Method for recovering hydrogen enrichment products and CO2 in a hydrogen generation unit.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- UOP LLC
- Filing Date
- 2023-06-09
- Publication Date
- 2026-08-03
Smart Images
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Abstract
Description
Technical Field
[0001] (Priority Claim) This application claims the priority of U.S. Patent Application No. 17 / 806,638, filed on June 13, 2022, which is hereby incorporated by reference in its entirety.
Background Art
[0002] Hydrogen is expected to have significant growth potential as it is a clean combustion fuel. However, hydrogen production has traditionally been a significant source of CO2 emissions, and government regulations and social pressure are increasingly taxing or penalizing CO2 emissions or encouraging CO2 capture. As a result, significant competition is expected to reduce the cost of hydrogen production while recovering the by-product CO2 for subsequent geological sequestration to capture the growing market. CO2 can be recovered as a high-pressure gas supplied to pipelines, but in many cases, it is produced in liquefied form for easy transportation by truck or ship due to the lack of CO2 pipeline infrastructure in certain regions of the world currently.
[0003] There is growing interest in minimizing CO2 emissions from hydrogen production processes based on steam reforming, autothermal reforming, partial oxidation, or gasification of hydrocarbon or carbonaceous feedstocks. A method to achieve this objective involves adding CO2 capture to the process, along with the recirculation of unconverted carbon-containing components (carbon monoxide and methane) within the process. Ideally, all unreacted carbon-containing components (carbon monoxide and methane) would be recirculated into the reaction for complete conversion to CO2 and hydrogen, resulting in zero carbon slip into the atmosphere. However, this approach presents problems if inert components such as nitrogen and argon are present in the hydrocarbon or carbonaceous feedstock, or oxygen feedstock, of such processes. These inert components accumulate in the recirculation loop and typically must be purged from the system as a fuel gas stream. This purge stream also contains carbon-containing components (carbon monoxide and methane), resulting in carbon emissions into the atmosphere. Therefore, a method is needed to efficiently and selectively purge inert components from the process without increasing carbon emissions.
[0004] Most existing hydrogen production processes utilize pressure swing adsorption (PSA) to recover high-purity product hydrogen from shift-sin gas. The low-pressure tail gas flow from the PSA unit is typically combusted to generate heat for the process. If the flow is not sent to a combustor, purging is required to prevent the accumulation of inert gas during the process.
[0005] U.S. Patent No. 8,021,464 describes a process for producing a combination of hydrogen and CO2 from a mixture of hydrocarbons converted to syngas. The syngas is separated in a PSA unit into a hydrogen-enriched flow and a PSA off-gas flow. The PSA off-gas is compressed and dried, followed by several sequential steps of condensing and separating a CO2-rich condensate, with the temperature decreasing at each step, ranging from ambient temperature to -56°C. However, this process results in a purge flow containing a significant amount of CO2 that must be removed from the process. Permeate modules can be used to improve separation, but at the cost of increased power requirements.
[0006] U.S. Patent No. 8,241,400 describes a process for recovering hydrogen and CO2 from a hydrocarbon mixture using a system comprising a reformer unit, an optional water-gas shift reactor, a PSA unit, and a cryogenic purification unit or catalytic oxidation unit. The PSA unit generates three flows: a high-pressure hydrogen flow, a low-pressure CO2 flow, and a CH4-rich flow which can be withdrawn during a CO2 co-purging step and recycled back into the reformer unit. The purified CO2 from the CO2 purification unit in the process is used as a co-purge in the PSA unit. The adsorption step is performed at a pressure of 250 psig to 700 psig. The pressure during the co-purging step is in the range of 300 psig to 800 psig, and the CO2 co-purge flow is preferably introduced at a higher pressure than the pressure during the adsorption step.
[0007] The use of a second high-pressure supply flow (CO2 co-purge flow) increases the cost and complexity of the process in U.S. Patent No. 8,241,400. The need for segmented adsorbents (or two separate vessels) and isolation valves between the two vessels and the intermediate side draw further increases the cost and complexity of the process.
[0008] U.S. Patent Application Publication 2021 / 175662(A1) describes a hydrogen production process based on the reforming of hydrocarbon feedstock, from which hydrogen and CO2 are recovered. The remaining gas, including unreacted carbon-containing components, is recycled within the process. As described above, a problem associated with this method is the carbon emissions caused by purging inert components (argon and / or nitrogen) from the recirculation loop.
[0009] As global demand for fuels such as aviation fuel increases, interest is also growing in using sources other than crude oil to produce fuel. One such source is so-called biorenewable feedstock. These biorenewable feedstocks include, but are not limited to, vegetable oils such as corn, jatropha, camelina, rapeseed, canola, soybean, and algal oils, animal fats such as animal fats and fish oils, and various waste flows such as yellow and brown grease and sewage sludge. A common characteristic of these feedstocks is that they consist of mono-di- and triglycerides and free fatty acids (FFAs). Another class of compounds suitable for these processes are fatty acid alkyl esters (FAAEs), such as fatty acid methyl esters (FAMEs) or fatty acid ethyl esters (FAEEs). These types of compounds generally contain aliphatic carbon chains with 8 to 24 carbon atoms. The aliphatic carbon chains in glycerides, FFAs, or FAAEs may be saturated, monovalent, divalent, or polyunsaturated. While the majority of glycerides in biorenewable feedstocks are triglycerides, some may be monoglycerides or diglycerides. Monoglycerides and diglycerides can be processed together with triglycerides.
[0010] There are reports disclosing the production of hydrocarbons from bio-based oils. For example, U.S. Patent No. 4,300,009 discloses the use of crystalline aluminosilicate zeolite to convert vegetable oils such as corn oil into hydrocarbons such as gasoline and chemicals such as paraxylene. U.S. Patent No. 4,992,605 discloses the production of hydrocarbon products within the diesel boiling point range by hydrogenating vegetable oils such as canola oil or sunflower oil. Finally, U.S. Patent Application Publication No. 2004 / 0230085(A1) discloses a process for treating bio-derived hydrocarbon components by hydrodesoxidation followed by isomerization. [Overview of the project]
[0011] Therefore, an improved hydrogen production process with minimal carbon intensity is needed. [Brief explanation of the drawing]
[0012] [Figure 1] This is a diagram of a low-carbon intensity process for generating a hydrogen stream from a hydrogen production process. [Figure 2] This figure shows one embodiment of a process for generating hydrogen and CO2 flows from a hydrogen production process unit of the present invention. [Figure 3] This is a diagram of another embodiment of the process shown in Figure 2. [Figure 4] This figure shows another embodiment of the process for generating hydrogen and CO2 flows from the hydrogen production process unit of the present invention. [Figure 5] This is a diagram of another embodiment of the process shown in Figure 4. [Modes for carrying out the invention]
[0013] Various processes have been developed for hydrogen production. Some of these processes involve reforming a hydrocarbon-containing feedstock and subjecting the resulting synthesis gas to a water-gas shift reaction to recover hydrogen and carbon dioxide. Hydrogen recovery and carbon dioxide processes involve recovering the purified hydrogen product stream from the shift synthesis gas stream. Hydrogen recovery processes also result in the generation of CO2.
[0014] It is desirable to minimize the carbon intensity of these processes. One low-carbon intensity scheme is shown in Figure 1. In this configuration, the purge gas from the biorenewable conversion process is separated in a membrane separation unit into a hydrogen-rich permeate flow that can be used as fuel gas in the steam reforming process and a hydrogen-depleted, carbon-enriched residual flow that can be used as an auxiliary reforming feedstock. This process reduces the amount of natural gas feedstock required and fuel consumption in the steam reforming process, resulting in lower carbon emissions. The shift gas is separated into CO2 and H2 products in a two-stage PSA system. The second-stage hydrogen recovery is regulated to provide a hydrogen-rich fuel gas sufficient to meet the load of the steam reformer, thereby avoiding direct ignition of natural gas.
[0015] Figure 1 shows one embodiment of a hydrogen production process 100 incorporating a triproduct PSA system. Further information relating to this process can be found in U.S. Patent Application No. 17 / 508,349 filed October 22, 2021, Provisional U.S. Patent Application No. 63 / 220,848 filed July 12, 2021, Provisional U.S. Patent Application No. 63 / 167,343 filed March 29, 2021, and Provisional U.S. Patent Application No. 63 / 167,341 filed March 29, 2021, each of which is incorporated herein by reference in whole.
[0016] The natural gas feed 105 and water 110 are sent to the reaction section 112 of the steam reforming process unit 120, and the auxiliary fuel gas 114 and air 115 are sent to the furnace 118 within the steam reforming process unit 120. Other feed streams containing hydrocarbons can be used instead of natural gas.
[0017] The steam reforming and water-gas shift reactions produce an outflow stream 125 containing hydrogen, CO2, water, and at least one of methane, carbon monoxide, and nitrogen. Flue gas stream 130 and steam stream 135 also exit the steam reforming process unit 120.
[0018] The spillway 125 has a temperature of 30°C to 50°C (after heat recovery and cooling in the steam reforming process) and a pressure of 2,000 to 3,000 kPa. The spillway 125 is sent to a hydrogen PSA unit 140, where it is separated into a hydrogen-enriched high-purity hydrogen stream 145 and a hydrogen-depleted tail gas stream 150 containing a portion of hydrogen, CO2, water, and at least a portion of at least one of methane, carbon monoxide, and nitrogen.
[0019] The hydrogen-depleted tail gas stream 150 is sent to the compressor 155, where it is compressed from a pressure in the range of 110 kPa to 200 kPa to a pressure in the range of 3,000 kPa to 6,000 kPa.
[0020] The compressed tail gas flow 160 is sent to the CO2 recovery unit 165, where it is dried, the water flow 167 is removed, it is cooled to a temperature of -20°C to -50°C, and separated into a bottom flow 170 and a top flow 175. The bottom flow 170, which contains liquid CO2, is recovered.
[0021] The top flow 175 is sent to a tri-product PSA system 180, which includes a tri-product PSA unit 185, where it is separated into three flows. A high-pressure hydrogen flow 190 is recovered. All or part of the high-pressure hydrogen flow 190 can be sent to a bio-renewable conversion process and combined with a supplement hydrogen flow for the bio-renewable conversion process. The low-pressure CO2 flow 195 is recycled to a compressor 155.
[0022] An intermediate pressure vent gas stream 200 containing at least a portion of at least one of methane, carbon monoxide, and nitrogen, and a small amount of hydrogen (e.g., less than 20%, or 10% to 20%), is sent to the steam reforming process unit 120 as fuel.
[0023] A purge gas stream containing hydrogen 44 from the bioregenerable conversion process is sent to a membrane separation unit 205 where it is separated into a permeate stream 210 containing hydrogen and CO2 and a residue stream 215 containing at least one of methane, ethane, propane, C4+ hydrocarbons and carbon monoxide. The permeate stream 210 is sent to a compressor 155 and then to a CO2 recovery system 165 and a three-product PSA system 180 to recover hydrogen and CO2 in the permeate stream 210. In one embodiment, all or a portion of the residue stream 215 is mixed with an intermediate pressure vent gas stream 200 and sent to a furnace 118 of a steam reforming process unit 120. In another embodiment, all or a portion of the residue stream 215 can be mixed with a natural gas feed 105 and sent to the steam reforming process unit 120. If the hydrogen process unit is an autothermal reforming unit having an optional gas heated reformer, a gasification unit, or a partial oxidation unit, all or a portion of the residue stream 215 can be mixed with a feed stream containing hydrocarbons and partially oxidized in the autothermal reforming unit, the gasification unit, or the partial oxidation unit. In yet another embodiment, all or a portion of the residue stream 215 can be sent back to a bioregenerable hydrocarbon production process for hydrocarbon recovery. 4+ It can be returned to a bioregenerable hydrocarbon production process for hydrocarbon recovery.
[0024] A bypass line 202 sends a hydrogen-depleted tail gas stream 150 to a furnace within the steam reforming process unit for combustion. Thereby, the steam reforming process unit can continue to operate without CO2 recovery in case there is a problem with the compressor 155, the CO2 recovery unit 165, or the three-product PSA system 180.
[0025] One drawback of this approach is that all of the carbon slip from the steam reforming process (methane and CO) is burned in the furnace, resulting in some fossil fuel-based CO2 emissions. This leads to constraints on the steam reforming process design to minimize carbon slip (e.g., lower operating pressure, high steam:carbon ratio, two-stage water gas shift, etc.), resulting in sub-optimal steam reforming process conditions and higher costs. Therefore, there is a need to improve the process configuration to achieve lower carbon intensity with a more efficient steam reforming design.
[0026] This process solves this problem by recycling syngas to the reforming feed after CO2 and H2 recovery, thereby avoiding carbon slip and reducing the overall carbon intensity. As a result, previous constraints on the reforming process are removed. One feature of this design is the selective removal of inert components (nitrogen and / or argon) in the PSA hydrogen unit, thereby avoiding the accumulation of inert gases in the recycle loop.
[0027] One aspect of the present invention is a method for generating a hydrogen-enriched gas flow. In one embodiment, the method includes: processing a feed stream containing hydrocarbons (such as natural gas, liquefied petroleum gas, or naphtha) or carbonaceous feed material (such as coal, petroleum coke, or biomass) in a hydrogen production process unit to produce a synthesis gas mixture containing hydrogen, carbon monoxide, methane, water, and an inert gas; performing a water-gas shift process on the synthesis gas mixture to form a shift synthesis gas containing carbon dioxide; performing a hydrogen pressure swing adsorption (PSA) separation process and a carbon dioxide separation process on the shift synthesis gas to form a high-pressure hydrogen product flow containing hydrogen, an inert gas-enriched off-gas flow from the hydrogen separation process containing an inert gas and depleted of carbon-containing components, a carbon dioxide product flow containing carbon dioxide, and a carbon-enriched off-gas flow containing carbon monoxide and methane, wherein the hydrogen PSA process includes a tri-product PSA unit or a tri-product PSA system comprising at least two PSA units; and recirculating the carbon-enriched off-gas flow to the hydrogen production process unit.
[0028] The feedstream, containing hydrocarbon or carbonaceous feedstock, is processed within a hydrogen production process unit. Suitable hydrogen production process units include, but are not limited to, a steam reforming unit with an optional gas-heated reformer, a self-thermal reforming unit with an optional gas-heated reformer, a gasification unit, a partial oxidation (POX) unit, or a combination thereof.
[0029] The synthesis gas mixture produced in the hydrogen production process contains hydrogen, carbon monoxide, methane, water, and inert gases such as nitrogen and argon. The synthesis gas mixture undergoes a water-gas shift reaction, converting carbon monoxide into carbon dioxide and additional hydrogen.
[0030] The hydrogen concentration in synthesis gas mixtures is generally in the range of 50 mol% to 80 mol%. For example, the hydrogen concentration in the shift gas of a steam methane reforming plant is 60 mol% to 80 mol%, while the hydrogen concentration in a POX reactor is 50 mol% to 70 mol%.
[0031] Shift synthesis gas is separated in a hydrogen PSA separation process and a carbon dioxide separation process.
[0032] The hydrogen PSA separation process and the carbon dioxide separation process produce a high-pressure hydrogen product stream containing hydrogen, an inert gas-enriched off-gas stream from the hydrogen separation process containing inert gases and depleted of carbon components, a carbon dioxide product stream containing carbon dioxide, and a carbon-enriched off-gas stream containing carbon monoxide and methane. The term "inert gas-enriched off-gas stream" means that the stream contains at least three times (mol%) more inert gas (e.g., nitrogen and argon) than the inflowing shift synthesis gas (mol%), typically in the range of 3 to 8 times more inert gas than the shift synthesis gas. The term "carbon-enriched off-gas stream" means that the stream contains at least five times (mol%) more carbon monoxide and methane than the shift synthesis gas (mol%), typically in the range of 5 to 15 times more.
[0033] The temperature of the feed gas mixture flowing into the hydrogen and CO2 recovery system is typically within the range of 20°C to 60°C, 30°C to 50°C, or 40°C (or any combination of these temperature ranges).
[0034] The high-pressure hydrogen product stream and the carbon dioxide product stream are recovered. The high-pressure hydrogen product stream typically contains more than 99.0 mol%, or more than 99.9 mol%, or more than 99.99 mol%, of hydrogen. The carbon dioxide product stream typically contains more than 95 mol%, or more than 99.0 mol%, or more than 99.9 mol%, of carbon dioxide.
[0035] An inert gas-enriched off-gas stream is enriched with inert gases such as nitrogen and argon, while carbon-containing components such as carbon dioxide, carbon monoxide, and methane are depleted. It also contains hydrogen, which can be burned as fuel in hydrogen production processes or elsewhere within the plant.
[0036] The carbon-enriched off-gas stream is recycled to the hydrogen production process unit and used as at least part of the feed for the hydrogen processing unit.
[0037] The amount of carbon-enriched off-gas flow recycled to the hydrogen production process unit may constitute less than 80%, less than 70%, less than 60%, less than 50%, or less than 40% of the total amount of carbon-enriched off-gas flow and inert gas-enriched off-gas flow.
[0038] The order of the separation processes is not important. Hydrogen PSA separation may be performed first and carbon dioxide separation second, or carbon dioxide separation may be performed first and hydrogen PSA separation second.
[0039] When shift synthesis gas is first introduced into the hydrogen PSA separation process, it is introduced into the tri-product PSA system to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a low-pressure hydrogen-depleted tail gas flow. Subsequently, the low-pressure hydrogen-depleted tail gas flow is introduced into the carbon dioxide capture system to form a carbon dioxide product flow and a carbon-enriched off-gas flow.
[0040] When shift synthesis gas is first introduced into the carbon dioxide capture system, a carbon dioxide product flow and a carbon dioxide depletion flow are formed. The carbon dioxide depletion flow is then introduced into the tri-product PSA system to form a high-pressure hydrogen flow, an inert substance-enriched off-gas flow, and a carbon-enriched off-gas flow.
[0041] The carbon dioxide recovery system may be any suitable recovery system known to those skilled in the art. Suitable carbon dioxide recovery systems include, but are not limited to, amine separation units, cryogenic separation units, carbon dioxide PSA units, or combinations thereof.
[0042] The hydrogen PSA separation process includes a tri-product PSA system. The tri-product PSA system includes a tri-product PSA unit or at least two PSA units.
[0043] A tri-product PSA unit comprises PSA adsorption vessels. Generally, there are at least six vessels, and typically eight to fourteen. Each vessel contains one or more adsorbent layers, generally one to five, and typically two to three. The percentage of the bed of adsorbent layers is typically 10% to 100%. Different layers of adsorbent have different selectivity for components in the feedstream, as is known to those skilled in the art. For example, in hydrogen production processes and CO2 recovery, some layers contain adsorbents for the selective adsorption of CO2 to methane, carbon monoxide, nitrogen, argon, and hydrogen, including but not limited to layers of activated alumina, silica gel, and sodium Y zeolite. Other layers contain, but are not limited to, layers of activated carbon, silica gel, and molecular sieve zeolite (e.g., 5A or sodium X zeolite), for the selective adsorption of CO2, methane, carbon monoxide, nitrogen, and argon to hydrogen. Those skilled in the art understand that other zeolites may be used and are familiar with methods for selecting appropriate adsorbents.
[0044] The container has a first opening at one end and a second opening at the opposite end. For convenience, these ends are referred to as the top and bottom of the container. The first opening at the bottom is selectively connected to the high-pressure supply gas inlet line and the low-pressure tail gas outlet line. The second opening at the top of the container is selectively connected to the high-pressure product outlet line, the intermediate-pressure vent gas outlet line, and the low-pressure purge gas inlet line.
[0045] The supply gas enters at high pressure through a first opening at the bottom of the vessel, and a high-pressure co-current adsorption and product removal step is performed, and the product exits the vessel at high pressure through a second opening at the top of the vessel. There is at least one co-current depressurization step, followed by an intermediate-pressure co-current depressurization and vent gas removal step. The second flow is removed at a second pressure through an opening at the top of the vessel. There are countercurrent blowdown and countercurrent purge steps. The purge gas enters at low pressure through an opening at the top of the vessel. CO2 can be removed at low pressure through an opening at the bottom of the vessel during either or both of the countercurrent blowdown and / or countercurrent purge steps. There is at least one countercurrent repressurization step following the countercurrent purge and tail gas removal step.
[0046] The tri-product PSA unit is described in detail, for example, in U.S. Patent Application No. 17 / 451,935, filed on October 22, 2021, which is incorporated herein by reference in its entirety.
[0047] Alternatively, the triproduct separation system may consist of at least two PSA units, in which case the two PSA units are connected in series. Shift synthesis gas is introduced into the first PSA unit to form a carbon-enriched tail gas stream enriched with carbon dioxide, carbon monoxide, and methane, as well as a hydrogen-enriched intermediate stream also enriched with inert components (nitrogen and / or argon). The hydrogen-enriched intermediate stream is introduced into the second PSA unit to form a high-pressure hydrogen product stream and an inert-enriched off-gas stream. The carbon-enriched tail gas stream is then introduced into the carbon dioxide capture system.
[0048] A tri-product PSA system comprising at least two PSA units is further described, for example, in U.S. Patent Application No. 17 / 508,349, filed on 22 October 2021, which is incorporated herein by reference in its entirety.
[0049] If hydrogen PSA separation is performed first, and the tri-product PSA system includes a tri-product PSA unit, the shift synthesis gas is introduced into the tri-product PSA unit to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a hydrogen-depleted tail gas flow. The hydrogen-depleted tail gas flow is then introduced into a carbon dioxide capture system, where it is separated into a carbon dioxide product flow and a carbon-enriched off-gas flow.
[0050] If hydrogen PSA separation is performed first, and the tri-product PSA system comprises at least two bi-product PSA units, the shift synthesis gas is introduced into the first PSA unit to form a carbon-enriched tail gas stream enriched with carbon dioxide, carbon monoxide, and methane, as well as a hydrogen-enriched intermediate stream also enriched with inert components (nitrogen and / or argon). The hydrogen-enriched intermediate stream is introduced into the second PSA unit to form a high-pressure hydrogen-product stream and an inert-enriched off-gas stream. The carbon-enriched tail gas stream is then introduced into the carbon dioxide capture system.
[0051] 70%–90% of the hydrogen in the synthesis gas mixture into the hydrogen PSA system is typically recovered in a high-pressure product stream, and in some cases the high-pressure hydrogen stream is substantially free of CO2, methane, carbon monoxide, nitrogen, and argon. Typically, it contains less than 1%, less than 0.1%, or less than 0.01% of CO2 relative to the feed gas mixture. Typically, it contains less than 10%, less than 5%, less than 2%, less than 1%, or less than 0.1% of methane, carbon monoxide, nitrogen, and argon relative to the feed gas mixture. The high-pressure product stream is typically removed at high pressures in the range of 1,000–6,000 kPa, 2,000–5,000 kPa, or 2,500–4,500 kPa.
[0052] Hydrogen-depleted tail gas flows are typically removed at low pressures in the range of 50 kPa to 250 kPa, or 100 kPa to 200 kPa.
[0053] Hydrogen-depleted tail gas streams typically contain 95%–100% CO2 in the feed gas mixture. They typically contain 10% hydrogen (e.g., 5%–15%) relative to the feed gas mixture, and 40% methane, carbon monoxide, nitrogen, and argon (e.g., 20%–60%) relative to the feed.
[0054] The inert gas-enriched flow from the tri-product PSA unit is removed at an intermediate pressure between high and low pressure, which is much closer to low pressure than high pressure, typically within 400 kPa, 300 kPa, or 200 kPa of low pressure. Typically, the intermediate-pressure product flow is removed at pressures in the range of 150 kPa to 450 kPa, or 250 kPa to 350 kPa. There is some overlap between the intermediate and low pressure ranges, but in certain cases, low pressure is understood to be lower than intermediate pressure.
[0055] In some embodiments, the carbon-enriched off-gas flow can be introduced into a membrane separation unit to form a hydrogen-enriched permeate flow (e.g., more than 80%, 90%, or 95% of the hydrogen in the carbon-enriched off-gas flow to the membrane separation unit is recovered in the permeate flow), and a carbon-monoxide and methane-enriched residual flow (e.g., more than 70%, 80%, or 90% of the carbon-monoxide and methane in the carbon-enriched off-gas flow to the membrane separation unit are recovered in the residual flow). In this configuration, recirculating the carbon-enriched off-gas flow to the hydrogen production process unit includes recirculating the residual flow to the hydrogen production process unit. The permeate flow can optionally be combined with an inert gas-enriched flow.
[0056] If the carbon dioxide separation process is the first step, the shift synthesis gas is introduced into the carbon dioxide capture system to form a carbon dioxide product stream and a carbon dioxide depletion stream. The carbon dioxide depletion stream is introduced into the tri-product PSA system to form a high-pressure hydrogen stream, an inert substance-enriched off-gas stream, and a carbon-enriched off-gas stream.
[0057] When a tri-product PSA system includes a tri-product PSA unit, the carbon dioxide depletion flow is introduced into the tri-product PSA unit to form a high-pressure hydrogen product flow, an inert gas enriched off-gas flow, and a carbon enriched off-gas flow.
[0058] If the tri-product PSA system comprises at least two PSA units, the carbon dioxide depletion flow is introduced into the first PSA unit to form a carbon-enriched off-gas flow and a hydrogen-enriched intermediate flow also enriched with inert components (nitrogen and / or argon). The hydrogen-enriched intermediate flow is introduced into the second PSA unit to form a high-pressure hydrogen-product flow and an inert-enriched off-gas flow.
[0059] In some embodiments, the carbon-enriched off-gas flow is introduced into a membrane separation unit to form a hydrogen-enriched permeate flow, as well as a residual flow enriched with carbon monoxide and methane. In this case, recirculating the carbon-enriched off-gas flow to the hydrogen production process unit includes recirculating the residual flow to the hydrogen production process unit. The permeate flow can optionally be combined with an inert gas-enriched flow.
[0060] The process for generating a hydrogen-enriched gas stream can be integrated with a biorenewable conversion process for producing hydrocarbon products from a biorenewable feedstock, which will be discussed in more detail below. In this case, a hydrogen-containing purge gas stream from the biorenewable conversion process can be introduced into a membrane separation unit. In addition, at least a portion of the feed stream to the hydrogen production process may include a hydrocarbon-containing stream from the biorenewable conversion process.
[0061] Another aspect of the present invention includes a process for generating a hydrogen-enriched gas flow. In one embodiment, the process involves processing a feed stream containing hydrocarbons or carbonaceous feedstock in a hydrogen production process unit to produce a synthesis gas mixture containing hydrogen, carbon monoxide, methane, water, and an inert gas; performing an aqueous gas shift process on the synthesis gas mixture to form a shift synthesis gas containing carbon dioxide; and performing a hydrogen pressure swing adsorption (PSA) separation process and a carbon dioxide separation process on the shift synthesis gas to form a high-pressure hydrogen product flow containing hydrogen, an inert gas-enriched off-gas flow from the hydrogen separation process containing an inert gas and depleted of carbon-containing components, a carbon dioxide product flow containing carbon dioxide, and a carbon-enriched off-gas flow containing carbon monoxide and methane, wherein the hydrogen PSA process includes a tri-product PSA unit or a tri-product PSA system comprising at least two PSA units. The carbon dioxide recovery system comprises an amine separation unit, or a cryogenic separation unit, or a carbon dioxide PSA unit, or a combination thereof, and the hydrogen PSA separation process and the carbon dioxide separation process are carried out by introducing shift synthesis gas into a tri-product PSA system to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a hydrogen-depleted tail gas flow; introducing the hydrogen-depleted tail gas flow into a carbon dioxide recovery system to form a carbon dioxide product flow and a carbon-enriched off-gas flow, or introducing shift synthesis gas into a carbon dioxide recovery system to form a carbon dioxide product flow and a carbon dioxide-depleted flow; and introducing the carbon dioxide-depleted flow into a tri-product PSA system to form a high-pressure hydrogen flow, an inert substance-enriched off-gas flow, and a carbon-enriched off-gas flow.
[0062] In some embodiments, carrying out a hydrogen PSA separation process and a carbon dioxide separation process includes introducing a shift synthesis gas into a triproduct PSA system to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a hydrogen-depleted tail gas flow, and introducing the hydrogen-depleted tail gas flow into a carbon dioxide recovery system to form a carbon dioxide product flow and a carbon-enriched off-gas flow.
[0063] In some embodiments, the process further includes introducing a carbon-enriched off-gas flow into a membrane separation unit to form a hydrogen-enriched permeate flow and a residual flow enriched with carbon monoxide and methane, optionally combining the permeate flow with an inert gas-enriched flow, and recirculating the carbon-enriched off-gas flow to a hydrogen production process unit, and recirculating the residual flow to a hydrogen production process unit.
[0064] In some embodiments, carrying out a PSA separation process and a carbon dioxide separation process includes introducing shift synthesis gas into a carbon dioxide recovery system to form a carbon dioxide product stream and a carbon dioxide depletion stream, and introducing the carbon dioxide depletion stream into a tri-product PSA system to form a high-pressure hydrogen stream, an inert substance-enriched off-gas stream, and a carbon-enriched off-gas stream.
[0065] In some embodiments, the process further includes introducing a carbon-enriched off-gas flow into a membrane separation unit to form a hydrogen-enriched permeate flow and a residual flow enriched with carbon monoxide and methane, optionally combining the permeate flow with an inert gas-enriched flow, and recirculating the carbon-enriched off-gas flow to a hydrogen production process unit, and recirculating the residual flow to a hydrogen production process unit.
[0066] Figure 2 shows a diagram of process 300 for generating a hydrogen-enriched gas stream, where hydrogen separation is performed before carbon dioxide separation. The feed stream 305 is introduced into a hydrogen production process unit 310, where it is converted into synthesis gas. The synthesis gas mixture contains hydrogen, carbon monoxide, methane, water, and an inert gas.
[0067] The synthesis gas stream 315 containing the synthesis gas mixture is sent to the water-gas shift reactor 320, where carbon monoxide is converted to carbon dioxide.
[0068] The shifted synthesis gas stream 325 is sent to the hydrogen PSA system 330. The hydrogen PSA system 330 may be either a triproduct PSA unit or at least two PSA units, as discussed above.
[0069] The hydrogen PSA system 330 generates a high-pressure hydrogen product stream 335, an inert gas enriched off-gas stream 340, and a hydrogen depletion tail gas stream 345. The high-pressure hydrogen product stream 335 is recovered. The inert gas enriched off-gas stream 340 is enriched with inert gases such as nitrogen and argon, and depleted with carbon-containing components such as carbon dioxide, carbon monoxide, and methane. The inert gas enriched off-gas stream 340 also contains hydrogen and can be sent for use as fuel in a hydrogen production process unit or elsewhere. The hydrogen depletion tail gas stream 345 is enriched with carbon dioxide, carbon monoxide, and methane.
[0070] The hydrogen-depleted tail gas stream 345 is sent to the carbon dioxide capture system 350, where it is separated into a carbon dioxide product stream 355 and a carbon-enriched off-gas stream 360. The carbon dioxide product stream 355 is then captured.
[0071] The carbon-enriched off-gas stream 360 is recycled to the hydrogen production process unit 310.
[0072] Figure 3 shows process 300' in which the carbon-enriched off-gas flow 360 undergoes further separation.
[0073] The carbon-enriched off-gas stream 360 is sent to a membrane separation unit 365, where it is separated into a hydrogen-enriched permeate stream 370 and a residual stream 375 enriched with carbon monoxide and methane. The permeate stream 370 can optionally be combined with an inert gas-enriched off-gas stream 340. The residual stream 375 enriched with carbon monoxide and methane is recycled to a hydrogen production process unit 310.
[0074] When the hydrogen production process is integrated with a biorenewable conversion process for producing hydrocarbon products from biorenewable feedstock, a hydrogen-containing purge gas stream 380 from the biorenewable conversion process can be introduced into a membrane separation unit 365. Additionally, a hydrocarbon-containing stream 385 from a biorenewable conversion process (not shown) can be used as at least part of the feed to the hydrogen production process unit 310.
[0075] Figure 4 shows a diagram of process 400 for generating a hydrogen-enriched gas stream, in which carbon dioxide separation is performed before hydrogen separation. The feed stream 405 is introduced into a hydrogen production process unit 410, where it is converted into synthesis gas. The synthesis gas mixture contains hydrogen, carbon monoxide, methane, water, and an inert gas.
[0076] The synthesis gas stream 415 containing the synthesis gas mixture is sent to the water-gas shift reactor 420, where carbon monoxide is converted to carbon dioxide.
[0077] The shift synthesis gas flow 425 is sent to the carbon dioxide capture unit 430, where it is separated into a carbon dioxide product flow 435 and a carbon dioxide depletion flow 440. The carbon dioxide product flow 435 is then captured.
[0078] The carbon dioxide depletion stream 440 is sent to the hydrogen PSA system 445, where it is separated into a high-pressure hydrogen product stream 450, an inert gas-enriched off-gas stream 455, and a carbon-enriched off-gas stream 460. The high-pressure hydrogen product stream 450 is recovered. The inert gas-enriched off-gas stream 455 may be sent to a hydrogen production process unit or elsewhere for use as fuel. The carbon-enriched off-gas stream 460, enriched with carbon monoxide and methane, is recycled to the hydrogen production process unit 410.
[0079] Figure 5 shows process 400' in which the carbon-enriched off-gas flow 460 undergoes further separation.
[0080] The carbon-enriched off-gas stream 460 is sent to a membrane separation unit 465, where it is separated into a hydrogen-enriched permeate stream 470 and a residual stream 475 enriched with carbon monoxide and methane. The permeate stream 470 can optionally be combined with an inert gas-enriched off-gas stream 455. The residual stream 475 is recycled to a hydrogen production process unit 410.
[0081] When the hydrogen production process is integrated with a biorenewable conversion process for producing hydrocarbon products from biorenewable feedstock, a hydrogen-containing purge gas stream 480 from the biorenewable conversion process can be introduced into a membrane separation unit 465. Additionally, a hydrocarbon-containing stream 485 from a biorenewable conversion process (not shown) can be used as at least part of the feed to the hydrogen production process unit 410. [Examples]
[0082] A computer simulation was performed on the steam reforming hydrogen production process according to the embodiment shown in Figure 3. The supply flow 305 to the steam reformer consisted of a hydrocarbon-containing flow 385 (e.g., naphtha) from natural gas and a biorenewable process. In addition, a hydrogen-containing purge gas flow 380 from a biorenewable process was combined with a carbon-enriched off-gas flow 360 to the membrane separation unit 365. The natural gas supply flow 305 contained an inert component (nitrogen).
[0083] To maximize hydrogen and CO2 recovery while minimizing CO2 emissions from the process, the system design was optimized by recirculating the carbon monoxide and methane-enriched residual flow 375 to the hydrogen production unit (e.g., steam reforming reactor) 310. The results are shown in Table 1 below. Comparing the inert gas-enriched off-gas flow 340 with the shift-syn gas flow 325, it can be seen that 38% of the nitrogen in the shift-syn gas flow 325 is removed into the off-gas flow 340, while only 0.5% of the carbon monoxide and only 0.7% of the methane in the shift-syn gas are removed. Furthermore, the membrane separation unit 365 selectively removes hydrogen from the recirculation loop, generating the carbon monoxide and methane-enriched residual flow 375.
[0084] [Table 1]
[0085] Specific Embodiments The following will be explained in conjunction with specific embodiments, but it should be understood that this explanation is intended to illustrate the scope of the above-mentioned description and the attached claims, and is not intended to limit them.
[0086] A first embodiment of the present invention is a process for producing hydrogen enrichment products, comprising: processing a feed stream containing hydrocarbons or carbonaceous feedstock in a hydrogen production process unit to produce a synthesis gas mixture containing hydrogen, carbon monoxide, methane, water, and an inert gas; performing a water-gas shift process on the synthesis gas mixture to form a shift synthesis gas containing carbon dioxide; performing a hydrogen pressure swing adsorption (PSA) separation process and a carbon dioxide separation process on the shift synthesis gas to form a high-pressure hydrogen product stream containing hydrogen, an inert gas-enriched off-gas stream from the hydrogen separation process containing an inert gas and depleted of carbon-containing components, a carbon dioxide product stream containing carbon dioxide, and a carbon-enriched off-gas stream containing carbon monoxide and methane, wherein the hydrogen PSA process includes a tri-product PSA unit or a tri-product PSA system comprising at least two PSA units; and recirculating the carbon-enriched off-gas stream to the hydrogen production process unit. One embodiment of the present invention is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, in which the hydrogen PSA separation process and the carbon dioxide separation process are carried out by introducing a shift synthesis gas into a triproduct PSA to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a hydrogen-depleted tail gas flow, and introducing the hydrogen-depleted tail gas flow into carbon dioxide recovery to form a carbon dioxide product flow and a carbon-enriched off-gas flow. One embodiment of the present invention is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, in which introducing a shift synthesis gas into a triproduct PSA system is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, in which the shift synthesis gas is introduced into a triproduct PSA unit to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a hydrogen-depleted tail gas flow.One embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, in which the introduction of shift synthesis gas into a triproduct PSA system includes introducing the shift synthesis gas into a first PSA unit to form a carbon-enriched tail gas stream enriched with carbon dioxide, carbon monoxide, and methane, as well as a hydrogen-enriched intermediate stream; introducing the hydrogen-enriched intermediate stream into a second PSA unit to form a high-pressure hydrogen-product stream and an inert substance-enriched off-gas stream; and introducing the carbon-enriched tail gas stream into carbon dioxide recovery. One embodiment of the present invention further includes introducing a carbon-enriched off-gas flow into a membrane separation unit to form a hydrogen-enriched permeate flow and a residual flow enriched with carbon monoxide and methane, and optionally combining the permeate flow with an inert gas-enriched flow, wherein the carbon-enriched off-gas flow is recirculated to a hydrogen production process unit, which is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, which includes recirculating the residual flow to a hydrogen production process unit. One embodiment of the present invention further includes introducing a hydrogen-containing purge gas flow from a biorenewable conversion process for producing hydrocarbon products from a biorenewable feedstock into a membrane separation unit together with a carbon-enriched off-gas flow, which is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph. One embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, which includes introducing a shift synthesis gas to carbon dioxide recovery to form a carbon dioxide product stream and a carbon dioxide depletion stream, and introducing the carbon dioxide depletion stream to a tri-product PSA to form a high-pressure hydrogen stream, an inert substance-enriched off-gas stream, and a carbon-enriched off-gas stream.One embodiment of the present invention is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, which includes introducing a carbon dioxide depletion flow into a tri-product PSA system, which includes introducing a carbon dioxide depletion flow into a tri-product PSA unit to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a carbon-enriched off-gas flow. Another embodiment of the present invention is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, which includes introducing a carbon dioxide depletion flow into a tri-product PSA system, which includes introducing a carbon dioxide depletion flow into a first PSA unit to form a carbon-enriched off-gas flow and a hydrogen-enriched intermediate flow, and introducing a hydrogen-enriched intermediate flow into a second PSA unit to form a high-pressure hydrogen product flow and an inert gas-enriched off-gas flow. One embodiment of the present invention further includes introducing a carbon-enriched off-gas flow into a membrane separation unit to form a hydrogen-enriched permeate flow and a residual flow enriched with carbon monoxide and methane, and optionally combining the permeate flow with an inert gas-enriched flow, wherein the carbon-enriched off-gas flow is recirculated to a hydrogen production process unit, which is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, which includes recirculating the residual flow to a hydrogen production process unit. One embodiment of the present invention further includes introducing a hydrogen-containing purge gas flow from a biorenewable conversion process for producing hydrocarbon products from a biorenewable feedstock into a membrane separation unit together with a carbon-enriched off-gas flow, which is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph. One embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, wherein the hydrogen production process unit comprises a steam reforming unit having an optional gas-heated reformer, a self-thermal reforming unit having an optional gas-heated reformer, or a gasification unit, or a partial oxidation (POX) unit, or a combination thereof.One embodiment of the present invention is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, wherein the amount of carbon-enriched off-gas flow recycled to a hydrogen production process unit is less than 80% of the total amount of carbon-enriched off-gas flow and inert gas-enriched off-gas flow. Another embodiment of the present invention is one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, wherein carbon dioxide recovery comprises an amine separation unit, or a cryogenic separation unit, or a carbon dioxide PSA unit, or a combination thereof. Embodiments of the present invention are one or all of the preceding embodiments of this paragraph, including the first embodiment of this paragraph, wherein at least a portion of the feed flow includes a hydrocarbon-containing flow from a biorenewable conversion process for producing hydrocarbon products from biorenewable feedstock.
[0087] A second embodiment of the present invention is a process for producing hydrogen enrichment products, comprising: processing a feed stream containing hydrocarbons or carbonaceous feedstock in a hydrogen production process unit to produce a synthesis gas mixture containing hydrogen, carbon monoxide, methane, water, and an inert gas; performing an aqueous gas shift process on the synthesis gas mixture to form a shift synthesis gas containing carbon dioxide; and performing a hydrogen pressure swing adsorption (PSA) separation process and a carbon dioxide separation process on the shift synthesis gas to form a high-pressure hydrogen product stream containing hydrogen, an inert gas enriched off-gas stream from the hydrogen separation process containing an inert gas and depleted of carbon-containing components, a carbon dioxide product stream containing carbon dioxide, and a carbon enriched off-gas stream containing carbon monoxide and methane, wherein the hydrogen PSA process is a tri-product PSA unit or a tri-product PSA unit comprising at least two PSA units. The process includes forming a carbon-enriched off-gas flow, including system A, and recirculating the carbon-enriched off-gas flow to a hydrogen production process unit, wherein carbon dioxide recovery comprises an amine separation unit, or a cryogenic separation unit, or a carbon dioxide PSA unit, or a combination thereof, and the hydrogen PSA separation process and carbon dioxide separation process include introducing shift synthesis gas into a tri-product PSA to form a high-pressure hydrogen product flow, an inert gas-enriched off-gas flow, and a hydrogen-depleted tail gas flow, introducing the hydrogen-depleted tail gas flow into carbon dioxide recovery to form a carbon dioxide product flow and a carbon-enriched off-gas flow, or introducing shift synthesis gas into carbon dioxide recovery to form a carbon dioxide product flow and a carbon dioxide-depleted flow, and introducing the carbon dioxide-depleted flow into a tri-product PSA to form a high-pressure hydrogen flow, an inert substance-enriched off-gas flow, and a carbon-enriched off-gas flow. One embodiment of the present invention is one, any, or all of the preceding embodiments of this paragraph, including the second embodiment of this paragraph, which includes introducing a shift synthesis gas into a triproduct PSA to form a high-pressure hydrogen product stream, an inert gas-enriched off-gas stream, and a hydrogen-depleted tail gas stream, and introducing the hydrogen-depleted tail gas stream into carbon dioxide recovery to form a carbon dioxide product stream and a carbon-enriched off-gas stream.One embodiment of the present invention further includes introducing a carbon-enriched off-gas flow into a membrane separation unit to form a hydrogen-enriched permeate flow and a residual flow enriched with carbon monoxide and methane, and optionally combining the permeate flow with an inert gas-enriched flow, and recirculating the carbon-enriched off-gas flow to a hydrogen production process unit, which includes recirculating the residual flow to a hydrogen production process unit, and is one, one or all of the preceding embodiments of this paragraph, including the second embodiment of this paragraph. One embodiment of the present invention is one, one or all of the preceding embodiments of this paragraph, including the second embodiment of this paragraph, which includes carrying out a PSA separation process and a carbon dioxide separation process, which includes introducing a shift synthesis gas into carbon dioxide recovery to form a carbon dioxide product flow and a carbon dioxide depletion flow, and introducing the carbon dioxide depletion flow into a tri-product PSA to form a high-pressure hydrogen flow, an inert substance-enriched off-gas flow, and a carbon-enriched off-gas flow. One embodiment of the present invention further includes introducing a carbon-enriched off-gas flow into a membrane separation unit to form a hydrogen-enriched permeate flow and a residual flow enriched with carbon monoxide and methane, and optionally combining the permeate flow with an inert gas-enriched flow, wherein the carbon-enriched off-gas flow is recirculated to a hydrogen production process unit, which is one, any, or all of the preceding embodiments of this paragraph, including the second embodiment of this paragraph, which includes recirculating the residual flow to a hydrogen production process unit.
[0088] Without further detail, it is expected that those skilled in the art will be able to utilize the invention to the fullest extent without departing from the spirit and scope of the invention, and will readily identify its essential characteristics, and will be able to make various changes and modifications to the invention to suit various uses and conditions. Accordingly, the prior preferred specific embodiments should be interpreted as merely illustrative examples and not in any way limit the remainder of this disclosure, but are intended to cover various modifications and equivalent configurations that fall within the scope of the appended claims.
[0089] In the above, all temperatures are given in degrees Celsius, and all parts and percentages are based on weight unless otherwise indicated.
Claims
1. A process for generating a hydrogen-enriched gas flow, In the hydrogen production process unit (310), a feed stream (305) containing hydrocarbons or carbonaceous feedstock is processed to produce a synthesis gas mixture containing hydrogen, carbon monoxide, methane, water, and an inert gas. The synthesis gas mixture (315) is subjected to a water-gas shift process to form a shift synthesis gas (325) containing carbon dioxide, The shift synthesis gas (325) is subjected to a hydrogen pressure swing adsorption (PSA) separation process and a carbon dioxide separation process to form a high-pressure hydrogen product stream (335) containing hydrogen, an inert gas-enriched off-gas stream (340) from the hydrogen separation process containing the inert gas and depleted of carbon-containing components, a carbon dioxide product stream (355) containing carbon dioxide, and a carbon-enriched off-gas stream (360) containing carbon monoxide and methane, wherein the hydrogen PSA separation process includes a tri-product PSA unit or a tri-product PSA system (330) comprising at least two PSA units. A process comprising recirculating the carbon-enriched off-gas flow (360) to the hydrogen production process unit (310).
2. The hydrogen PSA separation process and the carbon dioxide separation process are carried out as follows: The shift synthesis gas (325) is introduced into the tri-product PSA system (330) to form the high-pressure hydrogen product flow (335), the inert gas enriched off-gas flow (340), and the hydrogen depletion tail gas flow (345). The process according to claim 1, further comprising introducing the hydrogen-depleted tail gas flow (345) into a carbon dioxide capture system (350) to form the carbon dioxide product flow (355) and the carbon-enriched off-gas flow (360).
3. Introducing the shift synthesis gas (325) into the triproduct PSA system (330) The shift synthesis gas (325) is introduced into the tri-product PSA unit to form the high-pressure hydrogen product flow (335), the inert gas enriched off-gas flow (340), and the hydrogen depletion tail gas flow (345). Or, The shift synthesis gas (330) is introduced into the first PSA unit to form a carbon-enriched tail gas flow enriched with carbon dioxide, carbon monoxide, and methane, as well as a hydrogen-enriched intermediate flow. The hydrogen-enriched intermediate flow is introduced into the second PSA unit to form the high-pressure hydrogen product flow (335) and the inert substance-enriched off-gas flow (340), The process according to claim 2, further comprising introducing the carbon-enriched tail gas flow into the carbon dioxide capture system (345).