Process for producing hydrogen

Abstract

The present invention relates to a process for producing hydrogen, comprising a hydrodesulfurization step, a reforming step in an autothermal reformer, a water-gas shift step, a carbon dioxide separation step, and a hydrogen purification step. The hydropurification step produces a hydrocarbon-containing off-gas stream that is split, with a portion used as a fuel gas stream supplied to one or more combustion heaters used to heat one or more process streams in the process, and the remainder split into a hydrodesulfurization recycle stream that is compressed and used in a hydrodesulfurization unit, and a process recycle stream that is returned to the process. The present invention also relates to a chemical plant configured to carry out the process.

Description

[Technical Field]

[0001] The present invention relates to a process for converting hydrocarbons to hydrogen while minimizing carbon dioxide production. [Background technology]

[0002] Processes for producing hydrogen are well known and generally involve combustion steam methane reformers combined with water-gas shift and carbon dioxide (CO2) removal. Such processes produce significant volumes of carbon dioxide in the flue gas at pressures that are not suitable for efficient CO2 capture. There is a need for hydrogen production processes that produce lower levels of carbon dioxide emissions and allow for more efficient CO2 capture.

[0003] Some processes use a combustion reformer to produce syngas, where fuel is burned in a radiant box of the combustion reformer to provide heat to drive the steam reforming reaction. For example, U.S. Patent Application Publication No. 2009 / 0230359 (A1) discloses a method for making hydrogen and / or synthesis gas in a production facility where little or no excess steam is produced. Most or all of the steam generated from waste heat from the process is used in a steam-hydrocarbon reformer. The flowsheet shown in Figure 1 of this reference includes a combustion steam reformer (650), an optional water-gas shift reactor (602), and a pressure swing adsorber (330). The pressure swing adsorber produces residue gas (698) that is separated. A portion (630) is used as fuel in the combustion steam reformer. Another portion is optionally first processed to hydrodesulfurize and / or pre-reform, then compressed and used as feedstock for the combustion steam reformer.

[0004] As another example, U.S. Patent Application Publication No. 2012 / 0039794 A1 describes a process for producing hydrogen. The flowsheet shown in Figure 1 of this reference includes a combustion steam reformer (14), a shift vessel (34), a CO2-selective membrane shift reactor (40), a water separator (58), and a pressure swing adsorption unit (64). The pressure swing adsorption unit produces a high-purity hydrogen product and a purge stream that is purified and then used as part of the feedstock for the combustion steam reformer.

[0005] In an alternative process, an autothermal reformer is used instead of a combustion reformer. For example, U.S. Patent Application Publication No. 2004 / 0028595 (A1) describes a method for producing ammonia from natural gas. The flowsheet shown in Figure 1 of this reference includes a pretreatment unit (40), an autothermal reformer (3), a shift conversion stage (10), and a CO2 adsorber (14a). The partially purified synthesis gas generated by the CO2 adsorber is sent to a fine screening unit (23a) that produces several streams: synthesis gas that is fed to the ammonia synthesis section, a CO2-containing stream that is recycled upstream of the shift stage, and a methane-containing stream that is recycled to the pretreatment unit.

[0006] WO 2022 / 038089 A1 describes a plant and process for producing a hydrogen-rich gas, comprising reforming a hydrocarbon feed by optional pre-reforming, autothermal reforming (ATR), but without primary reforming, thereby obtaining a synthesis gas; shifting the synthesis gas in a shift section including a high-temperature shift step; removing CO2 upstream of a hydrogen purification unit, thereby producing a hydrogen-rich stream and an off-gas stream, wherein at least a portion of the off-gas stream is recycled to the process, the ATR and optional pre-reforming, and / or the shift section.

[0007] WO 2022 / 003313(A1) describes a process for producing hydrogen, comprising: (i) subjecting a gaseous mixture comprising hydrocarbons and steam, and having a steam to carbon ratio of at least 0.9:1, to adiabatic pre-reforming in a pre-reformer, followed by autothermal reforming with an oxygen-rich gas in an autothermal reformer to generate a reformed gas mixture; (ii) increasing the hydrogen content of the reformed gas mixture by subjecting the reformed gas mixture to one or more water-gas shift stages in a water-gas shift unit to provide a hydrogen-enriched reformed gas; The process includes: (iii) cooling the hydrogen-rich reformed gas and separating condensed water therefrom to provide a dehydrated hydrogen-rich reformed gas; (iv) transferring the dehydrated hydrogen-rich reformed gas to a carbon dioxide separation unit to provide a carbon dioxide gas stream and a crude hydrogen gas stream; and (v) transferring the crude hydrogen gas stream from the carbon dioxide removal unit to a purification unit to provide purified hydrogen gas and a fuel gas, the fuel gas being supplied to one or more combustion heaters used to heat one or more process streams in the process. In an embodiment, a natural gas feed stream containing more than 85% by volume of methane is combined with an H stream extracted from the purified hydrogen gas stream produced by the purification unit and sent to a hydrodesulfurization vessel. While the above process has very good carbon dioxide capture efficiency, there is a need for a hydrogen production process that provides a higher hydrogen yield per unit of hydrocarbon feed. The present invention addresses this problem. Summary of the Invention

[0008] The present inventors have improved the process described in WO 2022 / 003313 A1 to increase the yield of H per unit of hydrocarbon feed. Accordingly, the present invention provides a process for producing hydrogen, comprising: (i) transferring a hydrogen stream (220, 320, 420, 520) and a feed stream (201, 301, 401, 501) comprising hydrocarbons to a hydrodesulfurization unit (203, 303, 403, 503) to perform hydrodesulfurization to produce a refined hydrocarbon stream; (ii) adding steam (204, 304, 404, 504) to the refined hydrocarbon stream to produce a gaseous mixture (205, 305, 405, 505) comprising hydrocarbons and steam; (iii) subjecting the gaseous mixture comprising hydrocarbons and steam to steam reforming in a reforming section (207, 307, 407, 507) comprising an autothermal reformer to generate a reformed gas mixture (208, 308, 408, 508); (iv) increasing the hydrogen content of the reformed gas mixture by subjecting the reformed gas mixture to one or more water-gas shift stages in a water-gas shift section (210, 310, 410, 510) to provide a hydrogen-enriched reformed gas (211, 311, 411, 511); (v) cooling the hydrogen-enriched reformed gas and separating condensed water therefrom to provide a dehydrated hydrogen-enriched reformed gas; (vi) transferring the dehydrated hydrogen-rich reformed gas to a carbon dioxide separation unit (212, 312, 412, 512) to provide a carbon dioxide gas stream (213, 313, 413, 513) and a crude hydrogen gas stream (214, 314, 414, 514); (vii) transferring the crude hydrogen gas stream from the carbon dioxide removal unit to a purification unit (215, 315, 415, 515) to provide a purified hydrogen gas stream (216, 316, 416, 516) and a hydrocarbon-containing off-gas stream (217, 317, 417, 517); (viii) splitting the off-gas stream into a fuel gas stream (218, 318, 418, 518) and a recycle stream (219, 319, 419, 519), the fuel gas stream being fed to one or more fired heaters used to heat one or more process streams within the process; (ix) compressing the recycle stream; (x) dividing the compressed recycle stream into a hydrodesulfurization recycle stream (220, 320, 420, 520) and a process recycle stream (221, 321, 421, 521); (xi) feeding the hydrodesulfurization recycle stream to a hydrodesulfurization unit; (xii) separating the process recycle stream into (xii-a) downstream of the hydrodesulfurization unit and upstream of the autothermal reformer; (xii-b) downstream of the autothermal reformer and upstream of the water-gas shift section; (xii-c) downstream of the water-gas shift section and upstream of the carbon dioxide separation unit; or (xii-d) downstream of a carbon dioxide separation unit and upstream of a purification unit; and returning the object to one or more positions selected from the group consisting of:

[0009] The process of the present invention differs from the configuration in WO 2022 / 003313 A1 in two important respects. First, whereas in the prior art configuration, all offgas from the refinery unit is combusted as fuel in one or more fired heaters, in the present invention, the offgas from the refinery unit is split into a fuel gas stream and a recycle stream. The fuel gas stream is fed to one or more fired heaters, which are used to heat one or more process streams in the process. The recycle stream, which contains some unreacted hydrocarbons, is compressed and then split into a hydrodesulfurization recycle stream and a process recycle stream, both of which are returned to the process. The hydrodesulfurization recycle stream provides the hydrogen needed in the hydrodesulfurization unit, instead of removing a portion of the hydrogen product stream from the refinery unit as in the prior art configuration. This improves the overall H yield. The process recycle stream is returned at one or more of positions (xii-a) to (xii-d). Surprisingly, despite the increased complexity of this configuration, the overall hydrogen efficiency of the process (H produced per unit of hydrocarbon feed) is increased. This is achieved without sacrificing CO2 capture efficiency, which can be 98% or greater in the process of the present invention.

[0010] In a second aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: (i) a hydrodesulfurization unit (203, 303, 403, 503) configured to receive a hydrogen stream (220, 320, 420, 520) and a feed stream (201, 301, 401, 501) comprising hydrocarbons and to perform hydrodesulfurization to produce a refined hydrocarbon stream; (ii) means for adding steam (204, 304, 404, 504) to the refined hydrocarbon stream to produce a gaseous mixture (205, 305, 405, 505) comprising hydrocarbons and steam; (iii) a reforming section (207, 307, 407, 507) including an autothermal reformer configured to receive a gaseous mixture including hydrocarbons and water vapor and produce a reformed gas mixture (208, 308, 408, 508); (iv) a water-gas shift section (210, 310, 410, 510) including one or more water-gas shift stages configured to receive the reformed gas mixture and produce a hydrogen-enriched reformed gas (211, 311, 411, 511); (v) means for cooling the hydrogen-enriched reformed gas and separating condensed water therefrom to produce a dehydrated hydrogen-enriched reformed gas; (vi) a carbon dioxide separation unit (212, 312, 412, 512) configured to receive the dehydrated hydrogen-enriched reformate gas and produce a carbon dioxide gas stream (213, 313, 413, 513) and a crude hydrogen gas stream (214, 314, 414, 514); (vii) a purification unit (215, 315, 415, 515) configured to receive a crude hydrogen gas stream and produce a purified hydrogen gas stream (216, 316, 416, 516) and a hydrocarbon-containing off-gas stream (217, 317, 417, 517); (viii) means for splitting the off-gas stream into a fuel gas stream (218, 318, 418, 518) and a recycle stream (219, 319, 419, 519), wherein the fuel gas stream is supplied to one or more fired heaters used to heat one or more process streams within the process; (ix) means for compressing the recycle stream; and (x) means for dividing the compressed recycle stream into a hydrodesulfurization recycle stream (220, 320, 420, 520) and a process recycle stream (221, 321, 421, 521); (xi) means for supplying a hydrodesulfurization recycle stream to the hydrodesulfurization unit; (xii) separating the process recycle stream into (xii-a) downstream of the hydrodesulfurization unit and upstream of the autothermal reformer; (xii-b) downstream of the autothermal reformer and upstream of the water-gas shift section; (xii-c) downstream of the water-gas shift section and upstream of the carbon dioxide separation unit; or (xii-d) downstream of a carbon dioxide separation unit and upstream of a purification unit; and means for returning the water to one or more locations selected from the group consisting of:

[0011] A chemical plant may be constructed from scratch (e.g., a "greenfield" chemical plant), or an existing chemical plant may be retrofitted with the necessary units and associated piping, etc., to produce a chemical plant according to the present invention.

[0012] The chemical plant is preferably a hydrogen plant, i.e. it produces hydrogen as an end product. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a simplified diagram of the process described in WO 2022 / 003313 A1. A hydrocarbon stream (101) and a hydrogen stream (102) are fed to a desulfurization unit (103). Steam (104) is added to the output from the desulfurization unit to produce a stream (105) having a steam-to-carbon ratio of at least 0.9:1, which is sent to a reforming section (107). The reforming section includes a pre-reformer and an autothermal reformer. Steam (104) is added so that the feed to the autothermal reformer has a steam-to-carbon ratio of 1.30:1. An oxygen-rich gas stream (106) is also fed to the autothermal reformer. A steam reforming reaction occurs in the autothermal reformer to produce a reformate stream (108). The reformate stream can optionally be mixed with additional steam (109) (note that this is used in the modeled configuration) and sent to a water-gas shift section (110) to generate a hydrogen-rich reformate gas (111). The hydrogen-rich reformate gas is fed to a carbon dioxide separation unit (112) where it is separated into a carbon dioxide gas stream (113) and a crude hydrogen gas stream (114). The crude hydrogen gas stream is sent to a purification unit (115) where it is separated into a purified hydrogen gas stream (116) and an off-gas stream (117). The off-gas stream is used as fuel gas. [Figure 2] This shows an arrangement according to the present invention based on the arrangement shown in Figure 1. The off-gas stream (217) is split to produce a fuel gas stream (218) and a recycle stream (219). The recycle stream is compressed (not shown) and then split into a desulfurization recycle stream (220) that is fed to a purification unit, and a process recycle stream (221) that is reintroduced into the process downstream of the desulfurization unit (203) and upstream of the autothermal reformer (207). [Figure 3] 1 illustrates an arrangement according to the present invention based on the arrangement shown in Figure 1. The off-gas stream (317) is split to produce a fuel gas stream (318) and a recycle stream (319). The recycle stream is compressed (not shown) and then split into a desulfurization recycle stream (320) that is fed to a desulfurization unit, and a process recycle stream (321) that is reintroduced into the process downstream of the autothermal reformer (307) and upstream of the water-gas shift section (310). [Figure 4]1 shows a configuration according to the present invention based on the configuration shown in Figure 1. The off-gas stream (417) is split to produce a fuel gas stream (418) and a recycle stream (419). The recycle stream is compressed (not shown) and then split into a desulfurization recycle stream (420) that is fed to the desulfurization unit, and a process recycle stream (421) that is reintroduced into the process downstream of the water-gas shift section (410) and upstream of the carbon dioxide separation unit (412). [Figure 5] 1 shows an arrangement according to the present invention based on the arrangement shown in Figure 1. The off-gas stream (517) is split to produce a fuel gas stream (518) and a recycle stream (519). The recycle stream is compressed (not shown) and then split into a desulfurization recycle stream (520) that is fed to the desulfurization unit, and a process recycle stream (521) that is reintroduced into the process downstream of the carbon dioxide separation unit (512) and upstream of the purification unit (515). DETAILED DESCRIPTION OF THE INVENTION

[0014] Subheadings are included for clarity and are not intended to limit the invention.

[0015] The features relating to the configuration of the chemical plant described in relation to the present process also apply to the chemical plant according to the second aspect of the invention.

[0016] Treatment before the autothermal reformer The gaseous mixture fed to the autothermal reformer comprises hydrocarbons and steam. Preferably, the mixture comprises 90% or more by volume of methane, such as 95% or more by volume of methane, based on the % of hydrocarbons present in the mixture and excluding any steam. The hydrocarbon-containing feed is pretreated upstream of the autothermal reformer to remove contaminants, including at least a step of hydrodesulfurization.

[0017] A wide variety of feeds may be used, such as, for example, natural gas, associated gas, LPG, petroleum distillates, diesel, naphtha or mixtures thereof, or hydrocarbon-containing off-gases from chemical processes such as refinery off-gases or pre-reformed gases.

[0018] Hydrodesulfurization Step (i) comprises transferring the hydrogen stream and a feed stream comprising hydrocarbons to a hydrodesulfurization unit for hydrodesulfurization to produce a refined hydrocarbon stream.

[0019] The feed stream may be compressed before or after hydrodesulfurization, preferably before hydrodesulfurization. The feed may be compressed to a pressure in the range of 10 to 100 bar abs. The pressure of the feed stream can effectively influence the pressure throughout the process. The operating pressure is preferably in the range of 15 bar abs to 50 bar abs, more preferably 25 bar abs to 50 bar abs, in order to improve performance from the process.

[0020] The hydrodesulfurization step is typically catalytic hydrodesulfurization, which can be achieved using known catalysts such as CoMo or NiMo catalysts. This process generates hydrogen sulfide, which is absorbed using a suitable hydrogen sulfide adsorbent, such as a zinc oxide adsorbent. Ultra-purified adsorbents may be effectively used downstream of the hydrogen sulfide adsorbent to further protect the steam reforming catalyst. Suitable ultra-purified adsorbents may include copper-zinc oxide / alumina materials and copper-nickel-zinc oxide / alumina materials. It is preferable to add hydrogen to the compressed hydrocarbon to facilitate hydrodesulfurization and / or reduce the risk of carbon laydown in the reforming process. The amount of hydrogen in the resulting mixed gas stream can be in the range of 1 to 20% by volume, on a dry gas basis, but is preferably in the range of 1 to 10% by volume, and more preferably in the range of 1 to 5% by volume. In a preferred embodiment, a portion of the desulfurized recycle stream may be mixed with the compressed hydrocarbon (as described below).

[0021] The hydrogen stream to the hydrodesulfurization unit is provided at least in part by the hydrodesulfurization recycle stream separated in step (x) as described below. Although additional hydrogen may be added to the hydrodesulfurization stream, to maximize hydrogen yield, the hydrodesulfurization recycle stream is preferably fed to the hydrodesulfurization unit without the addition of supplemental hydrogen. In the latter case, the hydrogen stream and the hydrodesulfurization recycle stream are one and the same.

[0022] Compared to the configuration described in WO 2022 / 003313 A1, in which part of the crude hydrogen gas stream (from the carbon dioxide separation unit) or the purified hydrogen gas stream (from the purification unit) can be used to provide hydrogen for desulfurization, this configuration uses a different, less hydrogen-rich feed, which helps to improve the yield of hydrogen per unit of hydrocarbon feed.

[0023] If the feed contains chlorides or other contaminants, such as heavy metal contaminants, these may be removed either upstream or downstream of hydrodesulfurization using conventional adsorbents prior to upgrading. Suitable adsorbents for chloride removal are well known and include alkalized alumina materials. Similarly, adsorbents for heavy metals such as mercury or arsenic are known and include copper sulfide materials.

[0024] The feed may be preheated in one or more stages, preferably after compression and before desulfurization. The process provides a variety of hot gas sources that can be used for this application. For example, the feed may be heated by heat exchange with a shifted gas stream recovered from a water-gas shift stage, preferably a high-temperature shift stage. The desulfurized feed, also referred to herein as a refined hydrocarbon stream, may be heated, for example, in a combustion heater fueled by fuel gas.

[0025] Steam addition Step (ii) comprises adding steam to the refined hydrocarbon stream to produce a gaseous mixture comprising hydrocarbons and steam. The introduction of steam may be by direct injection of steam and / or by saturating the refined hydrocarbon stream by contact with a heated water stream. The steam added in step (ii) is preferably generated by burning a fuel gas stream in one or more combustion heaters. In a preferred embodiment, the gaseous mixture comprising hydrocarbons and steam is formed by directly mixing the refined hydrocarbon stream with steam, preferably steam generated in one or more combustion heaters, and / or by cooling the reformed gas mixture with water.

[0026] The steam-to-carbon ratio (defined as the steam to hydrocarbon carbon ratio at the inlet to the autothermal reformer) can vary over a wide range, but is typically between 0.9:1 and 3.5:1, e.g., between 0.9:1 and 2.4:1. For the avoidance of doubt, a feed containing 75 mol% HO and 25 mol% CH would have a steam-to-carbon ratio of 3.0:1, a feed containing 75 mol% HO, 23 mol%, and 2 mol% would have a steam-to-carbon ratio of 2.8:1, and so on. Operating the reforming section at a steam-to-carbon ratio in the range of 0.9:1 to 2.4:1 has the advantages of reduced heating and oxygen demands for the reforming stage, and smaller and lower cost front-end equipment (e.g., combustion heater, pre-reformer, and autothermal reformer), but typically requires the addition of additional steam to the reformed gas mixture upstream of the water-gas shift section. In one embodiment, the steam-to-carbon ratio of the gaseous mixture containing hydrocarbons and steam at the inlet to the autothermal reformer in step (iii) is between 0.9:1 and 2.4:1, and additional steam is added to the reformed gaseous mixture upstream of the water-gas shift section. When the steam-to-carbon ratio is in the range of 2.4:1 to 3.5:1, it is typically not necessary to add additional steam upstream of the water-gas section, which can be useful in situations where adding steam to the reformed gas is impractical. When a pre-reformer is present, the steam-to-carbon ratio at the inlet to the pre-reformer is preferably between 0.9:1 and 3.5:1, preferably between 0.9:1 and 2.4:1.

[0027] The gaseous mixture containing hydrocarbons and steam is then desirably preheated prior to reforming. In a preferred embodiment, the gaseous mixture is heated by passing it through a combustion heater fueled by at least a portion of the fuel gas, particularly the same combustion heater used to preheat the hydrocarbons. Desirably, the mixed stream is heated to between 400°C and 500°C, preferably between 420°C and 460°C.

[0028] Pre-reforming The gaseous mixture fed to the autothermal reformer preferably contains 90% or more by volume of methane, based on the percentage of hydrocarbons present in the mixture, excluding any steam. While not generally necessary for light gaseous hydrocarbon feedstocks, it may be preferable to include an adiabatic pre-reforming stage upstream of the autothermal reformer if the hydrocarbon feedstock contains higher hydrocarbons. In these cases, the gaseous mixture containing hydrocarbons and steam is first subjected to adiabatic steam reforming in a pre-reformer vessel. In such a process, the gaseous mixture containing hydrocarbons and steam is adiabatically passed through a bed of a steam reforming catalyst, usually with a high nickel content, e.g., greater than 40% by weight, at an inlet temperature typically in the range of 400°C to 650°C. During this adiabatic pre-reforming step, any hydrocarbons higher than methane are reacted with steam to produce a mixture of methane, carbon oxides, and hydrogen. The use of such an adiabatic steam reforming step, commonly referred to as pre-reforming, may be desirable to ensure that the feed to the autothermal reformer is free of hydrocarbons higher than methane and also contains some hydrogen. Thus, in preferred embodiments, the process includes a pre-reforming step either upstream of the hydrodesulfurization unit, or downstream of the hydrodesulfurization unit and upstream of the ATR. The pre-reforming is preferably adiabatic.

[0029] Modification Section Following purification and, if necessary, pre-reforming, the gaseous mixture comprising hydrocarbons and steam is subjected to steam reforming in a reforming section comprising an autothermal reformer, preferably without any other reforming units (e.g., combustion reformers or gas-heated reformers) other than the autothermal reformer.

[0030] In the present invention, the gaseous mixture comprising hydrocarbons and steam, which has optionally first been subjected to pre-reforming, is fed to an autothermal reformer where it is subjected to autothermal reforming. Preferably, all of the refined hydrocarbon stream, which has optionally first been subjected to pre-reforming, is fed to the autothermal reformer.

[0031] An autothermal reformer may comprise a burner located at the top of the reformer to which the steam reformate gas and oxygen-rich gas are fed, a combustion zone below the burner through which a flame extends, and a fixed bed of particulate steam reforming catalyst located below the combustion zone. Thus, in autothermal reforming, heat for the endothermic steam reforming reaction is provided by burning a portion of the hydrocarbons in the pre-reforming feed gas. The pre-reformate gas is typically fed to the top of the reformer, and the oxygen-rich gas is fed to the burner, where mixing and combustion occur downstream of the burner to generate a heated gas mixture whose composition is equilibrated as it passes through the steam reforming catalyst. The autothermal steam reforming catalyst may comprise nickel supported on a refractory support such as rings or pellets of calcium aluminate, magnesium aluminate, alumina, titania, zirconia, and the like. In a preferred embodiment, the autothermal steam reforming catalyst comprises a layer of catalyst comprising Ni and / or Ru on zirconia over a bed of Ni on alumina catalyst to reduce catalyst support volatilization that can result in reduced performance of the autothermal reformer.

[0032] The oxygen-rich gas may contain at least 50% O by volume and may be an oxygen-enriched air mixture. However, in the present invention, the oxygen-rich gas preferably contains at least 90% O by volume, more preferably at least 95% O by volume, and most preferably at least 98% O by volume, or at least 99% O by volume (e.g., a pure oxygen gas stream that may be obtained using a vacuum pressure swing adsorption (VPSA) unit or an air separation unit (ASU)). The ASU may be electrically powered, preferably powered using renewable electricity to further improve process efficiency and minimize CO2 emissions.

[0033] The amount of oxygen-rich gas added preferably adds 45 to 65 moles of oxygen per 100 moles of carbon in the hydrocarbons fed to the process. Preferably, the amount of oxygen added is such that the autothermal reforming gas exits the autothermal reforming catalyst at a temperature in the range of 800 to 1100°C. In a preferred embodiment, a small amount of steam purge may be added to the oxygen-rich gas to prevent backflow in the event of a plant trip.

[0034] After exiting the autothermal reformer, the reformed gas is then typically cooled in one or more steps of heat exchange. Heat recovered during this cooling may be used to preheat reactants and / or heat water used to provide the steam used in the steam reforming step. As described below, the recovered heat may additionally or alternatively be used in the carbon dioxide separation step.

[0035] Water Gas Shift Section The reformate gas contains hydrogen, carbon monoxide, carbon dioxide, steam, and small amounts of unreacted methane, and may contain small amounts of inert gases such as nitrogen and argon. For example, in processes where all process steam is added upstream of the reforming unit operation, the hydrogen content of the autothermal reformate gas may range from 35 to 45% by volume, and the CO content may range from 10 to 20% by volume. In current processes, the hydrogen content of the reformate gas mixture is increased by subjecting it to one or more water-gas shift stages in a water-gas shift section, thereby producing a hydrogen-enriched reformate gas stream and simultaneously converting carbon monoxide to carbon dioxide. The reaction can be illustrated as follows: CO+H2O⇔CO2+H2

[0036] Optionally, additional process steam can be added to the reformed gas to improve the equilibrium position in the water-gas shift stage, especially if the steam-to-carbon ratio of the gaseous mixture fed to the pre-reformer is less than 2.4:1. Thus, in some embodiments, the process optionally includes adding steam to the reformed gas. Steam may be added to the reformed gas upstream of the water-gas shift section, e.g., upstream of the high-temperature shift stage. The amount of steam added will vary depending on the amount of steam in the hydrocarbon-containing gaseous mixture fed to the reforming stage. The amount of steam added is desirably commensurate with maximizing carbon capture from the assisted process by minimizing carbon monoxide slip. Thus, if steam is added to the reformed gas, the steam-to-dry gas molar ratio of the reformed gas is preferably at least 0.7:1, more preferably in the range of 0.7:1 to 0.9:1.

[0037] If reforming is carried out with excess steam, it is generally not necessary to add steam to the reformed gas mixture recovered from the autothermal reformer.

[0038] The exit gas from the ATR typically has a temperature of about 1000°C, which is above the temperature required for the high temperature shift. Therefore, it is preferable to cool the reformed gas, preferably by raising water vapor, to produce a partially cooled reformed gas that is sent to the water gas shift section.

[0039] The partially cooled reformate gas is subjected to one or more water-gas shift stages in the water-gas shift section to form a "shifted" gas stream, which is a hydrogen-enriched reformate gas stream. The one or more water-gas shift stages may include a high-temperature shift stage, a medium-temperature shift stage, an isothermal shift stage, and a low-temperature shift stage.

[0040] Although the water gas shift section may include a single shift stage using a suitably stable and active shift catalyst, it is preferred that the water gas shift section include two or more water gas shift stages, including a high temperature shift, an intermediate temperature shift, an isothermal shift, and a low temperature shift.

[0041] The high temperature shift is operated adiabatically in a shift vessel having an inlet temperature in the range of 300°C to 400°C, preferably 320°C to 360°C, over a bed of a reduced iron catalyst such as chromia-promoted magnetite. Alternatively, a promoted zinc aluminate catalyst may be used. The partially cooled reformate gas is typically at a temperature of about 400°C, which is ideally suited for the high temperature shift. Thus, in a preferred embodiment, the water gas shift section includes at least one high temperature shift unit.

[0042] The intermediate and low-temperature shift stages may be carried out using a shift vessel containing a supported copper catalyst, particularly a copper / zinc oxide / alumina composition. In the low-temperature shift, gas containing carbon monoxide (preferably not more than 6% CO by volume on a dry basis) and water vapor (at a steam-to-total dry gas molar ratio in the range of 0.3 to 1.5) may be passed over the catalyst in an adiabatic fixed bed with an outlet temperature in the range of 200°C to 300°C. Typically, the inlet gas is the product of a "high-temperature shift" in which the carbon monoxide content is reduced by reaction on an iron-chromia catalyst with an outlet temperature in the range of 400°C to 500°C, followed by cooling by indirect heat exchange. The outlet carbon monoxide content from the low-temperature water-gas shift stage is typically in the range of 0.1 to 1.0% by volume on a dry basis, particularly less than 0.5% by volume. Alternatively, in a medium temperature shift, gas containing carbon monoxide and water vapor is fed to the catalyst at a pressure in the range 15-50 bar abs, and at an inlet temperature typically in the range 200-240°C, although the inlet temperature may be as high as 280°C, and the outlet temperature is typically no more than 300°C, but may be as high as 360°C.

[0043] A shift unit comprising a combination of a high-temperature shift stage and a low-temperature shift stage, each stage operated adiabatically, is preferred in the present process. Adiabatic operation of the shift stage results in an increase in the temperature of the shifted gas mixture, with subsequent heat exchange with one or more process streams generally being desirable. When the shift unit comprises a high-temperature shift stage, two stages of heat exchange are preferred, and the heat-shifted gas mixture may be cooled by heat exchange with water under pressure and together with hydrocarbons. In a preferred configuration, the heat-shifted gas from the high-temperature shift stage is cooled in a first stage of heat exchange with hydrocarbons and a second stage of heat exchange with water under pressure.

[0044] While the low-temperature and intermediate-temperature shift reactions can be operated adiabatically, they can also be operated isothermally, i.e., with heat exchange within the shift vessel, whereby the reaction within the catalyst bed occurs in contact with the heat exchange surfaces. The coolant can conveniently be water under pressure to cause partial or complete boiling. The resulting steam can be used, for example, to drive a turbine for electricity or to provide process steam for a water-gas shift or steam reforming reaction. The water can be in tubes surrounded by the catalyst, or vice versa. Although the term "isothermal" is used, there can be a slight increase in gas temperature between the inlet and outlet, and thus the temperature of the hydrogen-rich reformate stream at the outlet of the isothermal shift converter can be 1 to 25 degrees Celsius higher than the inlet temperature.

[0045] Following one or more shift stages, the hydrogen-rich reformed gas is cooled to a temperature below the dew point so that the water vapor condenses. One or more gas-liquid separators can then be used to separate the liquid condensate, which may have one or more additional cooling stages between them. Any cooling agent may be used. Preferably, the hydrogen-rich reformed gas stream is first cooled by heat exchange with process condensate, resulting in the formation of a heated water stream that can be used to provide some or all of the water vapor required for reforming. Thus, in one embodiment, condensate recovered from the hydrogen-rich reformed gas is used to provide at least a portion of the water vapor to the gas mixture fed to the steam reforming step in the autothermal reformer. Because the condensate may contain ammonia, methanol, hydrogen cyanide, and CO2, converting the condensate back into steam provides a useful process for returning hydrogen and carbon to the process.

[0046] One or more additional cooling stages are desirable. Cooling may be accomplished in one or more stages using demineralized water, air, or a combination thereof in heat exchange. In a preferred embodiment, cooling is achieved by heat exchange with one or more liquids in a CO2 separation unit. In a particularly preferred configuration, the hydrogen-enriched reformed gas stream is cooled by heat exchange with condensate, followed by cooling with CO2 reboiler liquid. The cooled shifted gas may then be fed to a first gas-liquid separator, and the separated gas may be further cooled with water and / or air and fed to a second separator, and then further cooled with water and / or air and fed to a third separator. A second or third stage condensate separation is preferred. Some or all of the condensate may be used to produce steam for steam reforming. Any condensate not used to produce steam may be sent to water treatment as effluent.

[0047] Carbon Dioxide Separation Unit The carbon dioxide separation step may be carried out using a physical or reactive scrubbing system, preferably a reactive scrubbing system, particularly an amine scrubbing system. Carbon dioxide may also be separated by acid gas recovery (AGR) processes. In the AGR process, the dehydrated hydrogen-rich reformed gas stream (i.e., the dehydrated shifted gas) is contacted with a stream of a suitable absorbent, such as an amine, particularly a methyl diethanolamine (MDEA) solution, whereby carbon dioxide is absorbed by the absorbent to obtain a loaded absorbent and a gas stream with a reduced carbon dioxide content. The loaded absorbent is then regenerated by heating and / or depressurization to desorb the carbon dioxide and obtain a regenerated absorbent, which is then recycled to the carbon dioxide adsorption step. Alternatively, methanol or glycol may be used to capture carbon dioxide in a manner similar to that of amines. In a preferred configuration, at least a portion of the heating to regenerate the absorbent is performed using steam generated in one or more fired heaters. If the carbon dioxide separation step is operated as a single pressure process, i.e., essentially the same pressure is employed in the adsorption and regeneration steps, only minor recompression of the recycled carbon dioxide is required.

[0048] For example, recovered carbon dioxide from AGR can be compressed and used to manufacture chemicals, sent for storage or sequestration, used in enhanced oil recovery (EOR) processes, or used to generate other chemicals. Compression may be achieved using an electrically driven compressor powered by renewable electricity. If the CO2 is to be compressed for storage, transport, or use in an EOR process, the CO2 may be dried to prevent traces of liquid water from condensing. For example, the CO2 may be dried to a dew point of −10° C. or below by passing it through a bed of a suitable desiccant, such as zeolite, or by contacting it with glycol in a glycol drying unit.

[0049] Upon separating the carbon dioxide, the process provides a crude hydrogen gas stream.

[0050] The crude hydrogen stream may comprise 85-99% by volume hydrogen, preferably 90-99% by volume hydrogen, with the remainder comprising methane, carbon monoxide, carbon dioxide, and inert gases. While this hydrogen gas stream is sufficiently pure for many applications, in the present invention the crude hydrogen gas stream is passed to a purification unit to provide purified hydrogen gas and off-gas, thereby allowing fuel gas to be used in the process as an alternative to an external fuel source in order to minimize CO2 emissions from the process.

[0051] Refining Unit The role of the purification unit is to receive the crude hydrogen gas stream from the water-gas shift section and separate it into a purified hydrogen gas stream and an off-gas stream. Any suitable purification unit may be used. Preferred examples include membrane systems, temperature swing adsorption systems, or pressure swing adsorption systems. Such systems are commercially available. The purification unit is preferably a pressure swing adsorption unit or a temperature swing adsorption unit. Such units include a regenerable porous adsorbent material that selectively captures and thereby purifies gases other than hydrogen. The purification unit produces a pure hydrogen stream, preferably greater than 99.5% by volume, more preferably greater than 99.9% by volume, which may be compressed and used in downstream power or heating processes, for example, by using it as fuel in a gas turbine (GT) or by injection into a domestic or industrial network gas piping system. The pure hydrogen may also be used in downstream chemical synthesis processes. Thus, the pure hydrogen stream may be used to produce ammonia by reaction with nitrogen in an ammonia synthesis unit. Alternatively, the pure hydrogen may be used with a carbon dioxide-containing gas to produce methanol in a methanol production unit. Alternatively, pure hydrogen may be used with carbon monoxide-containing gases to synthesize hydrocarbons in a Fischer-Tropsch production unit. Any known ammonia, methanol, or Fischer-Tropsch production technology may be used. Alternatively, the hydrogen may be used to upgrade hydrocarbons, for example, by hydrotreating or hydrocracking hydrocarbons in a hydrocarbon refinery, or in any other process where pure hydrogen may be used. Compression may again be achieved using an electrically driven compressor powered by renewable electricity.

[0052] recycling The off-gas stream is split into a fuel gas stream and a recycle stream (step (viii)). The fuel gas stream is fed to one or more fired heaters that are used to heat one or more process streams within the process. The recycle stream is then compressed (step (ix)) and split into a hydrodesulfurization recycle stream and a process recycle stream (step (x)). The hydrodesulfurization recycle stream is fed to a hydrodesulfurization unit (step (xi)) to provide hydrogen for the reaction taking place therein. The process recycle stream is returned to one or more locations (step (xii)). The process recycle stream can be reintroduced into the process at a variety of different locations (configurations (xii-a) to (xii-d)).

[0053] The relative mass flow rates of the combustion gas, process recycle, and hydrodesulfurization recycle streams depend on several factors, including the demand on the combustion heater, the H demand of the dehydrodesulfurization unit, and the H content of the hydrogen-containing off-gas stream. The percentage used as process recycle is determined by subtracting the percentage required to load the combustion heater, then subtracting the percentage required to load the HDS. The remainder is sent for recycle.

[0054] In an embodiment, the process recycle stream is reintroduced into the process downstream of the hydrodesulfurization unit and upstream of the autothermal reformer (configuration (xii-a)). In connection with configuration (xii-a), if a pre-reformer is present, the process recycle stream is preferably reintroduced downstream of the pre-reformer and upstream of the autothermal reformer. An advantage of this configuration is that it provides another opportunity to convert residual hydrocarbons in the off-gas to hydrogen, thereby improving the hydrogen yield per unit of hydrocarbon. A further advantage of this configuration is that it provides another opportunity to convert residual carbon monoxide in the off-gas to carbon dioxide, as it further passes through a water-gas shift section, thereby reducing carbon monoxide emissions from the process. A further advantage of this configuration is that it provides another opportunity to capture residual carbon dioxide in the off-gas, as it further passes through a carbon dioxide separation unit. It will be appreciated that the feed to the autothermal reformer is typically at a much higher temperature than the off-gas from the purification unit, and it may be necessary to heat the off-gas before reintroduction.

[0055] In one embodiment, the recycle stream is reintroduced into the process downstream of the autothermal reformer and upstream of the water gas shift section (configuration (xii-b)). This configuration offers the opportunity to reduce the carbon monoxide and carbon dioxide content of the off-gas.

[0056] In one embodiment, the recycle stream is reintroduced into the process downstream of the water-gas shift section and upstream of the carbon dioxide separation unit (configuration (xii-c)). This configuration offers the opportunity to reduce the carbon dioxide content of the off-gas, but since the carbon dioxide content of the off-gas is generally already very low, this configuration is the least preferred of options xii-a through xii-d.

[0057] In a preferred embodiment, the recycle stream is reintroduced into the process at a location downstream of the carbon dioxide removal unit and upstream of the purification unit (configuration (xii-d)). This configuration provides an additional opportunity to separate hydrogen from unconverted hydrocarbons.

[0058] It will be appreciated that more complex configurations are possible, for example where the recycle stream is introduced at two or more different locations from the options specified. For simplicity of design, it is preferred that the process recycle stream is returned to the process at only a single location (xii-a) through (xii-d), most preferably location (xii-d).

[0059] The combination of steps as described herein provides sufficient fuel gas to heat the process streams used in the process without significant additional fuel during normal operation. The volume of supplemental fuel in the process is desirably kept to a minimum to maximize CO2 capture efficiency. The amount of supplemental fuel, e.g., natural gas, supplied to one or more fired heaters along with the fuel gas is preferably less than 5% by volume of the total fuel provided, more preferably less than 3% by volume of the total fuel provided, and most preferably less than 2% of the total fuel provided.

[0060] In some situations, such as during start-up of the process, it may be necessary to temporarily supplement the fuel gas with hydrocarbon fuel, but this should not significantly reduce the efficiency of the process; during normal operation, the fuel gas recovered from the refinery unit is the primary source of fuel provided to one or more fired heaters.

[0061] In some embodiments, a single combustion heater fueled at least in part by fuel gas is sufficient to heat the hydrocarbons, the reformed gas recovered from a pre-reforming stage upstream of the autothermal reforming stage, and water to generate at least a portion of the steam for the process.

[0062] While all process streams requiring heating can be heated in a single fired heater, a preferred configuration is one fired heater dedicated to the hydrocarbon- and / or hydrogen-containing process gas stream and another dedicated to boiling water for steam generation. Therefore, the latter can also be described as a boiler. Thus, fuel gas can be split between the first fired heater, used to heat the hydrocarbon- and / or hydrogen-containing stream, and the second fired heater, used to boil water to generate steam. Using two fired heaters in this manner offers several distinct advantages: steam can be raised in the second fired heater and thereby used as part of plant startup; steam can be generated in the second fired heater while the plant is shut down and supplied to the plant during the shutdown process; the first and second fired heaters can be operated independently, facilitating startup by eliminating coil heating in a no-flow situation; and the isolation of the first fired heater allows nitrogen to be warmed as part of the startup procedure while the second fired heater is running or starting up. The fuel gas split to the first and second combustion heaters may be in the range of 10-90% by volume to 90-10% by volume, respectively, but is preferably in the range of 60-80% by volume for the first combustion heater and 40-20% by volume for the second combustion heater.

[0063] The steam generated in the second fired heater can be used to heat the CO2 absorption liquid in the carbon dioxide separation unit. The second fired heater can also be used to superheat steam recovered from a steam drum coupled to a waste heat boiler heated by the reformed gas. The waste heat boiler is also preferably used to generate steam used to preheat the oxygen-rich gas and / or to provide process steam added upstream of the water-gas shift section to maximize the conversion to hydrogen and carbon dioxide. A portion of the steam from the waste heat boiler can also be sent to a steam expander to generate electricity. [Example]

[0064] Example 1 (Comparative Example) This example corresponds to the flowsheet shown in Figure 1 of WO 2022 / 003313 A1. Selected heat and mass balance calculations from the example modeled in WO 2022 / 003313 A1 are shown in Table 1. A simplified version of the flowsheet is shown in Figure 1.

[0065] Example 2 (according to the present invention) The flowsheet shown in WO 2022 / 003313 A1 was modified by splitting the off-gas stream into a fuel gas stream and a recycle stream. The recycle stream was itself split into a process recycle stream (519) and a desulfurization recycle stream (520). This example corresponds to the configuration shown in Figure 5. Heat and mass balance calculations for selected streams are shown in Table 2.

[0066] [Table 1]

[0067] [Table 2]

Claims

1. 1. A process for producing hydrogen, comprising: (i) transferring a hydrogen stream (220, 320, 420, 520) and a feed stream (201, 301, 401, 501) comprising hydrocarbons to a hydrodesulfurization unit (203, 303, 403, 503) to perform hydrodesulfurization to produce a refined hydrocarbon stream; (ii) adding steam (204, 304, 404, 504) to the purified hydrocarbon stream to produce a gaseous mixture (205, 305, 405, 505) comprising hydrocarbons and steam; (iii) subjecting said gaseous mixture comprising hydrocarbons and steam to steam reforming in a reforming section (207, 307, 407, 507) comprising an autothermal reformer to generate a reformed gas mixture (208, 308, 408, 508); (iv) increasing the hydrogen content of the reformed gas mixture by subjecting the reformed gas mixture to one or more water-gas shift stages in a water-gas shift section (210, 310, 410, 510) to provide a hydrogen-enriched reformed gas (211, 311, 411, 511); (v) cooling the hydrogen-rich reformed gas and separating condensed water therefrom to provide a dehydrated hydrogen-rich reformed gas; (vi) transferring the dehydrated hydrogen-rich reformed gas to a carbon dioxide separation unit (212, 312, 412, 512) to provide a carbon dioxide gas stream (213, 313, 413, 513) and a crude hydrogen gas stream (214, 314, 414, 514); (vii) transferring the crude hydrogen gas stream from the carbon dioxide removal unit to a purification unit (215, 315, 415, 515) to provide a purified hydrogen gas stream (216, 316, 416, 516) and a hydrocarbon-containing off-gas stream (217, 317, 417, 517); (viii) splitting the off-gas stream into a fuel gas stream (218, 318, 418, 518) and a recycle stream (219, 319, 419, 519), wherein the fuel gas stream is supplied to one or more fired heaters used to heat one or more process streams within the process; (ix) compressing the recycle stream; (x) dividing the compressed recycle stream into a hydrodesulfurization recycle stream (220, 320, 420, 520) and a process recycle stream (221, 321, 421, 521); (xi) feeding the hydrodesulfurization recycle stream to the hydrodesulfurization unit; (xii) subjecting said process recycle stream to (xii-a) downstream of the hydrodesulfurization unit and upstream of the autothermal reformer; (xii-b) downstream of the autothermal reformer and upstream of the water gas shift section; (xii-c) downstream of the water gas shift section and upstream of the carbon dioxide separation unit; or (xii-d) downstream of the carbon dioxide separation unit and upstream of the purification unit; and returning the same to one or more positions selected from the group consisting of:

2. 10. The process of claim 1, comprising pre-reforming either upstream of the hydrodesulfurization unit or downstream of the hydrodesulfurization unit and upstream of the autothermal reformer.

3. 3. The process of claim 1 or claim 2, wherein there are no other reforming units in the reforming section other than the autothermal reformer.

4. 4. The process of claim 1, wherein the steam to carbon ratio of the gaseous mixture comprising hydrocarbons and steam at the inlet to the autothermal reformer in step (iii) is from 0.9:1 to 3.5:

1.

5. 5. The process of claim 4, wherein the gaseous mixture comprising hydrocarbons and steam at the inlet to the gas-heated reformer in step (iii) has a steam-to-carbon ratio of from 0.9:1 to 2.4:1, and additional steam is added to the reformed gas mixture upstream of the water-gas shift section.

6. The process of any of claims 1 to 5, wherein the water gas shift section comprises at least one high temperature shift unit.

7. The process of any preceding claim, wherein the recycle stream is returned to the process at location (xii-d).

8. The process of any preceding claim, wherein the process recycle stream is returned to the process at a single location.

9. A process according to any preceding claim, wherein the steam added in step (ii) is generated by burning a fuel gas stream in said one or more fired heaters.

10. A chemical plant, (i) a hydrodesulfurization unit (203, 303, 403, 503) configured to receive a hydrogen stream (220, 320, 420, 520) and a feed stream (201, 301, 401, 501) comprising hydrocarbons and to perform hydrodesulfurization to produce a refined hydrocarbon stream; (ii) means for adding steam (204, 304, 404, 504) to said refined hydrocarbon stream to produce a gaseous mixture (205, 305, 405, 505) comprising hydrocarbons and steam; (iii) a reforming section (207, 307, 407, 507) including an autothermal reformer configured to receive the gaseous mixture comprising hydrocarbons and water vapor and produce a reformed gas mixture (208, 308, 408, 508); (iv) a water-gas shift section (210, 310, 410, 510) including one or more water-gas shift stages configured to receive the reformed gas mixture and produce a hydrogen-enriched reformed gas (211, 311, 411, 511); (v) means for cooling the hydrogen-rich reformed gas and separating condensed water therefrom to produce a dehydrated hydrogen-rich reformed gas; (vi) a carbon dioxide separation unit (212, 312, 412, 512) configured to receive the dehydrated hydrogen-enriched reformed gas and produce a carbon dioxide gas stream (213, 313, 413, 513) and a crude hydrogen gas stream (214, 314, 414, 514); (vii) a purification unit (215, 315, 415, 515) configured to receive the crude hydrogen gas stream and produce a purified hydrogen gas stream (216, 316, 416, 516) and a hydrocarbon-containing off-gas stream (217, 317, 417, 517); (viii) means for splitting said off-gas stream into a fuel gas stream (218, 318, 418, 518) and a recycle stream (219, 319, 419, 519), said fuel gas stream being fed to one or more fired heaters used to heat one or more process streams within said process; (ix) means for compressing said recycle stream; (x) means for dividing the compressed recycle stream into a hydrodesulfurization recycle stream (220, 320, 420, 520) and a process recycle stream (221, 321, 421, 521); (xi) means for supplying said hydrodesulfurization recycle stream to said hydrodesulfurization unit; (xii) subjecting said process recycle stream to (xii-a) downstream of the hydrodesulfurization unit and upstream of the autothermal reformer; (xii-b) downstream of the autothermal reformer and upstream of the water gas shift section; (xii-c) downstream of the water gas shift section and upstream of the carbon dioxide separation unit; or (xii-d) downstream of the carbon dioxide separation unit and upstream of the purification unit; and means for returning the mixture to one or more locations selected from the group consisting of:

11. The chemical plant of claim 10, comprising a pre-reformer either upstream of the hydrodesulfurization unit or downstream of the hydrodesulfurization unit and upstream of the autothermal reformer.

12. 12. The chemical plant according to claim 10 or 11, wherein there are no other reforming units in the reforming section other than the autothermal reformer.

13. The chemical plant according to any one of claims 10 to 12, wherein the water-gas shift section comprises at least one high-temperature shift unit.

14. The chemical plant according to any one of claims 10 to 13, wherein the recycle stream is returned to the process at position (xii-d).

15. The chemical plant of any one of claims 10 to 14, wherein the process recycle stream is returned to the process at a single location.

16. 16. The chemical plant of any one of claims 10 to 15, wherein the steam added in step (ii) is generated by burning the fuel gas stream in the one or more fired heaters.

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