Steam-hydrocarbon reforming with low steam production

Abstract

The syngas may be generated in the reformer in a manner that minimizes steam generated for output by generating steam upstream of the water gas shift reactor using heat from the syngas stream and superheating the steam. The superheated steam may be combined with the reformer feed stream to improve overall thermal efficiency.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. non-provisional application No. 18 / 109,924, filed February 15, 2023, which is incorporated herein by reference. Background Art

[0003] Existing industrial processes, such as reforming hydrocarbon feeds to produce hydrogen and syngas, will 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 needed to drive the reforming reaction. Air-fired combustion produces a flue gas in which any carbon in the fuel gas is converted to CO2 at low pressure and concentration due to the large amount of inert nitrogen contributed by the air. Capturing carbon from the flue gas is costly, inefficient, and bulky. Eliminating carbon from the fuel gas in air-fired combustion can effectively capture almost 100% of the CO2 in the process by capturing the CO2 in the syngas, which has a much higher concentration and pressure of CO2.

[0004] Typical SMR processes generate excess heat that can be exported as steam to nearby customers, such as refineries. However, in the absence of steam customers, the heat generated by the SMR process must be used internally to maximize the overall thermal efficiency of hydrogen and syngas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present disclosure will be described below with reference to the accompanying drawings, wherein like numerals represent like elements:

[0006] Figure 1 is a diagram depicting an embodiment of a reforming process according to one or more aspects of the present disclosure, wherein heat from syngas is used to boil water and superheat steam for use in the process.

[0007] Figure 2 It depicts Figure 1 FIG. 1 is a diagram of an improvement in which a recuperative reformer is integrated with the reforming process.

[0008] Figure 3 It depicts Figure 1 Figure 1 is an improved diagram of a process for separating hydrogen from a synthesis gas stream upstream of a product purification unit.

[0009] Figure 4 It depicts Figure 3 FIG. 1 is an improved diagram in which the membrane comprises two stages.

[0010] 5 is a diagram depicting a prior art process for producing hydrogen with carbon capture. DETAILED DESCRIPTION

[0011] The following 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 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 present invention. Various changes may be made to the function and arrangement of the elements without departing from the spirit and scope of the present invention as set forth in the appended claims.

[0012] As used herein, the articles "a" or "an" when applied to any feature in the embodiments of the present invention described in the specification and claims mean one or more. 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 denotes one or more specific specified features and, depending on the context in which it is used, can have a singular or plural meaning.

[0013] The phrase "at least a portion" means "a portion or all." "At least a portion of a stream" has the same composition as the stream from which it originated, and has the same concentration of each species.

[0014] The term "and / or" placed between a first entity and a second entity includes any of the following meanings: (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 at least one of the entities in the list, including 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.

[0015] The adjective "any" means one, some, or all, without distinction of quantity.

[0016] The terms "depleted" or "lean" mean that the mole percent concentration of the indicated component is lower than the original stream from which it was formed. "Depleted" and "lean" do not mean that the stream is completely devoid of the indicated component.

[0017] The term "rich" or "enriched" means that the mole percent concentration of the indicated component is greater than the original stream from which it was formed.

[0018] "Downstream" and "upstream" refer to the intended direction of flow of the conveyed process fluid. If the intended direction of flow 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 recirculating flow, downstream and upstream refer to the first pass of the process fluid.

[0019] The term "indirect heat exchange" refers to the process of transferring sensible and / or latent heat between two or more fluids without the fluids coming into physical contact with each other. Heat can be transferred through the walls of the heat exchanger or through the use of 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" refers to a stream that leaves a heat exchanger at a higher temperature than the temperature at which it entered.

[0020] Figure 1 The embodiment of the reforming process 1 for producing hydrogen and capturing carbon dioxide from a hydrocarbon feedstock is shown. The hydrocarbon feedstock comprises at least one hydrocarbon material having one or more carbon atoms and can be straight-chain, branched, cyclic or aromatic. The hydrocarbon feedstock can comprise both saturated hydrocarbon material and unsaturated hydrocarbon material. The hydrocarbon feedstock can be derived from natural gas, liquefied petroleum gas, refinery off-gas, naphtha and / or other raw materials as known in the art.

[0021] A reformer feed stream 10 comprising 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 in the range of 700° C. to 1000° C. and a pressure in the range of 2 atmospheres to 50 atmospheres to form a first synthesis gas stream 12 comprising hydrogen, carbon monoxide, and carbon dioxide.

[0022] 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 comprising nickel.

[0023] The flue gas 110 leaves the reformer furnace 100 and can provide the heating duties required by the SMR process to improve the overall thermal efficiency, such as the shock boiler 112 and the boiler feed water preheater 114. Other heating duties may include preheating the air used in the one or more burners in the reformer furnace. Because the flue gas 110 has had carbon dioxide removed, it has a much lower heat capacity than a typical SMR process. For this reason, heating duties that would normally be applied to the flue gas 110 (such as superheated steam) are instead applied to the third synthesis gas stream 32. The flue gas 110 is then released to provide more heat to the air used in the one or more burners 102, which in turn reduces the fuel required by the one or more burners 102 to provide the same heat input to the reformer tubes 104.

[0024] In at least some embodiments, the reformer feed stream 10 can be generated by an optional pre-reformer 80, which is defined as any unfired vessel that converts a hydrocarbon feedstock by reaction with steam over a catalyst with or without heating. The pre-reformer 80 can be a fixed bed reactor or a tubular reactor. In at least some aspects, the pre-reformer can utilize 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 in , 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 atmospheres 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 comprise one or more compositions that may vary due to the reforming reactions 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. In at least some embodiments, the reformer feed stream may be heated against the flue gas 110 in a feed reheat exchanger 116 after the pre-reformer 80.

[0025] The pre-reforming catalyst 84 may comprise at least one metal selected from the group consisting of nickel, cobalt, platinum, palladium, rhodium, ruthenium, iridium, and mixtures thereof. Reforming catalysts suitable for pre-reforming, such as those discussed in US Pat. Nos. 4,105,591, 3,882,636, 3,988,425, GB 969,637, 1,150,066, and 1,155,843, may be used in at least some aspects.

[0026] The pre-reforming catalyst 84 can exist in a variety of shapes or forms, such as cylindrical pellets, Raschig rings, porous shape 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 allowed pressure drop. Catalysts with a porous shape having a diameter in the range 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.

[0027] In at least some exemplary embodiments, the reforming catalyst 84 may also be a structured packing catalyst, wherein the catalyst is applied to the structured packing as a washcoat. Structured packings are known in the art. As used herein, the term "structured packing" means a flow guide having a plurality of substantially parallel channels. Substantially parallel means parallel within manufacturing tolerances. Davidson, U.S. Patent 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.

[0028] In at least some embodiments, the first 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 first syngas stream 12 to partially oxidize the first 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 second syngas stream 22. In at least some embodiments, the oxygen-rich gas 26 can be combined with the first syngas stream 12 prior to the secondary reforming reactor 20, or can be combined with the first syngas stream 12 in the secondary reforming reactor 20, for example, via a burner.

[0029] Prior to introducing the resulting mixture into the secondary reforming reactor 20, a secondary feed stream 28 can be introduced into the first syngas stream 12. The feed gas 28 can be introduced into the first syngas stream 12 in the secondary reforming reactor 20. In most embodiments, an oxygen-rich gas will be introduced into the secondary reforming reactor 20 separately from the secondary feed stream 28 and the first syngas stream 12. The hydrocarbon source for the secondary feed stream 28 can be the same as the hydrocarbon source used for the reformer feed stream 10 and / or the pre-reformer feed stream 14.

[0030] Providing a feed gas comprising at least one hydrocarbon and reacting the feed gas in the secondary reforming reactor 20 allows additional hydrocarbon feedstock to be reformed without increasing the size of the reformer furnace 100 and, accordingly, the plurality of catalyst-containing reformer tubes. Those skilled in the art can appropriately optimize the size of the reformer furnace 100 and the secondary reforming reactor 20, as well as the amount of feedstock processed therein. Another benefit provided by the secondary reforming reactor 20 is that the fuel requirement in the reformer furnace 100 is reduced.

[0031] Secondary reforming reactor is well known in the art and is widely used in the production of ammonia and methanol. Secondary reforming reactor is a refractory-lined container with one or more burners and a bed of reforming catalyst. 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 it is mixed with the oxygen fed by the burner. The partial oxidation reaction occurs in a reaction zone near or just below the burner. The partially oxidized mixture then passes through the catalyst bed, where the mixture substantially reaches thermodynamic equilibrium on the reforming catalyst. U.S. Patent No. 3,479,298, incorporated herein by reference, 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 disclose an oxygen secondary reformer for producing hydrogen.

[0032] In at least some embodiments of the present disclosure, the second synthesis gas stream 22 is cooled in a first heat exchanger system E1 that includes a boiler to produce a first saturated steam stream 36 from an aqueous stream 34 by indirect heat exchange with the second synthesis gas stream 22. A third synthesis gas stream 32 is produced by the first heat exchanger system E1. The first saturated steam stream 36 can enter a saturated steam header (not shown). The first heat exchanger system E1 can also utilize heat from the second synthesis gas stream 22 to provide the heating duty required by the SMR process to improve overall thermal efficiency, such as preheating the reformer feed stream 10. In at least some embodiments, the temperature of the third synthesis gas stream 32 is in the range of 750F to 1050F, or 800F to 1050F, or 850F to 1050F. In a typical process, the temperature of the third synthesis gas stream 32 will be below 700F to provide sufficient safety margin to prevent failure mechanisms, such as metal dusting.

[0033] In at least some embodiments of the present disclosure, the third synthesis gas stream 32 is cooled in the second heat exchanger system E2, which includes a steam superheater to heat the saturated steam stream 122 and produce a superheated steam stream 124. The fourth synthesis gas stream 126 is produced by the second heat exchanger system E2. The saturated steam 122 can be supplied directly from the outlet of the first heat exchanger system E1 and / or the saturated steam header. The superheated steam stream 124 can be diverted to form a first superheated steam fraction 162 and enter the superheated steam header. In at least some embodiments, a portion of the third synthesis gas stream 32 can be diverted to form a steam superheater bypass stream 33, which is then combined with the fourth synthesis gas stream 136. Changing the fraction of the third synthesis gas stream 32 that bypasses the second heat exchanger system E2 can be used to control the temperature of the fourth synthesis gas stream 126.

[0034] The first water-gas shift reactor 40 can be used to react the carbon monoxide in the fourth syngas stream 126 with water in the presence of a shift catalyst 44 to produce a first shifted syngas stream 42 containing more hydrogen. The fourth syngas stream 126 enters at a first temperature, and in the exemplary embodiment in which the first water-gas shift reactor 40 is an adiabatic reactor, the third syngas stream 32 increases in temperature due to the exothermic shift reaction. In the case in which the first water-gas shift reactor 40 is cooled, the fourth syngas stream 126 can be kept at a constant temperature or cooled as a whole. In order to enhance the water-gas shift (WGS) reaction, at least a portion of the superheated steam stream 124 can be diverted to form a second superheated steam fraction 164, which is then combined with the fourth syngas stream 126. The second superheated steam fraction 164 can be combined with the fourth syngas stream 126 upstream of the first water-gas shift reactor 40 or inside the first water-gas shift reactor 40. The additional steam acts to change the equilibrium to produce more hydrogen and carbon dioxide. The first additional steam 46 can also be optionally introduced into the reactor. The WGS catalyst may be an iron-based high-temperature WGS catalyst, a copper-based intermediate-temperature WGS catalyst, a copper-based low-temperature WGS catalyst, or any other suitable WGS catalyst selected by a person skilled in the art. The first shift catalyst 44 may comprise 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 comprise copper, and the reaction temperature may be 200° C. to 400° C. or 200° C. to 350° C.

[0035] In at least some embodiments of the present disclosure, first shifted syngas stream 42 is cooled in a third heat exchanger system E3, which includes a mixed feed preheater, to heat first mixed feed stream 132 to produce second mixed feed stream 134. A second shifted syngas stream 136 is produced in the third heat exchanger system E3. In at least some embodiments, second mixed feed stream 134 can be heated in heat exchanger 118 against flue gas 110.

[0036] In at least some embodiments of the present disclosure, the second shifted synthesis gas stream 136 is cooled in a fourth heat exchanger system E4, which includes a feed preheater to heat the first feed stream 141 to produce a second feed stream 142. A third shifted synthesis gas stream 143 is produced in the third heat exchanger system E4. The second feed stream 142 can enter the desulfurization unit HDS to remove sulfur-containing materials by reacting with hydrogen to produce hydrogen sulfide (which can be removed by means such as absorption or adsorption), producing a third feed stream 144. The third feed stream 144 can be combined with a steam source to produce the first mixed feed stream 132. The steam source can include any combination of the first saturated steam stream 36, a saturated steam header, a superheated steam stream 124, and a saturated steam header. In Figure 1 In the embodiment shown in , a portion of the superheated steam stream 124 is diverted to form a third superheated steam fraction 166 and combined with the third feed stream 144 to produce the first mixed feed stream 132 .

[0037] In at least some exemplary embodiments, the third shifted syngas stream 143 can enter a second water-gas shift reactor 50 having a second shift catalyst 54 at a second temperature to produce a further shifted syngas stream 52. A second additional steam (not shown) can optionally be introduced into the second water-gas shift reactor 50. The second temperature can be lower than the first temperature to allow the shifted syngas stream 42 to react more carbon monoxide with water to produce hydrogen because the equilibrium shifts towards hydrogen at a lower temperature. The second shift catalyst 54 can comprise copper and / or zinc oxide, and the reaction temperature can be in the range of 190°C to 300°C. The second temperature can also be at the same temperature as the first temperature or a higher temperature than the first temperature, for example, when the third syngas stream 32 is heated in the first water-gas shift reactor 40, the first shifted syngas stream 42 can be cooled before entering the second water-gas shift reactor 50.

[0038] 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 in which 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.

[0039] 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 discharged via a product outlet port and a hydrogen-depleted tail gas stream 76 comprising hydrogen, methane, and carbon monoxide discharged via a tail gas outlet port. The product purification unit can 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 can be compressed in a tail gas compressor 75 to produce a compressed tail gas stream 78.

[0040] 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 connected in series and / or in parallel. The compressed tail gas stream 78 is separated by selective permeation into a hydrogen-enriched permeate stream 92, which is discharged via a permeate outlet port, and a hydrogen-depleted retentate stream 94, which is discharged via a retentate outlet port. Hydrogen selectively permeates through the membrane compared to slower-moving species such as methane and carbon monoxide. Due to the small size of the hydrogen molecule, it has high diffusivity and is therefore expected to permeate faster than methane and carbon monoxide for most membrane materials.

[0041] Sanders et al. (Polymer; Vol. 54; pp. 4729-4761; 2013) provide a convenient summary of current membrane technology. 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, polyimide (such as Matrimid 5218 or P-84), polyamide, polyvinyl alcohol, polyvinyl acetate, polyethylene oxide, polydimethylsiloxane, copolymer, block copolymer or polymer blend. Existing industrially useful gas separation is mainly carried out with polymers (such as those listed above) or rubbery materials (such as silicone). Additional membrane materials can include mixed matrix membranes, perfluoropolymers, thermally rearranged polymers, promoted transport membranes, metal-organic frameworks, zeolite-imidazolium salt 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 in which the membrane material comprises a metal that is highly selective for hydrogen, such as palladium, the membrane separation system 90 will operate at a high temperature, such as between 280° C. and 440° C.

[0042] Suitable membrane materials can be manufactured as hollow fibers and packaged as membrane bundles, or can be manufactured as flat sheets, packaged as spiral wound units or plate-and-frame units to provide a larger surface area to volume ratio and housed in modules. The gas entering the module contacts the membrane, and a portion of the gas permeates through the membrane and leaves the module in the form of a permeate stream at a lower pressure. Relative to the slower permeating gas, the faster permeating gas will be enriched in the permeate. The portion of gas that did not permeate through the membrane leaves the module in the form of a non-permeate stream or retentate stream, which is enriched in the slower permeating gas relative to the faster permeating gas.

[0043] In at least some exemplary embodiments, if there are any compounds that may impair the operation of the membrane, such as heavy hydrocarbons (hexane and heavier alkanes) and / or aromatic hydrocarbons such as benzene, toluene, and xylene (collectively referred to as BTX), the compressed tail gas stream 78 may be treated before being introduced 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 is expected to consume any hazardous compounds.

[0044] At least a portion of the hydrogen-enriched permeate stream 92 is burned 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 reformer tube 104 containing the catalyst. The fuel gas 74 can also include a tail gas fuel fraction 77, which is formed by diverting a portion of the tail gas stream 76 depleted in hydrogen. In at least some aspects, the tail gas fuel fraction 77 can also serve as a purge stream to allow the slow-permeating inert components (such as nitrogen and / or argon) retained by the membrane separation system 90 to leave the system. The slow-permeating inert components are not consumed in the reforming reaction, so the main way to leave the process is through one or more burners 102. In at least some aspects, the fuel gas 74 can include a hydrogen product fuel fraction 73 and / or supplemental fuel 18 formed by diverting a portion of the hydrogen-enriched product stream 72.

[0045] According to at least some embodiments of the present disclosure, the flue gas 110 in the disclosed processes and apparatuses contains a reduced amount of carbon dioxide compared to existing processes in which the hydrogen-depleted tail gas stream 76 may be combusted in the reformer furnace 100. In at least some exemplary embodiments, reducing the flow rate of the tail gas fuel fraction 77 will increase the overall carbon capture percentage because less carbonaceous material is exhausted via the flue gas 110. However, the load on the product purification unit 70 will increase as more inert gas is fed to the product purification unit. This presents a trade-off, where a higher carbon capture percentage requires a higher load on the product purification unit 70.

[0046] 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 first be 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 into 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.

[0047] In at least some aspects in which the majority 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 primarily composed of a hydrogen product fuel fraction 73 and a hydrogen-enriched permeate stream 92, carbon dioxide emissions from the flue gas 110 can be significantly 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 can be used in another process and / or disposed of, for example, a portion of the compressed retentate can be transported for use as fuel for another process located near a hydrogen plant (e.g., a fired heater or boiler).

[0048] The hydrogen-depleted retentate stream 94 may be recycled to another location, typically upstream of a reforming reactor such as the pre-reformer 80 or the secondary reformer 20 .

[0049] According to at least some embodiments of the present disclosure, carbon dioxide capture can be enhanced by injecting more carbon dioxide into any one of the pre-reformer feed stream 14, the reformer feed stream 10, the first 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. In fact, 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.

[0050] CO2+CH4=2H2+2CO (dry reforming)

[0051] H2O+CH4=3H2+CO (steam reforming)

[0052] CO2+H2=CO+H2O (reverse WGS)

[0053] Figure 2 The flow chart shown in illustrates an embodiment of a reforming process 2 according to an additional exemplary embodiment of the present disclosure, wherein a portion of the reformer feed stream 10 is diverted to form a regenerative reformer feed stream 214 and fed to a regenerative reformer 280. 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 important for applications requiring low or zero output steam. In at least some embodiments, steam (not shown) can be added to the regenerative reformer feed stream 214 upstream of the regenerative reformer 280. The regenerative reformer 280 can be implemented in a shell and tube arrangement. In Figure 2 In the exemplary embodiment shown in , the regenerative reformer feed stream 214 enters the tube side 284 of the regenerative reformer 280, which includes a regenerative reforming catalyst. The first synthesis gas stream 12 enters the shell side to provide heat to the regenerative reformer feed stream 214, which reacts in the presence of the regenerative reforming catalyst to form a regenerative reformer outlet stream 282. The regenerative reformer outlet stream 282 is combined with the cooled synthesis gas stream 286 and can be optionally fed to the 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).

[0054] In at least some embodiments, the regenerative reformer outlet stream 282 is diverted via line 288 and combined with the first syngas stream 12 before entering the hot side of the regenerative reformer 280. The piping of the regenerative reformer can be simplified by mixing the regenerative reformer outlet stream 282 and the first syngas stream 12 within the regenerative reformer 280.

[0055] Figure 3The flow chart shown in illustrates an embodiment of the reforming process 3 according to an additional exemplary embodiment of the present disclosure, wherein the membrane is moved upstream of the product purification unit 70. The carbon dioxide depleted synthesis gas stream 62 is fed to the inlet port of a membrane separation system 390, which may include a single membrane stage or multiple membrane stages connected in series and / or parallel. The carbon dioxide depleted synthesis gas stream 62 is separated by selective permeation into a hydrogen enriched permeate stream 392 which is discharged via a permeate outlet port and a hydrogen depleted retentate stream 394 which is discharged via a retentate outlet port. Hydrogen selectively permeates through the membrane compared to slower species such as methane and carbon monoxide. Due to the small size of the hydrogen molecule, it has a high diffusivity and is therefore expected to permeate faster than methane and carbon monoxide for most membrane materials. With Figure 1 As in the embodiment of the present invention, the carbon dioxide-depleted syngas stream 62 may be pretreated, for example to remove trace amine vapors, if protection of the membrane material is desired.

[0056] The hydrogen-enriched permeate stream 392 enters the product purification unit 70 to produce a hydrogen-enriched hydrogen product 72 and a hydrogen-depleted tail gas stream 376. In at least some embodiments, the membrane separation system 390 is designed to deliver the hydrogen-enriched permeate stream 392 at a sufficiently high pressure to feed the product purification unit 70 without the need for compression, which typically requires more membrane modules and / or a lower degree of hydrogen enrichment in the membrane separation system. The hydrogen-depleted tail gas stream 376 has had most of the methane and carbon monoxide removed in the upstream membrane separation system 390 and can therefore be directed to one or more combustors 102. At least a portion of the hydrogen-depleted retentate stream 394 can be combined with the first feed stream 141, as Figure 3 , or may be combined (not shown) with any other feed stream, such as the second feed stream 142 or the third feed stream 144. At least a portion of the hydrogen-depleted retentate stream 394 may be combined (not shown) with the pre-reformer feed stream 14 or the synthesis gas stream 12 upstream of the secondary reforming reactor 20. If desired, the hydrogen-depleted retentate stream 394 may be compressed (not shown).

[0057] Figure 4 The flow chart shown in shows an embodiment of the reforming process 4 according to an additional exemplary embodiment of the present disclosure, wherein the membrane separation system is a two-step process. The carbon dioxide-depleted synthesis gas stream 62 is fed to the inlet port of the first membrane separation step 490A and is separated by selective permeation into a first hydrogen-enriched permeate stream 492 discharged via a first permeate outlet port and a first hydrogen-depleted retentate stream 494 discharged via a first retentate outlet port. The hydrogen-enriched permeate stream 492 enters the membrane separation step 490A. Figure 3The product purification unit 70 in the embodiment of the present invention is not included in the product purification unit 70, but the first hydrogen-depleted retentate stream 494 enters the inlet port of the second membrane separation step 490B. If necessary, the first hydrogen-depleted retentate stream 494 can be compressed (not shown). The first hydrogen-depleted retentate stream 494 is separated by selective permeation into a second hydrogen-enriched permeate stream 496 discharged via a second permeate outlet port and a second hydrogen-depleted retentate stream 498 discharged via a second retentate outlet port. The second hydrogen-enriched permeate stream 496 can be directed to one or more combustors 102, and the second hydrogen-depleted retentate stream 498 can be combined with the first feed stream 141, or can be combined with any other feed stream such as the second feed stream 142 or the third feed stream 144 (not shown). If necessary, the second hydrogen-depleted retentate stream 498 can be compressed (not shown).

[0058] The flow diagram shown in FIG5 illustrates an embodiment of a prior art reforming process 5 in which the third synthesis gas stream 32 exits the first heat exchanger system El and enters the high temperature shift reactor 40 without recovering additional heat.

[0059] Although the principles of the present disclosure have been described above in conjunction with preferred embodiments, it should be clearly understood that this description is made by way of example only and is not intended to limit the scope of the present disclosure. Those skilled in the art will appreciate that various modifications and alternatives to the specific embodiments described in detail can be developed based on the overall teachings of the present disclosure. Therefore, any features and / or elements described herein can be combined with each other in any combination and still fall within the scope of the present disclosure.

[0060] Example

[0061] Commercially available Aspen TM Process modeling software to analyze Figure 1 An embodiment of the reforming process 1 with zero steam output is shown in Figure 5 and compared to a prior art process in which steam is produced for output in Figure 5. For both processes, 95% of the carbon dioxide produced in the overall process is captured. Table 1 compares the performance of utility consumption and performance parameters for the reforming process 1 with and without a membrane. The outlet steam is sent to the battery limit at 750°F and 625 psia. Derate is defined as the reduction in hydrogen production normalized to the same natural gas input compared to a 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.

[0062] As can be seen in Table 1, the lower derate for Reforming Process 1 compared to the prior art process indicates that the overall efficiency of the process is improved when steam export is eliminated. The lower derate indicates that less product hydrogen must be used in the furnace. Figure 1 In the case of the PSA, less exhaust gas from the PSA is burned in the burner 102. The temperature of the air entering the burner 102 is much higher than in the prior art due to the improved heat integration that reduces the fuel demand for heating the reformer tubes. In effect, the heat that would otherwise be used to generate export steam is used to improve the net efficiency of the process.

[0063] Table 1

[0064]

Claims

1. A method for producing a synthesis gas stream, the method 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 first synthesis gas stream comprising hydrogen, carbon monoxide, and carbon dioxide; transferring heat from the first syngas stream or a stream derived from the syngas stream to a water stream to produce a second syngas stream and a first saturated steam stream; transferring heat from the second syngas stream to a second saturated steam stream to produce a superheated steam stream and a third syngas stream; reacting the third syngas stream in the presence of a first shift catalyst to produce a first shifted syngas stream; wherein the second saturated steam flow comprises at least a portion of the first saturated steam flow.

2. The process of claim 1, wherein the reformer feed stream comprises at least a portion of the superheated steam stream.

3. The method of claim 1 , further comprising transferring heat from the shifted syngas stream or a stream derived from the first shifted syngas stream to a first mixed feed stream to produce a second mixed feed stream and a second shifted syngas stream; wherein the hydrocarbon feedstock comprises at least a portion of the second mixed feed stream.

4. The method of claim 1, further comprising combining at least a portion of the superheated steam stream with the third syngas stream.

5. The method of claim 1, wherein the temperature of the third syngas stream is in the range of 750°F to 1050°F.

6. The method of claim 1 further comprising diverting a portion of the second syngas stream to form a steam superheater bypass fraction; and At least a portion of the steam superheater bypass fraction is combined with the third syngas stream.

7. The method of claim 6, wherein the temperature of the third syngas stream is controlled by varying the flow rate of the steam superheater bypass fraction.

8. The process of claim 1 wherein the reacting of the reformer feed stream is carried out in a plurality of catalyst-containing reformer tubes.

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

10. The method of claim 1, further comprising combining an oxygen-rich gas with the first syngas stream to partially oxidize the syngas stream and react the syngas stream.

11. The method of 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.

12. A method for producing a hydrogen-enriched product stream, the method 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 first synthesis gas stream comprising hydrogen, carbon monoxide, and carbon dioxide; transferring heat from the first syngas stream or a stream derived from the syngas stream to a water stream to produce a second syngas stream and a first saturated steam stream; transferring heat from the second syngas stream to a second saturated steam stream to produce a superheated steam stream and a third syngas stream; reacting the third syngas stream in the presence of a first shift catalyst to produce a first shifted syngas stream; transferring heat from the first shifted syngas stream, or a stream derived therefrom, to a mixed feed stream to produce a second shifted syngas stream and a preheated mixed feed stream; separating the second shifted syngas stream to produce a carbon dioxide-enriched stream and a carbon dioxide-depleted stream; separating the carbon dioxide-depleted stream by selective permeation to produce a hydrogen-enriched permeate stream and a hydrogen-depleted retentate stream; as well as separating the hydrogen-enriched permeate stream to produce the hydrogen-enriched product stream and a hydrogen-depleted tail gas stream; combusting a fuel gas to supply heat to a reaction of the reformer feed stream; wherein the fuel gas comprises at least a portion of the hydrogen-depleted tail gas stream; wherein the second saturated steam flow comprises at least a portion of the first saturated steam flow; wherein the reformer feed stream comprises at least a portion of the preheated mixed feed stream or a stream derived from the preheated mixed feed stream; wherein the preheated mixed feed stream comprises at least a portion of the superheated steam stream.

13. A system for producing a hydrogen-enriched product stream, the system comprising: a reformer configured to receive a reformer feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide to contact a reforming catalyst and produce a first syngas stream comprising hydrogen, carbon monoxide, and carbon dioxide; a first heat exchanger configured to heat a water stream by indirect heat exchange with the first syngas stream to produce a first saturated steam stream and a second syngas stream; a second heat exchanger system configured to heat a second saturated steam stream by indirect heat exchange with the second syngas stream to produce a supersaturated steam stream and a third syngas stream; a shift reactor configured to receive the third syngas stream to produce a first shifted syngas stream, wherein the shift reactor includes a shift catalyst for reacting water with carbon monoxide to produce hydrogen and carbon dioxide; wherein the second saturated steam flow comprises at least a portion of the first saturated steam flow.

14. The system of claim 13, wherein the reformer feed stream comprises at least a portion of a superheated steam stream.

15. The system of claim 13, further comprising a third heat exchanger configured to heat the first mixed feed stream by indirect heat exchange with the first shifted syngas stream to produce a second mixed feed stream and a second shifted syngas stream; wherein the hydrocarbon feedstock comprises at least a portion of the second mixed feed stream.

16. The system of claim 13, wherein the second heat exchanger is configured to combine at least a portion of a superheated steam stream with the third syngas stream.

17. The system of claim 13, further comprising a steam superheater bypass conduit in fluid flow communication with the second syngas stream and the third syngas stream.

18. The system of claim 13, wherein the reformer comprises a plurality of reformer tubes containing catalyst.

19. The system of claim 13, further comprising a secondary reformer located downstream of the reformer and upstream of the first heat exchanger system, the secondary reformer configured to receive the first syngas stream and partially oxidize and react the first syngas stream in the presence of an oxygen-rich gas; wherein the secondary reformer comprises a secondary reforming catalyst.

20. The system of claim 13, further comprising a pre-reformer positioned upstream of the reformer, the pre-reformer configured to receive a second mixed feed stream comprising methane and a reactant selected from the group consisting of water and carbon dioxide to produce the reformer feed stream; wherein the pre-reformer comprises a pre-reforming catalyst.

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