and the feed gas flow rate is 80000 Nm³. 3 / h. The product hydrogen meets the requirements of 99.9% hydrogen purity and 0.001% CO content.

[0054] The specific process in this embodiment is as follows: S1: First stage pressure swing adsorption: The feed gas is continuously processed by the first stage pressure swing adsorption device to produce product hydrogen. The hydrogen purity in the product gas is 99.9% and the CO content is 0.001%.

[0055] In this embodiment, the first stage of the pressure swing adsorption device adopts the 10-2-4 / P rinsing process, and the timing is shown in Table 3. That is, each adsorption tower goes through the adsorption step, four pressure equalization and depressurization steps, forward adsorption step, reverse release step, rinsing step, four pressure equalization steps and final charging step in sequence. The adsorption pressure is 2.5 MPa and the regeneration pressure is 0.02 MPa. The product hydrogen is equipped with an online hydrogen analyzer and an online CO analyzer to monitor the hydrogen purity and impurity content online.

[0056] S2. Compression: The desorbed gas from the first stage pressure swing adsorption unit is compressed and pressurized to 0.8 MPa before being sent to the second stage pressure swing adsorption unit.

[0057] S3. Second stage pressure swing adsorption: The desorbed gas from the first stage pressure swing adsorption unit after compression is further concentrated in the second stage pressure swing adsorption unit to obtain crude hydrogen product gas, with a hydrogen content ≥95.0%; In this embodiment, the second stage pressure swing adsorption device adopts an 8-2-3 / V evacuation and regeneration process, and the timing is shown in Table 4. That is, each adsorption tower goes through an adsorption step, three pressure equalization and depressurization steps, a reverse release step, an evacuation step, three pressure equalization steps, and a final charging step in sequence. The adsorption pressure is 0.8 MPa and the regeneration pressure is -0.08 MPa.

[0058] S4. Pressurization and circulation: The product gas of the second stage pressure swing adsorption unit is crude hydrogen gas, which is pressurized to 2.5MPa by the second compressor and then mixed with the raw material gas and sent to the first stage pressure swing adsorption unit for repurification.

[0059] In this embodiment, both the first-stage pressure swing adsorption device and the second-stage pressure swing adsorption device adsorption tower adopt a composite adsorption bed of two adsorbents: activated alumina and molecular sieve, wherein the volume ratio of activated alumina to molecular sieve is 1:10.

[0060] In this embodiment, the first stage pressure swing adsorption (PSA) unit produces 99.9% hydrogen with a hydrogen recovery rate of 90%; the second stage PSA unit produces 95% crude hydrogen with a hydrogen recovery rate of 98%; the overall hydrogen recovery rate is 99.78%, and the total product hydrogen yield is 67518 Nm³. 3 / h.

[0061] In the traditional two-stage process, specifically the second-stage pressure swing adsorption (PSA) unit, when producing 99.9% pure hydrogen, the hydrogen recovery rate is 80%, the overall hydrogen recovery rate is 98%, and the total hydrogen production is 66248 Nm³. 3 / h.

[0062] The two-stage process of this invention differs from the traditional two-stage process (such as...). Figure 3 Compared to (as shown), this reduces the amount of trace impurities in the product gas of the second-stage pressure swing adsorption unit through online analysis equipment, and can increase annual output by 10.16 million Nm³. 3 hydrogen.

[0063] Table 3 10-2-4 / P Process Timing Table

[0064] In Table 3, A: Adsorption step, 1D: First pressure equalization and depressurization step, 2D: Second pressure equalization and depressurization step, 3D: Third pressure equalization and depressurization step, 4D: Fourth pressure equalization and depressurization step, PP: Forward release step, D: Reverse release step, P: Rinsing step, 4R: Fourth pressure equalization and pressurization step, 3R: Third pressure equalization and pressurization step, 2R: Second pressure equalization and pressurization step, 1R: First pressure equalization and pressurization step, FR: Final pressure increase step.

[0065] Table 4 8-2-3 / V Process Timing Table

[0066] In Table 4, A: adsorption step, 1D: first equalization and depressurization step, 2D: second equalization and depressurization step, 3D: third equalization and depressurization step, D: reverse release step, V: evacuation step, 3R: third equalization and pressure increase step, 2R: second equalization and pressure increase step, 1R: first equalization and pressure increase step, and FR: final pressure increase step.

[0067] In summary, this invention significantly reduces the separation requirements by setting the product gas purity of the second-stage pressure swing adsorption (PSA) unit to low-purity crude hydrogen, thereby increasing the hydrogen recovery rate of the second stage by 2-10%. The hydrogen recovery rate of the two-stage PSA purification process can reach up to 99.8%. Furthermore, the crude hydrogen in the second-stage PSA unit has a low impurity content, which does not significantly increase the investment in the first-stage PSA unit, eliminating the need for online analysis instruments for trace impurities in the product gas of the second-stage PSA unit; thus reducing equipment investment.

[0068] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the scope of the patent. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but which still solve the same technical problem as the present invention, should be included within the scope of protection of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the scope of patent protection of the present invention.

Claims

1. A two-stage pressure swing adsorption system for purifying hydrogen, characterized in that, It includes a first pressure swing adsorption unit (PSA1), a first compression unit, and a second pressure swing adsorption unit (PSA2) connected in sequence. The first stage pressure swing adsorption unit (PSA1) is used to produce product hydrogen. It is connected to a raw material gas conveying line (101) and outputs a product hydrogen conveying line (102) and a PSA1 desorption gas conveying line (103). The PSA1 desorption gas delivery line (103) is connected to the first compression unit, and the outlet of the first compression unit is then connected to the inlet of the second stage pressure swing adsorption unit (PSA2) via a pipeline. The second stage pressure swing adsorption unit (PSA2) is used to produce crude hydrogen. Its product gas outlet is connected to the feed gas conveying line (101) via the crude hydrogen conveying line (104).

2. The two-stage pressure swing adsorption system for purifying hydrogen according to claim 1, characterized in that, A second compression device is installed on the crude hydrogen conveying line (104).

3. The two-stage pressure swing adsorption system for purifying hydrogen according to claim 1, characterized in that, The second stage pressure swing adsorption unit (PSA2) is connected to a PSA2 desorption gas delivery line (105).

4. The two-stage pressure swing adsorption system for purifying hydrogen according to claim 1, characterized in that, The first-stage pressure swing adsorption unit (PSA1) and the second-stage pressure swing adsorption unit (PSA2) both contain multiple adsorption towers, preferably 4 to 18 adsorption towers.

5. The two-stage pressure swing adsorption system for purifying hydrogen according to claim 1, characterized in that, The product hydrogen delivery line (102) is equipped with an online hydrogen analyzer and a trace impurity analyzer, which are used to monitor the purity of hydrogen and the content of trace impurities online, respectively. An online hydrogen analyzer is installed on the crude hydrogen conveying line (104) to detect the hydrogen content in the crude hydrogen.

6. A two-stage pressure swing adsorption process for purifying hydrogen, characterized in that, The system described in any one of claims 1-5 is used, and the process includes the following steps: The feed gas is continuously processed by the first stage pressure swing adsorption unit to produce product hydrogen. The desorbed gas from the first stage pressure swing adsorption unit is compressed and sent to the second stage pressure swing adsorption unit for further concentration to obtain crude product hydrogen. The crude hydrogen is mixed with the feed gas and sent to the first stage pressure swing adsorption unit.

7. The two-stage pressure swing adsorption process for purifying hydrogen according to claim 6, characterized in that, The hydrogen content in the crude hydrogen gas shall not be lower than the hydrogen content in the raw material gas.

8. The two-stage pressure swing adsorption process for purifying hydrogen according to claim 6, characterized in that, The volume content of hydrogen in the crude hydrogen gas is greater than 90%, preferably greater than 95%.

9. The two-stage pressure swing adsorption process for purifying hydrogen according to claim 6, characterized in that, The pressure of the crude hydrogen gas is the same as that of the raw material gas.

10. The two-stage pressure swing adsorption process for purifying hydrogen according to claim 9, characterized in that, The crude hydrogen gas is pressurized to the same pressure as the raw material gas by the second compression device.

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