Process for breaking down ammonia

Abstract

A process for catalytic cracking of ammonia, the process comprising supplying an ammonia feed gas to one or more catalyst-containing reaction vessels located within an ammonia cracking reactor, and cracking ammonia in the ammonia feed gas in one or more catalyst-containing reaction vessels to produce a hydrogen-containing stream, wherein the ammonia feed gas is supplied to the reaction vessels or each reaction vessel at a pressure of at least 10 bar, the reaction vessels or each reaction vessel is heated to a temperature of at least 500°C, and the reaction vessels or each reaction vessel has walls comprising or made of an alloy selected to be resistant to both nitriding and creep deformation at said temperature and pressure without failure for an operating period of at least 1,000 hours, 5,000 hours, 10,000 hours, 50,000 hours, or 100,000 hours.

Description

Technical Field

[0001] The present invention relates to a process for the catalytic decomposition of ammonia. The present invention further relates to a reaction vessel for use in the catalytic decomposition of ammonia, optionally a tubular reaction vessel.

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.

[0004] Liquid ammonia can be burned directly after being transported or converted to hydrogen by a decomposition process.

[0005] The catalytic decomposition of ammonia into hydrogen and nitrogen has been known for many years. The reaction can be shown as follows. 2NH3⇔N2+3H2

[0006] The ammonia decomposition reaction is endothermic and can be usefully achieved by passing ammonia over a suitable catalyst in a heated catalyst-containing reaction vessel, such as a catalyst-containing reaction tube heated externally and placed in a furnace. For example, such furnaces for the steam reforming of natural gas or naphtha feedstocks are known.

[0007] However, reaction tubes containing heating catalysts placed in a furnace may react with ammonia-containing gases to form undesirable metal nitrides within the tube material. This undesirable material damage mechanism, known as nitriding or nitride formation, can accelerate the failure of the reaction tube, particularly at locations within the reaction tube where the nitriding potential is highest (e.g., locations where the partial pressure of ammonia / nitrogen is highest, where the temperature is highest, and / or where the combination of ammonia / nitrogen partial pressure and temperature produces the highest nitriding potential).

[0008] A malfunction in the reaction tube necessitates a complete shutdown of the ammonia decomposition reactor, resulting in significant plant downtime. Furthermore, nitriding and malfunction of the reaction tube pose a serious safety hazard.

[0009] The objective of this specification is to provide a process for catalytic cracking of ammonia that addresses the aforementioned nitriding problems and has improved operability and increased safety. [Overview of the project]

[0010] One option to address the nitriding problem in processes for catalytic cracking ammonia is to construct the reaction vessels / tubes from materials resistant to nitriding (e.g., alloys). However, most alloys resistant to nitriding do not possess the thermal and / or mechanical properties required to maintain mechanical integrity when exposed to high pressure and high temperature for extended periods. This was not as much of a problem in these low-pressure ammonia cracking processes, as previous ammonia cracking processes were typically not carried out at high pressure for extended periods. In other words, most ammonia cracking reactions have been carried out at low and medium scales where the mechanical properties at high temperature and pressure, and the economics of using nitride-resistant alloys, are more acceptable. Ammonia cracking at the scale required for hydrogen production in the energy industry requires high pressure and therefore higher required creep strength, but is also heavily influenced by the most economical metallurgy / design.

[0011] The applicant has developed a high-pressure, high-temperature ammonia decomposition process and identified that the reaction vessels / tubes must be formed from materials (e.g., alloys) that have good thermal and mechanical stability over long periods of operation at such high pressures and temperatures. Deformation of the catalyst-containing reaction tube can occur, which can lead to the eventual failure of the reaction tube. Heat-resistant materials must be resistant to attack by high-temperature gases, but also possess suitable mechanical properties at high temperatures under long-term loading. This property is known as creep strength. Alloys with high creep strength are known, however, many of these are susceptible to nitriding.

[0012] Therefore, the applicant has identified that in high-pressure, high-temperature ammonia decomposition processes, the reaction vessels must be formed from an alloy that has both good nitriding resistance and good thermal and mechanical stability over long periods of operation at such high pressures and high temperatures.

[0013] A process for catalytic cracking of ammonia, according to this specification, wherein the process is Supplying ammonia supply gas to one or more reaction vessels containing a heating catalyst located within the ammonia decomposition reactor, The process includes decomposing ammonia in an ammonia supply gas in one or more catalyst-containing reaction vessels to generate a hydrogen-containing stream, Ammonia supply gas is supplied to the reaction vessel or each reaction vessel at a pressure of at least 10 bar. The reaction vessel or each reaction vessel is heated to a temperature of at least 500°C. A process is provided in which the reaction vessel or each of the reaction vessels comprises or has walls made of an alloy selected to be resistant to both nitriding and creep deformation at the temperature and pressure, without failure for an operating period of at least 1,000 hours, 5,000 hours, 10,000 hours, 50,000 hours, or 100,000 hours.

[0014] The ammonia supply gas may be supplied to the reaction vessel or each reaction vessel at a pressure within the range defined by at least 20 bar, 30 bar, 40 bar, or 50 bar; 1000 bar, 500 bar, 100 bar, or 75 bar or less; or any combination of the aforementioned lower and upper limits.

[0015] The reaction vessel or each reaction vessel may be heated to a temperature within the range defined by at least 550°C, 600°C, 650°C, or 700°C; 1500°C, 1000°C, 950°C, 900°C, or 850°C or less; or any combination of the aforementioned lower and upper limits.

[0016] The reaction vessel or each reaction vessel may be in the form of a reaction tube in which the catalyst is placed. The reaction vessel / tube or each reaction vessel / tube may have a thickness of at least 3 mm, 5 mm, 8 mm, or 10 mm; 50 mm, 20 mm, 15 mm, or 14 mm or less; or within the range defined by any combination of the aforementioned lower and upper limits. An exemplary thickness range is 8–14 mm, optionally 10–14 mm.

[0017] The selection of alloys suitable to satisfy the criteria of the present invention requires knowledge of the operating conditions of high-pressure, high-temperature ammonia decomposition processes, an understanding of the combined effects of nitriding and creep deformation in such processes, and an understanding of the nitriding and creep deformation properties of alloys to select alloys suitable to satisfy all the operating requirements of the process. Only a small subset of metal alloy compositions meets the required criteria, such as being selected using expert knowledge of both alloys, their properties, their interaction with the high-pressure, high-temperature ammonia decomposition environment, and thermal, mechanical, and nitridation resistance requirements. Accordingly, this specification involves applying expert material knowledge to the field of ammonia decomposition at high pressure.

[0018] Suitable alloys may contain nickel and / or cobalt in amounts of 11% by weight, 15% by weight, 20% by weight, 30% by weight, 50% by weight, or more than 75% by weight. The total nickel + cobalt content (if present) of the alloy is preferably more than 40% by weight. Optionally, the alloy may also contain one or more of Cr, Si, or Al. For example, the alloy may contain at least 10% by weight, 14% by weight, 15% by weight, 20%, or 30% chromium, such as at least 40% by weight. Additionally, the alloy may contain at least 1% by weight, 3% by weight, or 4% by weight of aluminum, for example, in the range of 1 to 5% by weight.

[0019] The alloy may also have an oxide layer disposed on its surface. Such an oxide layer may be an aluminum oxide layer formed from aluminum in the alloy, or it may be silicon oxide, chromium oxide, or a combination of two or more of these. The alloy may undergo a pre-oxidation treatment to form the oxide layer. The ammonia feed gas may contain oxidizing species such as oxygen and / or water to ensure oxidation conditions in the reaction vessel and to help maintain the oxide layer. These oxidizing species may be naturally present in the ammonia feed gas or may be added intentionally. Maintaining water in the process flow gas is preferred in the background of high-pressure, high-temperature nitriding in ammonia because it offers significant advantages over other means of oxide formation and ensures good recovery of the oxide throughout the operating period if damaged.

[0020] Alloys include Alloy 600, Alloy 601, Alloy 602ca, Alloy 617, Alloy 625, Alloy 690, Alloy 693, Alloy 699, VDM(R) Alloy 699XA, Alloy 214, Alloy 230, Alloy 233, Alloy MA47P, Alloy X, Alloy S, Alloy 160, S+C(R) G 4879, G 4878 Micro, ET 45 Micro, ET 45 LC, HT E, ET 35 Co, Paralloy(R) OPTIM-AL, 35 / 45 Microalloy, 22H, Manurite(R) 40XO, XAl4, XTM Low C, 40X, XTM, 50W, Manaure 2, Kubota SCH42, KHR48N, KHR48NCo, KHRSA, KHR45A, UCX, Alloy 800 / H / HT, Cast grades The alloys may be selected from the list consisting of HT, HU, HW, HX, HP15Nb, HP, HPNb, HPNbS, CT15C, Kanthal® A-1, APM, AF, D, and NIKROTHAL 40, 60, 70, 80, alloy 120, and INCOLOY® alloys HX, 803, 890. Alloys 600 and 625 are preferred due to a balance between desirable properties, availability of good creep data, and cost. Alternatively, alloys 214, MA47P, 233, 699, and VDM® ALLOY 699XA are preferred due to having enough aluminum to provide a robust oxide scale against nitriding. Some of the other listed alloys are less preferred due to cost and / or availability.

[0021] While not bound by any particular theory, chromium-containing alloys are considered advantageous due to their ability to react with nitrogen-containing species on the alloy surface. This is thought to allow for the formation of a protective layer that acts to shield the alloy bulk from further nitriding.

[0022] Regarding the list of preferred alloys above, it can be noted that all alloys contain either cobalt or nickel, and some contain both. Preferred alloys typically contain at least nickel, but cobalt-based alloys can also be used. Those containing cobalt tend to have improved mechanical properties at the most extreme temperatures, but will be more expensive. Therefore, while cobalt-based alloys are useful, in practice this may not be economically preferable. In this process, the total nickel + cobalt (if present) content of the alloy is preferably more than 40% by weight, and greater advantages are added as the amount increases.

[0023] Some of the listed alloys contain aluminum. This can offer further advantages through the ability to form oxide layers with low nitrogen permeability and in environments with lower trace oxygen content than chromium oxide. For alloys containing aluminum for oxide layer formation, it is advantageous that they should have a sufficient aluminum content for good oxide layer formation. Increasing the amount tends to offer greater advantages until it begins to cause changes in mechanical properties through excessive gamma prime precipitation at high temperatures. Optionally, the aluminum content can range from 1 to 5 wt%, optimally 3 wt% if pre-oxidation is performed, and over 4 wt% if no pre-oxidation is performed.

[0024] All the alloys listed also contain chromium. Most alloys in this process have a minimum chromium content of over 14% by weight. Strength is primarily important when used to improve economic efficiency, for example, when thinner walls and less material are used. Therefore, strengthening elements need to be added to enhance economic efficiency. For example, cobalt adds high-temperature strength, but adding and processing the material can be more expensive than simply making thicker walls with a non-coal alloy. The optimal alloy composition depends on the reactor design and the details of the process conditions. However, chromium is present in the most commercially available alloys suitable for this process.

[0025] The above process provides a high-pressure and high-temperature method for decomposing ammonia to produce hydrogen, which has improved operability, reduced downtime, and increased safety. One or more reaction tubes / containers used in the process are resistant to nitridation and to creep and / or embrittlement damage under high-temperature and high-pressure ammonia decomposition processes.

[0026] This specification also provides a reaction vessel for use in the above process. The reaction vessel contains an ammonia decomposition catalyst and has a wall made of or containing an alloy selected to be resistant to both nitridation and creep deformation without failure for an operating period of at least 1000 hours, 5000 hours, 10,000 hours, 50,000 hours, or 100,000 hours at an operating pressure of at least 10 bar and an operating temperature of at least 500 °C. In another aspect, the reaction vessel is as described in relation to the process for decomposing ammonia. Also provided is an ammonia decomposition reactor comprising one or more of these reaction vessels.

Brief Description of the Drawings

[0027] For a better understanding of the present invention and to show how the present invention may be implemented, certain embodiments of the present invention are described herein by way of example only with reference to the accompanying drawings. [Figure 1] A schematic view of a reaction tube in the plane x,y along the axial length x is shown, and the circular cross-section of the reaction tube can be seen in the y,z plane. [Figure 2] A schematic view of a cross-section of the reaction tube in the plane y,z is shown, where "a" represents the thickness of the reaction tube and "o" represents an oxide layer on the inner surface of the tube. [Figure 3] A diagram of an ammonia decomposition reactor comprising a catalyst-filled reaction tube and a burner for providing thermal energy to the reaction tube is shown.

Modes for Carrying Out the Invention

[0028] The following describes preferred and / or optional features of the present invention. Any aspect of the present invention may be combined with any other aspect of the present invention unless otherwise required by context. Any preferred and / or optional feature of any aspect may be combined with any aspect of the present invention, either individually or in combination, unless otherwise required by context.

[0029] The process described herein includes supplying an ammonia feed gas to one or more reaction tubes containing a heated catalyst, which are located within an ammonia decomposition reactor. The ammonia feed gas can be derived from any source. The ammonia feed gas can be produced by a catalytic combination of hydrogen and nitrogen, for example, from the Haber-Bosch ammonia synthesis process. The ammonia feed gas can be produced in an ammonia production facility located upstream of the ammonia decomposition reactor. Alternatively, the ammonia feed gas can be supplied from an ammonia gas storage facility, an ammonia storage unit, an ammonia storage tank, or an ammonia gas pipeline.

[0030] The ammonia feed gas may be preheated before being supplied to one or more catalyst-containing reaction tubes. Therefore, the process may include a step of preheating the ammonia feed gas. The ammonia feed gas may be preheated to temperatures above 350°C, above 400°C, above 450°C, above 500°C, or above 550°C. The ammonia feed gas may be preheated to temperatures below 1000°C, below 950°C, below 850°C, below 750°C, or below 700°C. The ammonia feed gas may be preheated to temperatures between 500°C and 750°C, such as 350°C to 1000°C, 400°C to 950°C, 450°C to 850°C, or 550°C to 700°C.

[0031] A suitable ammonia decomposition reactor is known and may include a fuel combustion zone having a radiating section containing 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 comprise one or more catalyst-containing reaction tubes through which the ammonia supply gas 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, the fuel gas from the combustion of one or more fuel streams may be used to preheat one or more supply streams in a convection section. A reactor comprising a radiating section containing catalyst-containing reaction tubes and a convection section for preheating the feed is known in steam methane reforming and can be applied to this process for ammonia decomposition.

[0032] Alternative ammonia decomposition reactors may be used, for example, when 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 miniature reformers available from Johnson Matthey Davy Technologies Limited. Other alternative forms of reactors include plate or tubular exchangers heated by molten salt, rotary heaters such as Coolbrooks, or printed circuit heat exchangers. In certain configurations, the tubes may be combusted, and the outer regions of the tubes may contain ammonia. Alternatively, the tubes may be electrically heated, induction heated, or heated by concentrated solar energy.

[0033] The catalyst may be any ammonia decomposition catalyst. For example, a nickel catalyst and / or a ruthenium catalyst may be used. 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 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, available from Johnson Matthey PLC. RTM This is 27-2, which contains 12% nickel, represented as NiO, on cylindrical pellets formed from a high-surface-area calcium aluminate support.

[0034] The process of the present invention includes the step of decomposing ammonia in an ammonia supply gas in one or more heated catalyst-containing reaction tubes to generate a hydrogen-containing stream.

[0035] The ammonia supply gas is supplied to the reaction vessel / tube or each reaction vessel / tube at a pressure of at least 10 bar, 20 bar, 30 bar, 40 bar, or 50 bar; 1000 bar, 500 bar, 100 bar, or 75 bar or less; or within the range defined by any combination of the aforementioned lower and upper limits.

[0036] The reaction vessels / tubes or each reaction vessel / tube are heated to a temperature within the range defined by at least 500°C, 550°C, 600°C, 650°C, or 700°C; 1500°C, 1000°C, 950°C, 900°C, or 850°C or less; or any combination of the aforementioned lower and upper limits.

[0037] The temperature of the ammonia supply gas at the inlet to one or more catalyst-containing reaction tubes may be in the range of 500°C to 750°C, such as 350°C to 1000°C, 400°C to 950°C, 450°C to 850°C, or 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.

[0038] The ammonia decomposition reaction produces a hydrogen-containing stream. The hydrogen-containing stream contains H2. The hydrogen-containing stream also contains nitrogen and may further contain residual ammonia (e.g., unreacted ammonia).

[0039] The hydrogen-containing stream may contain 40 mol% or more of H2, 50 mol% or more of H2, or 60 mol% or more of H2. Optionally, the hydrogen-containing stream may contain 75 mol% or less of H2, 70 mol% or less of H2, or 65 mol% or less of H2. For example, the hydrogen-containing stream may contain 40 mol% to 75 mol% of H2, 50 mol% to 70 mol% of H2, or 60 mol% to 65 mol% of H2.

[0040] As described in the Overview section, the processes described herein use catalyst-containing reaction vessels (e.g., tubes) made of alloys selected to be resistant to both nitriding and creep deformation at the high operating temperatures and pressures of the process, without failure for an operating period of at least 1,000 hours, 5,000 hours, 10,000 hours, 50,000 hours, or 100,000 hours.

[0041] The reaction tube has an inlet and an outlet that define the axial length x of the reaction tube. It will be understood that the catalyst for the ammonia decomposition reaction is located inside the reaction tube along the axial length x. It will be further understood that the ammonia feed gas passes from the inlet side of the reaction tube over the ammonia decomposition catalyst located inside it, and the hydrogen stream exits the reaction tube through the outlet side. Figure 1 shows the axial length x of the reaction tube in the x,y plane.

[0042] The reaction tube has a cross-section in a plane perpendicular to its axial length in the y,z plane. The cross-section can take any shape and is not particularly limited. For example, the cross-section may be circular, elliptical, quadrilateral (e.g., square or rectangle), or triangular. Typically, the cross-section is circular. When the cross-section is circular, the reaction tube will be understood to be a cylindrical tube.

[0043] An example of a cross-section of a reaction tube in the y,z plane is shown in Figure 2, where the cross-section is circular and "a" represents the thickness of the alloy tube. The tube wall may have a thickness of at least 3 mm, 5 mm, 8 mm, or 10 mm; 50 mm, 20 mm, 15 mm, or 14 mm or less; or within the range defined by any combination of the aforementioned lower and upper limits. An exemplary thickness range is 8–14 mm, optionally 10–14 mm. However, it should be noted that these ranges are for a standard combustion reactor design, and the thickness may vary in other types of reactor configurations.

[0044] Figure 2 also shows an oxide layer on the inner surface of the tube. This oxide layer can be formed by the oxidation of the aluminum components of the alloy used to form the tube, for example, the aluminum that forms the aluminum oxide scale. Such an oxide layer can reduce nitriding. It is formed from the reaction of the alloy with oxygen in the air during fabrication. Also, the oxide layer grows and recovers in the process environment, provided that oxygen is available. A lower oxygen partial pressure is required to form alumina in aluminum-containing alloys. Controlling the content of oxide species (e.g., water and / or oxygen) in the process flow gas within the reaction tube during operation can ensure oxidation conditions and help maintain the protective oxide layer. Alternatively, naturally occurring oxide species in the process flow gas may perform this function. Nevertheless, maintaining water in the process flow gas is preferred in the background of high-pressure, high-temperature nitriding in ammonia because it shows a significant advantage over other means of oxide formation and ensures good recovery of the oxide throughout the operating period if damaged. The oxide layer can provide a layer that protects the reaction tube from the nitriding effect of the ammonia supply gas.

[0045] As described in the overview section, the transition from low-pressure to high-pressure ammonia decomposition processes presents challenges. Ammonia, when dissociated, is known to cause nitridation of metal alloys, particularly in this process. The ammonia decomposition section of a plant takes place in metal tubes that are externally burned to provide energy for the endothermic decomposition reaction. Metal tubes are required for good heat transfer and toughness, for example, because they are a proven method for driving such reactions in steam methane reforming (SMR). The nitridation potential correlates with the ammonia / nitrogen partial pressure, with the rate of nitridation increasing with increasing pressure. Nitriding reduces the effective wall thickness and embrittles the reaction tubes. Furthermore, especially when data on the creep performance of alloys over 100,000 hours is required for safe design, very few alloys can provide good mechanical strength at high temperatures and pressures and withstand nitriding for extended periods.

[0046] Most elements form nitrides at the temperatures and nitriding potential of ammonia decomposition furnaces. However, nitride formation with Ni and Co is thermodynamically very undesirable. Fortunately, Ni and Co are among the few elements used in high-pressure applications, such as high-temperature austenitic alloys for steam methane reformers (SMRs). Additionally, aluminum has been found to have high resistance to nitrogen transport through the substrate when used as an oxide scale-forming factor in the alloy. Furthermore, alloys with Ni and Co can be alloyed to allow for better integrity and better high-temperature mechanical properties, but also to use less material through the design of thinner walls. This is important in conjunction with the rising prices of Ni and Co due to the battery market. The selection of these alloying elements is important because, if they form nitrides on the base alloy, they must be controlled in a predictable manner to provide a suitable lifespan for the decomposition furnace without sudden failures due to destructive nitriding.

[0047] Suitable alloys may contain nickel and / or cobalt in amounts of 11% by weight, 15% by weight, 20% by weight, 30% by weight, 50% by weight, or more than 75% by weight. The total nickel + cobalt content (if present) of the alloy is preferably more than 40% by weight. Optionally, the alloy may also contain one or more of Cr, Si, or Al. For example, the alloy may contain at least 10% by weight, 14% by weight, 15% by weight, 20%, or 30% chromium. Additionally, the alloy may contain at least 1% by weight, 3% by weight, or 4% by weight of aluminum, for example, in the range of 1 to 5% by weight.

[0048] The alloy may be selected from the list consisting of alloy 600, alloy 601, alloy 602ca, alloy 617, alloy 625, alloy 690, alloy 693, alloy 699, alloy 214, alloy 230, alloy 233, alloy MA47P, alloy X, alloy S, alloy 160, S+C(registered trademark) G 4879, G 4878 Micro, ET 45 Micro, ET 45 LC, HT E, ET 35 Co, Paralloy(registered trademark) OPTIM-AL, 35 / 45 Microalloy, 22H, Manurite(registered trademark) 40XO, XAl4, XTM Low C, 40X, XTM, 50W, Manaure 2, Kubota SCH42, KHR48N, KHR48NCo, KHRSA, KHR45A, and UCX. Alloys 600 and 625 are preferred due to the balance between desirable properties, availability of good creep data, and cost. Alternatively, alloys 214, MA47P, 233, and 699 are preferred because they have enough aluminum to provide a robust oxide scale against nitriding. Some of the other listed alloys are less preferred due to cost.

[0049] Regarding the list of preferred alloys above, it can be noted that all alloys contain either cobalt or nickel, and some contain both. Preferred alloys typically contain at least nickel, but cobalt-based alloys can also be used. Those containing cobalt tend to have improved mechanical properties at the most extreme temperatures, but will be more expensive. Therefore, while cobalt-based alloys are useful, in practice this may not be economically preferable. In this process, the total nickel + cobalt (if present) content of the alloy is preferably more than 40% by weight, and greater advantages are added as the amount increases.

[0050] Some of the listed alloys contain aluminum. This can provide an additional advantage through a longer incubation time for nitrogen to permeate the material. For alloys containing aluminum for oxide layer formation, it is advantageous that they should have a sufficient aluminum content for good oxide layer formation. Higher amounts tend to provide greater advantages until mechanical problems begin to occur. Optionally, the aluminum content can range from 1 to 5 wt%, optimally 3 wt% if pre-oxidation is performed, and over 4 wt% if no pre-oxidation is performed.

[0051] All the alloys listed also contain chromium. Most alloys in this process have a minimum chromium content of, for example, more than 14% by weight. Strength is primarily important when used to improve economic efficiency, for example, by using thinner walls and less material. Therefore, strengthening elements need to add to the economic efficiency. For example, cobalt adds high-temperature strength, but adding and processing the material can be more expensive than simply making thicker walls with a non-cobalt alloy. The optimal alloy composition depends on the reactor design and the details of the process conditions. However, chromium is present in the most commercially available alloys suitable for this process.

[0052] In addition to the ammonia decomposition process described above, this specification also provides a reaction vessel, such as a reaction tube, for use in the catalytic cracking of ammonia, wherein the reaction tube contains an ammonia decomposition catalyst. The ammonia decomposition catalyst is contained inside the reaction tube; that is, the ammonia decomposition catalyst is contained inside the reaction tube along its axial length. The ammonia decomposition catalyst can be any catalyst known to be suitable for catalyzing the decomposition of ammonia to hydrogen and nitrogen. The catalyst may preferably be a nickel-based catalyst, such as nickel on an inert support (e.g., alumina, silica, or another refractory oxide). For example, the catalyst is KATALCO 27-2, available from Johnson Matthey PLC. RTMThis is possible. Alternatively, the catalyst may preferably be a noble metal catalyst, such as a ruthenium-based catalyst.

[0053] Also provided is an ammonia decomposition reactor comprising one or more catalyst-containing reaction vessels (e.g., reaction tubes) as described above. Figure 3 shows a diagram of an ammonia decomposition reactor comprising a catalyst-filled reaction tube and a burner for supplying thermal energy to the reaction tube.

[0054] The new scale of ammonia decomposition applications is pushing the limits of what is currently needed in terms of reactor vessel alloys, and we have not realized that the parallel issues of the need for economically viable creep strength and high nitridation resistance are required in other applications. The selection of materials for containment of high-pressure ammonia decomposition reactions is challenging. This specification describes a small subset of such materials and metal alloy compositions that meet the required criteria, such as being selected using expert knowledge of both alloys, their properties, and their interaction with the ammonia decomposition environment and mechanical requirements. This specification enables the safe and cost-effective utilization of ammonia as an energy vector through the use of carefully selected engineering alloys for the most severe chemical environments in ammonium decomposition processes at high pressure.

[0055] 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 process for catalytic cracking of ammonia, wherein the process is Supplying ammonia supply gas to one or more reaction vessels containing a heating catalyst located within the ammonia decomposition reactor, This includes decomposing ammonia in the ammonia supply gas in one or more catalyst-containing reaction vessels to generate a hydrogen-containing stream, The ammonia supply gas is supplied to the reaction vessel or each reaction vessel at a pressure of at least 10 bar. The reaction vessel or each reaction vessel is heated to a temperature of at least 500°C. A process wherein the reaction vessel or each of the reaction vessels comprises or has walls made of an alloy selected to be resistant to both nitriding and creep deformation at the temperature and pressure without failure for at least 1,000 hours of operation.

2. The process according to claim 1, wherein the ammonia supply gas is supplied to the reaction vessel or each reaction vessel at a pressure within the range defined by at least 20 bar, 30 bar, 40 bar, or 50 bar; 1000 bar, 500 bar, 100 bar, or 75 bar or less; or any combination of the aforementioned lower and upper limits.

3. The process according to claim 1 or 2, wherein the reaction vessel or each reaction vessel is heated to a temperature within the range defined by at least 550°C, 600°C, 650°C, or 700°C; 1500°C, 1000°C, 950°C, 900°C, or 850°C or less; or any combination of the aforementioned lower and upper limits.

4. The process according to any one of claims 1 to 3, wherein the reaction vessel or each reaction vessel is in the form of a reaction tube in which a catalyst is arranged.

5. The process according to any one of claims 1 to 4, wherein the alloy contains nickel and / or cobalt in an amount of 11% by weight, 15% by weight, 20% by weight, 30% by weight, 50% by weight, or more than 75% by weight.

6. The process according to claim 5, wherein the alloy contains a total nickel + cobalt content of more than 40% by weight.

7. The process according to any one of claims 1 to 6, wherein the alloy comprises one or more of Cr, Si, or Al.

8. The process according to any one of claims 1 to 7, wherein the alloy comprises at least 10% by weight, 14% by weight, 15% by weight, 20%, or 30% chromium, such as at least 40% chromium.

9. The process according to any one of claims 1 to 8, wherein the alloy comprises at least 1% by weight, 3%, or 4%, and optionally 5% by weight or less, of aluminum.

10. The process according to any one of claims 1 to 9, wherein the alloy has an oxide layer disposed on its surface.

11. The process according to claim 10, wherein the oxide layer is an aluminum oxide layer formed from aluminum in the alloy.

12. The process according to claim 10 or 11, wherein the ammonia supply gas contains oxidizing species during operation to ensure oxidation conditions and help maintain the oxide layer.

13. The aforementioned alloys are: Alloy 600, Alloy 601, Alloy 602ca, Alloy 617, Alloy 625, Alloy 690, Alloy 693, Alloy 699, VDM (registered trademark) ALLOY 699XA, Alloy 214, Alloy 230, Alloy 233, Alloy MA47P, Alloy X, Alloy S, Alloy 160, S+C (registered trademark) G 4879, G 4878 Micro, ET 45 Micro, ET 45 LC, HT E, ET 35 Co, Paralloy (registered trademark) OPTIM-AL, 35 / 45 Microalloy, 22H, Manurite (registered trademark) 40XO, XAl4, XTM Low C, 40X, XTM, 50W, Manurite 2, Kubota A process according to any one of claims 1 to 12, selected from the list consisting of SCH42, KHR48N, KHR48NCo, KHRSA, KHR45A, UCX, Alloy 800 / H / HT, Cast grades HT, HU, HW, HX, HP15Nb, HP, HPNb, HPNbS, CT15C, Kanthal® A-1, APM, AF, D, and NIKROTHAL 40, 60, 70, 80, Alloy 120, and INCOLOY® Alloy HX, 803, 890.

14. The process according to claim 13, wherein the alloy is alloy 600 or alloy 625.

15. The process according to claim 13, wherein the alloy is alloy 214, alloy MA47P, alloy 233, alloy 699, or VDM® ALLOY 699 XA.

16. The process according to any one of claims 1 to 15, wherein the wall of the reaction vessel or the wall of each reaction vessel has a thickness of at least 3 mm, 5 mm, 8 mm, or 10 mm; 50 mm, 20 mm, 15 mm, or 14 mm or less; or within the range defined by any combination of the aforementioned lower and upper limits.

17. The process according to any one of claims 1 to 16, wherein the alloy is selected to be resistant to both nitriding and creep deformation at the operating temperature and pressure without failure for an operating period of at least 5,000 hours, 10,000 hours, 50,000 hours, or 100,000 hours.

18. A reaction vessel for use in the process according to any one of claims 1 to 17, wherein the reaction vessel comprises an ammonia decomposition catalyst and has walls comprising or made of an alloy selected to be resistant to both nitriding and creep deformation without failure for an operating period of at least 1,000 hours, 5,000 hours, 10,000 hours, 50,000 hours, or 100,000 hours at an operating pressure of at least 10 bar and an operating temperature of at least 500°C.

19. An ammonia decomposition reactor comprising one or more reaction vessels as described in claim 18.

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