Process for producing hydrogen gas from catalytic decomposition of ammonia

Abstract

A process for producing hydrogen gas from the catalytic decomposition of ammonia. The process includes feeding hydrogen-containing recycle gas removed from downstream of an ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor. The present invention can be used to provide hydrogen gas as a non-carbon-containing fuel.

Description

[Technical Field]

[0001] The present invention relates to a process for producing hydrogen gas. More particularly, the present invention relates to a process for producing hydrogen gas by catalytic decomposition of ammonia. [Background technology]

[0002] There is renewed interest in using hydrogen as a green, carbon-free fuel in various industrial settings. Hydrogen can be burned to generate thermal energy or electricity, for example, using gas turbines. Alternatively, hydrogen can be used to generate electrochemical energy, for example, in fuel cells.

[0003] Ammonia has attracted interest as a potential compound for the storage and transport of hydrogen. Liquid ammonia has a higher hydrogen density than liquid hydrogen and can be transported using existing infrastructure already in use for this purpose, such as that used to transport ammonia in the pesticide and fertilizer industry.

[0004] Once the liquid ammonia is transported, it can be combusted directly or converted to hydrogen by a decomposition process.

[0005] The catalytic decomposition of ammonia to hydrogen and nitrogen has been known for many years. The reaction can be illustrated as follows:

[0006] [ka]

[0007] The ammonia decomposition reaction is endothermic and can be usefully accomplished by passing ammonia over a suitable catalyst in externally heated catalyst-containing reactor tubes located within a furnace. For example, such furnaces are known for steam reforming of natural gas or naphtha feedstocks.

[0008] However, heated catalyst-containing reactor tubes located within the furnace can react with ammonia-containing gas to form undesirable metal nitride layers. This undesirable side reaction, known as nitridation, can cause accelerated failure of the reactor tubes, particularly at the inlets to the reactor tubes. Such failures can require complete shutdown of the ammonia decomposition reactor, resulting in significant plant downtime. Furthermore, nitridation and potential failure of the reactor tubes pose a significant safety hazard.

[0009] There remains a need for an improved process for the catalytic decomposition of ammonia that addresses the problem of nitridation. Summary of the Invention

[0010] The present invention seeks to provide a process for decomposing ammonia to produce hydrogen while reducing the incidence of nitriding of catalyst-containing reactor tubes located within an ammonia decomposition reactor.

[0011] Thus, the present invention provides a process for the catalytic decomposition of ammonia, the process comprising: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing ammonia in the ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream; and feeding the hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor.

[0012] It has surprisingly been found that by feeding hydrogen-containing recycle gas removed from downstream of an ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor, the nitriding rate of the one or more catalyst-containing reactor tubes can be reduced, particularly at the inlet to the one or more catalyst-containing reactor tubes and in the region immediately downstream of the inlet.

[0013] Furthermore, although it would be expected that supplying a hydrogen-containing recycle gas to one or more catalyst-containing reactor tubes located within an ammonia decomposition reactor would reduce the amount of ammonia converted to H by shifting the equilibrium position of the ammonia decomposition reaction, it has surprisingly been found that the process of the present invention not only reduces the rate at which nitridation of the catalyst-containing reactor tubes occurs, but also provides a process having a high overall H recovery.

[0014] In a preferred process of the present invention, a process for catalytic decomposition of ammonia is provided, the process comprising: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing ammonia in the ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream; supplying the hydrogen-containing stream to a purification unit to increase the H content of the hydrogen-containing stream to produce a hydrogen-enriched stream and a tail gas; feeding hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor; The hydrogen-containing recycle gas comprises a portion of the hydrogen-rich containing stream.

[0015] When the hydrogen-containing recycle gas comprises a portion of the hydrogen-rich containing stream, the total gas stream in the process of the present invention can be minimized, allowing a smaller ammonia decomposition reactor to be used, thereby reducing the capital cost of operating the process of the present invention. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows a block flow diagram of a process not according to the present invention. [Figure 2] 1 shows a block flow diagram according to the process of the present invention, in which a portion of the hydrogen-rich containing stream (recycle gas) is fed to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor. [Figure 3]1 shows a block flow diagram according to the process of the present invention, in which a portion of the hydrogen-containing stream (recycle gas) is fed to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor. [Figure 4] 1 shows a block flow diagram according to the process of the present invention, in which a portion of the tail gas (recycle gas) produced from the hydrogen purification unit is fed to one or more catalyst-containing reaction tubes disposed within an ammonia decomposition reactor. [Figure 5] 1 illustrates the nitridability of various gas compositions as they pass through catalyst-containing reactor tubes located within an ammonia decomposition reactor. [Figure 6] 1 shows a schematic diagram of a miniature reactor available from Johnson Matthey Davy Technologies Limited. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred and / or optional features of the invention will now be described. Any aspect of the invention may be combined with any other aspect of the invention unless the context requires otherwise. Any preferred and / or optional feature of any aspect may be combined with any aspect of the invention, either singly or in any combination, unless the context requires otherwise.

[0018] The process of the present invention involves supplying an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor.

[0019] The ammonia stream can be obtained from any source. In a preferred method of the present invention, the ammonia stream is produced by catalytic combination of hydrogen and nitrogen, for example, the ammonia stream can be produced from the Haber-Bosch ammonia synthesis process. In a preferred method of the present invention, the ammonia stream can be produced in an ammonia production facility located upstream of the ammonia decomposition reactor. Alternatively, the ammonia stream can be provided from an ammonia gas storage facility, an ammonia storage unit, an ammonia storage tank, or an ammonia gas pipeline.

[0020] In a preferred process of the present invention, the ammonia stream may be preheated before being fed to one or more catalyst-containing reactor tubes. Accordingly, the method of the present invention may include a step of preheating the ammonia stream. The ammonia stream may be preheated to a temperature greater than 350°C, greater than 400°C, greater than 450°C, greater than 500°C, or greater than 550°C. The ammonia stream may be preheated to a temperature less than 1000°C, less than 950°C, less than 850°C, less than 750°C, or less than 700°C. The ammonia stream may be preheated to a temperature between 350°C and 1000°C, between 400°C and 950°C, between 450°C and 850°C, or between 500°C and 750°C, e.g., between 550°C and 700°C.

[0021] Suitable ammonia decomposition reactors are known and may include a fuel combustion zone with a radiant section including one or more burners supplied with one or more fuel streams and an oxygen-supplying gas, e.g., air, oxygen-enriched air, or oxygen. The radiant section may include one or more catalyst-containing reactor 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) for heating one or more catalyst-containing reactor tubes. There may be tens or hundreds of catalyst-containing reactor tubes in the radiant section. Optionally, downstream of the radiant section, fuel gas from the combustion of one or more fuel streams may be used to preheat one or more feed streams in the convection section. Reactors with a catalyst-containing radiant section including reactor tubes and a convection section for preheating the feed are known for steam methane reforming and may be applied to the present invention.

[0022] An alternative ammonia decomposition reactor may be used, for example, where the combustion of one or more fuel streams in a fuel combustion zone is split into reactors with catalyst-containing reactor tubes. Such a reactor is the mini-reformer available from Johnson Matthey Davy Technologies Limited, a schematic of which is shown in Figure 6.

[0023] The catalyst in the catalyst-containing reactor tubes can be any ammonia decomposition catalyst. For example, nickel and / or ruthenium catalysts may be used. A preferred catalyst is a nickel catalyst. The catalyst may comprise 3 to 30 wt. % nickel, preferably 8 to 20 wt. % nickel, expressed as NiO, on a suitable refractory support, such as alumina or a metal aluminate. The catalyst may be in the form of a pelletized unit, which may contain one or more perforations, or may be provided as a washcoat on a structured metal or ceramic catalyst. A particularly preferred catalyst is KATALCO Catalyst, available from Johnson Matthey PLC. RTM 27-2, which contains 12% nickel, expressed as NiO, on a cylindrical pellet formed from a high surface area calcium aluminate support.

[0024] The one or more catalyst-containing reactor tubes may suitably be formed from an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy. The iron-based alloy may be a stainless steel, preferably an iron-chromium-based alloy such as 316 stainless steel, or a high-nickel steel such as that described in WO 03 / 051771 A1. Preferably, the one or more catalyst-containing reactor tubes are formed from a nickel-based alloy or a cobalt-based alloy. More preferably, the one or more catalyst-containing reactor tubes are formed from a cobalt-based alloy.

[0025] The process of the present invention involves decomposing ammonia in an ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream.

[0026] The temperature of the ammonia stream at the inlet to the one or more catalyst-containing reactor 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, e.g., 550°C to 700°C. The temperature of the hydrogen-containing stream exiting the one or more catalyst-containing reactor tubes affects the equilibrium position of the decomposition reaction and may be in the range of 500 to 950°C. When a nickel catalyst is used in the one or more catalyst-containing reactor tubes, the temperature of the hydrogen-containing stream exiting the one or more catalyst-containing reactor tubes may preferably be greater than about 700°C.

[0027] The inlet pressure to the one or more catalyst-containing reactor tubes is set by the flowsheet design and may range from 1 to 100 bar absolute, preferably from 10 to 90 bar absolute, for example from 31 to 51 bar absolute.

[0028] The ammonia decomposition reaction produces a hydrogen-containing stream, which contains H. The hydrogen-containing stream also contains nitrogen and may further contain residual ammonia (e.g., unreacted ammonia).

[0029] The hydrogen-containing stream may contain 40 mol% or more H, 50 mol% or more H, or 60 mol% or more H. The hydrogen-containing stream may contain 75 mol% or less H, 70 mol% or less H, or 65 mol% or less H. For example, the hydrogen-containing stream may contain 40 mol% to 75 mol% H, 50 mol% to 70 mol% H, or 60 mol% to 65 mol% H.

[0030] In a preferred process of the present invention, the hydrogen-containing stream is fed to a purification unit, such as a pressure swing absorption unit, to increase the H content by separating H from other components. The purification unit thus produces a hydrogen-enriched stream and a tail gas. Thus, the process of the present invention preferably includes feeding the hydrogen-containing stream to a purification unit to increase the H content of the hydrogen-containing stream to produce a hydrogen-enriched stream and a tail gas.

[0031] It may be preferable to feed the hydrogen-containing stream to a first steam generation unit and / or heat recovery zone before feeding the hydrogen-containing stream to the purification unit. As will be appreciated by those skilled in the art, the first steam generation unit and / or heat recovery zone may be used to recover low or medium levels of heat.

[0032] The hydrogen-rich stream may contain 50 mol% or more H, 60 mol% or more H, or 75 mol% or more H. The hydrogen-rich stream may contain 100 mol% or less H, 90 mol% or less H, or 80 mol% or less H. For example, the hydrogen-rich stream may contain 50 mol% to 100 mol% H, 60 mol% to 90 mol% H, or 70 mol% to 80 mol% H, e.g., about 75 mol% H.

[0033] The tail gas may contain nitrogen and small amounts of ammonia and hydrogen. The tail gas may contain 1 mol% to 10 mol% ammonia (e.g., about 5 mol% or less ammonia). The tail gas may contain 1 mol% to 50 mol% H2, 2 mol% to 40 mol% H2. For example, the tail gas may contain 15 mol% to 25 mol% H2.

[0034] As used herein, the term "hydrogen-containing stream" may be used to refer to either a hydrogen-containing stream or a hydrogen-rich stream.

[0035] The process of the present invention involves feeding hydrogen-containing recycle gas removed from downstream of an ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor.

[0036] A hydrogen-containing recycle gas is removed downstream of the ammonia decomposition reactor. In preferred processes of the present invention, the hydrogen-containing recycle gas comprises one or more of a portion of the hydrogen-containing stream, a portion of the hydrogen-enriched stream, and / or a portion of the tail gas from a purification unit used to increase the H content of the hydrogen-containing stream. In more preferred processes of the present invention, the hydrogen-containing recycle gas comprises one or more of a portion of the hydrogen-containing stream and / or a portion of the hydrogen-enriched stream. In the most preferred processes of the present invention, the hydrogen-containing recycle gas comprises a portion of the hydrogen-enriched stream.

[0037] When the hydrogen-containing recycle gas comprises a portion of the hydrogen-rich containing stream, the total gas stream in the process of the present invention can be minimized, allowing a smaller ammonia decomposition reactor to be used, thereby reducing the capital cost of operating the process of the present invention.

[0038] A further advantage of using a hydrogen-containing recycle gas comprising a portion of the hydrogen-rich containing stream is that it has surprisingly been found that hydrogen (H) is more effective at reducing nitridation than other products of the ammonia decomposition reaction (e.g., tail gas or nitrogen (N) gas streams). Without being bound by any theory, it is believed that hydrogen inhibits nitridation by a different mechanism than nitrogen (N).

[0039] In certain processes of the invention, the recycle gas may consist of one or more of a portion of the hydrogen-containing stream, a portion of the hydrogen-enriched stream, and / or a portion of tail gas from a purification unit used to increase the H content of the hydrogen-containing stream. In certain processes of the invention, the recycle gas may consist of one or more of a portion of the hydrogen-containing stream and / or a portion of the hydrogen-enriched stream. In certain processes of the invention, the recycle gas may consist of or consist essentially of the hydrogen-enriched stream.

[0040] As will be readily understood, when the hydrogen-containing recycle gas comprises a portion of the tail gas from a purification unit used to increase the H content of the hydrogen stream, the process of the present invention comprises feeding the hydrogen-containing stream to a purification unit to increase the H content of the hydrogen-containing stream to produce a hydrogen-enriched stream and a tail gas. However, it will also be understood that when the hydrogen-containing stream is fed to a purification unit, the hydrogen-containing recycle gas can comprise or consist of one or more of the hydrogen-containing stream, the tail gas, and / or the hydrogen-enriched stream.

[0041] The hydrogen-containing recycle gas may be fed directly to one or more catalyst-containing reactor tubes or may be first mixed with an ammonia-containing stream before being fed to one or more catalyst-containing reactor tubes. The hydrogen-containing recycle gas may be subjected to intermediate process steps, such as heat recovery steps, before being fed to one or more catalyst-containing tubes.

[0042] The hydrogen-containing recycle gas may be fed to one or more catalyst-containing reactor tubes such that less than 50 mol% H, less than 40 mol% H, less than 30 mol% H, less than 20 mol% H, or less than 10 mol% H is fed to the one or more catalyst-containing reactor tubes.

[0043] The hydrogen-containing recycle gas may be supplied to one or more catalyst-containing reactor tubes such that greater than 0.5 mol% H2, greater than 1 mol% H2, greater than 2 mol% H2, greater than 4 mol% H2, or greater than 5 mol% H2 is supplied to the one or more catalyst-containing reactor tubes.

[0044] In a preferred process of the present invention, the hydrogen-containing recycle gas may be fed to one or more catalyst-containing reactor tubes such that 0.5 mol% to 50 mol% H, 1 mol% to 40 mol% H, 2 mol% to 30 mol%, or 4 mol% to 20 mol% H, or 5 mol% to 10 mol% H is fed to the one or more catalyst-containing reactor tubes.

[0045] For the avoidance of doubt, it will be understood that the mol% H in the hydrogen-containing recycle gas is expressed as a percentage of the total gas being fed to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor.

[0046] Surprisingly, it has been found that when a hydrogen-containing recycle gas is supplied to one or more catalyst-containing reactor tubes in the amounts specified above, a reduction in the nitridation rate of the catalyst-containing reactor tubes, particularly at the inlet to the catalyst-containing reactor tubes, can be achieved while maintaining a high overall hydrogen recovery rate. Surprisingly, it has been found that supplying up to 50 mol% H2, for example, up to 40 mol%, 30 mol%, 20 mol%, or 10 mol% H2 to one or more catalyst-containing reactor tubes has minimal or no effect on the overall hydrogen recovery rate of the process. In other words, it has been found that when a portion of the hydrogen-containing recycle gas is supplied to one or more catalyst-containing reactor tubes, the same or similar overall hydrogen recovery rate can be achieved using the process of the present invention as when no hydrogen-containing gas is supplied to one or more catalyst-containing reactor tubes.

[0047] For the avoidance of doubt, references to feeding an ammonia-containing stream, a hydrogen-containing stream, and / or a hydrogen-enriched-containing stream to one or more catalyst-containing reactor tubes refer to feeding one or more streams through a catalyst bed of the catalyst-containing reactor tubes, and do not refer to feeding any one of these streams as a combustible fuel source to provide thermal energy to one or more catalyst-containing reactor tubes. It will be further understood that "total gases being fed to one or more catalyst-containing reactor tubes" includes all gases being fed through a catalyst bed of the catalyst-containing reactor tubes, and does not refer to gases being fed as a combustible fuel source to provide thermal energy to one or more catalyst-containing reactor tubes.

[0048] In certain processes of the present invention, the hydrogen-containing recycle gas may be fed to a second steam generation unit and / or heat recovery zone before being fed to one or more catalyst-containing reactor tubes. As will be appreciated by those skilled in the art, the second steam generation unit and / or heat recovery zone may be used to recover low or moderate amounts of heat.

[0049] For the avoidance of doubt, the first steam generation unit and / or heat recovery zone and the second steam generation unit and / or heat recovery zone may be the same or different steam generation units and / or heat recovery zones.

[0050] In the process of the present invention, one or more fuel streams may be combusted with oxygen in a fuel combustion zone such that the combustion provides thermal energy used to support the endothermic ammonia decomposition reaction in the ammonia decomposition reactor. Thus, the process of the present invention may include combusting one or more fuel streams with oxygen in a fuel combustion zone to provide thermal energy to the ammonia decomposition reactor.

[0051] Alternatively, an electric heater may provide the thermal energy used to support the endothermic ammonia decomposition reaction in the ammonia decomposition reactor.

[0052] The fuel combustion zone may be within the ammonia decomposition reactor or may be in a separate vessel for combustion that is fluidly connected to the ammonia decomposition reactor.

[0053] The fuel combustion zone may suitably be a radiant section within a box furnace of the ammonia decomposition reactor. Thus, the fuel combustion zone may provide thermal energy (e.g., radiant heat) to the ammonia decomposition reactor. Alternatively, if the fuel combustion zone is in a separate vessel from the ammonia decomposition reactor, the ammonia decomposition reactor may be of a heat exchange design, such as a gas-fired reformer or mini-reformer, in which one or more catalyst-containing reactor tubes are heated by convection from hot combustion gases passing around the exterior surfaces of the catalyst-containing reactor tubes.

[0054] The one or more fuel streams may include one or more fuel streams that combust with oxygen to produce heat. Preferably, the one or more fuel sources may include a carbon-free fuel source (e.g., hydrogen or ammonia). It may be preferred that the one or more fuel sources do not include a carbon-containing fuel source.

[0055] The one or more fuel streams may comprise one or more of hydrogen, natural gas, methane, refinery by-product gas, biogas, tail gas from a hydrogen purification unit, the fuel portion of a hydrogen-containing stream from an ammonia cracking reactor, or the fuel portion of a hydrogen-rich containing stream from a purification unit.

[0056] The oxygen used to combust one or more fuel streams may suitably be or include air, compressed air, oxygen-enriched air, oxygen, oxygen, and an inert gas such as nitrogen.

[0057] As used herein, the term "fuel portion" is used to refer to the portion of a stream (e.g., a hydrogen-containing, hydrogen-enriched, or ammonia-containing stream) that is used as a fuel source. It is not used to refer to the portion of a stream that is used in the ammonia decomposition reaction.

[0058] In a preferred process of the present invention, the one or more fuel streams may comprise a hydrogen-containing fuel stream. Preferably, the hydrogen-containing fuel stream may be a fuel portion of a hydrogen-containing stream produced from an ammonia decomposition reactor. More preferably, the hydrogen-containing fuel stream may be a fuel portion of a hydrogen-rich containing stream from a purification unit. Thus, the process of the present invention may include removing the fuel portion of the hydrogen-containing stream or the fuel portion of the hydrogen-rich containing stream and combusting the fuel portion of the hydrogen-containing stream or the fuel portion of the hydrogen-rich containing stream with oxygen in a fuel combustion zone to provide thermal energy to support the endothermic ammonia decomposition reaction in the ammonia decomposition reactor.

[0059] The amount of hydrogen in the one or more fuel streams is not particularly limited. For example, the one or more fuel streams may contain hydrogen in an amount of 1 mol% to 100 mol% H2, for example, 5 mol% to 75 mol% H2, 10 mol% to 50 mol% H2, or 15 mol% to 30 mol% H2. Preferably, the one or more fuel streams may contain hydrogen in an amount of more than 10 mol% H2, more than 12 mol% H2, or more than 15 mol% H2. Preferably, the one or more fuel streams may contain hydrogen in an amount of less than 45 mol% H2, less than 35 mol% H2, or less than 35 mol% H2. For example, the one or more fuel streams may contain hydrogen in an amount of 10 mol% to 45 mol% H2, 12 mol% to 35 mol% H2, or 15 mol% to 25 mol% H2.

[0060] In a preferred process of the present invention, one or more fuel streams comprise an ammonia-containing fuel stream. The amount of ammonia in the one or more fuel streams is not particularly limited. For example, the one or more fuel streams may comprise ammonia in an amount of 1 mol% to 100 mol%, e.g., 5 mol% to 75 mol%, 10 mol% to 50 mol%, or 15 mol% to 30 mol%. Preferably, the one or more fuel streams may comprise ammonia in an amount greater than 10 mol%, greater than 12 mol%, or greater than 15 mol%. Preferably, the one or more fuel streams may comprise ammonia in an amount less than 45 mol%, less than 35 mol%, or less than 35 mol%. For example, the one or more fuel streams may comprise ammonia in an amount of 10 mol% to 45 mol%, 12 mol% to 35 mol%, or 15 mol% to 25 mol%.

[0061] When one or more fuel streams contain ammonia, the ammonia-containing fuel stream may be supplied from the same source as the ammonia stream being supplied to one or more catalyst-containing reactor tubes or from a different source. When one or more fuel streams contain ammonia, the ammonia-containing fuel stream may preferably be supplied from the same source as the ammonia stream being supplied to one or more catalyst-containing reactor tubes.

[0062] In a preferred process of the present invention, one or more fuel streams may be preheated before being combusted in the fuel combustion zone. The one or more fuel streams may be preheated to any temperature below the autoignition temperature of the fuel stream. For example, the one or more fuel streams may be preheated to a temperature greater than 100°C, greater than 150°C, or greater than 200°C. The one or more fuel streams may be preheated to a temperature below the autoignition temperature of the fuel stream, for example, less than 400°C, less than 350°C, or less than 300°C. For example, the one or more fuel streams may be preheated from 100°C to the autoignition temperature of the fuel stream, for example, from 100°C to 400°C. In a preferred process of the present invention, the one or more fuel streams are ammonia-containing fuel streams and may be provided from a preheated ammonia stream.

[0063] For the avoidance of doubt, one or more fuel streams may be mixed prior to combustion or may be mixed at a single point of combustion.

[0064] Combustion of one or more fuel streams in the fuel combustion zone generates flue gas, which can be recovered from the ammonia decomposition reactor. The flue gas may be cooled in one or more cooling stages and subjected to one or more purification stages before being discharged to the atmosphere. The one or more cooling stages may include preheating and / or steam generation stages for one or more reactants for the ammonia decomposition reactor. The one or more purification stages may include a selective catalytic reduction (SCR) stage in which nitrogen oxides react with ammonia to form nitrogen and water vapor. Any flue gas selective catalytic reduction technology may be used.

[0065] In certain embodiments of the process of the present invention, the process comprises: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing ammonia in the ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream; feeding the hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor; The hydrogen-containing recycle gas comprises a portion of the hydrogen-containing stream.

[0066] In certain embodiments of the process of the present invention, the process comprises: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing ammonia in the ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream; feeding the hydrogen-containing stream to a purification unit to increase the H content of the hydrogen-containing stream to produce a hydrogen-enriched stream and a tail gas; feeding hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor; The hydrogen-containing recycle gas comprises one or more of a portion of a hydrogen-containing stream, a portion of a hydrogen-enriched containing stream, or a portion of a tail gas from a refinery unit.

[0067] In certain embodiments of the process of the present invention, the process comprises: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing ammonia in the ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream; Optionally, supplying the hydrogen-containing stream to a first steam generation unit and / or a heat recovery zone; Optionally, feeding the hydrogen-containing stream to a purification unit to increase the H content of the hydrogen-containing stream to produce a hydrogen-enriched stream and a tail gas; Optionally, feeding the hydrogen-enriched containing stream to a second steam generation unit and / or a heat recovery zone; feeding hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor; removing a fuel portion of the hydrogen-containing stream or a fuel portion of the hydrogen-enriched stream; combusting a fuel portion of the hydrogen-containing stream or a fuel portion of the hydrogen-enriched containing stream with oxygen in a fuel combustion zone to provide thermal energy to support an endothermic ammonia decomposition reaction in an ammonia decomposition reactor; The hydrogen-containing recycle gas comprises one or more of a portion of a hydrogen-containing stream, a portion of a hydrogen-enriched containing stream, or a portion of a tail gas from a refinery unit.

[0068] In certain embodiments of the process of the present invention, the process comprises: Optionally, preheating the ammonia stream; feeding the ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing ammonia in the ammonia stream in one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor to produce a hydrogen-containing stream; Optionally, supplying the hydrogen-containing stream to a first steam generation unit and / or a heat recovery zone; Optionally, feeding the hydrogen-containing stream to a purification unit to increase the H content of the hydrogen-containing stream to produce a hydrogen-enriched stream and a tail gas; Optionally, feeding the hydrogen-enriched containing stream to a second steam generation unit and / or a heat recovery zone; feeding hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor; removing a fuel portion of the hydrogen-containing stream or a fuel portion of the hydrogen-enriched stream; combusting a fuel portion of the hydrogen-containing stream or a fuel portion of the hydrogen-enriched containing stream with oxygen in a fuel combustion zone to provide thermal energy to support an endothermic ammonia decomposition reaction in an ammonia decomposition reactor; The hydrogen-containing recycle gas may comprise one or more of a portion of a hydrogen-containing stream, a portion of a hydrogen-enriched containing stream, or a portion of tail gas from a refinery unit.

[0069] The invention will now be described in further detail with respect to the following non-limiting embodiments.

[0070] Figure 1 shows a block flow diagram of a process not in accordance with the present invention. Figure 1 illustrates a process for preheating ammonia (1) to produce an ammonia-containing stream (101). The ammonia-containing stream (101) is fed to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor (2). The ammonia in the ammonia-containing stream is decomposed in the one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (2) to produce a hydrogen-containing stream (102). The hydrogen-containing stream (102) is sent to a first steam generation unit and / or heat recovery zone (3) where thermal energy is recovered. The cooled hydrogen-containing stream (103) is sent to a purification unit (4) where the H content of the hydrogen-containing stream is enriched. The hydrogen-rich stream is recovered as purified hydrogen (5), and the fuel portion of the hydrogen-rich stream (105) is sent to a fuel combustion zone (6) of the ammonia decomposition reactor (2). The hydrogen-enriched stream (105) is combusted with oxygen (106), supplied as compressed air from the compressor (7), to produce thermal energy (108), which is fed to the ammonia decomposition reactor (2) to support the endothermic ammonia decomposition reaction. The ammonia decomposition reactor (2) produces flue gas (109), from which thermal energy can be recovered in a second steam generation unit and / or heat recovery zone (8). The cooled flue gas (110) can be vented to the atmosphere via an exhaust stack or sent for further processing (9).

[0071] Figure 2 shows a block flow diagram of a process according to the present invention. Figure 2 illustrates the steps of preheating ammonia (11) to produce an ammonia-containing stream (201). The ammonia-containing stream (201) is fed to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor (12). The ammonia in the ammonia-containing stream is decomposed in the one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (12) to produce a hydrogen-containing stream (202). The hydrogen-containing stream (202) is sent to a first steam generation unit and / or heat recovery zone (13), where thermal energy is recovered. The cooled hydrogen-containing stream (203) is sent to a purification unit (14), where the H content of the hydrogen-containing stream is enriched. The hydrogen-rich stream is recovered as purified hydrogen (15), and the fuel portion of the hydrogen-rich stream (205) is sent to a fuel combustion zone (16) of the ammonia decomposition reactor (12). The hydrogen purification unit (14) produces tail gas (212). A portion of the hydrogen-enriched stream (211) is mixed with the ammonia-containing stream (201) and fed to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (12). The hydrogen-enriched stream (205) is combusted with oxygen (206), provided as compressed air from the compressor (17), to generate thermal energy (208), which is fed to the ammonia decomposition reactor (12) to support the endothermic ammonia decomposition reaction. The ammonia decomposition reactor (12) produces flue gas (209), from which thermal energy can be recovered in a second steam generation unit and / or a heat recovery zone (18). The cooled flue gas (210) can be vented to the atmosphere via an exhaust stack or sent for further processing (19).

[0072] Figure 3 shows a block flow diagram of a process according to the present invention in which a portion of the hydrogen-containing stream (311) is fed to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor (22) prior to purification of the hydrogen-containing stream. Figure 3 illustrates a step of preheating ammonia (21) to produce an ammonia-containing stream (301). The ammonia-containing stream (301) is fed to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (22). The ammonia in the ammonia-containing stream is decomposed in one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (22) to produce a hydrogen-containing stream (302). A portion of the hydrogen-containing stream (311) is mixed with the ammonia-containing stream (301) and fed to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (22). The remaining hydrogen-containing stream (302) is sent to a first steam generation unit and / or a heat recovery zone (23) where thermal energy is recovered. The cooled hydrogen-containing stream (303) is sent to a purification unit (24), where the H content of the hydrogen-containing stream is enriched to produce a tail gas (312). The hydrogen-rich stream is recovered as purified hydrogen (25), and the fuel portion of the hydrogen-rich stream (305) is sent to a fuel combustion zone (26) of an ammonia decomposition reactor (22). The hydrogen-rich stream (305) is combusted with oxygen (306), provided as compressed air from a compressor (27), to produce thermal energy (308), which is supplied to the ammonia decomposition reactor (22) to support the endothermic ammonia decomposition reaction. The ammonia decomposition reactor (22) produces flue gas (309), from which thermal energy can be recovered in a second steam generation unit and / or a heat recovery zone (28). The cooled flue gas (310) can be vented to the atmosphere via an exhaust stack or sent for further processing (29).

[0073] Figure 4 shows a block flow diagram of a process according to the present invention. Figure 4 illustrates the steps of preheating ammonia (31) to produce an ammonia-containing stream (401). The ammonia-containing stream (401) is fed to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor (32). The ammonia in the ammonia-containing stream is decomposed in the one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (32) to produce a hydrogen-containing stream (402). The hydrogen-containing stream (402) is sent to a first steam generation unit and / or heat recovery zone (33) where thermal energy is recovered. The cooled hydrogen-containing stream (403) is sent to a purification unit (34) where the H content of the hydrogen-containing stream is enriched. The hydrogen-rich stream is recovered as purified hydrogen (35), and the fuel portion of the hydrogen-rich stream (405) is sent to a fuel combustion zone (36) of the ammonia decomposition reactor (32). A portion of the tail gas (412) from the purification unit (34) is mixed with the ammonia-containing stream (401) and fed to one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor (32). The hydrogen-enriched stream (405) is combusted with oxygen (406), provided as compressed air from a compressor (37), to generate thermal energy (408), which is fed to the ammonia decomposition reactor (32) to support the endothermic ammonia decomposition reaction. The ammonia decomposition reactor (32) produces flue gas (409), from which thermal energy can be recovered in a second steam generation unit and / or a heat recovery zone (38). The cooled flue gas (410) can be vented to the atmosphere via an exhaust stack or sent for further processing (39). [Example]

[0074] Example 1 Example 1 relates to a combustion ammonia decomposition reactor that is fed with an ammonia-containing stream that enters the reactor at 550°C and undergoes an ammonia decomposition reaction to produce a hydrogen stream containing ammonia in an amount of ≦1.1 mol%.

[0075] The hydrogen stream was mixed with the ammonia stream to produce feeds to the ammonia decomposition reactor containing 0 mol%, 1 mol%, 5 mol%, 10 mol%, 20 mol%, 30 mol%, 40 mol%, and 50 mol% H. N The effect on the nitridability (K N ) is defined according to Equation 1, where "p" represents the partial pressure of the gas.

[0076]

number

[0077] [Table 1]

[0078] The nitridation potential along the length of the catalyst-containing reactor tube was modeled for each of the above hydrogen-containing ammonia streams, and the results from these models are shown in FIG.

[0079] It can therefore be seen that a significant reduction in nitridation potential at the inlet of an ammonia decomposition reactor can be achieved with no or no significant impact on overall hydrogen recovery.

[0080] Example 2 Example 2 relates to a combustion ammonia decomposition reactor that is fed with an ammonia-containing stream that enters the reactor at 550°C and undergoes an ammonia decomposition reaction to produce a hydrogen stream containing ammonia in an amount of ≦1.1 mol%.

[0081] In Example 2, the tail gas from the hydrogen purification unit was used as the hydrogen-containing recycle gas. The amount of H2 and N2 in the tail gas, the nitriding potential, K N The effect on the hydrogen recovery rate and overall hydrogen recovery rate of the flowsheet are shown in Table 2.

[0082] [Table 2]

[0083] These results show that if tail gas from a purification unit used to increase the H content of a hydrogen-containing stream is used as a hydrogen-containing recycle gas, the same significant reduction in nitridability as in Example 1 can be achieved, while also realizing high hydrogen recovery for the process.

Claims

1. 1. A process for the catalytic decomposition of ammonia, comprising: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing the ammonia in the ammonia stream in the one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor to produce a hydrogen-containing stream; and supplying a hydrogen-containing recycle gas removed from downstream of said ammonia decomposition reactor to said one or more catalyst-containing reactor tubes disposed within said ammonia decomposition reactor.

2. 10. The process of claim 1, comprising preheating the ammonia stream to a temperature of from 350°C to 1000°C.

3. 3. The process of claim 1 or 2, wherein the pressure inlet to the one or more reactor tubes ranges from 1 to 100 bar absolute, from 10 to 90 bar absolute, or from 31 to 51 bar absolute.

4. The hydrogen-containing stream is 40 mol % to 75 mol % H ２ The process according to any one of claims 1 to 3, comprising:

5. The hydrogen-containing recycle gas is 0.5 mol % to 50 mol % H ２ , 1 mol% to 40 mol% H ２ , 2 mol% to 30 mol% H ２ , 4 mol% to 20 mol% H ２ , or 5 mol% to 10 mol% H ２ is supplied to the one or more reaction tubes disposed within the ammonia decomposition reactor such that

6. supplying the hydrogen-containing stream to a purification unit; and ２ and increasing the content to produce a hydrogen-enriched stream and a tail gas.

7. The hydrogen-rich stream is 50 mol % to 100 mol % H ２ , 60 mol% to 90 mol% H ２ , or 70 mol% to 80 mol% H ２ 7. The process of claim 6, comprising:

8. The process of any one of claims 1 to 7, wherein the hydrogen-containing recycle gas comprises a portion of the hydrogen-containing stream.

9. The process of any one of claims 6 to 8, wherein the hydrogen-containing recycle gas comprises a portion of the hydrogen-enriched containing stream and / or a portion of the tail gas from the purification unit.

10. 10. The process of any one of claims 1 to 9, comprising combusting one or more fuel streams with oxygen in a fuel combustion zone to provide thermal energy to support an endothermic ammonia decomposition reaction in the ammonia decomposition reactor.

11. 11. The process of claim 10, wherein the one or more fuel streams comprise one or more of hydrogen, natural gas, methane, refinery by-product gas, biogas, the tail gas from the hydrogen purification unit, a portion of the hydrogen-containing stream from the ammonia cracking reactor, or a portion of the hydrogen-enriched containing stream from the purification unit.

12. 12. The process of claim 10 or 11, wherein the one or more fuel streams comprise hydrogen in an amount between 10 mol% and 45 mol%, between 12 mol% and 35 mol%, or between 15 mol% and 25 mol%.

13. 13. The process of any one of claims 10 to 12, wherein the one or more fuel streams comprise ammonia in an amount of from 10 mol % to 45 mol %.

14. 14. The process of any one of claims 10 to 13, wherein the one or more fuel streams are preheated to a temperature of from 100°C to the autoignition temperature of the fuel streams before being combusted in the fuel combustion zone.

15. The tail gas is 1 mol % to 50 mol % H ２ , 2 mol% to 40 mol% H ２ , or 15 mol % to 25 mol % H ２ The process according to any one of claims 6 to 14, comprising:

16. The process of any one of claims 1 to 15, wherein the one or more catalyst-containing tubes are formed from an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy.

17. 1. A process for the catalytic decomposition of ammonia, comprising: providing an ammonia stream to one or more catalyst-containing reactor tubes disposed within an ammonia decomposition reactor; decomposing the ammonia in the ammonia stream in the one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor to produce a hydrogen-containing stream; The hydrogen-containing stream is fed to a purification unit, and H ２ increasing the content to produce a hydrogen-enriched stream and a tail gas; and supplying a hydrogen-containing recycle gas removed from downstream of the ammonia decomposition reactor to the one or more catalyst-containing reactor tubes disposed within the ammonia decomposition reactor; wherein said hydrogen-containing recycle gas comprises a portion of said hydrogen-enriched containing stream.

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