Process for preparing ultra-pure hydrogen by recovering and purifying hydrogen

Abstract

The invention discloses a process for preparing ultra-pure hydrogen by recovering and purifying hydrogen. The process comprises the following steps: nitrogen replacement: carrying out three times of pressurization-decompression circulation on an adsorption tower and a pipeline; pretreatment of raw materials: hydrogen-containing tail gas is treated by a buffer tank, a compressor, a desulfurization tower and a horizontal adsorption tower and then enters a PSA (Pressure Swing Adsorption) system; pSA purification: a 6-2-3 / P process is adopted, two towers in six adsorption towers perform adsorption at the same time, and hydrogen larger than or equal to 99.99% is produced; regeneration of the adsorbent is completed through three-stage pressure equalizing and reducing, clockwise / anticlockwise pressure reducing, product hydrogen flushing and three-stage pressure equalizing and boosting; refining by a membrane separation unit: carrying out membrane separation on PSA hydrogen to produce ultrapure hydrogen of which the purity is greater than or equal to 99.999%, and returning trapped gas to a compressor; and condensate water recovery: carrying out steam stripping and deoxygenization on the process condensate liquid, and then taking the process condensate liquid as boiler feed water. The process integrates PSA and membrane separation technologies, realizes efficient and energy-saving ultrapure hydrogen preparation, and is suitable for the fields of green hydrogen energy storage, electronic industry, high-end chemical industry and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of gas purification, and in particular to a process for recovering and purifying hydrogen to produce ultrapure hydrogen. Background Art

[0002] In industrial production, hydrogen, as an important clean energy and chemical raw material, is widely used in fields such as petroleum refining, chemical synthesis, electronic manufacturing and fuel cells. With the development of new energy and high-end manufacturing industries, the requirements for hydrogen purity are increasing, especially in the electronics and semiconductor industries, which require ultra-pure hydrogen (purity ≥ 99.999%). The hydrogen purity of conventional pressure swing adsorption (PSA) processes is usually 99.9% to 99.99%, which is difficult to meet the demand for ultra-pure hydrogen (≥ 99.999%). In addition, the recovery rate is low. The hydrogen recovery rate of a single PSA process is usually 85% to 90%, and the remaining hydrogen is discharged with the reverse venting, resulting in a waste of resources. The energy consumption is high, and the adsorbent regeneration process relies on a large amount of flushing hydrogen, and the pressure equalization energy recovery is not high. Insufficient efficiency (traditional secondary pressure equalization only recovers about 65% of the energy); membrane separation technology has poor adaptability to raw materials, and membrane separation is sensitive to feed gas impurities (such as CO2, CH4). If industrial exhaust gas containing a large number of impurities is directly treated, it is easy to cause membrane pollution and performance degradation; the pressure loss is large, and the pressure drop of traditional membrane components is high (≥0.5MPa), requiring additional pressurization, which increases energy consumption; sulfide (H2S) and moisture in the feed gas are not completely removed, which will poison the PSA adsorbent or clog the membrane component; the process condensate is directly discharged without recycling, increasing the consumption of desalted water and wastewater treatment costs.

[0003] Therefore, the present invention provides a process for recovering and purifying hydrogen to produce ultrapure hydrogen, which couples the integrated process of PSA-membrane separation and performs graded purification: PSA first removes most impurities (CO2, CH4, etc.) to produce 99.99% hydrogen; membrane separation refines the remaining trace impurities (N2, CO), and the final purity is ≥99.999%. Summary of the Invention

[0004] The purpose of the present invention is to provide a process for recovering and purifying hydrogen to produce ultrapure hydrogen, which couples the integrated process of PSA and membrane separation for graded purification: PSA first removes most impurities (CO2, CH4, etc.) to produce 99.99% hydrogen; membrane separation refines the remaining trace impurities (N2, CO) to achieve a hydrogen product purity of ≥99.999%.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A process for recovering and purifying hydrogen to produce ultrapure hydrogen comprises the following steps:

[0007] S1. Nitrogen replacement: When the device is first put into operation, nitrogen is used to perform three pressurization-depressurization cycles on the adsorption tower and related pipelines to reduce the oxygen content and prevent the formation of explosive mixtures of hydrogen and oxygen;

[0008] S2. Raw material pretreatment: After nitrogen replacement, the hydrogen-containing tail gas enters the hydrogen buffer tank, and then enters the hydrogen compressor from the hydrogen buffer tank. After being compressed by the hydrogen compressor to increase the pressure, it enters the desulfurization tower for desulfurization treatment. After desulfurization treatment, it enters the heat exchanger at the bottom of the desulfurization tower for cooling and then enters the horizontal adsorption tower. The gas after adsorption in the horizontal adsorption tower enters the PSA adsorption tower group for adsorption;

[0009] S3. PSA adsorption tower group adsorption: The PSA adsorption tower group includes 6 adsorption towers, each equipped with an integrated heat exchanger, with its shell side connected to the adsorption tower fluid and its tube side independently connected to the temperature control medium system; among the 6 adsorption towers (towers 1 to 6), 2 adsorption towers (such as towers 1 and 2) are always kept in the adsorption state; the feed gas enters the adsorption tower inlet, and hydrogen with a purity of ≥99.99% is obtained at the adsorption tower outlet;

[0010] S4, adsorbent regeneration stage:

[0011] a. Blood pressure reduction sub-stage:

[0012] a-1. Three-stage voltage balancing and boosting:

[0013] The first pressure reduction: equalize to 1.5MPa with the adsorption tower that has completed regeneration;

[0014] Second pressure equalization and pressure reduction: Second equalization to 1.0MPa, lasting 42 to 48 seconds;

[0015] The third pressure equalization and pressure reduction: three times equalization to 0.6MPa;

[0016] a-2. Forward pressure reduction: Slowly reduce the pressure to 0.3 MPa along the flow direction of the feed gas, and monitor the purity in real time using an online hydrogen analyzer;

[0017] a-3. Reverse pressure reduction: Rapidly reduce the pressure to 0.02 MPa in reverse flow, at which point the impurity capacity of the adsorbent drops to 40-45% of the initial value;

[0018] b. Flushing sub-stage: hydrogen is drawn from the hydrogen product tank to flush the adsorption bed to reduce the partial pressure of the adsorbed components and fully desorb them, thereby achieving the purpose of adsorbent regeneration;

[0019] c. Boost sub-stage:

[0020] c-1. Three-stage voltage balancing and boosting:

[0021] The third equalization and pressure raising: the gas is raised to 0.6MPa by using other towers for the third equalization and pressure reduction;

[0022] Second pressure equalization and pressure increase: Use the second pressure equalization and pressure reduction gas to increase to 1.0MPa;

[0023] First pressure equalization and pressure boost: Use the first pressure equalization and pressure reduction gas to raise the pressure to 1.5MPa;

[0024] c-2. Final boost:

[0025] Use product hydrogen to make up the pressure to 2.0MPa;

[0026] S5. Refining in the membrane separation unit: Hydrogen with a purity of ≥99.99% obtained at the outlet of the PSA adsorption tower group enters the membrane separation unit for membrane separation. Ultrapure hydrogen with a purity of ≥99.999% produced on the permeate side enters the hydrogen product tank for storage. A portion of the membrane separation retained gas returns to the inlet of the hydrogen compressor, and a portion of the membrane separation retained gas and the PSA desorption waste gas are combined into hydrogen-rich tail gas, which is transported to the thermal oil boiler combustion system and burned by a dedicated hydrogen burner for heat supply. The combustion products are discharged after condensation to recover water.

[0027] S6. Recover process condensate: The process condensate is drained and stripped in a stripping tower and then directly enters the deaerator. After deoxygenation, it is used as boiler feed water.

[0028] Preferably, in step S1, the nitrogen dosage is 4 Nm 3 , purity is 99.5%, pressure is 0.4~0.8MPa; said reducing oxygen content to <0.5% (v / v).

[0029] Preferably, in step a-1, the energy recovered after the third pressure equalization and pressure reduction is ≥85%; in step a-3, the rate of the countercurrent rapid pressure relief to 0.02 MPa is 0.8 MPa / min.

[0030] Preferably, in step b, the hydrogen product tank is drawn out with a purity of ≥99.99%, and the flow rate of the hydrogen flushing is 12-15 Nm 3 / min, the temperature is 38-42°C, and the flushing is terminated when the impurity concentration at the flushing gas outlet is ≤50ppm and the residual impurities in the adsorbent are ≤0.5wt%.

[0031] Preferably, in step c-2, the final pressurization is performed using product hydrogen to increase the pressure to 2.0 MPa at a rate of 0.3 MPa / min, and the final temperature of the pressurization is controlled at 50-55°C.

[0032] Preferably, in step S5, the hydrogen with a purity of ≥99.99% obtained at the outlet of the PSA adsorption tower group is subjected to membrane separation at an operating pressure of 3.0-5.0 MPa, and ultrapure hydrogen with a purity of ≥99.999% produced on the permeate side is stored in a hydrogen product tank.

[0033] Preferably, in step S5, the hydrogen volume concentration of the hydrogen-rich tail gas is 30% to 50%, the combustion temperature is 800 to 1000°C, the thermal efficiency of the thermal oil boiler is ≥95%, and the CO2 concentration in the combustion exhaust gas is ≤50ppm and the NOx concentration is ≤10ppm.

[0034] Preferably, in step S5, the ratio of the membrane separation retentate gas returned to the hydrogen compressor inlet is 30% to 70%, and the rest enters the thermal oil boiler combustion system.

[0035] Preferably, in step S5, the thermal oil boiler combustion system is provided with an online hydrogen concentration monitor and a flame detector, which automatically cuts off the gas source and starts nitrogen purge when the hydrogen concentration is lower than 20% or the flame is abnormal.

[0036] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0037] 1. The present invention conducts three pressurization-decompression cycles before the device is put into operation to ensure that the oxygen content is ≤0.5% (v / v), completely eliminating the explosion risk of hydrogen and oxygen mixing, and complying with the ISO15916 safety standard. During the PSA regeneration stage, the device uses a stepped pressure relief method of forward pressure reduction and reverse pressure reduction to avoid equipment damage caused by sudden pressure changes, extending the system's safe life by more than 30%;

[0038] 2. The present invention couples the integrated process of PSA and membrane separation for graded purification. The PSA stage produces 99.99% high-purity hydrogen (CO2 ≤ 10ppm), and the adsorbent regeneration efficiency is improved by 40% (compared to the traditional four-tower process). The membrane separation stage: further purifies to 99.999% ultra-pure hydrogen (CO ≤ 0.5ppm), meeting the SEMIC3.43 semiconductor-grade standard. By recycling the trapped gas (containing 30-50% H2 and returning it to the hydrogen compressor inlet), energy saving is 15% compared to the single PSA process (85-90%), and the hydrogen recovery rate is ≥95%;

[0039] 3. The present invention recovers PSA waste heat. The adsorption tower integrated heat exchanger uses the heat from the regeneration stage to preheat the feed gas, reducing energy consumption. The membrane separation pressure is optimized, and the PSA outlet residual pressure is directly utilized, reducing recompression energy consumption by 20%. Water resources are recycled, and the process condensate is treated in the stripping tower and then reused as boiler feed water, reducing desalted water consumption by 35%, thereby reducing overall costs.

[0040] 4. The present invention has zero wastewater discharge. The condensed water after treatment in the stripping tower meets the boiler feed water standard GB / T12145-2016, with COD ≤ 5mg / L. The waste gas is recovered, and the intercepted gas (containing H230-50%) is returned to the system by membrane separation, avoiding venting losses and achieving green and environmentally friendly production.

[0041] 5. The ultrapure hydrogen (grade 5N) of the present invention is suitable for high-end fields such as semiconductor chip manufacturing and optical fiber preform deposition, replacing imported high-cost hydrogen sources. It is especially suitable for green hydrogen energy storage, electronics industry, high-end chemical industry and other fields, and has significant market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, some of the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be made based on these drawings without paying any creative work.

[0043] Figure 1 This is a process flow chart of Example 1 of the present invention;

[0044] Among them, 1-hydrogen buffer tank; 2-hydrogen compressor; 3-desulfurization tower; 4-desulfurization tower bottom heat exchanger; 5-horizontal adsorption tower; 6-hydrogen product tank; 7-PSA adsorption tower group; 8-membrane separation unit; 9-stripping tower; 10-deaerator. DETAILED DESCRIPTION

[0045] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0046] The present invention is further described below with reference to the following examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific applications. The implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0047] Example 1

[0048] See attached Figure 1 This embodiment provides a process for recovering and purifying hydrogen to produce ultrapure hydrogen, comprising the following steps:

[0049] S1. Nitrogen replacement: When the device is first put into operation, nitrogen is used to perform three pressurization-depressurization cycles on the adsorption tower and related pipelines to reduce the oxygen content to <0.5% (v / v) to prevent hydrogen and oxygen from forming an explosive mixture. The nitrogen dosage is 4Nm 3 , purity is 99.5%, pressure is 0.6MPa;

[0050] S2. Raw material pretreatment: After nitrogen replacement, the hydrogen-containing tail gas enters the hydrogen buffer tank (1), then exits the hydrogen buffer tank and enters the hydrogen compressor (2), is compressed by the hydrogen compressor to increase the pressure, and then enters the desulfurization tower (3) for desulfurization treatment. After desulfurization treatment, it enters the heat exchanger (4) at the bottom of the desulfurization tower for cooling and then enters the horizontal adsorption tower (5). The gas adsorbed by the horizontal adsorption tower enters the PSA adsorption tower group (7) for adsorption;

[0051] S3. PSA adsorption tower group adsorption: The PSA adsorption tower group includes 6 adsorption towers, each equipped with an integrated heat exchanger, with its shell side connected to the adsorption tower fluid and its tube side independently connected to the temperature control medium system; among the 6 adsorption towers (towers 1 to 6), 2 adsorption towers (such as towers 1 and 2) are always kept in the adsorption state; the feed gas enters the adsorption tower inlet, and hydrogen with a purity of ≥99.99% is obtained at the adsorption tower outlet;

[0052] S4, adsorbent regeneration stage:

[0053] a. Blood pressure reduction sub-stage:

[0054] a-1. Three-stage voltage balancing and boosting:

[0055] The first pressure reduction: equalize to 1.5MPa with the adsorption tower that has completed regeneration;

[0056] Second pressure equalization and pressure reduction: Second equalization to 1.0MPa, lasting 42 to 48 seconds;

[0057] The third pressure equalization and pressure reduction: three equalizations to 0.6MPa, energy recovery ≥85%;

[0058] a-2. Forward pressure reduction: Slowly reduce the pressure to 0.3 MPa along the flow direction of the feed gas, and monitor the purity in real time using an online hydrogen analyzer;

[0059] a-3. Reverse pressure reduction: Rapidly reduce the pressure to 0.02 MPa at a rate of 0.8 MPa / min in reverse flow. At this time, the impurity capacity of the adsorbent is reduced to 40-45% of the initial value;

[0060] b. Flushing sub-stage: hydrogen is drawn from the hydrogen product tank (6) to flush the adsorption bed, thereby reducing the partial pressure of the adsorbed components and allowing them to be fully desorbed, thereby achieving the purpose of adsorbent regeneration;

[0061] Furthermore, the hydrogen product tank is drawn out with a purity of ≥99.99%, and the flow rate of the hydrogen flushing is 13Nm 3 / min, temperature 40℃, and stop flushing when the impurity concentration of flushing gas outlet is ≤50ppm and the residual impurities in adsorbent is ≤0.5wt%;

[0062] c. Boost sub-stage:

[0063] c-1. Three-stage voltage balancing and boosting:

[0064] The third equalization and pressure raising: the gas is raised to 0.6MPa by using other towers for the third equalization and pressure reduction;

[0065] Second pressure equalization and pressure increase: Use the second pressure equalization and pressure reduction gas to increase to 1.0MPa;

[0066] First pressure equalization and pressure boost: Use the first pressure equalization and pressure reduction gas to raise the pressure to 1.5MPa;

[0067] c-2. Final boost:

[0068] Product hydrogen was used to increase the pressure to 2.0 MPa at a rate of 0.3 MPa / min, and the pressure boost endpoint temperature was controlled at 52°C;

[0069] S5, membrane separation unit refining: hydrogen with a purity of ≥99.99% obtained at the outlet of the PSA adsorption tower group enters the membrane separation unit (8) for membrane separation, and ultrapure hydrogen with a purity of ≥99.999% produced on the permeate side enters the hydrogen product tank for storage, 70% of the membrane separation intercepted gas returns to the inlet of the hydrogen compressor, 30% of the membrane separation intercepted gas and the PSA desorption waste gas are combined into hydrogen-rich tail gas, which is transported to the thermal oil boiler combustion system, burned and heated by a hydrogen-specific burner, and the combustion products are discharged after condensation and water recovery;

[0070] Furthermore, the hydrogen volume concentration of the hydrogen-rich tail gas is 30% to 50%, the combustion temperature is 900°C, the thermal efficiency of the thermal oil boiler is ≥95%, and the CO2 concentration in the combustion exhaust gas is ≤50ppm and the NOx concentration is ≤10ppm;

[0071] Furthermore, the thermal oil boiler combustion system is equipped with an online hydrogen concentration monitor and a flame detector, which automatically cuts off the gas source and starts nitrogen purge when the hydrogen concentration is lower than 20% or the flame is abnormal.

[0072] S6. Recovering the process condensate: The process condensate is drained and stripped in a stripping tower (9) and then directly enters a deaerator (10). After deoxygenation, it is used as boiler feed water.

[0073] In summary, the present invention performs three pressurization-depressurization cycles before the device is put into operation to ensure that the oxygen content is ≤0.5% (v / v), completely eliminating the explosion risk of hydrogen and oxygen mixing, and complying with the ISO15916 safety standard; the PSA regeneration stage uses a stepped pressure relief of forward pressure reduction + reverse pressure reduction to avoid equipment damage caused by sudden pressure changes, and the safe life of the system is extended by more than 30%; the present invention couples the integrated process of PSA-membrane separation for graded purification. The PSA stage produces 99.99% high-purity hydrogen (CO2≤10ppm), and the adsorbent regeneration efficiency is improved by 40% (compared with the traditional 4-tower process); membrane separation stage: further purification to 99.999% ultra-pure hydrogen (CO≤0.5ppm), meeting the SEMIC3.43 semiconductor-grade standard; by circulating the trapped gas (containing 30-50% H2 returned to the hydrogen compressor inlet), energy saving is 15% compared with the single PSA process (85-90%). %,Hydrogen recovery rate≥95%;The present invention recovers PSA waste heat, and the adsorption tower integrated heat exchanger utilizes the heat of the regeneration stage to preheat the raw gas, thereby reducing energy consumption; The membrane separation pressure is optimized, and the PSA outlet residual pressure is directly utilized, reducing the recompression energy consumption by 20%; Water resource circulation, the process condensed water is treated in the stripping tower and then reused as boiler feed water, and the desalted water consumption is reduced by 35%, thereby reducing the cost as a whole; The present invention has zero wastewater discharge, and the condensed water after the stripping tower treatment meets the GB / T12145-2016 boiler feed water standard, COD≤5mg / L; Waste gas recovery, the membrane separation intercepted gas (containing H230-50%) is returned to the system, avoiding venting loss and realizing green and environmentally friendly production; The present invention's ultra-pure hydrogen (5N grade): is suitable for high-end fields such as semiconductor chip manufacturing and optical fiber preform deposition, replacing imported high-cost hydrogen sources, and is particularly suitable for green hydrogen energy storage, electronics industry, high-end chemical industry and other fields, with significant market competitiveness.

[0074] The above-described embodiment merely represents one embodiment of the present invention. While the description is relatively specific and detailed, it should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A process for recovering and purifying hydrogen to produce ultrapure hydrogen, characterized in that: The steps include: S1. Nitrogen replacement: When the device is first put into operation, nitrogen is used to perform three pressurization-depressurization cycles on the adsorption tower and related pipelines to reduce the oxygen content and prevent the formation of explosive mixtures of hydrogen and oxygen; S2. Raw material pretreatment: After nitrogen replacement, the hydrogen-containing tail gas enters the hydrogen buffer tank, and then enters the hydrogen compressor from the hydrogen buffer tank. After being compressed by the hydrogen compressor to increase the pressure, it enters the desulfurization tower for desulfurization treatment. After desulfurization treatment, it enters the heat exchanger at the bottom of the desulfurization tower for cooling and then enters the horizontal adsorption tower. The gas after adsorption in the horizontal adsorption tower enters the PSA adsorption tower group for adsorption; S3. PSA adsorption tower group adsorption: The PSA adsorption tower group includes 6 adsorption towers, each equipped with an integrated heat exchanger. Its shell side is connected to the adsorption tower fluid, and its tube side is independently connected to the temperature control medium system. Two of the 6 adsorption towers are always kept in the adsorption state. The feed gas enters the adsorption tower inlet, and hydrogen with a purity of ≥99.99% is obtained at the adsorption tower outlet. S4, adsorbent regeneration stage: a. Blood pressure reduction sub-stage: a-1. Three-stage voltage balancing and boosting: The first pressure reduction: equalize to 1.5MPa with the adsorption tower that has completed regeneration; Second pressure equalization and pressure reduction: Second equalization to 1.0MPa, lasting 42 to 48 seconds; The third pressure equalization and pressure reduction: three times equalization to 0.6MPa; a-2. Forward pressure reduction: Slowly reduce the pressure to 0.3 MPa along the flow direction of the feed gas, and monitor the purity in real time using an online hydrogen analyzer; a-3. Reverse pressure reduction: Rapidly reduce the pressure to 0.02 MPa in reverse flow, at which point the impurity capacity of the adsorbent drops to 40-45% of the initial value; b. Flushing sub-stage: hydrogen is drawn from the hydrogen product tank to flush the adsorption bed to reduce the partial pressure of the adsorbed components and fully desorb them, thereby achieving the purpose of adsorbent regeneration; c. Boost sub-stage: c-1. Three-stage voltage balancing and boosting: The third equalization and pressure raising: the gas is raised to 0.6MPa by using other towers for the third equalization and pressure reduction; Second pressure equalization and pressure increase: Use the second pressure equalization and pressure reduction gas to increase to 1.0MPa; First pressure equalization and pressure boost: Use the first pressure equalization and pressure reduction gas to raise the pressure to 1.5MPa; c-2. Final boost: Use product hydrogen to make up the pressure to 2.0MPa; S5. Refining in the membrane separation unit: Hydrogen with a purity of ≥99.99% obtained at the outlet of the PSA adsorption tower group enters the membrane separation unit for membrane separation. Ultrapure hydrogen with a purity of ≥99.999% produced on the permeate side enters the hydrogen product tank for storage. A portion of the membrane separation retained gas returns to the inlet of the hydrogen compressor, and a portion of the membrane separation retained gas and the PSA desorption waste gas are combined into hydrogen-rich tail gas, which is transported to the thermal oil boiler combustion system and burned by a dedicated hydrogen burner for heat supply. The combustion products are discharged after condensation to recover water. S6. Recover process condensate: The process condensate is drained and stripped in a stripping tower and then directly enters the deaerator. After deoxygenation, it is used as boiler feed water.

2. A process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, characterized in that: In step S1, the nitrogen dosage is 4Nm 3 , purity is 99.5%, pressure is 0.4~0.8MPa; said reducing oxygen content to <0.5%.

3. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, characterized in that: In step a-1, the energy recovered after the third pressure equalization and pressure reduction is ≥85%; in step a-3, the rate of the countercurrent rapid pressure relief to 0.02 MPa is 0.8 MPa / min.

4. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, wherein: In step b, the hydrogen product tank is drawn out with a purity of ≥99.99% and the flow rate of the hydrogen flushing is 12-15 Nm 3 / min, the temperature is 38-42°C, and the flushing is terminated when the impurity concentration at the flushing gas outlet is ≤50ppm and the residual impurities in the adsorbent are ≤0.5wt%.

5. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, characterized in that: In step c-2, the final pressure increase is performed using product hydrogen at a rate of 0.3 MPa / min to increase the pressure to 2.0 MPa, and the final temperature of the pressure increase is controlled at 50-55°C.

6. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, characterized in that: In step S5, the hydrogen with a purity of ≥99.99% obtained at the outlet of the PSA adsorption tower group is subjected to membrane separation at an operating pressure of 3.0-5.0 MPa, and ultrapure hydrogen with a purity of ≥99.999% produced on the permeate side is stored in a hydrogen product tank.

7. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, characterized in that: In step S5, the hydrogen volume concentration of the hydrogen-rich tail gas is 30% to 50%, the combustion temperature is 800 to 1000°C, the thermal efficiency of the thermal oil boiler is ≥95%, and the CO2 concentration in the combustion exhaust gas is ≤50ppm and the NOx concentration is ≤10ppm.

8. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, wherein: In step S5, the ratio of the membrane separation retentate gas returned to the hydrogen compressor inlet is 30% to 70%, and the rest enters the thermal oil boiler combustion system.

9. The process for recovering and purifying hydrogen to produce ultrapure hydrogen according to claim 1, characterized in that: In step S5, the thermal oil boiler combustion system is equipped with an online hydrogen concentration monitor and a flame detector, which automatically cuts off the gas source and starts nitrogen purge when the hydrogen concentration is lower than 20% or the flame is abnormal.

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