Process for production of hydrogen from catalytic cracking of ammonia

Abstract

Process A: a process for producing hydrogen from catalytic cracking of ammonia. The method includes the step of supplying a hydrogen-containing recycle gas taken downstream of an ammonia cracking reactor to one or more catalyst-containing reaction tubes disposed within the ammonia cracking reactor. The invention can be used to provide hydrogen as a carbon-free fuel.

Description

Technical Field

[0001] The present invention relates to a method for producing hydrogen. More specifically, the present invention relates to a method for producing hydrogen by catalytic cracking of ammonia. Background Art

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

[0003] Ammonia has attracted attention as a possible compound capable of storing and transporting hydrogen. Liquid ammonia has a higher hydrogen density than liquid hydrogen and can be transported using existing infrastructure already used for this purpose, such as that used to transport ammonia in the agrochemical fertilizer industry.

[0004] Once the liquid ammonia is transported, it may be burned directly or converted into hydrogen through a cracking process.

[0005] The catalytic cracking of ammonia into hydrogen and nitrogen has been known for many years. The reaction can be depicted as follows:

[0006]

[0007] The ammonia cracking reaction is endothermic and can be efficiently achieved by passing ammonia over a suitable catalyst in externally heated catalyst-containing reaction tubes arranged in a furnace. Such furnaces are known, for example, for steam reforming of natural gas or naphtha feedstocks.

[0008] However, heated catalyst-containing reaction tubes disposed in a furnace may react with ammonia-containing gases to form an undesirable metal nitride layer. This undesirable side reaction, known as nitridation, may cause accelerated failure of the reaction tubes, particularly at the inlet of the reaction tubes. Such failures require complete shutdown of the ammonia cracking reactor and result in significant plant downtime. Furthermore, nitridation and potential failure of the reaction tubes present serious safety hazards.

[0009] There remains a need for improved processes for the catalytic cracking of ammonia that address the nitridation problem. Summary of the invention

[0010] The present invention seeks to provide a method for the cracking of ammonia to produce hydrogen while reducing the occurrence of nitridation of reaction tubes containing catalysts arranged in an ammonia cracking reactor.

[0011] Therefore, the present invention provides a method for catalytic cracking of ammonia, the method comprising:

[0012] supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor;

[0013] cracking ammonia in the ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream; and

[0014] One or more catalyst-containing reaction tubes arranged in the ammonia cracking reactor are supplied with hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor.

[0015] It has surprisingly been found that by supplying one or more catalyst-containing reaction tubes arranged in an ammonia cracking reactor with hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor, the nitridation rate of the one or more catalyst-containing reaction tubes can be reduced, in particular the nitridation rate at the inlet of the one or more catalyst-containing reaction tubes and the area directly downstream of the inlet can be reduced.

[0016] Furthermore, although supplying a hydrogen-containing recycle gas to one or more catalyst-containing reaction tubes disposed within the ammonia cracking reactor would be expected to reduce the conversion to H by shifting the equilibrium position of the ammonia cracking reaction, 2 The amount of ammonia, but surprisingly it has been found that the process of the present invention not only reduces the rate at which nitridation occurs in the reaction tube containing the catalyst, but also provides a high total H 2 Methods of recycling.

[0017] In a preferred method of the present invention, a method for catalytic cracking of ammonia is provided, the method comprising:

[0018] supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor;

[0019] cracking ammonia in the ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream;

[0020] The hydrogen-containing stream is fed to a purification unit and the H 2 content to produce a hydrogen-rich stream and a tail gas; and

[0021] supplying hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor to one or more reaction tubes containing a catalyst arranged in the ammonia cracking reactor,

[0022] The hydrogen-containing recycle gas comprises a portion of the enriched hydrogen-containing stream.

[0023] When the hydrogen-containing recycle gas comprises a portion of the enriched hydrogen-containing stream, the total gas flow within the process of the invention can be minimized, thereby allowing the use of a smaller ammonia cracking reactor, thereby reducing the capital cost of practicing the process of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1A flow chart of a method not according to the present invention is shown.

[0025] Figure 2 A block flow diagram of the process according to the invention is shown, wherein a portion of the enriched hydrogen-containing stream (recycle gas) is supplied to one or more catalyst-containing reaction tubes arranged in an ammonia cracking reactor.

[0026] Figure 3 A block flow diagram of the process according to the invention is shown, wherein a portion of a hydrogen-containing stream (recycle gas) is supplied to one or more catalyst-containing reaction tubes arranged in an ammonia cracking reactor.

[0027] Figure 4 A flow chart of the method according to the present invention is shown, in which a portion of the tail gas (recycle gas) generated from the hydrogen purification unit is supplied to one or more catalyst-containing reaction tubes arranged in an ammonia cracking reactor.

[0028] Figure 5 The nitridation potential of various gas compositions as they pass through a catalyst-containing reaction tube disposed in an ammonia cracking reactor is shown.

[0029] Figure 6 Shown is a schematic diagram of a compact reactor available from Johnson Matthey Davy Technologies Limited. DETAILED DESCRIPTION

[0030] The preferred and / or optional features of the present invention will now be described. Unless the context otherwise requires, any aspect of the present invention may be combined with any other aspect of the present invention. Unless the context otherwise requires, any preferred and / or optional features of any aspect may be combined with any aspect of the present invention individually or in combination.

[0031] The method of the present invention comprises supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor.

[0032] The ammonia stream may be derived from any source. In a preferred method of the invention, the ammonia stream is produced by a catalytic combination of hydrogen and nitrogen, for example, the ammonia stream may be produced by a Haber-Bosch ammonia synthesis process. In a preferred method of the invention, the ammonia stream may be produced in an ammonia production facility upstream of the ammonia cracking reactor. Alternatively, the ammonia stream may be provided from an ammonia storage facility, an ammonia storage unit, an ammonia storage tank or an ammonia pipeline.

[0033] In a preferred method of the present invention, the ammonia stream may be preheated before being supplied to one or more reaction tubes containing a catalyst. Therefore, 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 of 350°C to 1000°C, 400°C to 950°C, 450°C to 850°C or 500°C to 750°C (such as 550°C to 700°C).

[0034] Suitable ammonia cracking reactors are known and may include a fuel combustion zone with a radiant section, the radiant section including one or more burners, wherein one or more fuel streams and an oxygen feed gas (such as air, oxygen-enriched air or oxygen) are fed to the one or more burners. The radiant section may include one or more catalyst-containing reaction tubes for the ammonia stream to pass through. The combustion of one or more fuel streams in the one or more burners in the fuel combustion zone produces thermal energy (e.g., radiant heat) for heating one or more catalyst-containing reaction tubes. There may be dozens or hundreds of catalyst-containing reaction tubes in the radiant section. If desired, flue gas from the combustion of one or more fuel streams can be used downstream of the radiant section to preheat one or more feed streams in the convection section. Reactors comprising a radiant section (containing a catalyst) containing a reaction tube and a convection section for preheating the feed are known in steam methane reforming and can be applied to the present invention.

[0035] Alternative ammonia cracking reactors may be used, for example where the combustion of one or more fuel streams in the fuel combustion zone is separated from the reactor comprising the reaction tubes containing the catalyst. Such a reactor is a compact reformer available from Johnson Matthey Davy Technologies Limited, a schematic diagram of which is shown in Figure 6 Shown in.

[0036] The catalyst in the reaction tube containing the catalyst can be any ammonia cracking catalyst. For example, a nickel catalyst and / or a ruthenium catalyst can be used. A preferred catalyst is a nickel catalyst. The catalyst may contain 3% to 30% by weight of nickel, preferably 8% to 20% by weight of 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 granular unit, which may include one or more through holes, or may be a washcoat on a structured metal or ceramic catalyst. A particularly preferred catalyst is KATALCO obtained from Johnson Matthey PLC RTM 27-2, which comprises 12% nickel, expressed as NiO, on cylindrical particles formed from a high surface area calcium aluminate support.

[0037] One or more reaction tubes containing catalysts may be suitably formed of iron-based alloys, nickel-based alloys or cobalt-based alloys. The iron-based alloy may be an iron-chromium-based alloy, such as stainless steel, preferably 316 stainless steel, or high nickel steel, such as those described by WO03 / 051771A1. Preferably, one or more reaction tubes containing catalysts are formed of nickel-based alloys or cobalt-based alloys. More preferably, one or more reaction tubes containing catalysts are formed of cobalt-based alloys.

[0038] The process of the present invention comprises cracking ammonia in an ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream.

[0039] The temperature of the ammonia stream at the inlet of the one or more reaction tubes containing the catalyst 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., such as 550° C. to 700° C. The temperature of the hydrogen-containing stream exiting the one or more reaction tubes containing the catalyst will affect the equilibrium position of the cracking reaction and may be in the range of 500° C. to 950° C. When a nickel catalyst is used in the one or more reaction tubes containing the catalyst, the temperature of the hydrogen-containing stream exiting the one or more reaction tubes containing the catalyst may preferably be greater than about 700° C.

[0040] The inlet pressure of the one or more reaction tubes containing the catalyst will be set by the flowsheet design and may be in the range of 1 to 100 bar absolute, preferably 10 to 90 bar absolute, such as 31 to 51 bar absolute.

[0041] The ammonia cracking reaction produces a hydrogen-containing stream. The hydrogen-containing stream contains H 2 The hydrogen-containing stream also contains nitrogen, and may further contain residual ammonia (eg, unreacted ammonia).

[0042] The hydrogen-containing stream may contain 40 mol % or more H 2 , 50 mol% or more H 2 , or 60 mol% or more H 2 The hydrogen-containing stream may contain 75 mol % or less of H 2 , 70 mol% or less H 2 , or 65 mol% or less H 2 For example, the hydrogen-containing stream may contain 40 mol % to 75 mol % H 2 , 50 mol% to 70 mol% H 2 , or 60 mol% to 65 mol% H 2 .

[0043] In a preferred process of the invention, the hydrogen-containing stream may be fed to a purification unit, such as a pressure swing adsorption unit, to separate the H 2 Separation from other components to increase H 2 Thus, the purification unit produces a hydrogen-rich stream and a tail gas. Therefore, the method of the present invention preferably comprises feeding a hydrogen-containing stream to the purification unit and increasing the H content of the hydrogen-containing stream. 2 The step of reducing the content to produce a hydrogen-rich stream and a tail gas.

[0044] It may be preferred that the hydrogen containing stream is fed to a first steam generation unit and / or a 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 the heat recovery zone may be used to recover low or medium grade heat.

[0045] The hydrogen-rich stream may contain 50 mol % or more H 2 , 60 mol% or more H 2 , or 75 mol% or more H 2 The hydrogen-rich stream may contain 100 mol % or less H 2 , 90 mol% or less H 2 , or 80 mol% or less H 2 For example, the hydrogen-rich stream may contain 50 mol % to 100 mol % H 2 , 60 mol% to 90 mol% H 2 , or 70 mol % to 80 mol % H 2 , such as about 75 mol % H 2 .

[0046] 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 % ammonia or less). The tail gas may contain 1 mol % to 50 mol % H 2 , 2 mol% to 40 mol% H 2 For example, the tail gas may contain 15 mol % to 25 mol % H 2 .

[0047] As used herein, the term "hydrogen-containing stream" may be used to refer to a hydrogen-containing stream or a hydrogen-rich stream.

[0048] The method of the present invention comprises the step of supplying hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor to one or more reaction tubes containing a catalyst arranged in the ammonia cracking reactor.

[0049] The hydrogen-containing recycle gas is taken from the downstream of the ammonia cracking reactor. In a preferred method of the present invention, the hydrogen-containing recycle gas comprises one or more of the following: a portion of the hydrogen-containing stream, a portion of the enriched hydrogen-containing stream and / or H from the hydrogen-containing stream for increasing the hydrogen-containing stream.2 In a more preferred method of the invention, the hydrogen-containing recycle gas comprises one or more of the following: a portion of a hydrogen-containing stream and / or a portion of an enriched hydrogen-containing stream. In a most preferred method of the invention, the hydrogen-containing recycle gas comprises a portion of an enriched hydrogen-containing stream.

[0050] When the hydrogen-containing recycle gas comprises a portion of the enriched hydrogen-containing stream, the total gas flow within the process of the invention can be minimized, thereby allowing the use of a smaller ammonia cracking reactor, thereby reducing the capital cost of practicing the process of the invention.

[0051] A further advantage of using a hydrogen-containing recycle gas comprising a portion of the enriched hydrogen-containing stream is that it has surprisingly been found that other products of the ammonia cracking reaction (e.g. tail gas or nitrogen (N 2 ) gas flow), hydrogen (H 2 ) is more efficient in reducing nitridation. Without being bound by any kind of theory, it is believed that hydrogen reacts with nitrogen (N 2 ) Different mechanisms inhibit nitridation.

[0052] In certain methods of the invention, the recycle gas may consist of one or more of: a portion of the hydrogen-containing stream, a portion of the enriched hydrogen-containing stream, and / or H from a stream used to enrich the hydrogen-containing stream. 2 In some methods of the invention, the recycle gas may consist of one or more of: a portion of a hydrogen-containing stream and / or a portion of an enriched hydrogen-containing stream. In some methods of the invention, the recycle gas may consist of or consist essentially of an enriched hydrogen-containing stream.

[0053] As will be readily appreciated, when the hydrogen-containing recycle gas comprises H from the feed stream used to increase the hydrogen flow, 2 When the tail gas of the purification unit is a part of the tail gas of the purification unit, the method of the present invention comprises feeding the hydrogen-containing stream to the purification unit and increasing the H 2 However, it is also understood that when a hydrogen-containing stream is fed to a purification unit, the hydrogen-containing recycle gas may comprise or may consist of one or more of the following: a hydrogen-containing stream, a tail gas and / or an enriched hydrogen-containing stream.

[0054] The hydrogen-containing recycle gas may be fed directly to one or more reaction tubes containing the catalyst, or the hydrogen-containing recycle gas may first be combined with an ammonia-containing stream and then fed to one or more reaction tubes containing the catalyst. The hydrogen-containing recycle gas may undergo an intermediate process step, such as a heat recovery step, before being fed to the one or more tubes containing the catalyst.

[0055] The hydrogen-containing recycle gas may be supplied to one or more reaction tubes containing the catalyst so that less than 50 mol % of the H 2 , less than 40 mol% H 2 , less than 30 mol% H 2 , less than 20 mol% H 2 or less than 10 mol% H 2 Supplied to one or more reaction tubes containing catalyst.

[0056] The hydrogen-containing recycle gas may be supplied to one or more reaction tubes containing the catalyst so that more than 0.5 mol % of H 2 , greater than 1 mol% H 2 , greater than 2 mol% H 2 , greater than 4 mol% H 2 or more than 5 mol% H 2 Supplied to one or more reaction tubes containing catalyst.

[0057] In a preferred process of the present invention, the hydrogen-containing recycle gas may be supplied to one or more reaction tubes containing the catalyst so that 0.5 mol % to 50 mol % of H 2 , 1 mol% to 40 mol% H 2 , 2 mol% to 30 mol% H 2 , or 4 mol% to 20 mol% H 2 , or 5 mol% to 10 mol% H 2 Supplied to one or more reaction tubes containing catalyst.

[0058] For the avoidance of doubt, it should be understood that the mol % H in the hydrogen-containing recycle gas is 2 It is expressed as a percentage of the total gas supplied to one or more catalyst-containing reaction tubes arranged in the ammonia cracking reactor.

[0059] It has surprisingly been found that when a hydrogen-containing recycle gas is supplied to one or more reaction tubes containing a catalyst in the amounts specified above, a reduction in the nitridation rate of the reaction tubes containing the catalyst, in particular a reduction in the nitridation rate at the inlet of the reaction tubes containing the catalyst, can be achieved while maintaining a high overall hydrogen recovery. It has surprisingly been found that supplying up to 50 mol % of H to the one or more reaction tubes containing the catalyst 2 , such as up to 40 mol%, 30 mol%, 20 mol% or 10 mol% H 2There is little or no effect on the overall hydrogen recovery of the process. In other words, it has surprisingly been found that using the process of the present invention in which a portion of the hydrogen-containing recycle gas is supplied to one or more reaction tubes containing a catalyst, the same or similar overall hydrogen recovery can be achieved as when no hydrogen-containing gas is supplied to the one or more reaction tubes containing a catalyst.

[0060] For the avoidance of doubt, reference to supplying an ammonia-containing stream, a hydrogen-containing stream and / or an enriched hydrogen-containing stream to one or more reaction tubes containing a catalyst refers to supplying one or more streams through a catalyst bed of a reaction tube containing a catalyst, and does not refer to supplying any of these streams as a combustible fuel source for providing thermal energy to one or more reaction tubes containing a catalyst. It should also be understood that "total gas supplied to one or more reaction tubes containing a catalyst" includes all gases fed through a catalyst bed of a reaction tube containing a catalyst, and does not refer to gas supplied as a combustible fuel source for providing thermal energy to one or more reaction tubes containing a catalyst.

[0061] In certain methods of the present invention, the hydrogen-containing recycle gas may be fed to a second steam generation unit and / or a heat recovery zone, which may then be supplied to one or more reaction tubes containing a catalyst. As will be appreciated by those skilled in the art, the second steam generation unit and / or the heat recovery zone may be used to recover low-grade or intermediate-grade heat.

[0062] For the avoidance of doubt, the first steam generating unit and / or heat recovery zone and the second steam generating unit and / or heat recovery zone may be the same or different steam generating units and / or heat recovery zones.

[0063] 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 for supporting the endothermic ammonia cracking reaction in the ammonia cracking reactor. Thus, the process of the present invention may include the step of combusting one or more fuel streams with oxygen in a fuel combustion zone to provide thermal energy to the ammonia cracking reactor.

[0064] Alternatively, the electric heater may provide thermal energy for supporting the endothermic ammonia cracking reaction in the ammonia cracking reactor.

[0065] The fuel combustion zone may be located within the ammonia cracking reactor or may be located in a separate vessel for combustion that is fluidly connected to the ammonia cracking reactor.

[0066] The fuel combustion zone may suitably be a radiant section in a box furnace of the ammonia cracking reactor. Thus, the fuel combustion zone may provide thermal energy (e.g., radiant heat) to the ammonia cracking reactor. Alternatively, if the fuel combustion zone is located in a separate vessel from the ammonia cracking reactor, the ammonia cracking reactor may be a heat exchange design, such as a gas heated reformer or a compact reformer, in which one or more catalyst containing reaction tubes are heated by convection of hot combustion gases flowing around the outer surface of the reaction tubes containing the catalyst.

[0067] The one or more fuel streams may include one or more fuel streams that are combusted with oxygen to generate 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.

[0068] The one or more fuel streams may include one or more of hydrogen, natural gas, methane, refinery off-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 an enriched hydrogen-containing stream from a purification unit.

[0069] The oxygen used to combust the 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.

[0070] As used herein, the term "fuel portion" is used to refer to a portion of a stream (eg, a hydrogen-containing stream, an enriched hydrogen-containing stream, or an ammonia-containing stream) used as a fuel source. It is not used to refer to a portion of a stream used for an ammonia cracking reaction.

[0071] In a preferred method of the present invention, one or more fuel streams may include a hydrogen-containing fuel stream. Preferably, the hydrogen-containing fuel stream may be the fuel portion of a hydrogen-containing stream produced from an ammonia cracking reactor. More preferably, the hydrogen-containing fuel stream may be the fuel portion of an enriched hydrogen-containing stream from a purification unit. Thus, the method of the present invention may include the steps of taking out a fuel portion of a hydrogen-containing stream or a fuel portion of a hydrogen-rich stream, and burning the fuel portion of the hydrogen-containing stream or the fuel portion of the enriched hydrogen-containing stream with oxygen in a fuel combustion zone to provide heat energy to support the endothermic ammonia cracking reaction in the ammonia cracking reactor.

[0072] 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 1 mol % to 100 mol % H 2 , such as 5 mol % to 75 mol % H 2 , 10 mol% to 50 mol% H 2 or 15 mol% to 30 mol% H 2 Preferably, one or more fuel streams may contain greater than 10 mol % H 2, greater than 12 mol% H 2 or more than 15 mol% H 2 Preferably, one or more fuel streams may contain less than 45 mol % H 2 , less than 35 mol% H 2 or less than 35 mol% H 2 For example, one or more fuel streams may preferably contain 10 mol % to 45 mol % H 2 , 12 mol% to 35 mol% H 2 or 15 mol% to 25 mol% H 2 The amount of hydrogen.

[0073] In a preferred method of the present invention, one or more fuel streams include an ammonia-containing fuel stream. The amount of ammonia in one or more fuel streams is not particularly limited. For example, one or more fuel streams may contain 1mol% to 100mol%, such as 5mol% to 75mol%, 10mol% to 50mol%, or 15mol% to 30mol% of ammonia. Preferably, one or more fuel streams may contain ammonia in an amount greater than 10mol%, greater than 12mol% or greater than 15mol%. Preferably, one or more fuel streams may contain ammonia in an amount less than 45mol%, less than 35mol% or less than 35mol%. For example, one or more fuel streams may preferably contain ammonia in an amount of 10mol% to 45mol%, 12mol% to 35mol%, or 15mol% to 25mol%.

[0074] When one or more fuel streams contain ammonia, the ammonia-containing fuel stream may be supplied from the same or different source as the ammonia stream supplied to the one or more reaction tubes containing the catalyst. 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 supplied to the one or more reaction tubes containing the catalyst.

[0075] In a preferred method of the present invention, one or more fuel streams may be preheated before combustion in the fuel combustion zone. One or more fuel streams may be preheated to any temperature below the autoignition temperature of the fuel stream. For example, one or more fuel streams may be preheated to a temperature greater than 100°C, greater than 150°C, or greater than 200°C. One or more fuel streams may be preheated to a temperature less than the autoignition temperature of the fuel stream, such as less than 400°C, less than 350°C, or less than 300°C. For example, one or more fuel streams may be preheated to a temperature of 100°C to the autoignition temperature of the fuel stream, such as 100°C to 400°C. In a preferred method of the present invention, one or more fuel streams may be an ammonia-containing fuel stream and may be provided from a preheated ammonia stream.

[0076] For the avoidance of doubt, one or more fuel streams may be combined prior to combustion, or may be combined at a single combustion point.

[0077] The combustion of one or more fuel streams in the fuel combustion zone produces flue gas, which can be recovered from the ammonia cracking reactor. The flue gas can be cooled in one or more cooling stages and can undergo one or more purification stages before being discharged into the atmosphere. The one or more cooling stages can include a preheating stage for one or more reactants in the ammonia cracking reactor and / or the reactants that produce steam. The one or more purification stages can include a selective catalytic reduction or SCR stage, in which nitrogen oxides react with ammonia to form nitrogen and water vapor. Any flue gas selective catalytic reduction technology can be used.

[0078] In certain embodiments of the method of the present invention, the method comprises the following steps:

[0079] supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor;

[0080] cracking ammonia in the ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream; and

[0081] supplying hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor to one or more reaction tubes containing a catalyst arranged in the ammonia cracking reactor,

[0082] The hydrogen-containing recycle gas comprises a portion of the hydrogen-containing stream.

[0083] In certain embodiments of the method of the present invention, the method comprises the following steps:

[0084] supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor;

[0085] cracking ammonia in the ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream;

[0086] The hydrogen-containing stream is fed to a purification unit and the H 2 content to produce a hydrogen-rich stream and a tail gas; and

[0087] supplying hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor to one or more reaction tubes containing a catalyst arranged in the ammonia cracking reactor,

[0088] The hydrogen-containing recycle gas comprises one or more of: a portion of the hydrogen-containing stream, a portion of the enriched hydrogen-containing stream, or a portion of the tail gas from the purification unit.

[0089] In certain embodiments of the method of the present invention, the method comprises the following steps:

[0090] supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor;

[0091] cracking ammonia in the ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream;

[0092] Optionally, feeding the hydrogen-containing stream to the first steam generation unit and / or the heat recovery zone;

[0093] Optionally, the hydrogen-containing stream is fed to a purification unit and the H 2 content to produce a hydrogen-rich stream and a tail gas;

[0094] Optionally, feeding the enriched hydrogen-containing stream to a second steam generation unit and / or a heat recovery zone;

[0095] supplying hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor to one or more reaction tubes containing a catalyst arranged in the ammonia cracking reactor;

[0096] removing a fuel portion of the hydrogen-containing stream or a fuel portion of the hydrogen-rich stream; and

[0097] combusting a fuel portion of the hydrogen-containing stream or a fuel portion of the enriched hydrogen-containing stream with oxygen in a fuel combustion zone to provide heat energy to support the endothermic ammonia cracking reaction in the ammonia cracking reactor,

[0098] The hydrogen-containing recycle gas comprises one or more of: a portion of the hydrogen-containing stream, a portion of the enriched hydrogen-containing stream, or a portion of the tail gas from the purification unit.

[0099] In certain embodiments of the method of the present invention, the method comprises the following steps:

[0100] Optionally, preheating the ammonia stream;

[0101] supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor;

[0102] cracking ammonia in the ammonia stream in one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor to produce a hydrogen-containing stream;

[0103] Optionally, feeding the hydrogen-containing stream to the first steam generation unit and / or the heat recovery zone;

[0104] Optionally, the hydrogen-containing stream is fed to a purification unit and the H 2 content to produce a hydrogen-rich stream and a tail gas;

[0105] Optionally, feeding the enriched hydrogen-containing stream to a second steam generation unit and / or a heat recovery zone;

[0106] supplying hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor to one or more reaction tubes containing a catalyst arranged in the ammonia cracking reactor;

[0107] removing a fuel portion of the hydrogen-containing stream or a fuel portion of the hydrogen-rich stream; and

[0108] combusting a fuel portion of the hydrogen-containing stream or a fuel portion of the enriched hydrogen-containing stream with oxygen in a fuel combustion zone to provide heat energy to support the endothermic ammonia cracking reaction in the ammonia cracking reactor,

[0109] The hydrogen-containing recycle gas may comprise one or more of the following: a portion of the hydrogen-containing stream, a portion of the enriched hydrogen-containing stream, or a portion of the tail gas from the purification unit.

[0110] The present invention will now be described in further detail with reference to the following non-limiting embodiments.

[0111] Figure 1 A flow chart of a method not according to the invention is shown. Figure 1 The steps of preheating ammonia (1) to produce an ammonia-containing stream (101) are shown. The ammonia-containing stream (101) is supplied to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor (2). Ammonia in the ammonia-containing stream is cracked in one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (2) to produce a hydrogen-containing stream (102). The hydrogen-containing stream (102) is conveyed to a first steam generation unit and / or a heat recovery zone (3) where heat energy is recovered. The cooled hydrogen-containing stream (103) is conveyed to a purification unit (4) where the H of the hydrogen-containing stream is enriched. 2 content. The hydrogen-rich stream is recovered as purified hydrogen (5), and the fuel portion of the enriched hydrogen-containing stream (105) is passed to the fuel combustion zone (6) of the ammonia cracking reactor (2). The enriched hydrogen-containing stream (105) is combusted with oxygen (106) supplied as compressed air from a compressor (7) to generate heat energy (108), which is supplied to the ammonia cracking reactor (2) to support the endothermic ammonia cracking reaction. The ammonia cracking reactor (2) produces flue gas (109), from which heat energy can be recovered in a second steam generation unit and / or a heat recovery zone (8). The cooled flue gas (110) can be discharged to the atmosphere via a chimney or sent for further treatment (9).

[0112] Figure 2 A flow chart of the method according to the present invention is shown. Figure 2The steps of preheating ammonia (11) to produce an ammonia-containing stream (201) are shown. The ammonia-containing stream (201) is supplied to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor (12). Ammonia in the ammonia-containing stream is cracked in one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (12) to produce a hydrogen-containing stream (202). The hydrogen-containing stream (202) is conveyed to a first steam generation unit and / or a heat recovery zone (13) where heat energy is recovered. The cooled hydrogen-containing stream (203) is conveyed to a purification unit (14) where H is enriched in the hydrogen-containing stream. 2 content. The hydrogen-rich stream is recovered as purified hydrogen (15), and the fuel portion of the enriched hydrogen-containing stream (205) is conveyed to the fuel combustion zone (16) of the ammonia cracking reactor (12). The hydrogen purification unit (14) produces a tail gas (212). A portion of the enriched hydrogen-containing stream (211) is combined with the ammonia-containing stream (201) and fed to one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (12). The enriched hydrogen-containing stream (205) is combusted with oxygen (206) supplied as compressed air from a compressor (17) to produce heat energy (208), which is supplied to the ammonia cracking reactor (12) to support the endothermic ammonia cracking reaction. The ammonia cracking reactor (12) produces flue gas (209), from which heat energy can be recovered in a second steam generation unit and / or a heat recovery zone (18). The cooled flue gas (210) can be discharged to the atmosphere via a chimney or sent for further treatment (19).

[0113] Figure 3 A flow chart of the method according to the present invention is illustrated, wherein a portion of a hydrogen-containing stream (311) is supplied to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor (22), and then the hydrogen-containing stream is purified. Figure 3 The steps of preheating ammonia (21) to produce an ammonia-containing stream (301) are shown. The ammonia-containing stream (301) is supplied to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor (22). Ammonia in the ammonia-containing stream is cracked in one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (22) to produce a hydrogen-containing stream (302). A portion of the hydrogen-containing stream (311) is combined with the ammonia-containing stream (301) and fed to one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (22). The remaining hydrogen-containing stream (302) is conveyed to a first steam generation unit and / or a heat recovery zone (23) in which heat energy is recovered. The cooled hydrogen-containing stream (303) is conveyed to a purification unit (24) in which the H of the hydrogen-containing stream is enriched. 2content and produces tail gas (312). The hydrogen-rich stream is recovered as purified hydrogen (25), and the fuel portion of the enriched hydrogen-containing stream (305) is passed to the fuel combustion zone (26) of the ammonia cracking reactor (22). The enriched hydrogen-containing stream (305) is combusted with oxygen (306) supplied as compressed air from a compressor (27) to produce heat energy (308), which is supplied to the ammonia cracking reactor (22) to support the endothermic ammonia cracking reaction. The ammonia cracking reactor (22) produces flue gas (309), from which heat energy can be recovered in a second steam generation unit and / or a heat recovery zone (28). The cooled flue gas (310) can be discharged to the atmosphere via a chimney or sent for further treatment (29).

[0114] Figure 4 A flow chart of the method according to the present invention is shown. Figure 4 The steps of preheating ammonia (31) to produce an ammonia-containing stream (401) are shown. The ammonia-containing stream (401) is supplied to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor (32). Ammonia in the ammonia-containing stream is cracked in one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (32) to produce a hydrogen-containing stream (402). The hydrogen-containing stream (402) is conveyed to a first steam generation unit and / or a heat recovery zone (33) where heat energy is recovered. The cooled hydrogen-containing stream (403) is conveyed to a purification unit (34) where the H of the hydrogen-containing stream is enriched. 2 content. The hydrogen-rich stream is recovered as purified hydrogen (35), and the fuel portion of the enriched hydrogen-containing stream (405) is transmitted to the fuel combustion zone (36) of the ammonia cracking reactor (32). A portion of the tail gas (412) from the purification unit (34) is combined with the ammonia-containing stream (401) and fed to one or more reaction tubes containing a catalyst disposed in the ammonia cracking reactor (32). The enriched hydrogen-containing stream (405) is combusted with oxygen (406) supplied as compressed air from a compressor (37) to generate heat energy (408), which is supplied to the ammonia cracking reactor (32) to support the endothermic ammonia cracking reaction. The ammonia cracking reactor (32) produces flue gas (409), from which heat energy can be recovered in a second steam generation unit and / or a heat recovery zone (38). The cooled flue gas (410) can be discharged to the atmosphere via a chimney or sent for further treatment (39).

[0115] Example

[0116] Example 1

[0117] Example 1 involves supplying an ammonia-containing stream to a fired ammonia cracking reactor. The ammonia-containing stream enters the reactor at 550°C and undergoes an ammonia cracking reaction to produce a hydrogen stream comprising ammonia in an amount of ≤ 1.1 mol%.

[0118] The hydrogen stream is combined with the ammonia stream to produce a feed to the ammonia cracking reactor, the feed comprising 0 mol%, 1 mol%, 5 mol%, 10 mol%, 20 mol%, 30 mol%, 40 mol% and 50 mol% H 2 The flow chart shows the nitriding potential, K N The influence of NH2+ and total hydrogen recovery is shown in Table 1. The nitridation potential (K) is defined according to Eq. N ), where "p" represents the partial pressure of the gas.

[0119]

[0120] <![CDATA[H 2 (mol%)]]> 0％ 1％ 5％ 10％ 20％ 30％ 40％ 50％ <![CDATA[Entrance K N (atm -1 / 2 )]]> ∞ 158.6 13.70 4.60 1.43 0.68 0.38 0.20 <![CDATA[Flowchart H 2 Recovery (%)]]> 74.00 73.92 73.62 73.24 71.75 70.27 68.08 67.04

[0121] Table 1

[0122] For each of the above hydrogen-ammonia streams, the nitridation potential along the length of the reactor tube containing the catalyst was modeled. The results of these models are given in Figure 5 Shown in.

[0123] It can therefore be seen that a significant reduction in the nitridation potential at the inlet to the ammonia cracking reactor can be achieved with no or no significant effect on the overall hydrogen recovery.

[0124] Example 2

[0125] Example 2 involves supplying an ammonia-containing stream to a fired ammonia cracking reactor. The ammonia-containing stream enters the reactor at 550°C and undergoes an ammonia cracking reaction to produce a hydrogen stream comprising ammonia in an amount of ≤ 1.1 mol%.

[0126] In Example 2, tail gas from a hydrogen purification unit is used as hydrogen-containing recycle gas. 2 and N 2 The amount, nitriding potential, K N The effects of and on the total hydrogen recovery are shown in Table 1.

[0127]

[0128] Table 2

[0129] From these results, it can be seen that when the H from the hydrogen-containing stream is used to increase 2 When the tail gas from the purification unit with a content of 200 wt % is used as the hydrogen-containing recycle gas, the same significant reduction in nitriding potential as in Example 1 can be achieved, while also achieving high hydrogen recovery in the process.

Claims

1. A method for catalytic cracking of ammonia, the method comprising: supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor; cracking ammonia in the ammonia stream in the one or more catalyst-containing reaction tubes disposed in the ammonia cracking reactor to produce a hydrogen-containing stream; as well as The one or more catalyst-containing reaction tubes disposed in the ammonia cracking reactor are supplied with hydrogen-containing recycle gas taken from the downstream of the ammonia cracking reactor.

2. The method according to claim 1, comprising the step of preheating the ammonia stream to a temperature of 350°C to 1000°C.

3. The method according to claim 1 or claim 2, wherein the inlet pressure of the one or more reaction tubes is in the range of 1 bar to 100 bar absolute pressure, 10 bar to 90 bar absolute pressure, or 31 bar to 51 bar absolute pressure.

4. A method according to any one of the preceding claims, wherein the hydrogen-containing stream comprises 40 mol% to 75 mol% H2.

5. The method according to any one of the preceding claims, wherein the hydrogen-containing recycle gas is supplied to the one or more reaction tubes arranged in the ammonia cracking reactor so that 0.5 mol% to 50 mol% H2, 1 mol% to 40 mol% H2, 2 mol% to 30 mol% H2, 4 mol% to 20 mol% H2 or 5 mol% to 10 mol% H2 is supplied to the one or more reaction tubes.

6. The method according to any one of the preceding claims, wherein the method further comprises the step of feeding the hydrogen-containing stream to a purification unit and increasing the H2 content of the hydrogen-containing stream to produce a hydrogen-rich stream and a tail gas.

7. The method of claim 6, wherein the hydrogen-rich stream comprises 50 mol% to 100 mol% H2, 60 mol% to 90 mol% H2, or 70 mol% to 80 mol% H2.

8. The method according to any one of the preceding claims, wherein the hydrogen-containing recycle gas comprises a portion of the hydrogen-containing stream.

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

10. A method according to any one of the preceding claims, comprising the step of combusting one or more fuel streams with oxygen in a fuel combustion zone to provide thermal energy to support the endothermic ammonia cracking reaction in the ammonia cracking reactor.

11. The method of claim 10, wherein the one or more fuel streams comprise one or more of: hydrogen, natural gas, methane, refinery off-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 enriched hydrogen-containing stream from the purification unit.

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

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

14. A method according to 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 auto-ignition temperature of the fuel stream prior to combustion in the fuel combustion zone.

15. The method of any one of claims 6 to 14, wherein the tail gas comprises 1 mol% to 50 mol% H2, 2 mol% to 40 mol% H2, or 15 mol% to 25 mol% H2.

16. A method according to any one of the preceding claims, 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. A method for catalytic cracking of ammonia, the method comprising: supplying an ammonia stream to one or more reaction tubes containing a catalyst disposed in an ammonia cracking reactor; cracking ammonia in the ammonia stream in the one or more catalyst-containing reaction tubes disposed in the ammonia cracking reactor to produce a hydrogen-containing stream; feeding the hydrogen-containing stream to a purification unit and increasing the H2 content of the hydrogen-containing stream to produce a hydrogen-rich stream and a tail gas; and supplying the one or more catalyst-containing reaction tubes disposed in the ammonia cracking reactor with a hydrogen-containing recycle gas taken from a downstream of the ammonia cracking reactor, wherein the hydrogen-containing recycle gas comprises a portion of the enriched hydrogen-containing stream.

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