Process and apparatus for producing hydrogen and separating carbon dioxide

Abstract

The invention relates to a process for producing hydrogen by reforming hydrocarbons with steam, and separating carbon dioxide. The process comprises an endothermic reforming step and an autothermal reforming step for producing a synthesis gas stream, wherein the heat produced in the autothermal reforming step is used for heating in the endothermic reforming step. The process further comprises a step of converting the obtained synthesis gas stream to enrich hydrogen, a step of separating the thus produced hydrogen by pressure swing adsorption, and a step of separating carbon dioxide from the residual gas obtained from the pressure swing adsorption. The reforming units for the endothermic reforming step and the autothermal reforming step are arranged in parallel to each other or in series.

Description

Technical Field

[0001] This invention relates to a method for producing hydrogen by steam reforming hydrocarbons and separating carbon dioxide. The invention further relates to an apparatus for producing hydrogen by steam reforming hydrocarbons and separating carbon dioxide. Background Technology

[0002] Global hydrogen production is currently estimated at 70 Mt / a, with the largest proportion coming from endothermic reforming of natural gas using steam over nickel-based reforming catalysts. In this process, known as steam methane reforming (SMR), methane and steam react primarily to produce a mixture mainly composed of hydrogen, carbon monoxide, and carbon dioxide. This steam reforming method generates significant amounts of carbon dioxide, as approximately 9 tons of carbon dioxide are emitted for every ton of hydrogen produced. It is estimated that steam reforming of natural gas alone accounts for 1.5% of global carbon dioxide emissions (Wisman et al., Science 364, 756-759, 2019).

[0003] Autothermal reforming (ATR) of natural gas can also produce hydrogen. ATR differs from steam reforming in that it involves an exothermic partial oxidation step preceding the endothermic reforming step, providing the heat of reaction required for the downstream endothermic catalytic reforming. Generally, air or oxygen, such as from an air fractionation unit, is used as the oxidizing medium for partial oxidation. Furthermore, ATR requires a burner, which uses fuel gas to provide the activation energy required for partial oxidation. The partial oxidation of methane and the subsequent intermediate products, along with the endothermic catalytic reforming of steam, both result in a synthesis gas primarily composed of hydrogen, carbon monoxide, and carbon dioxide.

[0004] To make the above methods more environmentally friendly, several methods have been developed to separate carbon dioxide produced in SMR or ATR from the syngas mixture as a primary product, resulting in carbon dioxide of the highest purity. For this purpose, gas scrubbing methods based on physical or chemical absorption in absorbents such as methanol or amines, as well as cryogenic liquid separation and purification of carbon dioxide through compression, condensation, and distillation, can be employed. However, large quantities of carbon dioxide are absorbed into the adsorbent and then desorbed again or separated at low temperatures by condensation, often preventing any feasible further industrial use. Therefore, the only remaining option is frequent, long-term storage of unusable carbon dioxide to prevent its release into the atmosphere. The combination of separating (by gas scrubbing or condensation) and storing carbon dioxide is also known as sequestration or CCS (carbon capture and storage).

[0005] Therefore, it is necessary to improve the known methods of hydrogen production in a way that reduces the amount of carbon dioxide generated per ton of hydrogen produced from the outset.

[0006] US 2015 / 0321914 A1 discloses a method in which syngas, produced as a primary product through steam reforming or autothermal reforming, is converted into carbon dioxide and hydrogen through the conversion of carbon monoxide present in the syngas produced as a primary product with steam (water-gas shift reaction). Subsequently, hydrogen is separated from the carbon dioxide- and hydrogen-rich syngas by means of a pressure swing adsorption unit. The residual gas, having exhausted its hydrogen content but still rich in carbon dioxide, is then treated in a device called a cryogenic purification unit (CPU) to separate carbon dioxide from the residual gas and liquefy it in its highest purity form. The liquefied carbon dioxide can then be sent for storage or used for industrial or consumption purposes. Summary of the Invention

[0007] The overall objective of this invention is to overcome the aforementioned shortcomings of the prior art.

[0008] More specifically, an object of the present invention is to modify known methods to reduce the amount of carbon dioxide produced per unit weight of hydrogen.

[0009] More specifically, an object of the present invention is to reduce carbon dioxide emissions in a method that combines autothermal reforming of methane with cryogenic carbon dioxide separation.

[0010] The independent claims contribute to at least partial achievement of at least one of the aforementioned objectives. The dependent claims provide preferred embodiments that facilitate at least partial achievement of at least one of the aforementioned objectives. Preferred embodiments of a component of one category according to the invention are, where applicable, equally preferred for the same-named or corresponding component of another category according to the invention.

[0011] The terms "have," "contain," or "include" do not exclude the possibility of other elements or components. The indefinite article "one" does not exclude the possibility of a plural form.

[0012] The object of the present invention is at least partially achieved by a method for producing hydrogen by steam reforming hydrocarbons and separating carbon dioxide, wherein the method comprises the following steps:

[0013] (a) A feed gas stream FG is provided, wherein the feed gas stream FG contains a hydrocarbon component and vapor, wherein the hydrocarbon component contains at least methane;

[0014] (b) In an endothermic reforming step using a reforming catalyst, at least a portion of the feed gas stream FG is reformed to produce a synthesis gas stream SG1, wherein the synthesis gas stream SG1 contains hydrogen, carbon monoxide, carbon dioxide and unreacted methane.

[0015] (c) In the autothermal reforming step, a portion of the feed gas stream FG is reformed to produce a synthesis gas stream SG2, and the synthesis gas streams SG1 and SG2 are combined to produce a synthesis gas stream SG3, or

[0016] In the autothermal reforming step, the syngas stream SG1 is reformed to produce the syngas stream SG3.

[0017] The autothermal reforming step includes exothermic partial oxidation and endothermic reforming using a reforming catalyst and steam.

[0018] The synthesis gas streams SG2 and SG3 contain hydrogen, carbon monoxide, carbon dioxide, and unreacted methane, and wherein,

[0019] The heat generated in the self-heating reforming step is used for heating in the endothermic reforming step in step (b);

[0020] (d) The carbon monoxide present in the synthesis gas stream SG3 is steam-converted to produce hydrogen and carbon dioxide to generate a synthesis gas stream SG4, wherein the synthesis gas stream SG4 contains hydrogen, carbon dioxide, unreacted methane, and carbon monoxide that was not converted in step (d).

[0021] (e) Hydrogen is separated from the synthesis gas stream SG4 by pressure swing adsorption to produce a hydrogen-rich stream HG1 and a residual gas stream RG1, wherein the residual gas stream RG1 contains carbon dioxide, carbon monoxide not converted in step (d), hydrogen not separated in step (e), and unreacted methane.

[0022] (f) Carbon dioxide is separated from the residual gas stream RG1 obtained in step (e) by low-temperature carbon dioxide separation, thereby producing a carbon dioxide-rich stream CG1 and a residual gas stream RG2, wherein the residual gas stream RG2 contains unconverted carbon monoxide in step (d), unseparated hydrogen in step (e), unseparated carbon dioxide in step (f), and unreacted methane.

[0023] Compared to known methods in the prior art, the method according to the present invention is characterized by the use of a combination of endothermic and autothermal reforming steps in steps (b) and (c), with the heat generated in the autothermal reforming step used for heating in the endothermic reforming step of step (b). The autothermal reforming step is carried out in an endothermic reforming unit (autothermal reformer). The endothermic reforming step is carried out in an endothermic reforming unit (endothermic reformer, e.g., a steam reformer). This unexpectedly and significantly reduces the specific CO2 emissions in the entire method. "Specific CO2 emissions" should be understood as the mass of CO2 formed per standard cubic meter of hydrogen produced in the entire method. For example, specific CO2 emissions can be expressed in units of kg CO2 / m³. 3 (STP) report.

[0024] In the endothermic reforming step of step (b), a suitable catalyst is used to convert the feed gas FG into syngas SG1 by supplying heat. For example, the catalyst is a nickel catalyst well known to those skilled in the art. The heat required for the endothermic reforming step is at least partially, preferably entirely, provided by the heat generated in the autothermal reforming step. Depending on the arrangement of these reforming units, part or all of the feed gas FG is introduced into the reforming unit in the endothermic reforming step and converted into syngas SG1.

[0025] The autothermal reforming step in step (c) includes a partial oxidation step of the feed gas stream FG and a subsequent endothermic reforming step with steam, the latter step being used to convert the feed gas stream FG into a synthesis gas stream SG2 or SG3. The partial oxidation step in the autothermal reforming step requires the supply of an oxidant, such as air, pure oxygen, or oxygen-enriched air. The oxidant is typically introduced into the autothermal reformer via a burner. The partial oxidation of the feed gas stream FG into a synthesis gas stream SG2 or SG3 during the autothermal reforming step is an exothermic reaction. The resulting waste heat is used for the "endothermic portion" of the autothermal reforming step. The autothermal reforming step is designed such that sufficient heat is generated in total across the two reaction stages (partial oxidation and endothermic reforming) for use in heating the endothermic reforming step to convert the feed gas FG into a synthesis gas SG1.

[0026] The method according to the invention includes two alternatives defined by step (c).

[0027] In the first alternative, a portion of the feed gas stream FG is reformed in the endothermic reforming step to produce a syngas stream SG1. Another portion of the feed gas stream FG, preferably the residue of the feed gas stream FG, is reformed in the autothermal reforming step to produce a syngas stream SG2. Then, syngas streams SG2 and SG3 are combined to produce a syngas stream SG3. This allows the reforming units for the endothermic reforming step and the autothermal reforming step to be arranged in parallel or connected.

[0028] In a second alternative to the method according to the invention, the feed gas FG is entirely introduced into the reforming unit of the endothermic reforming step and converted into a syngas stream SG1. This converts the feed gas FG only partially into syngas SG1, meaning that a considerable proportion of methane and possibly other reformable hydrocarbon components remain in syngas SG1. This residue is then reformed in an autothermal reforming step to produce syngas SG3. This allows for a series arrangement or connection of the reforming units for the endothermic and autothermal reforming steps, with the autothermal reforming step following the endothermic reforming step. In other words, the reforming unit for the autothermal reforming step is arranged downstream of the reforming unit for the endothermic reforming step in the gas flow direction.

[0029] Preferably, the syngas stream generated in the self-heating reforming step, i.e., syngas stream SG2 in the case of parallel arrangement of reforming units or syngas stream SG3 in the case of series arrangement of reforming units, is directly used for heat transfer in the endothermic reforming step. Here, syngas stream SG2 and / or syngas stream SG3 preferably have a temperature of 750 to 1100°C.

[0030] The feed gas stream FG contains at least one hydrocarbon component that can be reformed with steam to produce synthesis gases SG1, SG2, SG3, or SG4. The synthesis gases contain at least hydrogen, carbon monoxide, and carbon dioxide as product components. The feed gas stream FG contains at least methane as a hydrocarbon component. Similar higher molecular weight hydrocarbons, such as ethane, propane, or butane, may be present in the feed gas stream FG.

[0031] The feed gas can first be treated in a so-called primary reformer to convert higher molecular weight hydrocarbons into shorter chain hydrocarbons using steam, particularly to increase the methane content in the feed gas stream FG. The purpose of the primary reformer is therefore typically to convert hydrocarbons with at least two carbon atoms into carbon monoxide, hydrogen, and methane. The feed gas stream FG, having been treated in the pre-reformer, may therefore already contain a certain amount of carbon monoxide and hydrogen.

[0032] The syngas stream SG3, produced by a combination of autothermal and endothermic reforming steps, is fed to the conversion step (d). In this conversion step, carbon monoxide present in the syngas stream SG3 reacts with water over a suitable catalyst via a so-called water-gas shift reaction to produce hydrogen and carbon dioxide. The syngas SG3 is cooled before being introduced into step (d). Depending on whether step (d) is a so-called cryogenic or cryogenic shift, the syngas SG3 is cooled to a higher or lower temperature before being introduced into step (d).

[0033] The syngas stream SG4 formed by the conversion step (d) is rich in hydrogen and carbon dioxide and depletes carbon monoxide. The syngas stream SG4 then undergoes a separation step (e), in which substantially pure hydrogen is produced from the syngas stream SG4 by pressure swing adsorption (PSA). The hydrogen-rich stream HG1 obtained by PSA typically has a hydrogen content of at least 95 mol%, preferably at least 99 mol%, more preferably at least 99.5 mol%, and even more preferably at least 99.9 mol%. The byproduct of the depletion of hydrogen in the PSA step, namely the residual gas stream RG1, is significantly depleted of hydrogen and significantly enriched with carbon dioxide compared to the syngas stream SG4. It also contains unconverted carbon monoxide from step (d) and unconverted methane from steps (b) and (c). Due to the presence of gases with high calorific values ​​(methane, carbon monoxide, and hydrogen), it can be used as fuel within or outside this process.

[0034] To separate carbon dioxide from the residual gas stream RG1, it is fed to step (f) for cryogenic carbon dioxide separation, which produces a carbon dioxide-rich stream CG1 and a separate residual gas stream RG2. Separation step (f) requires partial condensation of the carbon dioxide present in the residual gas stream RG1, and, optionally, distillation of the carbon dioxide-rich stream CG1 is required to achieve a specific purity. Cryogenic carbon dioxide separation is preferably carried out at temperatures below 35°C, or below 20°C, or below 0°C, or below -20°C, or below -40°C, or below -50°C, or below -55°C. Cryogenic carbon dioxide separation is also preferably carried out at temperatures above -60°C.

[0035] Syngas stream SG1 may also be referred to as the first syngas stream, syngas stream SG2 may also be referred to as the second syngas stream, and so on. This also applies to all other fluid streams numbered RG, CG, and HG in the context of this disclosure.

[0036] A preferred embodiment of the method according to the invention is characterized in that hydrogen is separated from the residual gas stream RG2, thereby producing a hydrogen-rich stream HG2 and a residual gas stream RG3. Despite the preceding separation step by pressure swing adsorption, the residual gas stream RG2 typically contains a relatively large amount of residual hydrogen, up to 50 mol%. Therefore, it is advantageous to feed the residual gas stream RG2 to another separation step to separate or at least enrich hydrogen. It is preferably considered that hydrogen is separated from the residual gas stream RG2 by membrane separation.

[0037] In one embodiment of the method according to the invention, a hydrogen-rich stream HG2 is supplied to a synthesis gas stream SG4 for hydrogen separation by pressure swing adsorption in step (e). Specifically, membrane separation methods do not have sufficient selectivity to obtain a hydrogen stream with high purity, for example, greater than 99 mol%, from the residual gas stream RG2. Because a second pressure swing adsorption step would be too complex and expensive in the sense of a second pressure swing adsorption apparatus, the hydrogen-rich stream HG2 is advantageously fed to step (e), which improves the hydrogen yield based on the overall method.

[0038] Alternatively, the gas present in the hydrogen-rich stream HG2 is used as fuel gas for heating in the autothermal reforming step of step c). For the autothermal reforming step, the feed gas FG must be heated, for example, by a combustion heating unit. The combustion heating unit can be heated at least partially by means of gases with high calorific value present in the hydrogen-rich stream HG2, particularly carbon monoxide, methane, and hydrogen, to improve thermal integration in the method.

[0039] A preferred embodiment of the method according to the invention is characterized in that the carbon dioxide-rich stream CG1 contains unreacted methane, and the carbon dioxide-rich stream CG1 undergoes a thermal separation process to separate the methane, thereby producing a carbon dioxide-rich stream CG2. Due to the low-temperature carbon dioxide separation, the carbon dioxide-rich stream can contain a significant amount of methane, for example, up to 0.2 mol% or up to 0.5 mol% methane. Additional steps including the thermal separation method can further increase the carbon dioxide content in the carbon dioxide-rich stream CG1. This thermal separation method is preferably distillation. This can produce a high-purity carbon dioxide product, which can be more easily disposed of for environmental feasibility assessments than methane-contaminated carbon dioxide products. For example, pure carbon dioxide can be mixed with electrolytic hydrogen in the correct ratio and used as a syngas for methanol production. Pure carbon dioxide products also have advantages in terms of carbon dioxide isolation, because, in particular, methane-contaminated carbon dioxide, if accidentally released after isolation, can enhance the greenhouse effect in a known manner.

[0040] A preferred embodiment of the method according to the invention is characterized in that carbon dioxide is separated from the residual gas stream RG3, thereby producing a carbon dioxide-rich stream CG3 and a residual gas stream RG4. Preferably, carbon dioxide is separated from the residual gas stream RG3 by membrane separation to obtain the carbon dioxide-rich stream CG3 and the residual gas stream RG4.

[0041] In one example of the method according to the invention, the gas present in the residual gas stream RG4 is used as fuel gas for heating in the autothermal reforming step of step c).

[0042] The carbon dioxide-rich stream CG3 is preferably supplied to the residual gas stream RG1 for cryogenic carbon dioxide separation in step (f). This increases the yield of available carbon dioxide and minimizes actual carbon dioxide emissions.

[0043] A preferred embodiment of the method according to the invention is characterized in that, for the cryogenic carbon dioxide separation in step (f), the residual gas stream RG1 undergoes at least one compression step and at least one cooling step, thereby producing a carbon dioxide-rich stream CG1 that is at least partially in the form of a concentrated carbon dioxide stream. The cryogenic carbon dioxide separation is preferably carried out by compression under pressure, for example, 5 to 74 bar, accompanied by cooling of the residual gas stream RG1, preferably to a temperature above the triple point of carbon dioxide (-56°C) or another temperature suitable for condensation. Under these temperature and pressure conditions, carbon dioxide partially condenses, resulting in enrichment of carbon dioxide in the liquid phase and enrichment of uncondensed gas in the gas phase. Preferably, to the desired extent, step (f) includes multiple compression steps and / or multiple cooling steps, meaning that carbon dioxide is condensed from the residual gas stream RG1 in multiple successive compression and cooling steps.

[0044] Preferably, to the required extent, the residual gas stream RG1 is dried in one or more steps during step (f). The drying step may be performed before the compression step, between two compression steps, and / or after the compression step. The drying step may also be performed before the cooling step, between two cooling steps, and / or after the cooling step.

[0045] Preferably, to the required extent, the residual gas stream RG1 undergoes one or more separation steps during step (f) to remove condensable components, such as methanol. The separation steps may occur before, between, and / or after the compression step. The separation steps may also occur before, between, and / or after the cooling step.

[0046] The object of the present invention is also achieved, at least in part, by a device configured to perform the method according to the invention.

[0047] The object of the present invention is also achieved, at least in part, by an apparatus for producing hydrogen by reforming hydrocarbons with steam and separating carbon dioxide, wherein the apparatus comprises the following equipment components that are fluidly connected to each other:

[0048] (a) An apparatus for providing a feed gas stream FG, wherein the feed gas stream FG comprises a hydrocarbon component and vapor, wherein the hydrocarbon component comprises at least methane;

[0049] (b) A first reforming unit, wherein the first reforming unit is configured to reform at least a portion of the feed gas stream FG in an endothermic reforming step using a reforming catalyst, wherein a synthesis gas stream SG1 is obtained in the endothermic reforming step, wherein the synthesis gas stream SG1 contains hydrogen, carbon monoxide, carbon dioxide, and unreacted methane.

[0050] (c) A second reforming unit, which is arranged parallel to or downstream of the first reforming unit, wherein,

[0051] -The second reforming unit, arranged in parallel with the first reforming unit, is configured to reform a portion of the feed gas stream FG during the autothermal reforming step, wherein,

[0052] The autothermal reforming step includes exothermic partial oxidation and endothermic reforming using a reforming catalyst and steam.

[0053] In this autothermal reforming step, a synthesis gas stream SG2 can be obtained, and

[0054] In the parallel arrangement, the first and second reforming units are configured such that the syngas streams SG1 and SG2 can be combined to produce syngas stream SG3.

[0055] -The second reforming unit, when arranged downstream of the first reforming unit, is configured to reform at least a portion of the synthesis gas stream SG1 in the autothermal reforming step, wherein,

[0056] The autothermal reforming step includes exothermic partial oxidation and endothermic reforming using a reforming catalyst and steam, wherein...

[0057] In this autothermal reforming step, a synthesis gas stream SG3 can be obtained, wherein,

[0058] The synthesis gas streams SG2 and SG3 contain hydrogen, carbon monoxide, carbon dioxide, and unreacted methane, and

[0059] The first reforming unit (b) and the second reforming unit (c) are configured such that the heat generated in the second reforming unit (c) through the self-heating reforming step can be used for heating in the first reforming unit (b);

[0060] (d) Converter unit,

[0061] - In the case where the first and second reforming units are arranged in parallel, the converter unit is arranged downstream of the first and second reforming units, or

[0062] - In the case where the second reforming unit is located downstream of the first reforming unit, the converter unit is located downstream of the second reforming unit, wherein,

[0063] The converter unit is configured to use steam to convert the carbon monoxide present in the syngas stream SG3 to produce carbon dioxide and hydrogen, thereby generating the syngas stream SG3.

[0064] The synthesis gas stream SG3 contains hydrogen, carbon dioxide, unreacted methane, and unconverted carbon monoxide from the converter unit;

[0065] (e) A pressure swing adsorption unit, arranged downstream of the converter unit, wherein,

[0066] The pressure swing adsorption unit is configured to separate hydrogen from the synthesis gas stream SG3, wherein a hydrogen-rich stream HG1 and a residual gas stream RG1 are obtained, wherein the residual gas stream RG1 contains carbon dioxide, unconverted carbon monoxide in the converter unit, hydrogen not separated by the pressure swing adsorption unit, and unreacted methane.

[0067] (f) A separation unit arranged downstream of the pressure swing adsorption unit, wherein the separation unit is configured to cryogenically separate carbon dioxide from the residual gas stream RG1 generated in the pressure swing adsorption unit, wherein a carbon dioxide-rich stream CG1 and a residual gas stream RG2 are obtained, wherein the residual gas stream RG2 contains unconverted carbon monoxide in the converter unit, unseparated hydrogen in the pressure swing adsorption unit, unseparated carbon dioxide in the separation unit, and unreacted methane.

[0068] According to the present invention, the first reforming unit (b) and the second reforming unit (c) are configured such that the heat generated in the second reforming unit (c) through the self-heating reforming step can be used for heating in the first reforming unit (b). The first reforming unit is configured for the endothermic reforming step. The second reforming unit is configured for the self-heating reforming step. The second reforming unit is preferably a self-heating reformer. The second reforming unit is arranged parallel to the first reforming unit or downstream of the first reforming unit.

[0069] When arranged in parallel with the first reforming unit, the second reforming unit produces a syngas stream SG2, which can be combined with the syngas stream SG1 from the first reforming unit. The syngas stream SG2 is preferably used directly for heating in the first reforming unit, meaning that the heat present in the syngas stream SG2 is directly used for heating in the first reforming unit. In this respect, "directly" means that the heat present in the syngas stream SG2 is not transferred to any other heat transfer medium. The heat present in the syngas stream SG2 is thus used to generate the syngas stream SG1 during the endothermic process in the first reforming unit.

[0070] When positioned downstream of the first reforming unit, the second reforming unit generates a syngas stream SG3. The syngas stream SG3 is preferably used directly for heating within the first reforming unit, meaning that the heat present in the syngas stream SG3 is directly used for heating within the first reforming unit. In this respect, "directly" means that the heat present in the syngas stream SG3 is not transferred to any other heat transfer medium. The heat present in the syngas stream SG3 is thus used to generate a syngas stream SG1 during the endothermic process in the first reforming unit.

[0071] Work examples

[0072] The present invention will be described in detail below with two working examples of the present invention and one comparative example that is not of the present invention, together with three figures, wherein the working examples and figures do not represent any limitation on the present invention.

[0073] The attached diagram shows:

[0074] Figure 1 Based on the flowchart of existing technologies or equipment

[0075] Figure 2 A flowchart of a first alternative to the method or apparatus according to the invention, wherein reforming units for the endothermic reforming step and the autothermal reforming step are arranged in parallel.

[0076] Figure 3 A flowchart of a second alternative to the method or apparatus according to the invention, wherein reforming units for the endothermic reforming step and the autothermal reforming step are arranged in series.

[0077] Figure 1A very simplified process block diagram of a method or apparatus according to the prior art, such as that disclosed in US 2015 / 0321914, is shown. The feed gas stream FG is introduced into an autothermal reforming unit 100 and converted into a synthesis gas stream SG1. The synthesis gas stream SG1 is then introduced into a converter unit 101, which reacts the carbon monoxide present in the synthesis gas stream SG1 with steam to produce carbon dioxide and hydrogen. The hydrogen-rich synthesis gas stream SG2 is then introduced into a pressure swing adsorption (PSA) unit 102 to separate high-purity hydrogen from the synthesis gas stream SG2. The hydrogen separated from the PSA unit 102 is discharged from the PSA unit 102 as a hydrogen-rich stream HG1. The residual gas stream RG1, after hydrogen depletion, also leaves the PSA unit 102 and is introduced into a separation unit 103. In the separation unit 103, carbon dioxide is separated with high purity through multiple compression and cooling steps, as well as a drying step, and leaves the separation unit as a carbon dioxide-rich stream CG1. The carbon dioxide-rich stream CG1 still contains a significant amount of residual methane, which can optionally be removed by distillation (not shown). The resulting pure carbon dioxide product is suitable for carbon dioxide isolation or further use, such as the synthesis of methanol by reacting with hydrogen produced from the electrolysis stream. The highly depleted carbon dioxide residual gas stream RG2 also exits from separation unit 103 and is introduced into membrane unit 104. Membrane separation in membrane unit 104 produces a hydrogen-rich stream HG2, which is enriched in hydrogen compared to the residual gas stream RG2, and exits from membrane unit 104. In addition, a hydrogen-depleted residual gas stream RG3, which is depleted in hydrogen compared to the residual gas stream RG2, is produced and exits from membrane unit 104. For further use, the hydrogen-rich stream HG2 can optionally be recycled to pressure adsorption unit 102 to increase hydrogen yield, or it can be used as fuel gas in autothermal reforming unit 100.

[0078] Table 1 below shows the results based on Figure 1 The material balance was simulated using a method that employed the "Aspen Plus" software. The composition of the feed gas flow was reported without the addition of steam.

[0079] Table 1: Material Balance in Comparative Examples

[0080] FG SG1 SG2 HG1 RG1 RG2 CG1 HG2 RG3 temperature ℃ 40 975 40 40 40 40 40 40 40 pressure -bar 51 47 43 43 2 20 30 30 3 Molar flow kmol / h 3869 16768 14272 8923 5349 2570 2750 1841 729 <![CDATA[CO2]]> mol% 0.77 6.46 24.57 0.00 65.57 29.69 99.77 33.77 19.39 CO mol% 0.00 15.77 0.97 0.00 2.58 5.38 0.00 1.84 14.33 <![CDATA[H2]]> mol% 0.00 46.88 71.04 99.99 22.75 47.35 0.00 61.96 10.44 <![CDATA[N2]]> mol% 0.54 0.12 0.15 0.00 0.38 0.80 0.00 0.19 2.32 <![CDATA[CH4]]> mol% 94.31 2.17 2.55 0.00 6.81 13.93 0.23 2.24 43.44 <![CDATA[C2H6]]> mol% 3.96 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[C3H8]]> mol% 0.39 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[C4H 10 ]]> mol% 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[H2O]]> mol% 0.00 28.57 0.52 0.00 1.38 1.78 0.00 0.00 6.28 methanol mol% 0.00 0.00 0.17 0.00 0.46 0.92 0.00 0.00 3.24 Ar mol% 0.00 0.02 0.03 0.00 0.08 0.16 0.00 0.00 0.55

[0081] according to Figure 1 Based on the material balance in Table 1, the method yields a carbon dioxide emission of 0.140 kg CO2 per standard cubic meter of hydrogen (m³). 3 (STP)).

[0082] Instead of the self-heating reformer 100, an endothermic reformer can be used, as also disclosed in US 2015 / 0321914. More specifically, the endothermic reformer can be a steam reformer, well known to those skilled in the art. When using a steam reformer, the carbon dioxide emissions—0.396 kg CO2 per standard cubic meter of hydrogen—are several times higher than when using a self-heating reformer.

[0083] Figure 2 A very simplified flow diagram of the method or apparatus of the first embodiment (Example 1) of the present invention is shown, wherein the reforming units are arranged in parallel. The feed gas stream FG is divided into two sub-streams. The first sub-stream of the feed gas stream FG is introduced into an endothermic reforming unit 200 (first reforming unit, configured for the endothermic reforming step). The second sub-stream of the feed gas stream FG is introduced into a self-heating reforming unit 201 (second reforming unit, configured for the self-heating reforming step). In the endothermic reforming unit 200, the first sub-stream of the feed gas stream FG is converted into a synthesis gas stream SG1. In the self-heating reforming unit 201, the second sub-stream of the feed gas stream FG is converted into a synthesis gas stream SG2. The heat generated in the self-heating reforming step of the self-heating reforming unit 201 is used for heating in the endothermic reforming step of the endothermic reforming unit 200, represented by heat flow 202. The second synthesis gas stream SG2 is preferably used directly for heating in the endothermic reforming step of the endothermic reforming unit 200, meaning that the heat present in the second synthesis gas stream SG2 is used for heating in the endothermic reforming step of the endothermic reforming unit 200 without being transferred to another heat transfer medium.

[0084] Syngas streams SG1 and SG2 generated by the endothermic reforming unit 200 and the autothermal reforming unit 201 are combined to produce a mixed syngas stream SG3, which is introduced into the converter unit 203. As a result, carbon monoxide present in the syngas stream SG3 reacts with steam to produce carbon dioxide and hydrogen. The hydrogen-rich syngas stream SG4 is then introduced into the pressure swing adsorption (PSA) unit 204 to separate high-purity hydrogen from the syngas stream SG4. The hydrogen separated from the PSA unit 204 is discharged from the PSA unit 204 as a hydrogen-rich stream HG1. The first residual gas stream RG1, after hydrogen depletion, also leaves the PSA unit 204 and is introduced into the separation unit 205. In the separation unit 205, carbon dioxide is separated with high purity through multiple compression and cooling steps as well as a drying step, and leaves the separation unit 205 as a carbon dioxide-rich stream CG1. The carbon dioxide-rich stream CG1 still contains a significant amount of residual methane, which can optionally be removed by distillation of the carbon dioxide-rich stream CG1 (not shown). The resulting pure carbon dioxide product is suitable for carbon dioxide isolation or further use, such as the synthesis of methanol by reacting with hydrogen produced from electrolysis.

[0085] The carbon dioxide-depleted residual gas stream RG2 also exits from separation unit 205 and is introduced into membrane unit 206. Membrane separation in membrane unit 206 produces a hydrogen-rich stream HG2, which is enriched with hydrogen compared to the residual gas stream RG2, and exits from membrane unit 206. Furthermore, a hydrogen-depleted residual gas stream RG3, which is depleted of hydrogen compared to the residual gas stream RG2, is produced and exits from membrane unit 206. For further use, the hydrogen-rich stream HG2 can optionally be recycled to pressure adsorption unit 204 to increase the total hydrogen yield of the method, or it can be used as fuel gas in autothermal reforming unit 201.

[0086] Table 2 below shows the results based on Figure 2 The simulated material balance of a first example of the method according to the invention is shown. The simulation was performed using Aspen Plus software. The composition of the feed gas stream is reported without the addition of steam.

[0087] Table 2: Material Balance of Example 1

[0088] FG SG3 SG4 HG1 RG1 RG2 CG1 HG2 RG3 temperature ℃ 40 958 40 40 40 40 40 40 40 pressure -bar 51 47 42 41 2 20 20 40 5 Molar flow kmol / h 3252 15139 12476 8923 5400 2671 2729 1847 824 <![CDATA[CO2]]> mol% 0.77 6.07 22.93 0.00 64.40 28.32 99.71 33.36 17.01 CO mol% 0.00 13.96 0.88 0.00 2.70 5.46 0.00 1.93 13.36 <![CDATA[H2]]> mol% 0.00 47.34 72.13 99.99 22.53 45.54 0.00 61.74 9.24 <![CDATA[N2]]> mol% 0.54 0.12 0.14 0.00 0.38 0.78 0.00 0.20 2.08 <![CDATA[CH4]]> mol% 94.31 2.65 3.21 0.00 8.37 16.63 0.29 2.77 47.69 <![CDATA[C2H6]]> mol% 3.96 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[C3H8]]> mol% 0.39 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[C4H 10 ]]> mol% 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[H2O]]> mol% 0.00 29.85 0.53 0.00 1.23 2.49 0.00 0.00 8.07 methanol mol% 0.00 0.00 0.15 0.00 0.34 0.69 0.00 0.00 2.25 Ar mol% 0.00 0.02 0.02 0.00 0.05 0.10 0.00 0.00 0.31

[0089] according to Figure 2 Based on the material balance in Table 2, the method yields a carbon dioxide emission of 0.128 kg CO2 per standard cubic meter of hydrogen (m³). 3 (STP)). Compared to the comparative example, this corresponds to a 9% reduction in CO2 emissions.

[0090] Figure 3 A very simplified flowchart of the method or apparatus in a second embodiment (Example 2) of the present invention is shown. Figure 3 The method or apparatus and according to Figure 2The difference in method or apparatus lies in that the reforming units are arranged in series or connected. An endothermic reforming unit 200 (the first reforming unit, configured for the endothermic reforming step) is arranged upstream of a self-heating reforming unit 201 (the second reforming unit, configured for the self-heating reforming step) in the airflow direction, and the latter is correspondingly arranged downstream of the endothermic reforming unit 200 in the airflow direction. The feed gas stream FG is introduced into the endothermic reforming unit 200 and converted into a synthesis gas stream SG1. The synthesis gas stream SG1 is converted into a synthesis gas stream SG3 in the self-heating reforming unit 201. The heat generated in the self-heating reforming step of the self-heating reforming unit 201 is used for heating in the endothermic reforming step of the endothermic reforming unit 200, represented by heat flow 202. The synthesis gas stream SG3 is preferably used directly for heating in the endothermic reforming step of the endothermic reforming unit 200, meaning that the heat present in the synthesis gas stream SG3 is used for heating in the endothermic reforming step of the endothermic reforming unit 200 without being transferred to another heat transfer medium. All subsequent method steps correspond to... Figure 2 Example 1.

[0091] Table 3 below shows the results based on Figure 3 The simulated material balance of a second example of the method according to the invention is shown. The simulation was performed using Aspen Plus software. The composition of the feed gas stream is reported without the addition of steam.

[0092] Table 3: Material Balance of Example 2

[0093] FG SG3 SG4 HG1 RG1 RG2 CG1 HG2 RG3 temperature ℃ 40 975 40 40 40 40 40 40 40 pressure -bar 51 44 39 39 2 20 20 40 5 Molar flow kmol / h 2540 15037 11714 8923 4281 4281 2242 1491 549 <![CDATA[CO2]]> mol% 0.77 5.02 20.09 0.00 66.80 66.80 99.82 34.01 21.01 CO mol% 0.00 11.40 0.66 0.00 2.39 2.39 0.00 1.68 14.08 <![CDATA[H2]]> mol% 0.00 49.59 76.71 100.0 23.16 23.16 0.00 62.35 11.31 <![CDATA[N2]]> mol% 0.54 0.09 0.12 0.00 0.39 0.39 0.00 0.19 2.50 <![CDATA[CH4]]> mol% 94.31 1.37 1.76 0.00 5.44 5.44 0.18 1.77 36.91 <![CDATA[C2H6]]> mol% 3.96 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[C3H8]]> mol% 0.39 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[C4H 10 ]]> mol% 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 <![CDATA[H2O]]> mol% 0.00 32.52 0.56 0.00 1.54 1.54 0.00 0.00 12.04 methanol mol% 0.00 0.00 0.10 0.00 0.27 0.27 0.00 0.00 2.08 Ar mol% 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.09

[0094] according to Figure 3 Based on the material balance in Table 3, the method yields a carbon dioxide emission of 0.118 kg CO2 per standard cubic meter of hydrogen produced. 3 (STP). Compared to the comparative example, this corresponds to a 15% reduction in CO2 emissions. Furthermore, the series arrangement of reforming units 200 and 201 provides superior performance in reducing CO2 emissions compared to the previous method. Figure 2 The advantages of parallel arrangement of reforming units 200 and 201.

[0095] List of reference numerals

[0096] FG feed gas flow

[0097] SG1 Syngas Flow

[0098] SG2 Synthesis Gas Flow

[0099] SG3 Syngas Flow

[0100] SG4 Syngas Flow

[0101] HG1, a hydrogen-rich stream

[0102] HG2, a hydrogen-rich stream

[0103] CG1 Carbon dioxide-rich stream

[0104] RG1 Residual Gas Flow

[0105] RG2 Residual Gas Flow

[0106] RG3 Residual Gas Flow

[0107] 100 self-heating reforming units

[0108] 101 Converter Unit

[0109] 102 Pressure Swing Adsorption Unit

[0110] 103 Separation Unit

[0111] 104 membrane units

[0112] 200 heat-absorbing reforming units

[0113] 201 Self-heating reforming unit

[0114] 202 Heat Flow

[0115] 203 Converter Unit

[0116] 204 Pressure Swing Adsorption Unit

[0117] 205 Separation Unit

[0118] 206 membrane units

Claims

1. A method for producing hydrogen by reforming a hydrocarbon with steam, and separating carbon dioxide, wherein, The method comprises the steps of: (a) providing a feed gas stream FG, wherein the feed gas stream FG comprises a hydrocarbon component and steam, wherein the hydrocarbon component comprises at least methane; (b) reforming at least a part of the feed gas stream FG in an endothermic reforming step using a reforming catalyst to produce a synthesis gas stream SG1, wherein the synthesis gas stream SG1 comprises hydrogen, carbon monoxide, carbon dioxide and unreacted methane; (c) reforming a part of the feed gas stream FG in an autothermal reforming step to produce a synthesis gas stream SG2 and combining the synthesis gas streams SG1 and SG2 to produce a synthesis gas stream SG3, or reforming the synthesis gas stream SG1 in an autothermal reforming step to produce a synthesis gas stream SG3, wherein the autothermal reforming step comprises exothermic partial oxidation and endothermic reforming using a reforming catalyst with steam, wherein, the synthesis gas streams SG2 and SG3 comprise hydrogen, carbon monoxide, carbon dioxide and unreacted methane, and wherein, the heat produced in the autothermal reforming step is used to heat the endothermic reforming step of step (b); (d) converting carbon monoxide present in the synthesis gas stream SG3 with steam to produce hydrogen and carbon dioxide to produce a synthesis gas stream SG4, wherein the synthesis gas stream SG4 comprises hydrogen, carbon dioxide, unreacted methane and unconverted carbon monoxide in step (d); (e) separating hydrogen from the synthesis gas stream SG4 using pressure swing adsorption, thereby producing a hydrogen rich stream HG1 and a residual gas stream RG1, wherein the residual gas stream RG1 comprises carbon dioxide, unconverted carbon monoxide in step (d), unseparated hydrogen in step (e), and unreacted methane; (f) separating carbon dioxide from the residual gas stream RG1 obtained in step (e) by cryogenic carbon dioxide separation, thereby producing a carbon dioxide rich stream CG1 and a residual gas stream RG2, wherein the residual gas stream RG2 comprises unconverted carbon monoxide in step (d), unseparated hydrogen in step (e), unseparated carbon dioxide in step (f), and unreacted methane.

2. The method of claim 1, wherein, separating hydrogen from the residual gas stream RG2, thereby producing a hydrogen rich stream HG2 and a residual gas stream RG3.

3. The method of claim 2, wherein, separating hydrogen from the residual gas stream RG2 by membrane separation.

4. The method according to any one of claims 2 and 3, characterized in that, The hydrogen rich stream HG2 is supplied to the synthesis gas stream SG4 for separation of hydrogen by pressure swing adsorption in step (e).

5. The method according to any one of claims 2 to 4, characterized in that, The gases present in the hydrogen rich stream HG2 are used as fuel gas for heating in the autothermal reforming step of step c).

6. The method according to any one of claims 1 to 5, characterized in that, The carbon dioxide rich stream CG1 comprises unreacted methane and the carbon dioxide rich gas stream CG1 is subjected to a thermal separation process to separate methane, thereby producing a carbon dioxide rich stream CG2.

7. The method according to any one of claims 2 to 6, characterized in that, separating carbon dioxide from the residual gas stream RG3, thereby producing a carbon dioxide rich stream CG3 and a residual gas stream RG4.

8. The method of claim 7, wherein, separating carbon dioxide from the residual gas stream RG3 by membrane separation.

9. The method according to any one of claims 7 and 8, characterized in that, The gases present in the residual gas RG4 are used as fuel gas for heating in the autothermal reforming step of step c). The carbon dioxide rich stream CG1 comprises unreacted methane and the carbon dioxide rich gas stream CG1 is subjected to a thermal separation process to separate methane, thereby producing a carbon dioxide rich stream CG2. separating carbon dioxide from the residual gas stream RG3, thereby producing a carbon dioxide rich stream CG3 and a residual gas stream RG4. separating carbon dioxide from the residual gas stream RG3 by membrane separation. The gases present in the residual gas RG4 are used as fuel gas for heating in the autothermal reforming step of step c). The carbon dioxide rich stream CG1 comprises unreacted methane and the carbon dioxide rich gas stream CG1 is subjected to a thermal separation process to separate methane, thereby producing a carbon dioxide rich stream CG2.

10. The method according to any one of claims 7 to 9, characterized in that, The carbon dioxide rich stream CG3 is supplied to the residual gas stream RG1 for cryogenic carbon dioxide separation in step (f).

11. The method according to any one of claims 1 to 10, characterized in that, For cryogenic carbon dioxide separation in step (f), the residual gas stream RG1 is subjected to at least one compression step and at least one cooling step, thereby producing the carbon dioxide rich stream CG1 at least partly in the form of a concentrated carbon dioxide stream.

12. An apparatus for producing hydrogen by reforming a hydrocarbon with steam, and separating carbon dioxide, wherein, The apparatus comprises the following apparatus components which are fluidly connected to each other: (a) means for providing a feed gas stream FG, wherein the feed gas stream FG comprises a hydrocarbon component and steam, wherein the hydrocarbon component comprises at least methane; (b) a first reforming unit, wherein the first reforming unit is configured for reforming at least a part of the feed gas stream FG in an endothermic reforming step using a reforming catalyst, wherein a synthesis gas stream SG1 is obtainable in the endothermic reforming step, wherein the synthesis gas stream SG1 comprises hydrogen, carbon monoxide, carbon dioxide, and unreacted methane; (c) a second reforming unit which is arranged in parallel with the first reforming unit or downstream of the first reforming unit, wherein, - the second reforming unit, in case it is arranged in parallel with the first reforming unit, is configured for reforming a part of the feed gas stream FG in an autothermal reforming step, wherein, the autothermal reforming step comprises a exothermic partial oxidation and an endothermic reforming using a reforming catalyst with steam, and a synthesis gas stream SG2 is obtainable in the autothermal reforming step, and in case of the parallel arrangement, the first and second reforming units are configured such that the synthesis gas streams SG1 and SG2 can be combined to produce a synthesis gas stream SG3, - the second reforming unit, in case it is arranged downstream of the first reforming unit, is configured for reforming at least a part of the synthesis gas stream SG1 in an autothermal reforming step, wherein, the autothermal reforming step comprises a exothermic partial oxidation and an endothermic reforming using a reforming catalyst with steam, wherein, a synthesis gas stream SG3 is obtainable in the autothermal reforming step, wherein, the synthesis gas streams SG2 and SG3 comprise hydrogen, carbon monoxide, carbon dioxide, and unreacted methane, and the first reforming unit (b) and the second reforming unit (c) are configured such that heat produced in the second reforming unit (c) by the autothermal reforming step can be used for heating in the first reforming unit (b); (d) a converter unit, - in case of the parallel arrangement of the first and second reforming units, the converter unit is arranged downstream of the first and second reforming units, or - in case of the second reforming unit arranged downstream of the first reforming unit, the converter unit is arranged downstream of the second reforming unit, wherein, the converter unit is configured for converting carbon monoxide present in the synthesis gas stream SG3 with steam to produce carbon dioxide and hydrogen, thereby producing a synthesis gas stream SG4, and the synthesis gas stream SG4 comprises hydrogen, carbon dioxide, unreacted methane, and unconverted carbon monoxide in the converter unit; (e) a pressure swing adsorption unit arranged downstream of the converter unit, wherein, The pressure swing adsorption unit is configured for separating hydrogen from the synthesis gas stream SG4, wherein a hydrogen rich stream HG1 and a residual gas stream RG1 can be obtained, wherein the residual gas stream RG1 comprises carbon dioxide, unconverted carbon monoxide in the reformer unit, hydrogen not separated in the pressure swing adsorption unit, and unreacted methane; (f) a separation unit arranged downstream of the pressure swing adsorption unit, wherein the separation unit is configured for cryogenic separation of carbon dioxide from the residual gas stream RG1 produced in the pressure swing adsorption unit, wherein a carbon dioxide rich stream CG1 and a residual gas stream RG2 can be obtained, wherein the residual gas stream RG2 comprises unconverted carbon monoxide in the reformer unit, hydrogen not separated in the pressure swing adsorption unit, carbon dioxide not separated in the separation unit, and unreacted methane.

Images