Process and apparatus for decomposing ammonia

Abstract

To provide a process and an apparatus for cracking ammonia.SOLUTION: The invention concerns a process and apparatus for cracking ammonia in which heated ammonia gas at a super-atmospheric pressure is partially cracked catalytically in an adiabatic reaction unit so as to produce partially cracked ammonia gas, which is heated and fed to catalyst-containing reactor tubes in a furnace so as to cause cracking of further ammonia and produce cracked gas comprising hydrogen gas, nitrogen gas and residual ammonia gas. At least some, preferably all, of a duty required to heat the partially cracked ammonia gas is provided by heat exchange with the cracked gas, enabling more efficient heat integration within the process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of ammonia decomposition for hydrogen production, and more specifically to a process and apparatus for producing hydrogen gas from liquid ammonia. [Background technology]

[0002] Global interest in renewable energy, and the use of this renewable energy to generate "green" hydrogen, is increasing interest in converting "green" hydrogen to "green" ammonia, as ammonia is easier to transport over distances of hundreds or thousands of miles. In particular, while the transport of liquid hydrogen is not currently commercially feasible, the transport of ammonia in liquid form is currently being practiced.

[0003] When used in commercially available fuel cells, ammonia must be converted to hydrogen through a reaction.

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[0004] The process is known as decomposition (or sometimes "dissociation") and is often carried out via a catalyst. The resulting gas (or "decomposed gas") is a mixture of hydrogen (H2) and nitrogen (N2) gases, although some residual ammonia is also present because the decomposition reaction is an equilibrium reaction. Generally referred to as "ammonia slip," the amount of ammonia in the decomposed gas can change by altering the temperature and pressure, as ammonia decomposes at higher temperatures and pressures that facilitate the conversion, thereby reducing ammonia slip.

[0005] In most applications of current cracking equipment, the mixture of hydrogen and nitrogen is used as is. However, since ammonia can be harmful to fuel cells, this flow can be used directly in fuel cells after the ammonia has been suitably removed, such as by washing with water. However, when hydrogen is used in vehicle fuel supply, the presence of nitrogen imposes a penalty on the process. The fuel to the vehicle's fuel supply system is compressed to a significant pressure of up to 900 bar. This means that the nitrogen, which is merely a diluent in the process, is also compressed, requiring power, storage space, increasing anode gas purging requirements, and reducing efficiency. Therefore, when hydrogen is used in vehicle fuel supply, it is beneficial to separate the hydrogen and nitrogen.

[0006] In the field of this technology, there are many examples of ammonia decomposition processes, such as GB977830A, JP5330802A, CN111957270A, US2020 / 0398240A, and KR2022 / 0085469A.

[0007] In addition, GB1142941A discloses a process for producing a fuel gas interchangeable with city gas. Ammonia is decomposed to form a mixture of hydrogen and nitrogen, which is then concentrated by adding a gas having a higher calorific value than the mixture, such as methane, propane, or butane, or a mixture thereof. The liquid ammonia is pumped as a low-temperature liquid and vaporized by a closed hot water circuit. The vaporized ammonia gas is superheated by heat exchange with flue gas from the furnace and then decomposed on a suitable catalyst in the tubes of a direct combustion tubular furnace. The decomposed gas is washed with water to recover residual ammonia and is finally recycled from the ammonia supply to the furnace catalyst-filled tubes. The purified, decomposed gas is concentrated with propane and / or butane to produce a city gas product.

[0008] GB1142941A discloses that the decomposition of ammonia in a direct combustion tubular furnace in the presence of a suitable catalyst is preferred. However, the reference also discloses that other decomposition processes can be used instead. In this context, GB1142941 refers to heating ammonia to a suitable temperature, then passing the ammonia through an unheated bed of an ammonia decomposition catalyst to decompose some of the ammonia into hydrogen and nitrogen, and cooling the gas during the process. The unconverted ammonia can be recovered as described above. Alternatively, the gas mixture can be reheated and passed through a second bed of the catalyst to further reduce the ammonia content, and this can be repeated as many times as desired.

[0009] GB1353751A discloses a two-step decomposition process in which ammonia at a pressure in the range of 20 atm to 300 atm is decomposed in a heated reactor tube. In the first step, a gas at a temperature in the range of 450 to 800°C is passed through a layer of nickel, iron, or cobalt-containing catalyst produced by co-precipitating with a support of aluminum oxide and magnesium oxide or magnesium-aluminum spinel. Alternatively, the catalyst in the first step may consist of either an iron-impregnated ceramic material or iron impregnated with potassium oxide on a pre-formed support of magnesium oxide and aluminum oxide. Following the first step, the gas then passes through a layer of double or triple-promoted iron catalyst, forming the second step, at a temperature in the range of 450 to 600°C.

[0010] WO2022 / 189560A discloses an ammonia decomposition process involving a combustion reactor having tubes filled with an iron catalyst. Liquid ammonia is taken from a storage section, pumped, preheated, and evaporated to form ammonia gas, which is heated by heat exchange with the decomposed gas. The heated ammonia gas is further heated by heat exchange with the flue gas in the convection section of the combustion reactor and is then supplied to two series adiabatic reactors where it is partially decomposed (with interstage heating of the flue gas). The partially decomposed gas is then heated by heat exchange with the flue gas in the convection section and is subsequently supplied to the catalyst-filled tubes of the combustion reactor to decompose the remaining ammonia.

[0011] US11287089A discloses a hydrogen fuel supply system in which ammonia is decomposed in-situ into hydrogen and nitrogen in an ammonia cracker operating at pressures in the range of 5 bar to 40 bar, and the hydrogen is compressed to a pressure of at least 30 MPa (300 bar) and stored ready for distribution to vehicles. When distributed, the compressed gas from the storage unit is cooled to a temperature in the range of -40°C to 5°C by heat exchange with a heat exchange fluid such as D-limonene, FP40, or a water / glycol mixture circulating around a closed loop. The heat exchange fluid is cooled by heat exchange with the ammonia supply to the cracker and may be further cooled in a conventional cooling system. If the ammonia supply is liquid, at least a portion of the duty cycle required to vaporize the liquid ammonia is provided by the heat exchange fluid. Vaporization of liquid ammonia is often brought about at standard or near-atmospheric pressure. US11287089A illustrates a system that produces 7.5 tons / day of hydrogen gas.

[0012] However, there is still a need for improved processes for hydrogen production from ammonia, specifically processes that are more efficient in terms of energy consumption and / or processes that have a higher level of hydrogen recovery and / or processes that reduce or eliminate the need to burn fossil fuels. [Overview of the project]

[0013] According to a first aspect of the present invention, a process for decomposing ammonia is provided, comprising: providing heated ammonia gas at ultra-atmospheric pressure; partially decomposing the heated ammonia gas in an adiabatic reaction unit having at least one catalyst bed to produce partially decomposed ammonia gas; heating the partially decomposed ammonia gas to produce heated partially decomposed ammonia gas; burning fuel with an oxidizing gas in a furnace to heat a reactor tube containing a catalyst to produce flue gas; and supplying the heated partially decomposed ammonia gas to a reactor tube containing a catalyst to bring about further decomposition of ammonia to produce decomposed gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, wherein at least a portion of the duty cycle required to heat the partially decomposed ammonia gas is provided by heat exchange with the decomposed gas.

[0014] More than half of the duty cycle required to heat the partially decomposed ammonia gas to the feed temperature of the catalyst-filled reactor tube, i.e., more than 50% of the duty cycle, such as at least 75% or at least 90%, is typically provided by heat exchange with the decomposed gas. In a preferred embodiment, all of this heating duty is provided in this manner.

[0015] Partially decomposing ammonia in an adiabatic reaction unit containing at least one ammonia decomposition catalyst bed before completing the decomposition process in the catalyst-filled tubes of the combustion furnace provides an opportunity to optimize the decomposition process by fully utilizing the thermal energy in the decomposed gas and flue gas, resulting in reduced energy consumption, increased hydrogen production, and / or reduced reliance on hydrocarbon fuels such as natural gas.

[0016] Specifically, the inventors recognize that using decomposed gas, particularly decomposed gas taken directly from the outlet of a tube in the furnace, i.e., "hot" decomposed gas, rather than flue gas for heating the supply of partially decomposed ammonia gas to the combustion reactor, means that more heat is available in the flue gas elsewhere in the process, for example, for interstage heating between multiple adiabatic reactor vessels supplied in series within an adiabatic reaction unit, thereby enabling the use of higher temperatures for the adiabatic decomposition reaction and providing a more overall duty that can be transferred to the supply ammonia or partially decomposed ammonia between stages of the adiabatic reactor, thus enabling increased ammonia conversion and more efficient use of heat available in the process. High-temperature decomposed gas can thus be used to heat partially decomposed ammonia to a temperature close to the temperature of the high-temperature decomposed gas.

[0017] Several factors influence the carbon intensity of a decomposition process, two of which are the amount of ammonia that can pass through the decomposition unit, and the nature of the fuel burned in the decomposition unit, specifically whether and, if so, how much hydrocarbons such as natural gas are used. The inventors have found that, given a given amount of ammonia slip and a given recovery of hydrogen from the decomposed gas (e.g., PSA recovery), the overall carbon intensity of the process can be reduced if hot decomposed gas (not flue gas) is used to leave the reactor tube to provide at least a portion of the duty cycle required to heat the partially decomposed gas to the supply temperature of the decomposition unit.

[0018] According to a second aspect of the present invention, there is provided an apparatus for decomposing ammonia, for example, an ammonia decomposition system or plant, which is a heat-insulated reaction unit for partially decomposing superatmospheric-pressure heated ammonia gas, the unit comprising at least one catalyst bed having an inlet for the heated ammonia gas, an upstream end in fluid flow communication with the inlet, and a downstream end in fluid flow communication with an outlet for the partially decomposed ammonia gas, a heat-insulated reaction unit, at least one inlet for fuel and oxidant gas in fluid flow communication with at least one burner, a reactor tube comprising a catalyst having an upstream end in fluid flow communication with the outlet of the heat-insulated reaction unit and a downstream end in fluid flow communication with an outlet for the decomposed gas, a furnace, a convection section in fluid flow communication with the radiation section and having an outlet for flue gas, the apparatus comprising a heat exchanger arranged to heat the partially decomposed ammonia gas by heat exchange with the decomposed gas located between the heat-insulated reaction unit and the radiation section of the furnace.

[0019] The apparatus according to the second aspect of the present invention is suitable for carrying out the process according to the first aspect of the present invention.

Brief Description of the Drawings

[0020] [Figure 1] It is a simplified flow sheet relating to an embodiment of the present invention.

Embodiments of the Invention

[0021] Unless otherwise specified, the amounts of components given in parts per million (or ppm) are calculated by weight. In addition, unless otherwise specified, all percentages are calculated by mole. Further, any reference to pressure is, unless otherwise specified, a reference to absolute pressure.

[0022] In the context of the present invention, the activity of a catalyst is understood to refer to the conversion rate of ammonia at a given partial pressure over a given amount of catalyst over a given period at a specific temperature and overall pressure. The unit used to define the activity of a heterogeneous catalyst is the number of moles of ammonia converted per gram (or mole g -1 per second - 1) of the catalyst (including the substrate if present).

[0023] The expression "in fluid flow communication" is understood to mean that a pipe or other suitable conduit is used to convey fluid from one designated location to another. During passage between the two locations, the fluid can flow through one or more other units (e.g., a catalytic reactor) that are designed and / or arranged to change the composition of the fluid through physical conditions of the fluid, such as the temperature of the fluid (e.g., a heat exchanger) and / or pressure (e.g., a compressor or pump), or reactions of components within the fluid. The expression "in direct fluid flow communication" is understood to mean that the fluid flows directly from one location to the other, i.e., it does not flow through another such unit during its passage, and thus there is essentially no change in the composition or physical conditions of the fluid.

[0024] The term "superatmospheric pressure" is understood to mean a pressure significantly higher than atmospheric pressure, such as at least 5 bar, for example at least 10 bar, or at least 20 bar or at least 30 bar. Typically, the pressure is 60 bar or less.

[0025] The term "upstream" is understood to mean the direction opposite to the flow of the fluid during normal operation. The term "downstream" is interpreted accordingly.

[0026] The heated ammonia gas supply of the present invention typically originates from liquid ammonia that can be supplied at ambient pressure from either a pipeline or, more typically, a refrigerated storage tank. Water is often added to the ammonia to prevent stress corrosion cracking in storage tanks, trucks, and vessels used for ammonia transport. The presence of water in the supply ammonia transforms the supply into a multi-component flow, and the evaporation of the supply flow will then require a higher temperature to achieve complete evaporation.

[0027] Typical compositions for ammonia supply are shown in Table 1. Table 1 [Table 1]

[0028] Oil may be present in the ammonia in local storage tanks, production sites, or any other storage tanks in between, due to the boil-off gas compressor used for ammonia storage. The presence of oil is problematic because it poses a risk of blockage and / or contamination. This can lead to poor performance of heat exchangers or reduced catalytic activity in reactors. Therefore, if present, oil may need to be removed by some means. In this regard, oil can be removed by passing liquid ammonia through a bed of activated carbon. However, in preferred embodiments, the catalyst used in the adiabatic reaction unit decomposes the oil into short-chain hydrocarbons, which can react with any water present to form carbon monoxide, hydrogen, and methane.

[0029] Inert gases are not expected to pose a problem, except for the potential for hydrogen to be produced. In this regard, helium can be present in ammonia derived from natural gas, but ammonia derived from renewable hydrogen does not contain helium.

[0030] Liquid ammonia is typically drawn from storage and pumped to a pressure ranging from approximately 5 bar to 60 bar, e.g., approximately 10 bar to 30 bar, or 40 bar to 50 bar. The temperature of the liquid ammonia increases slightly from the storage temperature (e.g., approximately -34°C) to approximately -32°C. When liquid ammonia is drawn from a pipeline, its temperature is often higher, e.g., approximately +10°C.

[0031] The pumped (superatmospheric pressure) liquid ammonia is then preheated, ideally, to its boiling point by appropriate thermal integration within the process. Preferably, part of the preheating is achieved using a heat transfer circuit, where heat from the intercooling and postcooling of the PSA off-gas compressor is optionally recovered along with heat from the flue gas and / or decomposed gas using a heat transfer fluid such as an aqueous glycol solution, e.g., an aqueous glycol solution containing about 50% to about 60% by weight of ethylene glycol or propylene glycol, and used to preheat the liquid ammonia. If such integration is not possible, such as when the compressor is not running, heat from an external source, such as an electric heater, may be required to preheat the ammonia.

[0032] Preheated liquid ammonia is typically then evaporated, and the resulting ammonia gas is further heated before being supplied to the adiabatic reaction unit. In this regard, the ammonia gas is typically superheated, i.e., heated to a temperature above its boiling point, above 350°C, to ensure a useful reaction rate in the adiabatic reaction unit.

[0033] The duty for evaporation and further heating of the preheated liquid ammonia can be provided by heat exchange with decomposed gas, flue gas, or a combination of both decomposed gas and flue gas. In a preferred embodiment, decomposed gas is used to heat and evaporate the preheated liquid ammonia by heat exchange, and the ammonia gas is then further heated by heat exchange with flue gas.

[0034] The use of an adiabatic reaction unit allows some of the ammonia to decompose before it enters the reactor tubes filled with the catalyst in the furnace. The mole fraction of ammonia in the gas passing through the adiabatic reaction unit is typically reduced by at least 20%, e.g., at least 25%, or at least 30%, or even further by at least 35%, e.g., about 40%, and possibly up to about 50%. In other words, the mole fraction of ammonia can be reduced from 1 (or nearly 1) in heated ammonia gas to an amount in the range of about 0.5 to about 0.8, or in the range of about 0.5 to about 0.7, or in the range of about 0.55 to about 0.65, or in the range of about 0.58 to about 0.62, e.g., about 0.6, in partially decomposed ammonia gas.

[0035] Adiabatic reaction units are incorporated into the process design to improve overall efficiency, specifically by utilizing the heat available in the flue gas to provide heat for the adiabatic decomposition process within the unit. In this regard, the temperature around the adiabatic reaction unit is typically optimized to maximize heat recovery from the flue gas while avoiding temperatures above approximately 660°C due to material concerns.

[0036] The primary design parameter for an adiabatic reaction unit is the inlet temperature. Higher inlet temperatures allow for greater conversion within the unit because the ammonia decomposition reaction is endothermic. However, higher temperatures place greater demands on the building materials and catalysts. Inlet temperatures are typically in the range of approximately 350°C to 800°C, and can be in the range of approximately 400°C to 600°C or approximately 400°C to 450°C for lower temperature cycles. For higher temperature cycles, inlet temperatures can be in the range of approximately 500°C to 700°C or approximately 550°C to 650°C.

[0037] An adiabatic reaction unit comprises one or more adiabatic reactors, each of which comprises a catalyst bed. In a preferred embodiment, the adiabatic reaction unit comprises two or more adiabatic reactors, for example, two, three, four, five, or six reactors, with interstage heating as necessary. The reactors may be arranged in series, in parallel, or in a combination of series and parallel, depending on the requirements of the process. However, in a preferred embodiment, the adiabatic reaction unit preferably has two such reactors arranged in series with interstage heating of intermediate partially decomposed ammonia gas by heat exchange with the decomposed gas and / or flue gas.

[0038] Each adiabatic reactor has a bed containing at least one catalyst suitable for decomposing ammonia. Any conventional ammonia decomposition catalyst can be used in the bed of the adiabatic reactor or in the bed of each adiabatic reactor.

[0039] Numerous metals are known in the art and catalyze the decomposition of ammonia. These metals include transition metals of Group 6 of the periodic table, e.g., chromium (Cr) and molybdenum (Mo); Group 8, e.g., iron (Fe), ruthenium (Ru), and osmium (Os); Group 9, e.g., cobalt (Co), rhodium (Rh), and iridium (Ir); Group 10, e.g., nickel (Ni), palladium (Pd), and platinum (Pt); and Group 11, e.g., copper (Cu), silver (Ag), and gold (Au). Metalloids such as tellurium (Te) may also be used.

[0040] The activity of some of these metals as catalysts for ammonia decomposition has been reported by Masel et al. (Catalyst Letters, vol. 96, Nos. 3-4, July 2004) to change in the following order: Ru>Ni>Rh>Co>Ir>Fe>>Pt>Cr>Pd>Cu>>Te

[0041] The metal may not be supported, but in many cases it is supported on a suitable support (or substrate), typically a metal support such as silica (SiO2), alumina (Al2O3), or zirconia (ZrO2), or a mixed metal oxide support such as spinel (MgAl2O4) or perovskite (CaTiO3). Alternatively, the metal may be supported on a zeolite.

[0042] As those skilled in the art will understand, the activity of a supported metal catalyst typically depends in part on the loading of the catalytically active metal onto the support. In this regard, the loading of the metal varies according to specific requirements, but is typically in the range of about 0.1% to about 70% by weight. For more active metals, such as ruthenium, the loading may be towards the lower end of the range, for example, about 0.1% to about 10% or about 0.2% to about 5% by weight. For less active metals, such as nickel, the loading may be towards the upper end of the range, for example, about 20% to about 65% by weight.

[0043] The supported metal catalyst may not be promoted, or, as is known in the art, may be promoted with at least one other metal, e.g., one or more Group 1 metals, e.g., lithium (Li), sodium (Na), and potassium (K); Group 2 metals, e.g., magnesium (Mg) and calcium (Ca); or Group 13 metals, e.g., aluminum (Al), to improve its activity.

[0044] Any conventional catalyst known for ammonia decomposition can be used in the present invention. Suitable catalysts are disclosed in US2015 / 0217278A, Masel et al. (supra), Lamb et al. (Int. J. Hydrogen Energy, 44 (2019) pp3726 - 3736) and Boisen et al. (J. Catalysis 230 (2005) pp309 - 312).

[0045] Bimetallic catalysts, or catalysts containing two catalytically active metals, are also suitable for use with the present invention. Examples include composite metals, metal alloys or metal nanoclusters supported on perovskites, composite oxides or nitrides, or mixed oxides or mixed nitrides such as those disclosed in US2021 / 0001311A like CoNi - MgSrCeO4 and 1 wt% K - CoNi - MgSrCeO4.

[0046] The catalyst of the present invention typically comprises, for example, contains or consists of at least one metal - based catalyst. The catalytically active metal is typically selected from the transition metals of the periodic table. Suitable transition - metal - based catalysts are active at a temperature within the range of 475 °C to 600 °C suitable for achieving a reaction rate that is at least 0.2 times, or at least 0.5 times, or at least equal to, or at least 2 times, or at least 3 times, or at least 4 times, or at least 5 times the rate calculated according to Equation 9 proposed by Lamb et al., that is, r = 8.73exp[-76710 / RT].(P NH3 ) 0.28 .(P H2 ) -0.42 .(1 - β 2 ) Where: “r” is the reaction rate (or “activity”) of the catalyst, “RT” is the product of the ideal gas constant “R” (8.314 Jmol -1 K -1 ) and the temperature “T” in Kelvin, P NH3 is the partial pressure of ammonia, P H2This is the partial pressure of hydrogen, β is defined in the research paper as follows (see Equation 5 proposed by Lamb et al.):

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[0047] The inventors recognize that Lamb et al.'s equation 9 can be extrapolated to temperatures outside the 475°C to 600°C range, for example, within the range of 450°C to 700°C.

[0048] Transition metals that may be particularly suitable for use as the primary catalytic active metal of a catalyst in the catalyst bed of an adiabatic reactor are selected from chromium, manganese, iron, cobalt, nickel, ruthenium, and copper, for example, iron, cobalt, nickel, and ruthenium. The inventors understand that nickel and ruthenium are typically the most suitable catalytic active metals for use in the catalyst bed of an adiabatic reaction unit.

[0049] The term "ruthenium-based catalyst" refers to a catalyst containing ruthenium as the sole (or at least dominant) catalytically active metal, i.e., the metal that catalyzes the decomposition reaction. Ruthenium may be the sole metal in the catalyst, or alternatively, one or more other metals may be present in the ruthenium-supported material, for example. The terms "nickel-based catalyst" and "iron-based catalyst" are intended to be interpreted accordingly.

[0050] Suitable ruthenium-based and nickel-based catalysts can be supported, for example, on alumina (disclosed by Lamb et al. or Masel et al.) or spinel (disclosed by Boisen et al.), and can be optionally facilitated with Group 1 or Group 2 metals.

[0051] Ruthenium-based catalysts tend to be more active than nickel-based catalysts, but they are also more expensive. Therefore, further optimization is possible by the selection of catalysts and, when more than one type of catalyst is used, by the ordering of the catalyst layers in the floor of the adiabatic reaction unit. Suitable catalysts include conventional nickel-based or ruthenium-based catalysts for ammonia decomposition.

[0052] In some preferred embodiments having two adiabatic reactors, the catalyst bed of the first reactor comprises, for example, a monolayer of a first catalyst, such as a ruthenium-based catalyst, and the catalyst bed of the second reactor typically comprises, for example, an upstream layer of a second catalyst, such as a nickel-based catalyst, which is less active than the first catalyst, and a downstream layer of a third catalyst, such as a ruthenium-based catalyst, which is typically more active than the second catalyst, and comprises, for example, a

[0053] In these embodiments, the first and third catalysts may be identical. Alternatively, the first and third catalysts may be different, for example, by containing different catalytically active metals, or by containing the same catalytically active metal on different carriers, or by containing the same catalytically active metal on the same carrier in different loadings.

[0054] The volume of the upstream layer of the second catalyst in the bed of the second reactor may be about 40% to about 90% of the total volume of the bed, for example, about 50% to about 70% or about 60%. If no other layer of catalyst is present, the volume of the downstream layer of the third catalyst in the bed of the second reactor may be about 10% to about 60% of the total volume of the bed, for example, about 30% to about 50% or about 40%.

[0055] In adiabatic reaction units, other catalyst layers are typically not present on the floor.

[0056] The inventors recognize that ruthenium-based catalysts, along with carbon monoxide and hydrogen, can decompose hydrocarbon oils into shorter hydrocarbons such as methane. Therefore, the use of these catalysts in an adiabatic reaction unit can eliminate the need for a dedicated upstream unit to remove oil from liquid ammonia.

[0057] The reactor tubes of the furnace are also filled with an ammonia decomposition catalyst. Any of the conventional ammonia decomposition catalysts listed above can be used in the reactor tubes. However, with respect to adiabatic reaction units, nickel-based catalysts and ruthenium-based catalysts are particularly suitable catalysts for the reactor tubes.

[0058] In some embodiments, particularly those where the decomposition reaction is carried out at higher temperatures, the reactor tube may be filled with a less active catalyst, such as a nickel-based catalyst, as the sole catalyst in the tube. Less active catalysts tend to be less expensive than more active catalysts, and for this reason, this arrangement helps to reduce the overall capital cost.

[0059] However, the reactor tube can be filled with at least two different ammonia decomposition catalysts having different activities.

[0060] In these embodiments, a more active catalyst, such as a ruthenium-based catalyst, can be positioned downstream of a less active catalyst, such as a nickel-based catalyst, in the tube to ensure that the decomposition reaction approaches equilibrium.

[0061] Alternatively, a more active catalyst, such as a ruthenium-based catalyst, may be positioned upstream of a less active catalyst, such as a nickel-based catalyst, to control the inner wall temperature of the reactor tube in the region where ammonia temperature and partial pressure are highest, thereby helping to control the nitriding of the tube. In a preferred embodiment, the catalyst may be layered in this way, using the endothermic reaction inside the tube to keep the tube metal cool in the region where combustion is most intense outside the tube. Because ruthenium is more catalytically active than nickel, it generates strong endothermic cooling of the inner tube wall in the high ammonia concentration region on the process side, protecting the tube from excessive nitriding caused by high ammonia concentrations and high temperatures.

[0062] In these alternative embodiments, a second, more active catalyst, such as another ruthenium-based catalyst, can be positioned downstream of the less active catalyst to ensure that the decomposition reaction approaches equilibrium.

[0063] The activity of a more active catalyst is typically at least 50% greater than that of a less active catalyst. However, the relative difference in activity is often substantially greater than 50%. In this respect, the activity of a more active catalyst is often at least twice (i.e., double), or at least three times, or at least four times, or at least five times greater than that of a less active catalyst. In some embodiments, the activity of a more active catalyst is at least ten times (i.e., an order of magnitude), or at least fifteen times greater than that of a less active catalyst.

[0064] In some preferred embodiments, the catalyst in the upstream layer of the tube is a ruthenium-based catalyst, and the catalyst in the downstream layer is a nickel-based catalyst. If a third catalyst is present downstream of the nickel-based catalyst in these embodiments, the catalyst is preferably a ruthenium-based catalyst, but the catalyst may be a different ruthenium-based catalyst from the first catalyst, for example, the catalyst having a different carrier and / or catalyst loading, and / or both, then being promoted with a different metal.

[0065] The catalyst in the reactor tube may be the same as or different from the catalyst used in the adiabatic reaction unit.

[0066] Furthermore, it is known that catalyst sintering at higher temperatures reduces catalyst activity and lifespan. In this regard, those skilled in the art will recognize that improved conversion must be balanced with higher container costs and shorter catalyst lifespan.

[0067] As mentioned above, water is often present in ammonia as a contaminant. Water can be removed from ammonia, in which case a water-intolerant catalyst, such as an iron-based catalyst, can be used in the adiabatic reaction unit and / or reactor tube. However, in preferred embodiments, water is not removed in order to save capital and operating costs and reduce energy consumption. In these embodiments, water-intolerant catalysts, such as iron-based catalysts, are typically not used. Instead, the catalyst in the reactor tube can tolerate up to 1 mol% water in the ammonia supply. Examples of such catalysts include nickel-based and ruthenium-based catalysts.

[0068] The combustion process within the furnace is preferably fueled at least partially internally, i.e., at least part of the fuel is either ammonia or off-gas, or a mixture of both, generated during hydrogen recovery from decomposed gases. However, trim fuels such as C1-C3 hydrocarbons or natural gas may be used as needed, although the use of hydrocarbon trim fuels will increase the carbon intensity of the process. However, it is generally desirable to minimize or even eliminate the use of such trim fuels in order to reduce the carbon intensity of the process.

[0069] The oxidizing gas is typically air, but can be concentrated oxygen or pure oxygen if necessary.

[0070] Partially decomposed ammonia can be supplied to the reactor catalyst-filled tubes at temperatures up to approximately 800°C, provided the reactor wall material can withstand higher temperatures. For lower temperature cycles, the supply is typically in the range of approximately 400°C to approximately 600°C, or approximately 450°C to approximately 550°C, for example, approximately 500°C. For higher temperature cycles, the supply may be in the range of approximately 500°C to approximately 800°C, or approximately 600°C to approximately 700°C, for example, approximately 650°C.

[0071] The decomposition temperature and pressure typically determine that the ammonia slip in the reactor tube is 3 mol% or less, for example, about 0.5 mol% to about 1.5 mol%.

[0072] The heat from the decomposed gases and flue gases is then used to heat the feedflow to the adiabatic reaction unit and furnace, thereby reducing the overall energy consumed by the process. In this regard, the temperature of the decomposed gases depends on the operating cycle.

[0073] In lower temperature cycles, the temperature of the decomposed gas can reach up to approximately 700°C, for example, typically between approximately 550°C and 700°C, or between approximately 600°C and 650°C. The temperature of the flue gas can reach up to approximately 750°C at its peak. However, due to heat leakage, the temperature drops, typically between approximately 600°C and 700°C, where the heat can be effectively utilized.

[0074] At higher temperature cycles, the temperature of the decomposed gas can reach up to approximately 750°C, for example, typically between approximately 650°C and 750°C, or between approximately 675°C and 725°C. The temperature of the flue gas can reach up to approximately 840°C at its peak. However, due to heat leakage, the temperature drops to approximately 700°C to 800°C, where the heat can be effectively utilized.

[0075] At least a portion of the duty cycle required to heat the partially decomposed gas generated in the adiabatic reaction unit to the supply temperature of the reactor tube filled with the catalyst in the furnace is typically provided by heat exchange with the decomposed gas. In a preferred embodiment, the decomposed gas is used directly to provide this heating duty. In other words, the decomposed gas is typically not used elsewhere to heat another process fluid, for example, before heating the partially decomposed gas. Some of this heating duty may be provided by other means, for example, by heat exchange with the flue gas. However, more than half of this heating duty, i.e., 50% or more, is typically provided by the decomposed gas. In a preferred embodiment, at least 75%, or at least 90%, or all of this heating duty is provided by the decomposed gas.

[0076] Due to the high ammonia concentration in the supply gas, decomposition reactor vessels, such as adiabatic reactors and reactor tubes in furnaces, are typically constructed from materials resistant to ammonia and / or nitriding, especially when higher decomposition temperatures are used. Suitable materials include nickel-based alloys containing at least 40% by weight or at least 50% by weight of nickel. Such alloys typically contain 90% by weight or less of nickel, or 80% by weight or less. The alloys typically contain one or more other metals selected from chromium, cobalt, molybdenum, and iron.

[0077] Specific examples of suitable nickel alloys include UNS N06600, N06625, N06601, N06617, N06025, N06230, N07214, and N08811. In some embodiments, austenitic nickel-chromium superalloys such as Inconel may be used.

[0078] The Unified Numbering System (UNS) is a widely accepted alloying symbol system in North America. Each UNS number is associated with a specific metal or alloy and defines its specific chemical composition, or in some cases, specific mechanical or physical properties.

[0079] Other suitable materials include cobalt-based alloys such as UNS R30188. In addition, high-temperature alloys with low resistance to ammonia nitriding, such as UNS N08811, or cast alloys such as HPNb, HP Micro-Alloyed, and MA-1 (MetalTek International, USA) may be particularly suitable when the surface is modified or coated with a corrosion-resistant layer such as aluminization, aluminization followed by pre-oxidation, or ceramic coating. Nitriding-resistant alloys can also be used in conjunction with surface modification or coating for improved performance.

[0080] In preferred embodiments, the composition of the ammonia typically remains at least substantially unchanged from liquid ammonia in storage to heated ammonia gas supplied to the adiabatic reaction unit. Oil present in the liquid ammonia may be removed at some point before the partial decomposition of the ammonia, but in embodiments where the ammonia supply to the adiabatic reaction unit first encounters the ruthenium-based catalyst, oil removal is not necessary. In these embodiments, water is typically not removed, so any water present in the liquid ammonia is also present in the heated ammonia gas.

[0081] The decomposed gas is cooled during heat exchange with the partially decomposed gas. The cooled decomposed gas is then further cooled, typically by providing at least a portion of the heating duty required to generate heated ammonia gas from liquid ammonia. After cooling, hydrogen can be recovered as a product from the decomposed gas. Recovery can be achieved in a pressure fluctuation adsorption (PSA) process, by using one or more selective permeable membranes, or by a combination of PSA and membrane separation. In a preferred embodiment, hydrogen recovery is achieved by the PSA process alone, i.e., without using membrane separation.

[0082] In embodiments using the PSA process, a PSA off-gas is generated, containing nitrogen gas, residual ammonia, and residual hydrogen. The PSA off-gas is typically divided into two parts. The first part of the PSA off-gas is typically compressed in a compression unit and recycled back into the PSA process to improve hydrogen recovery. The second part is typically preheated and then supplied to the furnace as fuel.

[0083] Several factors influence the carbon intensity of a decomposition process, two of which are the amount of ammonia that can pass through the decomposition unit, and the nature of the fuel burned in the decomposition unit, specifically whether and, if so, how much hydrocarbons such as natural gas are used. The inventors found that, given a given amount of ammonia slip and natural gas burned in the decomposition unit, the overall carbon intensity of the process can be reduced if the decomposed gas (and not the flue gas) is used to provide at least a portion of the duty cycle required to heat the partially decomposed gas to the supply temperature of the decomposition unit.

[0084] The embodiments of the present invention include the following: #1. A process for breaking down ammonia, To provide heated, typically superheated, ammonia gas at ultra-atmospheric pressure, Partially decomposing heated ammonia gas in an adiabatic reaction unit having at least one catalyst bed to produce partially decomposed ammonia gas, Heating partially decomposed ammonia gas to produce heated partially decomposed ammonia gas, The process involves burning fuel together with an oxidizer gas in the reactor to heat the reactor tube containing the catalyst and generate flue gas, The process includes supplying heated, partially decomposed ammonia gas to a reactor tube containing a catalyst to induce further decomposition of ammonia, thereby producing a decomposed gas containing hydrogen gas, nitrogen gas, and residual ammonia gas. A process in which at least a portion of the duty required to heat partially decomposed ammonia gas is provided by heat exchange with the decomposed gas. #2. The process described in #1, in which all the duty required to heat the partially decomposed ammonia gas is provided by heat exchange with the decomposed gas. #3. The process described in #1 or #2, wherein heat exchange between partially decomposed ammonia gas and decomposed gas takes place in a shell-tube heat exchanger, with the partially decomposed ammonia gas passing through the tubes of the heat exchanger and the decomposed gas passing through the shell side of the heat exchanger. #4. The process described in any of #1 to #3, wherein the decomposed gas is not cooled by heat exchange with another process fluid before heat exchange with the partially decomposed ammonia gas. #5. The process according to any of #1 to #5, wherein at least a portion, preferably more than half, i.e., more than 50%, and possibly up to 99%, of the heating duty required to provide heated ammonia gas is provided by heat exchange with the decomposed gas downstream of the partially decomposed ammonia gas flow with respect to the flow of the decomposed gas. #6. The process described in any of #1 to #5, wherein the catalyst bed of the adiabatic reaction unit or each catalyst bed does not contain an iron-based catalyst. #7. The process according to any one of #1 to #6, wherein the catalyst bed of the adiabatic reaction unit or each catalyst bed contains, for example, a nickel-based catalyst and / or a ruthenium-based catalyst, or comprises them. #8. Pumping liquid ammonia containing at least 0.1 mol% water to produce pumped liquid ammonia, The process involves preheating liquid ammonia that has been pumped to produce preheated liquid ammonia, and The process involves vaporizing preheated liquid ammonia to produce ammonia gas at superatmospheric pressure, This includes heating ammonia gas to produce heated ammonia gas, The process described in any of #1 to #7, wherein water from liquid ammonia is present in heated ammonia gas. #9. Any of the processes described in #1 to #8, wherein water is present in heated ammonia in an amount of 1 mol% or less. #10. The adiabatic reaction unit comprises a first adiabatic reactor and a second adiabatic reactor in series, wherein the first adiabatic reactor comprises a catalyst bed containing, for example, a ruthenium-based catalyst or comprising thereof, and the second adiabatic reactor comprises a catalyst bed comprising an upstream layer containing a nickel-based catalyst and a downstream layer containing a ruthenium-based catalyst or comprising thereof, wherein the process is The heated ammonia gas is passed through the catalyst bed of the first adiabatic reactor to produce intermediate, partially decomposed ammonia gas, Heating the intermediate gas to produce a heated intermediate gas, A process according to any one of #1 to #9, comprising passing a heated intermediate gas through a catalyst bed of a second adiabatic reactor to produce partially decomposed ammonia gas. #11. The process described in #10, wherein at least a portion, preferably all, of the duty required to heat the intermediate partially decomposed gas is provided by heat exchange with the flue gas. #12. The process described in #11, wherein a portion of the heating duty required to provide heated ammonia gas is provided by heat exchange with the downstream flue gas against the flow of flue gas, with heat exchange with intermediate partially decomposed ammonia gas. #13. For example, after cooling to below 60°C, for example to about 50°C, hydrogen is recovered from the gas decomposed in the hydrogen recovery unit to produce hydrogen gas products and off-gases containing nitrogen gas, residual hydrogen gas, and residual ammonia gas. Heating at least a portion of the off-gas by heat exchange to produce heated off-gas, A process according to any one of #1 to #12, comprising supplying heated gas to a furnace as at least part of the fuel. #14. All of the off-gas is supplied to the reactor as fuel, as described in #13. #15. Dividing the off-gas into a first part and a second part, wherein the first part is heated and supplied to the furnace, The process described in #13, comprising compressing a second portion of the off-gas to produce a compressed off-gas, and recirculating the compressed off-gas to a hydrogen recovery unit for further hydrogen recovery. #16. A device for decomposing ammonia, An adiabatic reaction unit for partially decomposing heated ammonia gas at superatmospheric pressure, comprising: an inlet for heated ammonia gas; and at least one catalyst bed having an upstream end in fluid flow communication with the inlet and a downstream end in fluid flow communication with the outlet for partially decomposed ammonia gas; It is a furnace, A radiant section comprising a reactor tube containing a catalyst having at least one inlet for fuel and oxidizer gases having at least one burner in fluid-flow communication, an upstream end having an outlet for an adiabatic reaction unit in fluid-flow communication, and a downstream end having an outlet for decomposed gases in fluid-flow communication, and A furnace comprising a radiant section and a convection section having fluid flow communication and an outlet for flue gas, The apparatus comprises a heat exchanger positioned between an adiabatic reaction unit and a radiant section of a furnace to heat partially decomposed ammonia gas through heat exchange with the decomposed gas. #17. The apparatus described in #16, wherein the heat exchanger is a shell-tube type heat exchanger. #18. The apparatus described in #17, in which the shell side of the heat exchanger is in direct fluid flow communication with the outlet for the decomposed gases of the furnace's radiant section. #19. The apparatus according to any of #16 to #18, wherein the catalyst bed of the insulated reaction unit or each catalyst bed does not contain an iron-based catalyst. #20. The apparatus according to any one of #16 to #19, wherein the catalyst bed of the adiabatic reaction unit or each catalyst bed contains, for example, a nickel-based catalyst and / or a ruthenium-based catalyst. #21. The adiabatic reaction unit comprises a first adiabatic reactor and a second adiabatic reactor in series. The first adiabatic reactor comprises an inlet for heated ammonia gas, and a catalyst bed containing a ruthenium-based catalyst having an upstream end in fluid flow communication with the inlet and a downstream end in fluid flow communication with an outlet for intermediate partially decomposed ammonia gas, The second adiabatic reactor comprises an inlet for heated intermediate partially decomposed ammonia gas, which is in fluid flow communication with the outlet of the first adiabatic reactor, and a catalyst bed comprising, for example, an upstream layer containing a nickel-based catalyst and, for example, a downstream layer containing a ruthenium-based catalyst, wherein the catalyst bed has an upstream end in fluid communication with the inlet and a downstream end in fluid communication with the outlet for partially decomposed ammonia gas. The apparatus according to any of #16 to #20, wherein the apparatus comprises an intermediate gas heater positioned between a first adiabatic reactor vessel and a second adiabatic reactor vessel, which is arranged to heat an intermediate partially decomposed ammonia gas. #22. The apparatus according to #21, wherein the intermediate gas heater is a heating coil located within the convection section of the furnace, the heating coil having an inlet that is in direct fluid flow communication with the outlet of a first adiabatic reactor and an outlet that is in direct fluid flow communication with the inlet of a second adiabatic reactor. #23. A hydrogen recovery unit for recovering hydrogen gas from decomposed gas, preferably a PSA unit, The first inlet, which is in fluid flow communication with the decomposed gas outlet of the reactor's radiant section, The first outlet for hydrogen gas, A hydrogen recovery unit comprising at least one inlet for fuel in the radiant section of the reactor and a second outlet for off-gas containing nitrogen gas, residual ammonia gas, and residual hydrogen gas, which is in fluid flow communication with the fuel, The apparatus according to any of #16 to #22, wherein the apparatus comprises an off-gas heater positioned between a second outlet of a hydrogen recovery unit and at least one inlet for fuel in the radiant section of the reactor, wherein the apparatus is arranged for heating the off-gas. #24. A compression unit for compressing off-gas, The second outlet of the hydrogen recovery unit and the inlet, which is in fluid flow communication with it, A compressor is provided, comprising a first inlet of the hydrogen recovery unit and an outlet that is in fluid flow communication with it. The apparatus according to any one of #16 to #23, comprising a valve arrangement for controlling the flow of off-gas to a compression unit and an off-gas heater.

[0085] Here, the present invention will be described only as an example with reference to the drawings.

[0086] In Figure 1, a flow of liquid ammonia 2 at approximately -32°C is removed from the storage unit (not shown) and supplied to pump P101, where it is pumped to produce a flow of liquid ammonia 4 pressurized to a pressure of approximately 46 bar, which is preheated by heat exchange in heat exchanger E271 with a heat transfer fluid, which in this case is typically an aqueous solution of approximately 55 wt% ethylene glycol or propylene glycol, to produce a flow of liquid ammonia 6 preheated to approximately 55°C. An electric heater may be used to ensure that the temperature of the glycol solution supplied to heat exchanger E271 is sufficient to preheat the liquid ammonia to the required temperature.

[0087] The preheated liquid ammonia in flow 6 is further heated by heat exchange in heat exchanger E312 to produce a further heated liquid ammonia flow 8. The further heated liquid ammonia in flow 8 then evaporates by heat exchange in heat exchanger E311 to produce ammonia vapor gas flow 10. The ammonia vapor gas in flow 8 then superheats by heat exchange in heat exchanger E310 to produce ammonia gas flow 12 heated to approximately 260°C.

[0088] The heated ammonia gas in flow 12 is further heated by heat exchange in heat exchanger E2102 to produce a superheated ammonia gas flow 14 at approximately 420°C. For convenience, heat exchanger E2102 is shown as a single unit. However, in reality, there may be two separate heat exchangers with a selective catalytic reactor (SCR) positioned between them.

[0089] The superheated ammonia gas in flow 14 is supplied to the first adiabatic reactor vessel C141 at approximately 420°C and approximately 43 bar, and passes through a bed of ruthenium-based catalyst. A portion of the ammonia gas is decomposed on the catalyst to form an intermediate gas flow 16 containing the decomposed ammonia. The mole fraction of ammonia in the gas passing through the first adiabatic reactor vessel C141 decreases from approximately 1 to approximately 0.9.

[0090] The intermediate gas is at approximately 360°C before being heated by heat exchange in the heat exchanger E2103, generating a superheated intermediate gas flow 18, which is then supplied at approximately 590°C to the second adiabatic reactor vessel C142, passing through a bed containing an upstream layer of nickel-based catalyst and a downstream layer of ruthenium-based catalyst to generate a partially decomposed ammonia gas flow 20. The mole fraction of ammonia in the gas passing through the second adiabatic reactor vessel C142 decreases from approximately 0.9 to approximately 0.6.

[0091] The catalyst bed of the second adiabatic reactor vessel C142 has two layers—a layer of nickel-based catalyst on top of a layer of ruthenium-based catalyst—to utilize heat more efficiently and thus maximize ammonia conversion. The catalyst volume is also optimized, namely by limiting the outlet temperature of the second adiabatic reactor vessel to approximately 390°C, thereby minimizing the volume of the ruthenium-based catalyst. The inventors found that this temperature reduction further increases the volume required for the ruthenium-based catalyst.

[0092] The ruthenium-based catalyst is the same in both the first and second adiabatic reactor vessels. However, different ruthenium-based catalysts may be used.

[0093] The partially decomposed ammonia in flow 20 is heated by heat exchange in a heat exchanger (or "economizer") E305 before being supplied as flow 22 at a pressure of approximately 38 bar to a catalyst-filled tube in the radiant section F201 of the furnace (or reactor). Heating the feed to the tube increases the amount of decomposition that can be performed by the heat from the burner by reducing the duty cycle required to heat the partially decomposed flow to reaction temperature. By utilizing the decomposed flow from the tube, this high-temperature flow can be used efficiently. The inlet temperature of the direct combustion tubular furnace is limited to approximately 500°C to limit the inner wall temperature of the tube in the decomposition apparatus.

[0094] The airflow 62 passes through the forced draft fan K212 before being preheated by heat exchange in the heat exchanger E2141, generating a preheated airflow 64. The preheated air in flow 64 is supplied to the burner (not shown) of the furnace F201, in parallel with the natural gas flow 70 as trim fuel. Preheating the air in this way helps to reduce fuel requirements.

[0095] The tubes within the furnace's radiant section F201 are filled with two types of ammonia decomposition catalysts in two different layers. A ruthenium-based catalyst is used in the first layer within each tube, allowing for a faster reaction rate and thus keeping the metal temperature within the design limit of approximately 660°C. The second layer in the tube, downstream of the first layer, contains a lower-cost but less active nickel-based catalyst.

[0096] The decomposed gas stream 24 exits the radiant section F201 of the direct combustion tubular furnace at approximately 640°C and is then supplied to the economizer E305, which provides the duty cycle necessary to heat the partially decomposed ammonia, thereby reducing the temperature of the decomposed gas to approximately 530°C.

[0097] The E305 economizer is illustrated as a shell-tube type heat exchanger where partially decomposed ammonia gas passes through the tube and decomposed gas passes through the shell side. However, this configuration can be reversed, or different types of heat exchangers may actually be used.

[0098] Next, the decomposed gas flow 26 is supplied from the economizer E305 to the heat exchanger E310, providing the duty cycle necessary to superheat the ammonia gas, thereby further reducing the temperature of the decomposed gas to approximately 389°C.

[0099] Next, the decomposed gas flow 28 is supplied from heat exchanger E310 to heat exchanger E311, providing the duty cycle necessary to further evaporate the heated liquid ammonia, thereby further reducing the temperature of the decomposed gas to approximately 109°C.

[0100] Next, the decomposed gas flow 30 is supplied from heat exchanger E311 to heat exchanger E312, providing the duty cycle necessary to further heat the heated pressurized liquid ammonia, thereby further reducing the temperature of the decomposed gas to approximately 70°C.

[0101] Heat exchangers E310, E311, and E312 are each illustrated as individual shell-tube heat exchangers through which ammonia passes in the tubes and the decomposed gases pass through the shell side. However, this arrangement can be reversed for at least one, or even all, of these heat exchangers. Alternatively, the heat exchangers can be combined into a single shell-tube heat exchanger, or in practice, different types of heat exchangers can be used.

[0102] Next, the decomposed gas flow 32 from the heat exchanger E312 is further cooled by heat exchange with the heat transfer fluid in the cooler E323, and is then supplied as flow 34 to the PSA system U501, where it is separated into a hydrogen gas flow 40, which is removed as a product, and a PSA off-gas flow 42, which contains nitrogen gas, residual hydrogen gas, and residual ammonia gas. The hydrogen gas in flow 40 can be supplied to a hydrogen liquefaction unit (not shown) to produce liquid hydrogen.

[0103] All of the PSA off-gas in flow 42 can be directly sent as fuel (flow 60) for combustion in reactor F201. Alternatively, flow 42 can be split into two parts.

[0104] The first portion of the PSA off-gas in flow 44 is heated by heat exchange in heat exchanger E2112 to produce a heated PSA off-gas flow 60, which is then supplied to the burner in furnace F201 along with air supply 64 and, optionally, natural gas supply 70 when needed. A minimum amount of natural gas is used as trim fuel to provide the required fuel balance within the combustion section.

[0105] The second portion can be sent as flow 46 to a multi-stage compression unit K681 for compression. The compression unit K681 has five stages, with intercoolers between each stage, along with a postcooler, followed by the final stage. Heat is recovered from the compressed gas in the intercooler and postcooler by heat exchange with a heat transfer fluid. Heat can also be recovered from the lubricating oil used in the compression unit, and if a positive displacement compression unit is used, it can be recovered from the cylinder of the compression unit using a heat transfer fluid.

[0106] For convenience, the intercooler and postcooler are represented by a single heat exchanger (denoted E6816A~E) that recovers heat from the compressed PSA off-gas flow 48 through heat exchange with the heat transfer fluid flow 52 to produce a cooled compressed PSA off-gas flow 50 and a heated heat transfer fluid flow 54.

[0107] Next, the heat transfer fluid heated in the cooler E323, as well as the intermediate and postcoolers E6816A-E, is used to provide the duty cycle necessary to preheat the liquid ammonia through heat exchange in the heat exchanger E271.

[0108] The cooled and compressed PSA off-gas in flow 50 is fed into phase separator C6816, where any condensation is removed as flow 56. The compressed PSA off-gas is then recirculated into PSA system U501 as flow 58 to recover further hydrogen. In this way, the hydrogen recovery rate can be increased from 85% (without recirculation) to 95% (with recirculation).

[0109] As shown above, the process can operate without the compression unit K681, resulting in a reduced hydrogen recovery rate within the PSA unit 501. Reducing the hydrogen recovery rate obviously leads to a decrease in hydrogen gas products. However, when more hydrogen is present in the off-gas, the carbon intensity (CI) of the process decreases, thereby reducing the need for natural gas as trim fuel and lowering carbon dioxide emissions, so reducing hydrogen recovery may still be desirable.

[0110] The flue gas flow 72, at approximately 686°C, passes from the radiant section F201 through the convection section 90 of the furnace F201, where it first provides the duty cycle necessary to heat the intermediate gas from flow 16 in the heat exchanger E2103, thereby reducing the temperature of the flue gas used (as flow 74), and then provides the duty cycle necessary to further heat the heated ammonia gas from flow 12 in the heat exchanger E2102, thereby further reducing the temperature of the flue gas. Thus, the flue gas provides a heating duty cycle in the direction of flowing back against the flow rate of the supply gas to the radiant section F201 of the direct combustion tubular furnace.

[0111] Next, the cooled flue gas is used to provide the necessary duty cycle (as flow 76) to heat the air from flow 62 in heat exchanger E2142, thereby further reducing the temperature of the flue gas. Then, the further cooled flue gas is used to provide the necessary duty cycle (as flow 78) to heat the PSA off-gas from flow 44 in heat exchanger E2112, thereby further cooling the flue gas.

[0112] The cooled flue gas leaves the convection section 90 of the direct combustion tubular furnace F201 as flow 80 at a temperature of approximately 121°C, i.e., above the dew point of water, passes through the induction ventilator K211, and then leaves the process as flow 82. All practical energy has been extracted from the flue gas at this point and can be optionally, if required depending on its composition, discharged into the atmosphere after further processing.

[0113] Oil may be present in liquid ammonia in amounts of up to approximately 5 ppm from a boil-off gas compressor (not shown) used with an ammonia storage tank (not shown) at the site where ammonia is produced, at the site where ammonia is decomposed, or at any point where it actually passes between the two sites. The presence of oil in ammonia can cause difficulties because ammonia decomposition catalysts may not tolerate oil. Therefore, it may be desirable to remove the oil before the ammonia is exposed to the catalyst. Oil can be removed by passing the ammonia through an activated carbon bed.

[0114] When removing oil from ammonia, the oil removal unit (not shown) may then be positioned in flow 2 (i.e., in the supply line to pump P101), flow 4 (i.e., between pump P101 and glycol heater E271), flow 6 (i.e., between glycol heater E271 and heat exchanger E312), flow 8 (i.e., between heat exchangers E312 and E311), or flow 10 (i.e., between heat exchangers E311 and E310).

[0115] Herein, the present invention will be illustrated by the following non-limiting embodiments. [Examples]

[0116] The process illustrated in Figure 1 is simulated by a computer (Aspen Plus, ver. 10, Aspen Technology, Inc., Massachusetts, USA) for a plant designed to produce 30 tons of hydrogen per day (flow 40).

[0117] The activity of ruthenium-based and nickel-based catalysts in adiabatic reactors and tubes was modeled using the rate equation No. 9 (Int. J. Hydrogen Energy, 44 (2019) pp3726-3736) given by Lamb et al., based on this model. For the purpose of the simulation, the activity of the ruthenium-based catalyst was assumed to fit the rate equation, while the activity of the nickel-based catalyst was assumed to be 20% of the activity predicted by the rate equation.

[0118] The results are shown in Table 2. Table 2 [Table 2-1] [Table 2-2]

[0119] The results show that, with a 1.33 mol% ammonia slip (flow 24) from the cracking unit (tubular furnace 201) and the recovery of 95 mol% hydrogen in the PSA, 7626 kg / hour of ammonia (flow 2) is required as a supply, along with 472.7 kg / hour of natural gas (flow 70) as fuel, in addition to the PSA off-gas (flow 60) to burn the cracking unit.

[0120] With respect to a given hydrogen recovery and ammonia slip, the effect of using the decomposed gas (instead of flue gas) to provide the duty cycle necessary to heat the partially decomposed gas (flow 20) to the supply temperature of the catalyst-filled tube of the decomposition unit (F201) is to reduce the overall carbon intensity (CI) process.

[0121] Although the present invention has been described with reference to preferred embodiments illustrated in the figures, it will be understood that various modifications are possible within the spirit or scope of the invention as defined in the following claims.

[0122] In this specification, unless explicitly indicated otherwise, the word “or” is used to mean an operator that returns a true value when either or both of the stated conditions are met, as opposed to the “exclusive OR” operator, which requires only one of the conditions to be met. The word “comprising” is used to mean “including,” and does not mean “consisting of” exclusively, but rather “consisting of.”

[0123] All prior teachings described above are incorporated herein by reference. Approval of any previously published documents included herein shall not be construed as an acknowledgment or representation that such teachings were common knowledge in Australia or elsewhere at that time. The following embodiments can be cited as examples of the present invention. (Note 1) A process for breaking down ammonia, To provide heated ammonia gas at superatmospheric pressure, The heated ammonia gas is partially decomposed in an insulated reaction unit having at least one catalyst bed to produce partially decomposed ammonia gas, The partially decomposed ammonia gas is heated to produce heated partially decomposed ammonia gas, The process involves burning fuel together with an oxidizer gas in the reactor to heat the reactor tube containing the catalyst and generate flue gas, The heated, partially decomposed ammonia gas is supplied to a reactor tube containing the catalyst to cause further decomposition of ammonia, thereby producing a decomposed gas containing hydrogen gas, nitrogen gas, and residual ammonia gas. A process in which at least a portion of the duty cycle required to heat the partially decomposed ammonia gas is provided by heat exchange with the decomposed gas. (Note 2) The process according to Appendix 1, wherein all of the duty cycles required to heat the partially decomposed ammonia gas are provided by heat exchange with the decomposed gas. (Note 3) The process according to Appendix 1, wherein the heat exchange between the partially decomposed ammonia gas and the decomposed gas takes place in a shell-tube type heat exchanger, the partially decomposed ammonia gas passes through the tubes of the heat exchanger and the decomposed gas passes through the shell side of the heat exchanger. (Note 4) The process according to Appendix 1, wherein the decomposed gas is not cooled by heat exchange with another process fluid before heat exchange with the partially decomposed ammonia gas. (Note 5) The process according to Appendix 1, wherein at least a portion, preferably more than half, of the heating duty required to provide the heated ammonia gas is provided by heat exchange with the decomposed gas downstream of the heat exchange with the partially decomposed ammonia gas, relative to the flow of the decomposed gas. (Note 6) The process according to Appendix 1, wherein the catalyst-filled tube of the furnace and the catalyst bed or each catalyst bed of the adiabatic reaction unit do not contain an iron-based catalyst. (Note 7) The process according to Appendix 1, wherein the catalyst bed or each catalyst bed of the adiabatic reaction unit contains a nickel-based catalyst and / or a ruthenium-based catalyst. (Note 8) The process involves pumping liquid ammonia containing at least 0.1 mol% water to produce pumped liquid ammonia, The liquid ammonia pumped by the aforementioned pump is preheated to produce preheated liquid ammonia, The preheated liquid ammonia is vaporized to produce ammonia gas, This includes heating the pressurized ammonia gas to produce the superatmospheric pressure heated ammonia gas, The process according to Appendix 1, wherein the water from the liquid ammonia is present in the heated ammonia gas. (Note 9) The process according to Appendix 1, wherein the water is present in the heated ammonia in an amount of 1 mol% or less. (Note 10) The adiabatic reaction unit comprises a first adiabatic reactor and a second adiabatic reactor in series, the first adiabatic reactor comprises a catalyst bed containing a ruthenium-based catalyst, and the second adiabatic reactor comprises a catalyst bed containing an upstream layer containing a nickel-based catalyst and a downstream layer containing a ruthenium-based catalyst, and the process comprises, The heated ammonia gas is passed through the catalyst bed of the first adiabatic reactor to produce intermediate, partially decomposed ammonia gas. The intermediate gas is heated to produce a heated intermediate gas, The process according to Appendix 1, further comprising passing the heated intermediate gas through the catalyst bed of the second adiabatic reactor to produce the partially decomposed ammonia gas. (Note 11) The process according to Appendix 10, wherein at least a portion, preferably all, of the duty cycle required to heat the intermediate partially decomposed gas is provided by heat exchange with the flue gas. (Note 12) The process according to Appendix 11, wherein a portion of the heating duty required to provide the heated ammonia gas is provided by heat exchange with the flue gas downstream of the heat exchange with the intermediate partially decomposed ammonia gas, with respect to the flow of the flue gas. (Note 13) After cooling, hydrogen is recovered from the decomposed gas in the hydrogen recovery unit to produce hydrogen gas products and off-gas containing nitrogen gas, residual hydrogen gas, and residual ammonia gas. Heating at least a portion of the off-gas to generate heated off-gas, The process according to Appendix 1, comprising supplying the heated off-gas to the furnace as at least a portion of the fuel. (Note 14) The process described in Appendix 13, wherein all of the off-gas is supplied to the furnace as fuel. (Note 15) Dividing the off-gas into a first part and a second part, wherein the first part is heated and supplied to the furnace, The process according to Appendix 13, comprising compressing the second portion of the off-gas to produce a compressed off-gas, and recirculating the compressed off-gas to the hydrogen recovery unit for further hydrogen recovery. (Note 16) A device for decomposing ammonia, An adiabatic reaction unit for partially decomposing heated ammonia gas at superatmospheric pressure, comprising: an inlet for heated ammonia gas; and at least one catalyst bed having an upstream end in fluid flow communication with the inlet and a downstream end in fluid flow communication with an outlet for partially decomposed ammonia gas; It is a furnace, A radiant section comprising a reactor tube containing a catalyst having at least one inlet for fuel and oxidizer gases in fluid-flow communication with at least one burner, an upstream end in fluid-flow communication with the outlet of the adiabatic reaction unit and a downstream end in fluid-flow communication with the outlet for decomposed gases, and A furnace comprising a convection section having fluid flow communication with the aforementioned radiant section and an outlet for flue gas, The apparatus comprises a heat exchanger positioned between the adiabatic reaction unit and the radiant section of the furnace to heat ammonia gas that has been partially decomposed by heat exchange with the decomposed gas. (Note 17) The apparatus as described in Appendix 16, wherein the heat exchanger is a shell-tube type heat exchanger. (Note 18) The apparatus as described in Appendix 16, wherein the shell side of the heat exchanger is in direct fluid flow communication with the outlet for the decomposed gas of the radiant section of the furnace. (Note 19) The apparatus according to Appendix 16, wherein the catalyst bed or each catalyst bed of the catalyst-filled tube and the adiabatic reaction unit of the furnace does not contain an iron-based catalyst. (Note 20) The apparatus according to Appendix 16, wherein the catalyst bed or each catalyst bed of the adiabatic reaction unit contains a nickel-based catalyst and / or a ruthenium-based catalyst. (Note 21) The adiabatic reaction unit comprises a first adiabatic reactor and a second adiabatic reactor in series. The first adiabatic reactor comprises an inlet for heated ammonia gas, and a catalyst bed containing a ruthenium-based catalyst having an upstream end in fluid flow communication with the inlet and a downstream end in fluid flow communication with an outlet for intermediate partially decomposed ammonia gas, The second adiabatic reactor comprises an inlet for heated intermediate partially decomposed ammonia gas, which is in fluid flow communication with the outlet of the first adiabatic reactor, and a catalyst bed comprising an upstream layer containing a nickel-based catalyst and a downstream layer containing a ruthenium-based catalyst, wherein the catalyst bed has an upstream end in fluid communication with the inlet and a downstream end in fluid communication with the outlet for partially decomposed ammonia gas. The apparatus according to Appendix 16, wherein the apparatus comprises an intermediate gas heater positioned between the first adiabatic reactor vessel and the second adiabatic reactor vessel, which is arranged to heat the intermediate partially decomposed ammonia gas. (Note 22) The apparatus as described in Appendix 21, wherein the intermediate gas heater is a heating coil located within the convection section of the furnace, and the heating coil comprises an inlet that is in direct fluid flow communication with the outlet of the first adiabatic reactor and an outlet that is in direct fluid flow communication with the inlet of the second adiabatic reactor. (Note 23) A hydrogen recovery unit for recovering hydrogen gas from decomposed gas, preferably a PSA unit, The first inlet of the radiant section of the furnace is in fluid flow communication with the outlet for the decomposed gas, The first outlet for hydrogen gas, A hydrogen recovery unit comprising the at least one inlet for fuel in the radiant section of the reactor and a second outlet for off-gas including nitrogen gas, residual ammonia gas, and residual hydrogen gas, which is in fluid flow communication with the inlet, The apparatus according to Appendix 16, wherein the apparatus comprises an off-gas heater arranged for heating the off-gas and positioned between the second outlet of the hydrogen recovery unit and the at least one inlet for the fuel of the radiant section of the furnace. (Note 24) A compression unit for compressing off-gas, The inlet of the hydrogen recovery unit is in fluid flow communication with the second outlet, The hydrogen recovery unit comprises a first inlet and an outlet that is in fluid flow communication with the hydrogen recovery unit, and a compression unit. The apparatus as described in Appendix 23, further comprising a valve arrangement for controlling the flow of off-gas to the compression unit and the off-gas heater.

Claims

1. A process for breaking down ammonia, To provide heated ammonia gas at superatmospheric pressure, The heated ammonia gas is partially decomposed in an insulated reaction unit having at least one catalyst bed to produce partially decomposed ammonia gas, The partially decomposed ammonia gas is heated to produce heated partially decomposed ammonia gas, The process involves burning fuel together with an oxidizer gas in the reactor to heat the reactor tube containing the catalyst and generate flue gas, The heated, partially decomposed ammonia gas is supplied to a reactor tube containing the catalyst to cause further decomposition of ammonia, thereby producing a decomposed gas containing hydrogen gas, nitrogen gas, and residual ammonia gas. A process in which at least a portion of the duty cycle required to heat the partially decomposed ammonia gas is provided by heat exchange with the decomposed gas, and the decomposed gas is not cooled by heat exchange with another process fluid prior to the heat exchange with the partially decomposed ammonia gas.

2. The process according to claim 1, wherein all of the duty cycles required to heat the partially decomposed ammonia gas are provided by heat exchange with the decomposed gas.

3. The process according to claim 1, wherein the heat exchange between the partially decomposed ammonia gas and the decomposed gas takes place in a shell-tube type heat exchanger, the partially decomposed ammonia gas passes through the tubes of the heat exchanger and the decomposed gas passes through the shell side of the heat exchanger.

4. The process according to claim 1, wherein at least a portion, preferably more than half, of the heating duty required to provide the heated ammonia gas is provided by heat exchange with the decomposed gas downstream of the heat exchange with the partially decomposed ammonia gas with respect to the flow of the decomposed gas.

5. The process according to claim 1, wherein the catalyst-filled tube of the furnace and the catalyst bed or each catalyst bed of the adiabatic reaction unit do not contain an iron-based catalyst.

6. The process according to claim 1, wherein the catalyst bed or each catalyst bed of the adiabatic reaction unit comprises a nickel-based catalyst and / or a ruthenium-based catalyst.

7. The process involves pumping liquid ammonia containing at least 0.1 mol% water to produce pumped liquid ammonia, The liquid ammonia pumped by the aforementioned pump is preheated to produce preheated liquid ammonia, The preheated liquid ammonia is vaporized to produce ammonia gas, This includes heating the pressurized ammonia gas to produce the superatmospheric pressure heated ammonia gas, The process according to claim 1, wherein the water from the liquid ammonia is present in the heated ammonia gas.

8. The process according to claim 1, wherein the water is present in the heated ammonia in an amount of 1 mol% or less.

9. The adiabatic reaction unit comprises a first adiabatic reactor and a second adiabatic reactor in series, the first adiabatic reactor comprises a catalyst bed containing a ruthenium-based catalyst, and the second adiabatic reactor comprises a catalyst bed containing an upstream layer containing a nickel-based catalyst and a downstream layer containing a ruthenium-based catalyst, and the process comprises, The heated ammonia gas is passed through the catalyst bed of the first adiabatic reactor to produce intermediate, partially decomposed ammonia gas. The intermediate gas is heated to produce a heated intermediate gas, The process according to claim 1, further comprising passing the heated intermediate gas through the catalyst bed of the second adiabatic reactor to produce the partially decomposed ammonia gas.

10. The process according to claim 9, wherein at least a portion, preferably all, of the duty cycle required to heat the intermediate partially decomposed gas is provided by heat exchange with the flue gas.

11. The process according to claim 10, wherein a portion of the heating duty required to provide the heated ammonia gas is provided by heat exchange with the flue gas downstream of the heat exchange with the intermediate partially decomposed ammonia gas with respect to the flow of the flue gas.

12. After cooling, hydrogen is recovered from the decomposed gas in the hydrogen recovery unit to produce hydrogen gas products and off-gas containing nitrogen gas, residual hydrogen gas, and residual ammonia gas. Heating at least a portion of the off-gas to generate heated off-gas, The process according to claim 1, comprising supplying the heated off-gas to the furnace as at least a portion of the fuel.

13. The process according to claim 12, wherein all of the off-gas is supplied to the furnace as fuel.

14. The off-gas is divided into a first part and a second part, wherein the first part is heated and supplied to the furnace. The process according to claim 12, comprising compressing the second portion of the off-gas to produce a compressed off-gas, and recirculating the compressed off-gas to the hydrogen recovery unit for further hydrogen recovery.

15. A device for decomposing ammonia, An adiabatic reaction unit for partially decomposing heated ammonia gas at superatmospheric pressure, comprising: an inlet for heated ammonia gas; and at least one catalyst bed having an upstream end in fluid flow communication with the inlet and a downstream end in fluid flow communication with an outlet for partially decomposed ammonia gas; It is a furnace, A radiant section comprising a reactor tube containing a catalyst having at least one inlet for fuel and oxidizer gases in fluid-flow communication with at least one burner, an upstream end in fluid-flow communication with the outlet of the adiabatic reaction unit and a downstream end in fluid-flow communication with the outlet for decomposed gases, and A furnace comprising a convection section having fluid flow communication with the aforementioned radiant section and an outlet for flue gas, The apparatus comprises a heat exchanger positioned between the adiabatic reaction unit and the radiant section of the furnace to heat partially decomposed ammonia gas by heat exchange with the decomposed gas, wherein the apparatus is configured such that the decomposed gas is not cooled by heat exchange with another process fluid prior to the heat exchange with the partially decomposed ammonia gas, and the decomposed gas includes hydrogen gas, nitrogen gas, and residual ammonia gas.

16. The apparatus according to claim 15, wherein the heat exchanger is a shell-tube type heat exchanger.

17. The apparatus according to claim 15, wherein the shell side of the heat exchanger is in direct fluid flow communication with the outlet for the decomposed gas of the radiant section of the furnace.

18. The apparatus according to claim 15, wherein the catalyst-filled tube of the furnace and the catalyst bed or each catalyst bed of the adiabatic reaction unit do not contain an iron-based catalyst.

19. The apparatus according to claim 15, wherein the catalyst bed or each catalyst bed of the adiabatic reaction unit contains a nickel-based catalyst and / or a ruthenium-based catalyst.

20. The adiabatic reaction unit comprises a first adiabatic reactor and a second adiabatic reactor in series. The first adiabatic reactor comprises an inlet for heated ammonia gas, and a catalyst bed containing a ruthenium-based catalyst having an upstream end in fluid flow communication with the inlet and a downstream end in fluid flow communication with an outlet for intermediate partially decomposed ammonia gas, The second adiabatic reactor comprises an inlet for heated intermediate partially decomposed ammonia gas, which is in fluid flow communication with the outlet of the first adiabatic reactor, and a catalyst bed comprising an upstream layer containing a nickel-based catalyst and a downstream layer containing a ruthenium-based catalyst, wherein the bed has an upstream end in fluid communication with the inlet and a downstream end in fluid communication with the outlet for partially decomposed ammonia gas. The apparatus according to claim 15, wherein the apparatus comprises an intermediate gas heater positioned between the first adiabatic reactor vessel and the second adiabatic reactor vessel, which is arranged to heat the intermediate partially decomposed ammonia gas.

21. The apparatus according to claim 20, wherein the intermediate gas heater is a heating coil located within the convection section of the furnace, and the heating coil comprises an inlet that is in direct fluid flow communication with the outlet of the first adiabatic reactor and an outlet that is in direct fluid flow communication with the inlet of the second adiabatic reactor.

22. A hydrogen recovery unit for recovering hydrogen gas from decomposed gas, preferably a PSA unit, The first inlet of the radiant section of the furnace is in fluid flow communication with the outlet for the decomposed gas, The first outlet for hydrogen gas, A hydrogen recovery unit comprising the at least one inlet for fuel in the radiant section of the reactor and a second outlet for off-gas including nitrogen gas, residual ammonia gas, and residual hydrogen gas, which is in fluid flow communication with the inlet, The apparatus according to claim 15, wherein the apparatus comprises an off-gas heater arranged for heating the off-gas and positioned between the second outlet of the hydrogen recovery unit and the at least one inlet for the fuel of the radiant section of the furnace.

23. A compression unit for compressing off-gas, The inlet of the hydrogen recovery unit is in fluid flow communication with the second outlet, The hydrogen recovery unit comprises a first inlet and an outlet that is in fluid flow communication with the hydrogen recovery unit, and a compression unit comprising The apparatus according to claim 22, further comprising a valve arrangement for controlling the flow of off-gas to the compression unit and the off-gas heater.

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