Methods and equipment

Abstract

Methods and Systems This invention relates to methods and systems for cracking ammonia to produce hydrogen and nitrogen. The invention provides a method for controlling an ammonia cracking unit to place it in a low-load state, an ammonia cracking unit in a low-load state, and a method for returning the ammonia cracking unit from a low-load state to a normal operating state. [Figure 2]

Description

Technical Field

[0001] This invention relates to methods and systems for generating hydrogen. More specifically, this invention relates to methods for operating an ammonia cracking unit to generate hydrogen, and to ammonia cracking units for generating hydrogen. Background Technology

[0002] There has been renewed interest in using hydrogen as a green, carbon-free fuel in various industrial environments. Hydrogen can be burned to produce heat or electricity. Alternatively, hydrogen can be used as fuel to generate electrochemical energy, for example, in fuel cells.

[0003] Ammonia has attracted attention as a potential compound for 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 for transporting ammonia in the agrochemical fertilizer industry.

[0004] Once liquid ammonia is transported, it can be converted into hydrogen through a cracking process in an ammonia cracking unit.

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

[0006]

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

[0008] Combustion of a hydrogen stream in a gas turbine to generate electricity is known. US2022162999 and US2022162989 disclose processes involving a gas turbine driven by the combustion of a hydrogen-containing stream with a compressed air stream. The hydrogen-containing stream is generated in an ammonia cracker fed with an ammonia stream. The gas turbine is used to generate electrical and mechanical energy. The heat generated by the combustion of the hydrogen-containing stream is either supplied directly to the cracker or used to preheat the ammonia stream upstream of the cracker via a heat exchanger.

[0009] WO2024 / 018169A1 discloses a method comprising an ammonia cracking reactor and a gas turbine driven by combustion via a hydrogen-containing stream.

[0010] Alternatively, hydrogen can be fed into a so-called "hydrogen grid," where it can be extracted and burned directly to generate heat.

[0011] However, energy demand varies over time, and therefore the demand for hydrogen also varies over time. This is true whether hydrogen is used for power generation or for generating heat. For example, the demand for electricity to supply residential consumers or industrial plants will vary over a day, a week, or a year. Therefore, in the case of ammonia being cracked to produce hydrogen fuel, the ammonia cracking unit must be able to respond quickly to increases and decreases in energy demand. In other words, the ammonia cracking unit must be designed and operated in a way that produces more hydrogen when energy demand increases and less hydrogen when energy demand decreases.

[0012] Typically, ammonia cracking equipment must be able to return from a "turndown state" to normal operation (e.g., producing more than 40% of the maximum molar hydrogen production for energy generation purposes) within two hours.

[0013] Several possible solutions have been proposed to overcome the problem of variable energy and therefore hydrogen demand.

[0014] The first option is to shut down the ammonia cracking unit and restart it when the demand for hydrogen recovers. However, the startup and shutdown procedures may be too lengthy and will not meet the two-hour notification period required to return to normal operation. Additionally, the thermal cycling of the catalyst-containing reaction tubes within the ammonia cracking reactor can reduce the tubes' lifespan and cause significant damage to the catalyst.

[0015] The second option is to operate the ammonia cracking unit at a lower hydrogen production rate, for example, producing less than 40% of the unit's maximum molar hydrogen output (e.g., less than 30% or less than 20%). In this case, the unit's hydrogen output can be increased to normal operation in less than one hour to meet the required two-hour notification period. However, this option requires sending any hydrogen produced but not used for energy generation to the flame. This wastes a significant amount of ammonia feedstock and the fuel (which could also be ammonia) needed to heat the ammonia cracking reactor. Alternatively, the produced hydrogen can be stored. However, this requires the construction of large and expensive storage facilities.

[0016] Therefore, there is a need for ammonia cracking methods and equipment that can adapt to the variable demand for hydrogen and thus for energy. Summary of the Invention

[0017] Therefore, in a first aspect of the present invention, a method for controlling an ammonia cracking apparatus including a roasting ammonia cracking reactor is provided, the method comprising the following steps:

[0018] i) Reduce the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of the ammonia cracking reactor;

[0019] ii) Reduce the heat output of the fuel combustion zone in the ammonia cracking reactor;

[0020] iii) Obtain the cracked gas stream from the outlet of one or more reaction tubes containing catalyst;

[0021] iv) Cooling the pyrolysis gas stream;

[0022] v) Increase the pressure of the pyrolysis gas flow;

[0023] vi) Heating the pyrolysis gas stream;

[0024] vii) Recirculate the pyrolysis gas stream to the inlet of one or more reaction tubes containing catalyst; and

[0025] viii) Pass the pyrolysis gas stream through one or more reaction tubes containing a catalyst.

[0026] In a second aspect of the invention, an ammonia cracking unit under low load is provided. The ammonia cracking unit under low load is an ammonia cracking unit that has already operated the method of the first aspect of the invention. The ammonia cracking unit under low load may be an ammonia cracking unit that has already operated steps i) to viii) of the method of the first aspect of the invention and is repeating or continuing to operate steps iii) to viii) of the method of the first aspect of the invention.

[0027] In a third aspect of the invention, a method is provided for returning an ammonia cracking unit from a low-load state according to a second aspect of the invention to a normal operating state.

[0028] A method according to a third aspect of the invention for returning an ammonia cracking unit from a low-load state according to a second aspect of the invention to a normal operating state includes the following steps:

[0029] i) Increase the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located within the radiant section of the ammonia cracking reactor; and

[0030] ii) Increase the heat output of the fuel combustion zone in the ammonia cracking reactor;

[0031] iii) Cracking the ammonia in the ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2), and residual ammonia (NH3); and

[0032] iv) Obtain the cracked gas stream from the outlet of one or more reaction tubes containing catalyst.

[0033] Chemical equipment operating exothermic reactions (such as the synthesis of ammonia or methanol) can be relatively easily brought back to normal operation from a low-load state. In most cases, the equipment can be maintained at or below the minimum "ignition" temperature, and the flow rate of the reagents is reduced or stopped. Once the reagents are reintroduced into the method, the exothermic reaction generates the heat required to sustain the reaction (i.e., the method is self-heating).

[0034] In contrast, chemical equipment operating endothermic reactions, such as those used for ammonia cracking, does not benefit from the heat generated by the reaction. In ammonia cracking equipment, when the flow rate of ammonia feedstock to the catalyst-containing reaction tube decreases or stops, the temperature of the catalyst-containing reaction tube rises due to the continued combustion of fuel in the ammonia cracking reactor. However, if fuel combustion ceases, adding ammonia feedstock to the catalyst-containing reaction tube will drastically cool the temperature of the catalyst-containing reaction tube and the catalyst within it, thereby inhibiting the reaction.

[0035] The inventors have discovered that the method of the first aspect of the invention can place an ammonia cracking unit under a certain low-load condition, in which heated cracked gas is recirculated to one or more reaction tubes containing a catalyst. Surprisingly, the method of the first aspect of the invention can place the ammonia cracking unit under a certain low-load condition, which allows it to quickly return to normal operation (e.g., within a two-hour period) without wasting ammonia feedstock and / or hydrogen. The method of the first aspect of the invention and the low-load condition of the second aspect of the invention maintain the ammonia cracking unit at a temperature significantly above the minimum temperature required for the endothermic reaction to occur. Surprisingly, the method of the third aspect of the invention enables the ammonia cracking unit to return to normal operation from the low-load condition of the second aspect of the invention within a two-hour period. Attached Figure Description

[0036] Figure 1 A schematic diagram of a compact reformer available from Johnson Matthey Davy Technologies Limited is shown.

[0037] Figure 2 A block flowchart of a method according to a first aspect of the invention and an ammonia cracking unit under low load conditions according to a second aspect of the invention is shown. Detailed Implementation

[0038] Preferred and / or optional features of the invention will now be set forth. Unless the context otherwise requires, any aspect of the invention may be combined with any other aspect of the invention. Unless the context otherwise requires, any preferred and / or optional feature of any aspect may be combined with any aspect of the invention, alone or in combination. The lower and / or upper limits of any scope disclosed herein are contemplated to be combined with each other to provide new scopes, whether or not explicitly stated.

[0039] This invention relates to a method for controlling an ammonia cracking apparatus including an open-flame ammonia cracking reactor.

[0040] The ammonia cracking apparatus of the present invention includes a roasting ammonia cracking reactor. Suitable roasting ammonia cracking reactors are known and include a fuel combustion zone with a radiant section comprising one or more burners to which one or more fuel streams and an oxygen-containing feed (such as air, oxygen-enriched air, or oxygen) are fed. The radiant section includes one or more catalyst-containing reaction tubes, each having an inlet and an outlet, through which the ammonia feed stream passes. Combustion of one or more fuel streams in one or more burners within the fuel combustion zone generates thermal energy (e.g., radiant heat) for heating the one or more catalyst-containing reaction tubes. There may be tens, hundreds, or thousands of catalyst-containing reaction tubes in the radiant section. If desired, downstream of the radiant section, the flue gas from the combustion of one or more fuel streams can be used to preheat one or more feed streams in a convection section (such as a flue), through which the flue gas may pass. Typically, the convection section is the flue of the ammonia cracking reactor.

[0041] Reactors comprising a radiant section and a convection section for preheating the feed are known in steam methane reforming and can be used in this invention. The radiant section includes a reaction tube containing a catalyst.

[0042] Alternatively, a roasting ammonia cracking reactor can be used, wherein the combustion of the one or more fuel streams in the fuel combustion zone is separated from the reactor, which includes a reaction tube containing a catalyst. Such a reactor is a compact reformer available from Johnson MattheyDavy Technologies Limited, a schematic diagram of which is shown in […]. Figure 1 As shown in the image.

[0043] The catalyst in the reaction tube containing the catalyst can be any ammonia cracking catalyst. For example, nickel and / or ruthenium catalysts can be used. A nickel catalyst is preferred. The catalyst may contain 3% to 30% by weight of nickel, preferably 8% to 20% by weight, on a suitable refractory support such as alumina or aluminate, expressed as NiO. The catalyst may be in the form of particulate units, which may include one or more through-holes, or may be a support coating on a structured metal or ceramic catalyst. A particularly preferred catalyst is KATALCO obtained from Johnson Matthey PLC. RTM 27-2, which contains 12% nickel, represented by NiO, on cylindrical particles formed from high-surface-area calcium aluminate carriers.

[0044] One or more catalyst-containing reaction tubes may suitably be formed of an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy. The iron-based alloy may be an iron-chromium-based alloy, such as stainless steel, preferably 316 stainless steel, or a high-nickel steel, such as those described in WO03 / 051771A1. Preferably, one or more catalyst-containing reaction tubes are formed of a nickel-based alloy or a cobalt-based alloy. More preferably, one or more catalyst-containing reaction tubes are formed of a cobalt-based alloy.

[0045] The first aspect of the invention can be a method for controlling an ammonia cracking unit, including a roasting ammonia cracking reactor, to place the ammonia cracking unit in a low-load state. The method for controlling the ammonia cracking unit can also be a method for bringing the ammonia cracking unit from a normal operating state to a low-load state.

[0046] "Normal operation" of an ammonia cracker means that the ammonia cracker produces more than 40% of its maximum molar hydrogen production. Normal operation of an ammonia cracker will be understood to include the state in which the ammonia cracker produces hydrogen for energy generation purposes (e.g., for feeding hydrogen into a hydrogen network, or for combustion in a gas turbine to generate electricity). Normal operation of an ammonia cracker can also be understood to include situations where a majority (e.g., 70% or more, 80% or more, 90% or more, or 95% or more, such as up to 100%) of the cracked gas is removed from the ammonia cracker (e.g., for energy generation) and a majority (e.g., 70% or more, 80% or more, 90% or more, or 95% or more, such as up to 100%) of the cracked gas is not recycled to the inlet of one or more catalyst-containing reaction tubes.

[0047] Those skilled in the art are familiar with methods and apparatus suitable for operating ammonia cracking equipment under normal operating conditions. The description of suitable normal operating conditions provided herein should not be construed as limiting the methods or apparatus of the invention in any way. Alternative normal operating conditions may be known to those skilled in the art and may be suitable for combination with the methods or apparatus of the invention.

[0048] Normal operation of an ammonia cracking unit may include the following steps:

[0049] a) Provide an ammonia feedstock stream to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of a roasting ammonia cracking reactor;

[0050] b) Cracking the ammonia in the ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2), and residual ammonia (NH3); and

[0051] c) Obtain the cracked gas stream from the outlet of one or more reaction tubes containing catalyst.

[0052] During normal operation of the ammonia cracking unit, the heat output of the fuel combustion zone of the roasting ammonia cracking reactor can be operated such that one or more catalyst-containing reaction tubes are maintained at a temperature of 600°C or higher, 620°C or higher, 650°C or higher, 680°C or higher, 700°C or higher, or 720°C or higher, as measured at the outlet of one or more reaction tubes. During normal operation of the ammonia cracking unit, the heat output of the fuel combustion zone of the roasting ammonia cracking reactor can be operated such that one or more catalyst-containing reaction tubes are maintained at a temperature of 850°C or lower, 830°C or lower, 810°C or lower, 790°C or lower, 780°C or lower, or 770°C or lower, as measured at the outlet of one or more reaction tubes. For example, during normal operation of an ammonia cracking unit, the heat output of the fuel combustion zone of a roasting ammonia cracking reactor can be operated such that one or more catalyst-containing reaction tubes are maintained at temperatures such as 600°C to 850°C, 620°C to 830°C, 650°C to 810°C, or 680°C to 790°C, 700°C to 780°C, or 720°C to 770°C, as measured at the outlet of one or more reaction tubes, such as 730°C, 740°C, 750°C, or 760°C.

[0053] During normal operation of an ammonia cracking unit, there are no particular limitations on the one or more fuel streams used to provide heat for the ammonia cracking reaction, and these fuel streams may contain one or more different fuels that can be burned together with an oxygen-containing feed to generate heat. Typically, the one or more fuel streams used to provide heat for the ammonia cracking reaction can be carbon-free fuel streams and / or carbon-containing fuel streams. As used herein, the term "carbon-free fuel stream" should be understood to include combustible compounds that do not contain carbon, such as ammonia and / or hydrogen. As used herein, the term "carbon-containing fuel stream" will be understood to include combustible compounds such as hydrocarbons, such as methane, ethane, propane, and / or butane. Preferably, one or more fuel streams contain ammonia and / or hydrogen.

[0054] The ammonia feedstock can originate from any source. It can be generated via a catalytic combination of hydrogen and nitrogen, for example, through the Haber-Bosch ammonia synthesis process. Alternatively, the ammonia feedstock can be produced in an ammonia generation facility located upstream of the ammonia cracking reactor. Or, it can be supplied from ammonia storage facilities, ammonia storage units, ammonia storage tanks, or ammonia pipelines.

[0055] The ammonia feed stream may contain 90 mol% or more, 95 mol% or more, 97 mol% or more, or 99 mol% or more. The ammonia feed stream may be substantially 100 mol% ammonia. "Substantially 100 mol% ammonia" means any other component that may be present as an incidental impurity and may be present in amounts less than 1 mol%, less than 0.5 mol%, or less than 0.1 mol% of the ammonia feed stream.

[0056] During normal operation of an ammonia cracking unit, the ammonia feedstock can be heated before being supplied to the inlet of one or more catalyst-containing reaction tubes. During normal operation, the ammonia feedstock can be heated to temperatures greater than 350°C, greater than 400°C, greater than 450°C, greater than 500°C, or greater than 550°C. During normal operation, the ammonia feedstock can be heated to temperatures less than 1000°C, less than 950°C, less than 850°C, less than 750°C, or less than 700°C. For example, the ammonia feedstock can be heated to temperatures 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 or 550°C to 650°C).

[0057] During normal operation of an ammonia cracking unit, the temperature of the cracked gas stream obtained at the outlet of one or more catalyst-containing reaction tubes may be greater than 600°C, greater than 650°C, greater than 670°C, greater than 690°C, or greater than 700°C. During normal operation of the ammonia cracking unit, the temperature of the cracked gas stream obtained at the outlet of one or more catalyst-containing reaction tubes may be less than 900°C, less than 850°C, less than 800°C, less than 770°C, or less than 750°C. For example, during normal operation of the ammonia cracking unit, the temperature of the cracked gas stream obtained at the outlet of one or more catalyst-containing reaction tubes may be 600°C to 900°C, 650°C to 850°C, 670°C to 800°C, or 690°C to 770°C, such as 700°C to 750°C.

[0058] During normal operation of the ammonia cracking unit, the pressure at the inlet to one or more reaction tubes containing catalyst will be set by the flow chart design and can be in the range of 1 bar to 100 bar absolute pressure, preferably 10 bar to 90 bar absolute pressure (such as 31 bar to 51 bar absolute pressure).

[0059] Normal operation of an ammonia cracking unit may include the steps of cracking ammonia in an ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2) and optional residual ammonia (e.g., unreacted ammonia, NH3).

[0060] The pyrolysis gas stream may contain 60 mol% or more, 65 mol% or more, 70 mol% or more, 72 mol% or more, or 73 mol% or more of H2. The pyrolysis gas stream may contain up to 75 mol% or less of H2. For example, the pyrolysis gas stream may contain 60 mol% to 75 mol% of H2. Preferably, the pyrolysis gas stream contains 70 mol% to 75 mol% of H2, such as 72 mol% to 75 mol% of H2.

[0061] The pyrolysis gas stream may contain 20 mol% or more, 21 mol% or more, 22 mol% or more, or 23 mol% or more of N2. The pyrolysis gas stream may contain up to 25 mol% or less of N2. For example, the pyrolysis gas stream may contain 20 mol% to 25 mol% of N2. Preferably, the pyrolysis gas stream contains 22 mol% to 25 mol% of N2, such as 23 mol% to 25 mol% of N2.

[0062] The pyrolysis gas stream may contain less than 20 mol% NH3, less than 15 mol% NH3, less than 10 mol% NH3, less than 5 mol% NH3, less than 1 mol% NH3, or less than 0.1 mol% NH3. Preferably, the pyrolysis gas stream contains less than 4 mol% NH3, less than 2 mol% NH3, less than 1 mol% NH3, or less than 0.1 mol% NH3.

[0063] Preferably, the pyrolysis gas stream comprises an equilibrium mixture of ammonia, hydrogen, and nitrogen. In other words, the pyrolysis gas stream preferably comprises ammonia, hydrogen, and nitrogen at partial pressures such that no additional hydrogen and nitrogen are produced from further pyrolysis reactions. The equilibrium mixture may contain 72 mol% to 75 mol% H2, 23 mol% to 25 mol% N2, and less than 4 mol% NH3 (e.g., less than 1 mol% or less than 0.1 mol% NH3).

[0064] Normal operation of an ammonia cracking unit may include the step of obtaining cracked gas from the outlet of one or more catalyst-containing reaction tubes. Typically, the temperature of the cracked gas stream obtained from the outlet of one or more catalyst-containing reaction tubes of the ammonia cracking reactor can be greater than about 600°C, 700°C, 800°C, or 900°C. For example, the temperature of the cracked gas stream obtained from the outlet of one or more catalyst-containing reaction tubes can be in the range of 600°C to 900°C or 700°C to 800°C.

[0065] During normal operation of an ammonia cracking unit, the cracked gas stream can be fed into one or more purification units, such as a pressure swing absorption unit, to generate a hydrogen stream and a tail gas stream.

[0066] The hydrogen stream may contain 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, or 90 mol% or more of H2. The hydrogen stream may contain up to 100 mol% or less of H2. For example, the hydrogen stream may contain 70 mol% to 100 mol% H2, 75 mol% to 100 mol% H2, 80 mol% to 100 mol% H2, 85 mol% to 100 mol% H2, or 90 mol% to 100 mol% H2. Preferably, the hydrogen stream may contain more than 90 mol% H2, more than 95 mol% H2, more than 98 mol% H2, or more than 99 mol% H2. More preferably, the hydrogen stream may contain more than 99.9 mol% H2, more than 99.95 mol% H2, or about 100 mol% H2. Most preferably, the hydrogen-containing stream may contain more than 99.95 mol% H2 or about 100 mol% H2.

[0067] The exhaust gas stream may contain nitrogen (N2), hydrogen (H2), and residual ammonia (e.g., unreacted ammonia, NH3). Typically, the exhaust gas stream may contain 20 mol% to 95 mol% N2, 45 mol% to 85 mol% N2, or 65 mol% to 80 mol% N2. Typically, the exhaust gas stream may contain 10 mol% to 70 mol% H2, such as 20 mol% to 50 mol% H2. Preferably, the exhaust gas stream contains 15 mol% to 40 mol% H2, 20 mol% to 35 mol% H2, or 22 mol% to 30 mol% H2. Typically, the exhaust gas stream may contain 3 mol% to 10 mol% ammonia, 3.2 mol% to 7 mol% ammonia, or 3.3 mol% to 5 mol% ammonia.

[0068] Normal operation of an ammonia cracking unit may include combining the cracked gas stream with an oxygen-containing feed and burning the cracked gas stream together with the oxygen-containing feed to produce a combustible gas stream.

[0069] There are no particular restrictions on the oxygenated feed, and it may suitably be air, oxygen, oxygen-enriched air, a mixture of nitrogen and oxygen, or exhaust gas from a gas turbine (such as that disclosed in WO2024018169A1).

[0070] Normal operation of an ammonia cracking unit may include the step of using a combustion gas stream to drive a gas turbine to generate an oxygen-containing waste gas stream. Therefore, the oxygen-containing waste gas stream is the exhaust gas from the gas turbine.

[0071] When driving a gas turbine, the gas turbine can be used to generate energy, such as electrical energy and / or mechanical energy. The gas turbine can generate energy directly or indirectly. For example, the gas turbine can be connected to any suitable generator for generating electrical energy (i.e., electricity), and / or the gas turbine can be connected to a compressor for generating mechanical energy. Alternatively, the gas turbine can directly generate electrical or mechanical energy.

[0072] The gas turbine used for normal operation of an ammonia cracking unit can be of any suitable type. The cracked gas stream and the oxygen-containing feed stream, which are then combusted to produce combustion, can occur within the gas turbine combustion zone. The gas turbine combustion zone can be integrated within the gas turbine or located outside the gas turbine. Typically, the gas turbine combustion zone is integrated within the gas turbine.

[0073] The method of the first aspect of the invention will now be described in more detail. Generally, the method of the first aspect of the invention can be applied to normally operating ammonia cracking equipment, such as the normally operating equipment described above.

[0074] The method of the first aspect of the present invention includes the step of reducing the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes disposed in the radiant section of an ammonia cracking reactor.

[0075] The flow rate of the ammonia feedstock is reduced to 40% or lower, 35% or lower, 30% or lower, or 25% or lower relative to the ammonia cracking unit's maximum molar hydrogen production of 100%. There is no particular limitation on the lower limit to which the ammonia feedstock flow rate can be reduced, and the flow rate can be 0% or more (e.g., 1% or more, 2% or more, 3% or more, or 5% or more) relative to the ammonia cracking unit's maximum molar hydrogen production. In some methods of the invention, the flow rate of the ammonia feedstock can be terminated. For example, the flow rate of the ammonia feedstock can be reduced to 0% to 40%, 1% to 35%, 2% to 30%, or 5% to 25% of the flow rate at which the ammonia cracking unit produces 100% of the maximum molar hydrogen production.

[0076] As will be understood, the step of reducing the flow rate of the ammonia feedstock can occur in response to a reduction or cessation in the demand for energy and therefore for hydrogen (e.g., hydrogen contained in the cracked gas stream). Such a reduction or cessation may occur during periods of low energy demand. For example, in cases where the energy is electricity generated by, for example, a gas turbine and fed into the household grid, the demand for electricity may decrease at night.

[0077] The first aspect of the invention includes the step of reducing the heat production in the fuel combustion zone of an ammonia cracking reactor.

[0078] The heat output of the fuel combustion zone in an ammonia cracking reactor can be reduced to 5% or more, 8% or more, 10% or more, or 12% or more of the maximum heat output of the fuel combustion zone. The heat output of the fuel combustion zone in an ammonia cracking reactor can be reduced to 40% or less, 35% or less, 30% or less, or 25% or less of the maximum heat output of the fuel combustion zone. For example, the heat output of the fuel combustion zone in an ammonia cracking reactor can be reduced to 5% to 40%, 8% to 35%, 10% to 30%, or 12% to 25% of the maximum heat output of the fuel combustion zone, such as 18%, 20%, or 22% of the maximum heat output of the fuel combustion zone.

[0079] The heat output of the fuel combustion zone in an ammonia cracking reactor can be reduced so that the temperature of the cracked gas stream at the outlet of one or more catalyst-containing reaction tubes can be greater than 600°C, greater than 650°C, greater than 670°C, greater than 690°C, or greater than 700°C. Alternatively, the heat output of the fuel combustion zone in an ammonia cracking reactor can be reduced so that the temperature of the cracked gas stream at the outlet of one or more catalyst-containing reaction tubes can be less than 900°C, less than 850°C, less than 800°C, less than 770°C, or less than 750°C. For example, the heat output of the fuel combustion zone in an ammonia cracking reactor can be reduced so that the temperature of the cracked gas stream at the outlet of one or more catalyst-containing reaction tubes can be 600°C to 900°C, 650°C to 850°C, 670°C to 800°C, or 690°C to 770°C, such as 700°C to 750°C. The temperature of the recirculated cracked gas can be the temperature of the cracked gas obtained from the outlet of one or more catalyst-containing reaction tubes.

[0080] As those skilled in the art will understand, in the method of the first aspect of the invention, one or more fuel streams fed into the fuel combustion zone of the ammonia cracking reactor may be the same as or different from those fuel streams used when the ammonia cracking unit is in normal operation. For example, in the method of the first aspect of the invention, it may be advantageous for one or more fuel streams supplied to the fuel combustion zone to contain methane, especially when the ammonia cracking unit is in normal operation, (for example) when one or more fuel streams contain ammonia and / or hydrogen. Therefore, the method of the first aspect of the invention may include the step of supplementing or changing one or more fuel streams fed into the fuel combustion zone.

[0081] The method of the first aspect of the present invention includes the step of obtaining a cracked gas stream from the outlet of one or more reaction tubes containing a catalyst.

[0082] The cracked gas stream can be a cracked gas stream with the composition defined above for normal operation of an ammonia cracking unit.

[0083] The temperature of the cracked gas stream obtained from the outlet of one or more catalyst-containing reaction tubes can be greater than 600°C, greater than 650°C, greater than 670°C, greater than 690°C, or greater than 700°C. The temperature of the cracked gas stream obtained from the outlet of one or more catalyst-containing reaction tubes can be 900°C, less than 850°C, less than 800°C, less than 770°C, or less than 750°C. For example, the temperature of the cracked gas stream obtained from the outlet of one or more catalyst-containing reaction tubes can be 600°C to 900°C, 650°C to 850°C, 670°C to 800°C, or 690°C to 770°C, such as 700°C to 750°C.

[0084] The method of the first aspect of the present invention includes the step of cooling the pyrolysis gas flow.

[0085] The pyrolysis gas stream can be cooled to temperatures of 130°C or lower, 120°C or lower, 115°C or lower, or 110°C or lower. The pyrolysis gas stream can also be cooled to temperatures of 20°C or higher, 25°C or higher, 30°C or higher, or 35°C or higher. For example, the pyrolysis gas stream can be cooled to temperatures such as 45°C, 55°C, 65°C, or 75°C, from 20°C to 130°C, 25°C to 120°C, 30°C to 115°C, or 35°C to 110°C.

[0086] The step of cooling the pyrolysis gas stream can be accomplished in many ways. For example, the pyrolysis gas stream can be cooled by exchanging heat with water to generate steam (e.g., medium-pressure steam), and / or the pyrolysis gas stream can be cooled by exchanging heat with one or more process fluids (e.g., cooling water, oxygen-containing streams, and / or one or more fuel streams fed into the fuel combustion zone of the ammonia pyrolysis reactor, and / or the pyrolysis gas stream of step vi of the method of the first aspect of the invention).

[0087] The cracked gas stream is cooled so that its pressure can be increased in subsequent steps. The compressor used to increase the pressure of the hydrogen-containing gas stream (such as the cracked gas stream of this invention) must not exceed the temperature of 135°C as required by API Standard 618.

[0088] The first aspect of the invention includes the step of increasing the pressure of the pyrolysis gas flow.

[0089] The pressure of the cracked gas flow can be increased to 10 bar absolute pressure or higher, 20 bar absolute pressure or higher, 25 bar absolute pressure or higher, or 31 bar absolute pressure or higher. The pressure of the cracked gas flow can also be increased to 100 bar absolute pressure or lower, 90 bar absolute pressure or lower, 70 bar absolute pressure or lower, or 51 bar absolute pressure or lower. For example, the pressure of the cracked gas flow can be increased to 10 to 100 bar absolute pressure, 20 to 90 bar absolute pressure, 25 to 70 bar absolute pressure, or 31 to 51 bar absolute pressure, such as 40 bar absolute pressure or 45 bar absolute pressure.

[0090] The pressure of the pyrolysis gas stream can be increased using any suitable method known in the art. For example, a pump or compressor (such as a reciprocating compressor or a centrifugal compressor) can be used to increase the pressure of the pyrolysis gas.

[0091] The method of the first aspect of the present invention includes the step of heating the pyrolysis gas stream.

[0092] The pyrolysis gas stream can be heated to temperatures of 650°C or higher, 675°C or higher, 690°C or higher, or 700°C or higher. The pyrolysis gas stream can also be heated to temperatures of 900°C or lower, 850°C or lower, 800°C or lower, or 775°C or lower. For example, the pyrolysis gas stream can be heated to temperatures of 650°C to 900°C, 675°C to 850°C, 690°C to 800°C, or 700°C to 775°C (such as 720°C or 750°C).

[0093] The pyrolysis gas stream can be heated to the temperature described in step vi) above in one or more stages. The pyrolysis gas stream can be heated by one or more of the methods described below.

[0094] The pyrolysis gas stream can be heated using steam recovered from the cooling pyrolysis gas stream step. Typically, when the pyrolysis gas stream can be heated using steam recovered from the cooling pyrolysis gas stream step, the pyrolysis gas stream can be heated to a temperature of 100°C to 450°C or 200°C to 300°C (such as 250°C).

[0095] The pyrolysis gas stream can be heated by heat exchange with flue gas from the ammonia pyrolysis reactor. Preferably, the pyrolysis gas stream can be heated by heat exchange with flue gas from the ammonia pyrolysis reactor in the flue of the ammonia pyrolysis reactor. Typically, the pyrolysis gas stream can be heated to temperatures of 350°C to 650°C, 400°C to 600°C, or 450°C to 550°C (such as 500°C) by heat exchange with flue gas from the ammonia pyrolysis reactor.

[0096] As will be understood, the cracked gas stream can be heated by the heat output from the fuel combustion zone, as described above. That is, the cracked gas stream can be heated by the heat output from the fuel combustion zone as it passes through one or more reaction tubes containing a catalyst (e.g., as described in step viii of the method).

[0097] In a preferred method of the first aspect of the invention, an auxiliary heater can be used to heat the pyrolysis gas stream.

[0098] An auxiliary heater can generate heat for heating the pyrolysis gas stream by burning an auxiliary fuel stream with an oxygen-containing feed. The auxiliary fuel stream can be any combustible fuel. For example, the auxiliary fuel stream can be ammonia, hydrogen, and / or hydrocarbon fuels (e.g., methane, ethane, propane, butane, etc.). Preferably, the auxiliary fuel stream can be the same as one or more fuel streams used in the fuel combustion zone of the ammonia pyrolysis reactor. More preferably, one or more fuel streams and the auxiliary fuel stream of the ammonia pyrolysis reactor can contain ammonia.

[0099] The oxygen-containing feed used to assist the combustion of the fuel stream can suitably be air, oxygen, or oxygen-enriched air.

[0100] The auxiliary fuel stream and the combustion of oxygen-containing feed produce auxiliary flue gas.

[0101] Typically, where the auxiliary heater generates heat through the combustion of the auxiliary fuel stream, the pyrolysis gas stream can be heated by heat exchange with the auxiliary flue gas (e.g., convection heating). Alternatively or additionally, the pyrolysis gas stream can be heated by direct heating from the combustion of the auxiliary fuel stream (e.g., radiation heating).

[0102] The auxiliary heater can be any suitable roasting heater known to a technician. The auxiliary heater can be designed to be smaller and simpler than the fuel combustion zone of an ammonia cracking reactor, and can operate with high efficiency at very low loads.

[0103] In cases where the auxiliary heater generates heat through the combustion of the auxiliary fuel stream, the auxiliary heater can be arranged to generate heat in the flue of the ammonia cracking reactor. The auxiliary heater allows the auxiliary fuel stream to combust within the flue of the ammonia cracking reactor.

[0104] Alternatively, the auxiliary heater can be located outside the flue gas duct, and the auxiliary fuel stream can be combusted outside the flue gas duct of the ammonia cracking reactor. Here, the auxiliary heater can provide heat to the cracked gas stream through direct or indirect heat exchange with the auxiliary flue gas. For example, the auxiliary heater can provide heat to the cracked gas stream through direct heat exchange with the auxiliary flue gas via a heat exchanger. For example, the auxiliary heater can indirectly heat the cracked gas stream using an intermediate fluid (e.g., air or steam), wherein the intermediate fluid can be heated through heat exchange with the auxiliary flue gas and / or through direct heating via combustion of the auxiliary fuel stream.

[0105] In a preferred method of the present invention, the auxiliary heater can generate heat for heating the cracked gas stream by combustion of an ammonia-containing auxiliary fuel stream and an oxygen-containing feed, and the auxiliary heater can be arranged in the flue of the ammonia cracking reactor to generate heat.

[0106] It is advantageous for the auxiliary heater to burn an ammonia-containing auxiliary fuel stream. Specifically, it is advantageous for the auxiliary heater to burn an ammonia-containing auxiliary fuel stream, wherein one or more fuel streams burned in the fuel combustion zone of the ammonia cracking reactor include an ammonia-containing fuel stream. This is because any gas treatment system used to treat flue gas from the ammonia cracking reactor can also be used to treat auxiliary flue gas from the auxiliary heater, such as catalytic N2O and NO. x Emission reduction systems and / or afterburners.

[0107] Alternatively or additionally, the auxiliary heater may be an auxiliary electric heater configured to generate heat for heating the cracked gas stream. For example, the auxiliary electric heater may be an induction heater, a microwave heater, or include one or more heating elements configured to generate heat for heating the cracked gas stream. When the auxiliary heater is an auxiliary electric heater, the auxiliary heater may be arranged to heat the cracked gas stream upstream of the inlet of one or more catalyst-containing reaction tubes (e.g., on a process line that feeds the cracked gas stream to the inlet of one or more catalyst-containing reaction tubes outside the ammonia cracking reactor).

[0108] The method of the first aspect of the present invention includes the step of recirculating the pyrolysis gas stream to the inlet of one or more reaction tubes containing a catalyst.

[0109] The cracked gas stream can be recycled at a volumetric flow rate of 70%, 60%, 50%, or 45% or less of the ammonia feed stream relative to the volumetric flow rate of the ammonia feed stream when producing 100% of the maximum molar hydrogen yield of the ammonia cracking unit. The cracked gas stream can also be recycled at a volumetric flow rate of 5%, 10%, 20%, or 30% or greater of the ammonia feed stream relative to the volumetric flow rate of the ammonia feed stream when producing 100% of the maximum molar hydrogen yield of the ammonia cracking unit. For example, the cracked gas stream can be recycled at a volumetric flow rate of 5% to 70%, 10% to 60%, 15% to 50%, or 20% to 45% of the ammonia feed stream relative to the volumetric flow rate of the ammonia feed stream when producing 100% of the maximum molar hydrogen yield of the ammonia cracking unit, such as 30%, 35%, or 40%.

[0110] The method of a first aspect of the present invention includes the step of passing a pyrolysis gas stream through one or more reaction tubes containing a catalyst.

[0111] The step of passing the pyrolysis gas stream through one or more reaction tubes containing the catalyst serves to heat the catalyst within the reaction tubes. In other words, the pyrolysis gas stream acts as a heat transfer fluid to provide heat to the catalyst in the reaction tubes and retain that heat within the catalyst.

[0112] The method of the first aspect of the invention may include repeating or continuing steps iii) to viii) of the method of the first aspect of the invention. The method of the first aspect of the invention may include repeating or continuing steps iii) to viii), including any intermediate steps. The method of the first aspect of the invention may include repeating or continuing steps iii) to viii), and optionally any intermediate steps, until a time, such as when hydrogen demand recovers and the ammonia cracking unit can return to normal operation. Therefore, the method of the first aspect of the invention may include operating steps i) to viii), and repeating or continuing steps iii) to viii). For the avoidance of doubt, "intermediate step" includes any optional and / or preferred steps described herein, which may be performed between obtaining a cracked gas stream from the outlet of one or more catalyst-containing reaction tubes and recirculating the cracked gas stream to the inlet of one or more catalyst-containing reaction tubes.

[0113] The method of the first aspect of the present invention may include the step of removing ammonia from the pyrolysis gas stream.

[0114] Ammonia can be removed from the cracked gas stream by any means known in the art. For example, ammonia can be removed from the cracked gas stream by washing with water in a scrubber, or by adsorption.

[0115] The step of removing ammonia from the cracked gas stream can be suitably performed after the step of cooling the cracked gas stream and before the step of increasing the pressure of the cracked gas stream.

[0116] Advantageously, the step of removing ammonia from the cracked gas stream prevents ammonia from condensing, for example, in the pumping equipment, where condensation could cause damage due to the corrosive nature of ammonia. Furthermore, removing ammonia from the cracked gas stream prevents further endothermic decomposition of ammonia in one or more catalyst-containing reaction tubes, thereby preventing cooling of the one or more catalyst-containing reaction tubes and the catalyst therein.

[0117] In the method of the first aspect of the invention, it may be advantageous for the ammonia cracking unit to generate some cracked gas, which can be used, for example, to power the ammonia cracking unit itself and its associated facilities. Therefore, an additional ammonia feedstock stream can be supplied to the ammonia cracking reactor and cracked therein to supplement the cracked gas that can be removed from the ammonia cracking unit. As will be understood, the amount of ammonia feedstock stream supplied to the ammonia cracking reactor can be reduced to the flow rate described above.

[0118] Therefore, the method of the first aspect of the present invention may include the step of combining an ammonia feed stream with a cracked gas stream. The method of the first aspect of the present invention may include the step of cracking ammonia in the cracked gas stream in one or more reaction tubes containing a catalyst. The method of the first aspect of the present invention may include the step of combining an ammonia feed stream with a cracked gas stream, and cracking ammonia in the cracked gas stream in one or more reaction tubes containing a catalyst. The step of combining the ammonia feed stream with the cracked gas stream may occur before the step of recirculating the cracked gas stream to the inlet of one or more reaction tubes containing a catalyst.

[0119] The method of the first aspect of the invention may include the step of removing a portion of the pyrolysis gas stream. A portion of the pyrolysis gas stream may be removed for further processing steps, such as purification steps (e.g., pressure swing adsorption units), combustion steps that generate thermal energy, or combustion steps that generate electrical energy (e.g., in a gas turbine).

[0120] The method of the first aspect of the present invention may include the step of placing an ammonia cracking unit under low load. An ammonia cracking unit under low load is an ammonia cracking unit that has already operated the method of the first aspect of the present invention. Preferably, an ammonia cracking unit under low load may be an ammonia cracking unit that has already operated steps i) to viii) of the method of the first aspect of the present invention and is repeating or continuing to operate steps iii) to viii) of the method of the first aspect of the present invention. Therefore, the method of the first aspect of the present invention can be a method for controlling an ammonia cracking unit to place it under low load. An ammonia cracking unit under low load may be an ammonia cracking unit in which a majority (e.g., 70% or more, 80% or more, 90% or more, or 95% or more, e.g., up to 100%) of the cracked gas obtained from the outlet of one or more catalyst-containing reaction tubes is recycled to the inlet of one or more catalyst-containing reaction tubes.

[0121] In a second aspect of the invention, an ammonia cracking apparatus under low load conditions is provided.

[0122] The ammonia cracking unit under low load is an ammonia cracking unit that has already operated the method of the first aspect of the present invention. An ammonia cracking unit under low load may be an ammonia cracking unit that has already operated steps i) to viii) of the method of the first aspect of the present invention and is repeating or continuing to operate steps iii) to viii) of the method of the first aspect of the present invention. Therefore, the features already described with respect to the method of the first aspect of the present invention can be incorporated into the system of the second aspect of the present invention.

[0123] Ammonia cracking equipment under low load conditions can be configured as follows:

[0124] i) Reduce the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of the ammonia cracking reactor;

[0125] ii) Reduce the heat output of the fuel combustion zone in the ammonia cracking reactor;

[0126] iii) Obtain the cracked gas stream from the outlet of one or more reaction tubes containing catalyst;

[0127] iv) Cooling the pyrolysis gas stream;

[0128] v) Increase the pressure of the pyrolysis gas flow;

[0129] vi) Heating the pyrolysis gas stream;

[0130] vii) Recirculate the pyrolysis gas stream to the inlet of one or more reaction tubes containing catalyst; and

[0131] viii) Pass the pyrolysis gas stream through one or more reaction tubes containing a catalyst.

[0132] The ammonia cracking unit under low load conditions of the second aspect of the invention can be configured to perform steps i) and ii) and repeat or continue the operation of steps iii) to viii) above. For example, the ammonia cracking unit under low load conditions can be configured to perform steps i) and ii) and repeat or continue the operation of steps iii) to viii) to maintain the ammonia cracking unit under low load conditions. The ammonia cracking unit under low load conditions can optionally be configured to perform any intermediate step of the method of the first aspect of the invention. The ammonia cracking unit under low load conditions can be an ammonia cracking unit in which a majority (e.g., 70% or more, 80% or more, 90% or more, or 95% or more, e.g., up to 100%) of the cracked gas obtained from the outlet of one or more catalyst-containing reaction tubes is recycled to the inlet of one or more catalyst-containing reaction tubes.

[0133] In a third aspect of the invention, a method is provided for returning an ammonia cracking unit from a low-load state according to a second aspect of the invention to a normal operating state.

[0134] The method of the third aspect of the invention can be carried out by increasing (e.g., gradually increasing) the ammonia feed stream entering one or more reaction tubes containing a catalyst.

[0135] As will be understood, increasing the ammonia feedstock flow will cause the endothermic cracking of ammonia in one or more catalyst-containing reaction tubes to restart, producing cracked gas. Therefore:

[0136] • Heat energy will be absorbed from the catalyst in one or more catalyst-containing reaction tubes; and

[0137] • The amount of gas (e.g., number of gas moles or gas pressure) will increase in this method.

[0138] To compensate for the heat absorption, the fuel combustion zone must increase its heat output to maintain the temperature of one or more catalyst-containing reaction tubes and support the pyrolysis reaction. To compensate for the increased amount of gas in this method, pyrolysis gas can be removed from the method.

[0139] Therefore, the method of the third aspect of the present invention can be considered as bringing the ammonia cracking unit back from a low-load state to a normal operating state by balancing i) the rate of reintroducing the ammonia feedstock flow, ii) the rate of removing the cracked gas flow, and iii) the amount of heat introduced in the method.

[0140] Therefore, the method of the third aspect of the present invention for returning an ammonia cracking unit from a low-load state according to the second aspect of the invention to a normal operating state includes the following steps:

[0141] i) Increase the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located within the radiant section of the ammonia cracking reactor; and

[0142] ii) Increase the heat output of the fuel combustion zone in the ammonia cracking reactor;

[0143] iii) Cracking the ammonia in the ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2), and residual ammonia (NH3); and

[0144] iv) Obtain the cracked gas stream from the outlet of one or more reaction tubes containing catalyst.

[0145] The step of increasing the flow rate of the ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes can be carried out by incrementally increasing the flow rate of the ammonia feedstock. For example, it is preferable that the flow rate of the ammonia feedstock is 0% to 5% per minute relative to the flow rate of the ammonia feedstock when the ammonia cracking unit produces 100% of the maximum molar hydrogen production, such as 1% to 4% or 2% to 3% per minute relative to the flow rate of the ammonia feedstock when the ammonia cracking unit produces 100% of the maximum molar hydrogen production.

[0146] The heat output of the fuel combustion zone of the ammonia cracking reactor can be increased to sustain the cracking reaction. Based on one or more of the conditions described above for normal operation of the ammonia cracking unit, the heat output of the fuel combustion zone of the ammonia cracking reactor can be increased to maintain the ammonia cracking unit in normal operating condition. For example, the heat output of the fuel combustion zone of the ammonia cracking reactor can be increased to maintain the temperature of one or more catalyst-containing reaction tubes at 600°C to 850°C, 620°C to 830°C, 650°C to 810°C, or 680°C to 790°C, 700°C to 780°C, or 720°C to 770°C, such as 730°C, 740°C, 750°C, or 760°C, as measured at the outlet of one or more reaction tubes. For example, the heat output of the fuel combustion zone of an ammonia cracking reactor can be increased to maintain the temperature of the cracked gas stream at the outlet of one or more catalyst-containing reaction tubes at 600°C to 900°C, 650°C to 850°C, 670°C to 800°C, or 690°C to 770°C, such as 700°C to 750°C.

[0147] In a preferred method of the third aspect of the invention, the steps of increasing the flow rate of the ammonia feedstock and increasing the heat output of the fuel combustion zone can be performed simultaneously.

[0148] The method of a third aspect of the invention may include recirculating a portion of the cracked gas stream to the inlet of one or more reaction tubes containing a catalyst and passing that portion of the cracked gas stream through one or more reaction tubes containing a catalyst.

[0149] The method of a third aspect of the invention may include the step of removing a portion of the pyrolysis gas stream. A portion of the pyrolysis gas stream may be removed for further processing steps, such as purification (e.g., a pressure swing adsorption unit), flame processing, thermal combustion, or electrical combustion (e.g., in a gas turbine).

[0150] The amount of cracked gas removed in the step of removing a portion of the cracked gas flow can be determined by the flow rate (e.g., velocity) of the ammonia feedstock to the inlet of one or more catalyst-containing tubes, for example, by maintaining the pressure at the inlet of one or more catalyst-containing reaction tubes at an absolute pressure of 1 bar to 100 bar, preferably 10 bar to 90 bar, such as 31 bar to 51 bar.

[0151] The method of the third aspect of the present invention may include the step of reducing the recirculation flow rate of the cracked gas stream to the inlet of one or more catalyst-containing reaction tubes or terminating the recirculation, so as to bring the ammonia cracking unit into normal operating condition.

[0152] In a preferred method according to a third aspect of the present invention, the method may include the following steps:

[0153] i) Increase the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located within the radiant section of the ammonia cracking reactor; and

[0154] ii) Increase the heat output of the fuel combustion zone in the ammonia cracking reactor;

[0155] iii) Cracking the ammonia in the ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2) and residual ammonia (NH3);

[0156] iv) Obtain the cracked gas stream from the outlet of one or more reaction tubes containing catalyst;

[0157] v) Recirculate a portion of the cracked gas flow to the inlet of one or more catalyst-containing reaction tubes and pass that portion of the cracked gas flow through one or more catalyst-containing reaction tubes;

[0158] vi) Remove a portion of the split gas flow; and

[0159] vii) Once the ammonia cracking unit has returned to normal operation, reduce the recirculation rate of the cracked gas flow to the inlet of one or more catalyst-containing reaction tubes or terminate the recirculation.

[0160]

[0161] Figure 2 A process flow diagram is shown of an ammonia cracking unit operating according to the method of the first aspect of the invention and an ammonia cracking unit operating at low load according to the second aspect of the invention.

[0162] Herein is provided an ammonia cracking reactor (1) having one or more catalyst-containing reaction tubes disposed in a radiant section. The one or more catalyst-containing reaction tubes have inlets and outlets. The flow rate of the ammonia feedstock stream (11) to the inlet of the one or more catalyst-containing reaction tubes of the ammonia cracking reactor (1) is reduced. The heat production of the fuel combustion zone of the ammonia cracking reactor (1) is reduced by decreasing the amount of fuel stream (21) supplied to the fuel combustion zone. A cracked gas stream (101) is obtained from the outlet of the one or more catalyst-containing reaction tubes of the ammonia cracking reactor (1). The cracked gas stream (101) is cooled, for example, by heat exchange with water to generate steam (2), and the cooled cracked gas stream (102) is passed to a pump or compressor (3), where the pressure of the cracked gas stream is increased. The increased pressure of the cracked gas stream (103) is heated, for example, using an auxiliary heater (4). Optionally, the cracked gas stream (104) is combined with the ammonia feedstock stream (11). The heated cracked gas stream (104) is recirculated to the inlet of the one or more catalyst-containing reaction tubes of the ammonia cracking reactor (1) and passed through the one or more catalyst-containing reaction tubes. Optionally, any ammonia in the cracked gas stream fed into the ammonia cracking reactor (1) is cracked in one or more reaction tubes containing catalyst. Optionally, a portion of the cracked gas stream can be removed (105) and passed to further processing steps, such as generating electricity by combustion to drive a gas turbine. The ammonia cracking unit under low load conditions repeats or continues to operate the following steps: obtaining the cracked gas stream (101), cooling it (2), increasing its pressure (3), heating it (4), recirculating it, and passing it through one or more reaction tubes containing catalyst. In this case, the ammonia cracking unit retains the necessary heat to allow the ammonia cracking unit to return to normal operation within a 2-hour notification period without consuming ammonia feedstock or wasting hydrogen products.

Claims

1. A method for controlling an ammonia cracking device including a roasting ammonia cracking reactor, the method comprising the following steps: i) Reduce the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of the ammonia cracking reactor; ii) Reduce the heat output of the fuel combustion zone in the ammonia cracking reactor; iii) Obtain the cracked gas stream from the outlet of the one or more catalyst-containing reaction tubes; iv) Cool the pyrolysis gas stream; v) Increase the pressure of the pyrolysis gas flow; vi) Heating the pyrolysis gas stream; vii) Recirculate the pyrolysis gas stream to the inlet of the one or more catalyst-containing reaction tubes; as well as viii) The pyrolysis gas stream is passed through one or more reaction tubes containing catalyst.

2. The method according to claim 1, wherein the flow rate of the ammonia feedstock is reduced to 0% to 40%, 1% to 35%, 2% to 30%, or 5% to 25% of the flow rate of the ammonia feedstock when the ammonia cracking equipment produces 100% of the maximum molar hydrogen production.

3. The method according to claim 1 or claim 2, wherein the heat output of the fuel combustion zone of the ammonia cracking reactor is reduced to 5% to 40%, 8% to 35%, 10% to 30%, or 12% to 25% of the maximum heat output of the fuel combustion zone.

4. The method according to any one of the preceding claims, wherein the heat output of the fuel combustion zone of the ammonia cracking reactor is reduced such that the temperature of the cracked gas stream at the outlet of the one or more catalyst-containing reaction tubes is 600°C to 900°C, 650°C to 850°C, 670°C to 800°C, or 690°C to 770°C.

5. The method according to any one of the preceding claims, wherein the pyrolysis gas stream comprises a balanced mixture of ammonia, hydrogen and nitrogen.

6. The method according to any one of the preceding claims, wherein the temperature of the pyrolysis gas stream obtained from the outlet of the one or more catalyst-containing reaction tubes is 600°C to 900°C, 650°C to 850°C, 670°C to 800°C, or 690°C to 770°C.

7. The method according to any one of the preceding claims, wherein the pyrolysis gas stream is cooled to a temperature of 20°C to 130°C, 25°C to 120°C, 30°C to 115°C, or 35°C to 110°C.

8. The method according to any one of the preceding claims, wherein the pressure of the pyrolysis gas flow is increased to 10 to 100 bar absolute pressure, 20 to 90 bar absolute pressure, 25 to 70 bar absolute pressure, or 31 to 51 bar absolute pressure.

9. The method according to any one of the preceding claims, wherein the pyrolysis gas stream is heated to a temperature of 650°C to 900°C, 675°C to 850°C, 690°C to 800°C, or 700°C to 775°C.

10. The method according to any one of the preceding claims, wherein the pyrolysis gas stream is heated in one or more stages in step vi).

11. The method according to any one of the preceding claims, wherein the pyrolysis gas stream is heated using steam recovered from the step of cooling the pyrolysis gas stream, flue gas from the ammonia pyrolysis reactor, heat output from the fuel combustion zone of the ammonia pyrolysis reactor, and / or using an auxiliary heater.

12. The method of claim 11, wherein an auxiliary heater is used to heat the pyrolysis gas stream and the auxiliary heater generates heat for heating the pyrolysis gas stream through combustion of an ammonia-containing auxiliary fuel stream with an oxygen-containing feed.

13. The method according to any one of the preceding claims, wherein the cracked gas stream is recirculated at a volumetric flow rate of 5% to 70%, 10% to 60%, 15% to 50%, or 20% to 45% of the volumetric flow rate of the ammonia feed stream relative to the maximum molar hydrogen production of the ammonia cracking unit.

14. The method according to any one of the preceding claims, wherein the method comprises repeating steps iii) to viii).

15. The method according to any one of the preceding claims, the method further comprising the step of removing ammonia from the pyrolysis gas stream.

16. The method according to any one of the preceding claims, the method further comprising the step of combining the ammonia feed stream with the cracked gas stream.

17. The method according to any one of the preceding claims, the method further comprising the step of cracking ammonia in the cracked gas stream in the one or more reaction tubes containing a catalyst.

18. The method according to any one of the preceding claims, the method further comprising the step of removing a portion of the ruptured gas flow.

19. The method according to any one of the preceding claims, wherein the method includes the step of placing the ammonia cracking equipment under low load.

20. An ammonia cracking unit under low load conditions, wherein the ammonia cracking unit has been operated according to the method of any one of claims 1 to 19.

21. The ammonia cracking apparatus according to claim 20, wherein the ammonia cracking apparatus has been operated from step i) to step viii) and is repeating or continuing to operate from step iii) to step viii) according to any one of claims 1 to 19).

22. An ammonia cracking unit in a low-load state, wherein the ammonia cracking unit in the low-load state is configured to: i) Reduce the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of the ammonia cracking reactor. ii) Reduce the heat output of the fuel combustion zone in the ammonia cracking reactor; iii) Obtain the cracked gas stream from the outlet of the one or more catalyst-containing reaction tubes; iv) Cool the pyrolysis gas stream; v) Increase the pressure of the pyrolysis gas flow; vi) Heating the pyrolysis gas stream; vii) Recirculate the pyrolysis gas stream to the inlet of the one or more catalyst-containing reaction tubes; as well as viii) The pyrolysis gas stream is passed through one or more reaction tubes containing catalyst.

23. A method for returning an ammonia cracking unit from a low-load state according to any one of claims 20 to 22 to a normal operating state.

24. The method of claim 23, wherein the method comprises the following steps: i) Increase the flow rate of ammonia feedstock to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of the ammonia cracking reactor; as well as ii) Increase the heat output of the fuel combustion zone in the ammonia cracking reactor; iii) Cracking the ammonia in the ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2), and residual ammonia (NH3); and iv) Obtain the cracked gas stream from the outlet of the one or more catalyst-containing reaction tubes.

25. The method of claim 24, wherein the method comprises further steps: v) Recirculate a portion of the pyrolysis gas flow to the inlet of the one or more catalyst-containing reaction tubes and pass the portion of the pyrolysis gas flow through the one or more catalyst-containing reaction tubes; vi) Remove a portion of the ruptured gas flow; as well as vii) Reduce the recirculation rate of the cracked gas flow to the inlet of the one or more catalyst-containing reaction tubes or terminate the recirculation to bring the ammonia cracking unit into the normal operating state.

26. The method according to any one of claims 23 to 25, wherein the normal operation of the ammonia cracking equipment comprises the following steps: a) Provide an ammonia feedstock stream to the inlet of one or more catalyst-containing reaction tubes located in the radiant section of a roasting ammonia cracking reactor; b) Cracking the ammonia in the ammonia feed stream to produce a cracked gas stream containing hydrogen (H2), nitrogen (N2), and residual ammonia (NH3); and c) Obtain the cracked gas stream from the outlet of the one or more catalyst-containing reaction tubes.

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