Process and plant for producing a hydrogen product

Abstract

The invention proposes a process (100, 200) for producing a hydrogen product (320) essentially containing hydrogen, the process comprising using a reforming (31) and a water-gas shift (35) to provide a first component mixture (312) that contains carbon dioxide and components with a lower boiling point than carbon dioxide, including hydrogen and carbon monoxide, using a first adsorptive separation (36) to provide the hydrogen product and a second component mixture (305, 608) that contains a respective proportion of each of the components with a lower boiling point than carbon dioxide, using a carbon dioxide removal (50, 60) that comprises a cryogenic separation (54) and a second adsorptive separation (55, 65) to provide a carbon dioxide product (504), which essentially contains carbon dioxide, and a third component mixture (507, 607) which is essentially free from carbon dioxide and contains a respective proportion of each of the components with a lower boiling point than carbon dioxide, and the process (100) is conducted in a first alternative in which the first component mixture (312) or a portion thereof is supplied to the first adsorptive separation (36) without prior separation in the carbon dioxide removal (50), the second component mixture (305) containing carbon dioxide, wherein the second component mixture (305) or a portion thereof is supplied to the carbon dioxide removal (50), and wherein the third component mixture (507) or a portion thereof is supplied to a solid oxide fuel cell unit (10), or the process (200) is conducted in a second alternative in which the first component mixture (312) or a portion thereof is supplied to the carbon dioxide removal (60) without prior separation in the first adsorptive separation (36), the second component mixture (608) essentially being free from carbon dioxide, wherein the third component mixture (607) or a portion thereof is supplied to the first adsorptive separation (36), and wherein the second component mixture (608) or a portion thereof is supplied to the solid oxide fuel cell unit (10). The present invention also provides a corresponding system.

Description

[0001] Description

[0002] Process and plant for producing a hydrogen product

[0003] The invention relates to a method and a plant for producing a hydrogen product which essentially contains hydrogen.

[0004] background

[0005] The production of hydrogen on an industrial scale is currently still predominantly based on hydrocarbons. A number of processes are known and described in common reference works, for example, in the article "Hydrogen" in Ullmann's Encyclopedia of Industrial Chemistry, June 15, 2000, DOI: 10.1002 / 14356007. a13_297, Section 4, "Production."

[0006] Hydrogen can be produced by converting gaseous, solid, or liquid carbon sources such as natural gas, naphtha, or coal. In particular, catalytic reforming in forms such as steam methane reforming (SMR) or autothermal reforming (ATR) can be used. Another route for producing hydrogen from corresponding carbon sources involves catalytic partial oxidation (POX). Combinations of these processes can also be used. Because such processes have a significant carbon footprint, the hydrogen they produce is also referred to as "grey" hydrogen.

[0007] Embodiments of steam reforming processes for producing hydrogen are described, for example, in the applicant's European patent application 22020126.3. Reference is made in particular to Figures 1 to 3 therein and the corresponding figure descriptions in this application.

[0008] In the wake of the climate debate and corresponding regulatory measures, the avoidance and recovery of carbon dioxide is becoming increasingly important. A long-term solution, for example, could involve the production of hydrogen through electrolysis, which can be carbon-neutral when using renewable energy sources, so that hydrogen produced in this way is also referred to as "green."

[0009] At least until processes for producing "green" hydrogen are commercially viable, bridging technologies can be used. These include, in particular, the recovery and storage or utilization of carbon dioxide (carbon (dioxide) capture and storage, CCS, or carbon (dioxide) capture and utilization, CCU). In this case, the corresponding hydrogen is also referred to as "blue."

[0010] The present invention has for its object to improve the production of hydrogen using carbon-containing feedstocks and, in particular, to enable a particularly efficient and / or complete recovery of carbon dioxide.

[0011] Disclosure of the invention

[0012] Against this background, a process and a plant for producing a hydrogen product are specified with the features of the respective independent patent claims. Further embodiments are the subject of the dependent patent claims and the following description.

[0013] A process proposed herein for producing a hydrogen product containing essentially hydrogen comprises providing a first component mixture containing carbon dioxide and lower boiling components than carbon dioxide, including hydrogen and carbon monoxide, using reforming and a water gas shift.

[0014] If reference is made here to "a" reforming or "a" water gas shift in the singular, this does not preclude the use of serial and / or parallel reaction steps of any suitable type. In the case of the water gas shift, for example, this can involve a high-temperature and a low-temperature shift or a high-temperature and an isothermal shift, as are generally known from the prior art. Furthermore, it is not excluded that further steps can be carried out between the water gas shift and a subsequent step, such as one of the separation steps explained below, for example and in particular the cooling and condensation of process water that can be separated.

[0015] Within the scope of the present invention, it is further provided that, using a first adsorptive separation, the hydrogen product and a second component mixture which contains each of the components boiling lower than carbon dioxide in a proportion are provided, and that, using a carbon dioxide separation which comprises a cryogenic separation and a second adsorptive separation, a carbon dioxide product which essentially contains carbon dioxide and a third component mixture which is essentially free of carbon dioxide and contains each of the components boiling lower than carbon dioxide in a proportion are provided.

[0016] The process can be carried out in a first alternative in which the first component mixture or a part thereof is fed to the first adsorptive separation without prior separation in the carbon dioxide separation, wherein the second component mixture contains carbon dioxide, wherein the second component mixture or a part thereof is fed to the carbon dioxide separation, and wherein the third component mixture or a part thereof is fed to a solid oxide fuel cell unit.

[0017] A second alternative of the method, however, comprises feeding the first component mixture or a part thereof to the carbon dioxide separation without prior separation in the first adsorptive separation, wherein the second component mixture is substantially free of carbon dioxide, wherein the third component mixture or a part thereof is fed to the first adsorptive separation, and wherein the second component mixture or a part thereof is fed to the solid oxide fuel cell unit.

[0018] The term "essentially" should be understood here in particular to mean that in a claimed composition, material stream, etc., in addition to the mandatory components, further components are permitted, provided that the essential characteristics of the claimed composition are not significantly changed by these further components. For example, a product, a corresponding mixture, or the like that is "essentially free of carbon dioxide" is suitable for venting to the atmosphere without significantly increasing the carbon dioxide emissions of the process. Accordingly, a product that "essentially" contains hydrogen has no components other than hydrogen that significantly influence the use. A product, gas mixture, or the like that "essentially" contains hydrogen can, in particular, contain more than 95, 99, 99.9, or 99.99% hydrogen.Conversely, it is "essentially free" of carbon dioxide if it contains less than 5, 1, 0.1 or 0.01% carbon dioxide. The percentages can refer to molar, quantitative or volume fractions. The solution proposed within the scope of the present invention comprises a combination of one or more solid oxide fuel cells and adsorption, in particular pressure swing adsorption, for separating carbon dioxide. By using the present invention, a virtually emission-free hydrogen production process can be achieved, while at the same time a high process efficiency is or remains. Further advantages and embodiments are explained in more detail below and with reference to the figures.

[0019] In embodiments of the invention, the reforming may comprise one or more reforming steps selected from steam reforming, electrified steam reforming, partial oxidation, and autothermal reforming. The aforementioned processes can be selected according to their suitability and availability. For further details, please refer to the specialist literature cited at the beginning.

[0020] In embodiments of the invention, a methane-containing reforming feed can be supplied to the reforming process, and the reforming feed can be formed using one or more processing steps that include desulfurization and / or pre-reforming. In this way, the reforming feed can be suitably conditioned. The formation of the reforming feed can also include, for example, gasification of solid or liquid feedstocks.

[0021] The first component mixture, the second component mixture, and the third component mixture may contain methane as one of the components boiling lower than carbon dioxide. Such methane may, in particular, represent methane not converted during reforming, which can be converted within the scope of the present invention, particularly in a solid oxide fuel cell.

[0022] In embodiments of the invention, the carbon dioxide product can be provided using cryogenic separation. The cryogenic separation can, in particular, comprise condensing liquid, carbon dioxide-rich fractions and, if appropriate, further separation in a rectification column. In principle, all cryogenic separation steps suitable for the separation of carbon dioxide can be used.In a corresponding embodiment, using cryogenic separation, the carbon dioxide product and a fourth component mixture are provided, each containing a proportion of carbon dioxide and each of the components boiling lower than carbon dioxide, wherein the fourth component mixture or a portion thereof is fed to the second adsorptive separation, wherein using the second adsorptive separation, a fifth component mixture is provided, each containing a proportion of carbon dioxide and each of the components boiling lower than carbon dioxide, and wherein the fifth component mixture or a portion thereof is fed to the cryogenic separation step. The second adsorptive separation, like the first, can be designed as a pressure swing adsorption using a suitable adsorbent, which is suitably selected by the person skilled in the art.

[0023] In the first process alternative, the second component mixture or the portion thereof fed to the carbon dioxide separation, or (again) a portion thereof, can be fed to the cryogenic separation without having previously been separated in the second adsorptive separation. In this case, provision can also be made for feeding a portion of the third component mixture formed using a membrane separation to the solid oxide electrolysis cell unit.

[0024] The second process alternative, however, can comprise feeding the first component mixture or the portion thereof fed to the carbon dioxide separation, or (again) a portion thereof, to the second adsorptive separation without having previously been separated in the cryogenic separation. These variants include particularly advantageous feed positions in a corresponding separation circuit. Using the solid oxide fuel cell unit, in embodiments of the invention, an exhaust gas can be formed that contains carbon dioxide and one or more of the components boiling lower than carbon dioxide in one proportion or each in a proportion, wherein the exhaust gas is recirculated to the carbon dioxide separation and / or combusted in a heat generation unit. In particular, a corresponding exhaust gas can also contain water (vapor).Through the measures mentioned, a significant portion of the carbon dioxide in this carbon dioxide-containing exhaust gas can ultimately be converted into the carbon dioxide product formed in the cryogenic separation, which in turn can be put to suitable use (storage, storage, etc.).

[0025] In embodiments of the present invention, compaction and drying can be carried out upstream of the cryogenic separation in order to suitably condition the feed into the cryogenic separation.

[0026] In embodiments of the present invention, the first component mixture, the second component mixture, and the third component mixture may each comprise some or all of a group of components consisting of hydrogen, methane, carbon monoxide, water, nitrogen, and trace impurities. Furthermore, the fourth component mixture and the fifth component mixture may also comprise some or all of these components. For contents of corresponding components in different embodiments of the invention, reference is made to Tables 1 to 4, which are discussed in connection with Figures 5 and 6. The stream compositions can vary greatly depending on the feedstock, reformer type, and desired carbon dioxide recovery rate.

[0027] A plant for producing a hydrogen product which essentially contains hydrogen is also subject of the invention. The plant is designed to provide, using reforming and a water gas shift, a first component mixture which contains carbon dioxide and components which boil lower than carbon dioxide, including hydrogen and carbon monoxide; to provide, using a first adsorptive separation, the hydrogen product and a second component mixture which contains each of the components which boil lower than carbon dioxide in a respective proportion; and to provide, using carbon dioxide separation which comprises a cryogenic separation and a second adsorptive separation, a carbon dioxide product which essentially contains carbon dioxide and a third component mixture which is essentially free of carbon dioxide and contains each of the components which boil lower than carbon dioxide in a respective proportion.

[0028] In a first embodiment, the system is configured to feed the first component mixture or a portion thereof to the first adsorptive separation without prior separation in the carbon dioxide separation, wherein the second component mixture contains carbon dioxide, to feed the second component mixture or a portion thereof to the carbon dioxide separation, and to feed the third component mixture or a portion thereof to a solid oxide fuel cell unit. In a second embodiment, the system is configured to feed the first component mixture or a portion thereof to the carbon dioxide separation without prior separation in the first adsorptive separation, wherein the second component mixture is substantially free of carbon dioxide, to feed the third component mixture or a portion thereof to the first adsorptive separation, and to feed the second component mixture or a portion thereof to the solid oxide fuel cell unit.

[0029] For further features and advantages of a corresponding system and embodiments thereof, reference is expressly made to the above explanations concerning the method proposed according to the invention and its embodiments, since these apply equally to this.

[0030] The same applies to a system which, according to an embodiment of the invention, is designed to carry out a method according to any embodiment of the present invention.

[0031] Short description of the drawing

[0032] Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings, in which

[0033] Figure 1 illustrates a solid oxide fuel cell, Figure 2 illustrates a solid oxide fuel cell with carbon dioxide separation,

[0034] Figure 3 illustrates a reformation,

[0035] Figure 4 illustrates a reforming with carbon dioxide separation,

[0036] Figure 5 illustrates an embodiment of the invention,

[0037] Figure 6 illustrates an embodiment of the invention, and

[0038] Figure 7 illustrates an embodiment of the invention.

[0039] Embodiments of the invention

[0040] The embodiments described below are described solely for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting with regard to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described above and below are not to be considered as limitations on the scope of the invention as defined in the claims or as limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention.

[0041] Different embodiments of the invention may include, have, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein.

[0042] Furthermore, the disclosure may encompass other inventions that are not currently claimed but may be claimed in the future, particularly if they are encompassed by the scope of the independent claims. Explanations relating to devices, apparatuses, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to the embodiments of the present invention, and vice versa. Identical, functionally equivalent, structurally identical, or comparably constructed elements, method steps, etc. may be identified by identical reference numerals.

[0043] High-temperature solid oxide fuel cells (SOFCs) are well known. These are fuel cells that operate at an operating temperature of typically 550 to 900 °C. The electrolyte of a solid oxide fuel cell consists of a solid ceramic material that is capable of conducting oxygen ions but is insulating for electrons. The electrolyte is designed as a thin membrane to transport the oxygen ions with low energy. The aforementioned high temperatures are necessary for the transport of the oxygen ions. Gas-permeable electrical conductors are attached to the sides of the electrolyte as the cathode and anode. The outer side of the cathode, facing away from the electrolyte, is surrounded by air, while the outer anode side is surrounded by fuel gas. Unused air and fuel gas, as well as combustion products, are removed from the solid oxide fuel cell.

[0044] Solid oxide fuel cells are electrochemical devices that enable the conversion of chemical energy into electrical energy with high efficiency and without moving parts. These devices can operate with multiple fuel sources, including hydrocarbons, pure hydrogen, and mixtures thereof. Solid oxide fuel cells do not allow for full utilization of the fuel in the electrolysis cell, as this would deactivate the anode-side catalyst. In conventional solid oxide fuel cells, the unconverted fuel is burned in a catalyst or afterburner, generating heat for the auxiliary components and for heat export. The exiting flue gas contains nitrogen, oxygen, carbon dioxide, and water vapor and is conventionally released into the atmosphere.

[0045] Figure 1 shows a solid oxide fuel cell with associated equipment.

[0046] Devices are illustrated in the form of a simplified diagram that can be used according to embodiments of the present invention. The solid oxide fuel cell itself, or an arrangement referred to below as a "solid oxide fuel cell unit", is indicated by 10. If reference is made below to "a" solid oxide fuel cell (unit), it is understood, as mentioned, that a corresponding device can typically be a corresponding stack of solid oxide fuel cells. The solid oxide fuel cell unit 10, or each solid oxide fuel cell of a corresponding stack, has an anode A, a cathode C, and an electrolyte E. In the following, reference is also made to an anode side or a cathode side to express that the anodes or cathodes of several solid oxide fuel cells (units) are meant.

[0047] A water stream 101 is fed to a steam generation unit 11. A steam stream 102 generated in the steam generation unit 101 is combined with a feed stream 103 containing a fuel such as hydrogen and / or a hydrocarbon to form a collective stream 104. The collective stream 104 can be pretreated in an optional pre-reforming unit 12. This can be provided in particular for hydrocarbon-containing feed streams 103.

[0048] The appropriately pretreated collected stream 105 is fed to the anode side A of the solid oxide fuel cell unit 10 or a corresponding stack. An air stream 106 is fed to the anode side.

[0049] The fuel(s) of feed stream 103 are contacted with oxygen ions O 2-, indicated here with 107, which migrate through the membrane of the solid oxide fuel cell unit 10 or the membranes of a corresponding stack, are converted in a manner known per se with the production of electrical current, so that a gas mixture enriched in the fuel(s) and carbon dioxide can be taken from the anode side A in the form of a material stream 108 and oxygen-depleted air can be taken from the cathode side C in the form of a material stream 109.

[0050] As mentioned, in a solid oxide fuel cell unit 10 or a corresponding stack, the fuel(s) are not fully converted for operational reasons, so that stream 108 still contains a certain amount of these. Therefore, a catalytic unit 13 is provided, which converts the remaining residue using an oxygen-containing stream 110, thus obtaining an exhaust gas that is essentially fuel-free but contains carbon dioxide. This exhaust gas is discharged as exhaust gas stream 111.

[0051] The need to reduce carbon dioxide emissions to mitigate global warming underscores the need for carbon capture and / or avoidance in industrial processes. The long-term solution for decarbonizing the chemical and energy sectors is to replace fossil carbon-based energy sources with renewable electricity and storable derivatives, such as green hydrogen.

[0052] In this context, solid oxide fuel cells are well suited to converting stored green hydrogen into switchable or flexibly available green electricity. However, until green hydrogen solutions become economically viable, processes are needed that capture the resulting carbon dioxide and, if necessary, store it (carbon capture and storage, CCS) or utilize it (carbon capture and utilization, CCU).

[0053] Known post-combustion carbon dioxide capture processes can be applied to the exhaust gas leaving the solid oxide fuel cell catalyst. These include solvent absorption and pressure swing adsorption (PSA). Furthermore, the anode exhaust gas, which contains a high proportion of carbon dioxide, can be subjected to low-temperature or membrane-based carbon dioxide capture, producing a hydrogen-rich and low-carbon fuel stream and a carbon dioxide stream. Optionally, a water gas shift (WGS) reactor can be installed upstream of the carbon dioxide capture process. Finally, purified oxygen can be fed to the fuel cell afterburner instead of air, creating a stream consisting primarily of carbon dioxide and water, from which a high-purity carbon dioxide stream can be easily produced.

[0054] Figure 2 illustrates a solid oxide fuel cell unit 10 with means for carbon dioxide separation associated therewith, wherein the components already explained in detail in Figure 1 are indicated by identical reference numerals and are not explained again.

[0055] As illustrated in Figure 2, a carbon dioxide removal unit 21 and a carbon dioxide removal unit 22 can be provided jointly or as alternatives. In a compression unit 23, the material stream 108 can first be compressed with water separation.

[0056] The water can be fed into the steam generation unit 11 in the form of a water stream 202 instead of or in addition to the water stream 102 illustrated in Figure 1. A compressed and less water-containing stream 201 can be fed to the carbon dioxide removal unit 21, which is constructed in a conventional manner, from which a carbon dioxide stream 203 can be withdrawn.

[0057] A portion of a material stream 204 withdrawn from the carbon dioxide removal unit 21 can be returned to the pre-reforming unit 12 as a recycle stream 205, and a further portion 206 is fed into the catalysis unit 13, which can additionally be operated with an oxygen stream 10.

[0058] With appropriate fuel in the feed stream 103, the exhaust gas 111 contains carbon dioxide, which can be substantially separated in the carbon dioxide removal unit 21 to obtain an exhaust gas stream 211 depleted in carbon dioxide and a carbon dioxide stream 213.

[0059] Hydrocarbons can be converted into hydrogen using any type of reforming reactor (see the explanations above). The associated process typically includes pretreatment, a reforming unit, and one or more optional water-gas shift reactors, followed by a pressure swing adsorption unit. The latter produces the desired product and a waste stream that can be exported or combusted to heat the reforming unit and / or generate steam.

[0060] Figure 3 illustrates a reforming process that can be used in embodiments of the invention. For the reforming processes that can be used in this case, please refer to the explanations given above. Depending on the process, the following components or media may or may not be present.

[0061] Since reference is (also) increasingly made to pressure swing adsorption in the following, the corresponding principles and, in particular, aspects thereof relevant to the present invention will first be described.

[0062] Pressure swing adsorption is based on physical adsorption phenomena, whereby highly volatile compounds with low polarity such as hydrogen or helium are practically impossible to adsorb compared to molecules such as carbon dioxide, carbon monoxide, nitrogen, and hydrocarbons. The latter components can be separated due to their different adsorption forces. Pressure swing adsorption processes operate between two pressure stages. Adsorption takes place at a comparatively high adsorption pressure, during which a gas or gas mixture freed from the adsorbed components is discharged from the pressure swing adsorption. This is also referred to as a "high-pressure stream." Desorption, in contrast, takes place at a comparatively low desorption pressure, whereby a gas or gas mixture referred to here as a "low-pressure stream" can be provided.Pressure swing adsorption, in which desorption occurs at a subatmospheric pressure level, is typically referred to as “vacuum” PSA (VPSA).

[0063] Pressure swing adsorption typically involves several pressure vessels connected in parallel, each filled with an adsorbent. Using connecting lines and control valves, a feed gas, also called a "separator," can be passed through at least one of the pressure vessels at the adsorption pressure, thus forming a high-pressure stream. One or more additional pressure vessels are regenerated during this time while maintaining the low-pressure stream. Pressure swing adsorption therefore appears externally as a continuous process, while internally it is a discontinuous process consisting of a series of parallel sequences.

[0064] In the plant illustrated in Figure 3, a gas mixture 301 is fed to a reforming unit 31, which, in the example illustrated here, is taken from a pretreatment unit 32. A hydrocarbon-containing feed stream 302 is fed to the pretreatment unit 32, as well as, for example, in the case of steam reforming, a steam stream 303 from a steam generation unit 33, which is fed with a water stream 304.

[0065] In the example illustrated here, a heat generation unit 34 is provided, which may in particular have burners integrated into a reforming reactor or the reforming unit 31 and, in contrast to the example illustrated in Figure 3, is typically not provided externally.

[0066] The heat generation unit 34 is supplied with a suitable fuel stream 30 and an oxygen-containing stream 306, for example, combustion air. An exhaust gas stream 307 can be discharged from the heat generation unit 34. Heat can be supplied to the reforming unit 31 and, if appropriate, to the steam generation unit 33, as illustrated by dashed arrows 308, 309. Heat from the exhaust gas stream 307 can be used alternatively or additionally to heat other streams shown and not shown.

[0067] A product mixture 311 is withdrawn from the reforming unit 31, to which an additional oxygen stream 310 can be supplied, and fed to a water-gas shift unit 35, in which the hydrogen content in the product mixture 311 can be increased in a known manner by converting carbon monoxide into hydrogen and carbon dioxide. A correspondingly obtained downstream stream 312 can be separated in a hydrogen separation unit 36, which may comprise a pressure swing adsorption device and the like.

[0068] A (substantially) pure hydrogen stream 320 can be withdrawn from the hydrogen separation unit 36. A residual gas containing hydrogen and other gas components remains, which can be returned to the heat generation unit 34 in the form of the fuel gas stream 305.

[0069] Various strategies have been proposed to reduce carbon dioxide emissions from the described hydrogen production process. These include the capture of carbon dioxide from the process gas prior to pressure swing adsorption, the capture of carbon dioxide from the exhaust gas or residual gas from pressure swing adsorption, and the capture of carbon dioxide from the flue gas generated during the combustion of the residual gas from pressure swing adsorption and / or the additional fuel required for heating the reforming unit and steam generation.

[0070] Typical capture methods include absorption and adsorption processes, membrane-based separation, and low-temperature gas-liquid separation. When purified oxygen is used as an oxidant during the combustion of the aforementioned exhaust gas and / or co-fuel, a carbon dioxide-rich stream can also be obtained by condensing the water in the flue gas. An overview of the streams suitable for carbon dioxide capture is provided below.

[0071] Figure 4 illustrates a reforming with carbon dioxide separation which, apart from the use of three (alternatively or in any combination, or each provided alone) carbon dioxide separation units 41, 42, 43, in which carbon dioxide streams 401, 402, 403 are separated, can essentially correspond to the reforming shown in Figure 3.

[0072] The carbon dioxide-depleted streams are indicated by reference numerals incremented by 100 compared to Figure 3. These are provided or used instead of the original material streams 307, 412, and 405, respectively.

[0073] The capture of carbon dioxide from the process gas or the exhaust gas of pressure swing adsorption results in residual carbon dioxide emissions from the combustion of the carbon-containing residual gas and / or the additional fuel used to heat the reforming unit and / or preheat process gas and generate steam. The capture of carbon dioxide from the flue gas makes it possible to reduce carbon dioxide emissions to almost zero, but it is associated with high energy consumption because the carbon dioxide in the flue gas is present in a more dilute form than in the process gas and the residual gas from pressure swing adsorption. Finally, combustion with elevated oxygen content requires an on-site air separation unit (ASU) and is associated with energy loss due to the separation of oxygen from the air.It has been proposed to combine solid oxide fuel cells and steam reforming units to more efficiently utilize the residual gas generated in pressure swing adsorption. In such an arrangement, at least a portion of the residual gas generated by pressure swing adsorption provides at least a portion of the anode feed of the solid oxide fuel cell. Furthermore, the above-mentioned carbon dioxide capture processes for reducing emissions from the solid oxide fuel cells and steam reforming units can be applied as described if the solid oxide fuel cells and steam reforming units are combined accordingly.

[0074] In a typical hydrocarbon-to-hydrogen conversion process, the product stream from the (final) water gas shift reactor is the stream with the highest carbon dioxide partial pressure, and the residual gas leaving pressure swing adsorption for hydrogen separation has the highest carbon dioxide content. Therefore, it is thermodynamically advantageous to capture carbon dioxide from one of these streams. However, they contain at least some carbon monoxide and methane that has not been converted in the reforming unit or in the water gas shift reactors and is typically oxidized in a combustor or catalytic oxidizer to produce heat and carbon dioxide. Therefore, capturing only carbon dioxide in these streams does not achieve near-complete avoidance of carbon dioxide emissions.

[0075] In order to achieve near-zero carbon dioxide emissions using state-of-the-art technology, the carbon dioxide must therefore be separated in at least one stream other than the process gas and the residual gas from pressure swing adsorption.

[0076] The present invention proposes the use of one or more solid oxide fuel cells in conjunction with carbon dioxide-selective pressure swing adsorption, creating a "blue" hydrogen production process with high process efficiency. Carbon dioxide-selective pressure swing adsorption is also referred to below as "second adsorptive separation," "second pressure swing adsorption," etc., whereas the pressure swing adsorption used to produce hydrogen is referred to as "first adsorptive separation," "second pressure swing adsorption," etc. In alternative embodiments, it is proposed to separate carbon dioxide from the residual gas of the first pressure swing adsorption or the product stream of the (or the last) water gas shift reactor.It is further proposed to direct at least one stream that has undergone both the first pressure swing adsorption and the second pressure swing adsorption and is therefore enriched in methane and / or carbon monoxide to the anode side of one or more solid oxide fuel cells to generate electricity and / or heat and a carbon dioxide-rich anode off-gas. At least a portion of this anode off-gas can be recycled to the cryogenic separation carried out downstream of the second pressure swing adsorption in order to recover at least a portion of the carbon dioxide contained in this stream in a carbon dioxide product.

[0077] The proposed combination of one or more solid oxide fuel cells and pressure swing adsorption for carbon dioxide separation provides a nearly emission-free hydrogen production process while maintaining high process efficiency.

[0078] The proposed process may include preprocessing, e.g., removal of all sulfur components from the hydrocarbon feed and / or preforming the feed. A hydrogen-rich syngas is obtained in a hydrocarbon-to-syngas conversion unit as described above, with a downstream water-gas shift. A first pressure swing adsorption process is used to generate a high-purity hydrogen stream and a second stream, hereinafter referred to as the residual gas.

[0079] In one embodiment, the residual gas from the first pressure swing adsorption is compressed and fed into a dryer, followed by cryogenic carbon dioxide removal. The latter comprises the steps of condensing at least a portion of the carbon dioxide in the stream and optionally purifying the condensate by distillation or boiling off impurities. The cryogenic separation unit produces a high-purity carbon dioxide stream and a second stream. The second stream is fed into the second pressure swing adsorption, where a carbon dioxide-enriched and a carbon dioxide-depleted stream are generated. The carbon dioxide-enriched stream is combined with the residual gas from the first pressure swing adsorption and finally returned to the carbon dioxide purification.At least a portion of the low-carbon or carbon dioxide-free stream is passed to the anode side of one or more solid oxide fuel cells, where at least a portion of the carbon monoxide, carbon dioxide, and hydrogen present in the stream is oxidized and electricity is generated. A carbon dioxide-rich exhaust gas from the solid oxide fuel cell is combined with the residual gas from the first pressure swing adsorption and the carbon dioxide-enriched stream from the second pressure swing adsorption and finally recycled to the carbon dioxide separation unit. At least a second portion of the anode exhaust gas from the solid oxide fuel cell is cleaned and oxidized in a combustor, fired heater, or catalytic oxidation unit. The heat of combustion can be used to generate steam and / or to provide heat for reforming and / or to heat any stream in the process.

[0080] Figure 5 illustrates a method according to a corresponding embodiment of the invention and is designated overall by 100. For the basic components and method steps, reference is made in particular to Figure 3 and the associated explanations, which also apply here accordingly.

[0081] As illustrated in Figure 5, a high-temperature fuel cell 10 or a corresponding stack is provided here. For material flows 106, 108, and 109, reference is made to Figures 1 and 2.

[0082] The material stream or residual gas stream 305 is combined in a collector 51 with further material streams explained below to form a collective stream 501, which is compressed in a compressor unit 52. A correspondingly compressed collective stream 502 is dried in a separation unit 53, in particular comprising a temperature swing adsorption device, and then fed as a dried material stream 503 to a carbon dioxide purification unit 54. In the carbon dioxide purification unit 54, carbon dioxide can be separated in essentially pure form and converted into a carbon dioxide stream 504.

[0083] A material stream 505 remaining after the separation of carbon dioxide in the carbon dioxide purification unit 54 can be fed into a further separation unit 55, which in particular has a pressure swing adsorption device. In the further separation unit 55, a material stream 506 enriched in carbon dioxide and depleted of other components is formed, which can be fed back to the collector 51, as well as a material stream 507 depleted in carbon dioxide and other components, which, in the example shown, is expanded via a valve 56 and, like the material streams 104 and 105 in Figures 1 and 2, can be fed to the fuel cell 10 or a corresponding stack.

[0084] The exhaust gas 108 generated by the fuel cell 10 or in a corresponding stack can be partially recirculated to the heat recovery unit 34 via a distributor 57 and another portion can be fed back into the circuit to the compressor 52, etc., in the form of a material flow 507. As illustrated by a dashed arrow, direct recirculation to the fuel cell 10 is also possible.

[0085] As an alternative to the configuration of the operating units shown in Figure 5, the order in which the process gas enters the first and second pressure swing adsorption units can be reversed by first passing the product stream from the water gas shift to the second pressure swing adsorption unit to generate a carbon dioxide-enriched stream and a carbon dioxide-depleted stream, with the carbon dioxide-depleted stream being further passed to the first pressure swing adsorption unit. In this configuration, at least a portion of the residual gas from the first pressure swing adsorption unit is passed to the anode of one or more solid oxide fuel cells to generate electricity and a carbon dioxide-enriched solid oxide fuel cell anode exhaust gas.

[0086] At least a portion of the anode exhaust gas can be combined with the carbon dioxide-enriched stream from the second pressure swing adsorption and thus further fed to the carbon dioxide separation. As in the previously explained configuration, the separation is based on the use of two pressure swing adsorption steps to obtain a carbon dioxide-enriched stream, a hydrogen-enriched stream, and a third stream containing a significant proportion of carbon monoxide and / or methane, with the latter used as feed for one or more solid oxide fuel cells. In this way, an additional carbon dioxide-enriched stream can be generated, a portion of which is ultimately fed to the carbon dioxide purification process.

[0087] Figure 6 illustrates a method according to one embodiment of the invention and is designated overall by 200. For the basic components and method steps, reference is made in particular to Figures 3 and 5 and the associated explanations, which also apply here accordingly. The following explains, in particular, the differences compared to Figure 5 and Appendix 100.

[0088] Here, stream 312 is fed into a separation unit 65, which may, in particular, comprise a pressure swing adsorption device. In the further separation unit 55, a stream 606 enriched in carbon dioxide and depleted of other components is formed, which can be fed to the collector 51, and a stream 607 depleted in carbon dioxide and other components, which, in the example shown, is fed to the hydrogen separation unit 36 ​​instead of stream 312.

[0089] A material stream 608 remaining in the hydrogen separation unit 36 ​​can be fed to the fuel cell 10 or a corresponding stack, as in Figures 1 and 2, like the material streams 104 and 105, respectively. A dashed arrow illustrates how a partial stream of the material stream 508 can be recirculated.

[0090] In both embodiments, i.e., the processes 100 and 200 according to Figures 5 and 6, the invention can enable the separation of at least 90%, preferably at least 95%, and particularly preferably at least 98% of the carbon dioxide generated in the process. The advantages of using solid oxide fuel cells for industrial exhaust gas utilization are, in particular, the highly efficient production of electricity and the generation of a carbon dioxide-enriched stream, in particular a stream that is not diluted with nitrogen from the air. The advantages of the proposed configurations are the enabling of near-zero carbon dioxide emissions from a process for converting hydrocarbons into hydrogen and the highly efficient carbon dioxide capture in a stream for which separation is thermodynamically particularly advantageous.Table 1 below shows typical value ranges for the contents of the components hydrogen, nitrogen, carbon monoxide, carbon dioxide, water, and methane in the component mixtures referred to here as the "first" to "fifth" component mixtures (column 1, "KG") according to the design illustrated in Figure 5. The percentages refer to the molar fraction and add up to 100%. The corresponding component mixtures are each indicated here with the corresponding reference symbols with which they are referenced in Figure 5 (column 2, ("BZ")). Table 1. especially < 1%

[0091] Table 2 below corresponds to Table 1 and thus to the embodiment shown in Figure 5, but example values ​​are given which may deviate by 5 to 10% upwards or downwards.

[0092] Compositions apply to approximately 99% target carbon dioxide recovery and an electrically heated reforming reactor. Table 2

[0093] In Table 3 below, typical value ranges for the contents of the components hydrogen, nitrogen, carbon monoxide, carbon dioxide, water and methane in the component mixtures are again given, in accordance with Table 1, but here according to the design illustrated in Figure 6.

[0094] Table 4

[0095] * especially < 1%

[0096] Table 4 below corresponds to Table 3, and thus to the exemplary embodiment shown in Figure 6, although exemplary values ​​are given, which may vary by 5 to 10% upwards or downwards. Here, too, the exemplary compositions apply to approximately 99% of the desired carbon dioxide recovery and an electrically heated reforming reactor.

[0097] Table 2

[0098] Optionally, a hydrogen-selective membrane can be used to generate a hydrogen-enriched stream and a hydrogen-lean stream from the carbon dioxide-lean stream from the second pressure swing adsorption, wherein the hydrogen-enriched stream can be used as a low-carbon fuel and the hydrogen-lean stream can be passed to the anode side of the solid oxide fuel cell(s). This is illustrated in Figure 7 using a process 300, where a corresponding membrane separation is indicated by 71, but which otherwise essentially corresponds to the process 100 according to Figure 1. The corresponding material streams are designated 701 and 702. Express reference is made to the above explanations. If a fired reforming reactor is used to generate at least part of the hydrogen, the low-carbon fuel according to Figure 7, i.e. material stream 702, can be used, for example, to heat the reforming reactor.

[0099] Multiple solid oxide fuel cell units 10 or stacks may share one or more auxiliary devices. In the configuration shown in Figure 5, a pressure reduction section may be used to reduce the pressure of the carbon dioxide-depleted stream from the second pressure swing adsorption before it is fed to the one or more solid oxide fuel cell units 10 on the anode side, thereby generating one or more fluid streams having a lower pressure than the feed pressure of the pressure reduction section and a lower temperature than the feed temperature of the pressure reduction section. The pressure reduction section may include one or more valves and / or one or more turbine stages.

[0100] In one embodiment of the invention, one or more streams reaching a low temperature, preferably a temperature below 0°C, in the pressure reduction section may be used to cool any stream in the process that requires cooling, most preferably one or more streams in the carbon dioxide separation, indicated as 50 or 60 in all embodiments.

[0101] In conjunction with an electrically heated reforming reactor, at least a portion of the power generated by the solid oxide fuel cell unit 10 can supply at least a portion of the power used for heating there. The proportion of the power used for heating the electrically heated reforming reactor supplied by the solid oxide fuel cell unit 10 can be greater than 10%, in particular greater than 20%.

[0102] When using the proposed system with an electrically heated reforming reactor, at least a portion of the heat required to preheat the reformer feed can be provided by electricity. This can be achieved by one or more separate electric heaters and / or by heating the reformer feed in a first section of the reformer tubes in the absence of catalyst before contacting it with a suitable catalyst in a second section of the reformer tubes. A portion of the carbon dioxide-depleted gas from the second pressure swing adsorption can be recycled to a preprocessing unit, a reforming reactor, or one of the water gas shift reactors. The stream fed into the combustion chamber can alternatively be exported or used for energy purposes to generate heat and / or electricity.

Claims

A method (100, 200) for producing a hydrogen product (320) which essentially contains hydrogen, the method comprising providing a first component mixture (312) containing carbon dioxide and components boiling lower than carbon dioxide, including hydrogen and carbon monoxide, using a reforming step (31) and a water-gas shift step (35); providing the hydrogen product and a second component mixture (305, 608) containing each of the components boiling lower than carbon dioxide in a proportion, using a carbon dioxide separation step (50, 60) which comprises a cryogenic separation step (54) and a second adsorptive separation step (55, 65), a carbon dioxide product (504) which essentially contains carbon dioxide, and a third component mixture (507, 607),which is substantially free of carbon dioxide and contains each of the components boiling lower than carbon dioxide in a proportion, and the method (100) is carried out in a first alternative, in which the first component mixture (312) or a part thereof is fed to the first adsorptive separation (36) without prior separation in the carbon dioxide separation (50), wherein the second component mixture (305) contains carbon dioxide, wherein the second component mixture (305) or a part thereof is fed to the carbon dioxide separation (50), and wherein the third component mixture (507) or a part thereof is fed to a solid oxide fuel cell unit (10), or, the method (200) is carried out in a second alternative, in which the first component mixture (312) or a portion thereof is fed to the carbon dioxide separation (60) without prior separation in the first adsorptive separation (36), wherein the second component mixture (608) is substantially free of carbon dioxide, wherein the third component mixture (607) or a portion thereof is fed to the first adsorptive separation (36), and wherein the second component mixture (608) or a portion thereof is fed to the solid oxide fuel cell unit (10). Method (100, 200) according to claim 1, wherein the reforming (31) comprises one or more reforming steps selected from steam reforming, electrified steam reforming, partial oxidation, and autothermal reforming.The process (100, 200) of claim 1 or 2, further comprising supplying a methane-containing reforming feed (301) to the reforming (31), and forming the reforming feed (301) using one or more upgrading steps including desulfurization and / or pre-reforming (32). The process (100, 200) of any preceding claim, wherein the first component mixture (312), the second component mixture (305, 608), and the third component mixture (507, 607) contain methane as one of the lower-boiling components than carbon dioxide.A method (100, 200) according to any one of the preceding claims, wherein the carbon dioxide product (504) is provided using the cryogenic separation (54), wherein a fourth component mixture (505) containing carbon dioxide and each of the lower boiling than carbon dioxide components in a proportion is provided using the cryogenic separation (54), wherein the fourth component mixture (505) or a portion thereof is fed to the second adsorptive separation (55, 65), wherein a fifth component mixture containing carbon dioxide and each of the lower boiling than carbon dioxide components is provided using the second adsorptive separation (55, 65). boiling components each in a proportion, and wherein the fifth component mixture or a part thereof is fed to the cryogenic separation step (54).

6. The method (100) according to claim 5, which is carried out in the first method alternative, wherein the second component mixture (305) or its part fed to the carbon dioxide separation (50), or a part thereof, is fed to the cryogenic separation (54) without having previously been in the second adsorptive Separation (55) to have been separated.

7. The method (100) according to claim 6, wherein a portion of the third component mixture (507) formed using a membrane separation (71) is fed to the solid oxide electrolysis cell unit (10).

8. The method (200) according to claim 5, which is carried out in the second method alternative, wherein the first component mixture (312) or the part thereof fed to the carbon dioxide separation (60), or a part thereof, is fed to the second adsorptive separation (55) without having been previously separated in the cryogenic separation (54).

9. The method (100, 200) according to any one of the preceding claims, wherein using the solid oxide fuel cell unit (10) an exhaust gas (108) is formed which contains carbon dioxide and one or more of the components boiling lower than carbon dioxide in one proportion or each in one proportion, wherein the exhaust gas (108) is returned to the carbon dioxide separation unit (50, 60) and / or combusted in a heat generation unit (34).

10. Method (100, 200) according to one of the preceding claims, in which compaction (52) and drying (53) are carried out upstream of the cryogenic separation (54). 1 1 . Plant for producing a hydrogen product (320) which essentially contains hydrogen, the plant being designed to using a reforming (31) and a water-gas shift (35) to provide a first component mixture (312) containing carbon dioxide and components boiling lower than carbon dioxide, including hydrogen and carbon monoxide; using a first adsorptive separation (36) to provide the hydrogen product and a second component mixture (305, 608) containing each of the components boiling lower than carbon dioxide in a proportion; using a carbon dioxide separation (50, 60) comprising a cryogenic separation (54) and a second adsorptive separation (55, 65) to provide a carbon dioxide product (504) containing substantially carbon dioxide and a third component mixture (507, 607) which is substantially free of carbon dioxide and contains each of the components boiling lower than carbon dioxide in a proportion; and wherein the plant is designed in a first embodiment tofeeding the first component mixture (312) or a part thereof to the first adsorptive separation (36) without prior separation in the carbon dioxide separation (50), wherein the second component mixture (305) contains carbon dioxide, feeding the second component mixture (305) or a part thereof to the carbon dioxide separation (50), and feeding the third component mixture (507) or a part thereof to a solid oxide fuel cell unit (10), or, wherein the plant is designed in a second embodiment to supply the first component mixture (312) or a part thereof to the carbon dioxide separation (60) without prior separation in the first adsorptive separation (36), wherein the second component mixture (608) is substantially free of carbon dioxide, the third component mixture (607) or a Part thereof to the first adsorptive separation (36), and the second component mixture (608) or a part thereof to the solid oxide fuel cell unit (10).

12. Plant according to claim 11, which is used to carry out a method according to one of the Claims 1 to 10 are set up.