Methanation method and system
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-07-29
- Publication Date
- 2026-08-14
Smart Images
Figure 2026527486000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a methanation method and a system for performing methanation.
Background Art
[0002] Methanation is the conversion of carbon monoxide and / or carbon dioxide to methane through hydrogenation. The following reactions represent the methanation of carbon monoxide and carbon dioxide, respectively: CO + 3H2 → CH4 + H2O CO2 + 4H2 → CH4 + H2O
Summary of the Invention
[0003] The present invention aims to provide a novel methanation method and a novel electrolyzer system for performing methanation.
[0004] According to a first aspect of the present invention, there is provided a methanation method comprising: providing an electrolyzer system, where the electrolyzer system includes an electrolyzer having at least one electrolyzer cell, at least one fuel input for fuel to enter, and at least one off-gas output for off-gas to exit, supplying a fuel containing at least water (H2O) and either or both of carbon dioxide (CO2) and carbon monoxide (CO) to at least one fuel inlet, operating the electrolyzer system by supplying electricity to the electrolyzer cell to electrolyze the fuel in at least one electrolyzer cell and decompose a part of the water into hydrogen (H2) and oxygen (O2), further comprising, the electrolyzer operating at a temperature of 150 °C or higher, performing methanation on carbon dioxide and / or carbon monoxide in the electrolyzer, that is, generating methane (CH4) in the electrolyzer. A method is provided.
[0005] Methanation is the process of converting carbon monoxide and / or carbon dioxide into methane through hydrogenation. Hydrogen from water and / or hydrogen produced by the electrolysis of that water combine with carbon monoxide and / or carbon dioxide to form methane (CH4) and water (H2O). Since the hydrogenation / methanation reaction is an exothermic reaction, heat is also generated.
[0006] In a typical embodiment, the off-gas from at least one off-gas output unit is a mixed gas containing at least methane and vapor. Typically, it also contains carbon monoxide, carbon dioxide, and hydrogen. In some embodiments, this method includes returning and recirculating at least a portion of the vapor, carbon monoxide, carbon dioxide, and hydrogen in the mixed gas back to the electrolyzer.
[0007] Carbon dioxide can be supplied by the air. For example, water can be vapor mixed in the air.
[0008] In some embodiments, the electrolysis of the fuel also includes the decomposition of some of the carbon dioxide into carbon monoxide and oxygen.
[0009] In some embodiments, the electrolyzer operates at temperatures between 450 and 650°C. Such temperatures facilitate the methanation process and improve the efficiency of this method. Typically, the electrolyzer operates at temperatures not exceeding 550°C, above which methanation may decrease.
[0010] In some embodiments, the fuel is a mixture of vapor and carbon dioxide.
[0011] In some embodiments, separate streams of steam and carbon dioxide are supplied to the fuel inlet.
[0012] In some embodiments, the fuel inlet has at least two separate inlets, one for steam and the other for carbon dioxide.
[0013] In some embodiments, there are two off-gas output units, the first of which is for methane and vapor, and the second of which is for oxygen.
[0014] In some embodiments, the first off-gas output unit is also for carbon monoxide, carbon dioxide, and hydrogen in the mixed gas.
[0015] In some embodiments, the mixed gas released from at least one off-gas output unit passes through a gas separation process to separate at least methane from the mixed gas.
[0016] In some embodiments, the gas separation process includes a condensation step to condense most of the water from the gas mixture.
[0017] In some embodiments, the gas separation process includes a CO2 separation step to separate most of the CO2 from the mixed gas.
[0018] In some embodiments, the gas separation process includes an H2 and / or CO separation process to separate most of the H2 and / or CO from the mixed gas.
[0019] In some embodiments, the H2 and / or CO separation process includes a methane separation process to separate most of the methane from H2 and / or CO in the mixed gas, so that most of the CO2 and H2O have already been removed from the mixed gas.
[0020] H2, H2O, CO, and CO2 in a gas mixture are sometimes referred to as unreacted gases in the methanation process.
[0021] In some embodiments, unreacted gas in the mixed gas is recirculated to the electrolyzer via one or more gas inputs.
[0022] In some embodiments, the electro-reactor operates at a temperature from 500 to 600 °C, or more preferably from 525 to 575 °C.
[0023] In some embodiments, the temperature is from 500 to 550 °C. In some embodiments, the temperature can be up to 700 °C, or even up to 750 °C.
[0024] In some embodiments, a methanation catalyst is used in the electro-reactor or at least one electro-reactor cell to improve the efficiency of methanation occurring within the electro-reactor. Preferably, the methanation catalyst is disposed in a cooler region of the electro-reactor or stack or cell. For example, the methanation catalyst can be disposed at the outlet end of the electro-reactor cell, near the outlet end, or towards the outlet end. This is useful when the electro-reactor cell operates under endothermic conditions, i.e., underpotential or endothermic voltage. This is because methanation (CO + 2H2 → CH4 + 2H2O) preferentially occurs at lower temperatures.
[0025] In some embodiments, the methanation catalyst is a nickel-based catalyst.
[0026] In some embodiments, the electro-reactor comprises a reverse water gas shift catalyst. The reverse water gas shift catalyst acts to convert carbon dioxide to carbon monoxide by combining carbon dioxide and hydrogen to produce carbon monoxide and water. Preferably, the reverse water gas shift catalyst is disposed in a hotter region of the electro-reactor or stack or cell. For example, the reverse water gas shift catalyst can be disposed at the inlet end of the electro-reactor cell, near the inlet end, or towards the inlet end. This is useful when the electro-reactor cell operates under endothermic conditions, i.e., underpotential or endothermic voltage. This is because the reverse water gas shift reaction (CO2 + H2 → H2O + CO) has a higher yield at higher temperatures.
[0027] In some embodiments, the reverse water gas shift catalyst is made from a material different from the methanation catalyst.
[0028] In some embodiments, the reverse water gas shift catalyst is not a nickel-based catalyst.
[0029] In some embodiments, the methanation catalyst and / or the reverse water gas shift catalyst are provided at other locations within the electrolyzer system other than the electrolyzer cell. For example, they may be provided on the surface of a manifold within the electrolyzer through which the off-gas flows.
[0030] By providing the catalyst, the rate of methanation can be improved, and furthermore, methanation can be maintained even at higher or lower temperatures.
[0031] In some embodiments, the ratio of the fuel gas, typically the ratio of steam to carbon dioxide as the original source gas, is such that the ratio of methane to the unreacted gas in the electrolysis and methanation processes in the off-gas mixed gas is 5% by volume or more, that is, at least 5% of the total volume of the mixed gas exiting from at least one off-gas output section is methane. This can be measured at the temperature and pressure of the off-gas mixture at the off-gas output section.
[0032] In some embodiments, the target ratio is >1:10, preferably 10% or more (>1:9), and more preferably 3:7 to 1:1, i.e., 30 to 50%. In some embodiments, for example, this could be at least 10% methane, at least 15% methane, at least 20% methane, at least 30% methane, at least 50% methane, or even at least 80%, 90%, or 95% methane. In some well-optimized embodiments, it is also possible to generate off-gas with methane close to 100% (e.g., 95% to 100% methane). In other words, one or more of H2, H2O, CO, and CO2 from the fuel outlet may theoretically be present in trace amounts, minimal amounts, or not at all.
[0033] In some embodiments, the fuel gas ratio is controlled such that the ratio of methane in the off-gas mixed gas to the unreacted gas from the electrolysis and methanation processes is a target ratio, and therefore, at least 10% of the total volume of the mixed gas coming out of at least one off-gas output unit is methane.
[0034] The methanation of CO and H2 is an exothermic reaction. Therefore, in some embodiments, the heat from the methanation reaction is used to heat the fluid entering the electrolyzer, such as water (or steam), CO2, CO, recycled gas, or a gas mixture.
[0035] In some embodiments, the electrolyzer is a solid oxide type electrolyzer.
[0036] In some embodiments, at least one electrolyzer cell is part of a stack of electrolyzer cells.
[0037] In some embodiments, the electrolyzer has one or more stacks of electrolyzer cells.
[0038] Cells and / or stacks can be connected in series or in parallel. A combination of both may also exist.
[0039] In some embodiments, the electrolyzer cell, or each electrolyzer cell, is a solid oxide type electrolyzer cell. In other words, the electrochemically active region of the electrolyzer cell is a solid oxide. Solid oxide type electrolyzer cells (SOECs) typically operate in the range of 400–900°C. These include medium-temperature SOECs and high-temperature SOECs. For some chemicals, the cells operate in the temperature range of 400–700°C, or more specifically, 450–650°C. Such electrolyzer cells may be called medium-temperature solid oxide type electrolyzer cells, or IT-SOECs.
[0040] Typically, the present invention uses water in the form of vapor rather than liquid water. The advantage of a vapor-based electrolyzer is that, in vapor electrolysis, particularly in medium and high-temperature vapor electrolysis above 400°C, the high-temperature environment allows for reduced power requirements compared to the electrolysis of liquid water, thus enabling efficient hydrogen production. Furthermore, the higher the temperature, the relatively higher the reactivity with the electrolyzer compared to liquid water. Therefore, the present invention is very suitable for use in solid oxide type electrolyzer cells (or SOECs) (commonly known as medium-temperature SOECs) operating at temperatures above 400°C. It can also be used in high-temperature SOECs where the cell operating temperature exceeds 700°C. In some cases, the cutoff between medium-temperature and high-temperature SOECs is 750°C.
[0041] Many possible forms of SOEC exist using various electrochemically active electrolyte chemicals. For example, three well-known electrolyte materials are yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and gadolinium-doped ceria (GDC or CGO). The present invention can be used with any of these, as well as with many other forms of electrolyzers.
[0042] Due to the SOEC's operating temperature (usually exceeding 400°C), the liquid water passing through the electrolyzer cell evaporates into high-temperature steam. Furthermore, this usually occurs outside the cell, i.e., within or before the piping connected to at least one fuel input.
[0043] Alternatively, in some embodiments, the electrolyzer cell system comprises high-temperature electrolyzer cells with a stack operating temperature of 750°C to 1100°C.
[0044] According to a further aspect of the present invention, an electrolyzer system is provided which is configured to operate using the method defined above.
[0045] In some embodiments, the electrolyzer includes a methanation catalyst.
[0046] In some embodiments, the electrolyzer includes a reverse water-gas shift catalyst.
[0047] According to a further aspect of the present invention, an electrolyzer system is provided comprising an electrolyzer having at least one electrolyzer cell, at least one fuel input section, and at least one off-gas output section, wherein the off-gas output section is connected to a methane separator to separate methane from the off-gas exiting the off-gas output section during use of the electrolyzer system.
[0048] In some embodiments, the off-gas output unit is directly connected to the methane separator.
[0049] In some embodiments, the off-gas output section is fluidly connected to a methane separator, and methane separation is performed in a downstream operation.
[0050] By-products from the separation (e.g., steam or water, carbon dioxide, carbon monoxide, and / or hydrogen) can be returned to the electrolyzer and recycled. Thus, the electrolyzer system may further comprise one or more connections from the methane separator to at least one fuel input.
[0051] In some embodiments, the electrolyzer is connected to a source of steam and carbon dioxide.
[0052] In some embodiments, the electrolyzer is a solid oxide type electrolyzer.
[0053] In some embodiments, the electrolyzer has an operating temperature range of 450 to 650°C.
[0054] In some embodiments, at least one electrolyzer cell is part of a stack of electrolyzer cells.
[0055] In some embodiments, the electrolyzer has one or more stacks of electrolyzer cells.
[0056] In some embodiments, the methane separator is a methane separator whose operating temperature exceeds 400°C.
[0057] In some embodiments, the methane separator is a methane membrane.
[0058] In some embodiments, the methane separator is a cryogenic separator.
[0059] In some embodiments, a heat exchanger is provided that is configured to preheat the fuel by reusing heat from the mixed gas or its separated components in the off-gas output section.
[0060] The electrolyzer system can be configured to operate using the method described above.
[0061] A further aspect of the present invention relates to a method for producing methane using at least one electrochemical cell, The electrochemical cell must be supplied with at least water and carbon dioxide as inputs, To supply electrical energy to an electrochemical cell in order to perform at least a partial conversion of water into hydrogen and oxygen, Includes, At least a partial conversion of carbon dioxide to carbon monoxide and water, At least partial conversion of carbon monoxide to methane (CH4), A method is provided that further includes this.
[0062] In some embodiments, the method further includes taking the output fluid from the cell and extracting at least a portion of the methane from the output fluid. The methane can then be used, for example, as a product for future use.
[0063] In some embodiments, the electrochemical cell also performs at least part of the conversion of carbon dioxide to carbon monoxide and water.
[0064] In some embodiments, the reverse water-gas shift catalyst performs at least part of the conversion of carbon dioxide to carbon monoxide and water.
[0065] In some embodiments, the electrochemical cell is an electrolyzer cell.
[0066] This aspect of the present invention can be carried out using the electrolyzer system described above, wherein the electrolyzer cell is at least one electrolyzer cell of the electrolyzer.
[0067] This aspect of the present invention is a methanation method according to a first aspect of the present invention, wherein the electrolyzer cell is at least one electrolyzer cell of an electrolyzer.
[0068] A further aspect of the present invention relates to a method for operating an electrolyzer system comprising at least one electrochemical cell having a fuel inlet, a fuel outlet, and a fuel fluid passage connecting the fuel inlet and the fuel outlet, i) Supplying a fuel gas containing water and a carbon source selected from one or more of CO and CO2 to the fuel inlet, ii) Operating the electrolyzer system by passing an electric current through at least one electrochemical cell, iii) At least partially electrolyzing the vapor into hydrogen and oxygen, iv) Reacting hydrogen with a carbon source in the fuel fluid channel to produce methane, v) Discharging a product gas from the fuel outlet containing at least 5 volume percent methane and one or more of H2, H2O, CO, and CO2, A method including this is provided.
[0069] In some embodiments, the target ratio is >1:10, preferably 10% or more (>1:9), and more preferably 3:7 to 1:1, i.e., 30 to 50%. In some embodiments, for example, this could be at least 10% methane, at least 15% methane, at least 20% methane, at least 30% methane, at least 50% methane, or even at least 80%, 90%, or 95% methane. In some well-optimized embodiments, it is also possible to generate off-gas with methane close to 100% (e.g., 95% to 100% methane). In other words, one or more of H2, H2O, CO, and CO2 from the fuel outlet may theoretically be present in trace amounts, minimal amounts, or not at all.
[0070] In some embodiments, the electrochemical cell is a solid oxide type electrolyzer cell.
[0071] In some embodiments, the electrolyzer system, preferably at least one electrochemical cell or fuel fluid channel, further comprises a reverse water-gas shift catalyst.
[0072] In a preferred embodiment, the reverse water-gas shift catalyst is positioned in the fuel fluid passage.
[0073] In a preferred embodiment, the method further includes step iiia), which involves passing a mixture of fuel gas and hydrogen through a reverse water-gas shift catalyst after step iii), but before step iv).
[0074] The features of this method can be incorporated in conjunction with any of the methods described above. For example, an electrochemical cell can be at least one electrolyzer cell of the electrolyzer of such a method.
[0075] This method can be carried out using any one of the aforementioned electrolyzer systems, where the electrochemical cell is at least one electrolyzer cell of the electrolyzer.
[0076] Herein, the present invention will be described as merely an example with reference to the accompanying drawings. [Brief explanation of the drawing]
[0077] [Figure 1] This diagram schematically shows a typical electrolyzer cell, and multiple electrolyzer cells can be stacked on top of each other. [Figure 2] This figure shows the process for implementing the first embodiment of the present invention. [Figure 3] This is a schematic diagram of a possible configuration of the first embodiment. [Modes for carrying out the invention]
[0078] Referring first to Figure 1, the basic structure and operation of a typical conventional electrolyzer cell 11 within the electrolyzer 10 of the electrolyzer system 20 are shown with reference to one fuel / electrolyzer cell 11 in the electrolyzer cell stack 12, hereafter referred to as the stack. Note that other auxiliary components related to the electrolyzer cell 11 are included in the electrolyzer system 20. These typically include heat exchangers 52, 56, 88, 90 (Figure 3), heaters, valves, and sensors.
[0079] The electrolyzer cell 11 comprises an anode 33, a cathode 34, and an electrolyte 35. Such a structure of the electrolyzer cell 11 is well known in the art. In this prior art example, the electrolysis of water is described, but it is also known that carbon dioxide is supplied to the electrolyzer cell instead.
[0080] The input fluid (i.e., water / carbon dioxide) is at least partially electrolyzed within the electrolyzer cell 11 when electricity flows through it. This causes, for example, at least some of the water to break down into its constituent hydrogen (H2) and oxygen (O2). Conversely, carbon dioxide is at least partially broken down into oxygen (O2) and carbon monoxide (CO).
[0081] Water, usually in the form of steam 43, is generally supplied from a water source, which can be a steam source if it is desired to reduce internal heating of the water in the electrolyzer system 20. Water / steam flows to the cathode 34 of the electrolyzer cell 11 via an inlet 41, and hot air 42 flows to the anode 33 via another inlet 40. To power the electrolyzer cell, current is applied across the electrolyzer cell 11 via electrical terminals / connections 36, 37 on the anode and cathode sides of the electrolyzer cell 11. These terminals can be arranged adjacent to each other on one side or end of the stack 12 of the cell 11 by stacking the cells in parallel and using busbars to extend one terminal to the other end of the stack 12, for example, as is known in the art. A voltage can be applied across the stack 12 via terminals 36, 37, thereby causing current to flow through the cell 11. Powering the electrolyzer 10 in this manner is well known in the art.
[0082] As a result of the electric current, an electrolytic reaction occurs across the electrolyte 35, causing oxygen ions to flow from the cathode 34 through the electrolyte 35 to the anode 33. Some of the vapor is decomposed into hydrogen on the cathode side of the electrolyzer cell 11, and oxygen is produced on the anode side.
[0083] Oxygen is extracted via an airflow or sweep flow provided by the high-temperature air 42 and thus discharged from an off-gas outlet 38 on the anode side of the electrolyzer cell 11. Its output is generally oxygen-rich air (an oxygen-rich high-temperature gas flow). Hydrogen, on the other hand, is extracted on the cathode side of the electrolyzer cell 11 and discharged from another off-gas outlet 39.
[0084] Since the decomposition of steam into oxygen and hydrogen usually occurs only with respect to a portion of the supplied steam, the off-gas on the cathode side typically mixes with the remaining steam from the input fluid. Therefore, the hydrogen is discharged as "wet" hydrogen on the cathode side. The steam exiting from the cathode side is rich in hydrogen, while the air exiting from the anode side is rich in oxygen.
[0085] These off-gas temperatures are typically similar to the operating temperature of the electrolyzer cell 11. However, the specific delta from the input temperature will depend on the amount of power supplied to the electrolyzer and the internal resistance of the cell.
[0086] Such operating characteristics of electrolyzer cells, including SOECs, are well known in the art, and the input fluid is either steam or carbon dioxide. Since the goal is to produce hydrogen or carbon monoxide as the main products of the process, it is not common to supply both to the electrolyzer cell simultaneously, and oxygen is a potentially useful by-product in either of these. Therefore, the input fluid is appropriately selected to match the target output.
[0087] Due to the high operating temperature of the electrolyzer cell 11 (i.e., above 100°C in the case of a steam electrolyzer, and usually above 400°C in the case of a solid oxide electrolyzer cell (SOEC)), the heat of the off-gas from the off-gas outlets 38, 39 is effectively utilized by the electrolyzer system 20 without being wasted, and can provide at least some of the heat for, for example, steam generation on the input side of the stack, and similarly, for heating the hot air entering the electrolyzer before the inlets 40, 41. Therefore, as mentioned above, the heat exchanger is generally provided within the electrolyzer system 20.
[0088] Referring to Figures 2 and 3, one embodiment of the present invention is shown and will be described below.
[0089] In this invention, water and either or both carbon dioxide and carbon monoxide are used as the input fluid. Typically, this is supplied as a mixture to the inlet of the electrolyzer. According to this invention, methane is the target product, rather than hydrogen and / or carbon monoxide.
[0090] According to the present invention, water is converted at least partially to hydrogen and oxygen by passing through the electrolyzer, and carbon dioxide in the input fluid can also be converted at least partially, or instead, to carbon monoxide and oxygen. However, further chemical reactions, namely methanation, exist in the electrolyzer.
[0091] As mentioned above, methanation is the conversion of carbon monoxide and / or carbon dioxide into methane through hydrogenation. Hydrogen from water and / or hydrogen produced by the electrolysis of that water combine with carbon monoxide and / or carbon dioxide to form methane (CH4) and water (H2O). Furthermore, since the hydrogenation / methanation reaction is an exothermic reaction, heat is released during the reaction. As mentioned above, the following reactions represent the methanation of carbon monoxide and carbon dioxide, respectively: CO + 3H2 → CH4 + H2O CO2 + 4H2 → CH4 + H2O
[0092] According to the present invention, this methanation occurs within the electrolyzer system 20, ideally within the electrolyzer 10, within the stack 12 of the electrolyzer 10, or within the electrolyzer cell 11 itself (i.e., all three of these).
[0093] Referring first to Figure 2, the basic operation of a preferred embodiment of the present invention is shown.
[0094] As shown in Figure 2, the present invention is an electrolyzer system 20 that uses an electrolyzer 20 to combine electrolysis and methanation in order to produce methane by supplying both water and carbon dioxide (and / or carbon monoxide).
[0095] In this embodiment, the process operates in a substantially closed-loop system, but a steam and carbon dioxide (and / or carbon monoxide) supply line 48 is also provided to replenish the electrolyzer 10 with fresh input fluid or "fuel" (i.e., steam and carbon dioxide and / or carbon monoxide) at the first fuel input section 14. This is to keep the process going as the generated methane is extracted from the electrolyzer system 20 at the end of the process line 50.
[0096] The electrolyzer 11 of this embodiment comprises a single stack 12 of electrolyzer fuel cells 11 that function as electrochemical cells for electrolyzing water. Although the stack 12 is shown to have seven cells 11, generally the stack 12 has tens or even hundreds of cells 11, usually all in parallel, and the cells 11 may also be used in series or a combination of series and parallel. In some electrolyzers 10, multiple stacks 12 may be provided, electrically connected in series or in parallel.
[0097] During the operation of the electrolyzer system 20, both the reverse water-gas shift reaction and the methanation reaction occur within the stack in parallel with steam reforming and electrolysis. As mentioned above, the reverse water-gas shift reaction converts carbon dioxide to carbon monoxide by combining carbon dioxide and hydrogen to produce carbon monoxide and water. To facilitate this reaction, a catalyst can be provided, for example, as a coating on the electrolyzer cell or elsewhere in the stack, such as in the inlet or outlet manifold.
[0098] Following these reactions, a product gas is generated, which becomes a reformed mixture consisting of CO, CO2, CH4, H2, and H2O. Since these reactions typically act only on a portion of the fluid passing through the electrolyzer cell 11, this also mixes with the remaining input fluid.
[0099] The generated gas exits the electrolyzer through the off-gas outlet 46 and then passes through three different separation stages 100, 102, and 104 in this example.
[0100] In this embodiment, the first separation stage is a water condensation stage including a water condenser 100. This water condensation stage condenses at least a portion of the water (H2O) from the generated gas by cooling the generated gas to below 100°C or by passing the generated gas over a surface in the water condenser 10 that is cooled to below 100°C. This condenses the water (or at least a portion of the water in the generated gas) in the generated gas into a liquid form. The liquid water can then be recycled through the electrolyzer 10, stack 12, or electrolyzer cell 11. For this purpose, the liquid water exits the water condenser 100 at a condensate outlet 106 and returns to the electrolyzer 10, stack 12, or electrolyzer cell 11 via a condensate return pipe 114 and a recycling inlet 110. In some embodiments, the water is recycled back through a first fuel input section 14.
[0101] In this embodiment, the second separation stage is a carbon dioxide separation stage located in the carbon dioxide separation unit 102. This can be carried out using known techniques, including membrane separation techniques, air separation unit (ASU) separation techniques, and / or pressure swing adsorption (PSA) separation techniques. For example, cryogenic distillation can be used in this method. The carbon dioxide can then be recycled through the electrolyzer 10 or the stack 12 or the electrolyzer cell 11. For this purpose, the carbon dioxide exits the carbon dioxide separation unit 102 at the CO2 outlet 108 and is sent through p (which can be the same inlet as for water, including passing through the first fuel input section 14, or a different inlet).
[0102] In this embodiment, the third separation stage is a methane separation stage in the methane separation unit 104. This can be carried out using known techniques, including membrane separation techniques, air separation unit (ASU) separation techniques, and / or pressure swing adsorption (PSA) separation techniques. For example, cryogenic distillation can be used in this method.
[0103] In some embodiments, carbon dioxide removal and methane removal can be performed in the same process, albeit at different stages / temperatures. However, as will be discussed in relation to a particular embodiment in Figure 3, the separation temperatures for carbon dioxide in stage 2 and methane in stage 3 can be quite different, so in this case, separate separation units 102, 104 are preferred, and therefore are provided in this example.
[0104] The methane can then be collected for distribution at the end of the process 50, while the by-products (i.e., the remaining fractions of the original product gas, i.e., hydrogen and carbon monoxide) can be recycled through the electrolyzer 10, stack 12, or electrolyzer cell 11. For this purpose, the by-products exit the methane separation unit 104 at the by-product outlet 112 and are returned to the electrolyzer 10, stack 12, or electrolyzer cell 11 via the by-product return pipeline 118 and a recycling inlet (which can be the same inlet 110 as for water or carbon dioxide, including passing through the first fuel input section 14, or a different inlet).
[0105] As will be discussed with reference to Figure 3, it should be understood that the order of these three separation stages may be changed depending on the method used to separate the component gases of the product gas. However, the order described here is preferred because it removes the potentially largest amount of impurities first in each stage before moving to the downstream stage, and because it is the order in which each gas is separated when cooling techniques are used for various separations. Therefore, this results in higher energy efficiency of the process.
[0106] In particular, the separation of carbon dioxide and methane is optimally performed below 100°C, even when using membrane separation technology, in which case water is easily separated, and even more easily below 0°C. It should also be noted that when using ASU technology, these processes are almost always performed below 0°C, and therefore in a state where liquid or gaseous water is not already present. As a result, the remaining water is frozen and thus easily extracted.
[0107] Next, referring to Figure 3, a more specific configuration of the embodiment in Figure 2 is shown. In this example, the generated gas exits the electrolyzer 11 again at the off-gas output section 46. The generated gas exits the electrolyzer 11 at a temperature substantially corresponding to the operating temperature of the electrolyzer 11.
[0108] Using that heat, the generated gas passes through a first heat exchanger 52 to heat the fluid entering the electrolyzer 11 at the recycle inlet 110 (or first fuel input section 14), and the first heat exchanger 52 can be thermally connected to a pair of heat exchangers 88, 90 located in either or both of the CO2 return line 116 or the by-product return line 118. Thus, the heat of the generated gas can heat the recycled carbon dioxide or recycled carbon monoxide and hydrogen. This can also, or alternatively, be connected to the supply fluid via further heat exchangers not shown.
[0109] The product gas exiting the first heat exchanger is slightly cooled at this point, and some water may condense from the product gas. This is returned to the electrolyzer via the condensate return pipe 114 and the recycle inlet 110 for recycling. The product gas then passes through the first compressor 54. In this example, the pressure rises to 20 Barg (i.e., gauge pressure), but it may be higher or lower. This heats the product gas, and to utilize its heat, the product gas passes through the second heat exchanger 56. Thus, its heat can also be reused by the electrolyzer system for one of the fluid supply sources of the electrolyzer system 20.
[0110] The second heat exchanger 56 cools the generated gas sufficiently to condense the remaining (or at least most of) water from the generated gas, and the condensed water can then exit the second heat exchanger 56 via the condensate outlet 106 and be recirculated to the electrolyzer 11 via the condensate return pipe 114 and the recycle inlet 110, together with the water already returned.
[0111] In this embodiment, the first heat exchanger 52, the second heat exchanger 56, and the first compressor 54 can form a water condenser 100.
[0112] Here, the drier (or more dry) product gas exits the second heat exchanger and is sent through a distribution channel to the first cryogenic heat exchanger 58. This cryogenic heat exchanger is arranged in a counterflow configuration to maximize heating of the returning, in this case carbon dioxide (from the carbon dioxide separation unit 102) and to maximize cooling of the product gas.
[0113] In this embodiment, the generated gas exits the first cryogenic heat exchanger 58 at approximately -15°C, although this temperature may be higher or lower, preferably below 0°C. The low-temperature generated gas then flows through further distribution lines to a second cryogenic heat exchanger 60, where the gas is further cooled to -25°C in this embodiment, although this temperature may be higher or lower, depending on the pressure at this part of the process if the product is not compressed to that pressure by the first compressor 54.
[0114] This second cryogenic heat exchanger 60 is also arranged in a counterflow configuration to maximize the temperature change between the inflow and outflow of the generated gas. The other side of the second cryogenic heat exchanger 60 receives fluid from the refrigerant circuit 120. The refrigerant circuit will be described further below.
[0115] Next, the first valve 70 controls the distribution of the product gas to the first separation chamber 68, where carbon dioxide is separated from the remaining fraction of the product gas. The carbon dioxide exits through the CO2 outlet 108 and returns to the electrolyzer 11 via the CO2 return pipeline 116, the first pair of heat exchangers 90, and the recycle inlet 110. A second valve 72 can be used to control this flow.
[0116] The remaining fraction of the product gas after the separation of carbon dioxide exits the first separation chamber 68 and passes through a second compressor 66. In this embodiment, the second compressor 66 further increases the pressure of the product gas to 30 Barg, but it may be higher or lower. This increases the temperature of the product gas. To utilize this heat, the product gas passes through a third cryogenic heat exchanger 84. This is also a counterflow heat exchanger to maximize the temperature change between the inflow and outflow of the product gas, and the fluid corresponding to the fluid on the other side of this third cryogenic heat exchanger 84 is the byproduct of the third separation stage.
[0117] Therefore, the remaining fraction of the generated gas is cooled by a third cryogenic heat exchanger 84. In this embodiment, the fluid is cooled to around -50°C, although this temperature may be higher or lower and may depend on the pressure at which the product is compressed by the second compressor 66. These cooled remaining fractions are then sent to a fourth cryogenic heat exchanger 74 through another distribution channel. This allows the remaining fraction to be further cooled to around -100°C in this embodiment, although this temperature may be higher or lower and may depend on the pressure at which the product is compressed by the second compressor 66. This cooling is provided by a refrigerant circuit 120, as in the case of the second cryogenic heat exchanger 66.
[0118] The refrigerant circuit 120 includes a coolant distribution line between the fourth cryogenic heat exchanger 74 and the second cryogenic heat exchanger 60, a further coolant distribution line equipped with the refrigerant heat exchanger 64 and a compressor or pump 62, and a return loop through the fourth cryogenic heat exchanger 74.
[0119] The fluid pumped or circulating through the refrigerant circuit 120 passes through a first circuit path in the fourth cryogenic heat exchanger 74. The refrigerant circuit 120 then loops back through a second circuit path in the fourth cryogenic heat exchanger 74. A valve 76 controls its flow. These flow paths are arranged in a counter-flow configuration. The second circuit path is also counter-flowing to a third circuit path that passes through the fourth cryogenic heat exchanger 74. This third circuit path is the circuit path through which the remaining fraction flows.
[0120] The refrigerant heat exchanger 64 extracts heat from the refrigerant fluid leaving the second cryogenic heat exchanger 60 (i.e., about -15°C in this embodiment) and cools it to -100°C, preparing to cool the remaining fraction in the fourth cryogenic heat exchanger 74 to -100°C as described above. This heat can be used to heat the other of the pair of heat exchangers 88, 90, assuming that heat exchanger 56 is already thermally connected to one of them. Thus, each of the heat exchangers 52, 56, and 64 can be used to add heat to the fluid passing through heat exchangers 88 and 90.
[0121] Next, the remaining fraction can exit the fourth cryogenic heat exchanger 74 (at -100°C and about 30 Barg in this embodiment) and enter the second separation chamber 80. Here, methane is separated from the remaining fraction, and the final fraction can be returned to the electrolyzer 11 via a further valve 82, a third cryogenic heat exchanger 84, a by-product return line 118, and the other of the pair of heat exchangers 88. Meanwhile, the methane at this stage is in liquid form or easily compressible to liquid form and can be collected in a container 86 for later use elsewhere. For example, liquid methane can be separated by this cryogenic cooling to -100°C, then cooled to about -160°C to liquefy in a container, and recycled to the electrolyzer 11 along with the remaining fraction of the original product gas, i.e., hydrogen and carbon monoxide.
[0122] A major advantage of the present invention is that it is a "process-enhanced" system that does not require a methanation reactor. Furthermore, the exothermic nature of the methanation reaction can be used as a direct energy input to the stack, partially replacing the electrical energy requirements for maintaining heat within the cell, especially when a thermoneutral voltage is used in the stack.
[0123] Under optimal operating conditions, optimizing the fuel supply ratio (H2O:CO2), oxidant utilization rate, and stack temperature can minimize, reduce, or avoid the risk of carbon formation in the electrolyzer or stack, thereby maximizing, increasing, or improving methane yield.
[0124] Depending on the temperature of methane separation, methane may already be in liquid form or can be easily liquefied using pressure. Higher pressure throughout the process can also accelerate the methanation reaction and improve the yield. This also reduces the burden of liquefying methane.
[0125] The present invention is particularly applicable to electrolyzers 10 in the field of medium-temperature and high-temperature electrolyzer cells. In some embodiments, at least one electrolyzer cell in the stack is a solid oxide type electrolyzer cell, i.e., the electrochemically active region is a solid oxide. Solid oxide type electrolyzer cells (SOECs) typically operate in the temperature range of 400 to 900°C, and in the case of some chemicals, in the temperature range of 400 to 700°C, or more specifically, 450 to 650°C. Such electrolyzer cells may be called medium-temperature solid oxide type electrolyzer cells, or IT-SOECs.
[0126] The present invention operates with an electrolyzer system 20 that converts liquid water into steam, and an electrolyzer 11 that converts the steam into hydrogen and oxygen within the system 20. The advantage of a steam-based electrolyzer is that, in steam electrolysis, particularly in medium and high-temperature steam electrolysis at temperatures above 400°C, the high-temperature environment reduces the power requirements for electrolyzing water molecules from steam compared to the electrolysis of liquid water, thus efficiently producing hydrogen. Furthermore, the higher the temperature, the relatively higher the reaction activity with the electrolyzer compared to liquid water. Therefore, the present invention is very suitable for use in solid oxide type electrolyzer cells (or SOECs) operating at temperatures above 400°C (commonly known as medium-temperature SOECs, or high-temperature SOECs when above 750°C).
[0127] As mentioned above, there are many possible forms of SOEC using various electrochemically active electrolyte chemicals. For example, three well-known electrolyte materials are yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and gadolinium-doped ceria (GDC or CGO).
[0128] Due to the SOEC temperature (usually exceeding 400°C), liquid water passing through the electrolyzer (e.g., through the condensate return pipe 114) evaporates into high-temperature steam before entering or entering the electrolyzer or its stack. However, typically, the liquid water is already reliably converted into superheated steam before entering the stack by various heat exchangers and any other fluid temperature control systems (e.g., trim heaters) for controlling the temperature of the fluid entering the electrolyzer cell stack.
[0129] Alternatively, in some embodiments, the electrolyzer cell system comprises high-temperature electrolyzer cells whose stack operating temperature is between 750°C and 1100°C.
[0130] Another beneficial aspect of the present invention is when it is carried out in an electrolyzer cell, particularly in an electrolyzer cell operating under endothermic conditions. The electrolytic reaction that produces hydrogen can create a temperature gradient across the cell (at an endothermic voltage, it is hotter at the beginning and cooler at the outlet). A thermoneutral voltage can be used to control or eliminate this, but if a temperature gradient is present, it may be beneficial for optimizing the yield of the product gas.
[0131] Carbon monoxide is a crucial intermediate step in the conversion of carbon dioxide and water to methane. This is released by the reverse water-gas shift reaction (CO2 + H2 → H2O + CO), and this equilibrium reaction yields higher yields at higher temperatures. Once CO is produced, the second step, methanation (CO + 2H2 → CH4 + 2H2O), preferentially occurs at lower temperatures. These characteristics can be leveraged by optimizing catalyst coating in the high-temperature region (i.e., near the cell inlet) to enhance the reverse water-gas shift reaction and by optimizing the methanation catalyst in the lower-temperature region (i.e., near the cell outlet). This not only means that the overall system yield can "above" the combined thermodynamic equilibrium, but it can also represent optimized chemical heat recovery, and thus maximizing both the reactor's energy efficiency and yield.
[0132] Accordingly, the present invention has been described above merely as an example with reference to the accompanying drawings. Modifications to the details may be made within the scope of the claims appended to this specification.
Claims
1. A methanation method comprising providing an electrolyzer system, wherein the electrolyzer system comprises an electrolyzer having at least one electrolyzer cell, at least one fuel input section into which fuel is introduced, and at least one off-gas output section from which off-gas is released, and the method is A fuel containing at least water and either or both carbon dioxide and carbon monoxide is supplied to at least one fuel inlet. The electrolyzer system is operated by supplying electricity to the electrolyzer cell in order to electrolyze the fuel in at least one electrolyzer cell and decompose a portion of the water into hydrogen and oxygen, It further includes, The electrolyzer operates at a temperature of 150°C or higher. The carbon dioxide and / or carbon monoxide are methanated within the electrolyzer. method.
2. The method according to claim 1, wherein the fuel is a mixture of steam and carbon dioxide.
3. The method according to any one of the claims, wherein separate streams of steam and carbon dioxide are supplied to the fuel inlet.
4. The method according to any one of the claims, wherein there are two off-gas output units, the first off-gas output unit for methane and vapor, and the second off-gas output unit for oxygen.
5. The method according to any one of the claims, wherein the mixed gas discharged from the at least one off-gas output unit passes through a gas separation process to separate at least the methane from the mixed gas.
6. The method according to claim 5, wherein the gas separation process includes a condensation step to condense most of the water from the mixed gas.
7. The gas separation process involves CO from the mixed gas. ２ To separate most of it, CO ２ The method according to claim 5 or 6, comprising a separation step.
8. The gas separation process involves H from the mixed gas. ２ and / or H to separate most of CO ２ The method according to any one of claims 5 to 7, comprising and / or a CO separation process.
9. The aforementioned H ２ and / or CO separation process involves the H in the mixed gas. ２ and / or a methane separation process to separate most of the methane from the CO ２ and H ２ The method according to claim 8, wherein most of the oxygen has already been removed from the mixed gas.
10. The method according to any one of the claims, wherein the unreacted gas in the mixed gas is recirculated to the electrolyzer via the one or more gas inputs.
11. The method according to any one of the claims, wherein the electrolyzer operates at a temperature of 500 to 600°C, or more preferably 525 to 575°C.
12. The method according to any one of the claims, wherein a methanation catalyst is used in the electrolyzer or in at least one electrolyzer cell to improve the efficiency of methanation occurring in the electrolyzer.
13. The method according to claim 12, wherein the methanation catalyst is a nickel-based catalyst.
14. The method according to any one of the claims, wherein the ratio of the fuel gas is controlled such that the ratio of methane in the off-gas mixed gas to the unreacted gas of the electrolysis and methanation process is a target ratio, and so that at least 10% of the total volume of the mixed gas coming out of the at least one off-gas output unit is methane.
15. The method according to any one of the claims, wherein the heat from the methanation reaction is used to heat the fluid entering the electrolyzer.
16. The method according to any one of the claims, wherein the electrolyzer is a solid oxide type electrolyzer.
17. The method according to any one of the claims, wherein the at least one electrolyzer cell is part of a stack of electrolyzer cells.
18. The method according to any one of the claims, wherein the electrolyzer comprises one or more stacks of electrolyzer cells.
19. An electrolyzer system configured to operate using the method described in any one of the above claims.
20. The electrolyzer system according to claim 19, wherein the electrolyzer comprises a methanation catalyst.
21. The electrolyzer system according to claim 20, wherein the methanation catalyst is located in a lower temperature region of the electrolyzer or stack or cell.
22. The electrolyzer system according to claim 20 or 21, wherein the methanation catalyst is disposed at, near, or toward the outlet end of the electrolyzer cell.
23. The electrolyzer system according to any one of claims 19 to 22, wherein the electrolyzer comprises a reverse water-gas shift catalyst.
24. The electrolyzer system according to claim 23, wherein the methanation catalyst is located in a lower temperature region of the electrolyzer or stack or cell.
25. The electrolyzer system according to claim 23 or claim 24, wherein the methanation catalyst is disposed at, near, or toward the outlet end of the electrolyzer cell.
26. An electrolyzer system comprising an electrolyzer having at least one electrolyzer cell, at least one fuel input section, and at least one off-gas output section, wherein the off-gas output section is connected to a methane separator to separate methane from the off-gas exiting the off-gas output section during use of the electrolyzer system.
27. The electrolyzer system according to claim 26, wherein the electrolyzer is connected to a source of steam and carbon dioxide.
28. The electrolyzer is a solid oxide type electrolyzer, as described in claim 26 or the electrolyzer system according to claim 26.
29. The electrolyzer system according to any one of claims 26 to 28, wherein the electrolyzer has an operating temperature of 450 to 650°C.
30. The electrolyzer system according to any one of claims 26 to 29, wherein the at least one electrolyzer cell is part of a stack of electrolyzer cells.
31. The electrolyzer system according to any one of claims 26 to 30, wherein the electrolyzer has one or more stacks of electrolyzer cells.
32. The electrolyzer system according to any one of claims 26 to 31, wherein the methane separator is a methane separator whose operating temperature exceeds 400°C.
33. The electrolyzer system according to any one of claims 26 to 32, wherein the methane separator is a methane membrane.
34. The electrolyzer system according to any one of claims 26 to 31, wherein the methane separator is a cryogenic separator.
35. The electrolyzer system according to any one of claims 26 to 31, further comprising a heat exchanger configured to preheat fuel by reusing heat from the mixed gas or its separated components in the off-gas output section.
36. An electrolyzer system according to any one of claims 26 to 35, configured to operate using the method described in any one of claims 1 to 19.
37. A method for producing methane using at least one electrochemical cell, The electrochemical cell is supplied with at least water and carbon dioxide as input, To supply electrical energy to the electrochemical cell in order to perform at least a partial conversion of water into hydrogen and oxygen, Includes, At least a partial conversion of carbon dioxide to carbon monoxide and water, The aforementioned partial conversion of carbon monoxide to methane, Methods that further include the above.
38. The method according to claim 37, further comprising taking an output fluid from the cell and extracting at least a portion of methane from the output fluid.
39. The method according to claim 37 or claim 38, wherein the electrochemical cell also performs at least a portion of the at least partial conversion of the carbon dioxide to carbon monoxide and water.
40. The method according to any one of claims 37 to 39, wherein the reverse water-gas shift catalyst performs at least a portion of the at least partial conversion of carbon dioxide to carbon monoxide and water.
41. The method according to any one of claims 37 to 40, wherein the electrochemical cell is an electrolyzer cell.
42. The method according to claim 41, wherein the method is carried out using an electrolyzer system according to any one of claims 20 to 35, wherein the electrolyzer cell is at least one electrolyzer cell of the electrolyzer of the electrolyzer system.
43. The method according to claim 41, wherein the method is a methanation method according to any one of claims 1 to 19, and the electrolyzer cell is at least one electrolyzer cell of the electrolyzer of the electrolyzer system.
44. A method for operating an electrolyzer system comprising at least one electrochemical cell having a fuel inlet, a fuel outlet, and a fuel fluid passage connecting the fuel inlet and the fuel outlet, i) Supplying a fuel gas containing water and a carbon source selected from one or more of CO and CO ２ to the fuel inlet; ii) Operating the electrolyzer system by passing an electric current through at least one of the electrochemical cells, iii) At least partially electrolyzing the steam into hydrogen and oxygen, iv) Reacting hydrogen with a carbon source in the fuel fluid flow path to produce methane, v) At least 5 volume percent of methane and H from the fuel outlet. ２ , H ２ O, CO, and CO ２ Discharging a generated gas containing one or more of the following, A method that includes this.
45. The method according to claim 44, which is carried out using the electrolyzer system according to any one of claims 20 to 31, wherein the at least one electrochemical cell is the at least one electrolyzer cell of the electrolyzer.
46. The method according to claim 44, wherein the method is a methanation method according to any one of claims 1 to 19, and the at least one electrochemical cell is the at least one electrolyzer cell of the electrolyzer.