Steam hydrocarbon reforming with reduced carbon dioxide emissions

Abstract

A hydrogen production process with low carbon emissions may be achieved by first separating carbon dioxide from a reformer syngas stream and then purifying the carbon dioxide depleted syngas 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 combustor and the hydrogen-depleted retentate is recycled to the feed.

Description

Background Art

[0001] Existing industrial processes for producing hydrogen and syngas, such as reforming hydrocarbon feeds will require the capture of 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 fuel gas to generate the heat required to drive the reforming reaction. Air-fired combustion produces flue gas, where 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. Capturing carbon from flue gas is expensive, inefficient and general. In air-fired combustion, the removal of carbon from the fuel gas enables the effective capture of nearly 100% of the CO2 in the process by capturing the CO2 in the syngas, which has a much higher CO2 concentration and pressure.

[0002] Licht et al. (US 8,137,422) teach 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 using the product hydrogen to supply a majority of the fuel gas.

[0003] Adamopoulos et al. (US 9,517,933) teach a process for recovering hydrogen from the tail gas from the hydrogen purification step to improve the overall hydrogen recovery.The non-permeate stream is recycled to a point downstream of the catalytic reformer.

[0004] Guo et al. (WO 2013 / 131916) teach a process for operating an SMR process with high pressure tail gas, which is separated in a membrane system without using a compressor. The permeate stream is used as a fuel gas in the furnace, and the non-permeate stream is recycled to the SMR feed.

[0005] It is desirable to produce hydrogen using an SMR process that reduces CO2 emissions with minimal increase in total energy cost, which is defined herein as the net energy in MJ (hydrocarbon feed and fuel consumed minus steam exported) divided by the total hydrogen product in kg. Summary of the invention

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

[0007] Aspect 1: 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 a group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; separating the synthesis gas stream or a stream derived from the synthesis gas 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 retentate stream; burning a fuel gas to provide heat for 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 producing a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and reactants selected from a group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; reacting the synthesis gas stream or a stream derived from the synthesis gas stream in the presence of a first shift catalyst to produce a shifted synthesis gas stream; separating the synthesis gas stream or a stream derived from the synthesis gas 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 retentate stream; burning a fuel gas to provide 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 producing a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and reactants selected from a group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; reacting the synthesis gas stream or a stream derived from the synthesis gas stream in the presence of a first shift catalyst to produce a shifted synthesis gas stream; reacting the shifted synthesis gas stream in the presence of a second shift catalyst to produce another shifted synthesis gas stream; separating the synthesis gas stream or a stream derived from the synthesis gas 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 retentate stream; burning a fuel gas to provide heat to the reaction of the reformer feed stream; wherein the fuel gas includes 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 reactants selected from a group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; combining an oxygen-rich gas with the synthesis gas stream in the presence of a secondary reforming catalyst to partially oxidize and react the synthesis gas stream to produce a reacted synthesis gas stream; reacting the reacted synthesis gas stream in the presence of a first shift catalyst to produce a shifted synthesis gas stream; reacting the shifted synthesis gas stream in the presence of a second shift catalyst to produce another shifted synthesis gas stream; separating the synthesis gas stream or a stream derived from the synthesis gas 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 retentate stream; burning a fuel gas to provide heat to the reaction of the reformer feed stream; wherein the fuel gas includes at least a portion of the hydrogen-enriched permeate stream.

[0011] Aspect 5: A process for producing a hydrogen-enriched product stream, the process comprising reacting a reformer feed stream comprising a hydrocarbon feedstock and reactants selected from a group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; combining an oxygen-rich gas with the synthesis gas stream in the presence of a secondary reforming catalyst to partially oxidize and react the synthesis gas stream to produce a reacted synthesis gas stream; reacting the synthesis gas stream or a stream derived from the synthesis gas stream in the presence of a first shift catalyst to produce a shifted synthesis gas stream; separating the synthesis gas stream or a stream derived from the synthesis gas 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 retentate stream; burning a fuel gas to provide heat to the reaction of the reformer feed stream; wherein the fuel gas includes at least a portion of the hydrogen-enriched permeate stream.

[0012] Aspect 6: 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 a group consisting of water and carbon dioxide in the presence of a reforming catalyst to produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; combining an oxygen-rich gas with the synthesis gas stream in the presence of a secondary reforming catalyst to partially oxidize and react the synthesis gas stream to produce a reacted synthesis gas stream; separating the synthesis gas stream or a stream derived from the synthesis gas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; reacting the synthesis gas stream or a stream derived from the synthesis gas stream in the presence of a first shift catalyst to produce a shifted synthesis gas 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 retentate stream; burning a fuel gas to provide heat to the reaction of the reformer feed stream; wherein the fuel gas includes at least a portion of the hydrogen-enriched permeate stream.

[0013] Aspect 7: The process according to Aspect 3 or Aspect 4, wherein the temperature of the synthesis gas stream is greater than the temperature of the shifted synthesis gas stream.

[0014] Aspect 8: The process according to any one of Aspects 1 to 7, wherein the reaction of the reformer feed stream occurs within a plurality of reformer tubes containing the catalyst.

[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 retentate stream with the reformer feed stream.

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

[0019] Aspect 13: The process according to any one of aspects 1 to 12, wherein separating the hydrogen-depleted tail gas stream by selective permeation also produces a second hydrogen-enriched permeate stream; and the process further comprises 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 separating at least a portion of the hydrogen-depleted tail gas stream to form a tail gas fuel fraction; wherein the fuel gas comprises the tail gas fuel fraction.

[0021] Aspect 15: An apparatus for producing a hydrogen-enriched product stream, the apparatus comprising a reformer comprising a reforming catalyst and one or more burners, wherein the reformer is configured to receive a reformer feed stream comprising methane and reactants selected from the group consisting of water and carbon dioxide to contact the reforming catalyst and produce a synthesis gas stream comprising hydrogen, carbon monoxide and carbon dioxide; wherein the one or more burners are configured to combust fuel gas in the presence of the reforming catalyst and transfer heat energy to the reformer feed stream; a carbon dioxide removal system, the carbon dioxide removal system configured to receive the synthesis gas stream or a stream derived from the synthesis gas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; product purification A system, the product purification system comprising an inlet port, a product outlet port and a tail gas outlet port, the product purification system being configured to receive the carbon dioxide-depleted stream to produce a hydrogen-depleted tail gas stream and the hydrogen-enriched product stream; a membrane separation system, the membrane separation system comprising an inlet port, a permeate outlet port and a retentate outlet port, the membrane separation system being configured to receive the hydrogen-depleted tail gas stream to produce a hydrogen-enriched permeate stream and a hydrogen-depleted retentate stream; a tail gas conduit being fluidly connected to the tail gas outlet of the product purification system and the inlet port of the membrane separation system; and a fuel gas conduit being fluidly connected to 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 connected 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 reformer tubes containing the catalyst.

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

[0025] Aspect 19: An apparatus according to any one of Aspects 15 to 18, the apparatus further comprising a secondary reformer located downstream of the reformer and upstream of the carbon dioxide removal system, the secondary reformer being configured to receive the synthesis gas flow in the presence of an oxygen-rich gas and partially oxidize and react the synthesis gas flow; wherein the secondary reformer comprises a secondary reforming catalyst.

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

[0027] Aspect 21: An apparatus according to any one of Aspects 15 to 20, the apparatus further comprising a pre-reformer located upstream of the reformer, the pre-reformer being configured to receive a pre-reformer feed stream comprising methane and reactants selected from a group consisting of water and carbon dioxide to produce the reformer feed stream; wherein the pre-reformer comprises a pre-reforming catalyst.

[0028] Aspect 22: The apparatus according to Aspect 21, wherein the retentate 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; wherein 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 the one or more burners are in fluid flow communication with the tail gas conduit. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present disclosure will be described below with reference to the accompanying drawings, wherein like numerals represent like elements:

[0033] Figure 1 is a diagram depicting an embodiment of a reforming process according to one or more aspects of the present disclosure, wherein a portion of the tail gas is compressed and separated in a membrane. The hydrogen-enriched permeate is used as fuel gas, and the hydrogen-depleted retentate stream is recycled to the reformer feed.

[0034] Figure 2 It is a depiction Figure 1 Schematic representation of an improvement of the embodiment in which the hydrogen-depleted retentate stream is recycled to the pre-reformer feed.

[0035] Figure 3 It is a depiction Figure 1 Schematic representation of an improvement of the embodiment in which the hydrogen-depleted retentate stream is recycled to the secondary reforming reactor feed.

[0036] Figure 4 It is a depiction Figure 1 Schematic diagram of an improvement to an embodiment in which an adsorption system is used to capture carbon dioxide.

[0037] Figure 5 It is a depiction Figure 1 Schematic diagram of a modification of the embodiment in which a second hydrogen-enriched permeate is removed from the second stage membrane and recycled to the tail gas.

[0038] Figure 6 It is a depiction Figure 1 Schematic diagram of a modification of the embodiment in which a portion of the reformer feed is fed to a recuperative reformer and heated by the synthesis gas stream.

[0039] Figure 7 It is a depiction Figure 6 Schematic representation of an improvement of an embodiment in which the recuperative reformer is heated by a combination of synthesis gas and recuperative reformer outlet gas. DETAILED DESCRIPTION

[0040] The subsequent detailed description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability or configuration of the present invention. On the contrary, the subsequent detailed description of the preferred exemplary embodiments will provide an enabling description for implementing the preferred exemplary embodiments of the present invention to those skilled in the art. Various changes may be made to the functions and arrangements of the elements without departing from the spirit and scope of the present invention as described in the appended claims.

[0041] As used herein, the articles "a" or "an" mean one or more when applied to any feature in the embodiments of the present invention described in the specification and claims. The use of "a" and "an" does not limit the meaning to a single feature unless such limitation is explicitly stated. The article "the" preceding a singular or plural noun or noun phrase means one or several of the specific specified features and can have a singular or plural meaning depending on the context in which it is used.

[0042] The phrase "at least a portion" means "a portion or all." "At least a portion of the stream" has the same composition as the stream from which it is derived, with the concentration of each species being the same.

[0043] The term "and / or" placed between a first entity and a second entity includes any meaning of (1) only the first entity, (2) only the second entity, 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 that at least one entity in the list includes any specific combination of the entities in the 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) only A, (2) only B, (3) only C, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A, B, and C.

[0044] The adjective "any" means one, some, or all, without distinction of quantity.

[0045] The terms "depleted" or "lean" mean having a lower mole percent concentration of the named component than the original stream from which the original stream was formed. "Depleted" and "lean" do not mean that the stream is completely devoid of the named component.

[0046] The term "rich" or "enriched" means having a higher mole percent concentration of the indicated component than a raw stream from which the raw stream was formed.

[0047] "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 recirculating flow, downstream and upstream refer to the first passage of the process fluid.

[0048] The term "indirect heat exchange" refers to the process of transferring sensible and / or latent heat between two or more fluids without the fluids in question being in physical contact with one another. Heat can be transferred through the walls of a heat exchanger or using an intermediate heat transfer fluid. The term "hot stream" refers to any stream that leaves a heat exchanger at a lower temperature than the temperature at which it entered. Conversely, a "cold stream" is a cold stream that leaves a heat exchanger at a higher temperature than the temperature at which it entered.

[0049] Figure 1 An embodiment of a reforming process 1 for producing hydrogen and capturing carbon dioxide from a hydrocarbon feedstock is shown. The hydrocarbon feedstock includes at least one hydrocarbon material having one or more carbon atoms, and may be straight chain, branched, cyclic or aromatic. The hydrocarbon feedstock may include saturated hydrocarbon materials and unsaturated hydrocarbon materials. The hydrocarbon feedstock may be derived from natural gas, liquefied petroleum gas, refinery offgas, naphtha and / or other feedstocks known in the art.

[0050] A reformer feed stream 10 including steam and a hydrocarbon feedstock enters a plurality of catalyst-containing reformer tubes 104 in the reformer furnace 100. In the plurality of catalyst-containing reformer tubes 104, the hydrocarbon feedstock reacts with steam at a temperature of 700° C. to 1000° C. and a pressure of 2 to 50 atmospheres to form a synthesis gas stream 12 including hydrogen, carbon monoxide, and carbon dioxide.

[0051] Reformer furnaces having a plurality of catalyst-containing reformer tubes, i.e., tubular reformers, are well known in the art. Suitable materials and construction methods are known. The catalyst in the catalyst-containing reformer tubes 104 can be any suitable catalyst or combination of catalysts known in the art, such as a supported catalyst including nickel.

[0052] In at least some embodiments, the reformer feed stream 10 can be generated by an optional pre-reformer 80, which is defined as any uncalcined vessel that converts a hydrocarbon feedstock with or without heating by reaction with steam over a catalyst. The pre-reformer 80 can be a fixed bed reactor or a tubular reactor. In at least some aspects, the pre-reformer can employ a different type of catalyst than the catalyst-containing reformer tubes 104, such as a high activity, high nickel content catalyst. Figure 1 In the embodiment shown, a pre-reformer feed stream 14 comprising steam and a hydrocarbon feedstock enters a pre-reformer 80. In the presence of a 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 a 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 may vary due to the reforming reaction in the pre-reformer. For example, propane and butane in the pre-reformer feed stream 14 may react to form methane in the reformer feed stream 10.

[0053] The pre-reforming catalyst 84 may include at least one metal selected from nickel, cobalt, platinum, palladium, rhodium, ruthenium, iridium, and mixtures thereof. Reforming catalysts suitable for pre-reforming may be used in at least some aspects, such as those discussed in US 4,105,591, US 3,882,636, US 3,988,425, GB 969,637, GB 1,150,066, and GB 1,155,843.

[0054] The pre-reforming catalyst 84 can exist in various shapes or forms, such as cylindrical pellets, Raschig rings, porous catalysts, etc. or other forms known in the art. In at least some exemplary embodiments, the diameter of the catalyst size can be in the range of about 1 mm to about 15 mm, and the length of the catalyst can be in the range of about 3 mm to 10 mm. The preferred size for a given application depends on many factors, including catalyst shape and nickel loading, operating temperature, pressure and feed composition, and allowable pressure drop. Porous catalysts with a diameter of 5 mm to 25 mm and a height-to-diameter ratio of 0.5 to 1.2 are also suitable for pre-reforming catalysts 84. Those skilled in the art can select a suitable catalyst with a suitable shape for the pre-reforming catalyst 84.

[0055] In at least some exemplary implementations, the re-reforming catalyst 84 may also be a structured packing catalyst, wherein the catalyst is applied as a carrier coating on the structured packing. Structured packing is known in the art. As used herein, the term "structured packing" means a guide plate having a plurality of substantially parallel channels. Substantially parallel means parallel within manufacturing tolerances. Davidson, U.S. Pat. No. 4,340,501 describes a structure in a reactor vessel in which a fluid is intermittently but controllably in contact with the vessel wall, which would be suitable for a structured packing pre-reforming catalyst.

[0056] In at least some embodiments, the syngas stream 12 may also be combined with a secondary feed stream 28 and reformed in an optional secondary reforming reactor 20. The secondary reforming reactor 20 may 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 may be combined with the syngas stream 12 prior to the secondary reforming reactor 20, or may be combined with the syngas stream 12 in the secondary reforming reactor 20, for example, via a burner.

[0057] The secondary feed stream 28 may be introduced into the synthesis gas stream 12 prior to introducing the resulting mixture into the secondary reforming reactor 20. The feed gas 28 may be introduced into the synthesis gas stream 12 in the secondary reforming reactor 20. In most embodiments, the oxygen-rich gas will be introduced into the secondary reforming reactor 20 separately from the secondary feed stream 28 and the synthesis gas stream 12. The hydrocarbon source for the second feed stream 28 may be the same as the hydrocarbon source for the reformer feed stream 10 and / or the pre-reformer feed stream 14.

[0058] Providing a feed gas including at least one hydrocarbon and reacting the feed gas in the secondary reforming reactor 20 allows reforming additional hydrocarbon feedstock without increasing the size of the reformer furnace 100 and the corresponding plurality of catalyst-containing reforming tubes. Those skilled in the art can appropriately optimize the size and amount of feedstock processed in the reformer furnace 100 and the secondary reforming reactor 20. Another benefit provided by the secondary reforming reactor 20 is a reduction in fuel demand in the reformer furnace 100.

[0059] Secondary reforming reactors are well known in the art and are widely used in the production of ammonia and methanol. A secondary reforming reactor is a refractory lined vessel 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 the secondary reforming reactor, where the effluent is mixed with oxygen fed by the burner. The partial oxidation reaction occurs in a reaction zone adjacent to the burner or just below the burner. The partially oxidized mixture then passes through a catalyst bed, where the mixture is substantially thermodynamically balanced on the reforming catalyst. U.S. Patent No. 3,479,298 is incorporated herein by reference, and discloses a secondary reformer for producing hydrogen-containing gas, and discloses that if oxygen is used instead of air, the process gas leaving the secondary reformer is a gas suitable for further processing to produce methanol or high-purity hydrogen. Tindall et al., "Alternative technologies to steam-methane reforming," Hydrocarbon Processing, pp. 75-82, November 1995, also discloses an oxygen secondary reformer for producing hydrogen.

[0060] In at least some embodiments of the present disclosure, the reacted syngas stream 22 is cooled in a heat exchanger system 30 that includes a boiler to produce steam 36 from an aqueous 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 heat from the reacted syngas stream 22 to provide heating duties required by the SMR process to improve overall thermal efficiency, such as preheating the reformer feed stream 10.

[0061] The first water-gas shift reactor 40 can be used to react the carbon monoxide in the cooled syngas stream 32 with water in the presence of a shift catalyst 44 to produce a shifted syngas stream 42 including more hydrogen. The cooled syngas stream 32 enters at a first temperature, and in an exemplary embodiment where the first water-gas shift reactor 40 is an adiabatic reactor, the cooled syngas stream 32 increases in temperature due to the exothermic shift reaction. In the case where the first water-gas shift reactor 40 is cooled, the cooled syngas stream 32 can maintain a constant temperature or be cooled as a whole. In order to enhance the water-gas shift (WGS) reaction, a first additional steam 46 can be optionally introduced into the reactor to shift the balance to more hydrogen and carbon dioxide. The WGS catalyst can be an iron-based high-temperature WGS catalyst, or a copper-based medium-temperature WGS catalyst, a copper-based low-temperature WGS catalyst, or any other suitable WGS catalyst that can be selected by a person skilled in the art. The first shift catalyst 44 can include iron oxide and the reaction temperature can be 310°C to 500°C or 310°C to 400°C. The first shift catalyst 44 may include copper and the reaction temperature may be 200°C to 400°C or 200°C to 350°C. In at least some exemplary implementations, the shifted syngas stream 42 may enter a second water-gas shift reactor 50 having a second shift catalyst 54 at a second temperature to produce another shifted syngas stream 52. A second additional steam (not shown) may be optionally introduced into the second water-gas shift reactor 50. Since the equilibrium shifts toward hydrogen at a lower temperature, the second temperature may be lower than the first temperature to allow the shifted syngas stream 42 to react more carbon monoxide with water to produce hydrogen. The second shift catalyst 54 may include copper oxide and / or zinc oxide, and the reaction temperature may be 190°C to 300°C. The second temperature may also be the same as or higher than the first temperature, for example, when the temperature of the cooled syngas stream 32 in the first water-gas shift reactor 40 increases, the shifted syngas stream 42 may be cooled before entering the second water-gas shift reactor 50.

[0062] In the carbon dioxide removal system 60, carbon dioxide is removed from the further shifted syngas stream 52. The carbon dioxide removal system 60 may include a gas scrubber, wherein a scrubber stream 64 is contacted with the further shifted syngas stream 52 to produce a carbon dioxide-depleted syngas stream 62 and a carbon dioxide-enriched scrubber stream 66. The scrubber stream 64 may be any scrubbing fluid known in the art, such as N-methyldiethanolamine (aMDEA), monoethanolamine (MEA), other amine-based systems, or other scrubbing fluids associated with other scrubbing processes, such as and Sulfinol.

[0063] The carbon dioxide-depleted synthesis gas stream 62 is fed to the inlet port of a product purification unit 70 to produce a hydrogen-enriched product stream 72 exiting via a product outlet port and a hydrogen-depleted tail gas stream 76 including hydrogen, methane, and carbon monoxide exiting via a tail gas outlet port. The product purification unit may be a pressure swing absorption 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 a tail gas compressor 75 to produce a compressed tail gas stream 78.

[0064] The compressed tail gas stream 78 enters the inlet port of a membrane separation system 90, which may include a single membrane stage or multiple membrane stages in series and / or parallel. The compressed tail gas stream 78 is separated by selective permeation into a hydrogen-enriched permeate stream 92 that leaves via a permeate outlet port and a hydrogen-depleted retentate stream 94 that leaves via a retentate outlet port. Hydrogen selectively permeates slower species, such as methane and carbon monoxide. Due to the small size of hydrogen molecules, hydrogen molecules have a high diffusion rate, so for most membrane materials, it is expected that hydrogen molecules will permeate faster than methane and carbon monoxide.

[0065] Sanders et al. (Polymer; Vol. 54; pp. 4729-4761; 2013) provide a convenient overview of current membrane technology. They describe the physical parameters and performance characteristics of polymer membranes, which include polystyrene, polysulfone, polyethersulfone, polyvinyl fluoride, polyvinylidene fluoride, polyetheretherketone, polycarbonate, polyphenylene oxide, polyethylene, polypropylene, cellulose acetate, polyimide (such as Matrimid 5218 or P-84), polyamide, polyvinyl alcohol, polyvinyl acetate, polyethylene oxide, polydimethylsiloxane, copolymer, block copolymer or polymer blend. Mainly use polymers, such as those listed above or rubber materials, such as siloxane to carry out existing industrially useful gas separation. Other membrane materials can 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 includes a metal that is highly selective for hydrogen, such as palladium, the membrane separation system 90 will be operated at a high temperature, such as between 280° C. and 440° C.

[0066] Suitable membrane materials can be manufactured as hollow fibers and packaged into membrane bundles, or can be manufactured as flat sheets, packaged into spiral wound units or plate-and-frame units, to provide a large surface area to volume ratio and accommodated in modules. Gas entering the module contacts the membrane, and a portion of the gas permeates the membrane and leaves the module as a low-pressure permeate stream. The faster permeating gas will be enriched in the permeate relative to the slower permeating gas. The portion of the gas that has not permeated the membrane leaves the module in a non-permeate or retentate stream, which is enriched in the slower permeating gas relative to the faster permeating gas.

[0067] In at least some exemplary implementations, if there are any compounds that would impair membrane operation, such as heavy hydrocarbons (hexanes and heavy alkanes) and / or aromatic compounds such as benzene, toluene, and xylenes (collectively referred to as BTX), the compressed tail gas stream 78 may be treated prior to introduction into the membrane separation system 90. Pretreatment may be performed by adsorption, absorption, or partial condensation. In at least some embodiments, pretreatment will not be necessary because the reforming reaction in the upstream catalyst-containing reformer tubes 104 will be expected to consume any hazardous compounds.

[0068] At least a portion of the hydrogen-enriched permeate stream 92 is combusted as a fuel gas 74 in one or more burners 102, which provide heat to the reformer furnace 100 to drive the endothermic reforming reaction in the reformer furnace tubes 104 containing the catalyst. The fuel gas 74 may also include a tail gas fuel fraction 77 formed by separating a portion of the hydrogen-depleted tail gas stream 76. In at least some aspects, the tail gas fuel fraction 77 may also serve as a purge stream to allow slow-permeating inert components, such as nitrogen and / or argon, discharged by the membrane separation system 90 to leave the system. Since the slow-permeating inert components are not consumed in the reforming reaction, the main way to leave the process is through one or more burners 102. In at least some aspects, the fuel gas 74 may include a hydrogen product fuel fraction 73 formed by separating a portion of the hydrogen-enriched product stream 72 and / or the supplemental fuel 18. The flue gas 110 leaving the reformer furnace 100 can provide the heating duty required for the SMR process to improve the overall thermal efficiency, such as preheating the reforming feed stream 10. According to at least some embodiments of the present disclosure, the flue gas 110 in the disclosed process and apparatus includes a reduced amount of carbon dioxide compared to prior art processes in which hydrogen-depleted tail gas steam 76 may be combusted in the reformer furnace 100. In at least some exemplary implementations, reducing the flow rate of the tail gas fuel fraction 77 will increase the overall carbon capture percentage as less carbonaceous material exits via the flue gas 110, however, the load on the product purification unit 70 will increase as more inert gas is fed into the product purification unit. This provides a tradeoff in which a higher carbon capture percentage requires a higher load on the product purification unit 70.

[0069] The hydrogen-depleted retentate stream 94 is recycled to the steam methane reforming process by combining with the reformer feed stream 10. In at least some embodiments, the hydrogen-depleted retentate stream 94 can be first heated by one or more hot streams such as the reacted synthesis gas stream 22, the flue gas 110, and steam. According to at least some embodiments of the present disclosure, recycling the hydrogen-depleted retentate stream 94 allows additional carbon-containing compounds such as methane and carbon monoxide in the retentate stream 94 to be converted to carbon dioxide and captured by the carbon dioxide removal system 60, which can reduce the amount of carbon dioxide emitted from the reforming process. The amount of carbon dioxide emissions in the flue gas 110 can be adjusted by changing the amount of hydrogen product fuel fraction 73 used as fuel, the amount of tail gas fuel fraction 77, and the amount of supplemental fuel 18.

[0070] In at least some aspects, most of the carbon-containing compounds in the tail gas 76 are separated into a hydrogen-depleted retentate stream 94 in the membrane separation system 90 and recycled to the reforming process, and the fuel gas 74 is mainly composed of a hydrogen product fuel fraction 73 and a hydrogen-enriched permeate stream 92, and the carbon dioxide emissions in the flue gas 110 can be significantly reduced compared to the existing process. In at least some aspects, the tail gas fuel fraction 77 can be used as a 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 can be used for another process and / or be processed, for example, a portion of the compressed retentate can be sent to be used as a fuel for another process (e.g., a roasting heater or boiler) located near the hydrogen station.

[0071] The hydrogen-depleted retentate stream 94 may be recycled to another location, typically upstream of the reforming reactor. Figure 2 Shows Figure 1 An alternative embodiment of wherein the hydrogen-depleted retentate stream 94 is combined with the pre-reformer feed stream 14. Figure 3 Shows Figure 1 In an alternative embodiment, the hydrogen-depleted retentate stream 94 is combined with the syngas stream 12 upstream of the secondary reforming reactor 20. In at least some embodiments, the hydrogen-depleted retentate stream 94 can be combined with the cooled syngas stream 32 upstream of the first water-gas shift reactor 40 or with the shifted syngas stream 42 upstream of the second water-gas shift reactor 50 (not shown).

[0072] Figure 4The flow chart shown in shows an embodiment of the reforming process 4 according to another exemplary embodiment of the present disclosure, wherein the carbon dioxide removal system 60 includes an adsorption system, such as a vacuum pressure swing adsorption system. Hsu et al. (US8,709,136) teach an adsorption system of this type that can be used to remove carbon dioxide from a synthesis gas stream. The carbon dioxide enriched vent gas 166 can be at a low pressure or vacuum. In at least some aspects, an optional flushing stream 164 can be used to improve recovery.

[0073] Figure 5 The flowchart shown in shows an embodiment of the reforming process 5 according to another exemplary embodiment of the present disclosure, wherein the membrane separation system includes two stages, namely the first stage 90A and the second stage 90B. The hydrogen-depleted permeate stream 94 enters the inlet port of the second stage 90B. The second hydrogen-depleted permeate stream 594 leaves via the second permeate outlet port and is combined with the reformer feed stream 10. The second hydrogen-enriched permeate stream 592 leaves via the second permeate outlet port and can 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, the use of two-stage membrane separation can reduce the amount of hydrogen recycled to the reformer feed stream 100, improving the overall efficiency of the reforming process. The tail gas compressor 75 provides an effective point for recycling the low-pressure stream leaving the membrane separation system without the cost of an additional compressor.

[0074] According to at least some embodiments of the present disclosure, carbon dioxide capture can be enhanced by injecting more carbon dioxide into the process of any one of the pre-reformer feed stream 14, the reformer feed stream 10, the synthesis gas stream 12, the secondary feed stream 28 and / or the hydrogen-depleted retentate stream 94. In some aspects, carbon dioxide can partially or completely replace steam in the reforming reaction. Carbon dioxide is used as a reactant with the hydrocarbon feedstock, just as steam is a reactant with the hydrocarbon feedstock in steam reforming. Effectively, dry reforming can be considered to be stoichiometrically equivalent to a combination of a steam reforming reaction and a reverse WGS reaction as shown below.

[0075] CO2+CH4=2H2+2CO (dry reforming)

[0076] H2O+CH4=3H2+CO (steam reforming)

[0077] CO2+H2=CO+H2O (reverse WGS)

[0078] Figure 6The flow chart shown in illustrates an embodiment of a reforming process 6 according to another exemplary embodiment of the present disclosure, wherein a portion of the reformer feed stream 10 is split to form a regenerative reformer feed stream 614 and fed to a regenerative reformer 680. A regenerative reformer is a heat exchanger that transfers heat to drive catalytic reforming reactions. This allows more process heat to be used to drive more reforming reactions, which is particularly relevant for applications requiring low or zero output 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 as a shell and tube arrangement. In Figure 6 In the exemplary embodiment shown, a regenerative reformer feed stream 614 enters a tube side 684 of a regenerative reformer 680, which includes a regenerative reforming catalyst. Synthesis gas stream 12 enters the shell side to provide 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 a cooled synthesis gas stream 686 and can optionally be fed to a secondary reformer 20 as in the reforming process 1. In at least some embodiments, at least a portion of the hydrogen-depleted retentate stream 94 can be combined with the regenerative reformer feed stream 614 (not shown).

[0079] Figure 7 The flow diagram shown in shows an embodiment of a reforming process 7 according to additional exemplary embodiments of the present disclosure, wherein a regenerative reformer outlet stream 682 is combined with a synthesis gas stream 12 prior to entering the hot side of a regenerative reformer 680. According to the depicted exemplary embodiment, the piping of the regenerative reformer can be simplified, for example, the mixing point of the regenerative reformer outlet stream 682 and the synthesis gas stream 12 can occur within the regenerative reformer 680. In at least some embodiments, at least a portion of the hydrogen-depleted retentate stream 94 can be combined with a regenerative reformer feed stream 614 (not shown).

[0080] Example

[0081] Although the principles of the present disclosure have been described above in conjunction with the preferred embodiments, it should be clearly understood that this description is made by way of example only and not as a limitation of the scope of the present disclosure.

[0082] The commercially available Aspen TM Process model software analysis Figure 1 An embodiment of a reforming process 1 having a single-stage membrane and combining it with Figure 1 A modification of the process was compared in which the membrane separation system 90 was removed and the compressed tail gas stream 78 was combined directly with the reformer feed stream 10. For both processes, 100,000 Nm 3 / hr (9000 kg / hr) of hydrogen and captures 96% of the carbon dioxide produced in the entire process. Table 1 compares the utility consumption performance and performance parameters of the reforming process 1 with and without the membrane. The outlet steam is sent to the cell limit of 750°F and 625 psia. The derating is defined as the reduction in hydrogen production normalized to the same natural gas input compared to the process without carbon dioxide capture. The reduction in hydrogen production is effectively equal to the amount of hydrogen product that must be burned in the combustor as the hydrogen product fuel fraction 73.

[0083] As can be seen from Table 1, the lower derating for the reforming process 1 with membrane compared to the case without membrane indicates that less product hydrogen must be burned in the furnace when the membrane separation system 90 is used. Accordingly, the total natural gas consumption of the reforming process 1 using the membrane is also lower. The reforming process 1 with membrane does have a higher tail gas compressor power consumption, mainly due to the larger recirculation loop resulting in a higher tail gas flow rate entering the compressor. For the reforming process 1 with membrane, the energy cost (defined as the net energy consumed in the process minus the heating value of the output steam divided by the hydrogen production rate) is lower. The lower outlet steam flow rate indicates that the membrane separation system 90 is more efficient in converting natural gas to hydrogen, resulting in less waste heat being converted to steam.

[0084] Table 1

[0085]

Claims

1. 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 synthesis gas stream comprising hydrogen, carbon monoxide, and carbon dioxide; separating the synthesis gas stream or a stream derived from the synthesis gas 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 retentate stream; combusting a fuel gas to provide heat to said reaction of said reformer feed stream; wherein said fuel gas comprises at least a portion of said hydrogen enriched permeate stream.

2. The process of claim 1 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, thereby producing a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; Wherein the syngas stream or a stream derived from the syngas stream has a first temperature.

3. The process of claim 2, further comprising reacting the shifted synthesis gas stream in the presence of a second shift catalyst to produce a further shifted synthesis gas stream prior to separation, thereby producing a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; Wherein the shifted syngas stream has a second temperature.

4. The process of claim 3, wherein the first temperature is greater than the second temperature.

5. The process of claim 1 wherein said reacting of said reformer feed stream occurs within a plurality of catalyst-containing reformer tubes.

6. The process of claim 1 further comprising combining at least a portion of the hydrogen-depleted retentate stream with the reformer feed stream.

7. The process of claim 1, further comprising: An oxygen-rich gas is combined with the syngas stream in the presence of a secondary reforming catalyst to partially oxidize and react the syngas stream prior to separation to produce a carbon dioxide-rich stream and a carbon dioxide-depleted stream.

8. The process of claim 7 further comprising combining at least a portion of the hydrogen-depleted retentate stream with the synthesis gas stream in the presence of the secondary reforming catalyst prior to combining with the oxygen-rich gas.

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

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

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

12. The process of claim 1, wherein separating the hydrogen-depleted tail gas stream by selective permeation also produces a second hydrogen-enriched permeate stream; and the process further comprises The second hydrogen-enriched permeate stream is combined with the hydrogen-depleted tail gas stream.

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

14. An apparatus for producing a hydrogen-enriched product stream, the apparatus comprising: a reformer including a reforming catalyst and one or more burners, wherein the reformer is configured to receive a reformer feed stream including methane and reactants selected from the group consisting of water and carbon dioxide to contact the reforming catalyst and produce a synthesis gas stream including hydrogen, carbon monoxide, and carbon dioxide; wherein the one or more burners are configured to combust 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 to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; a product purification system, the product purification system comprising an inlet port, a product outlet port, and a tail gas outlet port, the product purification system being configured to receive the carbon dioxide-depleted stream to produce a hydrogen-depleted tail gas stream and the hydrogen-enriched product stream; a membrane separation system, the membrane separation system comprising an inlet port, a permeate outlet port, and a retentate outlet port, the membrane separation system being configured to receive the hydrogen-depleted tail gas stream to produce a hydrogen-enriched permeate stream and a hydrogen-depleted retentate stream; an off-gas conduit in fluid flow communication with an off-gas outlet of the product purification system and an inlet port of the membrane separation system; and A fuel gas conduit is in fluid flow communication with the one or more burners and the permeate outlet port of the membrane separation system.

15. The apparatus of claim 14, further comprising one or more water-gas shift reactors connected in series downstream of the reformer and upstream of the carbon dioxide removal system.

16. The apparatus of claim 14, wherein the reformer comprises a plurality of reformer tubes containing a catalyst.

17. The apparatus of claim 14, wherein a retentate outlet port of the membrane separation system is in fluid flow communication with the reformer feed stream.

18. The apparatus of claim 14, further comprising a secondary reformer located downstream of the reformer and upstream of the carbon dioxide removal system, the secondary reformer being configured to receive and partially oxidize and react the synthesis gas stream in the presence of an oxygen-rich gas; The secondary reformer comprises a secondary reforming catalyst.

19. The apparatus of claim 18, wherein the retentate outlet port of the membrane separation system is in fluid flow communication with the synthesis gas stream upstream of the secondary reformer.

20. The apparatus of claim 14, further comprising a pre-reformer located upstream of the reformer, the pre-reformer configured to receive a pre-reformer feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide to produce the reformer feed stream; The pre-reformer comprises a pre-reforming catalyst.

21. The apparatus of claim 20, wherein the retentate outlet port of the membrane separation system is in fluid flow communication with the pre-reformer feed stream.

22. The apparatus of claim 14, wherein the tail gas conduit comprises a tail gas compressor.

23. The apparatus of claim 14, wherein the membrane separation system comprises a second permeate outlet port; Wherein the second permeate outlet port is in fluid flow communication with the tail gas conduit.

24. The apparatus of claim 14, wherein the one or more burners are in fluid flow communication with the tail gas conduit.

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