Steam-hydrocarbon reforming with reduced carbon dioxide emissions

Abstract

The low-carbon emission hydrogen production process can be achieved by first separating carbon dioxide from the reformer synthesis gas stream and subsequently purifying the carbon dioxide-depleted synthesis gas stream to produce a hydrogen product and a hydrogen-depleted tail gas stream. The hydrogen-depleted tail gas stream is then separated using a semi-permeable membrane, after which the hydrogen-enriched permeate is used as fuel in the reformer burner and the hydrogen-depleted residue is recycled to the feed.

Description

Background Art

[0001] Existing industrial processes such as the reforming of hydrocarbon feeds to produce hydrogen and synthesis gas will likely need to capture carbon dioxide (CO2) to mitigate the effects of climate change. Steam methane reforming (SMR) is the most common reforming technology, but uses air-fired combustion of the fuel gas to generate the heat required to drive the reforming reaction. Air-fired combustion generates flue gas in which any carbon in the fuel gas is converted to CO2 at low pressure and low concentration due to the large amount of inert nitrogen contributed by the air. Carbon capture from flue gas is costly, inefficient, and bulky. Eliminating carbon from the fuel gas with air-fired combustion enables the efficient capture of nearly 100% of the CO2 in the process by capturing the CO2 in synthesis gas having much higher concentrations and much higher pressures of CO2.

[0002] Licht et al. (US8,137,422) teaches a process for reducing emissions from an SMR process by recycling a hydrogen-depleted waste stream or tail gas from a hydrogen purification step to a point upstream or downstream of the SMR and supplying a significant portion of the fuel gas with the product hydrogen.

[0003] Adamopoulos et al. (US9,517,933) teaches a process for recovering hydrogen from tail gas from a hydrogen purification step to improve overall hydrogen recovery. The non-permeate stream is recycled to a point downstream of the catalytic reformer.

[0004] Guo et al. (WO2013 / 131916) teaches a process for operating an SMR process using high-pressure tail gas separated in a membrane system without using a compressor. The permeate stream is used as fuel gas in the furnace and the non-permeate stream is recycled to the SMR feed.

[0005] It is necessary to produce hydrogen using an SMR process that reduces CO2 emissions while minimizing the overall increase in energy costs. As used herein, the net energy of MJ (the difference between the hydrocarbon feed and the exported steam from the consumed fuel) is defined as the net energy of MJ divided by the total hydrogen product (kg).

Summary of the Invention

[0006] The present disclosure relates to a process and apparatus for separating tail gas into a hydrogen-enriched permeate stream and a hydrogen-depleted non-permeate stream from a hydrogen purification step downstream of a reformer using a membrane. In at least some embodiments, the hydrogen-enriched permeate stream may then be combusted in the reformer to generate heat for the reforming reaction, and then the hydrogen-depleted non-permeate stream may be recycled to the SMR process.

[0007] Aspect 1: A process for generating a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; separating the syngas stream or a stream derived from the syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce a hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; and combusting a fuel gas to supply heat to the reaction of the reformer feed stream, wherein the fuel gas comprises at least a portion of the hydrogen-enriched permeate stream.

[0008] Aspect 2: A process for generating a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; reacting the syngas stream or a stream derived from the syngas stream in the presence of a first shift catalyst to produce a shifted syngas stream; separating the shifted syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce a hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; and combusting a fuel gas to supply heat to the reaction of the reformer feed stream, wherein the fuel gas comprises at least a portion of the hydrogen-enriched permeate stream.

[0009] Aspect 3: A process for generating a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; reacting the syngas stream or a stream derived from the syngas stream in the presence of a first shift catalyst to produce a shifted syngas stream; reacting the shifted syngas stream in the presence of a second shift catalyst to produce a further shifted syngas stream; separating the further shifted syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce a hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; and combusting a fuel gas to supply heat to the reaction of the reformer feed stream, wherein the fuel gas comprises at least a portion of the hydrogen-enriched permeate stream.

[0010] Aspect 4: A process for producing a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; combining an oxygen-rich gas with the syngas stream in the presence of a secondary reforming catalyst to partially oxidize and react the syngas stream to produce a reacted syngas stream; reacting the reacted syngas stream in the presence of a first shift catalyst to produce a shifted syngas stream; reacting the shifted syngas stream in the presence of a second shift catalyst to produce a further shifted syngas stream; separating the further shifted syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce a hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; and burning a fuel gas to supply heat to the reaction of the reformer feed stream, wherein the fuel gas comprises at least a portion of the hydrogen-enriched permeate stream.

[0011] Aspect 5: A process for generating a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; combining an oxygen-rich gas with the syngas stream in the presence of a secondary reforming catalyst to partially oxidize and react the syngas stream to produce a reacted syngas stream; reacting the reacted syngas stream in the presence of a first shift catalyst to produce a shifted syngas stream; separating the shifted syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce a hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; and combusting a fuel gas to supply heat to the reaction of the reformer feed stream, wherein the fuel gas comprises at least a portion of the hydrogen-enriched permeate stream.

[0012] Aspect 6: A process for generating a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; combining an oxygen-rich gas with the syngas stream in the presence of a secondary reforming catalyst to partially oxidize and react the syngas stream to produce a reacted syngas stream; separating the reacted syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce a hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; and combusting a fuel gas to supply heat to the reaction of the reformer feed stream, wherein the fuel gas comprises at least a portion of the hydrogen-enriched permeate stream.

[0013] Aspect 7: The process according to aspect 3 or 4, wherein the temperature of the syngas stream is higher than the temperature of the shifted syngas stream.

[0014] Aspect 8: The process according to any one of aspects 1 to 7, wherein the reaction of the reformer feed stream is carried out in a plurality of catalyst-containing reformer tubes.

[0015] Aspect 9: The process according to any one of aspects 1 to 8, further comprising combining at least a portion of the hydrogen-depleted residue stream with the reformer feed stream.

[0016] Aspect 10: The process according to any one of aspects 4 to 6, further comprising pre-combining at least a portion of the hydrogen-depleted residue stream with the reacted syngas stream.

[0017] Aspect 11: The process according to any one of aspects 1 to 10, further comprising reacting a pre-reformer feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide in the presence of a pre-reforming catalyst to produce a reformer feed stream.

[0018] Aspect 12: The process according to aspect 11, further comprising combining at least a portion of the hydrogen-depleted residue stream with the pre-reformer feed stream.

[0019] Aspect 13: The process according to any one of aspects 1 to 12, wherein the separation of the hydrogen-depleted tail gas stream by selective permeation also produces a second hydrogen-enriched permeate stream, and further comprising combining the second hydrogen-enriched permeate stream with the hydrogen-depleted tail gas stream.

[0020] Aspect 14: The process according to any one of aspects 1 to 13, further comprising dividing at least a portion of the hydrogen-depleted tail gas stream to form a tail gas fuel fraction, and wherein the fuel gas comprises the tail gas fuel fraction.

[0021] Aspect 15: An apparatus for generating a hydrogen-enriched product stream, the apparatus comprising a reformer including a reforming catalyst and one or more burners, the reformer being configured to receive a reformer feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide, contact the reforming catalyst, and generate a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide, the one or more burners being configured to combust a fuel gas in the presence of the reforming catalyst and transfer thermal energy to the reformer feed stream; a carbon dioxide removal system configured to receive the syngas stream or a stream derived from the syngas stream and generate a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; a product purification system comprising an inlet port, a product outlet port, and a tail gas outlet port, configured to receive the carbon dioxide-depleted stream and generate a hydrogen-depleted tail gas stream and a hydrogen-enriched product stream; a membrane separation system comprising an inlet port, a permeate outlet port, and a residue outlet port, configured to receive the hydrogen-depleted tail gas stream and generate a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; a tail gas conduit in fluid communication with the tail gas outlet of the product purification system and the inlet port of the membrane separation system; and a fuel gas conduit in fluid communication with the one or more burners and the permeate outlet port of the membrane separation system.

[0022] Aspect 16: The apparatus according to aspect 15, further comprising one or more water gas shift reactors in series downstream of the reformer and upstream of the carbon dioxide removal system.

[0023] Aspect 17: The apparatus according to aspect 15 or aspect 16, wherein the reformer comprises a plurality of catalyst-containing reformer tubes.

[0024] Aspect 18: The apparatus according to any one of aspects 15 to 17, wherein the residue outlet port of the membrane separation system is in fluid communication with the reformer feed stream.

[0025] Aspect 19: The apparatus according to any one of Aspects 15 to 18, further comprising a secondary reformer located downstream of the reformer and upstream of the carbon dioxide removal system, configured to receive a syngas stream in the presence of an oxygen-rich gas, partially oxidize it, and cause a reaction, wherein the secondary reformer contains a secondary reforming catalyst.

[0026] Aspect 20: The apparatus according to Aspect 19, wherein the residue outlet port of the membrane separation system is in fluid flow communication with the syngas stream upstream of the secondary reformer.

[0027] Aspect 21: The apparatus according to any one of Aspects 15 to 20, further comprising a pre-reformer located upstream of the reformer, configured to receive a pre-reformer feed stream containing methane and a reactant selected from the group consisting of water and carbon dioxide, and generate a reformer feed stream, wherein the pre-reformer contains a pre-reforming catalyst.

[0028] Aspect 22: The apparatus according to Aspect 21, wherein the residue outlet port of the membrane separation system is in fluid flow communication with the pre-reformer feed stream.

[0029] Aspect 23: The apparatus according to any one of Aspects 15 to 22, wherein the tail gas conduit comprises a tail gas compressor.

[0030] Aspect 24: The apparatus according to any one of Aspects 15 to 23, wherein the membrane separation system comprises a second permeate outlet port, and the second permeate outlet port is in fluid flow communication with the tail gas conduit.

[0031] Aspect 25: The apparatus according to any one of Aspects 15 to 24, wherein one or more burners are in fluid flow communication with the tail gas conduit.

Brief Description of the Drawings

[0032] The present disclosure will hereinafter be described in conjunction with the accompanying drawings, wherein like numerals represent like elements.

[0033]

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DETAILED DESCRIPTION OF THE INVENTION

[0034] The following detailed description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the following detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. Various changes can be made to the functions and arrangements of the elements without departing from the spirit and scope of the invention as set forth in the appended claims.

[0035] As used herein, the articles "a" or "an", when applied to any feature in the embodiments of the invention described herein and in the claims, mean one or more. The use of "a" and "an" does not limit the meaning to a single feature unless such a limitation is specifically stated. The article "the", preceding a singular or plural noun or noun phrase, indicates a particular specified feature or particular specified features and may have a singular or plural implication depending on the context in which it is used.

[0036] The phrase "at least in part" means "part or all". "At least in part of the stream" has the same composition, having each of the species at the same concentration as the stream from which it is derived.

[0037] The term "and / or", placed between a first entity and a second entity, includes any of (1) the first entity only, (2) the second entity only, or (3) the first entity and the second entity. The term "and / or", placed between the last two entities of a list of three or more entities, means at least one of the entities in the list, including any specific combination of the entities in this list. For example, "A, B, and / or C" has the same meaning as "A and / or B and / or C" and includes the following combinations of A, B, and C: (1) A only, (2) B only, (3) C only, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, (7) A and B and C.

[0038] The adjective "any" means one, some, or all of a quantity without distinction.

[0039] The terms "depleted" or "dilute" mean that the indicated component has a lower mole percent concentration than the original stream from which it was formed. "Depleted" and "dilute" do not mean that the stream is completely lacking in the indicated component.

[0040] The term "rich" or "enriched" means that the indicated component has a higher mole percent concentration than the original stream from which it was formed.

[0041] "Downstream" and "upstream" refer to the intended flow direction of the transferred process fluid. If the intended flow direction of the process fluid is from a first device to a second device, the second device is downstream of the first device. In the case of a recirculation flow, downstream and upstream refer to the first pass of the process fluid.

[0042] The term "indirect heat exchange" refers to a process in which sensible and / or latent heat is transferred between two or more fluids without the fluids in question physically contacting each other. Heat can be transferred through the walls of a heat exchanger or by using an intermediate heat transfer fluid. The term "hot stream" refers to any stream that exits the heat exchanger at a lower temperature than it entered. Conversely, a "cold stream" is one that exits the heat exchanger at a higher temperature than it entered.

[0043] Figure 1 shows an embodiment of a reforming process 1 for producing hydrogen from a hydrocarbon feedstock and capturing carbon dioxide. The hydrocarbon feedstock includes at least one hydrocarbon species having one or more carbon atoms and can be linear, branched, cyclic, or aromatic. The hydrocarbon feedstock can include both saturated and unsaturated hydrocarbon species. The hydrocarbon feedstock can be derived from natural gas, liquefied petroleum gas, refined off-gas, naphtha, and / or other feedstocks known in the art.

[0044] A reformer feed stream 10 containing steam and a hydrocarbon feedstock enters a plurality of catalyst-containing reformer tubes 104 within a reformer furnace 100. In the plurality of catalyst-containing reformer tubes 104, the hydrocarbon feedstock reacts with the steam at a temperature in the range of 700 °C to 1000 °C and a pressure in the range of 2 to 50 atmospheres to form a syngas stream 12 containing hydrogen, carbon monoxide, and carbon dioxide.

[0045] A reformer furnace having a plurality of catalyst-containing reformer tubes, i.e., tubular reformers, is well known to those skilled in the art. Suitable materials and construction methods are known. The catalyst in the catalyst-containing reformer tube 104 may be any suitable catalyst or combination of catalysts known in the art, for example, a supported catalyst containing nickel.

[0046] In at least some embodiments, the reformer feed stream 10 may be produced by an optional pre-reformer 80 defined as any unignited vessel that converts a hydrocarbon feedstock by reacting with steam over a catalyst, with or without heating. The pre-reformer 80 can be a fixed bed reactor or a tubular reactor. The pre-reformer may, in at least some aspects, use a different type of catalyst than the catalyst-containing reformer tube 104, for example, a high activity, high nickel content catalyst. In the embodiment shown in FIG. 1, a pre-reformer feed stream 14 containing steam and a hydrocarbon feedstock enters the pre-reformer 80. In the presence of the pre-reforming catalyst 84, the hydrocarbon feedstock reacts with steam at a temperature in the range of 400°C to 600°C and a pressure in the range of 2 to 50 atmospheres to form the reformer feed stream 10. The hydrocarbon feedstock in the pre-reformer feed stream 14 and the reformer feed stream 10 may include one or more compositions that can vary due to the reforming reaction in the pre-reformer. For example, propane and butane in the pre-reformer feed stream 14 can react to form methane in the reformer feed stream 10.

[0047] The pre-reforming catalyst 84 may include at least one metal selected from the group consisting of nickel, cobalt, platinum, palladium, rhodium, ruthenium, iridium, and mixtures thereof. For example, reforming catalysts suitable for pre-reforming as described in U.S. Patent No. 4,105,591, U.S. Patent No. 3,882,636, U.S. Patent No. 3,988,425, British Patent No. 969,637, British Patent No. 1,150,066, and British Patent No. 1,155,843 may be used in at least some aspects.

[0048] The pre-reforming catalyst 84 can exist in a variety of shapes or forms, such as, for example, cylindrical pellets, Raschig rings, multi-hole catalysts, or other forms known in the art. In at least some exemplary embodiments, the catalyst size can range from about 1 mm to about 15 mm in diameter and from about 3 mm to 10 mm in length. The preferred size for a given application depends on many factors, including the catalyst shape and nickel loading, operating temperature, pressure, and feed composition, as well as the allowable pressure drop. A catalyst having a multi-hole shape with a diameter in the range of 5 mm to 25 mm and a ratio of height to diameter of 0.5 to 1.2 is also suitable for the pre-reforming catalyst 84. One skilled in the art can select a suitable catalyst having a suitable shape for the pre-reforming catalyst 84.

[0049] In at least some exemplary embodiments, the re-reforming catalyst 84 can also be a structured packing catalyst where the catalyst is applied as a washcoat on a structured packing. Structured packings are known to those skilled in the art. As used herein, the term "structured packing" means a flow guide having a plurality of substantially parallel passages. Substantially parallel means parallel within manufacturing tolerances. U.S. Patent No. 4,340,501 to Davidson describes a structure in a reactor vessel that would be suitable for a pre-reforming catalyst of structured packing that intermittently but controllably contacts a fluid with a vessel wall.

[0050] In at least some embodiments, the syngas stream 12 can be further combined with a secondary feed stream 28 and reformed in an optional secondary reforming reactor 20. The secondary reforming reactor 20 can also combine an oxygen-rich gas 26 with the syngas stream 12 to partially oxidize the syngas stream 12 and react it in the presence of a secondary reforming catalyst 24 to further convert unreacted hydrocarbon species to produce carbon monoxide and hydrogen and form a reacted syngas stream 22. In at least some embodiments, the oxygen-rich gas 26 can be combined with the syngas stream 12 before the secondary reforming reactor 20 or, for example, can be combined with the syngas stream 12 in the secondary reforming reactor 20 by a burner.

[0051] The secondary feed stream 28 may be introduced into the syngas stream 12 before the resulting mixture is introduced into the secondary reformer 20. The feed gas 28 may be introduced into the syngas stream 12 in the secondary reformer 20. In most embodiments, the oxygen-rich gas will be introduced into the secondary reformer 20 separately from the secondary feed stream 28 and the syngas stream 12. The hydrocarbon source of the secondary feed stream 28 may be the same as the hydrocarbon source of the reformer feed stream 10 and / or the pre-reformer feed stream 14.

[0052] Providing a feed gas containing at least one hydrocarbon and reacting the feed gas in the secondary reformer 20 makes it possible to reform additional hydrocarbon feedstock without increasing the size of the reformer furnace 100 and, accordingly, the size of the plurality of catalyst-containing reformer tubes. One skilled in the art can suitably optimize the size and amount of the feedstock processed in the reformer furnace 100 and the secondary reformer 20. Another advantage provided by the secondary reformer 20 is that the fuel requirements in the reformer furnace 100 are reduced.

[0053] Secondary reformers are well known in the art and are widely used for the production of ammonia and methanol. A secondary reformer is a refractory-lined vessel equipped with one or more burners and a reforming catalyst bed. The heat required for the reforming reaction can be provided by partial oxidation (combustion) of a portion of the feed. The effluent from the primary reformer can be fed to a secondary reformer where it is mixed with oxygen supplied through the burners. The partial oxidation reaction occurs in a reaction zone adjacent to or immediately below the burner. The partially oxidized mixture then passes through a catalyst bed where the mixture is substantially thermodynamically equilibrated over the reforming catalyst. U.S. Patent No. 3,479,298, which is incorporated herein by reference, discloses a secondary reformer for the production of a hydrogen-containing gas and discloses that when oxygen is used in place of air, the process gas exiting the secondary reformer is a gas suitable for further processing to obtain methanol or high-purity hydrogen. Tindall et al., “Alternative technologies to steam-methane reforming,” Hydrocarbon Processing, pp. 75-82, November, 1995 also disclose an oxygen secondary reformer for producing hydrogen.

[0054] In at least some embodiments of the present disclosure, the reacted syngas stream 22 is cooled in a heat exchanger system 30 comprising a boiler for generating steam 36 from a moisture-containing stream 34 by indirect heat exchange with the reacted syngas stream 22. The cooled syngas stream 32 is produced by the heat exchanger system 30. The heat exchanger system 30 can also utilize the heat from the reacted syngas stream 22 to provide the heating duty required by the SMR process to improve the overall thermal efficiency, such as preheating the reformer feed stream 10.

[0055] Using the first water gas shift reactor 40, carbon monoxide in the cooled syngas stream 32 can be reacted with water in the presence of a shift catalyst 44 to produce a shifted syngas stream 42 containing more hydrogen. The cooled syngas stream 32 enters at a first temperature, and in an exemplary embodiment where the first aqueous gas shift reactor 40 is an adiabatic reactor, the temperature of the cooled syngas stream 32 increases for the exothermic shift reaction. When the first water gas shift reactor 40 is cooled, the cooled syngas stream 32 may remain at a constant temperature or may be cooled overall. Optionally, a first additional steam 46 can be introduced into the reactor to shift the equilibrium towards more hydrogen and carbon dioxide to enhance the water gas shift (WGS) reaction. The WGS catalyst can be an iron-based high-temperature WGS catalyst, a copper-based medium-temperature WGS catalyst, a copper-based low-temperature WGS catalyst, or any other suitable WGS catalyst, as can be selected by those skilled in the art. The first shift catalyst 44 may include iron oxide, and the reaction temperature may be 310°C to 500°C or 310°C to 400°C. The first shift catalyst 44 may also include copper, and the reaction temperature may be 200°C to 400°C or 200°C to 350°C. In at least some exemplary embodiments, the shifted syngas stream 42 can enter a second water gas shift reactor 50 equipped with a second shift catalyst 54 at a second temperature to produce a further shifted syngas stream 52. Optionally, a second additional steam (not shown) can be introduced into the second water gas shift reactor 50. The second temperature may be lower than the first temperature to enable the shifted syngas stream 42 to react more carbon monoxide with water to produce hydrogen when the equilibrium moves towards hydrogen at a lower temperature. The second shift catalyst 54 may include copper and / or zinc oxide, and the reaction temperature may range from 190°C to 300°C. The second temperature may also be the same as the first temperature or higher than the first temperature, for example, when the cooled syngas stream 32 increases in temperature in the first water gas shift reactor 40, and then the shifted syngas stream 42 may be cooled before entering the second water gas shift reactor 50.

[0056] Carbon dioxide is further removed from the further shifted syngas stream 52 in the carbon dioxide removal system 60. The carbon dioxide removal system 60 may include a gas scrubber where the scrubbing stream 64 contacts the further shifted syngas stream 52 to produce a carbon dioxide depleted syngas stream 62 and a carbon dioxide enriched scrubbing stream 66. The scrubbing stream 64 may be, for example, N-methyldiethanolamine (aMDEA), monoethanolamine (MEA), other amine-based systems, or other scrubbing methods such as Rectisol®, Selexol®, Genosorb®, and other scrubbing fluids associated with Sulfinol, or any scrubbing fluid known in the art.

[0057] The carbon dioxide depleted syngas stream 62 is supplied to the inlet port of the product purification unit 70 and produces a hydrogen enriched product stream 72 that exits through the product outlet port and a hydrogen depleted tail gas stream 76 that contains hydrogen, methane, and carbon monoxide and exits through the tail gas outlet port. This product purification unit may be a pressure swing adsorption unit for a hydrogen production process. In at least some embodiments, at least a portion of the tail gas stream 76 may be compressed in the tail gas compressor 75 to produce a compressed tail gas stream 78.

[0058] The compressed tail gas stream 78 enters the inlet port of a membrane separation system 90 that may comprise a single membrane stage or multiple membrane stages in series and / or in parallel. The compressed tail gas stream 78 is separated by selective permeation into a hydrogen enriched permeate stream 92 that exits through the permeate outlet port and a hydrogen depleted residue stream 94 that exits through the residue outlet port. Hydrogen permeates the membrane selectively over slower species such as methane and carbon monoxide. Due to the small size of hydrogen molecules, the diffusion rate is high, and thus it is expected to permeate faster than methane and carbon monoxide through most membrane materials.

[0059] Sanders et al (Polymer; vol 54; pp4729-4761; 2013) provide a convenient summary of current membrane technologies. They describe the physical parameters and performance characteristics of polymer membranes including polystyrene, polysulfone, polyethersulfone, polyvinyl fluoride, polyvinylidene fluoride, polyetheretherketone, polycarbonate, polyphenylene oxide, polyethylene, polypropylene, cellulose acetate, polyimides (such as Matrimid 5218 or P-84), polyamides, polyvinyl alcohol, polyvinyl acetate, polyethylene oxide, polydimethylsiloxane, copolymers, block copolymers, or polymer blends. Existing industrially useful gas separations are mainly carried out with polymers such as those listed above, or rubbery materials such as silicone. Additional membrane materials may include mixed matrix membranes, perfluoropolymers, thermally rearranged polymers, facilitated transport membranes, metal organic frameworks, zeolite-imidazolate frameworks, electrochemical membranes, metal membranes, and carbon molecular sieves. The membrane material in the membrane separation system 90 can be any of those listed above, or any other material that has a faster permeation rate for some compounds such as hydrogen and a slower permeation rate for some compounds such as methane and carbon monoxide. In an exemplary embodiment where the membrane material contains a metal that is highly selective for hydrogen such as palladium, the membrane separation system 90 would operate at a high temperature such as 280 - 440 °C.

[0060] Suitable membrane materials may be manufactured as hollow fibers and packaged as a membrane bundle, or manufactured as flat sheets and packaged as spiral wound or plate-frame units and housed in a module to provide a larger surface area to volume ratio. The gas entering the module contacts the membrane and a small amount of gas permeates through the membrane and exits the module as a low-pressure permeate stream. The faster permeating gas is concentrated in the permeate relative to the slower permeating gas. The small amount of gas that does not permeate through the membrane exits the module as a non-permeate stream, or residue stream, that is concentrated in the slower permeating gas relative to the faster permeating gas.

[0061] In at least some exemplary embodiments, if any compounds that impair the operation of the membrane are present, such as hydrocarbons (hexane and heavy alkanes) and / or aromatic compounds such as benzene, toluene, and xylene (collectively known as BTX), the compressed tail gas stream 78 may be treated prior to being introduced into the membrane separation system 90. The pretreatment can be carried out by adsorption, absorption, or partial condensation. In at least some embodiments, pretreatment may not be necessary since it is expected that the reforming reaction in the upstream catalyst-containing reformer tube 104 will consume any hazardous compounds.

[0062] At least a portion of the hydrogen-enriched permeate stream 92 is combusted as fuel gas 74 in one or more burners 102 to supply heat to the reformer furnace 100 to drive the endothermic reforming reaction in the catalyst-containing reformer tubes 104. The fuel gas 74 may also include a tail gas fuel fraction 77 formed by splitting a portion of the hydrogen-depleted tail gas stream 76. In at least some embodiments, the tail gas fuel fraction 77 may also function as a purge stream to allow slow-permeating inert components rejected by the membrane separation system 90, such as nitrogen and / or argon, to exit the system. Since the slow-permeating inert components are not consumed in the reforming reaction, the main route for exiting the process is through one or more burners 102. In at least some embodiments, the fuel gas 74 may include a hydrogen product fuel fraction 73 formed by splitting a portion of the hydrogen-enriched product stream 72 and / or auxiliary fuel 18. The flue gas 110 exiting the reformer furnace 100 may provide the heating duty required by the SMR process to improve the overall thermal efficiency, such as preheating the reformer feed stream 10. According to at least some embodiments of the present disclosure, the flue gas 110 of the disclosed process and apparatus has a reduced amount of carbon dioxide compared to existing processes where the hydrogen-depleted tail gas stream can be combusted within the reformer furnace 100. In at least some exemplary embodiments, reducing the flow rate of the tail gas fuel fraction 77 increases the overall carbon capture rate as the carbon-containing species exiting via the flue gas 110 decrease, but the load on the product purification unit 70 increases as more inert gas is supplied to it. This presents a trade-off where a higher carbon capture percentage requires a higher load on the product purification unit 70.

[0063] The hydrogen-depleted residual stream 94 is recycled to the steam methane reforming process by combining it with the reformer feed stream 10. In at least some embodiments, the hydrogen-depleted residual stream 94 can first be heated by one or more high-temperature streams such as the reacted syngas stream 22, the flue gas 110, and steam. According to at least some embodiments of the present disclosure, by recycling the hydrogen-depleted residual stream 94, additional carbon-containing compounds such as methane and carbon monoxide in the residual stream 94 are converted to carbon dioxide and can be captured by the carbon dioxide removal system 60, which can reduce the amount of carbon dioxide discharged from the reforming process. The carbon dioxide emissions in the flue gas 110 can be adjusted by changing the amount of the hydrogen product fuel fraction 73, the amount of the tail gas fuel fraction 77, and the amount of the auxiliary fuel 18 used as fuel.

[0064] Most of the carbon-containing compounds in the tail gas 76 are separated in the membrane separation system 90 into the hydrogen-depleted residual stream 94 and recycled to the reforming process. In at least some aspects where the fuel gas 74 consists mainly of the hydrogen product fuel fraction 73 and the hydrogen-enriched permeate stream 92, the carbon dioxide emissions in the flue gas 110 can be substantially reduced compared to existing processes. In at least some aspects, the tail gas fuel fraction 77 can be used as the fuel gas 74 to reduce the accumulation of inert gases (e.g., nitrogen and argon) in the process stream. In some embodiments of the present disclosure, a portion of the tail gas 76 may be used in another process and / or discarded. For example, a portion of the compressed retenate may be sent for use as fuel for another process located near the hydrogen plant, such as a fired heater or a boiler.

[0065] The hydrogen-depleted residue stream 94 can typically be recycled to other locations upstream of the reformer. FIG. 2 shows an alternative embodiment of FIG. 1 in which the hydrogen-depleted residue stream 94 is combined with the pre-reformer feed stream 14. FIG. 3 shows an alternative embodiment of FIG. 1 in which the hydrogen-depleted residue stream 94 is combined with the syngas stream 12 upstream of the secondary reformer 20. In at least some embodiments, the hydrogen-depleted residue stream 94 may be combined with the cooled syngas stream 32 upstream of the first water gas shift reactor 40 or with a shifted syngas stream 42 (not shown) upstream of the second water gas shift reactor 50.

[0066] The flowsheet shown in FIG. 4 shows an embodiment of the reforming process 4 according to an additional exemplary embodiment of the present disclosure in which the carbon dioxide removal system 60 comprises an adsorption system such as a vacuum swing adsorption system. Hsu et al. (US8,709,136) teach one such adsorption system that can be used to remove carbon dioxide from a syngas stream. The carbon dioxide-enriched blowdown gas 166 may be at low pressure or vacuum. In at least some aspects, an optional rinse stream 164 may be used to improve recovery.

[0067] The flowsheet shown in FIG. 5 shows an embodiment of the reforming process 5 according to an additional exemplary embodiment of the present disclosure in which the membrane separation system includes two stages, a first stage 90A and a second stage 90B. The hydrogen-depleted residue stream 94 enters the inlet port of the second stage 90B. A second hydrogen-depleted residue stream 594 exits through the second residue outlet port and is combined with the reformer feed stream 10. A second hydrogen-enriched permeate stream 592 exits through the second permeate stream outlet and may be combined with the hydrogen-depleted tail gas stream 76 upstream of the tail gas compressor 75. According to at least some embodiments of the present disclosure, using two stages of membrane separation can reduce the amount of hydrogen recycled to the reformer feed stream 100 and improve the overall efficiency of the reforming process. The tail gas compressor 75 provides an efficient point for recycling the low-pressure stream exiting the membrane separation system without incurring the cost of an additional compressor.

[0068] According to at least some embodiments of the present disclosure, carbon dioxide capture can be enhanced by injecting more carbon dioxide into the process into any of the pre-reformer feed stream 14, reformer feed stream 10, syngas stream 12, secondary feed stream 28, and / or hydrogen-depleted residue stream 94. In some aspects, the carbon dioxide can partially or completely replace the steam during the reforming reaction. The carbon dioxide functions as a reactant with the hydrocarbon feedstock, similar to how steam is a reactant with the hydrocarbon feedstock during steam reforming. Substantially, dry reforming can be considered stoichiometrically equivalent to a combination of a steam reforming reaction and a reverse water gas shift reaction, as shown below.

[0069] CO2 + CH4 = 2H2 + 2CO (dry reforming)

[0070] H2O + CH4 = 3H2 + CO (steam reforming)

[0071] CO2 + H2 = CO + H2O (reverse water gas shift)

[0072] The flow sheet shown in FIG. 6 shows an embodiment of a reforming process 6 according to an additional exemplary embodiment of the present disclosure, in which a portion of the reformer feed stream 10 is split to form a regenerative reformer feed stream 614 and is supplied to a regenerative reformer 680. The regenerative reformer is a heat exchanger that transfers heat to drive the catalytic reforming reaction. This enables more reforming reactions to be driven using more process heat, which is particularly relevant for applications that require low or zero export steam. In at least some embodiments, steam (not shown) may be added to the regenerative reformer feed stream 614 upstream of the regenerative reformer 680. The regenerative reformer 680 may be implemented in a shell and tube arrangement. In the exemplary embodiment shown in FIG. 6, the regenerative reformer feed stream 614 enters the tube side 684 of the regenerative reformer 680 that contains the regenerative reforming catalyst. The syngas stream 12 enters the shell side, provides heat to the regenerative reformer feed stream 614, which reacts in the presence of the regenerative reforming catalyst to form a regenerative reformer outlet stream 682. The regenerative reformer outlet stream 682 is combined with the cooled syngas stream 686 and may optionally be supplied to a secondary reformer 20, such as in reforming process 1. In at least some embodiments, at least a portion of the hydrogen-depleted residual stream 94 may be combined with the regenerative reformer feed stream 614 (not shown).

[0073] The flow sheet diagram shown in FIG. 7 shows an embodiment of a reforming process 7 according to an additional exemplary embodiment of the present disclosure, in which the regenerative reformer outlet stream 682 is combined with the syngas stream 12 before entering the high temperature side of the regenerative reformer 680. The piping of the regenerative reformer may be simplified according to the exemplary embodiment shown, for example, the mixing point of the regenerative reformer outlet stream 682 and the syngas stream 12 may occur within the regenerative reformer 680. In at least some embodiments, at least a portion of the hydrogen-depleted residual stream 94 may be combined with the regenerative reformer feed stream 614 (not shown).

Examples

[0074] It should be clearly understood that the principles of the present disclosure have been described above in connection with preferred embodiments, but this description is for illustrative purposes only and is not intended to limit the scope of the present disclosure.

[0075] An embodiment of the reforming process 1 of FIG. 1 using a single-stage membrane was analyzed using commercially available Aspen™ process modeling software and compared to a modification of FIG. 1 where the membrane separation system 90 was eliminated and the compressed tail gas stream 78 was combined directly with the reformer feed stream 10. For both processes, 100,000 Nm3 / hr (9000 kg / hr) of hydrogen was produced and 96% of the carbon dioxide produced in the overall process was captured. Table 1 compares the performance of the utility consumption and performance parameters of the reforming process 1 with and without the membrane. The export steam is sent to the battery limit at 750°F and 625 psia. The derate is defined as the reduction in hydrogen production normalized to the same natural gas input compared to a process that does not capture carbon dioxide. The reduction in hydrogen production is substantially equal to the amount of hydrogen product that must be burned in the burner as the hydrogen product fuel fraction 73.

[0076] As can be seen in Table 1, when using the membrane separation system 90, the lower derate of the reforming process 1 with the membrane compared to without the membrane indicates that less product hydrogen has to be burned in the furnace. Correspondingly, the total natural gas consumption of the reforming process 1 is also lower with the membrane. The reforming process 1 with the membrane has a higher compressor power consumption for the tail gas, mainly due to the larger recycle loop causing a higher flow rate of the tail gas entering the compressor. The energy cost (defined as the net energy consumed in the process minus the heat value of the exported steam divided by the hydrogen production rate) is lower for the reforming process 1 with the membrane. The lower export steam flow rate indicates that the membrane separation system 90 is more efficient in converting natural gas to hydrogen and results in less waste heat being converted to steam.

Table 1

Claims

Claim 1 A process for generating a hydrogen-enriched product stream, the process comprising: reacting a reformer feed stream comprising a hydrocarbon feedstock and a reactant selected from the group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; separating the syngas stream or a stream derived from the syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream to produce the hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; separating the hydrogen-depleted tail gas stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted residue stream; burning a fuel gas to supply heat to the reaction of the reformer feed stream; and the fuel gas comprising at least a portion of the hydrogen-enriched permeate stream. Claim 2 further comprising reacting the syngas stream or a stream derived from the syngas stream in the presence of a first shift catalyst to produce a shifted syngas stream prior to separation and produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; the syngas stream or a stream derived from the syngas stream having a first temperature, the process of claim 1. Claim 3 further comprising reacting the shifted syngas stream in the presence of a second shift catalyst to produce a further shifted syngas stream prior to separation and produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; the shifted syngas stream having a second temperature, the process of claim 2. Claim 4 the first temperature being greater than the second temperature, the process of claim 3. Claim 5 the reaction of the reformer feed stream being carried out in a plurality of catalyst-containing reformer tubes, the process of claim 1. Claim 6 further comprising combining at least a portion of the hydrogen-depleted residue stream with the reformer feed stream, the process of claim 1. Claim 7 further comprising combining an oxygen-rich gas with the syngas stream in the presence of a secondary reforming catalyst to partially oxidize and react the syngas stream prior to separation and produce a carbon dioxide-rich stream and a carbon dioxide-depleted stream, the process of claim 1. Claim 8 The process according to claim 7, further comprising combining at least a portion of the hydrogen-depleted residual stream with the syngas stream before combining with the oxygen-rich gas in the presence of the secondary reforming catalyst.

9. The process according to claim 1, further comprising reacting a pre-reformer feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide in the presence of a pre-reforming catalyst to produce the reformer feed stream.

10. The process according to claim 9, further comprising combining at least a portion of the hydrogen-depleted residual stream with the pre-reformer feed stream.

11. The process according to claim 1, further comprising compressing the hydrogen-depleted tail gas stream before separation by selective permeation.

12. Separation of the hydrogen-depleted tail gas stream by selective permeation also produces a second hydrogen-enriched permeate stream, The process according to claim 1, further comprising combining the second hydrogen-enriched permeate stream with the hydrogen-depleted tail gas stream.

13. The process according to claim 1, further comprising dividing at least a portion of the hydrogen-depleted tail gas stream to form a tail gas fuel fraction, The fuel gas comprising the tail gas fuel fraction.

14. An apparatus for producing a hydrogen-enriched product stream, the apparatus comprising A reformer comprising a reforming catalyst and one or more burners, the reformer configured to receive a reformer feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide, contact the reforming catalyst, and produce a syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide, The one or more burners configured to burn a fuel gas in the presence of the reforming catalyst and transfer thermal energy to the reformer feed stream, a reformer; A carbon dioxide removal system configured to receive the syngas stream or a stream derived from the syngas stream and produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; A product purification system comprising an inlet port, a product outlet port, and a tail gas outlet port configured to receive the carbon dioxide-depleted stream and produce a hydrogen-depleted tail gas stream and the hydrogen-enriched product stream; A membrane separation system comprising an inlet port, a permeate outlet port, and a residue outlet port configured to receive the hydrogen-depleted tail gas stream and produce a hydrogen-enriched permeate stream and a hydrogen-depleted residual stream; A tail gas conduit that is in fluid flow communication with the tail gas outlet of the product purification system and the inlet port of the membrane separation system; A fuel gas conduit that is in fluid flow communication with the one or more burners and the permeate outlet port of the membrane separation system. An apparatus comprising. **Claim 15** The apparatus according to claim 14, further comprising one or more water gas shift reactors that are in series downstream of the reformer and upstream of the carbon dioxide removal system. **Claim 16** The apparatus according to claim 14, wherein the reformer comprises a plurality of catalyst-containing reformer tubes. **Claim 17** The apparatus according to claim 14, wherein the residue outlet port of the membrane separation system is in fluid flow communication with the reformer feed stream. **Claim 18** Further comprising a secondary reformer that is located downstream of the reformer and upstream of the carbon dioxide removal system, and is configured to receive the syngas stream in the presence of an oxygen-rich gas, partially oxidize it, and cause a reaction. The apparatus according to claim 14, wherein the secondary reformer contains a secondary reforming catalyst. **Claim 19** The apparatus according to claim 18, wherein the residue outlet port of the membrane separation system is in fluid flow communication with the syngas stream upstream of the secondary reformer. **Claim 20** Further comprising a pre-reformer that is located upstream of the reformer and is configured to receive a pre-reformer feed stream containing methane and a reactant selected from the group consisting of water and carbon dioxide, and generate the reformer feed stream. The apparatus according to claim 14, wherein the pre-reformer contains a pre-reforming catalyst. **Claim 21** The apparatus according to claim 20, wherein the residue outlet port of the membrane separation system is in fluid flow communication with the pre-reformer feed stream. **Claim 22** The apparatus according to claim 14, wherein the tail gas conduit comprises a tail gas compressor. **Claim 23** The membrane separation system comprises a second permeate outlet port. The apparatus according to claim 14, wherein the second permeate outlet port is in fluid flow communication with the tail gas conduit. **Claim 24** The apparatus according to claim 14, wherein the one or more burners are in fluid flow communication with the tail gas conduit.

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