Process and apparatus for producing hydrogen by thermal reforming of ammonia
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-07-30
- Publication Date
- 2026-08-14
Smart Images
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Abstract
Description
Detailed Description of the Invention
[0001] [Technical Field] The present invention relates to the production of hydrogen by thermal reforming of ammonia, also called decomposition or cracking. Furthermore, the present invention relates to an apparatus for the production of hydrogen.
[0002] [Background] Due to the global interest in renewable energy, there is a renewed interest in using ammonia (NH3) as a suitable hydrogen carrier. Ammonia has a low risk of flammability and can be easily obtained and handled in liquid form without the need for expensive and complex refrigeration technology. Ammonia is a liquid hydrogen carrier with a high energy density. In its liquid form, ammonia contains approximately 1.7 times more hydrogen per unit volume than liquid hydrogen, thus enabling efficient transportation of hydrogen fuel. Ammonia can be decomposed into hydrogen (H2) and nitrogen (N2) by an endothermic reaction: 2NH3 → 3H2 + N2.
[0003] This endothermic reaction is an endothermic process, i.e., a process that requires heat, and is carried out via a catalyst. This process is known as cracking. The gas thus produced (“cracked gas”) is a combination of hydrogen (H2) and nitrogen (N2). Since the cracking reaction is an equilibrium reaction, some residual ammonia will also be present.
[0004] On the one hand, including thermal reforming and photocatalytic reforming, and on the other hand, including oxidative reforming which is an exothermic reaction, the basis of ammonia reforming is discussed in the following paper: “Catalytic ammonia reforming: alternative routes to net-zero-carbon hydrogen and fuel” by Luis C. Cabellero et al in Chem. Sci., 2022, 13, 12945 - 12956. The present invention focuses on thermal reforming, i.e., In the absence of oxygen reforming. The technology for producing hydrogen from ammonia was already described in British Patent Application No. 462531, published in 1937. This patent discloses an apparatus for decomposing ammonia into nitrogen and hydrogen, wherein a catalyst chamber is heated by radiation from an electric heater completely isolated from the ammonia or the decomposition products. Since this initial publication, the technology has developed significantly. For example: For example, high-purity hydrogen can be obtained by using one or more hydrogen separation units such as a pressure swing absorption unit and a membrane separation unit, and the quality of the hydrogen product; Energy management resulting from an optimized zero-carbon method of heating the catalyst chamber of an ammonia cracking reactor using a heat exchanger; Selective ammonia decomposition catalyst, and Exhaust control to avoid ammonia release and prevent NOx generation and release. Improvements have been made regarding this.
[0005] International Publication No. 2022243410 discloses a process for synthesizing hydrogen by catalytic cracking of ammonia, comprising the step of subjecting an ammonia-containing flow to a catalytic cracking step in the presence of heat to produce a thermally cracked flow containing nitrogen, hydrogen, optionally residual ammonia, and optionally water. The process further comprises subjecting the thermally cracked flow to a hydrogen recovery step to produce a high-purity hydrogen flow and a reject gas (referred to herein as a tail gas). The thermally cracked flow may be subjected to a scrubbing step in the presence of water. The process according to this reference includes the step of recirculating at least a portion of the reject gas as a fuel gas to supply heat to the catalytic cracking step.
[0006] Technology for ammonia decomposition catalysts is widespread and continues to grow. The thermodynamic conversion of ammonia to hydrogen is possible even at low temperatures of 400°C. However, in practice, the conversion rate depends on the type of catalyst used. Typically, nickel (Ni) is used. Ni is active at higher temperatures (600-900°C) than Ru (Ru, which is active from 400°C). The latter catalysts and newer generations of catalysts are more expensive. Nickel-based catalysts on a support (such as alumina or silica) are disclosed, for example, in: UK Patent Application No. 768091, UK Patent Application No. 1000772, UK Patent Application No. 750234, Korean Registered Patent No. 100455009, and European Patent No. 687494.
[0007] From various documents, processes for producing hydrogen gas from ammonia by thermal reforming are known, in which a catalyst chamber is indirectly heated using high-temperature flue gas from an external combustion unit. In addition to International Publication No. 2022243410, for example, U.S. Patent No. 2601221, UK Patent Application No. 1092380, and U.S. Patent No. 3198604 describe an external combustion unit operating with a fuel containing ammonia and flammable reject gas downstream of a hydrogen separation unit. The present invention similarly focuses on producing hydrogen gas from ammonia by thermal reforming in a catalyst chamber indirectly heated using high-temperature flue gas from an external combustion unit.
[0008] External combustion units require fuel. Ideally, ammonia reacts with oxygen to form nitrogen and water. However, ammonia may also react with oxygen to form nitric oxide and other oxides. These nitrogen oxides ("NOx") should be removed. Selective catalytic reduction (SCR) is considered particularly suitable for this purpose because, in the presence of a solid catalyst, nitrogen oxides in the flue gas can be chemically reacted with oxygen and added ammonia at high temperatures to produce nitrogen and water, after which the treated flue gas can be released into the atmosphere. For example, International Publication No. 2022265648 uses an SCR unit that utilizes ammonia extracted from the productive logistics of a catalyst cracking step. NOx formation can also be mitigated using controlled stepwise combustion, as disclosed in International Publication No. 2013036124.
[0009] European Patent Application Publication No. 2276693 discloses an apparatus for converting ammonia gas to nitrogen and hydrogen gases, comprising: (a) a heater for heating ammonia to convert it into gases; (b) a reactor including a first pathway for housing a catalyst for facilitating the conversion of ammonia to nitrogen and hydrogen; (c) a first heat exchange component outside the reactor for heating ammonia before sending it into the reactor; and (d) a second heat exchange component in the reactor including a second pathway in the reactor for passing nitrogen and hydrogen gases through the reactor, which is in a heat exchange relationship with the first pathway, resulting in further heating of the ammonia. This reference discloses a pipe-in-pipe configuration, and therefore a bayonet-type reactor.
[0010] The use of hydrogen separation units, such as pressure swing absorption units (PSAs) or membrane separation units, for hydrogen purification is also part of the public domain. An example of a PSA is U.S. Patent No. 4,475,929, which has at least three absorbent beds. The value of the waste gas as fuel is also disclosed here. Similar technology can be seen in membrane separation units.
[0011] However, it should be noted that separation of the (pure) hydrogen stream may not always be necessary. The cracked gas can be used as is, or after removing some of the nitrogen gas contained in the cracked gas (using a higher energy content).
[0012] Cracking gas can be applied, for example, in blast furnaces. Current steelmaking processes involve the step of combining iron ore with carbon to produce pig iron. This process is mainly carried out in blast furnaces, where carbon in the form of coke or crushed coal is consumed. Consequently, this process produces a residual gas called blast furnace gas, which constitutes the largest source of emissions in most steel plants. Various efforts have been made to mitigate these emissions, including replacing PCI with alternative energy-containing gases such as hydrogen-concentrated gas. One approach to supplying hydrogen-concentrated gas involves cracking green ammonia, or ammonia with a low (preferably zero) carbon footprint. One embodiment of the present invention provides a solution for directly delivering cracked ammonia to a blast furnace without requiring prior purification. By directly supplying unpurified cracked ammonia to the blast furnace, the need for costly and time-consuming purification processes is eliminated, resulting in increased operational efficiency and cost savings.
[0013] Another interesting application of cracked gas is in direct iron reduction plants. With increasing pressure to decarbonize steelmaking, alternative routes based on renewable hydrogen rather than carbon as a reducing agent are being studied and practiced. These processes, known as hydrogen-based direct iron reduction (H-DRI), require supplying hydrogen to a shaft furnace where hydrogen interacts with iron for reduction. Due to the endothermic nature of this process, hydrogen is often supplied in excess at high temperatures (above 1000°C) to create thermodynamically and kinetically favorable conditions for the reduction process. One embodiment of the present invention provides a solution of supplying cracked ammonia containing nitrogen and hydrogen to the shaft furnace at high temperatures. The presence of nitrogen assists thermal management, as it acts as an energy carrier, minimizing gas cooling and allowing for higher outlet temperatures compared to supplying hydrogen alone.
[0014] A further interesting application of cracked gas is power generation (gas turbines). A common method of generating electricity from gaseous fossil fuels such as natural gas is by gas turbine. These units consist of a compressor, a combustion system, and a turbine. The compressor draws in air and pressurizes it. The pressurized air is injected at high speed into the combustion chamber together with compressed fossil fuel such as natural gas. The mixture burns in the combustion chamber at high temperature and pressure. The high temperature and pressure of the gas expands in the turbine, and the rotational energy of the turbine is used to drive the compressor, which in turn rotates the generator to produce electricity. Again, due to the growing demand for decarbonization, alternatives to fossil fuels are being explored. This invention offers a solution to this demand: cracking (green) ammonia can produce hydrogen, nitrogen, and unconverted ammonia. This gas can replace fossil fuels in existing gas turbines or in newly constructed gas turbines specifically for burning lower carbon mixtures. Combustion may use either cracked gas alone or a mixture of cracked gas and fossil fuels. Extending the invention in this way provides options for phased decarbonization and the utilization of existing assets.
[0015] Cracking gas can also be applied to boilers (steam and / or electricity). Methods utilizing fossil fuels such as coal or natural gas involve burning the fuel in the presence of air in a boiler. The boiler uses the heat released from the fossil fuel to generate steam from water. The steam can be either saturated steam or superheated steam. The steam can be used as steam or converted into electricity. If superheated steam is produced, it can be expanded in a turbine, and the rotational energy of the turbine is used to rotate a generator to produce electricity. One embodiment of this invention provides a solution to this method in which (green) ammonia can be cracked to produce hydrogen, nitrogen, and unconverted ammonia. This gas can replace fossil fuels in existing boilers or newly constructed gas turbines. Combustion may use only the cracked gas or a mixture of the cracked gas and fossil fuel. Extending the invention in this way provides options for phased decarbonization and the utilization of existing assets.
[0016] Furthermore, cracked gases can be applied in ships (prime engines). The use of fossil fuels in maritime transport results in significant CO2 emissions, with approximately 3 tons of CO2 emitted per ton of heavy fuel oil consumed. These emissions primarily arise from the combustion of various marine fuels in ship engines, such as heavy fuel oil, heavy gas oil, marine diesel oil, and similar fuels. In light of ongoing decarbonization efforts, engine manufacturers and shipowners are actively researching engines that can operate on low-carbon fuels. Ammonia is one of the options investigated. However, due to the suboptimal combustion characteristics of ammonia, the incorporation of a pilot fuel is necessary. This pilot fuel can be either an existing fossil fuel or an alternative gas mixture with more easily combustible properties. One embodiment of the present invention provides a solution in which cracked ammonia can be used as a pilot fuel.
[0017] U.S. Patent Application Publication No. 2022388841 describes a reforming apparatus that burns ammonia gas with air to generate heat for reforming ammonia gas. In this process, ammonia gas and air are introduced into a combustion zone and ignited, and the ammonia gas to be reformed is introduced downstream of this combustion zone. Thus, the flue gas from the ammonia combustion is combined with the ammonia gas to be reformed, and the reformed gas contains not only hydrogen but also combustion products generated by the combustion of ammonia gas, thereby complicating further processing and purification of the reformed gas for hydrogen production.
[0018] Korean Patent No. 102538689 describes a combined system for electricity generation. This system comprises a gas turbine, a heat recovery steam generator (HRSG), and an ammonia cracker that cracks ammonia by heat exchange with a portion of the gas turbine exhaust gas and sends the cracked ammonia gas as fuel to a gas turbine burner. Hydrogen is not produced in this process.
[0019] International Publication No. 202301879 relates to a method for extracting hydrogen from methanol or ammonia, for example, to power a fuel cell. The method is characterized in that methanol or ammonia is evaporated in a first step and reformed into a hydrogen-containing gas mixture in a second step. In a third step, hydrogen is separated from the gas mixture at a temperature of 300-600°C in a membrane process, and in a fourth step, the gaseous retained material from the membrane process is combusted in ambient air. The combustion gas is introduced through various heat exchangers to evaporate, heat, and reform the methanol or ammonia. The permeate from the membrane process preheats the ambient air to the burners of the heat exchangers. Since the permeate from the membrane process is obtained under high pressure, efficient hydrogen transport and delivery require the energy-intensive compression of the separated hydrogen products.
[0020] An improved process for producing hydrogen from ammonia is needed, specifically a process that is efficient in terms of energy consumption and hydrogen production while reducing or eliminating the need to burn fossil fuels. Furthermore, the process must be carried out while minimizing ammonia losses or NOx emissions.
[0021] While heat exchanger technology is extensive, challenges remain regarding how to effectively supply the necessary heat to the ammonia cracking reactor in a controlled manner, minimizing the amount of ammonia fuel used, reducing the emission of ammonia and NOx into the environment, (1) ensuring that the peak temperature of the heat exchange section of the cracking reactor remains below the critical material limit, (2) obtaining a less difficult and more homogeneous temperature profile to prevent frequent material failure, and (3) ensuring that ammonia cracking occurs at a temperature optimized for the catalyst used in the ammonia cracking reactor. The inventors have devised a process that brings improvements in all these aspects. [Overview of the prefecture] The present invention relates to a process for producing hydrogen by thermal reforming of ammonia, preferably an ammonia stream or ammonia-containing stream, in a catalyst chamber of an ammonia cracking reactor that is indirectly heated using high-temperature flue gas from an external combustion unit, the following steps: a) A step of incompletely combusting a fuel containing ammonia in the first stage of an external multi-stage combustion unit to generate a high-temperature flue gas flow T1 in the range of 750 to 2000°C, preferably in the range of 1200 to 2000°C, b) In the second stage of an external multi-stage combustion unit, a step of completely burning a fuel containing ammonia to generate a flue gas flow with a temperature T3 of less than T1, c) A step of exchanging the heat from the flue gas supplied in step b) with the ammonia cracking reactor to raise the temperature of the catalyst chamber to a catalyst cracking temperature T2 in the range of 400 to 1000°C, more preferably in the range of 600 to 800°C, d) subjecting the ammonia in the heated ammonia cracking reactor of step c) to a catalytic ammonia cracking step to produce a thermally cracked stream containing hydrogen; e) separating the thermally cracked stream into a reject gas stream and a concentrated hydrogen stream and withdrawing the concentrated hydrogen stream; including, T3 is at least 50 °C higher than T2 and up to 1600 °C, preferably, T3 is at least 100 °C higher than T2 and up to 1200 °C, and T3 is at least 50 °C lower than T1, preferably, T3 is at least 100 °C lower than T1, more preferably, T3 is at least 200 °C lower than T1, and the fuel for the first combustion stage of step (a) consists of ammonia and the reject gas stream of step e), relating to the process.
[0022] The controlled combustion in the second stage results in a temperature drop of the flue gas, which enables more controllable catalytic conversion of the ammonia in the ammonia cracking reactor. Thereby, the heat exchange surface and the catalyst of the cracking reactor are protected (i.e., there is no excessive heat load due to the lower gas temperature). The appropriate flue gas temperature generated in the present invention results in a more homogeneous temperature profile that is less difficult for these materials, preventing common material damage due to high temperatures.
[0023] The combustion of the fuel occurs in two stages. In the first stage, less oxygen than the stoichiometric amount is used, and in the second stage downstream, more oxygen than the stoichiometric amount is used, and optionally, an additional amount of quench fluid is added.
[0024] The present invention also provides an apparatus for producing hydrogen by thermal reforming of ammonia.
Brief Description of the Drawings
[0025] [Figure 1] It is a schematic diagram of the prior art showing an apparatus for producing hydrogen by thermal reforming of ammonia. [Figure 2] This is a schematic diagram of the present invention, in which a stepped combustion unit using an additional air supply flow is used. [Figure 3] This is a schematic diagram of a more preferred embodiment of the present invention, with detailed information about the ammonia cracking reactor.
[0026] [Detailed description of the invention] In the embodiments of the present invention discussed below, unless otherwise specified, the pressures given are absolute pressures. Furthermore, unless otherwise specified, the amounts in percentages and ppm are in terms of volume.
[0027] It is important to note that, unlike devices in which combustion and ammonia cracking are combined in a single unit, the ammonia cracking reactor and the stepwise combustion unit of the present invention are separate units. Therefore, the stepwise combustion unit is sometimes referred to as an "external" unit. Heat transfer is achieved by heat exchange between the flue gas from the external stepwise combustion unit and the ammonia cracking reactor, without mixing the flue gas with the ammonia being thermally cracked in the ammonia cracking reactor.
[0028] Figure 1 is a schematic diagram of the prior art showing an apparatus (1) for producing hydrogen by thermal reforming of ammonia, comprising one or more burners (10) connected to an ammonia cracking reactor (20) which includes one or more burner-generating flame zones in thermal contact with one or more catalyst-filled reactor tubes (36). The ammonia can be in the form of an ammonia stream or a flow containing ammonia. Fuel is introduced through an inlet (21), and an oxygen-containing gas, typically air, is introduced through an inlet (22). The ammonia is introduced through an inlet (31) into a catalyst-filled reactor tube (36), where a catalytic ammonia cracking step takes place to produce a thermally cracked flow that exits through an outlet (32). The cooled flue gas, which has heat-exchanged with the catalyst-filled reactor tube (36), exits the ammonia cracking reactor at an outlet (33). Typically, the thermally cracked flow is sent to a hydrogen separator unit (4). At the outlet (41), the concentrated hydrogen stream can be withdrawn, while the ejected gas can be recirculated to the burner (10) through line (42). The concentrated hydrogen stream will contain more than 75 volume percent hydrogen, and will further contain nitrogen and other inert gases, by-products, and optionally unconverted ammonia. Typically, the concentrated hydrogen stream will contain more than 98%, preferably more than 99%, hydrogen. Such other components, if present, may be present in amounts of 0.1 volume percent or more. Various additional optional equipment components such as heat exchangers, scrubbers, and tanks are not shown in Figure 1. Figure 2 is a schematic diagram of the present invention using an external multi-stage combustion unit. Here, (i) A first combustion unit (2A) having one or more burners (not shown) inside, a fuel inlet (21), an inlet (22) for a first oxygen-containing gas, typically air, and an integrated outlet / inlet (23) for a first flue gas flow at temperature T1. Equipped with, A second stage combustion unit (2B) connected to an integrated outlet / inlet (23) for a first flue gas at temperature T1, an inlet (24) for a second oxygen-containing gas, and an outlet (25) for a second flue gas flow at temperature T3. Furthermore, it includes a staged combustion unit (2), (ii) Ammonia cracking reactor (3), (iii) Hydrogen separator unit (4) and An apparatus (1) for producing hydrogen by thermal reforming of ammonia, which is equipped with the following, is shown.
[0029] Furthermore, the ammonia-containing flow is introduced into the ammonia cracking reactor (3) through the inlet (31), while the thermally cracked flow leaves the outlet (32), and the third flue gas flow, which has undergone heat exchange in the ammonia cracking reactor, exits the ammonia cracking reactor (3) at the outlet (33). The thermally cracked flow is sent to the hydrogen separator unit (4). At the outlet (41) of the hydrogen separator, the concentrated hydrogen flow can be extracted, while the rejected gas is recirculated through line (42) to the first stage (2A) of the stepwise combustion unit. In the process of the present invention, the concentrated hydrogen flow will also contain more than 75 volume percent hydrogen. In fact, the concentrated hydrogen flow will preferably contain more than 98%, preferably more than 99%, hydrogen.
[0030] An optional SCR unit (5) for handling a third flue gas flow, having an outlet (51) for a fourth flue gas flow with very low NOx, is also shown as a dotted line in Figure 2. A second stage unit (2B) comprises an optional additional burner (not shown). Optionally, the stage combustion unit (2) may be provided with an additional inlet (26) (shown as a dotted line) for additional quenched fluids, including various gases, liquids, and recirculated and cooled flue gas, particularly in the second stage combustion unit (2B).
[0031] Figure 3 is a schematic diagram of a preferred embodiment of the present invention, further illustrating an ammonia cracking reactor (3) in a preferred form of a bayonet-type reactor, comprising an inlet (31) for ammonia, an outlet (33) for cooled flue gas, an inlet (25) for heated flue gas at temperature T3, and an outlet (32) connected to an inner pipe (37) passing through the reaction chamber (36), all connected to a catalyst-filled reaction chamber (36).
[0032] Although not shown in any of the figures, the first combustion unit (2A) and / or the second stage combustion unit (2B) may, and preferably are, be equipped with analyzers capable of analyzing the flue gas content and analyzers capable of measuring temperature. Similarly, although not shown in any of the figures, there are optional flow control means for adjusting the amount of fuel, the amount of oxygen-containing gas, and / or the amount of quenched fluid. Preferably, data from the analyzers are sent to an optional process control unit (not shown) that operates and adjusts the flow control means.
[0033] The present invention enables the external combustion of ammonia-containing fuels and optimized heating of an ammonia cracking reactor while controlling the temperature within a desired range for a given catalyst. For example, when using a nickel-based ammonium cracking catalyst in an ammonia cracking reactor, the flue gas introduced into the ammonia cracking reactor is preferably at a temperature T3 at least 50°C, preferably at least 100°C, higher than the reaction temperature T2 in the reaction chamber. Temperatures below 50°C are less desirable to ensure efficient heat transfer. The flue gas is preferably introduced into the ammonia cracking reactor at a temperature T3 of less than 1600°C, preferably less than 1200°C. This has the advantage of better catalyst control and limits the requirements for the ammonia cracking reactor. When using a nickel-based catalyst in an ammonia cracking reactor, a suitable range for T3 is 700 to 1600°C, preferably 750 to 1200°C. When using a ruthenium-based catalyst, the preferred temperature range is 700 to 1000°C.
[0034] In combination with ammonia, any form of fuel that is combustible and gaseous under combustion conditions can be used. Any form of oxygen-containing gas can be used. For example, this oxygen-containing gas may be pure oxygen, an oxygen-concentrated air stream, or even a nitrogen-concentrated air stream. Preferably, air is used.
[0035] Combustion is a highly exothermic reaction. While some of the excess energy can be removed by using a heat exchanger, this invention more cleverly addresses this reaction by generating a lower-temperature flue gas through two-stage combustion of the fuel. This approach avoids unwanted transfer and loss of thermal energy to other media, and allows for improved control of the flue gas temperature when used to heat an ammonia cracking reactor.
[0036] Optionally, the first and / or second flue gases may be mixed with a quenching fluid, such as water, steam, and / or other gases and liquids. The recirculated flue gas from outlet (33) or (51) may also be used after the flue gas has transferred some of its heat to the ammonia cracking reactor. For example, some of the recirculated flue gas may be introduced into a combustion unit downstream of the flame zone. The quenching fluid itself may be at ambient temperature or a high temperature. For example, the quenching fluid may have a temperature in the range of 20 to 500°C.
[0037] In this invention, a second oxygen-containing stream introduced in the second stage of a multi-stage combustion unit ensures the combustion of the ammonia-containing fuel. In this process, combustion occurs in two stages: in the first stage with less than stoichiometric amounts of oxygen, and in the second stage with more than stoichiometric amounts of oxygen. The oxygen source in both cases can be any O2-containing stream, but is preferably air. By burning the fuel in (at least) two stages and using the excess oxygen in the second stage, the temperature of the flue gas exiting the combustion unit can be effectively controlled and adjusted to a desired temperature T3 for use in an ammonia cracking reactor.
[0038] Preferably, the fuel has zero carbon content. According to the present invention, a secondary fuel source is used. The second fuel source includes, or further comprises, a reject gas containing unrecovered hydrogen from hydrogen separation (4), nitrogen, optionally other inert gases and impurities, and unconverted ammonia from the ammonia cracking reactor (3), the reject gas being obtained after concentrated hydrogen has been removed from the cracked gas after ammonia cracking. This process can be carried out in the apparatus illustrated in Figure 2.
[0039] The staged combustion unit preferably includes an analyzer for analyzing the ammonia and / or NOx content of the flue gas stream before it enters the second stage (2B) of the combustion unit in the first stage of the combustion unit (2). Furthermore, in this case, preferably, a process control unit is used that is programmed to control the partial oxidation in unit (2A) to below stoichiometric conditions by measuring the concentrations of chemical compounds (e.g., ammonia, hydrogen, and / or NOx species) in the flue gas. Complete oxidation in unit (2B) should avoid the emission of ammonia, hydrogen, and other combustible compounds, and NOx emissions should be further controlled by promoting the reaction of NOx with residual ammonia from the first combustion stage. An analyzer for analyzing the NOx content in or after the second combustion unit (2B) may also be part of the process control.
[0040] A two-stage combustion unit is known from European Patent No. 2753416, incorporated herein by reference. This patent discloses a process for incinerating ammonia in an ammonia incinerator, comprising a first incineration step under controlled stoichiometric-less incineration conditions and a second incineration step with more than stoichiometric oxygen, wherein a product stream with reduced NOx formation is produced. While it is beneficial to use the analyzer shown in this patent to avoid NOx formation, it should be noted that in this apparatus, the two-stage combustion unit is preferably equipped with a temperature analyzer and is optimized with respect to the flue gas temperature so that the flue gas can be used to heat the ammonia cracking reactor.
[0041] To initiate the reaction in a preferred two-stage combustion unit, the fuel flow is preferably ignited with oxygen in the first stage (2A) of the combustion unit (2) to reach the desired combustion conditions. For burning ammonia in unit (2A) of the stage combustion unit, a temperature in the range of 750 to 2000°C, preferably 1200 to 2000°C, is desirable. Stable combustion of the ammonia-containing flow below 750°C can be achieved by adding hydrogen, etc., but it is more difficult to control. Above 2000°C, however, often above 1800°C, the commonly applied refractory lining materials used for insulation are not very suitable. After reaching a suitable temperature, the ammonia-containing flow is introduced. Additional fuel can be mixed with the ammonia-containing flow, in which case the additional fuel co-reacts with the first oxygen-containing flow. For example, it is beneficial to recirculate the ejected gas flow from the hydrogen separation flow containing unrecovered hydrogen, nitrogen, and optionally other inert substances and impurities, and unconverted ammonia from the ammonia cracking reactor (3).
[0042] In a two-stage combustion unit, if no combustible components other than ammonia are introduced into unit (2A) as fuel, the ammonia fuel is preferably burned in this first stage at 80 to slightly less than 100% of the stoichiometric amount of oxygen required for the combustion of the ammonia fuel, for example, 90 to 99%, or 95 to 98%. If the ammonia-containing stream or secondary fuel stream contains additional combustible components such as hydrogen, the amount of oxygen should be adjusted accordingly, preferably to an amount of oxygen in the range of 50 to 99% of the combustion stoichiometry for all combustible components present in the fuel stream to unit (2A). The use of the analyzer according to a preferred embodiment of the present invention has the advantage of being able to control and adjust the amount of reactants, even though the interrelationships are quite complex when multiple reactions occur when combustion conditions change due to the presence of multiple components. For example, the amount of oxygen can be adjusted by changing the oxygen inlet flow rate to the ammonia-containing stream. Alternatively, the air used as the oxygen stream may be oxygen-concentrated or nitrogen-concentrated.
[0043] The oxygen-containing flow can be introduced through one or more inlets (22a, 22b, etc.), but introduction through one inlet is sufficient. For example, one inlet is sufficient if design precautions are taken to ensure proper combustion and mixing in the first combustion stage (2A). The same applies to the ammonia supplied as fuel flow at inlet (21) and the recirculated reject gas flow through line (42). The residence time of the reactants in the first stage (2A) of the stepped combustion unit (2) may be short, i.e., less than 1 second, or even less than 0.2 seconds.
[0044] According to the present invention, ammonia is almost completely combusted in unit (2A), but not all of it is combusted, and some non-zero residual ammonia content and hydrogen (and optionally other combustible compounds) remain in the flue gas stream. The residual ammonia content is greater than zero and may be less than 1000 ppm, preferably less than 100 ppm. If the combustion process in unit (2A) is too complete, high levels of NOx formation occur in the first combustion stage. On the other hand, if the combustion process in unit (2A) is too incomplete, the flue gas stream (23) will have high ammonia and hydrogen content, thereby resulting in a high NOx content when this gas stream is combusted in the second stage (2B). In other words, the inventors have found that, in order to reduce NOx in the second stage flue gas (25) and thus avoid the potential need for an SCR unit, it is possible to achieve a negligible residual ammonia content, preferably less than 100 ppm, more preferably less than 50 ppm, by aiming for completion of combustion in the first stage (2A).
[0045] In the second stage (2B) of the multi-stage combustion unit, a temperature is maintained that is at least 50°C lower than the temperature in the first stage, preferably in the range of 700 to 1200°C, more preferably in the range of 750 to 1150°C, and even more preferably in the range of 800 to 1100°C. These reaction temperatures help to bring essential temperature control to the ammonia cracking reactor (3), ensuring the complete combustion of the combustible compounds exiting the first flue gas stream (23), and further controlling the NOx formation and reduction reactions in the second combustion stage (2B) to achieve negligible emission levels for ammonia and other combustible substances, while simultaneously achieving low NOx emissions from the second flue gas stream at the integrated outlet / inlet (25). An amount of oxygen is supplied to the unit (2B) to ensure complete combustion. If the reaction temperature as a result of the combustion of the combustible components in the first stage (2A) falls below the lower limit, it may be advantageous to add additional fuel, for example, via the inlet (21). It may also be advantageous to rapidly cool the temperature in the second stage (2B) with an additional quenching fluid, including water, steam, other gases or liquids, and / or recirculated flue gas (e.g., the flue gas flow at outlet (33) or (51)).
[0046] The design of the burner for the first stage (2A) and the optional burner for the second stage (2B) of the staged combustion unit is not particularly important. Multiple different types of burners can be used. Preferably, a burner that mixes the combustible flow(s) and the oxygen-containing flow is used. The burner may be equipped with an igniter. The design of the staged combustion unit including (2A) and (2B) is also not particularly important. In fact, the staged combustion unit may have both units as part of a single reactor vessel, or it may consist of two separate reactor vessels connected together. Furthermore, unit (2B) may also include an additional burner. One or more inlet or outlet nozzles can be used for the process flows of the (integrated) inlet / outlet (21), (22), (23), (24), (25) to and from the staged combustion unit (2).
[0047] The conversion of ammonia to nitrogen and hydrogen can be carried out by the techniques described in the background section of this specification. For example, an ammonia cracking reactor can be used, as described in European Patent Application Publication No. 2276693. Figure 3 shows a schematic diagram of a pipe-in-pipe configuration showing a preferred form of an ammonia cracking reactor with a bayonet-type reactor. As shown in Figure 3, the reactor comprises a reaction chamber (36) filled with catalyst. The reactor may also comprise additional reaction chambers (36a, 36b, etc.). By using this bayonet-type reactor, it is possible to arrange considerable heat transfer to the ammonia while it passes through the reactor and before it is cracked.
[0048] Various catalysts can be used. U.S. Patents 5,055,282 and 5,976,723 disclose a method for cracking ammonia into hydrogen and nitrogen in a cracking reactor. This method consists of exposing ammonia to a suitable cracking catalyst under conditions effective in producing nitrogen and hydrogen. In this case, the cracking catalyst consists of an alloy of zirconium, titanium, and aluminum doped with two elements from the group consisting of chromium, manganese, iron, cobalt, and nickel. U.S. Patent 6,936,363 discloses a method for producing hydrogen from ammonia based on a cracker at 500–750°C. A fixed bed catalyst can be used. The catalyst may be Ni, Ru, and Pt on Al2O3 or other carriers. European Patent Application Publication 3253487 describes a nickel-based catalyst for the thermal decomposition of ammonia (e.g., at relatively high temperatures such as 700–800°C). The catalyst contains at least 25% by weight of nickel oxide and exists in powder / powder form (i.e., not in the form of pellets, for example). Any of these catalysts, or any of the catalysts disclosed in UK Patent Application No. 768091, UK Patent Application No. 1000772, UK Patent Application No. 750234, Korean Registered Patent No. 100455009, and European Patent No. 687494, may be used. When using a catalyst other than Ni, it may be desirable to adjust the temperature in the reaction chamber.
[0049] The ammonia-containing stream may optionally contain other components such as water. Preferably, the ammonia-containing stream contains 10% by volume or less, preferably 5% by volume or less, of other components, more preferably 0.5% by volume or less. Preferably, this stream consists of ammonia. Additives may be intentionally added in effective amounts as needed to improve the properties of the fluid (such as reduced corrosiveness), to promote chemical transformations in the cracking reactor (3), or to suppress undesirable reactions in the reactor (3) or other units or piping.
[0050] As previously shown, the process of the present invention generates a cracked flow containing hydrogen. The introduction described various uses of the cracked flow. In applications where a concentrated hydrogen gas is required, the apparatus preferably includes a unit (4) for separating hydrogen from the cracked flow. The concentrated hydrogen flow can be obtained, for example, by the use of membrane technology, the use of a scrubber (for removing residual ammonia), or the use of a pressure swing absorption unit. As previously mentioned, PSA has been used in the prior art, and U.S. Patent No. 4,475,929 discloses an example having at least three absorbent beds. International Publication No. 2021,257,944 uses a membrane in combination with PSA. International Publication No. 2022,265,651 uses two parallel PSA units.
[0051] As previously indicated, the concentrated hydrogen stream preferably contains 95% or more hydrogen by volume. This means that the remaining hydrogen is left in the cracked stream. If the cracked stream is used to fuel the combustion unit, this means that the hydrogen is still being used efficiently.
[0052] This process offers the advantages of effective and efficient temperature control of the ammonia cracking reactor, and a controlled combustion process that ensures the complete conversion of combustible compounds and minimizes NOx concentration in the combustion flue gas, even when using pure ammonia or high-ammonia content flows as fuel. These advantages enable safe, controlled, and reliable operation of the ammonia cracking process for hydrogen production, reducing the risk of unwanted nitrogen oxides, as well as residual ammonia, hydrogen, and other combustible substances in the exhaust gas. Further reduction of NOx levels may be advantageous, and for this purpose, selective catalytic reduction (SCR) is considered particularly suitable because, in the presence of a solid catalyst, residual nitrogen oxides in the flue gas are chemically reacted at high temperatures with oxygen and added nitrogen compounds such as ammonia or urea to produce nitrogen and water, after which the treated flue gas can be released into the atmosphere with even lower emissions. Therefore, SCR units such as those disclosed in, for example, International Publication No. 2022265648 or European Patent No. 2301650 can be used. The present invention (i) A staged combustion unit comprising a first stage unit (2A) having an inlet (21) for fuel, an inlet (22) for a first oxygen-containing flow, and an integrated outlet / inlet (23) for a first flue gas, connected to a second stage unit (2B) having an inlet (24) for a second oxygen-containing gas and an integrated outlet / inlet (25) for a second flue gas flow, (ii) an ammonia cracking reactor (3) having an integrated outlet / inlet (25) for high-temperature flue gas from a stage combustion unit, i.e., a second flue gas flow, and an outlet (33) for a heat-exchanged, and therefore lower-temperature, flue gas flow, i.e., a third flue gas flow, and an inlet (31) for an ammonia flow that acts as a reaction zone containing an ammonia cracking catalyst, connected to the reactor chamber of the ammonia cracking reactor, and an outlet (32) for a thermally cracked flow, (iii) Hydrogen separation unit (4), preferably PSA and We also provide an apparatus (1) for producing hydrogen by thermal reforming of ammonia, which is the apparatus shown in Figure 2. The second stage unit (2B) may also have more than one inlet (24) (inlet 26 shown by the dotted line) for introducing, for example, an additional quenching fluid. Optionally, the apparatus may also have a further unit (5) for removing NOx, for example in the form of an SCR unit, shown here by the dotted line.
[0053] The present invention also provides apparatus (1), in the form of a bayonet-type reactor, in which the ammonia cracking reactor (3) is provided, comprising an inlet (31) for ammonia connected to a catalyst-filled reaction chamber (36), an outlet (33) for cooled flue gas downstream of the reaction chamber, an inlet (25) for heated flue gas from a stepwise combustion unit (2), and an outlet (32) connected to an inner pipe (37) passing through the reaction chamber (36). Apparatus (1) is the apparatus shown in Figure 3. The apparatus also comprises a further unit (5) for removing NOx, preferably in the form of a hydrogen separation unit (4), preferably a PSA, and / or an SCR unit, for example.
Claims
1. A process for producing hydrogen by thermal reforming of ammonia in an apparatus comprising an ammonia cracking reactor having a catalyst chamber and a stepwise combustion unit, wherein the catalyst chamber of the ammonia cracking reactor is indirectly heated by heat exchange with flue gas from the stepwise combustion unit, and the following steps: a) In the first stage of the stepped combustion unit, a step of incomplete combustion of a fuel containing ammonia in a first oxygen-containing flow to generate a first flue gas flow at a high temperature T1 in the range of 750 to 2000°C, preferably in the range of 1200 to 2000°C, b) The first flue gas flow is further combusted in a second oxygen-containing flow in the second stage of the stepped combustion unit to completely combust the fuel containing ammonia and generate a second flue gas flow with a temperature T3 of less than T1, c) A step of exchanging the heat from the second flue gas flow supplied in step b) with the ammonia cracking reactor to raise the temperature of the catalyst chamber to a catalyst cracking temperature T2 in the range of 400 to 1000°C, more preferably in the range of 600 to 800°C, d) A step of subjecting the ammonia-containing flow from the ammonia cracking reactor heated in step c) to a catalytic ammonia cracking step to generate a thermally cracked flow containing hydrogen, e) Separating the thermally cracked flow into a reject gas flow and a concentrated hydrogen flow, and extracting the concentrated hydrogen flow. A process comprising, wherein T3 is at least 50°C higher than T2 and up to 1600°C, and T3 is at least 50°C lower than T1, the reject gas flow of step e) is recirculated to the first stage of the stepwise combustion unit, and the fuel of step a) consists of ammonia and the reject gas flow of step e).
2. The process according to claim 1, wherein the fuel is burned in the first stage of the stepwise combustion unit using an amount of oxygen less than the stoichiometric amount which is preferably supplied as air, and then burned in the second stage of the downstream stepwise combustion unit using an excess amount of oxygen which is preferably supplied as air.
3. The process according to claim 1 or 2, wherein ammonia is burned in the first stage of the combustion unit to a residual ammonia content greater than 0 and less than 1000 ppm, preferably less than 100 ppm, and more preferably less than 50 ppm.
4. The process according to any one of claims 1 to 3, wherein T3 is at least 100°C higher than T2 and up to 1200°C, and / or T3 is at least 100°C lower than T1, more preferably T3 is at least 200°C lower than T1.
5. The process according to any one of claims 1 to 4, wherein the amount of oxygen used in the first stage of the combustion unit that is less than the stoichiometric amount is less than 80 to 100% of the stoichiometric amount, preferably 90 to 99%, and more preferably 95 to 98%.
6. The process according to any one of claims 1 to 5, wherein the combustion in the first stage of the combustion unit is carried out at a temperature in the range of 1500 to 1800°C.
7. The process according to any one of claims 1 to 6, wherein the combustion in the second stage of the combustion unit is carried out at a temperature in the range of 700 to 1200°C, preferably in the range of 750 to 1150°C, and more preferably in the range of 800 to 1100°C.
8. The process according to any one of claims 1 to 7, wherein the first oxygen-containing stream, preferably air, has a temperature in the range of 20 to 500°C.
9. The process according to any one of claims 1 to 8, wherein the second oxygen-containing stream, preferably air, has a temperature in the range of 20 to 500°C.
10. The process according to any one of claims 1 to 9, wherein a rapidly cooling fluid is added to the second stage of the combustion unit.
11. Apparatus (1) for producing hydrogen by thermal reforming of ammonia, (i) A staged combustion unit (2) comprising: a first stage unit (2A) configured to partially combust fuel, having an inlet (21) for fuel, an inlet (22) for a first oxygen-containing flow, and an integrated outlet / inlet (23) for a first flue gas flow; and a second stage unit (2B) configured to completely combust fuel, having an inlet (24) for a second oxygen-containing gas and an integrated outlet / inlet (25) for a second flue gas flow; (ii) an ammonia cracking reactor (3) having a catalyst chamber (36), wherein the reactor (3) is connected to the outlet / inlet (25) of the stepwise combustion unit and configured to exchange heat with the second flue gas flow from the stepwise combustion unit, the reactor (3) is further provided with an outlet (33) for a third flue gas after heat exchange, the catalyst chamber (36) is provided with an inlet (31) for an ammonia flow and an outlet (32) for a thermally cracked flow containing hydrogen, (iii) Hydrogen separation unit (4) and A device (1) comprising the following:
12. The apparatus (1) according to claim 11, wherein the second stage unit (2B) comprises a further inlet for a rapidly cooled fluid.
13. The apparatus (1) according to claim 11, wherein the ammonia cracking reactor (3) is in the form of a bayonet-type reactor, and the outlet (32) for the thermally cracked flow containing hydrogen is connected to an inner pipe (37) that passes through the catalyst chamber (36).
14. The apparatus (1) according to claim 11 or 12, wherein the hydrogen separation unit (4) is a PSA.
15. The apparatus (1) according to any one of claims 11 to 13, further comprising a unit (5) for removing NOx.