Process and plant for producing hydrogen by thermal reforming of ammonia

Abstract

The present invention provides a process for producing hydrogen by thermally reforming ammonia in a plant comprising an ammonia cracking reactor having a catalyst chamber and a staged combustion unit, in which the catalyst chamber of the ammonia cracking reactor is indirectly heated by heat exchange with hot flue gas from the staged combustion unit, the process comprises the steps of: a) incompletely combusting a fuel comprising ammonia in a first stage of a staged combustion unit to produce a flue gas stream having an elevated temperature T1 in the range of 750 DEG C to 2000 DEG C, preferably in the range of 1200 DEG C to 2000 DEG C; b) completely combusting the fuel comprising ammonia in a second stage of the staged combustion unit to produce a flue gas stream having a temperature T3 of less than T1; c) exchanging heat from the flue gas provided in step b) with an ammonia cracking reactor to raise the temperature in the catalyst chamber to a catalytic cracking temperature T2 in the range of 400 DEG C to 1000 DEG C, more preferably in the range of 600 DEG C to 800 DEG C; d) subjecting the ammonia stream in the heated ammonia cracking reactor of step c) to a catalytic ammonia cracking step to produce a thermally cracked stream comprising hydrogen, and e) separating the thermally cracked stream into an exhaust gas stream and a hydrogen-rich gas stream and withdrawing the hydrogen-rich gas stream, where T3 is at least 50 DEG C higher than T2, T3 is at most 1600 DEG C, and where T3 is at least 50 DEG C lower than T1, and wherein the fuel consists of ammonia and the exhaust gas stream of step e). An apparatus for carrying out the process is also provided.

Description

Technical Field

[0001] This invention relates to the production of hydrogen through the thermal reforming of ammonia, also known as decomposition or cracking. Furthermore, this invention relates to equipment for producing hydrogen. Background Technology

[0002] The renewed global interest in renewable energy has fueled interest in using ammonia (NH3) as a suitable hydrogen carrier. Ammonia has low flammability risk, is readily available, and can be handled in liquid form without the need for expensive and complex refrigeration technologies. Ammonia is an energy-intensive liquid hydrogen carrier. For a given volume of liquid form, it contains approximately 1.7 times the amount of hydrogen found in liquid form; thus allowing for efficient transport of hydrogen fuels. Ammonia can decompose into hydrogen (H2) and nitrogen (N2) via an endothermic reaction. 2NH3→3H2+N2.

[0003] This is an endothermic process, meaning it requires heating and takes place over a catalyst. This process is called cracking. The resulting gas ("cracking gas") is a combination of hydrogen (H2) and nitrogen (N2). Because the cracking reaction is an equilibrium reaction, there will also be some residual ammonia.

[0004] The basic principles of ammonia reforming include thermal and photocatalytic reforming on one hand, and oxidative reforming, an exothermic reaction on the other, discussed in the following article: "Catalytic ammonia reforming: alternative routes to net-zero-carbon hydrogen and fuel" by Luis C. Cabello et al., Chem. Sci., 2022, 13, 12945-12956. This invention focuses on thermal reforming, i.e., in the absence of oxygen.

[0005] A technique for producing hydrogen from ammonia was described in GB462531(A), published in 1937. This patent disclosed an apparatus for decomposing ammonia into nitrogen and hydrogen, wherein a catalyst chamber is heated by radiation from an electric heater, which is completely isolated from the ammonia or decomposition products. Since this earlier publication, the prior art has seen significant development. Improvements have been made to, for example: • The quality of hydrogen products can be improved by obtaining high-purity hydrogen, for example, through the use of one or more hydrogen separation units (such as pressure swing absorption units and membrane separation units); • By using a heat exchanger, an optimized zero-carbon energy management method is achieved for heating the catalyst chamber within the ammonia cracking reactor; • Selective ammonia decomposition catalysts, and • Emissions management to prevent the release of ammonia and the generation and release of NOx.

[0006] WO2022243410A1 discloses a process for synthesizing hydrogen via the catalytic cracking of ammonia. This process includes the following steps: subjecting an ammonia-containing stream to a catalytic cracking step in the presence of heat to produce a thermally cracked stream containing nitrogen, hydrogen, and possibly residual ammonia and, optionally, water. The process also includes subjecting the thermally cracked stream to a hydrogen recovery step to produce a high-purity hydrogen stream and exhaust gas (referred to as tail gas in this reference). The thermally cracked stream may be subjected to a washing step in the presence of water. The process according to this reference includes a step of recycling at least a portion of the exhaust gas as fuel gas to provide heat for the catalytic cracking step.

[0007] Technology regarding catalysts for ammonia decomposition is extensive and still evolving. Thermodynamic conversion of ammonia to hydrogen is possible at temperatures as low as 400°C. However, in practice, the conversion rate depends on the type of catalyst used. Typically, Ni is used. It is active at higher temperatures (600°C–900°C) than Ru (which is active from 400°C onwards). The latter catalyst and newer generations of catalysts are more expensive. Ni-based catalysts on supports (such as alumina or silica) have been disclosed, for example, in the following: GB768091A; GB1000772A; GB750234A; KR100455009B1 and EP687494B1.

[0008] Methods for producing hydrogen from ammonia by thermal reforming are known from various documents, wherein the catalyst chamber is indirectly heated by hot flue gas from an external combustion unit. Besides WO 2022243410 A1, in examples such as US 2601221A, GB1092380A, and US3 198604A, the external combustion unit operates on fuel comprising ammonia and combustible exhaust gases downstream of a hydrogen separation unit. This invention also focuses on producing hydrogen from ammonia by thermal reforming in a catalyst chamber that is indirectly heated by hot flue gas from an external combustion unit.

[0009] External combustion units require fuel. Ideally, ammonia reacts with oxygen to form nitrogen and water. However, ammonia can 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, by chemically reacting nitrogen oxides in flue gas with oxygen and added ammonia at elevated temperatures in the presence of a solid catalyst to produce nitrogen and water, allowing the treated flue gas to be subsequently released into the atmosphere. For example, an SCR unit using ammonia extracted from the product stream of a catalytic cracking step is used in WO2022265648A1. Controlled-stage combustion, as disclosed in WO2013036124, can also be used to mitigate NOx formation.

[0010] EP2276693A2 discloses an apparatus for converting ammonia into nitrogen and hydrogen, comprising: (a) a heater for heating ammonia to convert it into gas; (b) a reactor including a first path for housing a catalyst for promoting the conversion of ammonia into nitrogen and hydrogen; (c) a first heat exchange device outside the reactor for heating ammonia before it enters the reactor; and (d) a second heat exchange device within the reactor including a second path for allowing nitrogen and hydrogen to pass through the reactor in a heat-exchange relationship with the first path to further heat the ammonia. This reference also discloses a tube-and-tube assembly, thus disclosing a bayonet reactor.

[0011] The use of hydrogen separation units such as pressure swing absorption units (“PSA”) or membrane separation units to purify hydrogen is also in the public domain. Examples of PSAs include US4475929, which has at least three absorption beds. The value of exhaust gases as fuel is also disclosed therein. Similar techniques can be found for membrane separation units.

[0012] However, it should be noted that separation of the (pure) hydrogen stream may not be necessary. The cracked gas can be used in this way, or (with a higher energy content) after removing a portion of the nitrogen it contains.

[0013] Cracked gas can be applied, for example, to blast furnaces. Current steel production processes involve steps in which iron ore is combined with carbon to produce pig iron. This process takes place primarily within blast furnaces, where carbon is consumed in the form of coke or pulverized coal. Consequently, this process produces residual gases known as blast furnace gases, which constitute the largest source of emissions in most steel facilities. Numerous efforts have been made to mitigate these emissions, including replacing PCI with alternative energy-containing gases such as hydrogen-rich gases. One method of supplying hydrogen-rich gases involves the cracking of green ammonia or ammonia with a low (preferably zero) carbon footprint. One embodiment of the invention provides a solution for directly feeding cracked ammonia to a blast furnace without prior purification. Directly supplying unpurified cracked ammonia to the blast furnace eliminates the need for expensive and time-consuming purification processes, resulting in increased operational efficiency and cost savings.

[0014] Another interesting application of cracked gas is in direct reduced iron plants. With increasing pressure on steel production to reduce carbon emissions, alternative pathways relying on renewable hydrogen as a reducing agent instead of carbon are being explored and implemented. These processes, known as hydrogen-based direct reduced iron (H-DRI), require the supply of hydrogen to a shaft furnace where it interacts with iron for reduction. Due to the endothermic nature of this process, hydrogen is often supplied in excess and at high temperatures (>1000°C) to create thermodynamically and kinetically favorable conditions for the reduction process. One embodiment of the invention provides a solution in which cracked ammonia containing nitrogen and hydrogen is supplied to the shaft furnace at high temperatures. The presence of nitrogen aids in thermal management as it acts as an energy carrier, minimizing gas cooling and allowing for higher outlet temperatures compared to feeding only hydrogen.

[0015] Another interesting application of cracked gas is in power generation (gas turbines). A common method for generating electricity from gaseous fossil fuels such as natural gas is to use gas turbines. These units consist of a compressor, a combustion system, and a turbine. The compressor draws in air and increases it to high pressure. The high-pressure air, along with compressed fossil fuels such as natural gas, is injected at high speed into the combustion chamber. The mixture is burned in the combustion chamber at high temperature and pressure. The high-temperature, high-pressure gas expands in the turbine, and the rotational energy of the turbine is used to drive the compressor and a rotary generator to generate electricity. Again, due to the increasing demand for carbon reduction, alternatives to fossil fuels are being considered. This invention provides a solution to this problem, wherein (green) ammonia can be cracked to produce hydrogen, nitrogen, and unconverted ammonia. This gas can replace fossil fuels in existing or newly built gas turbines (particularly for burning low-carbon mixtures). The combustion can be using only cracked gas or a mixture of cracked gas and fossil fuels. Deploying the invention in this way provides the option of incremental carbon reduction and the use of existing assets.

[0016] The cracked gas can also be used in boilers (steam and / or electricity). A method of utilizing fossil fuels (such as coal or natural gas) involves burning the fuel in a boiler in the presence of air. The boiler uses the heat released from the fossil fuel to raise steam from water. The steam can be saturated steam or superheated steam. The steam can be used as steam or converted into electricity. If superheated steam is produced, it can expand in a turbine, and the rotational energy of the turbine is used to rotate a generator to produce electricity. One embodiment of the invention provides a solution to this, wherein (green) ammonia can be cracked to produce hydrogen, nitrogen, and unconverted ammonia. This gas can replace fossil fuels in existing boilers or new gas turbines. The combustion can be using only cracked gas or a mixture of cracked gas and fossil fuels. Deploying the invention in this way provides the option of incremental carbon reduction and the use of existing assets.

[0017] Furthermore, cracked gas can be used in transportation (primary power source). The use of fossil fuels in maritime transport results in approximately 3 tons of CO2 emissions per ton of heavy fuel oil consumed, leading to significant CO2 emissions. These emissions primarily originate from the combustion of various marine fuels (such as heavy fuel oil, heavy gas oil, marine diesel, and similar fuels) within the ship's engines. Given ongoing carbon reduction initiatives, engine manufacturers and ship owners are actively exploring engines capable of operating on low-carbon fuels. Ammonia represents one of the options under investigation. However, due to the less-than-ideal combustion properties of ammonia, the use of an ignition fuel becomes necessary. This ignition fuel can be an existing fossil fuel or an alternative gas mixture with easier combustion characteristics. Embodiments of the present invention provide a solution in which cracked ammonia can be used as an ignition fuel.

[0018] US2022388841 describes a reforming apparatus in which ammonia is burned with air to generate heat for reforming ammonia. According to this method, ammonia and air are introduced into a combustion zone and ignited, and ammonia to be reformed is introduced downstream of this combustion zone. Therefore, the flue gas from ammonia combustion combines with the ammonia to be reformed, resulting in a reformed gas containing combustion products from ammonia combustion in addition to hydrogen. This complicates further processing and purification of the reformed gas used to generate hydrogen.

[0019] KR102538689 describes a combined system for power generation. This system includes a gas turbine, a heat recovery steam generator (HRSG), and an ammonia cracker. The ammonia cracker cracks ammonia through heat exchange with a portion of the gas turbine exhaust gas and sends the cracked ammonia gas as fuel to the gas turbine combustor. No hydrogen is produced in this process.

[0020] WO 202301879 relates to a method for extracting hydrogen from methanol or ammonia, for example, for operating a fuel cell. The method is characterized by the evaporation of methanol or ammonia in a first step and reforming into a hydrogen-containing gas mixture in a second step. In a third step, hydrogen is separated from the gas mixture in a membrane process at a temperature of 300°C to 600°C, and in a fourth step, the gaseous permeate from the membrane process is combusted with ambient air. The combustion gas is directed 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 combustor in the heat exchangers. Because the permeate from the membrane process is obtained at a significantly reduced pressure, energy-intensive compression of the separated hydrogen products is required for efficient hydrogen transport and delivery.

[0021] There is a need for improved processes for producing hydrogen from ammonia, and specifically for methods that efficiently reduce or eliminate the need to burn fossil fuels in terms of both energy consumption and hydrogen production. Furthermore, this needs to be done with minimal ammonia loss or NOx emissions.

[0022] However, while the technology regarding heat exchangers is extensive, the challenge remains how to efficiently supply the heat required for the ammonia cracking reaction to the ammonia cracking reactor with minimal ammonia fuel use, minimal ammonia and NOx emissions to the environment, and in a controlled manner such that (1) the peak temperature in the heat exchange section of the cracking reactor is kept below the critical material limit, (2) a less challenging and more uniform temperature distribution is achieved to prevent frequent material failure, and (3) ammonia cracking occurs at a temperature optimized for the catalyst used in the ammonia cracking reactor. The inventors have devised a process that provides improvements in all these respects. Summary of the Invention

[0023] This invention relates to a process for producing hydrogen by thermal reforming ammonia (preferably an ammonia stream or an ammonia-containing stream) in the catalyst chamber of an ammonia cracking reactor, the reactor being indirectly heated by means of hot flue gas from an external combustion unit. The process includes the following steps:

[0024] a) Incomplete combustion of fuel including ammonia in the first stage of an external staged combustion unit to produce a flue gas stream with an elevated temperature T1 in the range of 750°C to 2000°C, preferably in the range of 1200°C to 2000°C.

[0025] b) The fuel, including ammonia, is completely combusted in the second stage of the external staged combustion unit to produce a flue gas flow with a temperature T3 less than T1;

[0026] c) The heat from the flue gas provided in step b) is exchanged with an ammonia cracking reactor to raise the temperature in the catalyst chamber to the catalytic cracking temperature T2, which is in the range of 400°C to 1000°C, more preferably in the range of 600°C to 800°C.

[0027] d) subjecting the ammonia in the heated ammonia cracking reactor of step c) to a catalytic ammonia cracking step to produce a thermal cracking stream including hydrogen, and

[0028] e) Separate the pyrolysis stream into an exhaust gas stream and a hydrogen-rich gas stream, and remove the hydrogen-rich gas stream.

[0029] Wherein T3 is at least 50°C higher than T2, and T3 is up to 1600°C, preferably T3 is at least 100°C higher than T2, and T3 is up to 1200°C, and wherein 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 wherein the fuel entering the first combustion stage of step (a) consists of ammonia and the exhaust gas stream of step (e).

[0030] The controlled combustion in the second stage results in a lower flue gas temperature, which enables more controlled catalytic conversion of ammonia in the ammonia cracking reactor. This protects the heat exchange surfaces and catalyst in the cracking reactor (i.e., without excessive heat load due to the lower gas temperature). The moderate flue gas temperature generated in this invention presents less challenge to the materials and results in a more uniform temperature profile, preventing common material failures caused by high temperatures.

[0031] Combustion of the fuel occurs in two stages, with less than stoichiometric amounts of oxygen used in the first stage and greater than stoichiometric amounts of oxygen used in the second stage downstream thereafter, with an optional addition of additional quench fluid.

[0032] The present invention also provides an apparatus for producing hydrogen through thermal reforming of ammonia. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of existing technology, showing an apparatus for producing hydrogen through the thermal reforming of ammonia.

[0034] Figure 2 This is a schematic diagram according to the present invention, in which a staged combustion unit with an additional air feed flow is used.

[0035] Figure 3 This is a schematic diagram of a more preferred embodiment of the present invention, with detailed information about the ammonia cracking reactor. Detailed Implementation

[0036] In the following discussion of embodiments of the invention, unless otherwise stated, the pressures given are absolute pressures. Furthermore, unless otherwise specified, percentages and ppm amounts are expressed by volume.

[0037] It is important to note that the ammonia cracking reactor and the staged combustion unit of the present invention are separate units, unlike devices in which combustion and ammonia cracking are combined in a single unit. Therefore, the staged combustion unit can be referred to as an "external" unit. Heat transfer occurs through heat exchange between the flue gas from the external staged combustion unit and the ammonia cracking reactor, without mixing the flue gas with the ammonia that has been thermally cracked in the ammonia cracking reactor.

[0038] Figure 1 This is a schematic diagram of the prior art, illustrating an apparatus (1) for producing hydrogen through the thermal reforming of ammonia, comprising one or more burners (10) connected to an ammonia cracking reactor (20), the ammonia cracking reactor comprising a flame zone generated by one or more burners in thermal contact with one or more catalyst-filled reactor tubes (36). Ammonia may be in the form of an ammonia stream or a stream containing ammonia. Fuel is introduced through inlet 21, and oxygen-containing gas (typically air) is introduced through inlet (22). Ammonia is introduced through inlet (31) into the catalyst-filled reactor tubes (36), where a catalytic ammonia cracking step occurs to produce a thermally cracked stream, which exits at outlet (32). Cooled flue gas, having exchanged heat with the catalyst-filled reactor tubes (36), exits the ammonia cracking reactor at outlet (33). The thermally cracked stream is typically fed into a hydrogen separator unit (4). The enriched hydrogen stream can be recovered at outlet (41), while the exhaust gas can be recirculated back to the burner (10) via line (42). The hydrogen-rich gas stream contains more than 75% hydrogen by volume, as well as nitrogen and other inert gases, byproducts, and possibly unconverted ammonia. Typically, it will contain more than 98%, preferably more than 99%, of hydrogen. Such other components may be present, if present, in amounts of 0.1% or more by volume. Figure 1 Various additional optional equipment components, such as heat exchangers, scrubbers, and tanks, are not shown.

[0039] Figure 2 This is a schematic diagram of the use of an external staged combustion unit according to the present invention. An apparatus (1) for producing hydrogen by thermal reforming of ammonia is shown here, the apparatus comprising... (i) Staged combustion unit (2), the staged combustion unit includes A first combustion unit (2A) having internal (not shown) one or more burners, 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, the staged combustion unit also includes The second-stage combustion unit (2B) is connected to an integrated outlet / inlet (23) for the first flue gas at temperature T1, an inlet (24) for the second oxygen-containing gas, and an outlet (25) for the second flue gas flow at temperature T3. (ii) Ammonia cracking reactor (3), and (iii) Hydrogen separator unit (4).

[0040] Next, an ammonia-containing stream is introduced into the ammonia cracking reactor (3) through inlet (31), while the thermally cracked stream exits at outlet (32), and the third flue gas stream, which undergoes heat exchange within the ammonia cracking reactor, exits at outlet (33). The thermally cracked stream is then fed into a hydrogen separator unit (4). At the outlet (41) of the hydrogen separator, the enriched hydrogen stream can be recovered, while the exhaust gas is recirculated through pipeline (42) to the first stage (2A) of the staged combustion unit. In the process of the present invention, the hydrogen-rich stream also contains more than 75% hydrogen by volume. In practice, the hydrogen-rich stream preferably contains more than 98%, and more preferably more than 99%, of hydrogen.

[0041] Figure 2 The optional SCR unit (5) is also shown in dashed lines. The SCR unit is used to treat the third flue gas with an outlet (51) in the fourth flue gas with extremely low NOx. The second stage unit 2B includes an optional additional burner (not shown). Optionally, the staged combustion unit (2), and particularly the second stage combustion unit (2B), may include an additional inlet (26) for additional quenching fluid, including various gases, liquids, and recirculated and cooled flue gas, etc. (shown in dashed lines).

[0042] Figure 3 This is a schematic diagram of a preferred embodiment of the present invention, further illustrating the preferred form of the bayonet reactor, an ammonia cracking reactor (3), which includes an ammonia inlet (31) connected to a catalyst-filled reaction chamber (36), an outlet (33) for cooling flue gas, an inlet (25) for heating flue gas at temperature T3, and an outlet (32) connected to an inner tube (37) passing through the reaction chamber (36).

[0043] Not shown in any of the accompanying drawings, but the first combustion unit (2A) and / or the second-stage combustion unit (2B) may, and preferably, be equipped with an analyzer capable of analyzing flue gas content, as well as an analyzer equipped with a temperature measuring device. Optional flow control devices for adjusting the amount of fuel, oxygen-containing gas, and / or quenching fluid are also not shown in any of the accompanying drawings. Preferably, data from these analyzers is transmitted to an optional process control unit (not shown), which operates and adjusts the flow control device.

[0044] This invention provides optimized heating for external combustion of fuels including ammonia and for ammonia cracking reactors, wherein the temperature is controlled to a desired range for a given catalyst. For example, when using a nickel-based ammonium cracking catalyst in the ammonia cracking reactor, the flue gas introduced into the reactor is preferably at a temperature T3 at least 50°C, but preferably at least 100°C, higher than the reaction temperature T2 in the reaction chamber. Temperatures below 50°C are less preferred to ensure efficient heat transfer. These flue gases are preferably introduced into the ammonia cracking reactor at a temperature T3 below 1600°C, preferably below 1200°C. This has the advantage of better catalyst control and limits the requirements on the ammonia cracking reactor. When using a nickel-based catalyst in the ammonia cracking reactor, a suitable range for T3 is 700°C–1600°C, preferably 750°C–1200°C. When using a ruthenium-based catalyst, the preferred temperature is in the range of 700°C–1000°C.

[0045] When combined 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 could be pure oxygen, an oxygen-enriched air stream, or even a nitrogen-enriched air stream. Air is preferred.

[0046] Combustion is a highly exothermic reaction. While some excess energy can be removed by using a heat exchanger, this invention addresses this issue better by burning fuel in two stages, resulting in flue gas with a lower temperature. This avoids unwanted heat transfer and loss to other media and allows for improved temperature control of the flue gas when used to heat an ammonia cracking reactor.

[0047] Optionally, the quenching fluid can be mixed into the first and / or second flue gas, such as water, steam, and / or other gases and liquids. It is also possible to use recirculated flue gas from outlet (33) or (51), provided that the flue gas has already transferred some of its heat to the ammonia cracking reactor. For example, a portion of the recirculated flue gas can be introduced into a combustion unit downstream of the flame zone. The quenching fluid itself can be at ambient temperature or elevated temperature. For example, it can have a temperature in the range of 20°C to 500°C.

[0048] In this invention, a second oxygen-containing stream introduced in the second stage of the staged combustion unit ensures the combustion of the ammonia-containing fuel. In this process, combustion occurs in two stages, with oxygen in the first stage at a stoichiometric level and oxygen in the second stage at a stoichiometric level. In both cases, the oxygen source can be any O2-containing stream, but air is preferred. By burning the fuel in (at least) two stages and using excess oxygen in the second stage, the temperature of the flue gas leaving the combustion unit can be effectively controlled and adjusted to the desired temperature T3 for use in the ammonia cracking reactor.

[0049] Preferably, the fuel has zero carbon content. According to the invention, an auxiliary fuel source is used. The second fuel source comprises exhaust gas containing unrecovered hydrogen, nitrogen, possibly other inert gases and impurities from the hydrogen separator (4) and unconverted ammonia from the ammonia cracking reactor (3), or even consists of exhaust gas containing unrecovered hydrogen, nitrogen, possibly other inert gases and impurities from the hydrogen separator (4) and unconverted ammonia from the ammonia cracking reactor (3), which is the exhaust gas obtained after removing enriched hydrogen from the cracked gas following ammonia cracking. It can be... Figure 2 The process is performed on the device shown in the diagram.

[0050] The staged combustion unit preferably includes an analyzer in the first stage of the combustion unit (2) for analyzing the ammonia and / or NOx content of the flue gas before it enters the second stage of the combustion unit (2B). Furthermore, in this case, a process control unit is preferably used, programmed to control partial oxidation in unit (2A) to below stoichiometric levels by measuring the concentration of chemical compounds (e.g., ammonia, hydrogen, and / or NOx-like substances) in the flue gas. Complete oxidation in unit (2B) is to avoid the emission of ammonia, hydrogen, and other combustible compounds, and to further control NOx emissions by promoting the reaction between NOx and residual ammonia leaving the first combustion stage. An analyzer for analyzing the NOx content in or after the second combustion unit (2B) can also be part of the process control.

[0051] A two-stage combustion unit is known from EP2753416, which is incorporated herein by reference. This patent discloses a process for incinerating ammonia in an ammonia incinerator, comprising a first combustion step under controlled, substoichiometric combustion conditions and a second combustion step with a greater than stoichiometric amount of oxygen, thereby producing a product stream with reduced NOx formation. While it is advantageous to utilize the analyzer shown in this patent to avoid NOx formation, it should be recognized that in this apparatus, the staged combustion unit is preferably equipped with a temperature analyzer and the temperature relative to the flue gas is optimized so that it can be used to heat the ammonia cracking reactor.

[0052] To initiate the reaction in the preferred two-stage combustion unit, the fuel stream is preferably ignited with oxygen in the first stage (2A) of the combustion unit (2) to achieve the desired combustion conditions. For the combustion of ammonia in the staged combustion unit (2A), a temperature of 750°C to 2000°C is desired, preferably 1200°C to 2000°C. Stable combustion of the ammonia stream below 750°C can be achieved, for example, by adding hydrogen, but this is more difficult to control. Above 2000°C, but typically above 1800°C, commonly used refractory lining materials for insulation are less suitable. After the suitable temperature has been reached, the ammonia stream is introduced. Additional fuel can be mixed with the ammonia stream, which is then co-reacted with the first oxygen stream. For example, it is advantageous to recycle the exhaust gas stream from the hydrogen separation stream, which will contain unrecovered hydrogen, nitrogen, possibly other inert substances and impurities, and unconverted ammonia from the ammonia cracking reactor (3).

[0053] In a two-stage combustion unit, if no combustible components other than ammonia are introduced as fuel into the unit (2A), the ammonia fuel is preferably burned in this first stage at between 80% and slightly less than 100% (e.g., 90% to 99%, or 95% to 98%) of the stoichiometric amount of oxygen required for the combustion of ammonia fuel. If the ammonia-containing stream or secondary fuel stream includes other combustible components, such as hydrogen, the amount of oxygen should be adjusted accordingly, preferably to the amount of oxygen in the range of 50% to 99% of the stoichiometric amount of oxygen relative to all combustible components present in the fuel stream to unit (2A). Using an analyzer according to a preferred embodiment of the invention has the advantage that the amount of reactants can be controlled and adjusted, despite the rather complex interrelationships when multiple components are present and therefore multiple reactions occur under varying combustion conditions. For example, the amount of oxygen can be adjusted by changing the inlet flow rate of oxygen to the ammonia-containing stream. Alternatively, the air used as the oxygen stream can be enriched with oxygen or nitrogen.

[0054] Oxygen-containing flow can be introduced through one or more inlets (22a, 22b, etc.), but one inlet is sufficient. For example, if design precautions are taken to ensure proper combustion and mixing in the first combustion stage (2A), one inlet is sufficient. The same applies to ammonia supplied as fuel at inlet (21) and the exhaust gas flow recirculated through line (42). The residence time of reactants in the first stage (2A) of the staged combustion unit (2) can be very short, i.e., 1 second or less, or even 0.2 seconds or less.

[0055] According to the invention, ammonia is nearly completely burned in unit (2A), but not completely burned, with some non-zero residual ammonia content and hydrogen (and possibly other combustible compounds) remaining in the flue gas stream. The residual ammonia content greater than zero can be less than 1000 ppm, and preferably less than 100 ppm. If the combustion process in unit (2A) is too complete, a high level of NOx formation is produced 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 a high ammonia and hydrogen content, which will result in a high NOx content when the gas stream is burned in the second stage (2B). In other words, the inventors have discovered that, in order to reduce NOx in the second stage flue gas (25) and thus avoid the potential need for an SCR unit, complete combustion in the first stage (2A) can be aimed at achieving a negligible residual ammonia content, preferably less than 100 ppm, more preferably less than 50 ppm.

[0056] The temperature maintained in the second stage (2B) of the staged combustion unit is at least 50°C lower than that of the first stage, and preferably in the range of 700°C to 1200°C, more preferably in the range of 750°C to 1150°C, and even more preferably in the range of 800°C to 1100°C. These reaction temperatures help to provide the necessary temperature control for the ammonia cracking reactor (3), ensuring complete combustion of combustible compounds leaving the first flue gas stream (23), and further controlling NOx formation and reduction reactions in the second combustion stage (2B) to achieve negligible emission levels of ammonia and other combustibles, while simultaneously achieving low NOx emissions in the second flue gas stream at the integrated outlet / inlet (25). Oxygen is supplied to the unit (2B) in an amount sufficient to ensure complete combustion. If the reaction temperature caused by the combustion of combustible components in the first stage (2A) drops below the lower limit, it may be advantageous to add additional fuel, for example, via the inlet (21). It may also be advantageous to quench the temperature in the second stage (2B) with an additional quenching fluid, which may include water, steam, other gases or liquids, and / or recirculated flue gas (e.g., flue gas flow at outlet (33) or (51)).

[0057] The design of the burner in the first stage (2A) and the optional burner in the second stage (2B) of the staged combustion unit is not particularly relevant. Multiple and various types of burners can be used. Preferably, a burner that mixes the combustible stream and the oxygen-containing stream is used. This burner can be equipped with an igniter. The design of the staged combustion unit including (2A) and (2B) is also not particularly relevant. In fact, the staged combustion unit can have two units as part of a single reactor vessel or include two separate reactor vessels connected together. In addition, unit (2B) may also contain an additional burner. One or more inlet or outlet nozzles may be used for the process flow arriving at and from the (integrated) inlet / outlet (21), (22), (23), (24), (25) of the staged combustion unit (2).

[0058] The conversion of ammonia to nitrogen and hydrogen can be carried out according to the techniques described in the background section of this specification. For example, an ammonia cracking reactor can be used as described in EP2276693. Figure 3 The diagram provides a schematic of the tube-to-tube arrangement, illustrating a preferred form of the bayonet-type reactor for ammonia cracking. For example... Figure 3 As shown, the reactor includes a reaction chamber (36) filled with a catalyst. The reactor may include additional reaction chambers (36a, 36b, etc.). By using this bayonet-type reactor, it is possible to arrange a large amount of heat transfer into the ammonia during its passage through the reactor and before it is cracked.

[0059] Various catalysts can be used. U.S. Patent Nos. 5,055,282 and 5,976,723 disclose methods for cracking ammonia into hydrogen and nitrogen in a decomposition reactor. This method involves exposing ammonia to a suitable cracking catalyst under conditions that effectively produce nitrogen and hydrogen. In this case, the cracking catalyst consists of an alloy of zirconium, titanium, and aluminum doped with two elements selected from chromium, manganese, iron, cobalt, and nickel. U.S. Patent No. 6,936,363 discloses a method for producing hydrogen from ammonia in a cracker at 500°C–750°C. A catalytic fixed bed can be used. The catalyst can be Ni, Ru, and Pt on Al₂O₃ or other supports. In EP 3253487, a nickel-based catalyst is provided for the thermal decomposition of ammonia (e.g., at relatively high temperatures such as 700°C to 800°C). This catalyst contains at least 25% nickel oxide by weight and is present in powder / powder form (i.e., not in the form of, for example, pellets). Any of these catalysts or any of the catalysts disclosed in GB768091A, GB1000772A, GB750234A, KR100455009B1 and EP687494B1 can be used. If a catalyst other than Ni is used, it may be desirable to regulate the temperature in the reaction chamber.

[0060] The ammonia-containing stream may optionally contain other components such as water. Preferably, the ammonia-containing stream contains no more than 10% by volume, preferably no more than 5% by volume, and more preferably no more than 0.5% by volume of other components. Preferably, the stream consists of ammonia. If desired, additives may be intentionally added in effective amounts to improve fluid properties (such as reduced corrosivity) or to promote chemical conversion in the pyrolysis reactor (3) or to inhibit undesirable reactions in the reactor (3) or other units or pipelines.

[0061] As described above, the method of the present invention produces a cracked stream comprising hydrogen. Various uses of the cracked stream are mentioned in the introduction. For applications where hydrogen enrichment is required, the apparatus preferably includes a unit (4) for separating hydrogen from the cracked stream. The enriched hydrogen stream can be obtained, for example, by using membrane technology, by using a scrubber (for removing residual ammonia), or by using a pressure swing absorption unit. As previously mentioned, PSA has been used in the prior art; the example disclosed in US 4475929 has at least three absorption beds. Membranes combined with PSA have been used in WO 2021257944 A1. In WO2022265651A1, two PSA units are used in parallel.

[0062] As mentioned above, the hydrogen-rich gas stream preferably contains 95% or more hydrogen by volume. This means that the remaining hydrogen is retained in the cracked stream. When the cracked stream is used to fuel the combustion unit, this means that the hydrogen is still effectively utilized.

[0063] This process offers the following advantages: effective and efficient temperature control of the ammonia cracking reactor, and a controlled combustion method that ensures complete conversion of combustible compounds and minimizes NOx concentration in the flue gas, even when pure ammonia or high-ammonia streams are used as fuel. This enables safe, controlled, and reliable operation of the ammonia cracking process for hydrogen production and mitigates the risks of undesirable nitrogen oxides and residual ammonia, hydrogen, and other combustibles in the exhaust gas. Further reduction of NOx levels may be advantageous, for which selective catalytic reduction (SCR) is considered particularly suitable. This involves chemically reacting residual nitrogen oxides in the flue gas with oxygen and added ammonia or nitrogen compounds such as urea at elevated temperatures in the presence of a solid catalyst to produce nitrogen and water, allowing the treated flue gas to be subsequently released into the atmosphere with even lower emissions. Therefore, SCR units disclosed, for example, in WO 2022265648A1 or EP 2301650 or similar documents can be used.

[0064] The present invention also provides an apparatus (1) for producing hydrogen by thermal reforming of ammonia, the apparatus comprising:

[0065] (i) A staged combustion unit having a first stage unit (2A), the 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, the outlet / inlet (23) being connected to a second stage unit (2B), the 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, and

[0066] (ii) an ammonia cracking reactor (3), which is connected to an integrated outlet / inlet (25) for flue gas at an elevated temperature from a staged combustion unit (i.e., the second flue gas stream), the ammonia cracking reactor (3) having an outlet (33) for a flue gas stream that has exchanged heat and is therefore at a lower temperature (i.e., the third flue gas stream) and an inlet (31) for an ammonia stream that connects to the reactor chamber within the ammonia cracking reactor and acts as a reaction zone containing an ammonia cracking catalyst, and an outlet (32) for a thermal cracking stream, and

[0067] (iii) Hydrogen separation unit (4), preferably PSA. This is Figure 2 The device is shown. The second-stage unit (2B) may also include more than one inlet (24), for example for introducing additional quench fluid (inlet 26, shown in dashed lines). Optionally, the device may include an additional unit (5) for NOx removal, for example in the form of an SCR unit, shown in dashed lines here.

[0068] The present invention also provides an apparatus (1) in which the ammonia cracking reactor (3) is in the form of a bayonet reactor, including an ammonia inlet (31) connected to a catalyst-filled reaction chamber (36), an outlet (33) downstream of the reaction chamber for cooling flue gas, an inlet (25) for heating flue gas from a staged combustion unit (2), and an outlet (32) connected to an inner tube (37) passing through the reaction chamber (36). This is Figure 3 The device shown. In addition, the device includes a hydrogen separation unit (4), preferably a PSA, and / or an additional unit (5) for NOx removal, for example in the form of an SCR unit.

Claims

1. A process for producing hydrogen through the thermal reforming of ammonia, said process being carried out in an apparatus comprising an ammonia cracking reactor having a catalyst chamber and a staged combustion unit, wherein, The process includes the following steps: indirectly heating the catalyst chamber of the ammonia cracking reactor through heat exchange with flue gas from the staged combustion unit. a) A fuel including ammonia is incompletely combusted with a first oxygen-containing stream in the first stage of the staged combustion unit to produce a first flue gas stream at an elevated temperature T1, wherein the temperature T1 is in the range of 750°C to 2000°C, preferably in the range of 1200°C to 2000°C. b) The fuel including ammonia is completely combusted by further burning the first flue gas stream and the second oxygen-containing stream in the second stage of the staged combustion unit to produce a second flue gas stream at a temperature T3 lower than T1; c) The heat from the second flue gas flow provided in step b) is exchanged with the ammonia cracking reactor to raise the temperature in the catalyst chamber to the catalytic cracking temperature T2, which is in the range of 400°C to 1000°C, more preferably in the range of 600°C to 800°C. d) subjecting the ammonia-containing stream in the ammonia cracking reactor heated in step c) to a catalytic ammonia cracking step to produce a thermal cracking stream including hydrogen, and e) Separate the pyrolysis stream into an exhaust gas stream and a hydrogen-rich gas stream, and remove the hydrogen-rich gas stream. Wherein, T3 is at least 50°C higher than T2, T3 is up to 1600°C, and T3 is at least 50°C lower than T1, wherein the exhaust gas stream of step e) is recirculated to the first stage of the staged combustion unit, and wherein the fuel of step a) consists of ammonia and the exhaust gas stream of step e).

2. The process according to claim 1, wherein, The fuel is burned in the first stage of the staged combustion unit with a substoichiometric amount of oxygen, which is preferably supplied by air, and in the downstream of the second stage of the staged combustion unit with an excess amount of oxygen, which is preferably supplied by air.

3. The process according to any one of claims 1-2, wherein, In the first stage of the combustion unit, ammonia is burned until the residual ammonia content is greater than zero 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 1-3, wherein, T3 is at least 100°C higher than T2, and T3 can reach a maximum value of 1200°C, and / or where, 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 1-4, wherein, The oxygen used in the first stage of the combustion unit is less than 80% to less than 100% of the stoichiometric amount, and preferably 90% to 99%, more preferably 95% to 98%.

6. The process according to any one of claims 1-5, wherein, Combustion in the first stage of the combustion unit is performed at a temperature within the range of 1500℃-1800℃.

7. The process according to any one of claims 1-6, wherein, Combustion in the second stage of the combustion unit is performed at a temperature ranging from 700°C to 1200°C, preferably from 750°C to 1150°C, and more preferably from 800°C to 1100°C.

8. The process according to any one of claims 1-7, wherein, The first oxygen-containing stream, preferably air, has a temperature in the range of 20°C to 500°C.

9. The process according to any one of claims 1-8, wherein, The second oxygen-containing stream, preferably air, has a temperature in the range of 20°C to 500°C.

10. The process according to any one of claims 1-9, wherein, A quenching fluid is added to the second stage of the combustion unit.

11. An apparatus (1) for producing hydrogen through thermal reforming of ammonia, comprising: (i) A staged combustion unit (2) having a first stage unit (2A) and a second stage unit (2B), the first stage unit (2A) being configured for partial combustion of fuel, the first stage unit (2A) having an inlet (21) for fuel and an inlet (22) for a first oxygen-containing flow and an integrated outlet / inlet (23) for a first flue gas flow, the second stage unit (2B) being configured for complete combustion of fuel, the 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, and (ii) An ammonia cracking reactor (3) having a catalyst chamber (36), wherein the reactor (3) is connected to the outlet / inlet (25) of the staged combustion unit and configured for heat exchange with a second flue gas stream from the staged combustion unit, wherein the reactor (3) is further provided with an outlet (33) for a third flue gas after heat exchange, and wherein the catalyst chamber (36) is provided with an inlet (31) for an ammonia stream and an outlet (32) for a thermally cracked stream including hydrogen, and (iii) Hydrogen separation unit (4).

12. The device (1) according to claim 11, wherein, The second-stage unit (2B) includes another inlet for quenching fluid.

13. The device (1) according to claim 11, wherein, The ammonia cracking reactor (3) is in the form of a bayonet reactor, wherein the outlet (32) of the thermal cracking stream, which includes hydrogen, is connected to an inner tube (37) passing through the catalyst chamber (36).

14. The device (1) according to any one of claims 11 to 12, wherein, The hydrogen separation unit (4) is a PSA.

15. The device (1) according to any one of claims 11 to 13 further includes a unit (5) for removing NOx.

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