Ammonia cracking for hydrogen production

Abstract

A process for the synthesis of hydrogen by catalytic cleavage of ammonia; the process comprising the step of subjecting an ammonia-containing stream (10) to a catalytic cleavage step (11) in the presence of heat to produce a combustion gas and a hot cleavage stream (14) containing nitrogen, hydrogen and potentially residual ammonia, and optionally water; the process further comprising the step of subjecting the hot cleavage stream to a hydrogen recovery step to produce a high-purity hydrogen stream (22).

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production, and particularly relates to a method and apparatus for producing hydrogen from an ammonia cracking unit. Background Technology

[0002] The excessive use of fossil fuels in the power and transportation sectors has had harmful effects on human health and well-being, as well as the environment. There is an urgent need to provide environmentally friendly and sustainable alternatives to fossil fuels.

[0003] Hydrogen and ammonia are carbon-free carriers and are considered ideal alternatives to fossil fuels.

[0004] On a small scale, hydrogen can be produced using various domestic resources (such as solar and wind power) and electrolysis. In contrast, on an industrial scale, hydrogen is obtained through the reforming of fossil fuels, primarily through the reforming of natural gas (steam reforming) or the water-gas shift reaction of coal-derived syngas.

[0005] Hydrogen produced by steam reforming requires a multi-step process, starting with natural gas purification, high-temperature reforming, high-low temperature water-gas shift conversion (WGS), and purification.

[0006] Unfortunately, the reforming process releases a large amount of CO2 into the atmosphere.

[0007] In this field, there is a desire to find an industrial-scale hydrogen synthesis method that can produce clean hydrogen without emitting any carbon dioxide into the atmosphere. This method should also be economically competitive with conventional methods.

[0008] Green ammonia synthesized from renewable energy sources is a carbon-free storage carrier for hydrogen and has many potential energy applications, including the production of green hydrogen. Hydrogen can be obtained from ammonia through a thermal decomposition process known as catalytic cracking.

[0009] During catalytic cracking, ammonia decomposes or cracks back to H2 and N2 according to the following endothermic equilibrium in the presence of heat and a catalyst (Ni, Ru, or Pt):

[0010] 2NH3↔3H2+N2

[0011] Ammonia can be thermodynamically converted to hydrogen at temperatures as low as 425°C. However, in practice, the conversion rate depends on the type of catalyst used. Typically, Ni is active at higher temperatures (500-750°C) than Ru (400°C), but the latter's catalysts are more expensive.

[0012] The heat required for the thermocatalytic conversion of ammonia is typically provided by electric heating in an electric furnace or in a reformer through fuel combustion.

[0013] Unfortunately, the aforementioned ammonia cracking technology has several drawbacks. First, ammonia cracking technology is mature and commercially available mainly for small-scale applications (i.e., hydrogen production rates of less than 100 kg H2 / h).

[0014] The main challenge in scaling up this technology is designing a cracking unit that is compact enough yet capable of breaking down ammonia at a rate consistent with consumption.

[0015] Furthermore, a typical problem observed in programs using adiabatic pyrolysis units is the relatively low ammonia conversion rate (i.e., high ammonia slip). In contrast, pyrolysis units utilizing oxygen-blown autothermal reformers require the installation of expensive air separation units (ASUs).

[0016] Furthermore, for high hydrogen production rates (>1000 m³ / h) 3 ( / h), natural gas reforming remains the most cost-effective option.

[0017] Therefore, considering the above factors, it is highly desirable to provide a cost-effective hydrogen synthesis method and equipment suitable for large-scale hydrogen production. Furthermore, the improved hydrogen synthesis method should be environmentally friendly, thus not resulting in carbon dioxide emissions into the atmosphere. Summary of the Invention

[0018] The present invention aims to overcome the aforementioned shortcomings of the prior art. In particular, the present invention addresses how to reduce carbon dioxide emissions and equipment costs, and how to provide methods and equipment suitable for large-scale production.

[0019] The present invention relates to a method in which a high-purity hydrogen gas stream is obtained by cracking ammonia.

[0020] The first aspect of the present invention is a method for producing carbon-free hydrogen for catalytic synthesis of hydrogen.

[0021] The method includes the following steps: subjecting an ammonia stream, optionally with added water, to a preheating step to produce an ammonia-containing stream, and subjecting the ammonia-containing stream to a catalytic ammonia cracking step in the presence of heat to produce a thermally cracked stream containing nitrogen, hydrogen, and potentially residual ammonia and water.

[0022] The method further includes the following steps: subjecting the pyrolysis stream to a hydrogen recovery step to generate a high-purity hydrogen stream and tail gas, or subjecting the pyrolysis stream to a washing step in the presence of water to generate a purified gas stream, and further subjecting the purified gas stream to a hydrogen recovery step to generate a high-purity hydrogen stream and tail gas.

[0023] In addition, the method includes the steps of: recycling at least a portion of the exhaust gas as fuel gas to provide heat for the catalytic cracking step and discharging the high-purity hydrogen gas stream.

[0024] Another aspect of the present invention is a method for producing hydrogen.

[0025] The method includes the following steps: subjecting an ammonia stream to a heating stage to produce an ammonia-containing stream, and subjecting the ammonia-containing stream to a catalytic ammonia cracking step in the presence of heat to produce combustion gases and a thermal cracking stream containing nitrogen, hydrogen and residual ammonia.

[0026] The method further includes the following steps: optionally mixing the pyrolysis stream with water to generate a water-added pyrolysis stream, and feeding the pyrolysis stream or the water-added pyrolysis stream to a cooling stage to generate a cooling stream, subjecting the cooling stream to a flash separation step to generate a lean ammonia stream and an ammonia stream or an ammonia solution, and further subjecting the lean ammonia stream to a hydrogen recovery step to generate a high-purity hydrogen stream and tail gas.

[0027] Alternatively, the ammonia-deficient gas stream may be subjected to a washing step in the presence of water to produce purified gas. The purified gas may then undergo a hydrogen recovery step to produce a high-purity hydrogen stream and tail gas.

[0028] In addition, the method includes the steps of: recycling at least a portion of the exhaust gas as fuel gas to provide heat for the catalytic cracking step and discharging the high-purity hydrogen gas stream.

[0029] Another aspect of the invention is an apparatus for producing hydrogen.

[0030] Hydrogen production equipment suitable for carrying out the method of the present invention includes at least one furnace suitable for ammonia cracking, which includes a plurality of externally heated catalytic tubes, an input line configured to feed an ammonia-containing stream into the tubes, and an output line configured to collect the thermally cracked stream from the tubes.

[0031] Apparatus suitable for carrying out the method of the present invention includes a hydrogen recovery unit configured to recover a stream of high-purity hydrogen gas and a tail gas, a pipeline configured to recycle at least a portion of the tail gas separated from the hydrogen recovery unit back into the furnace for use as supplementary fuel, and a pipeline configured to extract a stream of high-purity hydrogen gas from the hydrogen recovery unit.

[0032] Apparatus suitable for carrying out the method of the present invention includes a furnace suitable for ammonia cracking, comprising a plurality of externally heated catalytic tubes, an input line configured to feed an ammonia-containing stream into the tubes, an output line configured to collect the pyrolysis stream from the tubes, and optionally a line configured to supply water to the pyrolysis stream.

[0033] The apparatus suitable for carrying out the method of the present invention further includes a flash separator unit connected to the output line and configured to separate a lean ammonia gas stream from an ammonia stream or an ammonia solution; a hydrogen recovery unit connected in fluid communication with the flash separator and configured to recover a high-purity hydrogen stream and tail gas; a line configured to recycle at least a portion of the tail gas separated from the hydrogen recovery unit back into the furnace for use as supplementary fuel; and a line configured to extract a high-purity hydrogen stream from the hydrogen recovery unit.

[0034] Advantageously, by feeding air instead of oxygen into the furnace, an air separation unit is unnecessary. Even more advantageously, by adjusting the fuel-air ratio (i.e., operating with excess air), the NOx content of the combustion gases leaving the furnace can be minimized. Furthermore, by installing SCR (Selective Catalytic Reduction) or non-selective catalytic reduction to reduce the system's NSCR, NOx present in the system can be completely removed or reduced to a few ppm.

[0035] Even more advantageously, in contrast to reforming methods that use natural gas as a fuel source in the method of the present invention, a carbon-free source (e.g., ammonia) is used as the combustible gas, thereby preventing the release of carbon dioxide emissions into the atmosphere.

[0036] Advantageously, in the method and equipment configuration, in which the electrocracking unit is located before or integrated with the furnace, a high degree of flexibility in hydrogen synthesis can be envisioned.

[0037] Preferred embodiments

[0038] According to a particularly preferred embodiment of the invention, the heat required to sustain the endothermic cracking of ammonia is provided by the combustion reaction of fuel gas in the presence of preheated air to produce combustion gas.

[0039] Preferably, the fuel gas used as a combustible gas in the catalytic cracking step comprises ammonia, or a mixture of nitrogen and hydrogen, or a mixture of ammonia, nitrogen, and hydrogen. Advantageously, no carbon dioxide emissions are released into the atmosphere.

[0040] According to an alternative embodiment of the invention, remaining fossil fuels (e.g., natural gas) can be added to the fuel gas to sustain combustion. Due to the low amount of natural gas used, the carbon dioxide emissions of this method in this alternative embodiment are still lower than those expected in conventional hydrogen synthesis methods.

[0041] According to an alternative embodiment of the invention, the method further includes the steps of: subjecting the fuel gas containing ammonia to cracking in the presence of electric heating to produce a gas mixture containing hydrogen and nitrogen and potentially unconverted ammonia, and further subjecting the gas mixture to combustion in the presence of preheated air to provide reforming heat in the catalytic cracking step.

[0042] Alternatively, the fuel gas retaining ammonia can also undergo a catalytic cracking step, in which the heat required to sustain the cracking reaction is recovered from the combustion gas. The thermal cracking and electrocracking steps can be carried out in a single furnace. In this specific embodiment, the furnace may include a burner and an electrocracking unit.

[0043] Preferably, the burner is designed to burn ammonia, or a mixture of ammonia and hydrogen-rich streams, or a mixture of ammonia and hydrogen-rich streams and exhaust gas, or a mixture of hydrogen-rich streams and exhaust gas. Furthermore, the burner can operate in a mixture of the aforementioned streams with added natural gas or fossil fuels.

[0044] According to a particularly preferred embodiment, before undergoing the pyrolysis step or before undergoing combustion in the furnace, the fuel gas further undergoes a heat recovery step, wherein heat is indirectly transferred from the combustion gas to the fuel gas.

[0045] The reforming heat required for the ammonia catalytic cracking step can be provided by the combustion of fuel gas in the presence of preheated air.

[0046] According to an alternative embodiment, the ammonia solution may undergo a distillation step to separate the ammonia stream from the aqueous solution, and at least a portion of the ammonia stream may be recycled as fuel to provide heat for the catalytic cracking step.

[0047] In addition, a portion of the ammonia stream can be recycled to the heating stage to undergo ammonia catalytic cracking steps together with the main ammonia stream.

[0048] The method may further include the steps of: recovering heat from the combustion gas by indirectly contacting a portion of the aqueous solution with the combustion gas, and feeding said portion of the aqueous solution into the distillation step after heat recovery to provide heat for distillation. Advantageously, thermal integration between the distillation step and the ammonia catalytic cracking step can be achieved, and the energy consumption of the process can be reduced.

[0049] The method may further include the following steps: feeding a portion of the aqueous solution obtained from distillation into a pyrolysis stream, optionally supplemented with a water replenishment stream.

[0050] According to a particularly preferred embodiment of the invention, the hydrogen purification step is performed by means of a pressure swing adsorption unit, a cryogenic separation unit, or a membrane purification unit. Those skilled in the art are well aware of when to choose one unit over another based on the concentration of hydrogen retained by the pyrolysis stream.

[0051] Preferably, the high-purity hydrogen obtained after the hydrogen purification step has a concentration of more than 95% wt, more preferably more than 99% wt, and even more preferably more than 99.9% wt.

[0052] Preferably, the temperature of the thermal cracking stream leaving the catalytic cracking step is between 400 and 950°C, more preferably between 550 and 650°C.

[0053] Preferably, the catalytic cracking step is carried out at a pressure of about 5 to 65 barg, more preferably 15 to 30 barg (bar gauge).

[0054] According to a particularly preferred embodiment of the invention, the combustion gases exiting the catalytic cracking step undergo a NOx reduction step before being released into the atmosphere. Alternatively, the NOx reduction step can be performed in a portion of the furnace.

[0055] According to an embodiment of the invention, the apparatus may further include a purification unit and a pipeline, the purification unit being configured to recover ammonia from the pyrolysis stream to generate a purified gas stream and a recirculated gas, and the pipeline being configured to feed at least a portion of the recirculated gas into the furnace.

[0056] Furthermore, the apparatus may include an electrocracking unit configured to crack fuel gas that retains ammonia. Alternatively, the apparatus may include a coil filled with catalyst and disposed in the convection section of the furnace. The catalyst-filled coil is configured to utilize the heat retained by the combustion gases passing through the convection section to catalytically crack the fuel gas.

[0057] According to an embodiment of the present invention, the catalytic cracking of fuel can be carried out in a combined method, wherein the fuel is partially cracked in a coil disposed in the convection section of the furnace, and then the portion of the cracked fuel leaving the coil is further cracked in an electrocracking unit.

[0058] The electrocracking unit can be located before the furnace and can be connected to the furnace via a gas flowline. Alternatively, the electrocracking unit can be integrated into the furnace and can be used to crack fuel gases before combustion.

[0059] According to a particularly preferred embodiment of the invention, the apparatus includes a distillation unit and a pipeline, the distillation unit being configured to separate water and ammonia from an ammonia solution, and the pipeline connecting a flash separator unit to the distillation unit and being configured to deliver the ammonia solution to the distillation unit.

[0060] In addition, the equipment may also include a gas sampling line connecting the distillation unit to the furnace, a heat exchanger section, and a pipeline that connects the distillation unit to the furnace and is configured to recover heat from the combustion gases in the furnace via a water flow. The pipeline connects the distillation unit to the heat exchanger section and is configured to deliver a water flow that will be used for thermal integration purposes between the furnace and the distillation unit.

[0061] According to embodiments of the invention, the furnace may include a unit suitable for NOx removal (also called a NOx removal unit), preferably an SCR unit, or an SNCR unit, or a combination of both. NOx removal by SCR can be carried out in a temperature range of 150-600°C, or preferably in a temperature range including 350-600°C. Conversely, NOx removal by SNCR can be carried out in a temperature range of 850-1200°C, or preferably in a range including 900-1050°C. The term NOx refers to nitrogen oxides, primarily NO and NO2.

[0062] Preferably, the hydrogen recovery unit is a pressure swing adsorption unit, a cryogenic separation unit, or a membrane separation unit.

[0063] According to an embodiment of the invention, the ammonia catalytic cracking step is carried out in a furnace equipped with a radiation section and a convection section. The radiation section retains a tube bundle preferably containing a nickel-based catalyst, a ruthenium-based catalyst, a molybdenum-based catalyst, or a platinum-based catalyst, wherein the platinum-based catalyst may contain molybdenum, cobalt, and lithium.

[0064] In a particularly interesting embodiment of the invention, the convection section of the furnace includes a plurality of heat exchangers (coil assemblies) disposed within the convection section of the furnace. Preferably, at least one of the heat exchangers is a steam superheater; additionally, waste heat boiler coils and boiling water coils may also be integrated into the furnace. The heat recovered in the convection section of the furnace can be used for thermal integration purposes in the process or for energy production. Alternatively, heat recovery can also be completed downstream of the furnace.

[0065] The furnace outlet can be directly quenched using a cooling medium (preferably water, ammonia, or a cooler gaseous flow).

[0066] Downstream of the cooling process, the ammonia solution can preferably be separated from the gas phase in a flash evaporator, and the liquid can be distilled in a dedicated column using the heat available in the convection section of the furnace, and ammonia can be recovered in the same distillation column. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of a hydrogen synthesis method according to an embodiment of the present invention.

[0068] Figure 2 This is a schematic diagram of a hydrogen synthesis method according to another embodiment of the present invention.

[0069] Figure 3 This is a schematic diagram of a hydrogen synthesis method according to an alternative embodiment of the present invention.

[0070] Figure 4 This is a schematic diagram of a hydrogen synthesis method according to another embodiment. Detailed Implementation

[0071] Figure 1 A schematic diagram of a hydrogen synthesis method according to a first embodiment of the present invention is shown.

[0072] The liquid ammonia stream 2 is taken out from the storage feed tank 1 and fed to the first preheating unit 6 via the pump 3, thereby obtaining an evaporated or partially evaporated ammonia stream 7 or hot liquid ammonia 7.

[0073] Ammonia stream 7 is mixed with water 8 and preheated in the second preheating unit 9 to complete the evaporation of the ammonia-water stream, thereby generating an ammonia-containing stream 10. Then, the ammonia-containing stream 10 is fed into the catalytic cracking unit 11 for catalytic cracking in the presence of heat, thereby generating a cracked stream 14.

[0074] The catalytic cracking unit 11 typically includes a furnace with a radiant section and a convection section. The radiant section includes a tube bundle that retains the cracking catalyst (typically a nickel-based catalyst).

[0075] The heat required to sustain the endothermic ammonia cracking reaction is provided by the combustion of fuel gas 12 in the presence of preheated air 28.

[0076] The preheated air 28, fed into the catalytic cracking furnace as a combustion aid, is obtained by preheating the airflow 27 exiting the blower 26 in the convection section of the furnace. In the convection section, pressurized steam 29 is also generated by recovering heat from the combustion gases 60. The combustion gases are then treated in a NOx removal stage (not shown) to remove NOx before being released into the atmosphere.

[0077] The pyrolysis stream 14 (typically retaining residual ammonia) undergoes a washing step 20 in the presence of water 17 to produce a purified gas stream 51 and a recirculated gas stream 21. Water 17 is used as an absorbent in the washing step to utilize the high solubility of ammonia in water, thereby removing ammonia from the stream.

[0078] The purified gas stream 51 is then fed into the hydrogen recovery step 19 to generate a high-purity hydrogen stream 22 and a tail gas 23. The hydrogen stream 22 is removed from the hydrogen recovery step and stored and / or discharged as needed for hydrogen production.

[0079] Then, the exhaust gas 23 and the recirculated gas 21 are mixed together to generate a mixed stream 25 and recirculated back to the ammonia cracking step / unit 11.

[0080] exist Figure 2 The present invention illustrates a method for hydrogen synthesis according to another embodiment of the present invention.

[0081] When the ammonia content retained by the pyrolysis stream 14 is on the order of several ppm, preferably on the order of ppb, Figure 2 The method described herein can be used to synthesize hydrogen.

[0082] In this specific embodiment, the pyrolysis stream 14 is fed directly to the hydrogen recovery step 19 without a washing stage. The hydrogen recovery step is performed in a pressure swing adsorption unit.

[0083] Alternatively, hydrogen can be recovered in a cryogenic unit, where a series of compression and cooling stages are performed to remove nitrogen from the purified gas stream, or hydrogen can be recovered in a hydrogen membrane separation unit, where the selective permeability of hydrogen on a specific membrane is utilized.

[0084] exist Figure 3 An alternative embodiment of the hydrogen synthesis method is shown in the figure.

[0085] The ammonia stream 7 undergoes heating stages 6 and 51, during which it exchanges heat with the thermally cracked stream 14 exiting the furnace 11. Furthermore, prior to the ammonia catalytic cracking step fed into the furnace, the ammonia stream 9 is further heated in the convection section of the furnace to produce an ammonia-containing stream 10.

[0086] The thermal cracking stream 14, containing nitrogen, hydrogen, and residual ammonia, is mixed with water 74 after leaving the furnace to produce a water-added thermal cracking stream 75. This water-added thermal cracking stream 75 exchanges heat with the ammonia stream 7 in heat exchangers 51 and 6, and is then further air-cooled in tower 70 to produce a cooling stream 79.

[0087] Then, the cooling stream 79 is sent to the flash separator 80, where the ammonia-depleted gas stream 81 is separated from the ammonia solution 82.

[0088] Then, the lean ammonia stream 81 is fed into the hydrogen recovery step 19 to generate a high-purity hydrogen stream 22 and tail gas 23.

[0089] Then, after exchanging heat 120 with the aqueous solution 74, the exhaust gas 23 is used as fuel feed to provide heat to the catalytic cracking step 11.

[0090] Hydrogen gas 22 is removed from hydrogen recovery step 19 and stored or discharged as needed. Then, the ammonia solution 82 is sent to distillation 83 to separate the aqueous solution 84 from the ammonia stream 86.

[0091] The first portion 91 of the ammonia stream 86 is recycled back into the furnace as fuel to provide heat for the catalytic cracking step 11, while the second portion 92 of the ammonia stream is mixed with the ammonia stream 7 and then fed into the ammonia catalytic cracking step 11 in the furnace after preheating.

[0092] A portion 87 of the aqueous solution 84 is used to recover heat from the combustion gas 60 via indirect heat transfer with the combustion gas 60 in the convection section of the furnace. The combustion gas undergoes a NOx removal step 131 before being removed from the furnace.

[0093] The second portion 88 of the aqueous solution 84 obtained from distillation 83 is mixed with the supplementary water stream 17 and fed into the thermal cracking stream 14.

[0094] exist Figure 4 The present invention illustrates a method for hydrogen synthesis according to an alternative embodiment.

[0095] As can be understood from the figure, the fuel gas 12 containing ammonia undergoes a cracking step 100 in the presence of electric heating to produce a gas mixture 101 containing hydrogen and nitrogen, and optionally unconverted ammonia.

[0096] The gas mixture 101 is then mixed with the exhaust gas 23 and then subjected to combustion in the presence of preheated air 28 to provide reforming heat in the catalytic cracking step 11.

[0097] As an alternative embodiment not shown in the figures, the pyrolysis step performed in the presence of electric heating can also be carried out in a furnace.

Claims

1. A method for catalytic synthesis of hydrogen, comprising the following steps: a) subject the ammonia stream (7) to a heating stage to produce an ammonia-containing stream (10); b) The ammonia-containing stream (10) is subjected to a catalytic ammonia cracking step in the presence of heat to produce combustion gas (60) and a thermal cracking stream (14) containing nitrogen, hydrogen and residual ammonia. c) Optionally, the pyrolysis stream is mixed with water (74) to produce a pyrolysis stream (75) with added water. d) Feed the pyrolysis stream (14) or the pyrolysis stream (75) with added water into the cooling stage to generate a cooling stream (79). e) subjecting the cooling stream (79) to a flash separation step to produce a lean ammonia stream (81) and an ammonia stream (86) or an ammonia solution (82), and further subjecting the lean ammonia stream (81) to the following steps: e1) Hydrogen recovery steps to produce a high-purity hydrogen stream (22) and tail gas (23). or e2) A washing step (20) in the presence of water (17) to generate a purified gas stream (51), and further subjecting the purified gas stream (51) to a hydrogen recovery step to generate a high-purity hydrogen stream (22) and tail gas (23). f) Recycle at least a portion of the exhaust gas (23) as fuel to provide heat for the catalytic cracking step; g) Take out the high-purity hydrogen gas stream (22).

2. The method according to claim 1, wherein the heat for the ammonia catalytic cracking step is provided by combustion of fuel gas (12) in the presence of preheated air (28).

3. The method according to claim 1, further comprising the following step: The fuel gas (12) containing ammonia is subjected to a cracking step (100) in the presence of electric heating to produce a gas mixture (101) containing hydrogen and nitrogen and optionally unconverted ammonia, and the gas mixture (101) is further subjected to combustion in the presence of preheated air (28) to provide heat in the catalytic cracking step.

4. The method according to claim 1, further comprising the following steps: h) subject the ammonia solution (82) to a distillation step to separate the ammonia stream (86) from the aqueous solution (84); i) Recycle at least a portion of the ammonia stream (86) as fuel to provide heat for the catalytic cracking step; j) Optionally, a portion of the ammonia stream (86) is recycled to step a) to undergo the heating phase in the presence of the ammonia stream (7); k) Heat is recovered from the combustion gas (60) by indirectly contacting a portion (87) of the aqueous solution (84) with the combustion gas (60), and the portion of the aqueous solution is fed into the distillation step after heat recovery to provide distillation heat.

5. The method according to claim 4, further comprising the following step: The second portion (88) of the aqueous solution (84) obtained from the distillation step is mixed with a thermally cracked stream (14) optionally supplemented with water.

6. The method according to claim 1, wherein the hydrogen recovery step is performed by a pressure swing adsorption unit, a cryogenic separation unit, or a membrane purification unit.

7. The method according to claim 1, wherein the concentration of the high-purity hydrogen gas stream (22) is higher than 99% wt.

8. The method according to claim 1, wherein the concentration of the high-purity hydrogen gas stream (22) is higher than 99.9%wt.

9. The method according to claim 1, wherein the temperature of the thermal cracking stream (14) exiting the catalytic cracking step is between 400 and 950°C.

10. The method according to claim 1, wherein the temperature of the thermal cracking stream (14) exiting the catalytic cracking step is between 550 and 650°C.

11. The method of claim 1, wherein the catalytic cracking step is carried out at a pressure of 5 to 65 barg.

12. The method of claim 1, wherein the catalytic cracking step is carried out at a pressure between 15 and 30 barg.

13. The method of claim 1, wherein the combustion gas (60) undergoes a nitrogen oxide (NOx) reduction step.

14. An apparatus for producing hydrogen according to the method of claim 1, comprising at least: A furnace (11) suitable for ammonia cracking includes multiple externally heated catalytic tubes; An input line is configured to feed an ammonia-containing stream (10) into the tube, and an output line is configured to collect a pyrolysis stream (14) from the tube; Optionally configured to feed water into an output line set to collect the pyrolysis stream (14); A flash separator unit (80) is connected to the output line and is configured to separate ammonia-lean stream (81) and ammonia stream or ammonia solution (82). Hydrogen recovery unit (19), which is in fluid communication with flash separator unit (80) and configured to recover high-purity hydrogen stream (22) and tail gas (23). The pipeline is configured to recycle at least a portion of the tail gas (23) separated from the hydrogen recovery unit (19) back to the furnace (11) for use as an additional fuel. The pipeline is configured to extract a stream of high-purity hydrogen gas (22) from the hydrogen recovery unit (19).

15. The device according to claim 14, further comprising: A distillation unit (83) configured to separate water and ammonia from the ammonia solution (82); The flash separator unit (80) is connected to the distillation unit (83) and configured to deliver the ammonia solution (82) to the distillation unit (83) via a pipeline; Gas sampling line, which connects the distillation unit (83) to the furnace (11). The heat exchanger section is configured to recover heat from the combustion gases in the furnace (11) by means of a water flow; The distillation unit (83) is connected to the heat exchanger section and configured to deliver the water flow for the purpose of thermal integration between the furnace (11) and the distillation unit (83).

16. The apparatus of claim 14, wherein the furnace (11) further comprises a unit for removing nitrogen oxides (NOx).

17. The apparatus of claim 14, wherein the furnace (11) further comprises an SCR unit for removing nitrogen oxides (NOx).

18. The device according to claim 14, wherein the hydrogen recovery unit (19) is one of the following units: pressure swing adsorption unit; cryogenic separation unit; membrane separation unit.

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