Process technology and device for simultaneously recovering hydrogen and methane gas and other gases from petrochemical emission tail gas

Abstract

The present application relates to a kind of process technology and device for simultaneously recovering hydrogen and methane gas and other multiple gases from petrochemical emission tail gas.The volume percentage of hydrogen in the tail gas is 28-55%, the volume percentage of hydrocarbon in the tail gas is 30%-56%, the process technology uses vacuum pressure swing adsorption-pressure swing adsorption composite integrated device, comprising: (a) hydrocarbon gas-vacuum pressure swing adsorption stage: using vacuum pressure swing adsorption device, separating hydrocarbon gas product gas from the tail gas and producing intermediate gas;(b) hydrogen-pressure swing adsorption stage: using pressure swing adsorption device, separating hydrogen product gas from the intermediate gas produced in step (a).The process technology can simultaneously produce high-purity hydrogen, hydrocarbon gas and higher heat value carbon-rich fuel gas.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas separation and recovery, specifically a process technology and apparatus for simultaneously recovering multiple gases such as hydrogen and methane from petrochemical exhaust gases. Background Technology

[0002] The petrochemical industry consumes large quantities of hydrogen in processes such as hydrogen reforming, hydrocracking, oil and gas hydrogenation, and others. Since the introduction of pressure swing adsorption (PSA) for syngas separation in the early 1980s, methane steam reforming and coal-to-syngas reforming have become the main hydrogen production methods in the petrochemical industry. Simultaneously, the petrochemical industry routinely produces or processes large quantities of industrial emissions or tail gases containing hydrogen and carbon (such as methane (CH4) and carbon dioxide (CO2)), including tail gas from methane steam reforming, cracking dry gas, hydrogen production tail gas, and flare gas. These tail gases contain a significant amount of hydrogen, which is typically burned in a combustion furnace to provide heat. However, hydrogen (H2), as a high-value energy carrier and chemical product, should generate greater economic benefits than simple combustion for heat recovery. Furthermore, it is well known that tail gas combustion produces large amounts of CO2, a major greenhouse gas that contributes to climate change and global warming. Therefore, recovering hydrogen and carbon-containing gases from petrochemical tail gases offers both environmental and economic benefits. The world is currently in a transition to low-carbon emissions, and many countries are introducing or have already introduced carbon tax / carbon trading programs to reduce carbon emissions and improve energy efficiency.

[0003] To meet the needs of various gas separation / purification processes, many technologies, including cryogenic condensation, liquid absorption, solid adsorption, and membrane methods, have been developed and used, each with its own advantages and disadvantages. Pressure swing adsorption / vacuum pressure swing adsorption (PSA / VSA) technology, due to its recognized energy efficiency and simple material handling process, has been applied in many situations in various forms. When using these cyclic adsorption technologies, the feed gas containing CH4, CO2, and other gases passes through a fixed / moving bed filled with adsorbent material, adsorbing gases such as CH4, CO2, nitrogen (N2), and water (H2O) onto the adsorbent. Gases rich in carbon or hydrocarbons are generated through a depressurization process, while simultaneously generating an H2-rich gas at the other end of the adsorption tower. In these gas separation processes, existing processes typically use multi-stage compressors to pressurize the tail gas to a gauge pressure of 8-24 bar before starting separation. High-pressure PSA systems are commonly used to recover / remove carbon-containing components from gases.

[0004] In addition, some other processes also use the tail gas from a high-pressure water-gas shift reaction (VPSA) as feed gas in a high-pressure PSA system to obtain H2-rich gas. This tail gas is then decarbonized or treated with hydrocarbons before being fed into a standard hydrogen PSA system to produce high-purity hydrogen. For example, US Patent Application US2010 / 0287981 A1 describes a process for recovering H2 and CO2 in a steam reforming system. The target gas in this invention is the water-gas shift product. After recovering H2 using a conventional hydrogen PSA, the tail gas is compressed to a certain pressure and then fed into a PSA system and / or membrane system for the recovery of carbon- or hydrocarbon components. However, this invention does not disclose any embodiments, specific processes (cycles), or detailed performance characteristics. Similarly, in US Patent Application US2008 / 0072752 A1, a process based on VPSA and PSA is used to separate CO2 and H2. The target gas for these prior art processes is the exhaust gas after the water-gas shift reaction.

[0005] DIMER has invented a highly efficient VSA / PSA coupling technology in Australian patent AU2016201267, which simultaneously captures carbon dioxide and separates and purifies hydrogen from the tail gas of a methane steam reforming hydrogen production system in petrochemical refining processes (which mainly contains approximately 31% hydrogen and 49.8% carbon dioxide). This technology can simultaneously produce CO2 with a purity of 96%-99% and high-purity H2 with a purity of 99.99%.

[0006] US Patent Application US2011 / 0011128 A1 describes a method for recovering carbon dioxide and hydrogen from a steam reforming unit. Co-feed / co-purge is used in the PSA unit to produce high concentrations of CO2 while simultaneously generating high-purity H2 products. Furthermore, the patent application also introduces a conceptual CO2 purification process.

[0007] Haohua Chemical Technology Group Co., Ltd.'s Chinese invention patent ZL00132036.X utilizes VPSA technology to separate and recover hydrogen and methane from coke oven gas. This type of coke oven gas typically contains (by volume percentage) approximately 50% H2, 26% CH4, and other gaseous impurities. The technology employs a separation process that combines compression of the feed gas to an absolute pressure of 1-1.6 MPa with VPSA to remove high-hydrocarbon impurities, releasing methane gas while simultaneously purifying hydrogen. For coke oven gas, this method claims to recover over 85% of H2 and over 95% of methane.

[0008] US Patent Application US 2010 / 0098601 A1 describes a method for recovering H2, CH4 and removing carbon dioxide, particularly from a mixture of hydrogen and methane in natural gas.

[0009] US Patent 7,695,545 B2 describes a PSA method for separating hydrogen from a gas containing 5-50% hydrogen. The process employs a periodic pressure distribution across multiple adsorption towers for gas separation. The process flow includes an adsorption step, at least two equalization steps (gas recovery), a purge step, a reverse release step, a purge step, at least one equalization step (gas introduction), and a repressurization step.

[0010] The aforementioned existing technologies typically use the exhaust gas from the water-gas shift conversion section as feed gas, lacking specific methods for treating the final tail gas emitted from petrochemical / refinery alkane and olefin recovery units (such as C2 systems) and similar industrial plants. This final tail gas contains a high concentration of carbon or hydrocarbons (such as methane) (e.g., approximately 50%) and saturated water vapor at low temperatures, but the carbon or hydrocarbon concentration is not high enough to be treated by a simple process. Simultaneously, the hydrogen concentration is very low (approximately ~30%), compared to the typical requirement of over 70% hydrogen in conventional hydrogen PSA technologies. Furthermore, the feed gas pressure from PSA systems such as petrochemical / refinery tail gas is low (approximately 5-600 kPa gauge pressure), while existing PSA technologies, for cases involving carbon or hydrocarbon mixtures (H2), typically require pressures >8 bar absolute pressure. Additionally, to achieve high commercial value for the separated gas products, the separated gas purity needs to reach a high quality of >92% CH4 and 99.9% H2. As mentioned earlier, existing technologies have only proposed some superficial concepts and have not disclosed specific hydrogen-pressure swing adsorption (H2-PSA) and methane-vacuum pressure swing adsorption (CH4-VSA) mixed recovery systems to simultaneously achieve high-purity hydrogen and high-purity methane from the tail gas of alkane and olefin recovery and treatment units (such as C2 systems) in petrochemical / refinery plants and similar industrial units. Summary of the Invention

[0011] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a process technology and apparatus that can simultaneously recover multiple gases such as hydrogen and methane from petrochemical exhaust gas with low energy and generate high-calorific-value fuel gas.

[0012] This invention provides a process technology for simultaneously recovering multiple gases, including hydrogen and methane, from petrochemical exhaust gases. The process is characterized by the following: the volume percentage of hydrogen in the exhaust gas is 28-55%, and the volume percentage of hydrocarbon gases in the exhaust gas is 30%-56%. The process technology utilizes a vacuum pressure swing adsorption-pressure swing adsorption integrated device. The process technology includes:

[0013] (a) Hydrocarbon gas-vacuum pressure swing adsorption stage: using a vacuum pressure swing adsorption device, hydrocarbon gas product gas is separated from the tail gas and intermediate gas is generated;

[0014] (b) Hydrogen-pressure swing adsorption stage: using a pressure swing adsorption device, hydrogen product gas is separated from the intermediate gas produced in step (a);

[0015] in,

[0016] The exhaust gas is not compressed before adsorption in the hydrocarbon gas-vacuum pressure swing adsorption stage; the hydrocarbon gas-vacuum pressure swing adsorption stage recovers hydrocarbon gas product gas through a desorption step, and the hydrocarbon gas-vacuum pressure swing adsorption stage includes a light reflux step after the desorption step.

[0017] Preferably, the exhaust gas is the exhaust gas from the alkane and olefin recovery and treatment unit of a petrochemical refinery.

[0018] More preferably, the alkane and olefin recovery and treatment unit in the petrochemical refinery is a C2 hydrocarbon-pressure swing adsorption system or a similar unit.

[0019] Preferably, the exhaust gas contains hydrogen, oxygen, nitrogen, carbon monoxide, hydrocarbon gases, and water.

[0020] Preferably, the hydrocarbon gas-vacuum pressure swing adsorption stage includes:

[0021] a-1) Feed adsorption step: The tail gas enters the first adsorption tower through the bottom of the tower, the hydrocarbon gas is adsorbed by the adsorbent in the first adsorption tower, and the tail gas is transformed into an intermediate gas that is lean hydrocarbon gas and rich in hydrogen gas.

[0022] a-2) First co-current depressurization step: Stop the tail gas from entering the first adsorption tower, open the connection between the first adsorption tower and the top or intermediate gas buffer tank of the adsorption tower that performs the light reflux step or the countercurrent pressurization step, and the intermediate gas enters the adsorption tower or intermediate gas buffer tank that performs the light reflux step or the countercurrent pressurization step.

[0023] a-3) Second co-current depressurization step: Close the connection between the first adsorption tower and the top or intermediate gas buffer tank of the adsorption tower performing the light reflux step or countercurrent pressurization step in step a-2), open the connection between the first adsorption tower and the intermediate gas buffer tank or the top of another adsorption tower performing the light reflux step or countercurrent pressurization step, and discharge gas into the adsorption tower or intermediate gas buffer tank performing the light reflux step or countercurrent pressurization step.

[0024] a-4) Desorption step: Close the connection between the first adsorption tower in step a-3) and the top or intermediate gas buffer tank of the adsorption tower that performs the light reflux step or countercurrent pressurization step, connect the first adsorption tower to the hydrocarbon product gas tank, and then turn on the vacuum pump to recover the hydrocarbon gas product gas to the hydrocarbon product gas tank.

[0025] a-5) Light reflux step: Keep the vacuum pump connected, connect the top of the first adsorption tower to the intermediate gas buffer tank or the top of the adsorption tower that performs the first or second co-current depressurization step, and let the hydrocarbon-rich gas in the intermediate gas buffer tank or the adsorption tower that performs the co-current depressurization step enter the first adsorption tower.

[0026] a-6) Countercurrent pressurization step: Turn off the vacuum pump connection, connect the top of the first adsorption tower to the top of the adsorption tower that is performing the first or second cocurrent depressurization step, so that the pressure of the first adsorption tower and other adsorption towers is equalized.

[0027] a-7) Repressurization step: Introduce the tail gas or the gas in the intermediate gas buffer tank into the first adsorption tower to increase the pressure inside the tower;

[0028] a-8) Repeat the above steps;

[0029] In this process, at least a portion of the gas in the intermediate gas buffer tank enters the hydrogen-pressure swing adsorption stage. When the first adsorption tower is connected to the intermediate gas buffer tank in step a-2), the first adsorption tower is not connected to the intermediate gas buffer tank in step a-3).

[0030] Preferably, the adsorbent in the feed adsorption step is selected from one or a combination of activated carbon, activated alumina, zeolite A, zeolite X, zeolite Y, metal-organic framework, and silica gel.

[0031] Preferably, the pressure inside the adsorption tower in the feed adsorption step is 5-600 kPa (gauge pressure), and the temperature of the tail gas is below 60°C.

[0032] More preferably, the pressure inside the adsorption tower during the desorption step is an absolute pressure of 10-50 kPa.

[0033] Preferably, the ratio of the duration of the feed adsorption step to the duration of the first co-current depressurization step or the counter-current pressurization step is between 3:1 and 3:2; the ratio of the duration of the light reflux step to the duration of the repressurization step is between 1:6 and 1:8.

[0034] Preferably, the hydrocarbon gas-vacuum pressure swing adsorption stage further includes a hydrocarbon product gas purging step, which is between steps a-2) and a-3).

[0035] Preferably, the ratio of the duration of the feed adsorption step to the duration of the first co-current depressurization step or the counter-current pressurization step is between 3:1 and 3:2; the ratio of the duration of the hydrocarbon gas product gas purging step to the duration of the desorption step is between 1:4 and 1:8; and the ratio of the duration of the light reflux step to the duration of the repressurization step is between 1:6 and 1:8.

[0036] Preferably, the vacuum pressure swing adsorption device includes two or more adsorption towers filled with adsorbent, and the adsorption towers are coupled and circulated.

[0037] Preferably, the purity of hydrogen in the intermediate gas produced during the hydrocarbon gas-vacuum pressure swing adsorption stage is 88%-99%.

[0038] Preferably, the intermediate gas is compressed to a gauge pressure of 10-24 bar for the hydrogen-pressure swing adsorption stage treatment.

[0039] This invention also provides an apparatus for implementing the above-mentioned process technology for simultaneously recovering multiple gases, such as hydrogen and methane, from petrochemical exhaust gases. The apparatus is a vacuum pressure swing adsorption-pressure swing adsorption integrated device, comprising a vacuum pressure swing adsorption unit for separating hydrocarbon gaseous product gas from the exhaust gas and generating an intermediate gas rich in hydrogen and lean hydrocarbons, and a pressure swing adsorption unit for separating hydrogen product gas from the intermediate gas.

[0040] The hydrocarbon gas vacuum pressure swing adsorption (VSA) device includes: a tail gas buffer tank, a VSA adsorption tower, a first programmable valve group, a vacuum pump, and a first piping system; the first programmable valve group includes a first inlet valve, a first exhaust valve, a first tower top valve, and a first tower bottom valve; the first piping system includes a tail gas pipeline, an intermediate gas discharge pipeline, a first connecting pipeline, a first waste gas pipeline, and a hydrocarbon product gas pipeline; a first adsorbent is placed inside the VSA adsorption tower, and the bottom of the VSA adsorption tower contains a first diverter plate;

[0041] The hydrogen-pressure swing adsorption (PSA) device includes: an intermediate gas compressor, an intermediate gas buffer tank, a PSA adsorption tower, a second programmable valve group, and a second piping system; the second programmable valve group includes a second inlet valve, a second exhaust valve, a second tower top valve, and a second tower bottom valve; the second piping system includes an intermediate gas inlet pipe, a second waste gas pipe, and a hydrogen product gas pipe; a second adsorbent is placed inside the PSA adsorption tower, and the bottom of the PSA adsorption tower contains a second diverter plate;

[0042] In the hydrocarbon gas-vacuum pressure swing adsorption (VSA) device, one end of the tail gas buffer tank is connected to the tail gas pipeline, and the other end is connected to the bottom of the VSA adsorption tower through the first inlet valve. During the feeding adsorption step, the tail gas enters the VSA adsorption tower from the tail gas buffer tank via the bottom of the VSA adsorption tower. The hydrocarbons are adsorbed by the first adsorbent in the VSA adsorption tower, and the tail gas is transformed into a hydrocarbon-lean, hydrogen-rich gas. The top of each VSA adsorption tower is connected to the intermediate gas buffer tank through the intermediate gas discharge pipeline, the first exhaust valve, and the intermediate gas compressor. This connection is used to recover the intermediate gas and to equalize the pressure within the VSA adsorption tower during the co-current depressurization or counter-current pressurization steps. The tops of each VSA adsorption tower are interconnected through the first tower top valve. By controlling the first tower top valve, the gas flows between the VSA adsorption towers. During the co-current depressurization step, the first inlet valve is closed to stop the tail gas from entering the VSA adsorption tower, and the first inlet valve is opened. The first top valve at the top of the vacuum pressure swing adsorption (VSA) adsorption tower and the first top valve at the top of other VSA adsorption towers undergoing light reflux or countercurrent pressurization steps discharge the hydrocarbon-poor, hydrogen-rich gas from the top of the VSA adsorption tower into other VSA adsorption towers, thus equalizing the pressure of the VSA adsorption tower with the other VSA adsorption towers. In the countercurrent pressurization step, the first bottom valve at the bottom of the VSA adsorption tower is closed, maintaining communication between the top of the VSA adsorption tower and the top of other VSA adsorption towers undergoing cocurrent depressurization steps, thus equalizing the pressure of the VSA adsorption tower with the other VSA adsorption towers. In the repressurization step, the first top valve at the top of the VSA adsorption tower and the first top valve at the top of other VSA adsorption towers undergoing feed adsorption steps are opened, allowing the hydrocarbon-poor, hydrogen-rich gas to enter the VSA adsorption tower from the other VSA adsorption towers, thereby increasing the pressure of the adsorption tower. The bottom of each vacuum pressure swing adsorption (VSA) adsorption tower is connected to the first bottom valve, a vacuum pump, and the hydrocarbon product gas pipeline. In the desorption step, the first top valve at the top of the VSA adsorption tower is closed, and the first bottom valve at the bottom of the VSA adsorption tower is opened to connect the VSA adsorption tower with the hydrocarbon product gas pipeline. Then, the vacuum pump is turned on to recover the hydrocarbon product gas.In the light reflux step, the vacuum pressure swing adsorption device (VPSA) adsorption tower is kept connected to the vacuum pump, and the first top valve at the top of the VPSA adsorption tower and the top valves at the top of the other VPSA adsorption towers in the co-current depressurization step are opened, so that the hydrocarbon-poor hydrogen-rich gas discharged from the other VPSA adsorption towers enters the VPSA adsorption tower.

[0043] In the hydrogen-pressure swing adsorption (PSA) device, one end of the intermediate gas compressor is connected to the intermediate gas pipeline, and the other end is connected to the intermediate gas buffer tank; one end of the intermediate gas buffer tank is connected to the intermediate gas compressor, and the other end is connected to the bottom of the PSA adsorption tower via the second inlet valve; the top of each PSA adsorption tower is connected to the hydrogen product gas pipeline via the second exhaust valve, and is connected to other PSA adsorption towers via the second tower top valve; the bottom of each PSA adsorption tower is connected to the intermediate gas buffer tank via the second inlet valve, and is connected to the second waste gas pipeline via the second tower bottom valve.

[0044] Preferably, the first adsorbent is selected from one or a combination of activated carbon, activated alumina, zeolite A, zeolite X, zeolite Y, metal-organic framework materials, and silica gel.

[0045] Preferably, the hydrocarbon gas-vacuum pressure swing adsorption device includes two or more vacuum pressure swing adsorption towers filled with the first adsorbent, and the vacuum pressure swing adsorption towers are operated in a coupled manner in a cyclic operation; the hydrogen-pressure swing adsorption device includes four or more pressure swing adsorption towers filled with the second adsorbent, and the pressure swing adsorption towers are operated in a coupled manner in a cyclic operation.

[0046] The process technology of this invention has the following beneficial effects:

[0047] 1) Through the process technology of the present invention, high-purity hydrogen and hydrocarbon gases can be recovered from petrochemical exhaust gases. Through the light reflux step, the purity of the hydrocarbon gases obtained by volume percentage is greater than 86% and the recovery rate is greater than 98%. The purity of the hydrocarbon gases obtained by the process technology of the present invention can meet international standards and can be supplied to the plant for use or sold directly to the external market.

[0048] 2) The hydrogen obtained through the process technology of this invention can reach a purity of 99.99%, and the recovery rate of this pure hydrogen is greater than 83%. Compared with direct combustion, the recovered hydrogen significantly improves the overall hydrogen production efficiency of the enterprise (overall recovery increases by 8-10%), and can generate huge economic value.

[0049] 3) Typical exhaust gas treatment involves returning it to the fuel gas pipeline for combustion to provide heating energy, but the resulting calorific value is relatively low, such as 5475 kcal / Nm³. 3 However, through the process technology of this invention, in addition to obtaining high-purity hydrocarbon gases and hydrogen, it is also possible to obtain fuel gases with higher calorific value, such as those reaching 8200 kcal / Nm³. 3 The gas has a relatively high calorific value. Such high-calorific-value gas streams (mainly methane and other hydrocarbon gases) can also be used as fuel for methane steam reforming systems or other systems that require energy injection.

[0050] 4) This invention utilizes vacuum pressure transformation technology to avoid the energy required for compressing exhaust gas in conventional exhaust gas treatment technologies, thus greatly saving energy consumption.

[0051] 5) This invention improves the process energy efficiency of industrial alkane and olefin processing units (such as C2-PSA), reduces carbon emissions, and can greatly reduce the total carbon emission footprint of alkane and olefin recovery and processing unit systems. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0053] Figure 2 This is a schematic diagram of the apparatus and structure of the process flow of the present invention;

[0054] Figure 3 This is a schematic diagram of the adsorption tower operation steps and process cycle design for the CHx-VSA stage of the present invention.

[0055] Figure 4 This is a schematic diagram of the adsorption tower operation steps and process cycle design for the H2-PSA stage of the present invention. Detailed Implementation

[0056] The process technology and apparatus of the present invention will be further explained below with reference to the accompanying drawings, but the present invention is not limited to the specific embodiments described herein.

[0057] Throughout this specification, the term "high-purity gas stream" refers to a gas stream containing at least 90% H2 or hydrocarbons by volume, or more precisely, a gas stream with a volume or molar ratio >92% or even >99%.

[0058] Throughout this manual, the terms “tower” and “bed” are used synonymously.

[0059] Throughout this manual, "co-current" refers to the direction that is the same as the direction of the feed gas flow, that is, the direction from the bottom of the adsorption tower to the top of the tower; "counter-current" is the direction that is opposite to the "co-current" direction.

[0060] The petrochemical exhaust gas of this invention contains 28-55% hydrogen by volume and 30-56% hydrocarbon gases by volume. These hydrocarbon gases include methane (CH4), ethane, ethylene, acetylene, propane, propylene, propyne, butane, butene, and propyne. Furthermore, the exhaust gas suitable for the process technology of this invention may also contain any one or more components other than hydrogen and hydrocarbon gases, such as oxygen (O2), nitrogen (N2), carbon monoxide (CO2), carbon dioxide (CO2), and water (H2O). Preferably, the exhaust gas suitable for the process technology of this invention contains hydrogen, oxygen, nitrogen, carbon monoxide, hydrocarbon gases, and water. The content of various components varies in different exhaust gases. A representative exhaust gas is the exhaust gas from an alkane and olefin recovery treatment unit in a petrochemical refinery, such as a C2 hydrocarbon-pressure swing adsorption system (C2-PSA). The pressure range of the petrochemical exhaust gas is 5-600 kPa (gauge pressure), and the normal temperature range is 40°C.

[0061] This invention utilizes a vacuum pressure swing adsorption-pressure swing adsorption integrated device to recover high-purity hydrogen and hydrocarbon gases from petrochemical tail gas. For example... Figure 1 As shown, the process technology of this invention includes a composite integrated gas treatment process: a hydrocarbon gas-vacuum pressure swing adsorption (CHx-VSA) stage and a hydrogen-pressure swing adsorption (H2-PSA) stage. The tail gas is treated in the CHx-VSA stage to separate and recover high-purity hydrocarbon gases containing hydrocarbons such as methane, and to produce hydrocarbon-lean, hydrogen-rich gas (also referred to as "intermediate gas" in this document). The intermediate gas is treated in the H2-PSA stage to separate and recover high-purity hydrogen, and to produce high-calorific-value fuel gas.

[0062] The apparatus used in this invention includes a CHx-VSA unit and an H2-PSA unit. Figure 2 The apparatus of the present invention will be described using an example.

[0063] The CHx-VSA unit includes: a tail gas buffer tank 31, vacuum pressure swing adsorption (VSA) adsorption towers 11-14, a first programmable valve group 101a-104e, a vacuum pump 32, and a first piping system 100, 200, 400, 600, and 800. The first programmable valve group includes first inlet valves 101a, 102a, 103a, and 104a, first exhaust valves 101e, 102e, 103e, and 104e, first tower top valves 101c, 102c, 103c, 104c, 101d, 102d, 103d, and 104d, and first tower bottom valves 101b, 102b, 103b, and 104b; the first piping system includes a tail gas pipe 100, an intermediate gas discharge pipe 200, a first connecting pipe 400, a first waste gas pipe 600, and a hydrocarbon product gas pipe 800.

[0064] The H2-PSA unit includes: an intermediate gas compressor 34, an intermediate gas buffer tank 35, pressure swing adsorption (PSA) towers 21-28, a second programmable valve group 201-208, and a second piping system 300, 500, 600, and 700. The second programmable valve group includes a second inlet valve 201a, a second exhaust valve 201c, tower top valves 201d, 201e, and 201f, and a tower bottom valve 201b (taking the second programmable valve group 201 as an example, the specific settings of 202-208 are the same as 201); the second piping system includes an intermediate gas inlet pipe 300, a second exhaust gas pipe 500, and a hydrogen product gas pipe 700.

[0065] The tail gas buffer tank 31 in the CHx-VSA unit is used to buffer petrochemical tail gas to avoid incomplete adsorption caused by excessive tail gas flow rate. The vacuum pump 32 is used to reduce the pressure inside the adsorption tower during the desorption step, so that the adsorbed hydrocarbon gases inside the adsorption tower are desorbed from the adsorbent. The VSA adsorption tower has a four-tower structure (11, 12, 13, 14, respectively). Each VSA adsorption tower has a first inlet valve (101a, 102a, 103a, 104a, respectively), a first exhaust valve (101e, 102e, 103e, 104e, respectively), two sets of first tower top valves (101c, 101d; 102c, 102d; 103c, 103d; 104c, 104d, respectively), and a first tower bottom valve (101b, 102b, 103b, 104b, respectively). However, the number of VSA adsorption towers in this invention is not limited to this. Figure 2 The four shown. The number of first top valves in each VSA adsorption tower is not limited to... Figure 2As shown in the two examples, when the number of VSA adsorption towers in the device is small (e.g., a two-tower structure), each VSA adsorption tower can contain one first-tower-top valve. When the number of VSA adsorption towers in the device is large (e.g., an eight-tower structure), each VSA adsorption tower can contain three or more first-tower-top valves. The function of the first-tower-top valve is to allow gas flow between the VSA adsorption towers. A multi-valve structure can reduce valve wear and extend the service life of the device. Figure 2 The adsorption tower 11 shown has top valves 101c and 101d. Top valve 101c can be used for pressure balancing between adsorption tower 11 and other adsorption towers during co-current depressurization or counter-current pressurization steps. Top valve 101d can be used for the entry and exit of lean hydrocarbon-rich gas into and out of adsorption tower 11 during light reflux steps. The uses of top valves 101c and 101d can also be interchanged depending on the situation, and 101c and 101d can also perform the above uses independently. The VSA adsorption tower contains a first adsorbent that preferentially adsorbs hydrocarbon gases under the adsorption pressure and temperature. The bottom of the VSA adsorption tower also contains a first diverter plate to ensure that the gas flow entering the VSA adsorption tower can uniformly enter the first adsorbent.

[0066] The following is based on Figure 2 For example, combined with Figure 3The operation of each component of the CHx-VSA unit is described. One end of the tail gas buffer tank 31 is connected to the tail gas pipeline 100, and the other end is connected to the bottom of the VSA adsorption tower 11-14 through the first inlet valves 101a, 102a, 103a, and 104a. In the feed adsorption step (taking VSA adsorption tower 11 as an example), the tail gas buffer tank 31 is connected to the bottom of the VSA adsorption tower 11 through the first inlet valve 101a, allowing the tail gas to enter the VSA adsorption tower 11 from the bottom. Hydrocarbons are adsorbed by the first adsorbent in the VSA adsorption tower 11, and the tail gas is transformed into a hydrocarbon-lean and hydrogen-rich gas. The top of each VSA adsorption tower 11-14 is connected to the intermediate gas discharge pipe 200, the first exhaust valves 101e, 102e, 103e, 104e, the intermediate gas compressor 34, and the intermediate gas buffer tank 35, for recovering intermediate gas and equalizing the pressure inside the adsorption tower of the vacuum pressure swing adsorption device in the co-current depressurization step or the countercurrent pressurization step; the tops of each VSA adsorption tower 11-14 are interconnected through the first tower top valve, and the gas between the VSA adsorption towers 11-14 can flow between them by controlling the first tower top valves 101c, 102c, 103c, 104c, 101d, 102d, 103d, 104d.For example, in the co-current depressurization step (taking VSA adsorption tower 11 as an example), the first inlet valve 101a is closed to stop the tail gas from entering the VSA adsorption tower 11. The first top valve 101c at the top of the VSA adsorption tower 11 and any one of the other VSA adsorption towers 12-14 that are undergoing a light reflux step or a countercurrent pressurization step, such as the first top valve 104c or 104d at the top of the VSA adsorption tower 14, are opened to discharge the hydrocarbon-poor and hydrogen-rich gas in the VSA adsorption tower 11 from the top of the VSA adsorption tower 11 into the VSA adsorption tower 14, so that the VSA adsorption tower 11 and the VSA adsorption tower 14 are connected. Pressure equalization at 14: In the countercurrent pressurization step (taking VSA adsorption tower 11 as an example), the first bottom valve 101b at the bottom of the VSA adsorption tower 11 is closed, maintaining communication between the top of the VSA adsorption tower 11 and the top of other VSA adsorption towers undergoing the cocurrent depressurization step, such as the top of VSA adsorption tower 14, to equalize the pressure between VSA adsorption tower 11 and VSA adsorption tower 14; In the repressurization step (taking adsorption tower 11 as an example), the first top valve 101c or 101d at the top of the VSA adsorption tower 11 is coupled open to any one of the other VSA adsorption towers 12-14 undergoing the feed adsorption step, such as the adsorption tower 14. The first top valve 104c or 104d at the top of VSA adsorption tower 14 allows lean hydrocarbon gas rich in hydrogen to enter VSA adsorption tower 11, increasing the pressure of the adsorption tower. The bottom of each VSA adsorption tower 11-14 is connected to the first bottom valves 101b, 102b, 103b, 104b, vacuum pump 32, and hydrocarbon product gas pipeline 800. In the desorption step (taking VSA adsorption tower 11 as an example), the first top valve 101c or 101d at the top of VSA adsorption tower 11 is closed, and the first bottom valve 101b at the bottom of VSA adsorption tower 11 is opened, allowing the hydrocarbon product gas to enter the VSA adsorption tower 11. SA adsorption tower 11 is connected to the hydrocarbon product gas pipeline 800, and then vacuum pump 32 is turned on to recover hydrocarbon product gas; in the light reflux step (taking VSA adsorption tower 11 as an example), the VSA adsorption tower 11 is kept connected to vacuum pump 32, and the first tower top valve 101c or 101d at the top of VSA adsorption tower 11 and any one of the other VSA adsorption towers 11-14 that are performing the co-current pressure reduction step, such as the tower top valve 104c or 104d at the top of VSA adsorption tower 14, are opened to allow the lean hydrocarbon hydrogen-rich gas discharged from VSA adsorption tower 14 to enter VSA adsorption tower 11.

[0067] The intermediate gas compressor 34 in the H2-PSA unit is used to compress the intermediate gas, giving the hydrogen-rich intermediate gas entering the H2-PSA unit a certain pressure to improve the purity and recovery rate of hydrogen. The intermediate gas buffer tank 33 is used to buffer the intermediate gas to avoid incomplete adsorption caused by excessively high intermediate gas flow rates. The pressure swing (PSA) adsorption tower has an eight-tower structure (21, 22, 23, 24, 25, 26, 27, 28 respectively). Each PSA adsorption tower has a second inlet valve (203a (taking adsorption tower 21 as an example)), a second exhaust valve (201c (taking adsorption tower 21 as an example)), three sets of second top valves (201d, 201e, 201f (taking adsorption tower 21 as an example)), and a second bottom valve (201b (taking adsorption tower 21 as an example)). However, the number of PSA adsorption towers in this invention is not limited to this. Figure 2 The eight shown. The number of second top valves in each PSA adsorption tower is not limited to... Figure 2 As shown in the three diagrams, when the number of PSA adsorption towers in the device is small (e.g., a four-tower structure), each PSA adsorption tower can contain two second top valves. When the number of PSA adsorption towers in the device is large (e.g., a ten-tower structure), each PSA adsorption tower can contain four or more second top valves. The function of the PSA top valves is to allow gas flow between the PSA adsorption towers. The multi-valve structure can reduce valve wear and extend the service life of the device. The H2-PSA adsorption tower contains a second adsorbent that preferentially adsorbs hydrocarbons under the adsorption pressure and temperature. The bottom of the PSA adsorption tower also contains a second diverter plate to ensure that the gas flow entering the PSA adsorption tower can uniformly enter the second adsorbent.

[0068] The following is based on Figure 2 For example, combined with Figure 4The operation of each component of the H2-PSA unit is described. In the H2-PSA unit, one end of the intermediate gas compressor 34 is connected to the intermediate gas discharge pipe 200, and the other end is connected to the intermediate gas buffer tank 33. One end of the intermediate gas buffer tank 33 is connected to the intermediate gas compressor 34, and the other end is connected to the bottom of the PSA adsorption towers 21-28 through the second inlet valve 201a. The top of each PSA adsorption tower 21-28 is connected to the hydrogen product gas pipe 700 through the second exhaust valve 201c, and is connected to other PSA adsorption towers 21-28 through the second tower top valves 201d, 201e, and 201f. The bottom of each PSA adsorption tower 21-28 is connected to the intermediate gas buffer tank 33 through the second inlet valve 201a, and is connected to the second waste gas pipe 500 through the second tower bottom valve 201b.In the feed adsorption step (taking PSA adsorption tower 21 as an example), the intermediate gas buffer tank 33 is connected to the bottom of the PSA adsorption tower 21 through the second inlet valve 201a, allowing the intermediate gas to enter the PSA adsorption tower 21 from the bottom. Hydrocarbons are adsorbed by the adsorbent in the PSA adsorption tower 21, and the intermediate gas is converted into hydrogen product gas. In the co-current depressurization step (taking PSA adsorption tower 21 as an example), the second inlet valve 201a is closed to stop the intermediate gas from entering the PSA adsorption tower 21, and the PSA adsorption tower 21 is opened. The second top valves 201d, 201e, and 201f at the top of adsorption tower 21, and any of the other PSA adsorption towers 22-28 that have just completed the desorption and venting step or are about to undergo a countercurrent pressurization step or a repressurization step, such as the second top valve at the top of PSA adsorption tower 28, discharge the hydrogen product gas in PSA adsorption tower 21 from the top of PSA adsorption tower 21 into PSA adsorption tower 28, so that the pressure of PSA adsorption tower 21 and PSA adsorption tower 28 are equalized; in the desorption and venting step (taking adsorption tower 21 as an example), the P The second top valves 201d, 201e, and 201f at the top of the PSA adsorption tower 21 are closed, and the second bottom valve 201b at the bottom of the PSA adsorption tower 21 is opened, connecting the PSA adsorption tower 21 to a low-pressure waste gas tank (not shown) to reduce the pressure of the PSA adsorption tower 21 and recover the hydrogen-poor waste gas; in the countercurrent pressurization step (using adsorption tower 21 as an example of PSA), the second bottom valve 201b at the bottom of the PSA adsorption tower 21 is closed, keeping the top of the PSA adsorption tower 21 and any of the other PSA adsorption towers 22-28 undergoing the cocurrent depressurization step maintained. One example is the connection at the top of PSA adsorption tower 28, which balances the pressure of PSA adsorption tower 21 and PSA adsorption tower 28. In the repressurization step (taking PSA adsorption tower 21 as an example), the second tower top valves 201d, 201e, and 201f at the top of PSA adsorption tower 21 are closed, and the second exhaust valve 201c or the second tower top valves 201d, 201e, and 201f at the top of PSA adsorption tower 21 are opened, allowing hydrogen product gas to enter PSA adsorption tower 21 from the top, thereby increasing the pressure of PSA adsorption tower 21.

[0069] In the CHx-VSA stage, the tail gas feedstock is treated by a vacuum pressure swing adsorption unit, such as... Figure 3 As shown, the CHx-VSA stage may include the following steps (taking VSA adsorption tower 11 as an example):

[0070] Feed adsorption step (tail gas injection pressurization (RF) and adsorption (AD)): Without further compression of the tail gas feedstock, the feedstock gas is injected into the VSA adsorption tower 11 through a programmable valve (first inlet valve 101a) at the bottom of the VSA adsorption tower 11. At this point, the feedstock gas pressure ranges from 0.05 to 6 bar gauge pressure, typically 0.30 to 0.40 kPa gauge pressure, and the temperature is below 60°C, more suitable at 10-50°C, and even more suitable at 40°C. The VSA adsorption tower 11 contains at least one adsorbent that preferentially adsorbs hydrocarbons at the feed pressure and temperature. These adsorbents can include one or more of the following: activated carbon, activated alumina, zeolites (zeolite A, zeolite X, zeolite Y, etc.), metal-organic framework materials, silica gel, or any solid granular material that selectively adsorbs hydrocarbons more preferentially than non-hydrocarbons. Furthermore, adsorbents such as zeolites, activated alumina, or silica gel can also adsorb water from the gas stream. Considering the high humidity and other trace impurities in the exhaust gas, multiple layers of adsorbent can be arranged in the VSA adsorption tower 11 of the CHx-VSA stage to achieve better separation. The feed gas flows from bottom to top through the VSA adsorption tower 11. Most of the hydrocarbons in the feed gas are adsorbed by the adsorbent during the gas flow, transforming the feed gas into a hydrocarbon-lean, hydrogen-rich gas, which is then discharged from the top of the adsorption tower. The discharged hydrocarbon-lean, hydrogen-rich gas can: be discharged to the intermediate gas buffer tank 35 for further processing in the downstream H2-PSA; enter any one of the VSA adsorption towers 12-14 that will undergo a light reflux step, serving as light reflux gas to expel residual hydrocarbons in the adsorbent voids and on the adsorbent, thereby improving hydrocarbon recovery; or enter any one of the VSA adsorption towers 12-14 that will undergo a countercurrent pressurization step or a repressurization step to increase the pressure within that VSA adsorption tower. During the feed adsorption stage, the pressure drop between the bottom and top of the VSA adsorption tower 11 is <50 kPa.

[0071] First co-current pressure reduction step (co-current pressure equalization 1 (PE1)): After the feed adsorption step, there are one or more co-current pressure reduction steps. When the adsorption front of the hydrocarbon gas moves to a certain position in the bed, the programmable valve (first inlet valve 101a) at the bottom of the VSA adsorption tower 11 is closed to stop the feed gas from entering the VSA adsorption tower 11 and stop adsorption. By connecting the VSA adsorption tower 11 to any of the other VSA adsorption towers 12-14 that have just completed the depressurization step (such as a light reflux step or a countercurrent pressurization step) via a programmable valve (first tower top valve 101c, 101d) in the pressure balancing pipeline, such as VSA adsorption tower 14, the lean hydrocarbon hydrogen-rich gas discharged from VSA adsorption tower 11 enters VSA adsorption tower 14 through the top of VSA adsorption tower 14, so that the pressure between the two is equalized, thereby increasing the pressure of VSA adsorption tower 14 that has just completed the depressurization step; or by opening the programmable valve (first exhaust valve 101e) between VSA adsorption tower 11 and intermediate gas buffer tank 35, the lean hydrocarbon hydrogen-rich gas in VSA adsorption tower 11 enters intermediate gas buffer tank 35. This step reduces the pressure inside the VSA adsorption tower 11 after the feed adsorption process, allowing the residual hydrocarbon-lean, hydrogen-rich gas in the VSA adsorption tower 11 to be discharged, and releasing other gaseous components besides hydrocarbons remaining in the adsorbent, thereby increasing the concentration of hydrocarbons in the hydrocarbon product gas. Furthermore, the small amount of hydrocarbons in the hydrocarbon-lean, hydrogen-rich gas recirculated into the vacuum transformer can be further adsorbed, improving the hydrocarbon recovery rate. Through the first co-current pressure reduction step, as the pressure inside the VSA adsorption tower 11 decreases, the adsorbed hydrocarbons in the adsorbent are gradually desorbed. Depending on the pressure changes inside the VSA adsorption tower 11, the co-current pressure reduction step can be performed once or multiple times until the pressure inside the VSA adsorption tower 11 reaches a certain value.

[0072] The first co-current pressure reduction step is followed by a second co-current pressure reduction step (co-current equalization pressure 2 (PE2)). The VSA adsorption tower 11 is then closed from the VSA adsorption tower 14 or intermediate gas buffer tank 35, which has just completed a pressure reduction step (such as a light reflux step or a counter-current pressurization step). This is achieved by connecting it via a pressure balancing manifold control valve (first tower top valve 101c, 101d) to any of the other VSA adsorption towers 12-13 that have just completed a co-current pressure reduction or desorption step (such as a light reflux step or a counter-current pressurization step), for example, the top of VSA adsorption tower 12 or intermediate gas buffer tank 35 (when the first co-current pressure reduction step is complete). When the VSA adsorption tower 11 and the intermediate gas buffer tank are connected during the depressurization step (in this step, the VSA adsorption tower 11 will not be connected to the intermediate gas buffer tank), the lean hydrocarbon-rich gas discharged from the VSA adsorption tower 11 enters the VSA adsorption tower 12 through the top of the VSA adsorption tower 12, so that the pressure between the two is equalized, thereby increasing the pressure of the VSA adsorption tower 12 after the depressurization step; or the lean hydrocarbon-rich gas in the VSA adsorption tower 11 enters the intermediate gas buffer tank 35. When the VSA adsorption tower 11 is connected to the VSA adsorption tower 12 that is performing the light reflux step, the lean hydrocarbon-rich gas is used as a purge gas to push out the hydrocarbons remaining in the adsorbent voids and on the adsorbent, thereby improving the recovery rate of hydrocarbon product gas.

[0073] Desorption Steps (Desorption Drainage (DP) and Vacuum Desorption (V)): Close the connection between this VSA adsorption tower 11 and the top or intermediate gas buffer tank 35 of another VSA adsorption tower 12 that has just completed a depressurization step (such as a light reflux step or a countercurrent pressurization step). Open the programmable valve (first bottom valve 101b) at the bottom of this VSA adsorption tower 11, and then turn on the vacuum pump 32. As the pressure inside the VSA adsorption tower 11 decreases, the adsorbed hydrocarbon gas is desorbed from the adsorbent, and the desorbed hydrocarbon gas enters the hydrocarbon product gas tank (not shown). In the desorption step, the gas flow direction is countercurrent to the feed gas flow direction. The pressure inside the VSA adsorption tower 11 in the desorption step is an absolute pressure of 10-50 kPa.

[0074] Light reflux step (countercurrent equalization 1 (RPE1)): Maintain the connection between the VSA adsorption tower 11 and the vacuum pump 32. Connect the top of the VSA adsorption tower 11 to the intermediate gas buffer tank 35 or to any of the other VSA adsorption towers 12-14 that have undergone the first or second co-current pressure reduction step, such as the top of VSA adsorption tower 13. The hydrocarbon-lean but hydrogen-rich gas from the intermediate gas buffer tank 35 or discharged from VSA adsorption tower 13 enters the VSA adsorption tower 11 through the top of the tower. Since the vacuum pump 32 is always operational, the VSA adsorption tower 11 is maintained at a certain vacuum pressure. The large flow rate and good fluidity of the hydrocarbon-lean but hydrogen-rich gas entering the VSA adsorption tower 11 from the top facilitate the removal of residual hydrocarbons in the adsorbent voids and on the adsorbent. The hydrocarbons further desorbed by the adsorbent, propelled by the hydrocarbon-lean but hydrogen-rich gas, enter the hydrocarbon product gas tank (not shown) through the vacuum pump 32. The recovery rate of hydrocarbon product gas can be further improved by using a light reflux step.

[0075] Countercurrent pressurization step (countercurrent equalization 2 (PE2)): Following the light reflux step is one or more countercurrent pressurization steps, which are complementary to the cocurrent depressurization step. The connection between the VSA adsorption tower 11 and the vacuum pump 32 is closed. The VSA adsorption tower 11 is then connected to the top of any of the other VSA adsorption towers 12-14 that have just completed the feed adsorption step, for example, the top of VSA adsorption tower 14. The hydrogen-rich gas containing lean hydrocarbons discharged from VSA adsorption tower 14 through the cocurrent depressurization step enters VSA adsorption tower 11 through the top of the tower, equalizing the pressure of both and increasing the pressure inside VSA adsorption tower 11. Depending on the pressure changes inside VSA adsorption tower 11, the countercurrent pressurization step can be performed once or multiple times until the pressure inside VSA adsorption tower 11 reaches a certain value.

[0076] Repressurization Step (RP): This step is a pre-feed pressurization step for VSA adsorption tower 11, which can be achieved in two ways: First, pressurizing the feed gas, i.e., only opening the programmable valve (first inlet valve 101a) at the bottom of VSA adsorption tower 11 to introduce feed gas for pressurization; Second, pressurizing lean hydrocarbons with hydrogen-rich gas, i.e., only opening the programmable valve (first exhaust valve 101e or first tower top valve 101c or 101d) at the top of VSA adsorption tower 11 to introduce lean hydrocarbons with hydrogen-rich gas from the waste gas tank (not shown) or other VSA adsorption towers 12-14 that have undergone feed adsorption steps for pressurization. Through the repressurization step, the pressure inside VSA adsorption tower 11 reaches a certain value to prevent laminar fluidization of adsorption due to excessive pressure difference during the next feed, which would cause wear and consumption of adsorbent and affect the long-term stable operation of the system.

[0077] After completing the repressurization step, the VSA adsorption tower 11 returns to the feed adsorption step and repeats the above steps for adsorption.

[0078] These steps are repeated alternately and repeatedly among the multiple adsorption towers in the vacuum pressure swing adsorption unit. This can be done according to... Figure 3 Perform the above steps in the order shown.

[0079] The CHx-VSA stage of this invention requires at least two adsorption towers filled with adsorbents that preferentially adsorb hydrocarbon gases under the adsorption pressure and temperature. The number of adsorption towers can also be three or more, with each tower operating in a coupled, cyclic manner. Those skilled in the art can implement this invention by setting the number of adsorption towers and the coupling operation according to actual needs, based on the spirit of this patent.

[0080] In one embodiment, the ratio of the duration of the feed adsorption step to the duration of the first co-current depressurization step or counter-current pressurization step is between 3:1 and 3:2; the ratio of the duration of the light reflux step to the duration of the repressurization step is between 1:6 and 1:8. These settings improve the purity and recovery rate of hydrocarbon gases.

[0081] In one embodiment, the CHx-VSA stage may further include a hydrocarbon product gas purging step to improve hydrocarbon purity. In this step, the hydrocarbon product gas is countercurrently returned from the bottom of the adsorption tower to the adsorption tower from the hydrocarbon product tank. The hydrocarbon product gas is re-adsorbed onto the adsorbent, and other gaseous components remaining in the adsorbent besides hydrocarbons are released, thereby increasing the hydrocarbon concentration in the hydrocarbon product gas and improving hydrocarbon purity. The resulting hydrocarbon-lean, hydrogen-rich gas may be sent to an intermediate gas collection tank or enter the adsorption tower for a light reflux step or a countercurrent pressurization step. This hydrocarbon purging step may, for example, be located between the first and second cocurrent depressurization steps. At this point, after the first co-current depressurization step (taking VSA adsorption tower 11 as an example), the connection between VSA adsorption tower 11 and any of the other adsorption towers 12-14, such as VSA adsorption tower 14 or intermediate gas collection tank 35, is closed, and the first bottom valve 101b at the bottom of VSA adsorption tower 11 is opened to connect it to the hydrocarbon product gas tank (not shown).

[0082] In one embodiment of the hydrocarbon product gas purging step, the ratio of the duration of the feed adsorption step to the duration of the first co-current depressurization step or counter-current pressurization step is between 3:1 and 3:2; the ratio of the duration of the hydrocarbon product gas purging step to the duration of the desorption step is between 1:4 and 1:8; and the ratio of the duration of the light reflux step to the duration of the repressurization step is between 1:6 and 1:8. These settings improve the purity and recovery rate of the hydrocarbon gas.

[0083] In one embodiment, the adsorbent is preferably an activated alumina, silica gel, activated carbon, zeolite A, or X, etc., with a volume ratio of 1:(4-8):(1-3). By using the adsorbent in the above ratio, the recovery rate of hydrocarbon gases can be significantly improved. The improved recovery rate of hydrocarbon gases is beneficial to the purity of hydrogen in the intermediate gas of hydrocarbon-poor hydrogen-rich gas, and thus to improving the recovery rate and purity of hydrogen product gas.

[0084] The hydrocarbon-rich gas produced in the CHx-VSA stage contains mostly hydrogen and a small portion of hydrocarbons not adsorbed by the CHx-VSA stage, with a hydrogen purity of 88%-99%. This hydrocarbon-rich intermediate gas is then compressed to a gauge pressure of 10-24 bar and subjected to the H2-PSA stage for further processing, separation, and recovery of hydrogen product gas and higher calorific value fuel gas. The vacuum pressure swing adsorption unit in the CHx-VSA stage is connected in series with the pressure swing adsorption unit in the H2-PSA stage.

[0085] The H2-PSA stage can be performed using pressure swing adsorption (PSA) technology for hydrogen production known in the art, such as the PSA process disclosed in U.S. Patent 7,695,545 B2. In the process technology of this invention, the intermediate gas in the H2-PSA stage is processed by a PSA device, such as... Figure 4 As shown, the H2-PSA stage may include the following steps (taking PSA adsorption tower 21 as an example):

[0086] Feed Adsorption Step (AD): Intermediate gas is injected into PSA adsorption tower 21 through a programmable valve (second inlet valve 203a) at the bottom of the tower. The pressure of the intermediate gas at this stage is between 10 bar and 24 bar, and the normal temperature is 40°C. PSA adsorption tower 21 contains at least one adsorbent that preferentially adsorbs adsorbable gases at the feed pressure and temperature, thereby converting the intermediate gas into a non-adsorbent hydrogen product gas stream. Adsorbable gases refer to one or more gases other than hydrogen in the intermediate gas. The intermediate gas flows upward through PSA adsorption tower 21. Most of the adsorbable gases in the intermediate gas are adsorbed by the adsorbent during the gas flow, and the intermediate gas is converted into hydrogen product gas, which is discharged from the top of PSA adsorption tower 21. The hydrogen product gas discharged in this step can be discharged to a hydrogen product tank (not shown) or enter another PSA adsorption tower 21 for a countercurrent pressurization step or a repressurization step.

[0087] First Co-current Pressure Reduction Step (Co-current Pressure Equalization 1 (PE1)): Following the feed adsorption step are one or more co-current pressure reduction steps. When the adsorption front of the adsorbable gas moves to a certain position in the bed, the programmable valve (second inlet valve 203a) at the bottom of the PSA adsorption tower 21 is closed to stop the intermediate gas from entering the PSA adsorption tower 21, thus stopping adsorption. The programmable valves (second tower top valves 201d, 201e, 201f) at the top of the PSA adsorption tower 21 are opened, connecting it to any one of the other PSA adsorption towers 22-28 that are undergoing counter-current pressurization or re-pressurization steps, such as PSA adsorption tower 28. The hydrogen-rich gas discharged from the PSA adsorption tower 21 enters the other PSA adsorption tower 28 through the top of the other PSA adsorption tower 28, equalizing the pressure between them and thereby increasing the pressure of the other PSA adsorption tower 28. The adsorption pressure is reduced by at least one first co-current pressure reduction step. The adsorbable gas is further concentrated in the tower. Depending on the pressure changes inside the PSA adsorption tower 21, the co-current pressure reduction step can be performed once or multiple times (co-current pressure equalization 2 (PE2) - co-current pressure equalization 6 (PE6)) until the pressure inside the PSA adsorption tower 21 reaches a certain value.

[0088] Following the first co-current pressure reduction step are multiple co-current pressure reduction steps (co-current pressure equalization 2 (PE2) - co-current pressure equalization 6 (PE6)). The connection between this PSA adsorption tower 21 and the other PSA adsorption towers 28 that have undergone the counter-current pressurization or re-pressurization steps is closed. Through the pressure balancing pipe thread control valves (second tower top valves 201d, 201e, 201f), it is connected to any one of the other PSA adsorption towers 22-27 undergoing the counter-current pressurization or re-pressurization steps, for example, the top of tower 27. The hydrogen product gas discharged from this PSA adsorption tower 21 enters PSA adsorption tower 27 through the top of PSA adsorption tower 27, balancing the pressure between the two and thereby increasing the pressure of the other PSA adsorption towers 27.

[0089] Desorption and venting step (DP): Close the connection between this PSA adsorption tower 21 and other PSA adsorption towers 22-28 in the co-current pressure reduction step, connect this PSA adsorption tower 21 to a low-pressure waste gas tank (not shown), reduce the pressure of the PSA adsorption tower 21, as the pressure inside the PSA adsorption tower 21 decreases, the adsorbed gas is desorbed from the adsorbent, and the desorbed gas enters the waste gas tank (not shown) to obtain high-calorific-value fuel gas, mainly methane and other hydrocarbons.

[0090] First countercurrent pressurization step (countercurrent equalization 1 (RPE1)): Following the desorption and venting step is one or more countercurrent pressurization steps. The connection between the PSA adsorption tower 21 and the low-pressure waste gas tank (not shown) is closed. The PSA adsorption tower 21 is then connected to the top of any of the other PSA adsorption towers 22-28 that are undergoing the cocurrent depressurization step, for example, the top of PSA adsorption tower 22. The hydrogen product gas discharged from PSA adsorption tower 22 through the cocurrent depressurization step enters PSA adsorption tower 21 through the top of the tower, equalizing the pressure of both and increasing the pressure within PSA adsorption tower 21. Depending on the pressure changes within PSA adsorption tower 21, the countercurrent pressurization step can be performed once or multiple times (countercurrent equalization 2 (RPE2) - countercurrent equalization 6 (RPE6)) until the pressure within PSA adsorption tower 21 reaches a certain value.

[0091] Based on the first countercurrent pressurization step, several countercurrent pressurization steps (countercurrent equalization 2 (RPE2) - countercurrent equalization 6 (RPE6)) are then performed. The top of the PSA adsorption tower 21 is closed from the top of the PSA adsorption tower 22, which underwent the cocurrent depressurization step. The PSA adsorption tower 21 is then connected to the top of any one of the other PSA adsorption towers 23-28 undergoing the cocurrent depressurization step, such as the top of PSA adsorption tower 23. The hydrogen product gas discharged from PSA adsorption tower 23 through the cocurrent depressurization step enters PSA adsorption tower 21 through its top, balancing the pressures and increasing the pressure within PSA adsorption tower 21. Based on the pressure changes within PSA adsorption tower 21, countercurrent pressurization continues until the pressure within PSA adsorption tower 21 reaches a certain value.

[0092] Then, H2-rich gas is pressurized (RP), that is, only the programmable valve (second exhaust valve 201c) at the top of PSA adsorption tower 21 is opened to introduce hydrogen product gas from the hydrogen product gas tank (not shown) or any of the other PSA adsorption towers 22-28 that have undergone co-current depressurization steps to pressurize until the pressure is equalized, completing one complete cycle of this tower; then the next cycle begins.

[0093] After completing the pressurization step, PSA adsorption tower 21 returns to the feed adsorption step, repeating the above steps for adsorption and desorption. These steps are alternately and repeatedly performed among the multiple adsorption towers of the pressure swing adsorption unit. This can be done according to... Figure 4 Perform the above steps in the order shown.

[0094] The process of this invention requires at least four PSA adsorption towers filled with adsorbent, and the number of adsorption towers can also be six or more, with each adsorption tower operating in a coupled, cyclical manner. Those skilled in the art can implement this invention by setting the number of adsorption towers and the coupling operation according to actual needs, in accordance with the spirit of this patent.

[0095] In one embodiment of the invention, the H2-PSA stage may further include a countercurrent purging step. In one embodiment, the adsorption tower performing the countercurrent purging step may be connected to the adsorption tower performing the cocurrent depressurization step. In this case, the H2-rich gas discharged from the cocurrent depressurization adsorption tower serves as the purging gas, which helps to expel the adsorbable gas remaining in the adsorbent voids and on the adsorbent. In one embodiment, the countercurrent purging step occurs between the desorption venting and countercurrent pressurization steps. In this case, after the desorption venting step (taking PSA adsorption tower 21 as an example), while the low-pressure waste gas tank remains connected to PSA adsorption tower 21, the programmable valves (second tower top valves 201d, 201e, 201f) at the top of PSA adsorption tower 21 are opened, connecting the top of PSA adsorption tower 21 to the hydrogen product gas tank or any one of the other PSA adsorption towers 22-28 performing the cocurrent depressurization step, such as the top of PSA adsorption tower 22. The H2-rich gas enters PSA adsorption tower 21 through the top of the tower.

[0096] In one embodiment of the present invention containing a countercurrent purging step, the pressure difference in the adsorption tower from the first cocurrent pressure equalization step to the countercurrent purging step is ΔP1, and the pressure difference in the adsorption tower from the countercurrent purging step to the desorption and venting step is ΔP2. ΔP2 / ΔP1 is 1.5 or more and less than 5.0, preferably 2.5 or more and less than 5.0, and more preferably 4.5. Example

[0097] Example 1

[0098] Hydrogen and hydrocarbon gases are separated and recovered from the tail gas of Sinopec's C2-PSA unit, and high-calorific-value fuel gas is generated.

[0099] The exhaust gas composition of the C2-PSA unit is as follows (in actual operation, the exhaust gas composition often fluctuates within a range of 10%):

[0100] Table 1. Components of exhaust gas from C2-PSA unit

[0101]

[0102] Use the parameters listed in Tables 3 and 4 as follows: Figure 1 The gas separation and recovery process technology of the present invention shown herein, and its application, are as follows: Figure 2 The device shown, such as Figure 3 The CHx-VSA adsorption tower operation steps and process cycle design shown are as follows: Figure 4 The H2-PSA adsorption tower operation steps and process cycle design shown are used to separate the above-mentioned tail gas. Specifically, the CHx-VSA unit has four adsorption towers, each with a diameter of 30 cm and a working length of 200 cm; the H2-PSA unit has eight adsorption towers, each with a diameter of 10 cm and a working length of 300 cm. Each adsorption tower is filled with adsorbents such as activated alumina, silica gel or activated carbon, or zeolite A or X in a volume ratio of 1:5:2.

[0103] The purity and recovery rate of the produced hydrocarbon gases and hydrogen are shown in Tables 3 and 4.

[0104] Example 2

[0105] Hydrogen and hydrocarbon gases are separated and recovered from the tail gas of Sinopec's C2-PSA unit system, and high-calorific-value fuel gas is generated.

[0106] The exhaust gas composition in this embodiment is shown below (in actual operation, the exhaust gas composition often fluctuates within a range of 10%).

[0107] Table 2. Exhaust gas components of C2-PSA-like device systems

[0108]

[0109] Use the parameters listed in Tables 3 and 4 as follows: Figure 1 The gas separation and recovery process technology of the present invention shown herein, such as Figure 2 The device shown, such as Figure 3 The CHx-VSA adsorption tower operation steps and process cycle design shown are as follows: Figure 4 The H2-PSA adsorption tower operation steps and process cycle design shown are used to separate the above-mentioned tail gas. Specifically, the CHx-VSA unit has four adsorption towers, each with a diameter of 300 cm and a working length of 360 cm; the H2-PSA unit has eight adsorption towers, each with a diameter of 80 cm and a working length of 360 cm. Each adsorption tower is filled with adsorbents such as activated alumina, silica gel or activated carbon, or zeolite A or X in a volume ratio of 1:6:2.

[0110] The purity and recovery rate of the produced hydrocarbon gas and hydrogen are as follows:

[0111] The purity of hydrocarbon gas is >86%, and the recovery rate is 98%; the purity of the intermediate gas hydrogen is 99%.

[0112] The final product, hydrogen, has a purity of 99.99% and a recovery rate of 85%.

[0113] Table 3. Process parameters of the CHx-VSA unit in typical examples, and purity and recovery rate of hydrocarbons (CHx).

[0114]

[0115] Table 4. Process parameters, H2 purity, and recovery rate of the H2-PSA unit in a typical embodiment.

[0116]

[0117] Comparative example

[0118] This comparative example uses the technology and process of our company's patent AU2016201267, which was granted in 2016, to separate and recover the exhaust gas of Example 1.

[0119] The exhaust gas components processed in this comparative example are shown in Table 1. The CHx-VSA adsorption tower operation steps and process cycle design, as well as the H2-PSA adsorption tower operation steps and process cycle design, were performed according to the process technology in patent AU2016201267 to separate the above-mentioned exhaust gases. Specifically, the CHx-VSA device contains four adsorption towers, each with a diameter of 30 cm and a working length of 200 cm; the H2-PSA device contains eight adsorption towers, each with a diameter of 10 cm and a working length of 300 cm. Each adsorption tower is filled with an adsorbent such as activated alumina, silica gel or activated carbon, or zeolite A or X in a volume ratio of 0.2:1:5.

[0120] After the implementation of this technology and process, the purity of the produced hydrocarbon gas is 82% and the recovery rate is 85%; the purity of the produced hydrogen gas is 99% and the recovery rate is 68%.

[0121] In Example 1, the hydrocarbon gas had a purity greater than 86% and a recovery rate of 99%; the produced hydrogen gas had a purity greater than 99.99% and a recovery rate of 85.1%.

[0122] Compared with the comparative example, the purity and recovery rate of hydrocarbon gases, as well as the purity and recovery rate of hydrogen, were greatly improved in Example 1. By using the process technology and apparatus of the present invention, high-purity hydrogen and hydrocarbon gases with high recovery rates were obtained from petrochemical exhaust gases, significantly improving the overall comprehensive hydrogen and hydrocarbon gas recovery production efficiency of the enterprise, generating enormous economic value and environmental benefits.

[0123] In embodiments of the present invention, the purity of the produced hydrocarbon gas and hydrogen is determined by online analyzer or offline mass spectrometer testing. The recovery rates of the hydrocarbon gas and hydrogen are calculated as follows:

[0124] The calculation method for CHx gas product gas recovery rate is as follows:

[0125]

[0126] The calculation method for H2 product gas recovery rate is as follows:

[0127]

[0128] This invention produces three high-value-added products from the tail gas of low-value olefin processing units (such as C2 pressure swing adsorption PSA systems, i.e., C2-PSA) in low-value petrochemical refineries: high-purity hydrogen, high-purity hydrocarbon gases, and high-calorific-value fuel gases. As demonstrated in Examples 1 and 2, the hydrogen produced by this invention has a purity greater than 99.99% and a recovery rate greater than 85%; the CHx gases such as methane have a purity greater than 85% and a recovery rate greater than 99%.

[0129] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include undisclosed common knowledge or customary techniques in the art. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

[0130] It should be understood that the present invention is not limited to the processes, structures, and precise structures shown in the accompanying drawings of the embodiments described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited by the appended claims.

Claims

1. A process for simultaneously recovering hydrogen and hydrocarbon gases from petrochemical exhaust gases, characterized in that, The exhaust gas contains 28%-55% hydrogen by volume, 30%-56% hydrocarbons by volume, and has a pressure range of 5-600 kPa (gauge pressure). The process utilizes a vacuum pressure swing adsorption-pressure swing adsorption integrated device and includes: (a) Hydrocarbon gas-vacuum pressure swing adsorption stage: using a vacuum pressure swing adsorption device, hydrocarbon gas product gas is separated from the tail gas and intermediate gas is generated; (b) Hydrogen-pressure swing adsorption stage: using a pressure swing adsorption device, hydrogen product gas is separated from the intermediate gas produced in step (a); in, The exhaust gas is not compressed before adsorption in the hydrocarbon gas-vacuum pressure swing adsorption stage; the hydrocarbon gas-vacuum pressure swing adsorption stage recovers the hydrocarbon gas product gas through a desorption step, and the hydrocarbon gas-vacuum pressure swing adsorption stage includes a light reflux step after the desorption step; the vacuum pressure swing adsorption device includes two or more vacuum pressure swing adsorption towers filled with a first adsorbent, and the vacuum pressure swing adsorption towers operate in a coupled cyclic manner; the pressure swing adsorption device includes four or more pressure swing adsorption towers filled with a second adsorbent, and the pressure swing adsorption towers operate in a coupled cyclic manner. The hydrocarbon gas-vacuum pressure swing adsorption stage includes: a-1) Feed adsorption step: The tail gas enters the first adsorption tower through the bottom of the tower, the hydrocarbon gas is adsorbed by the adsorbent in the first adsorption tower, and the tail gas is transformed into an intermediate gas that is lean hydrocarbon gas and rich in hydrogen gas. a-2) First co-current depressurization step: Stop the tail gas from entering the first adsorption tower, open the connection between the first adsorption tower and the top or intermediate gas buffer tank of the adsorption tower that performs the light reflux step or the countercurrent pressurization step, and the intermediate gas enters the adsorption tower or intermediate gas buffer tank that performs the light reflux step or the countercurrent pressurization step. a-3) Second co-current depressurization step: Close the connection between the first adsorption tower and the top or intermediate gas buffer tank of the adsorption tower performing the light reflux step or countercurrent pressurization step in step a-2), open the connection between the first adsorption tower and the intermediate gas buffer tank or the top of another adsorption tower performing the light reflux step or countercurrent pressurization step, and discharge gas into the adsorption tower or intermediate gas buffer tank performing the light reflux step or countercurrent pressurization step. a-4) Desorption step: Close the connection between the first adsorption tower in step a-3) and the top or intermediate gas buffer tank of the adsorption tower in the light reflux step or countercurrent pressurization step, connect the first adsorption tower to the hydrocarbon product gas tank, and then turn on the vacuum pump. The hydrocarbon gas product gas is recovered to the hydrocarbon product gas tank. The pressure in the adsorption tower in the desorption step is an absolute pressure of 10-50 kPa. a-5) Light reflux step: Keep the vacuum pump connected, connect the top of the first adsorption tower to the intermediate gas buffer tank or the top of the adsorption tower that performs the first or second co-current depressurization step, and let the hydrocarbon-rich gas in the intermediate gas buffer tank or the adsorption tower that performs the co-current depressurization step enter the first adsorption tower. a-6) Countercurrent pressurization step: Turn off the vacuum pump connection, connect the top of the first adsorption tower to the top of the adsorption tower that is performing the first or second cocurrent depressurization step, so that the pressure of the first adsorption tower and other adsorption towers is equalized. a-7) Repressurization step: Introduce the tail gas or the gas in the intermediate gas buffer tank into the first adsorption tower to increase the pressure inside the tower; a-8) Repeat the above steps; In this process, at least a portion of the gas in the intermediate gas buffer tank enters the hydrogen-pressure swing adsorption stage. When the first adsorption tower is connected to the intermediate gas buffer tank in step a-2), the first adsorption tower is not connected to the intermediate gas buffer tank in step a-3). The ratio of the duration of the light reflux step to the duration of the repressurization step is between 1:6 and 1:

8.

2. The process according to claim 1, characterized in that: The exhaust gas is the exhaust gas from the alkane and olefin recovery and treatment unit of a petrochemical refinery.

3. The process according to claim 2, characterized in that: The alkane and olefin recovery and treatment unit in the petrochemical refinery is a C2 hydrocarbon-pressure swing adsorption system.

4. The process according to claim 1, characterized in that: The exhaust gas contains hydrogen, oxygen, nitrogen, carbon monoxide, hydrocarbon gases, and water.

5. The process according to claim 1, characterized in that: The adsorbent in the feed adsorption step is selected from one or a combination of activated carbon, activated alumina, zeolite A, zeolite X, zeolite Y, metal-organic framework materials, and silica gel.

6. The process according to claim 1, characterized in that: The pressure inside the adsorption tower in the feed adsorption step is 5-600 kPa (gauge pressure), and the temperature of the exhaust gas is below 60°C.

7. The process according to claim 5, characterized in that: The ratio of the duration of the feed adsorption step to the duration of the first co-current depressurization step or counter-current pressurization step is between 3:1 and 3:

2.

8. The process according to claim 1, characterized in that: The hydrocarbon gas-vacuum pressure swing adsorption stage further includes a hydrocarbon product gas purging step, which is between steps a-2) and a-3).

9. The process according to claim 8, characterized in that: The ratio of the duration of the feed adsorption step to the duration of the first co-current depressurization step or counter-current pressurization step is between 3:1 and 3:2; the ratio of the duration of the hydrocarbon product gas purging step to the duration of the desorption step is between 1:4 and 1:8; and the ratio of the duration of the light reflux step to the duration of the repressurization step is between 1:6 and 1:

8.

10. The process according to claim 1, characterized in that: The purity of hydrogen in the intermediate gas produced during the hydrocarbon gas-vacuum pressure swing adsorption stage is 88%-99%.

11. The process according to claim 1, characterized in that: The intermediate gas is compressed to a gauge pressure of 10-24 bar for the hydrogen-pressure swing adsorption stage.

12. An apparatus for simultaneously recovering hydrogen and hydrocarbon gases from petrochemical exhaust gases according to any one of claims 1-11, said apparatus being a vacuum pressure swing adsorption-pressure swing adsorption integrated apparatus, said apparatus comprising a hydrocarbon gas-vacuum pressure swing adsorption unit for separating hydrocarbon gas product gas from the exhaust gas and generating an intermediate gas of hydrocarbon-lean and hydrogen-rich gas, and a hydrogen-pressure swing adsorption unit for separating hydrogen product gas from the intermediate gas, wherein... The hydrocarbon gas vacuum pressure swing adsorption (VSA) device includes: a tail gas buffer tank, two or more VSA adsorption towers, a first programmable valve group, a vacuum pump, and a first piping system; the first programmable valve group includes a first inlet valve, a first exhaust valve, a first tower top valve, and a first tower bottom valve; the first piping system includes a tail gas pipeline, an intermediate gas discharge pipeline, a first connecting pipeline, a first waste gas pipeline, and a hydrocarbon product gas pipeline; a first adsorbent is placed inside the VSA adsorption tower, the bottom of the VSA adsorption tower contains a first diverter plate, and the VSA adsorption tower operates in a coupled manner in a circulating manner; The hydrogen-pressure swing adsorption (PSA) device includes: an intermediate gas compressor, an intermediate gas buffer tank, four or more PSA adsorption towers, a second programmable valve group, and a second piping system; the second programmable valve group includes a second inlet valve, a second exhaust valve, a second tower top valve, and a second tower bottom valve; the second piping system includes an intermediate gas inlet pipe, a second waste gas pipe, and a hydrogen product gas pipe; a second adsorbent is placed inside the PSA adsorption tower, the bottom of the PSA adsorption tower contains a second diverter plate, and the PSA adsorption tower operates in a coupled manner for circulation; In the hydrocarbon gas-vacuum pressure swing adsorption (VSA) device, one end of the tail gas buffer tank is connected to the tail gas pipeline, and the other end is connected to the bottom of the VSA adsorption tower through the first inlet valve. During the feed adsorption step, the tail gas enters the VSA adsorption tower from the tail gas buffer tank via the bottom of the VSA adsorption tower without compression. The hydrocarbon gas is adsorbed by the first adsorbent in the VSA adsorption tower, transforming the tail gas into a hydrocarbon-lean, hydrogen-rich gas. The top of each VSA adsorption tower is connected to the intermediate gas discharge pipeline, the first exhaust valve, the intermediate gas compressor, and the intermediate gas buffer tank. The tanks are connected to recover intermediate gas and to equalize the pressure within the vacuum pressure swing adsorption (VSA) adsorption towers during the co-current depressurization or counter-current pressurization steps. The tops of each VSA adsorption tower are interconnected via a first top valve. By controlling the first top valve, gas flow between the adsorption towers is facilitated. During the co-current depressurization step, the first inlet valve is closed to stop the tail gas from entering the VSA adsorption tower. The first top valves at the top of the VSA adsorption tower and the first top valves at the top of other VSA adsorption towers undergoing the light reflux or counter-current pressurization steps are opened, allowing gas to flow between the adsorption towers. The hydrocarbon-poor, hydrogen-rich gas inside the vacuum pressure swing adsorption (VSA) unit is discharged from the top of the adsorption tower and enters other VSA adsorption towers, thus equalizing the pressure of the adsorption towers. In the countercurrent pressurization step, the first bottom valve of the adsorption tower is closed, maintaining communication between the top of the adsorption tower and the tops of other VSA adsorption towers undergoing the cocurrent depressurization step, thus equalizing the pressure of the adsorption towers. In the repressurization step, the first top valve of the adsorption tower is opened, and the valve for the repressurization step is opened. In the feed adsorption step, the first top valve of the adsorption tower of other vacuum pressure swing adsorption (VPS) devices allows the lean hydrocarbon-rich gas to enter the adsorption tower of the VPS device from other VPS devices to increase the pressure of the adsorption tower. The bottom of each VPS adsorption tower is connected to the hydrocarbon product gas pipeline via the first bottom valve, a vacuum pump, and the first bottom valve of the adsorption tower. In the desorption step, the first top valve of the adsorption tower is closed, and the first bottom valve of the adsorption tower is opened to connect the adsorption tower to the hydrocarbon product gas pipeline. Then, the vacuum pump is turned on to recover the hydrocarbon product gas.In the light reflux step, the vacuum pressure swing adsorption device (VPSA) adsorption tower is kept connected to the vacuum pump, and the first top valve at the top of the VPSA adsorption tower and the top valves at the top of the other VPSA adsorption towers in the co-current depressurization step are opened, so that the hydrocarbon-poor hydrogen-rich gas discharged from the other VPSA adsorption towers enters the VPSA adsorption tower. In the hydrogen-pressure swing adsorption (PSA) device, one end of the intermediate gas compressor is connected to the intermediate gas discharge pipeline, and the other end is connected to the intermediate gas buffer tank; one end of the intermediate gas buffer tank is connected to the intermediate gas compressor, and the other end is connected to the bottom of the PSA adsorption tower via the second inlet valve; the top of each PSA adsorption tower is connected to the hydrogen product gas pipeline via the second exhaust valve, and is connected to other PSA adsorption towers via the second tower top valve; the bottom of each PSA adsorption tower is connected to the intermediate gas buffer tank via the second inlet valve, and is connected to the second waste gas pipeline via the second tower bottom valve.

13. The apparatus according to claim 12, characterized in that, The first adsorbent is selected from one or a combination of activated carbon, activated alumina, zeolite A, zeolite X, zeolite Y, metal-organic framework materials, and silica gel.

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