Process and apparatus for producing ultra-high purity hydrogen from low grade hydrogen

Abstract

This invention discloses a process and a multi-tower vacuum pressure swing adsorption (VPSA) apparatus for producing ultra-high purity hydrogen (≥99.997 vol%) from a feed gas containing 95.0 vol%–99.9 vol% hydrogen and one or more impurities at a pressure of 1.2 MPa–3.0 MPa. The apparatus comprises six adsorption towers connected in parallel, five control valves corresponding to each tower, a feed gas buffer tank, a product gas buffer tank, and a vacuum pump. The process for implementing the VPSA cycle in the apparatus includes three or more co-current depressurization steps, three or more counter-current pressurization steps, and one vacuum purging step. The process can be automated or programmed, optimized for output, and operated at low cost, on a specially designed skid or container, for the production and supply of ultra-high purity hydrogen for industrial, pharmaceutical, and hydrogen energy applications.

Description

[0001] High-purity hydrogen (H2) is a traditional industrial gas used in various industrial processes, aerospace, and medical applications. It also significantly drives emerging hydrogen energy applications. The dynamically evolving hydrogen fuel cell offers a wide range of advantages, including minimizing carbon dioxide emissions, powering fuel cell vehicles, and converting electrical energy into hydrogen for energy conversion and storage. To ensure high energy efficiency and reliability in hydrogen fuel cells, hydrogen requires a purity of at least 99.97 vol%. Crucially, impurities in the hydrogen are strictly limited to certain levels, such as less than 100 ppm for methane, less than 2 ppm for total hydrocarbons (excluding methane), less than 5 ppm for oxygen, less than 300 ppm for nitrogen, less than 2 ppm for carbon dioxide, and less than 0.2 ppm for carbon monoxide. The anticipated surge and application of hydrogen fuel cells necessitates the efficient and effective production of ultra-high-purity hydrogen. Technical Field

[0002] This invention relates to a vacuum pressure swing adsorption (VPSA) process and a multi-tower apparatus corresponding to the VPSA process, the process and apparatus being used to produce ultra-high purity hydrogen (≥99.997 vol%) from a low-grade pure hydrogen stream (≥95 vol%). Background Technology

[0003] Currently, the production of pure hydrogen via Pressure Swing Adsorption (PSA) is an industrially mature process. A typical PSA system comprises multiple adsorption towers (also known as "adsorption beds"), each operating in a programmed and planned sequence, known as a PSA cycle. A PSA cycle includes many well-known steps, and a specific PSA application requires technicians to combine these known steps in a suitable manner to achieve the desired separation objective. These known steps include, but are not limited to: feed and adsorption steps, co-current equalization steps, co-current purging steps, counter-current purging and desorption steps, counter-current equalization steps, and repressurization steps. US Patent (9,381,460B2) includes a comprehensive description of various hydrogen PSA steps, as well as several practical cycles combining these steps used in industry to separate hydrogen from gas mixtures. However, in each listed cycle, the specifications of the hydrogen product are not defined; presumably, they fall within the range of typical industrial-grade pure hydrogen.

[0004] Industrial-grade pure hydrogen is typically produced using steam reforming (SMR) or similar processes. The purity of hydrogen from industrial PSA processes is usually in the range of 95.0 vol%–99.9 vol%, but the impurity levels from these processes are not strictly controlled according to the requirements for fuel cell hydrogen. Therefore, more advanced purification technologies than conventional PSA processes are needed to obtain high / ultra-high purity hydrogen.

[0005] Currently, purification methods for upgrading low-grade hydrogen products (typically ranging from 95.0 vol% to 99.9 vol%) obtained from conventional PSA processes to ultra-high-purity hydrogen include multi-stage hydrogen PSA, cryogenic temperature-switching adsorption (Cryo-TSA), palladium-based alloy membrane hydrogen separation technology, and methods for purifying hydrogen using metal hydrides. Multi-stage hydrogen PSA inevitably requires higher investment costs and additional energy consumption.

[0006] The Cryo-TSA process requires cooling the hydrogen feedstock and adsorption tower to liquid nitrogen temperature (-196°C). At this temperature, the adsorbent adsorbs impurities while simultaneously producing high-purity hydrogen (over 99.999 vol%) as the product gas. To regenerate the adsorbent, the temperature in the adsorption tower needs to be reheated to ambient temperature. Due to the larger temperature fluctuation range and the use of refrigerant, Cryo-TSA requires significantly higher energy consumption, special considerations for construction materials, and additional control mechanisms for the liquid system compared to the conventional PSA process.

[0007] Palladium-based alloy membranes exhibit single selectivity for hydrogen at relatively high temperatures (400-500°C). This property can be utilized with carefully designed equipment to produce ultra-high purity hydrogen products containing more than 99.999 vol% hydrogen. However, the high cost and low yield of palladium membranes hinder the widespread adoption of this process for large-scale production of ultra-high purity hydrogen.

[0008] Hydrogen purification via metal hydrides is a chemisorption process where a metal alloy reacts with hydrogen to form a metal hydride. Most of the hydrogen is fixed in the solid phase, while impurities remain in the gas phase, thus separating the hydrogen from the impurities. Subsequently, ultra-high purity hydrogen (≥99.999 vol%) can be collected by reversing the hydride formation reaction to decompose the metal hydride. The main problem with this process is the stability of the metal alloy; its performance rapidly declines after a few adsorption / release cycles, requiring frequent maintenance and replacement of the adsorbent.

[0009] To avoid the drawbacks of the aforementioned processes, Beijing Huanyu Jinghui Jingcheng Gas Technology Co., Ltd. has proposed a new method. Their Chinese patent (CN105,268,282A) describes a low-temperature PSA process comprising four parallel adsorption towers and 11 consecutive steps (one adsorption step, three sets of supply and receiving equalization steps, co-current and counter-current blowing steps, and a repressurization step) to purify a feed gas containing 99.999 vol% hydrogen into ultra-high purity hydrogen containing 99.99999 vol% hydrogen at -30 to -35°C. This invention proposes a technological approach to innovate a mature PSA process into a new PSA cycle to obtain ultra-high purity hydrogen, although the specifications of the hydrogen product produced by this invention far exceed the goal of obtaining ultra-high purity hydrogen. Furthermore, the sub-zero temperatures used in this invention require a significant additional energy consumption. Summary of the Invention

[0010] This invention is proposed under the aforementioned circumstances. This invention provides a process and a multi-tower vacuum pressure swing adsorption (VPSA) apparatus for producing hydrogen with a purity exceeding 99.997 vol% from a feed gas containing 95.0 vol%-99.9 vol% hydrogen and one or more impurities. In this invention, the apparatus includes six or more adsorption towers connected in parallel, five control valves corresponding to each tower, a feed gas buffer tank, a product gas buffer tank, and a vacuum pump. The process for realizing the vacuum pressure swing adsorption cycle in the apparatus of this invention includes three or more co-current depressurization steps, three or more counter-current pressurization steps, and one vacuum purging step. Attached Figure Description

[0011] In the attached diagram: Figure 1 [ Figure 1 [This is a schematic diagram of a six-bed VPSA system for purifying high-purity hydrogen using the VPSA process of this invention;] Figure 2 [ Figure 2 This is a process and flow chart of the 12-step VPSA cycle operated by the six-bed VPSA device of the present invention. Detailed Implementation

[0012] According to a first aspect of the invention, a process is provided for purifying low-grade hydrogen to ultra-high-purity hydrogen via vacuum pressure swing adsorption, the process using six or more adsorption towers, each individually filled with adsorbent. Each adsorption tower is programmed to repeatedly perform the same sequential cycle of 12 steps. However, at any given time, the six adsorption towers operate on different steps so that the six adsorption towers can operate collaboratively to meet the needs of continuous utilization of hydrogen feedstock and continuous production of ultra-high-purity hydrogen. The process described below focuses on one of the six adsorption towers.

[0013] Repeated multi-step loops include: (a) Adsorption step: The raw gas is passed through an adsorption tower to adsorb impurities onto the adsorbent and the exhaust gas is obtained as an ultra-high purity hydrogen product.

[0014] (b) Adsorption and repressurization step: Based on the adsorption step, a portion of the exhaust gas from the adsorption tower is introduced into another adsorption tower that is undergoing a repressurization step.

[0015] (c) First co-current pressure equalization and depressurization step: After the adsorption step, the gas in the adsorption tower flows co-currently to another adsorption tower that is undergoing a counter-current pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level.

[0016] (d) Second co-current pressure equalization and depressurization step: After the first co-current pressure equalization and depressurization step, the gas in the adsorption tower flows co-currently to another adsorption tower that is undergoing the second counter-current pressure equalization and pressurization step, until the pressure in the two connected adsorption towers reaches the same level.

[0017] (e) Third co-current pressure equalization and depressurization step: After the second co-current pressure equalization and depressurization step, the gas in the adsorption tower flows co-currently to another adsorption tower that is undergoing the third counter-current pressure equalization and pressurization step, until the pressure in the two connected adsorption towers reaches the same level.

[0018] (f) Downstream purging step: After the third downstream equalization and depressurization step, the remaining gas in the adsorption tower flows downstream to another adsorption tower that is undergoing the receiving purging step.

[0019] (g) Desorption step: The gas in the adsorption tower is forced to flow countercurrently out of the bottom of the adsorption tower. The venting force is provided by a vacuum pump connected to the adsorption tower. All extracted gas is considered as desorbed gas product.

[0020] (h) Countercurrent vacuum purging step: After the desorption step, the adsorption tower receives gas flow from the top from another adsorption tower that is currently performing a cocurrent purging step, while evacuation from the vacuum pump located at the bottom continues to generate desorbed gas product.

[0021] (i) Third countercurrent pressure equalization and pressurization step: The gas flow flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower, the gas flow comes from another adsorption tower that is undergoing the third cocurrent pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level.

[0022] (j) Second countercurrent pressure equalization and pressurization step: The gas flow flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower, the gas flow comes from another adsorption tower that is undergoing the second cocurrent pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level.

[0023] (k) First countercurrent pressure equalization and pressurization step: The gas flow flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower, the gas flow comes from another adsorption tower that is undergoing the first cocurrent pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level.

[0024] (l) Product gas repressurization step: Gas flow from the product gas buffer tank flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower. After step (l), the adsorption tower will run step (a) again for another VPSA cycle.

[0025] Accordingly, ultra-high purity hydrogen (≥99.997 vol%) was obtained through the vacuum pressure swing adsorption process.

[0026] Preferably, the pure hydrogen feed gas to be purified by the process contains 95.0 vol%-99.9 vol% hydrogen, with the balance being byproducts including nitrogen (N2), oxygen (O2), methane (CH4), hydrocarbons (HCs), carbon dioxide (CO2), and carbon monoxide (CO), and the pressure of the pure hydrogen feed gas is in the range of 1.2 MPa-3.0 MPa gauge pressure.

[0027] Preferably, in step (g) desorption and step (h) countercurrent purging, the vacuum pump evacuates the adsorption tower to an absolute pressure level of 10-50 kPa.

[0028] In one variation, each adsorption tower includes a layer of activated carbon (first adsorbent) or the like, packed at 25%-75% in the upstream portion of the pure hydrogen feed gas flow direction, and a layer of zeolite-based adsorbent (second adsorbent) or the like, packed at 25%-75% in the downstream portion of the pure hydrogen feed gas flow direction. Suitable activated carbon includes, but is not limited to, coconut shell activated carbon. Suitable zeolite-based adsorbents include, but are not limited to, 5A, CaX, LiX, 13X, and LiA zeolites.

[0029] Hydrogen recovery rate is defined as the total molar amount of hydrogen in ultra-high purity hydrogen product (>99.997 vol%) divided by the molar amount of hydrogen in pure hydrogen feed gas. The hydrogen recovery rate of the process described in this invention is very high, typically greater than 85%, more preferably greater than 90%. This is generally much higher than other disclosed hydrogen PSA processes for ultra-high purity hydrogen production, which typically achieve hydrogen recovery rates of 60%-80%.

[0030] Two inventive designs are applied in the process of this invention: (1) unlike the traditional hydrogen PSA process which uses hydrogen product gas as the purge carrier gas, this invention uses the residual gas in the adsorption tower as the purge carrier gas; (2) a vacuum pump is used to provide additional evacuation driving force for the desorption and purge steps. Without either of these two inventive designs, the recovery rate and purity of the hydrogen product gas would be significantly affected.

[0031] Using the residual gas instead of the hydrogen product gas as the purge carrier gas improves hydrogen recovery because it avoids any purified hydrogen flowing back into the adsorption tower and subsequently remaining at the bottom as waste gas. Essentially, the reason this alternative purge carrier gas works effectively in this invention is that the hydrogen feed gas has a purity greater than 95%. Due to the low impurity content in the feed gas, the residual gas in the adsorption tower after all equalization steps will still be a sufficiently pure hydrogen stream, similar to the product gas in conventional hydrogen PSA processes. Therefore, the conventional approach of using hydrogen product gas as the purge carrier gas in conventional hydrogen PSA processes is no longer optimal. Instead, due to the specific feed gas conditions in this invention, using the residual gas in the adsorption tower after all equalization steps as the purge carrier gas offers significant advantages in hydrogen recovery.

[0032] The use of a vacuum pump is another important feature of this invention. As is a general rule in adsorption processes, improving the regeneration capacity of the adsorbent always improves the performance of the adsorption process. Especially in the case of low impurity content as described in this invention, a stronger regeneration driving force—in this invention, a vacuum—is required to deeply clean the impurities adsorbed on the adsorbent in each VPSA cycle, thereby enabling the adsorbent to adsorb most of the new impurities in the next adsorption cycle.

[0033] According to the present invention, a specially constructed device, namely a VPSA device using six adsorption towers filled with carefully designed adsorbents, can purify low-grade pure hydrogen into ultra-high purity hydrogen of 99.997% or higher.

[0034] This VPSA device can implement the process of the first aspect of the invention, and therefore has the same advantages as those described above with respect to the invention. The following embodiments section provides examples of applications of the invention.

[0035] The following is in conjunction with the appendix Figure 1 and 2 A preferred embodiment of the apparatus of the present invention is described.

[0036] Adsorption towers 1, 2, 3, 4, 5, and 6 are arranged in parallel. The adsorption towers are configured to adsorb target components other than hydrogen from the feed gas supplied by path 8 using an adsorbent, and then produce product gas discharged through path 10.

[0037] The feed gas supply path 8, used to supply feed gas, connects the feed gas buffer tank 8a to the lower part of the six adsorption towers. The feed gas supply control valves 1a, 2a, 3a, 4a, 5a, and 6a on the feed gas supply path of each adsorption tower open and close to supply feed gas to the corresponding individual adsorption tower.

[0038] Desorption path 9, used to discharge desorbed gas, is connected to the lower part of six adsorption towers. A vacuum pump 7 is installed on the desorption path to reduce the pressure in the desorption path to an absolute pressure of 10-50 kPa·A. Desorbed gas control valves 1b, 2b, 3b, 4b, 5b, and 6b on the desorption paths of the corresponding adsorption towers open and close the desorbed gas discharge path leading to the vacuum pump 7. A side-channel control valve is connected in parallel with the vacuum pump and is programmed to open the discharge side channel when the absolute pressure in the desorption discharge path is higher than 0.11 MPa·A, and conversely, to close the side channel when the absolute pressure in the desorption discharge path is lower than 0.11 MPa·A. The gas outlet side of the vacuum pump 7 is connected to a desorbed gas buffer tank 9a.

[0039] Product gas path 10, used to supply hydrogen product gas, is connected between the upper part of the six adsorption towers and the product gas buffer tank 10a. Product gas control valves 1f, 2f, 3f, 4f, 5f, and 6f on the product gas path of each adsorption tower open and close the product gas discharge path of the corresponding adsorption tower leading to the product gas buffer tank.

[0040] Furthermore, two sets of pressure equalization control valves are connected to the upper part of the adsorption tower. On the first pressure equalization path 11, pressure equalization control valves 1c, 2c, 3c, 4c, 5c, and 6c control the connection mode between any two adsorption towers by opening / closing their corresponding control valves. Similarly, on the second pressure equalization path 12, pressure equalization control valves 1d, 2d, 3d, 4d, 5d, and 6d control the connection mode between any two adsorption towers by opening / closing their corresponding control valves. Preferably, in this embodiment, the first pressure equalization path 11 is used for the aforementioned third pressure equalization step and purging step, while the second pressure equalization path 12 is used for the second and first pressure equalization steps.

[0041] Another set of control valves 1e, 2e, 3e, 4e, 5e, and 6e connect the product gas buffer tank 10a and the adsorption tower on the repressurization path 13. The repressurization control valves 1e, 2e, 3e, 4e, 5e, and 6e open and close the corresponding repressurization paths, which allow ultrapure hydrogen from the product gas tank to flow back to the adsorption tower to pressurize the adsorption tower to the feed pressure.

[0042] Referring to the above embodiment, the 12-step VPSA cycle can be implemented to purify pure hydrogen feed gas to obtain ultra-high purity hydrogen product. Specifically, all 12 VPSA steps are controlled to operate in parallel in six adsorption towers. The 12-step VPSA cycle is described below.

[0043] In step (a), adsorption tower 1 undergoes a first feeding and adsorption process. Specifically, hydrogen feed gas is introduced into the adsorption tower 1 from the bottom by opening control valve 1a to adsorb most of the impurities. Simultaneously, product gas control valve 1f is opened, and purified hydrogen gas is discharged from the top of adsorption tower 1 as a high-purity hydrogen product.

[0044] The adsorption tower 4 undergoes a desorption step, whereby the desorbed gas product is drawn from the bottom of the adsorption tower 4 by the vacuum pump 7 through the opened desorption control valve 4b. The pressure inside the adsorption tower 4 decreases to the desorption pressure, which is determined by the power of the vacuum pump.

[0045] Adsorption towers 3 and 5 utilize the first pressure equalization path 11 for a third pressure equalization step. Specifically, adsorption tower 5 receives a co-current airflow through an open pressure equalization control valve 5c, resulting in a pressure decrease within adsorption tower 5. Adsorption tower 3 receives a counter-current airflow through an open pressure equalization control valve 3c, resulting in a pressure increase within adsorption tower 3. The overall result of the third pressure equalization step is that the higher pressure in adsorption tower 5 at the beginning of step (a) and the lower pressure in adsorption tower 3 at the beginning of step (a) reach the same level at the end of step (a).

[0046] Adsorption towers 2 and 6 undergo a first pressure equalization step using pressure equalization path 12. Specifically, adsorption tower 6 receives a co-current airflow through an open pressure equalization control valve 6d, resulting in a pressure decrease within adsorption tower 6. Adsorption tower 2 receives a counter-current airflow through an open pressure equalization control valve 2d, resulting in a pressure increase within adsorption tower 2. The overall result of the first pressure equalization step is that the higher pressure in adsorption tower 6 at the beginning of step (a) and the lower pressure in adsorption tower 2 at the beginning of step (a) reach the same level at the end of step (a).

[0047] In step (b), adsorption tower 1 undergoes a second feeding and adsorption step, similar to step (a), by opening the feed gas control valve 1a and the product gas control valve 1f. Adsorption tower 2 undergoes a repressurization step. High-purity hydrogen product gas is introduced from the product gas buffer tank into adsorption tower 2 through repressurization path 13 by opening the repressurization control valve 2e. At the end of step (b), the pressure inside adsorption tower 2 increases to the same level as the feed gas.

[0048] Adsorption tower 4 undergoes a purging step, while adsorption tower 5 provides a co-current purging step. Specifically, after step (a), the desorbed gas control valve 4b remains open to continuously extract the desorbed gas from adsorption tower 4. Simultaneously, another gas flow from adsorption tower 5 enters adsorption tower 4 via pressure equalization control valve 4c and the first pressure equalization path 11. The pressure equalization control valve 5c is opened, allowing gas to flow out of adsorption tower 5 and purging adsorption tower 4. Through this interaction between adsorption towers 4 and 5, at the end of step (b), the pressure in adsorption tower 5 decreases to a specific level above the desorption pressure, while the pressure in adsorption tower 4 remains at the desorption pressure.

[0049] Adsorption towers 3 and 6 undergo a second pressure equalization step using pressure equalization path 12. Specifically, adsorption tower 6 receives a co-current airflow through an open pressure equalization control valve 6d, resulting in a pressure decrease within adsorption tower 6. Adsorption tower 3 receives a counter-current airflow through an open pressure equalization control valve 3d, causing a pressure increase within adsorption tower 3. The overall result of the second pressure equalization step is that the higher pressure in adsorption tower 6 at the beginning of step (b) and the lower pressure in adsorption tower 3 at the beginning of step (b) reach the same level at the end of step (b).

[0050] Steps (a) and (b) comprise all 12 steps of the VPSA cycle: feed and adsorption step, adsorption and repressurization step, first equalization step, second equalization step, third equalization step, desorption step, vacuum purging and repressurization step, although each step is performed by a different adsorption tower. Thereafter, steps (a) and (b) are the basic “building blocks” and can be extended to produce the entire VPSA cycle by switching adsorption towers to perform each individual step.

[0051] For example, in steps (c) and (d), adsorption tower 1 performs a first pressure equalization step and a second pressure equalization step, the same as the steps performed by adsorption tower 6 in steps (a) and (b). In steps (e) and (f), adsorption tower 1 performs a third pressure equalization step and a co-current purging step, the same as the steps performed by adsorption tower 5 in steps (a) and (b). In steps (g) and (h), adsorption tower 1 performs a desorption step and a purging step, the same as the steps performed by adsorption tower 4 in steps (a) and (b). In steps (i) and (j), adsorption tower 1 performs a third and a second pressure equalization step, the same as the steps performed by adsorption tower 3 in steps (a) and (b). In steps (k) and (l), adsorption tower 1 performs a first pressure equalization step and a repressurization step, the same as the steps performed by adsorption tower 2 in steps (a) and (b). Subsequently, adsorption tower 1 can repeat the feeding and adsorption steps in steps (a) and (b) to restart the VPSA cycle. Adsorption towers 2 to 6 operate in the same manner as adsorption tower 1, completing a full VPSA cycle by switching between steps (a) and (l).

[0052] The sequential operation of the adsorption process steps is controlled by opening and closing programmable control valves in an orderly manner. To achieve the above process, the programmable control valves in this embodiment can be remotely or wirelessly controlled via an automatic control and communication system. As a preferred embodiment of the present invention, the device includes an automatic control system, such as a programmable logic controller (PLC) with a communication module or a distributed control system (DCS) with a communication module. Technicians can remotely / wirelessly control the device of the present invention via an automated PLC / DCS control system, according to the gas separation requirements.

[0053] While embodiments of the present invention have been described above, the invention is not limited to these embodiments. The specific VPSA process and apparatus for producing ultra-high purity hydrogen can be further improved in various ways without departing from the scope of the invention. For example, six adsorption towers have been described above, but the number of adsorption towers is not limited to six. Any number of adsorption towers (not less than four) combined with a matched VPSA cycle can perform the same process as the present invention and obtain the same advantages, said VPSA cycle including an adsorption step, multiple pressure equalization steps, a purging step, a desorption step, a vacuum purging step, and a product repressurization step. Example

[0054] Example 1: This embodiment uses the VPSA device of the present invention, taking pure hydrogen from the refinery's SMR hydrogen PSA system as the feed gas, and further purifying it into ultra-high purity hydrogen using the method described in the above embodiments. Specifically, the hydrogen purification is carried out under the following conditions.

[0055] [Table 1] The six adsorption towers are cylindrical with the same diameter of 0.8 meters. The adsorbent packing section is 3.0 meters high, with 1.5 meters of coconut shell activated carbon at the bottom and 1.5 meters of 5A zeolite at the top. The pure hydrogen feedstock gas from the purified hydrogen-rich tail gas of the oil refinery contains 99.31 vol% hydrogen and various byproducts. The feedstock gas is supplied at a flow rate of 3500 Nm³. 3 The system receives a volumetric flow rate of / hr. The adsorption pressure (maximum pressure) during the adsorption step is 2.5 MPa (absolute pressure: all pressures described below apply), and the desorption pressure achieved by the vacuum pump is 20 kPa·A. Table 1 above discloses the operating conditions and results of the VPSA process.

[0056] Example 2: In this embodiment, the hydrogen purity of the feed gas from the hydrogen-rich tail gas of the ethane reforming process is 95.3601 vol%. The feed gas is further purified to high-purity hydrogen using the method described in the foregoing embodiments. Specifically, the hydrogen purification is carried out under the following conditions.

[0057] [Table 2] This embodiment shows that when the feed gas has a low hydrogen purity (about 95 vol%) and a low feed pressure (1.2 MPa), the process and apparatus of the present invention can produce ultra-high purity hydrogen product gas (>99.997 vol%).

[0058] Those skilled in the art will understand that many variations and modifications can be made to the specific implementations and embodiments without departing from the spirit and scope of the invention.

[0059] It should be understood that if this article cites any prior art publication, such citation does not constitute an admission that such publication is part of general knowledge in the field in Australia or any other country.

Claims

1. A process for purifying a low grade hydrogen feed gas into ultra-high purity hydrogen by vacuum swing adsorption, characterized in that, The feed gas contains 95.0 vol%-99.9 vol% hydrogen and one or more impurities. The process uses six or more adsorption towers connected in parallel, each filled with adsorbent. Each adsorption tower is programmed to repeatedly perform the same sequential cycle of 12 steps. At any given time, the six adsorption towers operate different steps respectively, so that the six adsorption towers can work together to meet the continuous utilization of the feed gas and provide continuous production of ultra-high purity hydrogen. The cycle includes the following steps: (a) Adsorption step: The raw gas is passed through one of the adsorption towers to adsorb impurities onto the adsorbent and the exhaust gas is obtained as ultra-high purity hydrogen product gas. (b) Adsorption and repressurization step: Based on the adsorption step, a portion of the exhaust gas from one adsorption tower is introduced into another adsorption tower in which the product gas repressurization step is underway; (c) First co-current pressure equalization and depressurization step: After the adsorption step and the adsorption and repressurization step, the gas in one adsorption tower flows co-currently to another adsorption tower that is undergoing the first counter-current pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level. (d) Second co-current pressure equalization and depressurization step: After the first co-current pressure equalization and depressurization step, the gas in one adsorption tower flows co-currently to another adsorption tower that is undergoing the second counter-current pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level. (e) Third co-current pressure equalization and depressurization step: After the second co-current pressure equalization and depressurization step, the gas in one adsorption tower flows co-currently to another adsorption tower that is undergoing the third counter-current pressure equalization and pressurization step, until the pressure in the two connected adsorption towers reaches the same level. (f) Co-current purging step: After the third co-current pressure equalization and depressurization step, the remaining gas in one adsorption tower flows co-currently to another adsorption tower that is undergoing a counter-current vacuum purging step; (g) Desorption step: The gas in the adsorption tower is forced to flow countercurrently out of the bottom of the adsorption tower, and the venting force is provided by a vacuum pump connected to the adsorption tower. All extracted gas is used as desorbed gas product. (h) Countercurrent vacuum purging step: After the desorption step, one adsorption tower receives gas flow from the top from another adsorption tower that is performing the cocurrent purging step, while evacuation from the vacuum pump located at the bottom continues to generate desorbed gas product. (i) Third countercurrent pressure equalization and pressurization step: The gas flow flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower, the gas flow comes from another adsorption tower that is performing the third cocurrent pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level. (j) Second countercurrent pressure equalization and pressurization step: The gas flow flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower, the gas flow comes from another adsorption tower that is undergoing the second cocurrent pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level; (k) First countercurrent pressure equalization and pressurization step: The gas flow flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower, the gas flow comes from another adsorption tower that is performing the first cocurrent pressure equalization and depressurization step, until the pressure in the two connected adsorption towers reaches the same level; (l) Product gas repressurization step: The gas flow from the product gas buffer tank flows countercurrently from the top of the adsorption tower to pressurize the adsorption tower.

2. The process according to claim 1, characterized in that, The ultra-high purity hydrogen produced by the process has a purity greater than 99.997 vol and a hydrogen yield greater than 85%.

3. The process according to claim 1, characterized in that, The impurities include oxygen, nitrogen, carbon monoxide, carbon dioxide, and hydrocarbons.

4. The process according to claim 1, characterized in that, The pressure during the adsorption step is in the range of 1.2 MPa - 3.0 MPa (gauge pressure).

5. The process of claim 1, wherein, The pressure range for the desorption step and the countercurrent vacuum purging step is 10 kPa·A to 50 kPa·A.

6. The process of claim 1, wherein, Each of the adsorption towers includes an activated carbon layer packed in the upstream portion of the flow direction of the feed gas at a ratio of 25-75%, and a zeolite adsorbent layer packed in the downstream portion of the flow direction of the feed gas at a ratio of 25-75%; wherein the zeolite adsorbent includes 5A, CaX, LiX, 13X, and LiA zeolites.

7. An apparatus for carrying out the process according to any one of claims 1-6, the apparatus comprising six or more adsorption towers connected in parallel, a vacuum pump, a side-channel control valve, a feed gas supply path, a feed gas buffer tank, a desorption path, a desorption gas buffer tank, a product gas path, a product gas buffer tank, a first pressure equalization path, a second pressure equalization path, and a repressurization path; each of the adsorption towers is connected to a feed gas supply control valve, a desorption gas control valve, a first pressure equalization regulating control valve, a second pressure equalization regulating control valve, a repressurization control valve, and a product gas control valve; The raw gas supply path for supplying raw gas connects the raw gas buffer tank to the lower part of each adsorption tower, and supplies raw gas to the corresponding adsorption tower by opening and closing the raw gas supply control valve on the raw gas supply path of each adsorption tower. The desorption path for discharging the desorbed gas product is connected to the lower part of each of the adsorption towers. The vacuum pump is installed on the desorption path. The desorption path leading to the vacuum pump is opened and closed by the desorbed gas control valve on the desorption path of each adsorption tower. The side control valve is connected in parallel with the vacuum pump and is programmed to open or close the side path. The gas outlet side of the vacuum pump is connected to the desorbed gas buffer tank. The product gas path for providing hydrogen product gas is connected between the upper part of each of the adsorption towers and the product gas buffer tank, and the product gas control valve on the product gas path of each adsorption tower opens and closes the product gas path of the corresponding adsorption tower leading to the product gas buffer tank. On the first pressure equalization path, the connection mode between any two adsorption towers is controlled by opening or closing the corresponding first pressure equalization regulating control valve. On the second pressure equalization path, the connection mode between any two adsorption towers is controlled by opening or closing the corresponding second pressure equalization regulating control valve. The repressurization control valve is connected to the product gas buffer tank and each of the adsorption towers on the repressurization path. The repressurization control valve opens or closes the corresponding repressurization path, which allows ultra-high purity hydrogen in the product gas buffer tank to flow back to the adsorption tower to pressurize the adsorption tower to the feed pressure. In the adsorption step, the raw gas is introduced into the adsorption tower from the bottom by opening the raw gas supply control valve and the product gas control valve corresponding to the adsorption tower in which the adsorption step is performed, while the purified hydrogen is discharged from the top of the adsorption tower as ultra-high purity hydrogen product gas. In the adsorption and repressurization step and the product gas repressurization step, the raw material gas is introduced and the product gas is discharged by opening the raw material gas supply control valve and the product gas control valve corresponding to the adsorption tower for the adsorption and repressurization step. At the same time, the repressurization control valve corresponding to the adsorption tower for the product gas repressurization step is opened, and the product gas is introduced from the product gas buffer tank into the adsorption tower for the product gas repressurization step through the repressurization path. In the first co-current pressure equalization and decompression step and the first counter-current pressure equalization and pressurization step, the second pressure equalization regulating control valve of the adsorption tower performing the first co-current pressure equalization and decompression step is opened to provide co-current airflow to the second pressure equalization path. At the same time, the second pressure equalization regulating control valve of the adsorption tower performing the first counter-current pressure equalization and pressurization step is opened to receive airflow from the second pressure equalization path in the counter-current direction. In the second co-current pressure equalization and depressurization step and the second counter-current pressure equalization and pressurization step, the second pressure equalization regulating control valve of the adsorption tower performing the second co-current pressure equalization and depressurization step is opened to provide co-current airflow to the second pressure equalization path. At the same time, the second pressure equalization regulating control valve of the adsorption tower performing the second counter-current pressure equalization and pressurization step is opened to receive airflow from the second pressure equalization path in the counter-current direction. In the third co-current pressure equalization and depressurization step and the third counter-current pressure equalization and pressurization step, the first pressure equalization regulating control valve of the adsorption tower performing the third co-current pressure equalization and depressurization step is opened to provide co-current airflow to the first pressure equalization path. At the same time, the first pressure equalization regulating control valve of the adsorption tower performing the third counter-current pressure equalization and pressurization step is opened to receive airflow from the first pressure equalization path in the counter-current direction. In the co-current purging step and the counter-current vacuum purging step, the first pressure equalization regulating control valve of the adsorption tower performing the co-current purging step and the adsorption tower performing the counter-current vacuum purging step is opened, and the desorption gas control valve of the adsorption tower performing the counter-current vacuum purging step is kept open, so that the gas in the adsorption tower performing the co-current purging step enters the adsorption tower performing the counter-current vacuum purging step through the first pressure equalization path. In the desorption step, the desorption gas control valve of the adsorption tower in which the desorption step is performed is opened so that the desorption gas product is drawn out from the bottom of the adsorption tower by a vacuum pump, and the discharged gas enters the desorption gas buffer tank.

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