Systems and processes for the decomposition of ammonia

Abstract

A system for catalytically cracking ammonia to produce hydrogen, comprising: a main ammonia cracking reactor, which includes one or more reaction tubes containing an ammonia cracking catalyst; a fuel combustion zone surrounding one or more reaction tubes, which provides thermal energy to assist in the cracking of ammonia in one or more reaction tubes and generates a main hydrogen-containing gas stream; and an auxiliary ammonia cracking reactor, which cracks ammonia to generate an auxiliary hydrogen-containing gas stream, wherein the auxiliary hydrogen-containing gas stream is directed to both the ammonia cracking catalyst in one or more reaction tubes of the main ammonia cracking reactor and the combustion zone of the main ammonia cracking reactor, thereby supplying fuel to the main ammonia cracking reactor at least partially.

Description

Technical Field

[0001] This specification relates to systems and processes for producing hydrogen gas by catalytic decomposition of ammonia.

Background Art

[0002] In various industrial environments, there is a new interest in using hydrogen as an environmentally friendly carbon-free fuel. Hydrogen can be burned to generate thermal energy or electricity. Alternatively, hydrogen can be used, for example, to generate electrochemical energy in a fuel cell.

[0003] Ammonia has gathered interest as a compound that may enable the storage and transportation of hydrogen. Liquid ammonia has a higher hydrogen density than liquid hydrogen and can be transported using existing infrastructure that is already used for this purpose, such as that used for the transportation of ammonia in the agrochemical fertilizer industry. Liquid ammonia can be burned directly after being transported or can be converted to hydrogen by a decomposition process.

[0004] The catalytic decomposition of ammonia into hydrogen and nitrogen has been known for many years. The reaction can be shown as follows.

[0005]

Number

[0006] [[ID=3V2]]The ammonia decomposition reaction is endothermic and can be effectively achieved by passing ammonia through a suitable catalyst in a reaction tube containing a heated catalyst placed in a furnace. For example, such furnaces for steam reforming of natural gas or naphtha feedstocks are known. In an industrial process used for the catalytic decomposition of ammonia, the gas produced by the ammonia decomposition reaction is purified to produce a purified hydrogen stream and a waste gas stream.

[0007] Improved processes for the catalytic cracking of ammonia are still needed. [Overview of the Initiative]

[0008] One issue to consider is how to most effectively fuel the reactor to support the endothermic ammonia decomposition reaction. One option is to use some of the hydrogen produced to at least partially fuel the reactor. Alternatively or additionally, the exhaust gas stream from the ammonia decomposition system, containing residual hydrogen, residual ammonia, and nitrogen, may be used to at least partially fuel the reactor. However, none of these fuel sources are available when the ammonia decomposition system is started up.

[0009] Another issue to consider is that ammonia decomposition catalysts tend to be in an oxidizing form when the ammonia decomposition system is started, making them inefficient at promoting the decomposition reaction, at least during the initial period of operation.

[0010] Another issue to consider is that the reaction tubes containing the heated catalyst placed inside the furnace may react with ammonia-containing gases to form an undesirable metal nitride layer. This undesirable side reaction, known as nitriding, can accelerate the failure of the reaction tubes.

[0011] Another issue to consider is the efficiency of the ammonia decomposition reactor in converting the high-partial-pressure ammonia gas stream into hydrogen.

[0012] This specification relates to a system for producing hydrogen by catalytic cracking of ammonia, A main ammonia decomposition reactor comprising: one or more reaction tubes containing an ammonia decomposition catalyst; and a fuel combustion zone surrounding one or more reaction tubes, providing thermal energy to support the decomposition of ammonia in the one or more reaction tubes and generate a main hydrogen-containing gas flow; It comprises an auxiliary ammonia decomposition reactor for decomposing ammonia and generating an auxiliary hydrogen-containing gas stream, We aim to address these problems by providing a system configured to supply fuel to the main ammonia decomposition reactor at least partially by guiding an auxiliary hydrogen-containing gas stream to both the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor and the combustion zone of the main ammonia decomposition reactor.

[0013] This specification also provides a process for operating the system. The system and method are characterized by an auxiliary ammonia decomposition reactor that generates a hydrogen-containing gas stream, which the system directs to both the ammonia decomposition catalyst in the reaction tube of the main ammonia decomposition reactor and the combustion zone of the main ammonia decomposition reactor, thereby supplying fuel to the reactor. Such a configuration allows the auxiliary ammonia decomposition reactor to address one, more, or all of the aforementioned problems, as follows: (i) After installation, the auxiliary ammonia decomposition reactor generates a hydrogen-containing gas stream, which is directed to the ammonia decomposition catalyst in the reaction tube of the main ammonia decomposition reactor, thereby reducing the oxide ammonia decomposition catalyst. This ensures that the catalyst efficiently promotes the decomposition reaction from the start of the main ammonia decomposition reactor. (ii) The auxiliary ammonia decomposition reactor may also generate a hydrogen-containing gas stream, particularly at startup of the main ammonia decomposition reactor before the main reactor generates hydrogen and waste gas (e.g., from the purification unit), and direct it into the combustion zone of the main ammonia decomposition reactor to supply at least partially fuel to the main ammonia decomposition reactor, and the hydrogen and waste gas itself may be used independently or in combination to supply at least partially fuel to the main reactor. (iii) The auxiliary ammonia decomposition reactor may generate a hydrogen-containing gas stream during operation and guide it through the reaction tube of the main ammonia decomposition reactor in order to reduce the partial pressure of ammonia in the reaction tube and thereby reduce the rate of nitridation of the reaction tube. (iv) Since at least a portion of the ammonia is decomposed by the auxiliary ammonia decomposition reactor, the main ammonia decomposition reactor can be configured to use less fuel (for example, by allowing the use of a smaller main reactor that requires less fuel), thus improving the efficiency of the system and reducing capital and / or operating costs. (v) The auxiliary ammonia decomposition reactor is configured to direct the hydrogen-containing gas stream to both the ammonia decomposition catalyst in the reaction tube of the main ammonia decomposition reactor and the combustion zone of the main ammonia decomposition reactor for supplying fuel to the reactor. This configuration provides a system with a much greater degree of flexibility for controlling both the reaction gas and the fuel gas, both during startup and long-term operation of the ammonia decomposition system, thereby improving the efficiency, safety, and lifespan of the system. [Brief explanation of the drawing]

[0014] For a better understanding of the present invention and to illustrate how it can be implemented, certain embodiments of the present invention are described hereby by reference only to the accompanying drawings. [Figure 1] A schematic diagram of a system for decomposing ammonia is shown. [Figure 2] A schematic diagram of another system for breaking down ammonia is shown. [Figure 3] A schematic diagram of another system for breaking down ammonia is shown.

[0015] In all figures, the same reference numerals are used for the same parts. A list of references is provided below.

[0016] Reference number item 2. Ammonia decomposition system 4. Main ammonia decomposition reactor 6. Reaction tubes in the main ammonia decomposition reactor 8. Ammonia decomposition catalyst in the reaction tube 10. Fuel combustion zone of the main ammonia decomposition reactor 11 Hydrogen-containing gas stream from the main ammonia decomposition reactor 12 Auxiliary ammonia decomposition reactor 14 Ammonia gas input stream 16 Auxiliary Hydrogen Containing Gas Stream (AHCGS) 18 Part of the AHCGS to the ammonia decomposition catalyst in the main reactor 20 Part of the AHCGS to the combustion zone of the main reactor 21 First ammonia decomposition route 22 Second ammonia decomposition route 24 Purification unit 26 Purified hydrogen gas stream 28 Exhaust gas (waste gas stream) to the combustion zone of the main ammonia decomposition reactor

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] As described in the summary section and shown in FIG. 1, this specification provides a system 2 for the catalytic decomposition of ammonia to produce hydrogen. The system 2 includes one or more reaction tubes 6 containing an ammonia decomposition catalyst 8, and a fuel combustion zone 10 surrounding the one or more reaction tubes 6 to provide thermal energy for assisting the decomposition of ammonia in the one or more reaction tubes 6 to generate a main hydrogen-containing gas stream 11, and includes a main ammonia decomposition reactor 4. The system 2 further includes an auxiliary ammonia decomposition reactor 12 for decomposing ammonia to generate an auxiliary hydrogen-containing gas stream 16. The system 2 is configured to direct at least a portion 18 of the auxiliary hydrogen-containing gas stream 16 to the ammonia decomposition catalyst 8 in the one or more reaction tubes 6 of the main ammonia decomposition reactor 4, and at least a portion 20 of the auxiliary hydrogen-containing gas stream 16 to the combustion zone 10 of the main ammonia decomposition reactor 4 to at least partially supply fuel to the main ammonia decomposition reactor 4.

[0018] Therefore, the process for decomposing ammonia using this system includes supplying an ammonia gas input stream 14 to an auxiliary ammonia decomposition reactor 12 to decompose the ammonia gas input stream and generate an auxiliary hydrogen-containing gas stream 16. A portion 18 of the auxiliary hydrogen-containing gas stream is supplied to an ammonia decomposition catalyst 8 in one or more reaction tubes 6 of the main ammonia decomposition reactor 4. Furthermore, a portion 20 of the auxiliary hydrogen-containing gas stream is supplied to the combustion zone 10 of the main ammonia decomposition reactor 4 to supply at least partially with fuel.

[0019] The auxiliary ammonia decomposition reactor is optionally electrically heated and / or uses an electric heater at the reactor's gas inlet. Therefore, the auxiliary ammonia decomposition reactor can be used to generate decomposition gas (H2 / N2) independently of the rest of the ammonia decomposition plant. The auxiliary ammonia decomposition reactor can be used to generate fuel that can be burned in the main-fired ammonia decomposition reactor during startup, and can also be used after installation to reduce the ammonia decomposition catalyst of oxides in the main reactor. The auxiliary ammonia decomposition reactor provides a hydrogen source without the need to operate a larger plant, thus providing startup-related benefits.

[0020] The system may be configured to vary the amount of the auxiliary hydrogen-containing gas stream directed to the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor, and the amount of the auxiliary hydrogen-containing gas stream directed to the combustion zone of the main ammonia decomposition reactor, supplying at least partially fuel to the main ammonia decomposition reactor. For example, the system can switch between supplying all of the auxiliary hydrogen-containing gas stream to the ammonia decomposition catalyst and supplying all of the auxiliary hydrogen-containing gas stream to the combustion zone, or the auxiliary hydrogen-containing gas stream can be divided so that, at any point during system startup and long-term operation, a certain proportion is directed to the ammonia decomposition catalyst and a certain proportion to the combustion zone as needed. This configuration provides a system with a much greater degree of flexibility for controlling both the reaction gas and fuel gas, both during startup and long-term operation of the ammonia decomposition system, thereby improving the system's operability, efficiency, safety, and lifespan.

[0021] Regarding startup, the ammonia decomposition catalyst may be installed in oxide form in one or more reaction tubes of the main ammonia decomposition reactor. After installation at system startup, at least a portion of the auxiliary hydrogen-containing gas stream is supplied to the oxide ammonia decomposition catalyst to reduce it. Furthermore, at least a portion of the auxiliary hydrogen-containing gas stream can be supplied to the combustion zone of the main ammonia decomposition reactor to supply at least partially fuel to start the main ammonia decomposition reactor.

[0022] Therefore, adding a secondary / auxiliary ammonia decomposition reactor upstream of or in parallel with a thermal ammonia decomposition reactor provides a good solution for starting up an ammonia decomposition plant. The auxiliary ammonia decomposition reactor may be an insulated floor with or without an electric heater upstream, or it may be an electrically heated reactor. Alternatively, energy can be supplied to the auxiliary reactor by other means, including the combustion of an alternative gas.

[0023] Ammonia decomposition catalysts are likely to be supplied in oxide form and require reduction with hydrogen or a hydrogen-containing stream to activate them during plant commissioning or after catalyst replacement. Ammonia can be used as a reducing agent, but it must first undergo decomposition to hydrogen. Experimental studies have shown that catalysts reduced under pure ammonia exhibit lower activity than those reduced under hydrogen. At low temperatures, significant decomposition of ammonia is not expected. As a result, the catalyst at the top of a thermally heated decomposition tube may not be completely reduced. This can be overcome by using an auxiliary (e.g., adiabatic) ammonia decomposition reactor to generate a decomposition gas stream. The decomposed gas, which may still contain high levels of ammonia, can be supplied to a thermal decomposition unit, and hydrogen in the gas can be used to reduce the catalyst from oxide form to the active metal.

[0024] For starting at any given time, an auxiliary decomposition reactor can be used to generate hydrogen / decomposition gas to ignite the main reactor burner. At startup, only ammonia is available as fuel. However, experimental studies have shown that using 100% ammonia fuel will not ignite the burner in a thermal ammonia decomposition reactor (i.e., no flame will be formed). Examples of fuel compositions known to successfully ignite include: • Decomposition gas (75% H2, 25% N2, residual ammonia) 80% NH3 and 20% H 2.

[0025] Furthermore, experiments have shown that after successful ignition, hydrogen can be removed from the fuel, allowing the flame to continue burning with 100% NH3 fuel.

[0026] Therefore, a secondary / auxiliary ammonia decomposition reactor can be used to generate decomposition gas that can be used directly as a starting fuel, or to generate decomposition gas that can then be separated and blended with ammonia used as a starting fuel to produce hydrogen. The fuel can also be used to heat the gas circulating in the plant, such as ammonia or nitrogen, so that the plant can be brought to the required / optimized temperature before the ammonia decomposition reaction and hydrogen production begin.

[0027] As shown in Figure 2, the system may include, or consist of, a first ammonia decomposition pathway 21 in which the ammonia gas input flow 14 first passes through the auxiliary ammonia decomposition reactor 12 to generate an auxiliary hydrogen-containing gas flow 16, and then passes through one or more reaction tubes of the main ammonia decomposition reactor 4 to generate a main hydrogen-containing gas flow. Furthermore, as shown in Figure 2, the system may include a second ammonia decomposition pathway 22 in which the ammonia gas input flow passes through one or more reaction tubes 6 of the main ammonia decomposition reactor 4 without first passing through the auxiliary ammonia decomposition reactor 12. Thus, during the operation of the main ammonia decomposition reactor 4, the input gas to the ammonia decomposition catalyst 8 in one or more reaction tubes 6 may include a fresh (undecomposed) ammonia gas input flow 22, at least partially decomposed ammonia gas input flow 16 (auxiliary hydrogen-containing gas flow) from the auxiliary ammonia decomposition reactor, or a combination of a fresh (undecomposed) ammonia gas input flow 22 and an auxiliary hydrogen-containing gas flow 16. Alternatively, during operation of the main ammonia decomposition reactor, the input gas to the ammonia decomposition catalyst in one or more reaction tubes may consist solely of an auxiliary hydrogen-containing gas stream.

[0028] As shown in Figure 3, the system may further include at least one purification unit 24 to increase the hydrogen content of the main hydrogen-containing gas stream to produce a purified hydrogen gas stream 26. Furthermore, the system may further include at least one purification unit (not shown in Figure 3) to increase the hydrogen content of the auxiliary hydrogen-containing gas stream 16. The same or different purification units can be provided to increase the hydrogen content of the main hydrogen-containing gas stream and the auxiliary hydrogen-containing gas stream. Furthermore, the system may be configured to supply at least partially fuel to the main ammonia decomposition reactor by directing exhaust or waste gas 28 from at least one of the purification units 24 to the combustion zone 10 of the main ammonia decomposition reactor 4. In this regard, it can be noted that the fuel gas for combustion to heat the main reactor may consist of one or more of the following: fresh (undecomposed) ammonia, an auxiliary hydrogen-containing gas stream from an auxiliary reactor, purified hydrogen from one or more purification units, waste / exhaust gas from one or more purification units, or an external fuel gas (e.g., methane) source.

[0029] While the system described above is particularly useful for commissioning and starting up an ammonia decomposition plant, this configuration is also advantageous for continuous plant operation. After the main ammonia decomposition reactor is started, at least a portion of the auxiliary hydrogen-containing gas stream can be continuously (continuously or intermittently) supplied to the combustion zone of the main ammonia decomposition reactor, thereby supplying at least partially of fuel to the main ammonia decomposition reactor during operation. Furthermore, after the main ammonia decomposition reactor is started, at least a portion of the auxiliary hydrogen-containing gas stream can be continuously (continuously or intermittently) supplied to the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor, thereby reducing the partial pressure of ammonia in one or more reaction tubes and, consequently, the nitridation rate in one or more reaction tubes. Therefore, this configuration provides a system with far greater flexibility for controlling both reaction gases and fuel gases, both during startup and long-term operation of the ammonia decomposition system, thereby improving the system's operability, efficiency, safety, and lifespan. In this regard, the auxiliary ammonia decomposition reactor can be controlled to control the composition of the auxiliary hydrogen-containing gas stream, as well as the resulting composition of the reaction gas and fuel gas, as desired for optimal performance during startup and operation. For example, the auxiliary ammonia decomposition reactor can be controlled so that the auxiliary hydrogen-containing gas stream contains at least 10 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, or 60 mol% of H2, or 100 mol%, 90 mol%, 80 mol%, or 70 mol% or less of H2, or within the range defined by any combination of the aforementioned lower and upper limits.

[0030] In connection with the above, it should be noted that International Publication No. 2022189560 discusses pre-decomposing an ammonia gas stream and then sending the partially decomposed gas stream to a reactor for further decomposition. U.S. Patent Application Publication No. 20220403775 discusses an ammonia processing system comprising one or more reactor modules configured to generate hydrogen from ammonia-containing feedstock, and it should also be noted that the hydrogen generated by one of the reactor modules can also be used to provide additional heating to other reactor modules via hydrogen combustion. However, neither document discloses nor suggests a system configured for both reducing an oxide catalyst in the main reactor and supplying fuel to the main reactor, for example, for system startup or for optimizing both the reaction gas mixture and the fuel gas mixture.

[0031] Suitable thermal ammonia decomposition reactors for the main reactor of this system are known and may include a fuel combustion zone having a radiating section with one or more burners supplied with one or more fuel streams and an oxygen supply gas, e.g., air, oxygen-enriched air, or oxygen. The radiating section may include one or more catalyst-containing reaction tubes through which the ammonia stream passes. Combustion of one or more fuel streams in one or more burners in the fuel combustion zone produces thermal energy (e.g., radiant heat) to heat one or more catalyst-containing reaction tubes. Dozens or hundreds of catalyst-containing reaction tubes may be present in the radiating section. If necessary, downstream of the radiating section, fuel gas from the combustion of one or more fuel streams may be used to preheat one or more feed streams in a convection section. Reactors comprising a radiating section containing catalyst-containing reaction tubes and a convection section for preheating feed materials are known in steam methane reforming and can be applied to the present invention.

[0032] Alternatively, a thermal ammonia decomposition reactor can be used if the combustion of one or more fuel flows in the fuel combustion zone is divided into reactors equipped with catalyst-containing reaction tubes. Such reactors are small reformers available from Johnson Matthey Davy Technologies Limited.

[0033] The catalyst in the catalyst-containing reaction tube can be any ammonia decomposition catalyst. For example, a nickel catalyst and / or a ruthenium catalyst may be used. A preferred catalyst is a nickel catalyst. The catalyst may contain 3 to 30% by weight of nickel, preferably 8 to 20% by weight, expressed as NiO, on a suitable refractory carrier, such as alumina or a metallic aluminate. The catalyst may also be in the form of pelletized units, which may contain one or more through-holes, or it may be provided as a washcoat on a structured metal or ceramic catalyst. A particularly preferred catalyst is KATALCO® 27-2, available from Johnson Matthey PLC, which contains 12% nickel, expressed as NiO, on cylindrical pellets formed from a high-surface-area calcium aluminate carrier. Another preferred catalyst is KATALCO® 27-200MQ, available from Johnson Matthey PLC, which contains 14% nickel, expressed as NiO.

[0034] The type of reactor that can be used in an auxiliary ammonia decomposition reactor is not particularly limited. Furthermore, more than one auxiliary ammonia decomposition reactor can be provided. One or more auxiliary ammonia decomposition reactors may be adiabatic reactors, packed-bed reactors, electric heating reactors, and / or gas-fired reactors. Preferably, one or more secondary ammonia reactors are adiabatic or electric heating reactors, such as adiabatic packed-bed reactors. An adiabatic reactor includes a reactor that does not transfer heat from the reactor to the ammonia stream supplied thereto. For example, an adiabatic reactor does not include a reactor that provides thermal energy to the ammonia stream.

[0035] The thermal energy required to support the decomposition reaction in one or more auxiliary ammonia decomposition reactors may be provided by heating the input ammonia stream and / or by providing auxiliary ammonia decomposition reactors that supply thermal energy. The thermal energy may be supplied from an external source outside the process (e.g., introduced electricity).

[0036] One or more auxiliary ammonia decomposition reactors include a catalyst. The catalyst may be any catalyst for decomposing ammonia. The catalyst may preferably be one of those described above that are suitable for use with a main-fire ammonia decomposition reactor.

[0037] The input ammonia stream may be heated before being supplied to the auxiliary ammonia decomposition reactor and / or the main thermal ammonia decomposition reactor. Therefore, the process of the present invention may include a step of heating the input ammonia stream. The input ammonia stream may be heated to a temperature above 350°C, above 400°C, above 450°C, above 500°C, or above 550°C. The input ammonia stream may be heated to a temperature below 1000°C, below 950°C, below 850°C, below 750°C, or below 700°C. The input ammonia stream may be heated to a temperature between 350°C and 1000°C, 400°C and 950°C, 450°C and 850°C, or 500°C and 750°C, for example, between 550°C and 700°C.

[0038] The temperature of the ammonia stream at the inlet to one or more catalyst-containing reaction tubes may be in the range of 350°C to 1000°C, 400°C to 950°C, 450°C to 850°C, or 500°C to 750°C, for example, 550°C to 700°C. The temperature of the hydrogen-containing stream exiting one or more catalyst-containing reaction tubes may be in the range of 500°C to 950°C, influencing the equilibrium position of the decomposition reaction. When nickel catalysts are used in one or more catalyst-containing reaction tubes, the temperature of the hydrogen-containing stream exiting one or more catalyst-containing reaction tubes may preferably be higher than about 700°C.

[0039] The inlet pressure to one or more catalyst-containing reaction tubes is set by the flow sheet design and may be in the range of 1 to 100 bar absolute pressure, preferably 10 to 90 bar absolute pressure, for example, 31 to 51 bar absolute pressure.

[0040] The auxiliary ammonia decomposition reactor may use a nickel-containing catalyst such as Katalco 27-2. In this case, the ammonia stream fed into the auxiliary reactor may be heated to temperatures of 700°C to 1000°C, 750°C to 900°C, or 800°C to 850°C. Alternatively, the auxiliary ammonia decomposition reactor may use a noble metal catalyst (e.g., a ruthenium-based catalyst), such as Katalco 27-612. In this case, the ammonia stream fed into the auxiliary reactor may be heated to temperatures of 400°C to 650°C, 450°C to 650°C, 500°C to 600°C, or 525°C to 575°C (e.g., about 550°C).

[0041] The hydrogen-containing stream from the main reactor and optionally from auxiliary reactors can be supplied to one or more purification units to increase the hydrogen content of the hydrogen-containing stream and generate a hydrogen-enriched stream and an exhaust gas stream. An example of a purification unit is a pressure swing absorption unit for increasing the H2 content by separating H2 from other components. The exhaust gas stream can be recycled and burned as fuel in the combustion zone of the main reactor.

[0042] It may be preferable to supply the hydrogen-containing stream to a steam generation unit and / or heat recovery zone before supplying the main hydrogen-containing stream and / or auxiliary hydrogen-containing stream to one or more purification units. As those skilled in the art will understand, the steam generation unit and / or heat recovery zone may be used to recover low or moderate amounts of heat.

[0043] The main hydrogen-containing stream and the auxiliary hydrogen-containing stream may preferably contain an equilibrium mixture of hydrogen, nitrogen, and ammonia.

[0044] The hydrogen-enriched flow after purification may contain 70 mol% or more of H2, 75 mol% or more of H2, 80 mol% or more of H2, 85 mol% or more of H2, or 90 mol% or more of H2. The hydrogen-enriched flow may contain 100 mol% or less of H2. For example, the hydrogen-enriched flow may contain 70 mol% to 100 mol% of H2, 75 mol% to 100 mol% of H2, 80 mol% to 100 mol% of H2, 85 mol% to 100 mol% of H2, or 90 mol% to 100 mol% of H2. Preferably, the hydrogen-enriched flow may contain more than 90 mol% of H2, more than 95 mol% of H2, more than 98 mol% of H2, or more than 99 mol% of H2. More preferably, the hydrogen-enriched flow may contain more than 99.9 mol% of H2, more than 99.95 mol% of H2, or about 100 mol% of H2. Most preferably, a stream containing high-concentration hydrogen may contain more than 99.95 mol% H2 or about 100 mol% H2.

[0045] Although the present invention has been specifically illustrated and described with reference to certain examples, it will be understood by those skilled in the art that various modifications of form and detail can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A system for producing hydrogen by catalytic decomposition of ammonia, A main ammonia decomposition reactor comprising: one or more reaction tubes containing an ammonia decomposition catalyst; and a fuel combustion zone surrounding the one or more reaction tubes, which provides thermal energy to support the decomposition of ammonia in the one or more reaction tubes and generate a main hydrogen-containing gas flow; It comprises an auxiliary ammonia decomposition reactor for decomposing ammonia and generating an auxiliary hydrogen-containing gas stream, A system configured to supply fuel to the main ammonia decomposition reactor at least partially by directing the auxiliary hydrogen-containing gas stream to both the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor and the combustion zone of the main ammonia decomposition reactor.

2. The system according to claim 1, further comprising an electric heater for generating the auxiliary hydrogen-containing gas flow by assisting in the decomposition of ammonia.

3. The system according to claim 1 or 2, configured to change the amount of the auxiliary hydrogen-containing gas stream that is led to the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor, and the amount of the auxiliary hydrogen-containing gas stream that is led to the combustion zone of the main ammonia decomposition reactor and supplies fuel to the main ammonia decomposition reactor at least partially.

4. The system according to any one of claims 1 to 3, comprising, or consisting of, a first ammonia decomposition pathway, wherein the ammonia gas input flow first passes through the auxiliary ammonia decomposition reactor to generate the auxiliary hydrogen-containing gas flow, and then passes through one or more reaction tubes of the main ammonia decomposition reactor to generate the main hydrogen-containing gas flow.

5. The system according to claim 4, further comprising a second ammonia decomposition pathway through which the ammonia gas input flow passes through one or more reaction tubes of the main ammonia decomposition reactor without passing through the auxiliary ammonia decomposition reactor.

6. The system according to any one of claims 1 to 5, further comprising at least one purification unit for increasing the hydrogen content of the main hydrogen-containing gas stream.

7. The system according to any one of claims 1 to 6, further comprising at least one purification unit for increasing the hydrogen content of the auxiliary hydrogen-containing gas stream.

8. The system according to claims 6 and 7, configured to use the same purification unit to increase the hydrogen content in both the main hydrogen-containing gas stream and the auxiliary hydrogen-containing gas stream.

9. The system according to any one of claims 6 to 8, wherein exhaust gas from at least one of the purification units is directed to the combustion zone of the main ammonia decomposition reactor to supply fuel to the main ammonia decomposition reactor at least partially.

10. A process for decomposing ammonia using the system described in any one of claims 1 to 9, The ammonia gas input stream is supplied to the auxiliary ammonia decomposition reactor to decompose the ammonia gas input stream and generate an auxiliary hydrogen-containing gas stream. A portion of the auxiliary hydrogen-containing gas stream is supplied to the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor. A portion of the auxiliary hydrogen-containing gas stream is supplied to the combustion zone of the main ammonia decomposition reactor, thereby supplying fuel to the main ammonia decomposition reactor at least partially. A process that includes this.

11. The process according to claim 10, wherein the ammonia decomposition catalyst is installed in oxide form in one or more reaction tubes of the main ammonia decomposition reactor, and after installation at the start of the system, at least a portion of the auxiliary hydrogen-containing gas stream is supplied to the oxide ammonia decomposition catalyst to reduce the oxide ammonia decomposition catalyst.

12. The process according to claim 10 or 11, wherein at least a portion of the auxiliary hydrogen-containing gas stream is supplied to the combustion zone of the main ammonia decomposition reactor, thereby supplying fuel to the main ammonia decomposition reactor at least partially and starting the main ammonia decomposition reactor.

13. The process according to any one of claims 10 to 12, wherein, after the start of the main ammonia decomposition reactor, at least a portion of the auxiliary hydrogen-containing gas stream is continuously supplied to the combustion zone of the main ammonia decomposition reactor, thereby supplying at least a portion of the fuel to the main ammonia decomposition reactor during operation.

14. The process according to any one of claims 10 to 13, wherein, after starting the main ammonia decomposition reactor, at least a portion of the auxiliary hydrogen-containing gas stream is continuously supplied to the ammonia decomposition catalyst in one or more reaction tubes of the main ammonia decomposition reactor to reduce the partial pressure of ammonia in the one or more reaction tubes, and consequently reduce the nitriding rate of the one or more reaction tubes.

15. The process according to any one of claims 10 to 14, wherein, during the operation of the main ammonia decomposition reactor, the input gas to the ammonia decomposition catalyst in one or more reaction tubes includes a combination of an ammonia gas input stream and an auxiliary hydrogen-containing gas stream.

16. The process according to any one of claims 10 to 14, wherein, during the operation of the main ammonia decomposition reactor, the input gas to the ammonia decomposition catalyst in one or more reaction tubes consists of the auxiliary hydrogen-containing gas stream.

17. The auxiliary ammonia decomposition reactor is configured such that the auxiliary hydrogen-containing gas stream contains at least 10 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, or 60 mol% H ２ , 100 mol%, 90 mol%, 80 mol%, or 70 mol% or less of H ２ , or within the range defined by any combination of the aforementioned lower and upper limits H ２ The process according to any one of claims 10 to 16, which is controlled to include a certain content.

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