Process and apparatus for cracking ammonia

Abstract

To provide a process and apparatus for cracking ammonia.SOLUTION: In a process in which ammonia is cracked to form a hydrogen gas product and an off-gas comprising nitrogen gas, residual hydrogen gas and residual ammonia gas, residual ammonia is recovered from the off-gas from the hydrogen recovery process by partial condensation and phase separation, and hydrogen is recovered from the resultant ammonia-lean off-gas by partial condensation and phase separation. The recovered ammonia may be recycled to the cracking process and the recovered hydrogen may be recycled to the hydrogen recovery process to improve hydrogen recovery from the cracked gas. Overall hydrogen recovery from the ammonia may thereby be increased to over 99%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention is in the field of ammonia cracking to produce hydrogen, and specifically relates to the recovery of ammonia and hydrogen from tail gases produced in primary hydrogen recovery processes. [Background technology]

[0002] The global interest in renewable energy and its use to produce "green" hydrogen has fueled 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 transportation of liquid hydrogen is not currently commercially possible, the transportation of ammonia in the liquid state is currently practiced.

[0003] For use in commercial fuel cells, ammonia must be converted reactively back to hydrogen.

number

[0004] This is an endothermic process, i.e., one that requires heat, and therefore higher temperatures favor the production of the product. The standard heat of reaction (per mole of ammonia) at 1 bar and 0°C is 45.47 kJ / mol. The endothermic nature of the process dictates the need for a furnace.

[0005] This process is known as cracking (or sometimes "dissociation") and is usually carried out over a catalyst. The gas produced (or "cracked gas") is a mixture of hydrogen (H) and nitrogen (N), but because the cracking reaction is an equilibrium reaction, some residual ammonia is also present. The amount of ammonia in the cracked gas, commonly referred to as "ammonia slip," can be varied by changing the temperature and pressure at which ammonia is cracked, with higher temperatures and pressures favoring conversion, thereby reducing ammonia slip.

[0006] In this regard, conducting the cracking reaction at higher pressures is preferred because it reduces the amount of compression force required to deliver renewable hydrogen at product pressure. However, higher pressure reactions mean more unconverted ammonia in the cracked stream. On the other hand, using higher temperatures reduces ammonia slip and increases the conversion of ammonia to hydrogen, but the temperature is limited by factors such as nitridation of reactor metals. Therefore, typical ammonia slip in the cracked gas is about 1.3% to 1.5%.

[0007] Currently, in most cracker applications, the hydrogen and nitrogen mixture is utilized as is. However, because ammonia can be harmful to fuel cells, this stream can be used directly in fuel cells with suitable removal of the ammonia, such as by scrubbing with water. However, when hydrogen is used in vehicle fueling, the nitrogen present presents a penalty to the process. Fuel to vehicle fueling systems is compressed to significant pressures, up to 900 bar. This means that nitrogen, which is merely a diluent in the process, is also compressed, requiring power, storage, increasing anode gas purge requirements, and reducing efficiency. Therefore, when hydrogen is used in vehicle fueling, it is beneficial to separate the hydrogen and nitrogen.

[0008] There are many examples of ammonia decomposition processes in the art, for example, WO2019 / 038251A, WO2022 / 189560A, and US2023 / 0242395A.

[0009] WO2019 / 038251A discloses a process for producing hydrogen and nitrogen from ammonia, which comprises non-catalytically oxidizing ammonia with oxygen to produce a process gas containing nitrogen, water, nitrogen oxides, and a residual amount of ammonia, then decomposing the residual ammonia in the process gas and simultaneously reducing the nitrogen oxides with hydrogen to form nitrogen and water over a nickel catalyst. Unconverted ammonia is recovered from the process gas by washing with water.

[0010] WO 2022 / 189560A discloses a process for decomposing ammonia, which comprises partially decomposing a feed in an adiabatic reactor and decomposing the partially decomposed ammonia in a decomposition reactor, such as an electrically heated reactor. Hydrogen is recovered from the decomposed gas in a hydrogen recovery unit, which produces a hydrogen product gas and a tail gas comprising hydrogen, nitrogen, and optionally unconverted ammonia, which can be scrubbed from the tail gas using water.

[0011] US 2023 / 0242395A discloses an ammonia decomposition process in which hydrogen is recovered from the cracked gas using a pressure swing adsorption (PSA) device. The hydrogen is recovered from the PSA tail gas using a membrane and either recycled to the PSA device for further processing or mixed with the hydrogen product gas. Ammonia can be recovered from the tail gas before or after the membrane by adsorption, e.g., by temperature swing adsorption (TSA), by absorption, by washing with water, e.g., in a scrubber column, or by partial condensation and phase separation and recycling the recovered ammonia to the ammonia decomposition stage.

[0012] The use of a PSA, when properly designed, can recover up to 97% of the hydrogen from the cracked gas. Ammonia recovery from the cracked gas is not necessary for a PSA. However, without ammonia recovery from the cracked gas, hydrogen recovery from ammonia cannot exceed about 93%, and PSA recovery is about 95%.

[0013] If ammonia recovery is desired in terms of improved hydrogen recovery, the art teaches the use of a water wash / absorber column configuration, where a stripping column is required to recover the ammonia from the water. Such a column has a reboiler to boil the ammonia-containing water from the absorber. However, heat must be applied to the reboiler, resulting in additional fuel costs and associated carbon dioxide emissions in addition to the heat already used in the cracking process.

[0014] However, there remains a need for improved processes for the production of hydrogen from ammonia in general, and specifically for improved processes having higher levels of hydrogen recovery from the feed ammonia. Summary of the Invention

[0015] According to a first aspect of the present invention, there is provided a process for decomposing ammonia, comprising: providing heated ammonia gas at superatmospheric pressure; decomposing the heated ammonia gas in an ammonia decomposition system to produce a cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia gas; cooling the cracked gas by heat exchange to produce a cooled cracked gas; recovering hydrogen from the cooled cracked gas in a hydrogen recovery unit to produce a hydrogen gas product and a tail gas comprising nitrogen gas, residual hydrogen gas, and residual ammonia gas; recovering the residual ammonia from at least a portion of the tail gas, or from a combined gas comprising the tail gas, by partial condensation and phase separation to produce recovered liquid ammonia and an ammonia-lean tail gas comprising nitrogen gas and residual hydrogen gas; and recovering the residual hydrogen from the ammonia-lean tail gas, or from an ammonia-free tail gas derived therefrom, by partial condensation and phase separation to produce a hydrogen-rich gas and a nitrogen-rich liquid.

[0016] Embodiments of the present invention allow for increased recovery of hydrogen from feed ammonia. For example, in embodiments where hydrogen is recovered from gas cracked in a PSA system, the PSA system may be operated at 85% recovery, while the overall hydrogen recovery from ammonia is typically about 99% or greater.

[0017] Another advantage is that the performance of the ammonia cracking system is less sensitive to catalyst performance. In fact, slip variations up to the design maximum (e.g., 3 mol.%) can be accommodated as catalyst life increases.

[0018] According to a second aspect of the present invention, there is provided an ammonia decomposition system comprising an inlet for heated ammonia gas at superatmospheric pressure and an outlet for cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia gas; a hydrogen recovery unit comprising an inlet for cooled cracked gas in fluid flow communication with the outlet of the ammonia decomposition system, a first outlet for hydrogen gas product, and a second outlet for tail gas comprising nitrogen gas, residual hydrogen gas, and residual ammonia gas; a first phase separator comprising an inlet for partially condensed tail gas in fluid flow communication with the second outlet of the hydrogen recovery unit, a first outlet for recovered liquid ammonia, and a second outlet for ammonia-lean tail gas comprising nitrogen gas and residual hydrogen gas; and a second outlet for the partially condensed ammonia-lean tail gas in fluid flow communication with the second outlet of the first phase separator. and a second phase separator having an inlet, a first outlet for hydrogen-rich gas, and a second outlet for nitrogen-rich liquid, the apparatus comprising a heat exchange system including: a heat exchanger located between an outlet of the ammonia decomposition system and an inlet of a hydrogen recovery unit, the heat exchanger being arranged to cool the cracked gas by heat exchange with one or more "cold" process fluids; a heat exchanger located between a second outlet of the hydrogen recovery unit and the first phase separator, the heat exchanger being arranged to condense residual ammonia gas in the tail gas by heat exchange with one or more "cold" process fluids; and a heat exchanger located between a second outlet of the first phase separator and an inlet of the second phase separator, the heat exchanger being arranged to condense nitrogen in the ammonia-lean tail gas by heat exchange against one of a plurality of "cold" process fluids.

[0019] The apparatus of the second aspect of the invention is suitable for carrying out the process of the first aspect of the invention. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a simplified flowsheet for a reference process for cracking ammonia and recovering hydrogen from the cracked gas using PSA system U501. [Figure 2] 2 is a simplified flowsheet for an embodiment of the present invention comprising a cryogenic recovery system 200 for recovering ammonia from the PSA tail gas produced by PSA system U501. [Figure 3] 3 is a simplified flowsheet for a first configuration of the cryogenic recovery system 200 depicted in FIG. 2. [Figure 4] 3 is a simplified flowsheet for a second configuration of the cryogenic recovery system 200 depicted in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] Unless otherwise specified, throughout this specification any reference to pressure is a reference to absolute pressure. Additionally, all percentages are calculated on a molar basis, i.e., mol.%, unless otherwise specified or clear from the context.

[0022] The term "superatmospheric pressure" will be understood to mean a pressure significantly higher than atmospheric pressure, for example a pressure of at least 5 bar, for example a pressure of at least 10 bar, or at least 20 bar, or at least 30 bar. Typically the pressure will be 60 bar or less.

[0023] The term "hydrogen-enriched" in the context of hydrogen-enriched gas (or other fluid) is intended to describe a composition of the product fluid in which the proportion of hydrogen is greater than in the feed of the product fluid being produced. Corresponding terms involving different gases, such as "nitrogen-enriched," should be interpreted accordingly. A hydrogen-enriched fluid may, for example, contain at least 50 mol.% hydrogen, and a nitrogen-enriched fluid may, for example, contain at least 95 mol.% nitrogen.

[0024] The term "hydrogen-rich" in the context of a hydrogen-rich gas (or other fluid) is intended to describe a fluid mixture containing hydrogen as the primary or most abundant component, along with at least one other component. Typically, at least 50 mol.% or at least 75 mol.% of the fluid mixture is hydrogen. Corresponding terms involving a different gas, such as "nitrogen-rich," should be interpreted accordingly. In practice, nitrogen-rich fluids typically contain at least 90 mol.%, e.g., at least 95 mol.% or at least 98 mol.% nitrogen.

[0025] The term "ammonia-depleted" in the context of an ammonia-depleted gas (or other fluid) is intended to describe a composition of the product fluid that is less than the proportion of ammonia in the feed from which the product fluid is generated. The term "ammonia-lean" in the context of an ammonia-lean gas (or other fluid) is intended to describe a fluid that contains a small amount of ammonia, e.g., 1 mol.% or less. The term "ammonia-free" in the context of an ammonia-free gas (or other fluid) is intended to describe a fluid that contains no ammonia or only trace amounts of ammonia, e.g., 10 ppm or less, preferably 1 ppm or less. Corresponding terms with different gases should be interpreted accordingly.

[0026] The term "partially condensed" in the context of a partially condensed fluid is intended to refer to a fluid that has both a vapor phase and a liquid phase.

[0027] The expression "refrigeration capacity" is intended to refer to the cooling capacity provided by the transfer of latent and / or sensitive heat between fluids at different temperatures.

[0028] A "cold" process fluid is any fluid from the low temperature end of a process that can provide refrigeration capacity and includes nitrogen-rich liquids (or gases), nitrogen-enriched liquids (or gases), hydrogen-rich gases, and hydrogen-enriched gases, and may also include one or more of liquid ammonia, recovered ammonia liquid, and ammonia-lean tail gas.

[0029] The expression "located between," in the context of a heat exchanger located between two other equipment units that are in fluid flow communication with each other, will be understood to mean that the heat exchanger is provided in a location intermediate the locations of the other equipment units where it is capable of changing the temperature of the process fluid flowing from one equipment unit to the other equipment unit.

[0030] In the context of the present invention, the activity of a catalyst will be understood to refer to the rate of conversion of ammonia at a given partial pressure for a given amount of catalyst over a given period of time at a particular temperature and overall pressure. The units used to define the activity of a heterogeneous catalyst are per gram (or mol g) of catalyst (including substrate, if present) per second. -1 s -1 ) is the moles of ammonia converted

[0031] The phrase "in fluid flow communication" will be understood to mean that piping or other suitable conduits are used to transport a fluid from one designated location to another. During passage between two locations, the fluid may flow through one or more other units that may be designed and / or arranged to change the physical conditions of the fluid, such as the temperature (e.g., heat exchangers) and / or pressure (e.g., compressors, pumps, pressure reducing valves, or expanders) of the fluid, or the composition of the fluid through reaction of components within the fluid (e.g., catalytic reactors). If the fluid is a gas, the gas may additionally or alternatively be used to regenerate one or more adsorbent beds. The phrase "in direct fluid flow communication" will be understood to mean that the fluid flows directly from one location to the other, i.e., does not pass through another such unit during its passage, and therefore there is at least essentially no change in the composition or physical condition of the fluid.

[0032] The term "downstream" will be understood to mean in the same direction as fluid flow during normal operation, and the term "upstream" will be interpreted accordingly.

[0033] The heat exchange system of the present invention comprises a plurality of heat exchangers, one or more of which may be individual heat exchangers, such as shell-and-tube style heat exchangers, or alternatively, two or more of the heat exchangers may be adjacent passages within a single heat exchanger having multiple passages in which various process streams are cooled by heat exchange with one or more of a "cold" process stream and / or an external refrigerant stream.

[0034] The heated ammonia gas feed of the present invention is typically generated from liquid ammonia, which may be supplied at ambient pressure from either a pipeline or, more typically, from a refrigerated storage tank. Water is often added to the ammonia to prevent stress corrosion decomposition in the storage tanks, trucks, and ships used to transport the ammonia. The presence of water in the ammonia feed transforms the feed into a multi-component stream, and vaporization of the feed stream would then require higher temperatures to achieve complete vaporization.

[0035] A typical composition of the ammonia feed is shown in Table 1. [Table 1]

[0036] Oil may be present either in local storage tanks for boiler exhaust gas compressors used for ammonia storage, at the production site, or any other storage tanks in between. The presence of oil is problematic due to the risk of clogging and / or contamination. This can lead to poor performance of heat exchangers or reduced catalytic activity in the reactor. Therefore, if present, the oil may need to be removed in some manner. In this regard, oil can be removed by passing the liquid ammonia through a bed of activated carbon. However, in a preferred embodiment, the catalyst used in the adiabatic reaction unit cracks the oil into short-chain hydrocarbons, which can react with any water present to form carbon monoxide, hydrogen, and methane.

[0037] Inert gases are not expected to be a problem, except that they may end up in the product hydrogen. In this regard, helium may be present in ammonia derived from natural gas, but ammonia derived from renewable hydrogen does not contain helium.

[0038] Liquid ammonia is typically removed from storage and pumped from storage pressure (e.g., about 1 bar) to a pressure in the range of about 5 bar to about 60 bar, e.g., about 10 bar to about 50 bar, e.g., about 10 bar to about 30 bar, or about 40 bar to about 50 bar. The temperature of the liquid ammonia is raised slightly from the storage temperature (e.g., about −34° C.) to about −32° C. When liquid ammonia is removed from a pipeline, the temperature of the liquid ammonia is usually higher, e.g., about +10° C.

[0039] The pumped liquid ammonia (at superatmospheric pressure) is then ideally preheated, typically to its boiling point, by suitable heat integration within the process. Preferably, part of the preheating is achieved using a heat transfer circuit, where, for example, heat from intercooling and post-cooling of the PSA exhaust gas compressor is recovered using a heat transfer fluid such as an aqueous solution of glycol, e.g., an aqueous solution containing about 50% to about 60% by weight of a glycol, such as ethylene glycol or propylene glycol, and used to preheat the liquid ammonia, optionally together with heat from the flue gas and / or cracked gas. 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.

[0040] The preheated liquid ammonia is typically then vaporized and the resulting ammonia gas is further heated before being fed 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 useful reaction rates in the ammonia decomposition system.

[0041] The capacity for vaporization and further heating of the preheated liquid ammonia can be provided by heat exchange with cracked gas, flue gas, or a combination of both cracked gas and flue gas. In a preferred embodiment, cracked gas is used to heat and vaporize the preheated liquid ammonia by heat exchange, and the ammonia gas is then further heated by heat exchange with the flue gas.

[0042] Heated ammonia gas is fed to an ammonia decomposition system at superatmospheric pressure. Any suitable system may be used, which may include catalyst-containing reactor tubes heated by electric heating elements in an electrically heated tube reactor, or by the combustion of fuel in a direct-fired tube reactor, or some combination of these two types of reactors.

[0043] Renewable electricity, i.e., electricity generated from sustainable energy sources such as sunlight and / or wind, can be used to power an electrically heated tube reactor, reducing the carbon intensity of the cracking process.

[0044] In a direct-fired tube reactor, fuel is combusted with an oxidant gas in a furnace to heat the catalyst-containing reactor tubes and produce flue gas. At least a majority of the fuel for combustion—e.g., at least 50%, or at least 75%, or at least 90%—is typically provided by one of several fuels selected from C1-C3 hydrocarbons, natural gas, etc., although the use of such fuels increases the carbon intensity of the process. To reduce carbon intensity, natural gas fuel can be replaced with a low-carbon-intensity fuel, such as "blue" hydrogen, i.e., hydrogen from hydrocarbon processes with CO2 capture (e.g., natural gas reforming). Other alternative fuels targeting low carbon intensity may include renewable natural gas (RNG), biogas, etc. The oxidant gas is typically air, but may also be oxygen-enriched gas or pure oxygen, if desired.

[0045] The reactor tube is filled with at least one ammonia decomposition catalyst. Many metals that catalyze the decomposition of ammonia are known in the art. These metals include transition metals such as 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) can also be used.

[0046] The activity of some of these metals as catalysts for ammonia decomposition is in the following order: It has been reported by Masel et al. (Catalyst Letters, vol. 96, Nos. 3-4, July 2004) to vary in the order Ru>Ni>Rh>Co>Ir>Fe>>Pt>Cr>Pd>Cu>>Te.

[0047] The metals may be unsupported but are usually supported on a suitable support, typically a metal oxide support such as silica (SiO), alumina (AlO), zirconia (ZrO), or a mixed metal oxide support such as spinel (MgAlO) or perovskite (CaTiO).

[0048] As will be appreciated by those skilled in the art, the activity of a supported metal catalyst typically depends in part on the loading of the catalytically active metal on the support. In this regard, metal loadings will vary depending on specific requirements, but are typically within the range of about 0.1 wt. % to about 70 wt. %. For more active metals, such as ruthenium, the loading may be toward the lower end of the range, e.g., about 0.1 wt. % to about 10 wt. %, or about 0.2 wt. % to about 5 wt. %. For less active metals, such as nickel, the loading may be toward the higher end of the range, e.g., about 20 wt. % to about 65 wt. %.

[0049] Supported metal catalysts may be unpromoted or may be promoted with at least one other metal, for example, one or more Group 1 metals, such as lithium (Li), sodium (Na), and potassium (K), Group 2 metals, such as magnesium (Mg) and calcium (Ca), or Group 13 metals, such as aluminum (Al), to improve activity as is well known in the art.

[0050] Any conventional catalyst known for ammonia decomposition may 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) pp 3726-3736), Boisen et al. (J. Catalysis 230 (2005) pp 309-312), US5055282A, US5976723A, and US2020 / 0164346A.

[0051] Bimetallic catalysts, or catalysts containing two catalytically active metals, are also suitable for use in the present invention. Examples include complex metals or metal alloys or metal nanoclusters supported on perovskites, complex oxides or nitrides, or mixed oxides or mixed nitrides disclosed in US 2021 / 0001311 A, such as CoNi-MgSrCeO4 and 1 wt. % K-CoNi-MgSrCeO4.

[0052] The catalyst of the present invention comprises, e.g., contains, or consists of, at least one metal-based catalyst. Catalytically active metals are typically selected from the transition metals of the periodic table. Suitable transition metal-based catalysts are those that are suitable for catalytic activity at temperatures in the range of 475°C to 600°C, as described by Lamb et al., i.e., r=8.73exp[-76710 / RT].(P NH3 )0.28.(P H2 )-0.42.(1-β 2 ) has an activity greater than 0.2 times, or greater than 0.4 times, or greater than 0.6 times, or greater than 0.8 times the rate calculated according to equation 9 proposed by During the ceremony: "r" is the reaction rate (or "activity") of the catalyst; "RT" is the ideal gas constant "R" (8.314 Jmol -1 K -1 ) multiplied by the temperature in Kelvin, "T", P NH3 is the partial pressure of ammonia, P H2 is the partial pressure of hydrogen, β is defined in the paper as follows (see equation 5 proposed by Lamb et al.):

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[0053] The inventors have recognized that Equation 9 of Lamb et al. can be extrapolated to temperatures outside of the 475°C-600°C range, for example, within the range of 450°C-700°C.

[0054] Also, suitable transition metals are typically significantly cheaper than the noble metals, i.e., gold, silver, and platinum group metals, i.e., ruthenium, rhodium, palladium, osmium, iridium, and platinum, especially ruthenium. For example, the unit price of suitable transition metals is typically at least 100 times, e.g., at least 300 times, or at least 500 times, lower than the unit price of ruthenium. Noble metals are typically not suitable for use as the primary catalytically active metal of a catalyst in a catalyst bed because they are too expensive.

[0055] Particularly suitable transition metals for use as the main catalytically active metal of the catalyst in the catalyst bed of the reactor tubes are selected from the first row transition metals, i.e., scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, and in particular may be selected from chromium, manganese, iron, cobalt, nickel, and copper. The catalyst may also be a zeolite supporting chromium, copper, iron, nickel, and / or cobalt.

[0056] Catalytically, the metal may be selected from the group consisting of iron, cobalt, and nickel, with nickel typically being the most preferred metal in this regard.

[0057] However, in other embodiments, the reactor tubes of the furnace are packed with at least two different ammonia decomposition catalysts having different activities, with the first (less active) catalyst, e.g., a first-row transition metal-based catalyst, typically located in a layer upstream of the second (more active) catalyst, e.g., a ruthenium-based catalyst. The purpose of the more active downstream layer is to ensure that the decomposition reaction approaches equilibrium. In some embodiments, each reactor tube bed has only two layers: an upstream layer of the first catalyst and a downstream layer of the second catalyst.

[0058] In embodiments having a downstream layer of more active catalyst, the upstream layer has a volume that may be at least 50%, or at least 60%, or at least 70%, or at least 80% of the volume of the entire catalyst bed. Typically, the volume of the upstream layer is no more than 95% of the volume of the catalyst bed.

[0059] Although there may be an intervening layer between the upstream and downstream layers, in these embodiments there usually is not, and the remainder of the catalyst bed is typically a downstream layer of more active catalyst. Thus, the downstream layer has a volume that may be 50% or less, or 40% or less, or 30% or less, or 20% or less of the volume of the entire catalyst bed. Typically, the volume of the downstream layer is at least 5% of the volume of the catalyst bed.

[0060] The term "nickel-based catalyst" refers to a catalyst that contains nickel as the only (or at least predominant) catalytically active metal, i.e., the metal responsible for catalyzing the decomposition reaction. Nickel may be the only metal in the catalyst, or alternatively, one or more other metals may be present, for example, in a material that supports the nickel. The terms "ruthenium-based catalyst," "iron-based catalyst," and "first-row transition metal-based catalyst" are intended to be interpreted accordingly.

[0061] Suitable nickel- and ruthenium-based catalysts may be supported, for example, on alumina (as disclosed in Lamb et al. or Masel et al.) or spinel (as disclosed in Boisen et al.), and may optionally be promoted with a Group 1 or 2 metal.

[0062] As mentioned above, water is typically present in ammonia as a contaminant. Water can be removed from the ammonia, in which case a water-intolerant catalyst, such as an iron-based catalyst, can be used in the reactor tubes. However, water is not removed in preferred embodiments to save capital and operating costs and reduce energy consumption. In these embodiments, a catalyst that cannot tolerate water, such as an iron-based catalyst, is not used. Instead, the catalyst in the reactor tubes can tolerate up to 1 mol.% water in the ammonia feed. Such catalysts include nickel-based and ruthenium-based catalysts.

[0063] The feed to the catalyst-filled reactor tubes of the furnace may be at a temperature of up to about 800° C. Typically, the feed is at a temperature in the range of about 500° C. to about 800° C., or about 600° C. to about 700° C., e.g., about 650° C.

[0064] The decomposition temperature and pressure typically dictate that the ammonia slip in the reactor tubes be no more than 3 mol.%, for example, about 0.5 mol.% to about 1.5 mol.%. One advantage of embodiments of the present invention is that slight increases in ammonia slip within the process design specifications, perhaps due to catalyst poor performance due to aging, can be accommodated due to improved hydrogen recovery.

[0065] The heated ammonia gas is typically fed directly to a catalyst-containing reactor tube, i.e., causing the ammonia to decompose to produce decomposed gas, without first decomposing a portion of the ammonia to form partially decomposed ammonia gas. However, in some embodiments, the heated ammonia gas is partially decomposed in an adiabatic reaction unit containing at least one catalyst bed to produce partially decomposed ammonia gas for feeding to a catalyst-filled reactor tube, such as an electrically heated or direct-fired tube reactor.

[0066] 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 at least 35%, e.g., at least about 40%, and / or up to about 50%. Stated another way, 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 in partially decomposed ammonia gas, or to an amount in the range of about 0.5 to about 0.7, or to an amount in the range of about 0.55 to about 0.65, or to an amount in the range of about 0.55 to about 0.60, e.g., about 0.57.

[0067] An adiabatic reaction unit may be incorporated into the process design to improve overall efficiency, particularly by using 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.

[0068] The primary design parameter for an adiabatic reactor unit is the inlet temperature. Because the ammonia decomposition reaction is endothermic, higher inlet temperatures allow for greater conversion in the unit. However, higher temperatures place greater demands on construction materials and catalysts. Therefore, inlet temperatures are typically in the range of about 350°C to about 800°C, or about 500°C to about 700°C, or about 550°C to about 650°C.

[0069] Due to the high temperatures and ammonia concentrations involved, reactor tubes for decomposition reactors may typically be constructed from materials that are resistant to ammonia and / or ammonia nitridation. Suitable materials include nickel-based alloys containing at least 40% or at least 50% nickel by weight. Such alloys typically have up to 90% or up to 80% nickel by weight. The alloys typically contain one or more other metals selected from chromium, cobalt, molybdenum, and iron.

[0070] Specific examples of suitable nickel-based alloys include UNS N06600, N06625, N06601, N06617, N06025, N06230, N07214, and N08811. In some embodiments, austenitic nickel-chromium based superalloys such as Inconel may be used.

[0071] The Unified Numbering System (UNS) is an alloy designation system widely accepted 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.

[0072] Other suitable materials include cobalt-based alloys such as UNSR30188. In addition, high-temperature alloys with low resistance to ammonia nitriding, such as UNSN08811 or cast alloys such as HPPb, HPMicro-Alloyed, MA-1 (MetalTek International, USA), may be suitable, especially if surface-modified or coated with a corrosion-resistant layer such as aluminizing, aluminizing and then oxidizing, or a ceramic coating. Nitriding-resistant alloys can also be used with surface modifications or coatings for improved performance.

[0073] An adiabatic reaction unit typically comprises one or more adiabatic reactors, each comprising a catalyst bed, and the or each adiabatic reactor may be made from one or more of the ammonia-resistant and / or ammonia nitridation-resistant materials described above.

[0074] 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 needed. The reactors may be arranged in series or parallel, or a combination of series and parallel, depending on the process requirements. However, in a preferred embodiment, the adiabatic reaction unit has two such reactors arranged in series with intermediate interstage heating of the partially cracked ammonia gas by heat exchange against the cracked gas or flue gas.

[0075] Each adiabatic reactor has a bed containing at least one catalyst suitable for decomposing ammonia. Any conventional ammonia decomposition catalyst may be used in the bed of the or each adiabatic reactor. Suitable catalysts are discussed above in the context of the reactor tube catalysts.

[0076] In embodiments in which water is removed from ammonia prior to decomposition, a water-intolerant catalyst, such as an iron-based catalyst, may be used in the adiabatic reactor. However, water is not removed in preferred embodiments to save capital and operating costs and reduce energy consumption. In these embodiments, the catalyst bed of the adiabatic reaction unit does not contain an iron-based catalyst; instead, a water-tolerant catalyst, i.e., a metal-based catalyst that can tolerate the presence of up to 1 mol.% water, is preferred. In this regard, either a nickel-based catalyst or a ruthenium-based catalyst, or a combination of a nickel-based catalyst and a ruthenium-based catalyst, may be used in the bed of the adiabatic reactor unit.

[0077] As mentioned above, ruthenium-based catalysts tend to be more active but more expensive than nickel-based catalysts, so further optimization is possible through catalyst selection and, if more than one type of catalyst is used, through the ordering of catalyst layers within the bed of the adiabatic reaction unit.

[0078] In some embodiments having two adiabatic reactors in series, the catalyst bed of the first reactor comprises, e.g., contains or consists of, e.g., a single layer of a first catalyst, e.g., a ruthenium-based catalyst, and the catalyst bed of the second reactor comprises, e.g., contains or consists of, an upstream layer of a second catalyst, e.g., a nickel-based catalyst, that is typically less active than the first catalyst, and a downstream layer of a third catalyst, e.g., a ruthenium-based catalyst, that is typically more active than the second catalyst.

[0079] In these embodiments, the first and third catalysts can be the same. Alternatively, the first and third catalysts can be different, for example, containing different catalytically active metals, or the same catalytically active metals but on different supports, or the same catalytically active metals on the same support but at different loadings.

[0080] In other embodiments having two adiabatic reactors in series, the catalyst bed of the first reactor comprises, e.g., contains or consists of, for example, a single layer of a first catalyst, e.g., a nickel-based catalyst, and the catalyst bed of the second reactor typically comprises, e.g., contains or consists of, an upstream layer of a second catalyst, e.g., a nickel-based catalyst, that has similar activity to the first catalyst, and a downstream layer of a third catalyst, e.g., a ruthenium-based catalyst, that is typically more active than the first and second catalysts.

[0081] In these embodiments, the first and second catalysts can be the same. Alternatively, the first and second catalysts can be different, for example, containing different catalytically active metals, or the same catalytically active metals but on different supports, or the same catalytically active metals on the same support but at different loadings.

[0082] In both sets of embodiments, the volume of the upstream layer of the second catalyst in the bed of the second reactor can be about 40% to about 90%, e.g., about 50% to about 70%, or about 60%, of the total volume of the bed. If no additional layer of catalyst is present, the volume of the downstream layer of the third catalyst in the bed of the second reactor can be about 10% to about 60%, e.g., about 30% to about 50%, or about 40%, of the total volume of the bed.

[0083] The present inventors have recognized that ruthenium-based catalysts are not only tolerant to water, but also capable of cracking hydrocarbon oils into shorter hydrocarbons, such as methane, along with carbon monoxide and hydrogen. Thus, the use of these catalysts in an adiabatic reaction unit can eliminate the need for an upstream dedicated unit for removing oil from liquid ammonia.

[0084] Also, at higher temperatures, catalyst sintering is known to reduce catalyst activity and life. In this regard, those skilled in the art will recognize the need to balance improved conversion with higher vessel costs and shorter catalyst life.

[0085] However, in the most preferred embodiment, the bed of the or each adiabatic reactor contains a nickel-based catalyst which may or may not be the same as the catalyst used in the reactor tubes.

[0086] Heat from the cracked gas and flue gas is typically used to heat the feed streams to the adiabatic reaction unit (if present) and furnace, thereby reducing the overall energy consumed by the process. In this regard, the temperature of the cracked gas can be up to about 750°C, e.g., typically about 650°C to about 750°C, or about 675°C to about 725°C. The temperature of the flue gas can be up to about 840°C at its highest point. However, the temperature drops due to heat leaks, and is typically about 700°C to about 800°C, at which point the heat can be effectively utilized.

[0087] When an adiabatic reaction unit is used to partially decompose heated ammonia gas and the partially decomposed gas is heated to the feed temperature of the catalyst-filled reactor tubes of the furnace, at least a portion of the capacity required to heat the partially decomposed gas is provided by heat exchange with the decomposed gas. In a preferred embodiment, the decomposed gas is not used to heat another process fluid prior to heating the partially decomposed gas. Some of this heating capacity may be provided in another manner, for example, by heat exchange with flue gas. However, all of this heating capacity is preferably provided by the decomposed gas.

[0088] In a preferred embodiment, the composition of the ammonia typically remains at least substantially unchanged from the liquid ammonia in storage to the 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, although if a ruthenium-based catalyst is used, oil removal is not necessary. However, water is typically not removed, so any water present in the liquid ammonia will also be present in the heated ammonia gas.

[0089] When the partially cracked gas is heated by heat exchange with the cracked gas, the temperature of the cracked gas is reduced. The cooled cracked gas is then typically further cooled by providing at least a portion of the heating capacity required to produce heated ammonia gas from liquid ammonia. After cooling, hydrogen can be recovered as a product from the cracked gas. Recovery can be achieved in a PSA process, by using one or more selectively permeable membranes, or by a combination of PSA and membrane separation. In a preferred embodiment, hydrogen recovery is achieved by a PSA process alone, i.e., without the use of membrane separation.

[0090] In embodiments using a PSA process, an exhaust gas containing nitrogen gas, residual ammonia, and residual hydrogen is produced. This exhaust gas can be used as fuel for combustion in a furnace. Alternatively, a portion of the exhaust gas can be used as fuel, while another portion can be compressed and returned to the PSA process for improved hydrogen recovery.

[0091] Aspects of the present invention include the following: #1. A process for decomposing ammonia, the process comprising: providing heated ammonia gas at superatmospheric pressure; decomposing the heated ammonia gas in an ammonia decomposition system to produce a cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia gas; cooling the cracked gas by heat exchange to produce a cooled cracked gas; recovering hydrogen from the cooled cracked gas in a hydrogen recovery unit to produce a hydrogen gas product and an exhaust gas comprising nitrogen gas, residual hydrogen gas, and residual ammonia gas; recovering the residual ammonia from at least a portion of the exhaust gas, or from a combined gas comprising the exhaust gas, by partial condensation and phase separation to produce recovered liquid ammonia and an ammonia-lean exhaust gas comprising nitrogen gas and residual hydrogen gas; and recovering the residual hydrogen from the ammonia-lean exhaust gas, or from an ammonia-free exhaust gas derived therefrom, by partial condensation and phase separation to produce a hydrogen-rich gas and a nitrogen-rich liquid.

[0092] #2. The process of #1, wherein at least a portion of the recovered liquid ammonia, or liquid ammonia derived therefrom, is recycled to the ammonia decomposition system.

[0093] #3. The process of #1 or #2, wherein recovering the residual ammonia from the flue gas or from a combined gas containing the flue gas comprises compressing the flue gas or the combined gas containing the flue gas to form a compressed flue gas; drying the compressed flue gas to form a dried, compressed flue gas; cooling the dried, compressed flue gas by heat exchange against one or more "cold" process fluids to condense the residual ammonia and produce a partially condensed flue gas; and phase separating the partially condensed flue gas to produce recovered liquid ammonia and an ammonia-lean flue gas.

[0094] #4. The process according to #3, wherein the compressed exhaust gas is dried in a TSA process.

[0095] #5. A process described in any of #1 to #4, comprising reducing the pressure of the recovered liquid ammonia to produce reduced pressure liquid ammonia and an ammonia-rich flash gas, separating the reduced pressure liquid ammonia and the ammonia-rich flash gas, and recycling the reduced pressure liquid ammonia to an ammonia decomposition system.

[0096] #6. The process of #5, wherein the recovered liquid ammonia is warmed by heat exchange against one or more cooled process fluids before being depressurized.

[0097] #7. The process of #5 or #6, wherein the ammonia decomposition system involves the combustion of fuel to provide heat for the decomposition process, and the ammonia-rich flash gas is used to provide a portion of the fuel.

[0098] #8. A process described in any of #1 to #7, wherein recovering the residual hydrogen from the ammonia-lean tail gas comprises cooling the ammonia-lean tail gas, or an ammonia-free tail gas derived therefrom, by heat exchange against one or more "cold" process fluids to condense the nitrogen and produce a partially condensed fluid, and optionally reducing the pressure of the partially condensed fluid and then separating the partially condensed fluid to produce a hydrogen-rich gas and a nitrogen-rich liquid.

[0099] #9. A process according to any of #1 to #8, wherein more than trace amounts of ammonia are present in the ammonia-lean exhaust gas, and the process removes ammonia from the ammonia-lean exhaust gas by an adsorption process to produce an ammonia-free exhaust gas.

[0100] #10. The process according to #9, wherein the adsorption process is a TSA process.

[0101] #11. A process according to any one of #1 to #10, wherein the hydrogen-rich gas, or a regeneration outlet gas derived therefrom, is recycled to a hydrogen recovery unit.

[0102] #12. The process of #11, wherein the recycling of the hydrogen-rich gas comprises warming the hydrogen-rich gas by heat exchange against one or more cooled process fluids to produce a warmed hydrogen-rich gas, compressing the warmed hydrogen-rich gas to produce a compressed hydrogen-rich gas, and recycling the compressed hydrogen-rich gas, or a regeneration outlet gas derived therefrom, to a hydrogen recovery unit.

[0103] #13. A process described in any of #1 to #12, wherein at least a portion of the nitrogen-rich liquid and / or nitrogen-enriched liquid derived therefrom is warmed by heat exchange against one of a plurality of cooled process fluids to produce waste nitrogen gas.

[0104] #14. The process of #13, wherein the ammonia decomposition system involves the combustion of fuel to provide heat for the decomposition process, and wherein waste nitrogen gas containing hydrogen and / or ammonia, or a regeneration outlet gas derived therefrom, is used to provide a portion of the fuel.

[0105] #15. A process described in any of #1 to #14, comprising reducing the pressure of at least a portion of the nitrogen-rich liquid to produce a reduced-pressure nitrogen-enriched liquid and a hydrogen-enriched flash gas, separating the reduced-pressure nitrogen-enriched liquid from the hydrogen-enriched flash gas, and recycling the hydrogen-enriched flash gas to the exhaust gas from the hydrogen recovery unit.

[0106] #16. The process of #15, wherein said recycling of the hydrogen-enriched flash gas includes warming the hydrogen-enriched flash gas by heat exchange against one or more cooled process fluids to produce a warmed hydrogen-enriched flash gas, and combining the hydrogen-enriched flash gas, or a reduced-pressure hydrogen-enriched flash gas derived therefrom, with exhaust gas from a hydrogen recovery unit at a suitable point in the compression system to form a combined gas.

[0107] #17. An apparatus for decomposing ammonia, comprising: an ammonia decomposition system having an inlet for heated ammonia gas at superatmospheric pressure and an outlet for cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia gas; an inlet for cooled cracked gas in fluid flow communication with the outlet of the ammonia decomposition system, a first outlet for hydrogen gas product, and a second outlet for a tail gas comprising nitrogen gas, residual hydrogen gas, and residual ammonia gas; a hydrogen recovery unit having an inlet for partially condensed tail gas in fluid flow communication with the second outlet of the hydrogen recovery unit, a first outlet for recovered liquid ammonia, and a second outlet for an ammonia-lean tail gas comprising nitrogen gas and residual hydrogen gas; and a first phase separator having an inlet for partially condensed ammonia-lean tail gas in fluid flow communication with the second outlet of the first phase separator. and a second phase separator having an inlet for lean tail gas, a first outlet for hydrogen-rich gas, and a second outlet for nitrogen-rich liquid, wherein the apparatus comprises a heat exchange system comprising: a heat exchanger located between an outlet of the ammonia decomposition system and an inlet of the hydrogen recovery unit, the heat exchanger being arranged to cool the cracked gas by heat exchange against an ammonia feed to the ammonia decomposition system; a heat exchanger located between a second outlet of the hydrogen recovery unit and the first phase separator, the heat exchanger being arranged to condense residual ammonia gas in the tail gas by heat exchange against one of a plurality of "cold" process fluids; and a heat exchanger located between a second outlet of the first phase separator and an inlet of the second phase separator, the heat exchanger being arranged to condense nitrogen in the ammonia-lean tail gas by heat exchange against one of a plurality of "cold" process fluids.

[0108] #18. The apparatus of #17, wherein the first outlet of the first phase separator is in fluid flow communication with an inlet of the ammonia decomposition system.

[0109] #19. An apparatus as described in #17 or #18, comprising an exhaust gas compression system having an inlet for exhaust gas in fluid flow communication with the second outlet of the hydrogen recovery unit and an outlet for compressed exhaust gas, and a dryer having an inlet for compressed exhaust gas in fluid flow communication with the outlet of the exhaust gas compression system and an outlet for dried compressed exhaust gas in fluid flow communication with the inlet of the first phase separator.

[0110] #20. The apparatus according to #19, wherein the dryer is a TSA unit.

[0111] #21. The apparatus of any of #17 to #20, comprising a pressure reducing valve having an inlet for recovered liquid ammonia in fluid flow communication with a first outlet of the first phase separator and an outlet for a two-phase fluid comprising reduced pressure liquid ammonia and ammonia-rich flash gas, and a further phase separator having an inlet for a two-phase fluid comprising reduced pressure liquid ammonia and ammonia-rich flash gas in fluid flow communication with the outlet of the pressure reducing valve, a first outlet for liquid ammonia, and a second outlet for the ammonia-rich flash gas in fluid flow communication with an inlet of an ammonia decomposition system.

[0112] #22. The apparatus described in #21, wherein the heat exchange system comprises a heat exchanger located between the first outlet of the first phase separator and the inlet of the pressure reducing valve and arranged to warm the recovered liquid ammonia by heat exchange against the exhaust gas / ammonia lean exhaust gas from the hydrogen recovery unit.

[0113] #23. The apparatus described in #21 or #22, wherein the ammonia decomposition system comprises: a furnace having at least one inlet for fuel and oxidant gas in fluid flow communication with at least one burner; a catalyst-containing reactor tube having an upstream end in fluid flow communication with the inlet of the ammonia decomposition system and a downstream end in fluid flow communication with an outlet for decomposed gas; and a convection section in fluid flow communication with the radiant section and having an outlet for flue gas; and wherein the second outlet of the further phase separator is in fluid flow communication with at least one inlet of the furnace.

[0114] #24. An apparatus described in any of #17 to #23, comprising a pressure reducing valve having an inlet in fluid flow communication with the second outlet of the first phase separator and an outlet in fluid flow communication with the inlet of the second phase separator.

[0115] #25. An apparatus described in any of #17 to #24, comprising an ammonia removal unit having an inlet for ammonia-lean exhaust gas in fluid flow communication with the second outlet of the first phase separator and an outlet for ammonia-free exhaust gas in fluid flow communication with the inlet of the second phase separator.

[0116] #26. The apparatus according to #25, wherein the ammonia removal unit is a TSA unit.

[0117] #27. An apparatus according to any one of #17 to #27, wherein the first outlet of the second phase separator is in fluid flow communication with the inlet of the hydrogen recovery unit.

[0118] #28. An apparatus as described in any of #17 to #27, comprising a recovered hydrogen compression system having an inlet for hydrogen-rich gas in fluid flow communication with the first outlet of the second phase separator and an outlet for compressed hydrogen-rich gas in fluid flow communication with the inlet of the hydrogen recovery unit, wherein the heat exchange system is located between the first outlet of the second phase separator and the inlet of the recovered hydrogen compression system, the heat exchanger being positioned to warm the hydrogen-rich gas by heat exchange against one or more cooled process streams.

[0119] #29. An apparatus described in any of #17 to #29, comprising an expander for expanding nitrogen-rich gas or nitrogen-enriched gas derived therefrom to generate refrigeration for the process.

[0120] #30. An apparatus described in any of #17 to #29, comprising a pressure reducing valve having an inlet for nitrogen-rich liquid in fluid flow communication with the second outlet of the second phase separator and an outlet for a two-phase fluid comprising nitrogen-enriched liquid and hydrogen-enriched gas, and a third phase separator having an inlet for two-phase fluid comprising nitrogen-enriched liquid and hydrogen-enriched gas in fluid flow communication with the outlet of the pressure reducing valve, a first outlet for the nitrogen-enriched liquid, and a second outlet for hydrogen-enriched gas in fluid flow communication with the inlet of the exhaust gas compression system.

[0121] #31. An apparatus described in any of #17 to #30, wherein the ammonia decomposition system comprises: a furnace having at least one inlet for fuel and oxidant gas in fluid flow communication with at least one burner; a catalyst-containing reactor tube having an upstream end in fluid flow communication with the inlet of the ammonia decomposition system and a downstream end in fluid flow communication with an outlet for decomposed gas; and a convection section in fluid flow communication with the radiant section and having an outlet for flue gas, wherein at least one inlet of the furnace is in fluid flow communication with the second outlet of the second phase separator.

[0122] The inventors note that because ammonia and hydrogen are recovered, it is typically a small penalty to add a column to the process to purify the nitrogen to the point where it can be sold as a product. With this in mind, those skilled in the art will understand that the present invention can be modified to produce pure nitrogen by further recovering hydrogen from the liquid nitrogen and augmenting the cold ends partial condensation step with distillation to deliver a pure nitrogen stream.

[0123] The invention will now be described, by way of example only, with reference to the drawings in which:

[0124] 1 depicts an ammonia decomposition process 1 in which liquid ammonia stream 2 supplied at about −32° C. is removed from storage (not shown) and pumped through pump P101 to produce pressurized liquid ammonia stream 4 at a pressure of about 46 bar, which is preheated by heat exchange with a heat transfer fluid, in this case typically about 55% by weight ethylene glycol or propylene glycol in water, to produce preheated liquid ammonia stream 6 at about 55° C. in heat exchanger E271. 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.

[0125] The preheated liquid ammonia in stream 6 is further heated by heat exchange in heat exchanger E312 to produce further heated liquid ammonia stream 8. The further heated liquid ammonia in stream 8 is then vaporized by heat exchange in heat exchanger E311 to produce ammonia vapor stream 10. The ammonia vapor in stream 10 is then superheated by heat exchange in heat exchanger E310 to produce ammonia gas stream 12 heated at about 260°C.

[0126] The heated ammonia gas in stream 12 is further heated by heat exchange in heat exchanger E2102 to produce superheated ammonia gas stream 14 at about 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) located between them.

[0127] Superheated ammonia gas in stream 14 at about 420°C and about 43 bar is fed to an ammonia cracker system, which in this embodiment comprises, arranged in series, a first adiabatic reactor vessel C141, a second adiabatic reactor vessel C142, and a direct-calcined tube furnace F201.

[0128] Thus, Stream 14 is fed to first adiabatic reactor vessel C141 and passed through a bed of ruthenium-based catalyst. A portion of the ammonia gas is decomposed over the catalyst to form intermediate gas stream 16 containing a portion of the decomposed ammonia. The mole fraction of ammonia in the gas passing through first adiabatic reactor vessel C141 is reduced from approximately 1 to about 0.9.

[0129] The intermediate gas is at about 360°C before being heated by heat exchange in heat exchanger E2 103 to produce superheated intermediate gas stream 18, which is then fed to second adiabatic reactor vessel C142 at about 590°C and passed through beds containing an upstream layer of nickel-based catalyst and a downstream layer of ruthenium-based catalyst to produce partially decomposed ammonia gas stream 20. The mole fraction of ammonia in the gas passing through second adiabatic reactor vessel C142 drops to about 0.9 to about 0.6.

[0130] The catalyst bed in the second adiabatic reactor vessel C142 has two layers: a layer of nickel-based catalyst over a layer of ruthenium-based catalyst to more efficiently use heat, thus maximizing ammonia conversion. The catalyst volume is also optimized; the volume of the ruthenium-based catalyst is minimized by limiting the outlet temperature of the second adiabatic reactor vessel to about 390°C. The inventors have found that lowering this temperature further increases the volume required for the ruthenium-based catalyst.

[0131] The ruthenium-based catalyst is the same in both the first and second adiabatic reactor vessels, however, different ruthenium-based catalysts may be used.

[0132] The partially cracked ammonia in Stream 20 is heated by heat exchange in heat exchanger (or "economizer") E305 before being fed as Stream 22 at a pressure of about 38 bar to the catalyst-filled tubes in the radiant section F201 of the furnace (or reactor). Heating the feed to the tubes increases the amount of cracking that can be done with heat from the burner by reducing the capacity required to heat the partially cracked stream to reaction temperature. Utilizing the cracked stream from the tubes allows for efficient use of this high-temperature stream. The inlet temperature of the direct-fired tube furnace is limited to about 500°C to limit the interior wall temperature of the cracker tubes.

[0133] Air stream 62 was passed through forced draft fan K212 before being preheated by heat exchange in heat exchanger E2142 to produce preheated air stream 64. The preheated air in stream 64 was supplied to the burners (not shown) of furnace F201 along with natural gas stream 70 as fuel. Preheating the air in this manner helps reduce fuel requirements.

[0134] The tubes in the furnace's radiant section F201 are packed with two types of ammonia decomposition catalyst in two different layers. A ruthenium-based catalyst is used in the first layer in each tube, where its faster reaction rate allows the metal temperature to be kept within the design limit of about 660°C. The second layer in the tube, downstream of the first layer, contains a lower-cost, but less active, nickel-based catalyst.

[0135] Cracked gas stream 24 exits the radiant section F201 of the direct-fired tube furnace at approximately 640°C and is then fed to economizer E305, which provides the necessary capacity to heat the partially cracked ammonia, thereby reducing the temperature of the cracked gas to approximately 530°C.

[0136] Economizer E305 is depicted as a shell-and-tube style heat exchanger with partially cracked ammonia gas passing through the tubes and cracked gas passing through the shell side, however, this arrangement could be reversed or indeed a different style heat exchanger could be used.

[0137] Cracked gas stream 26 is then fed from economizer E305 to heat exchanger E310, which provides the capacity necessary to superheat the ammonia gas, thereby further reducing the temperature of the cracked gas to approximately 389°C.

[0138] Cracked gas stream 28 is then fed from heat exchanger E310 to heat exchanger E311 to provide the capacity necessary to vaporize the further heated liquid ammonia, thereby further reducing the temperature of the cracked gas to about 109°C.

[0139] Cracked gas stream 30 is then fed from heat exchanger E311 to heat exchanger E312 to provide the capacity necessary to further heat the heated pressurized liquid ammonia, thereby further reducing the temperature of the cracked gas to about 70°C.

[0140] Each of heat exchangers E310, E311, and E312 is depicted as an individual shell-and-tube style heat exchanger, with ammonia passing through the tubes and cracked gas passing through the tube side. However, this arrangement could be reversed for at least one, e.g., all, of these heat exchangers. Alternatively, the heat exchangers could be combined into a single shell-and-tube style heat exchanger, or different styles of heat exchangers could actually be used.

[0141] Cracked gas stream 32 from heat exchanger E312 is then further cooled by heat exchange with a heat transfer fluid in cooler E323 and then fed as stream 34 to PSA system U501 where it is separated into hydrogen gas stream 40, which is removed as product, and PSA tail gas stream 42, which contains nitrogen gas, residual hydrogen gas, and residual ammonia gas. The hydrogen gas in stream 40 may be fed to a hydrogen liquefaction unit (not shown) to produce liquid hydrogen.

[0142] All of the PSA off-gas in stream 42 can be sent directly as fuel (stream 60) for combustion in furnace F201. Alternatively, stream 42 can be split into two portions.

[0143] A first portion of the PSA tail gas in stream 44 is heated by heat exchange in heat exchanger E2112 to produce warmed PSA tail gas stream 60, which is then fed to burners in furnace F201, along with air feed 64 and optionally natural gas feed 70, as needed. A minimal amount of natural gas is used as trim fuel to provide the balance of the fuel required in the calciner section.

[0144] The second portion may be sent as stream 46 to multi-stage compression unit K681 for compression. Compression unit K681 has five stages with intercoolers between each stage and an aftercooler following the last stage. Heat is recovered from the compressed gas in the intercoolers and aftercoolers by heat exchange with a heat transfer fluid. Heat may also be recovered from the lubricating oil used in the compression unit, or, if a positive displacement compression unit is used, from the compression unit cylinder using a heat transfer fluid.

[0145] For convenience, the intercooler and aftercooler are represented by a single heat exchanger (labeled E6816A-E) that recovers heat from compressed PSA exhaust gas stream 48 by heat exchange with heat transfer fluid stream 52 to produce cooled compressed PSA exhaust gas stream 50 and warmed heat transfer fluid stream 54.

[0146] The heat transfer fluid warmed in chiller E323 and intercoolers and aftercoolers E6816A-E is then used to provide the capacity required to preheat the liquid ammonia by heat exchange in heat exchanger E271.

[0147] The cooled, compressed PSA tail gas in stream 50 is fed to phase separator C6816, where any condensate is removed as stream 56. The compressed PSA tail gas is then recycled as stream 58 to PSA system U501 for additional hydrogen recovery. In this way, hydrogen recovery can be increased from 85% (without recycle) to 95% (with recycle). This figure can be increased up to 97% with a sufficiently large vessel.

[0148] As noted above, the process can be operated without compression unit K681, resulting in a reduced hydrogen recovery in PSA unit 501. Reducing the hydrogen recovery rate obviously results in less hydrogen gas product. However, reducing the hydrogen recovery rate may still be desirable because having more hydrogen in the exhaust gas reduces the carbon intensity (CI) for the process, thereby reducing the need for natural gas as fuel and reducing carbon dioxide emissions.

[0149] Flue gas stream 72, at about 686°C, passes from radiant section F201 to the convection section 90 of the furnace, where it first provides the capacity needed to heat the intermediate gas from stream 16 in heat exchanger E2103, thereby reducing the temperature of the flue gas that is then used (as stream 74), and provides the capacity needed to further heat the heated ammonia gas from stream 12 in heat exchanger E2102, thereby further reducing the temperature of the flue gas. The flue gas thus provides heating capacity in a direction opposite to the flow of feed gas to the radiant section 23 of the direct-fired tube furnace.

[0150] The cooled flue gas (as stream 76) is then used to provide the power needed to heat the air from stream 62 in heat exchanger E2142, thereby further reducing the temperature of the flue gas. The further cooled flue gas (as stream 78) is then used to provide the power needed to heat the PSA exhaust gas from stream 42 in heat exchanger E2112, thereby further cooling the flue gas.

[0151] The cooled flue gas exits the convection section 90 of the direct-fired tube furnace F201 as stream 80 at approximately 121°C, i.e., above the dew point of water, passes through induced draft fan K211, and then exits the process as stream 82. All of the useful energy has been extracted from the flue gas at this point, which can now be released to the atmosphere, optionally after further processing if necessary depending on its composition.

[0152] Oil may be present in liquid ammonia in amounts up to about 5 ppm from a boiler exhaust gas compressor (not shown) used in conjunction with an ammonia storage tank (not shown), and may be present either at the location where the ammonia is produced, or at the site where the ammonia is decomposed, or indeed anywhere in transit between the two sites. The presence of oil in ammonia can cause difficulties because ammonia decomposition catalysts may not tolerate the 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 a bed of activated carbon.

[0153] If oil is removed from ammonia, an oil removal unit (not shown) can be located in stream 2 (i.e. in the feed line to pump P101), stream 4 (i.e. between pump P101 and glycol heater E271), stream 6 (i.e. between glycol heater E271 and heat exchanger E312), stream 8 (i.e. between heat exchangers E312 and E311), or stream 10 (i.e. between heat exchangers E311 and E310).

[0154] The process of Figure 1 does not recover ammonia other than in the exhaust gas used as fuel in the furnace. However, the present invention allows the cycle of Figure 1 to be run with PSA system U501 operating at 85% recovery, i.e., without PSA recycle, while still achieving an overall recovery of at least 99% of the contained hydrogen from the feed ammonia by further processing the PSA exhaust gas as discussed below.

[0155] Figure 2 is a simplified flowsheet depicting the process of Figure 1 integrated with a cryogenic recovery system 200 in accordance with the present invention. The flowsheet is similar to that depicted in Figure 1, and features common to both flowsheets have been given the same reference numerals. Below is a discussion of the different features.

[0156] PSA tail gas stream 300 is removed from PSA system U501 and fed to cryogenic recovery system 200 where it is compressed, cooled, and partially condensed to recover liquid ammonia in stream 312. The remaining vapor is further processed, and recycled hydrogen is recovered to PSA system U501 in stream 323 to produce a waste gas containing primarily nitrogen with some residual hydrogen gas, which is fed as stream 44 to heat exchanger E2112, where it is warmed by heat exchange against flue gas before being fed as stream 60 to the burners in the radiant section of furnace F201. Finally, an ammonia-containing aqueous condensate stream is removed from cryogenic recovery system 200 as stream 302. Stream 302 may be fed to a selective catalytic reduction (SCR) unit, as disclosed in PCT / US2021 / 037996 (WO2022 / 265648A).

[0157] Figure 3 is a simplified flowsheet depicting a first configuration of the process in the cryogenic recovery system 200 of Figure 2. Features common to both flowsheets are given the same reference numerals. Below is a discussion of the different features.

[0158] A PSA exhaust gas stream 300 at about 1.2 bar is fed to a compression system 301 where it is compressed to form a compressed PSA exhaust gas stream 303 at about 35 bar. The compressed exhaust gas is fed to a dryer 304 where it is dried to form a dried compressed exhaust gas stream 305. Water is removed from the gas as it would otherwise freeze in the next step.

[0159] Any suitable dryer may be used, however, in a preferred embodiment, the dryer 304 is an adsorption unit, such as a TSA unit.

[0160] Dry stream 305 is then fed to heat exchanger 306 where it is cooled by heat exchange to approximately −68° C. to condense the ammonia in the tail gas to form partially condensed tail gas stream 307. The vapor and liquid phases in stream 307 are separated in first separator 308 to form recovered liquid ammonia stream 309 and ammonia-lean tail gas stream 314.

[0161] Approximately 82% of the ammonia in the PSA tail gas is recovered as a liquid phase in the first separator 308, the temperature of which is a few degrees, eg, about 10 degrees, warmer than the freezing point of ammonia, which is about -78°C.

[0162] Recovered liquid ammonia stream 309 may be recycled to the ammonia decomposition system. As will be readily understood by those skilled in the art, recovered liquid ammonia cannot be recycled directly to the decomposition system, i.e., without first being at least heated and vaporized. However, there are many options for effecting this recycling. For example, the recovered liquid ammonia may be reduced in pressure and returned to a storage tank (not shown), or may be combined with pumped liquid ammonia and transported separately to delivery pressure before being heated and vaporized in heat exchangers E271, E312, E311, and E310, or may be reduced in pressure and fed directly to feed pump P101, or may be reduced to an intermediate pressure and fed to a "hold-up tank" between feed pump P101 and heat exchanger E271.

[0163] However, recovered liquid ammonia stream 309 is depicted in Figure 3 as being fed to heat exchanger 306 where it is warmed by the heat exchanger and reduced in pressure across valve 350 to produce warmed liquid ammonia which is fed as stream 310 to further separator 311. Note that warming of the recovered liquid ammonia in heat exchanger 306 is optional, and stream 309 can simply be reduced in pressure across valve 350 to form the two-phase feed to separator 311. Separator 311 may be a hold-up tank, a storage tank, or a separate vessel.

[0164] The recovered liquid ammonia, Stream 312, can be recycled along one of the options discussed above. For example, Stream 312 can be combined with Stream 2 in Figure 2. Additionally, flash vapor resulting from the pressure reduction (Stream 313) can be sent as part of the flow of Stream 44 to the burners in the radiant section of furnace F201 via heat exchanger E2112.

[0165] According to the present invention, the remaining hydrogen is recovered from the ammonia-lean tail gas.

[0166] In embodiments where the ammonia-lean exhaust gas is at least essentially ammonia-free, i.e., free of trace levels of ammonia (e.g., 1 ppm or less), the ammonia-lean exhaust gas itself may be cooled and partially condensed in heat exchanger 306 and then separated to produce a hydrogen-rich gas and a nitrogen-rich liquid.

[0167] In other embodiments where the ammonia-lean tail gas contains more than trace amounts of ammonia, the ammonia must be removed before the tail gas is cooled to prevent the ammonia from freezing and thereby blocking heat exchangers, etc. In these embodiments, ammonia may be removed from the ammonia-lean tail gas by, for example, adsorption in a TSA unit.

[0168] The ammonia-lean tail gas does not need to be warmed before the adsorption process removes residual ammonia. Alternatively, the ammonia-lean tail gas can be warmed first, as depicted in FIG. 3. In this regard, ammonia-lean tail gas stream 314 from first separator 308, which contains primarily nitrogen (e.g., about 66%) along with some hydrogen (e.g., about 33%) and residual ammonia (e.g., up to about 1%), is fed to heat exchanger 306, where it is warmed by heat exchange to ambient temperature to provide cooling to the feed stream to the warming end of heat exchanger 306, producing warmed ammonia-lean tail gas stream 315, which is fed to an ammonia removal unit 316 (e.g., a TSA unit), where residual ammonia is removed to form ammonia-free tail gas stream 317. The residual ammonia is removed from the gas, as it would otherwise freeze in the next step.

[0169] At this point, we note that part of this process could be used to recover only ammonia by using stream 315 as fuel in the ammonia cracking system, i.e., without recovering hydrogen from this stream. Refrigeration could be provided by expanding stream 315 to provide refrigeration in heat exchanger 306, since fuel to the burner is needed at low pressure, or by expanding another process stream or an external stream available at pressure if another source of refrigeration is available, for example, as part of an open-loop or closed-loop refrigeration system; stream 315 could then be warmed above ambient temperature before expansion, such as by utilizing waste heat generated by compression, to maximize the power recovered from expanding stream 315. We have found that this arrangement provides some (if not all) of the advantages of the present invention, especially when combined with the operation of a purge gas compressor to achieve 95% recovery in the PSA.

[0170] The ammonia-free tail gas in stream 317 is fed to heat exchanger 306 where it is cooled by the heat exchanger to about −187° C., thereby condensing the nitrogen to form partially condensed fluid stream 318. The pressure of stream 318 is optionally reduced, for example, to about 10.9 bar across a first Joule-Thomson (or JT) valve 351, and fed to second separator 319 where the fluid vapor and liquid phases are separated to form hydrogen-rich gas stream 320, for example, containing about 80% hydrogen, and nitrogen-rich liquid stream 324, for example, containing about 97.8% nitrogen.

[0171] In embodiments where a pure nitrogen product is required, the nitrogen-rich liquid may be fed to a distillation column (not shown) where it is separated into pure liquid nitrogen and hydrogen-enriched overhead vapor. However, in Figure 3, the pressure of impure liquid nitrogen stream 324 from second separator 319 is depicted in Figure 3 as being reduced (e.g., to about 3.8 bar) across second JT valve 352 to lower its temperature, and the resulting two-phase fluid is separated in third separator 325 to form nitrogen-enriched liquid stream 328 containing, e.g., about 99.5% nitrogen, and hydrogen-enriched flash gas stream 326 containing, e.g., about 55% hydrogen.

[0172] The first phase separator 308 (and further phase separator 311) may be referred to as an intermediate temperature separator, or even a "warm" separator, while the second phase separator 319 and the third phase separator 325 may each be referred to as a "cold end" separator.

[0173] The hydrogen-enriched flash gas in stream 326 may be separately heated through heat exchanger 306 (thereby providing refrigeration capacity to the feed stream) before being recycled to an appropriate point in compression system 301, i.e., a point in the compression system from the feed end to the product end, that is, a point of highest pressure so as to receive the recycle stream with minimal loss of pressure, such as an intermediate stage in compression system 301. However, in Figure 3, stream 326 is recycled after pressure reduction across valve 353 as stream 327 to the feed to compression system 301.

[0174] 3, stream 327 is depicted as being combined with PSA exhaust gas feed stream 300 to compression system 301. However, in embodiments in which compression system 301 is a multi-stage compressor, stream 327 may be recycled to intermediate stages of compression system 301, if desired.

[0175] Alternatively, the warmed hydrogen-enriched flash gas can be mixed with waste nitrogen gas, as described in the next step, and similarly used as burner fuel, regeneration gas in dryer 304 and / or unit 316, or vented.

[0176] Partially condensed fluid stream 318 is optionally reduced in pressure to provide a cold end temperature differential to heat exchanger 306 to cool the ammonia-free tail gas in stream 317 to the required temperature, for example, about −187° C. Reducing the pressure of the partially condensed fluid improves hydrogen recovery and increases the surface tension of the liquid phase, thereby improving gas-liquid separation.

[0177] Nitrogen-rich liquid stream 328 is then evaporated and warmed by heat exchange in heat exchanger 306 (thereby providing refrigeration capacity to the process) and fed as stream 329 to expander 330 where the gas is decompressed to provide cooled waste nitrogen gas stream 331 which is then warmed to ambient and provides further cooling to the warmer end of heat exchanger 306 to form warmed waste nitrogen gas stream 332.

[0178] The expansion work may optionally (or preferably) be utilized to generate electrical power or power that may be used to drive (either in whole or in part) a compression system, such as compression system 301 and / or compression system 322, discussed further below.

[0179] In some embodiments, the third separator 325 may be omitted. In these embodiments, the nitrogen-rich liquid stream 324 is not reduced in pressure, but instead is warmed by heat exchange in heat exchanger 306 and expanded in expander 330, with the resulting cooled nitrogen gas being used to provide additional refrigeration capacity at the warmer end of heat exchanger 306.

[0180] Waste nitrogen gas stream 332 may contain 98% or more nitrogen and still contain enough hydrogen to positively impact the fuel to the burners of the ammonia cracker system. The gas is also useful, for example, as regeneration gas for the adsorption beds in dryer 304 and / or, if applicable, ammonia removal unit 316. Thus, a portion of this stream can be used to regenerate those beds (not shown). The regeneration outlet gas (containing discarded water and / or ammonia impurities from the beds) may then be recombined with an unused portion of the gas to form waste gas (not shown), which may be combined with any flash gas 313 produced by reducing the pressure of the recycled ammonia to form a combined waste gas (not shown). The combined waste gas is fed as stream 44 to heat exchanger E2112 on its way to the burners in the radiant section of furnace F201 to be used as fuel, similar to the operation of the cracker in the reference process.

[0181] The warmed hydrogen-rich gas is fed as stream 321 to compression system 322 where it is compressed to form compressed hydrogen-rich gas stream 323, which is returned to PSA system U501 for hydrogen recovery. The warmed hydrogen-rich gas or compressed hydrogen-rich gas may also be used as a regeneration gas for the adsorbent beds, for example in ammonia removal unit 316 and / or dryer 304. This allows ammonia picked up by the hydrogen-rich gas during regeneration of either or both systems to be recovered and recycled through PSA system U501 back to cryogenic process 200, thereby achieving near 100% recovery of ammonia in cracked ammonia stream 34 returned to decomposition process 1.

[0182] Alternatively, the portion of the gas in stream 332 not used for regeneration (and therefore not containing ammonia) can be vented rather than being used as part of the exhaust gas fuel stream. This stream is only about 0.5 mol.% hydrogen in the process of Figure 3 (or about 1.2 mol.% hydrogen in the configuration of Figure 4). However, if an ammonia cracking system is designed to burn the exhaust gas from a PSA system without ammonia and hydrogen recovery by cryogenic partial condensation, its performance will be affected by venting this nitrogen, and cracker performance will need to be evaluated with reduced nitrogen levels in the burner fuel because this nitrogen is heated in the flame and its heat is released in the convection section.

[0183] Hydrogen-rich flash gas stream 320 from second separator 319 is heated to ambient temperature by heat exchange in heat exchanger 306 to provide refrigeration to the feed stream. The warmed hydrogen-rich gas is fed as stream 321 to compression system 322 where it is compressed to form compressed hydrogen-rich gas stream 323, which is returned to PSA system U501 for hydrogen recovery. PSA system U501 operates at 85% hydrogen recovery, but the recycle loop created by the cryogenic recovery process increases the overall hydrogen recovery from the cracked ammonia to over 99%.

[0184] Because hydrogen and ammonia are recovered from the PSA exhaust gas, the heating value of the purge gas to the burner is reduced compared to the reference process. Therefore, the amount of other fuel 70, such as natural gas, required for the ammonia cracker burner must increase. This purge recovery process therefore improves the overall hydrogen recovery rate from the cracker, but the carbon intensity of the product hydrogen will be higher. In some sectors, regulations regarding green or renewable hydrogen may mean that higher recovery rates are preferred over lower carbon intensity. To reduce carbon intensity, natural gas fuel can be replaced with lower-carbon-intensity fuels, such as renewable natural gas (RNG), biogas, or blue hydrogen.

[0185] Figure 4 is a simplified flowsheet depicting a second configuration of the process within the cryogenic recovery system 200 of Figure 2. Features common to the flowsheets of Figures 3 and 4 are given the same reference numerals. Below is a discussion of the different features.

[0186] The nitrogen-rich liquid from the second separator 319 is split into two portions.

[0187] First portion 324 is dropped in pressure (to near ambient pressure) across JT valve 352 and fed to third separator 325. Hydrogen-enriched flash gas 326 produced in third separator 325 is returned to the warming end via heat exchanger 306, thereby providing refrigeration capacity for the feed stream and used as described above. Nitrogen-enriched liquid 328 produced in third separator 325 is returned to the warming end via heat exchanger 306 as regeneration gas / waste in stream 332 (thereby providing further cooling to the feed stream).

[0188] A second portion 360 of the nitrogen-rich liquid from second separator 319 is sent directly to heat exchanger 306 where it is warmed by heat exchange against the dried tail gas in stream 305 and / or the ammonia-free tail gas in stream 317, and the resulting warmed stream 329 is fed to expander 330. Expander discharge 331 is returned to the warming end by heat exchanger 306 to provide further cooling to the feed stream and is also used as regeneration gas / waste in stream 332. This configuration allows returning stream 328 to be colder, e.g., about −198° C., than the configuration of FIG. 3 (where stream 328 is about −191° C.), and allows partially condensed fluid stream 318 to be colder, e.g., about −195° C.

[0189] The refrigeration capacity of the process can be provided in other ways.

[0190] In the first option, a refrigerant may be injected. For example, liquid nitrogen (LIN) may be pumped into the second separator 319 or into the liquid exiting the second separator 319 (e.g., stream 360 in FIG. 4). Injecting LIN in this manner has the advantage of increasing the flow of liquid ultimately flowing to the expander 330 and providing refrigeration in the temperature range required. Less preferably, low-pressure LIN may also / alternatively be added to the third separator 325. Alternatively, some other refrigerant may be used, such as a hydrocarbon-based refrigerant. Such a refrigerant would have to be a separate circuit of the heat exchanger 306 and could include, for example, a closed-loop compression-expansion refrigeration system.

[0191] The second option is to increase the discharge pressure of the compression system 301 which ultimately translates into a higher pressure ratio on the expander 330 .

[0192] These options may be desirable, for example, if the ammonia content in the PSA exhaust gas 300 is higher than expected, thereby requiring additional refrigeration to condense the additional ammonia, however, either or both may form part of the basic process.

[0193] The ammonia feed in Stream 2 can also be used as a refrigerant in heat exchanger 306, thereby warming the ammonia feed to the cracking process. This option eliminates the glycol integration used to provide intercooling to PSA tail gas compressor 301. In addition, the ammonia feed is at a temperature of approximately −33° C., which is warmer than the ideal temperature for providing refrigeration in heat exchanger 306. Refrigeration to condense the ammonia in Stream 305 is needed down to approximately −70° C.

[0194] Heat exchanger 306 is depicted as a single heat exchanger having multiple passages for the various process streams to be cooled by heat exchange with one or more of the refrigerant streams (internal and / or external). However, it will be understood that heat exchanger 306 may be replaced by multiple individual heat exchangers in other embodiments. In a preferred embodiment, the heat exchange system is a multi-pass brazed aluminum heat exchanger.

[0195] If dryer 304 and / or ammonia removal unit 316 are adsorption-based units (e.g., TSA), details of the adsorption cycle, such as the regeneration step, can be carefully planned. For example, adsorption cycles can be staggered to avoid simultaneous transient disturbances in an otherwise steady-state process. Regeneration gas can be formed from recycled streams, such as warmed hydrogen-rich gas stream 321 or compressed hydrogen-rich gas stream 323, allowing ammonia desorbed from the bed to be recycled for improved ammonia recovery.

[0196] Ideally, the dry adsorbent has negligible capacity for ammonia. If the dry adsorbent also co-adsorbs at least a portion of the ammonia in the feed, the regeneration gas for at least the last portion of the regeneration step can be selected from available ammonia-containing vapor streams. This can include dry stream 305, regeneration outlet gas from ammonia removal unit 316, or other process streams. A parallel feed step can also be used. If an ammonia-lean or ammonia-free stream is used to regenerate the dryer bed, anhydrous ammonia can also be recycled from the process, for example, from stream 309, and injected into stream 305 to achieve a constant ammonia composition in heat exchanger 306. [Example]

[0197] The invention will now be illustrated by the following non-limiting examples.

[0198] Reference example The process depicted in FIG. 1 has been simulated by computer (Aspen Plus, version 10, Aspen Technology, Inc., Massachusetts, USA) for a plant designed to produce 35 tons / day of hydrogen (Stream 40) from an 8897 kg / hour ammonia feed.

[0199] The activity of ruthenium- and nickel-based catalysts in adiabatic reactors and tubes was modeled using the rate equation given by Lamb et al. (Int. J. Hydrogen Energy, 44 (2019) pp3726-3736) as a basis. For the purposes of the simulation, the activity of the ruthenium-based catalyst was fitted to the rate equation, while the activity of the nickel-based catalyst was assumed to be 20% of the activity predicted by the rate equation.

[0200] The resulting heat and mass balance (HMB) data is provided in Table 2. [Table 2-1] [Table 2-2] [Table 2-3]

[0201] Example 1 The process depicted in FIG. 2, in which the cryogenic recovery system 200 has the configuration depicted in FIG. 3, has been simulated by a computer (Aspen Plus, ver. 10, Aspen Technology, Inc., Massachusetts, USA) using the same parameters as in the reference example.

[0202] The resulting HMB data for the flowsheet depicted in FIG. 2 is provided in Table 3. [Table 3-1] [Table 3-2] [Table 3-3]

[0203] The resulting HMB data for the flowsheet depicted in FIG. 3 is provided in Table 4. [Table 4-1] [Table 4-2] [Table 4-3]

[0204] The data show that hydrogen was produced (Stream 40) at a rate of 1566 kg / hr (or 37.59 tonnes / day) with a hydrogen recovery of 99.16%, representing a 6.8 percentage point improvement over the reference example.

[0205] Example 2 The process depicted in FIG. 2, in which the cryogenic recovery system 200 has the configuration depicted in FIG. 4, has been simulated by a computer (Aspen Plus, ver. 12.1, Aspen Technology, Inc., Massachusetts, USA) using the same parameters as in the reference example.

[0206] The resulting HMB data for the flowsheet depicted in FIG. 2 is provided in Table 5. [Table 5-1] [Table 5-2] [Table 5-3]

[0207] The resulting HMB data for the flowsheet depicted in FIG. 4 is provided in Table 6. [Table 6-1] [Table 6-2] [Table 6-3]

[0208] The data show that hydrogen was produced (Stream 40) at a rate of 1561 kg / hr (or 37.46 tonnes / day) with a hydrogen recovery of 98.80%, representing an improvement of approximately 7 percentage points over the reference example.

[0209] overview A summary of key data for the illustrated process is provided in Table 7. [Table 7]

[0210] The present invention provides higher recovery of hydrogen from ammonia (99.16% or 98.80%) than the prior art (92.32%), but at the cost of additional power and fuel. The increased power and fuel consumption may also increase the carbon intensity of the product hydrogen.

[0211] A comparison of the embodiments of the present invention depicted in Figures 3 and 4 highlights a similar trade-off: higher recovery rates require more power and fuel.

[0212] Different solutions may be considered better depending on various factors, which may include the relative values ​​of power / fuel / products, carbon intensity constraints or incentives, carbon intensity of electricity and fuel sources, etc.

[0213] Although the invention has been described with reference to the preferred embodiments illustrated in the drawings, it will be understood that various modifications can be made within the spirit and scope of the invention as defined in the following claims.

[0214] In this specification, unless expressly stated otherwise, the word "or" is used in the sense of an operator that returns a value of true when either or both of the stated conditions are met, as opposed to the operator "exclusive-or," which requires only that one of the conditions be met. The word "comprising" is used in the sense of "including" and incorporates "consisting of," rather than meaning "consisting of" exclusively.

[0215] All prior teachings set forth above are incorporated herein by reference. Any acknowledgement herein of any prior-published document should not be construed as an admission or representation that the teachings were general general knowledge in Australia or elsewhere at that date.

Claims

1. 1. A process for decomposing ammonia, comprising: providing heated ammonia gas at superatmospheric pressure; decomposing the heated ammonia gas in an ammonia decomposition system to produce a decomposed gas comprising hydrogen gas, nitrogen gas, and residual ammonia gas; cooling the cracked gas by heat exchange to produce a cooled cracked gas; recovering hydrogen from the cooled cracked gas in a hydrogen recovery unit to produce a hydrogen gas product and an exhaust gas comprising nitrogen gas, residual hydrogen gas, and residual ammonia gas; recovering residual ammonia from at least a portion of the exhaust gas or from a combined gas comprising the exhaust gas by partial condensation and phase separation to produce an ammonia-lean exhaust gas comprising recovered liquid ammonia and nitrogen gas and residual hydrogen gas; recovering residual hydrogen from said ammonia-lean tail gas, or from an ammonia-free tail gas derived therefrom, by partial condensation and phase separation to produce a hydrogen-rich gas and a nitrogen-rich liquid.

2. 10. The process of claim 1, wherein at least a portion of the recovered liquid ammonia or liquid ammonia derived therefrom is recycled to the ammonia decomposition system.

3. recovering the residual ammonia from the exhaust gas or from a combined gas comprising the exhaust gas, compressing the exhaust gas or the combined gas including the exhaust gas to form a compressed exhaust gas; drying the compressed exhaust gas, for example in a TSA process, to form a dried compressed exhaust gas; cooling the dried, compressed exhaust gas by heat exchange against one or more "cold" process fluids to condense residual ammonia and produce a partially condensed exhaust gas; and phase separating the partially condensed tail gas to produce the recovered liquid ammonia and the ammonia-lean tail gas.

4. reducing the pressure of the recovered liquid ammonia to produce reduced pressure liquid ammonia and an ammonia-rich flash gas; separating the reduced pressure liquid ammonia and the ammonia-rich flash gas; and recycling the reduced pressure liquid ammonia to the ammonia decomposition system.

5. recovering the residual hydrogen from the ammonia-lean tail gas; cooling the ammonia-lean tail gas, or an ammonia-free tail gas derived therefrom, by heat exchange against one or more "cold" process fluids to condense the nitrogen and produce a partially condensed fluid; and optionally reducing the pressure of the partially condensed fluid before separating the partially condensed fluid to produce the hydrogen-rich gas and the nitrogen-rich liquid.

6. 10. The process of claim 1, wherein more than trace amounts of ammonia are present in the ammonia-lean tail gas, and the process comprises removing ammonia from the ammonia-lean tail gas by an adsorption process, e.g., a TSA process, to produce an ammonia-free tail gas.

7. 10. The process of claim 1, wherein the hydrogen-rich gas, or a regeneration outlet gas derived therefrom, is recycled to the hydrogen recovery unit.

8. The recycling of the hydrogen-rich gas comprises: warming the hydrogen-rich gas by heat exchange against one or more cooled process fluids to produce a warmed hydrogen-rich gas; compressing the heated hydrogen-rich gas to produce a compressed hydrogen-rich gas; and recycling the compressed hydrogen-rich gas, or a regeneration outlet gas derived therefrom, to the hydrogen recovery unit.

9. 10. The process of claim 1, wherein at least a portion of the nitrogen-rich liquid and / or a nitrogen-enriched liquid derived therefrom is warmed by heat exchange against one of a plurality of cooled process fluids to produce waste nitrogen gas.

10. reducing the pressure of at least a portion of the nitrogen-rich liquid to produce a reduced-pressure nitrogen-enriched liquid and a hydrogen-enriched flash gas; separating said reduced pressure nitrogen enriched liquid from said hydrogen enriched flash gas; and recycling the hydrogen-enriched flash gas to the exhaust gas from the hydrogen recovery unit.

11. said recycling of said hydrogen-enriched flash gas comprising: warming the hydrogen-enriched flash gas by heat exchange against one or more cooled process fluids to produce a warmed hydrogen-enriched flash gas; and combining the hydrogen-enriched flash gas, or a reduced pressure hydrogen-enriched flash gas derived therefrom, with the exhaust gas from the hydrogen recovery unit at a suitable point in a compression system to form the combined gas.

12. 1. An apparatus for decomposing ammonia, comprising: an ammonia decomposition system having an inlet for heated ammonia gas at superatmospheric pressure and an outlet for decomposed gases comprising hydrogen gas, nitrogen gas, and residual ammonia gas; a hydrogen recovery unit comprising an inlet for cooled cracked gas in fluid flow communication with the outlet of the ammonia decomposition system, a first outlet for hydrogen gas product, and a second outlet for tail gas comprising nitrogen gas, residual hydrogen gas, and residual ammonia gas; a first phase separator comprising an inlet for partially condensed tail gas in fluid flow communication with the second outlet of the hydrogen recovery unit, a first outlet for recovered liquid ammonia, and a second outlet for an ammonia-lean tail gas comprising nitrogen gas and residual hydrogen gas; a second phase separator comprising an inlet for partially condensed ammonia-lean tail gas in fluid flow communication with the second outlet of the first phase separator, a first outlet for hydrogen-rich gas, and a second outlet for nitrogen-rich liquid; The device, a heat exchanger located between the outlet of the ammonia decomposition system and the inlet of the hydrogen recovery unit, the heat exchanger being arranged to cool the cracked gas by heat exchange against ammonia; a heat exchanger located between the second outlet of the hydrogen recovery unit and the inlet of the first phase separator, the heat exchanger being arranged to condense residual ammonia gas in the tail gas by heat exchange against one of a plurality of "cold" process fluids; a heat exchanger located between the second outlet of the first phase separator and the inlet of the second phase separator, the heat exchanger being arranged to condense nitrogen in the ammonia-lean tail gas by heat exchange against one of a plurality of "cold" process fluids.

13. an exhaust gas compression system comprising an inlet for exhaust gas in fluid flow communication with the second outlet of the hydrogen recovery unit and an outlet for compressed exhaust gas; 13. The apparatus of claim 12, comprising a dryer, e.g., a TSA unit, comprising an inlet for compressed exhaust gas in fluid flow communication with the outlet of the exhaust gas compression system and an outlet for dried, compressed exhaust gas in fluid flow communication with the inlet of the first phase separator.

14. a pressure reducing valve comprising an inlet for recovered liquid ammonia in fluid flow communication with the first outlet of the first phase separator and an outlet for a two-phase fluid comprising reduced pressure liquid ammonia and an ammonia-rich flash gas; 14. The apparatus of claim 13, comprising: a further phase separator comprising: an inlet for a two-phase fluid comprising reduced-pressure liquid ammonia and an ammonia-rich flash gas in fluid flow communication with the outlet of the pressure reducing valve; a first outlet for liquid ammonia; and a second outlet for ammonia-rich flash gas in fluid flow communication with the inlet of the ammonia decomposition system.

15. 13. The apparatus of claim 12 comprising a pressure reducing valve having an inlet in fluid flow communication with the second outlet of the first phase separator and an outlet in fluid flow communication with the inlet of the second phase separator.

16. 13. The apparatus of claim 12, comprising an ammonia removal unit, e.g., a TSA unit, comprising an inlet for an ammonia-lean tail gas in fluid flow communication with the second outlet of the first phase separator and an outlet for an ammonia-free tail gas in fluid flow communication with the inlet of the second phase separator.

17. 13. The apparatus of claim 12, wherein the first outlet of the second phase separator is in fluid flow communication with the inlet of the hydrogen recovery unit.

18. a recovered hydrogen compression system comprising an inlet for hydrogen-rich gas in fluid flow communication with the first outlet of the second phase separator and an outlet for compressed hydrogen-rich gas in fluid flow communication with the inlet of the hydrogen recovery unit; the heat exchange system, 13. The apparatus of claim 12, comprising a heat exchanger located between the first outlet of the second phase separator and the inlet of the recovered hydrogen compression system, the heat exchanger being positioned to warm the hydrogen-rich gas by heat exchange against one or more cooled process streams.

19. 13. The apparatus of claim 12, comprising an expander for expanding the nitrogen-rich gas, or a nitrogen-enriched gas derived therefrom, to generate refrigeration for the process.

20. a pressure reducing valve having an inlet for nitrogen-rich liquid in fluid flow communication with the second outlet of the second phase separator and an outlet for a two-phase fluid comprising nitrogen-enriched liquid and hydrogen-enriched gas; 13. The apparatus of claim 12, comprising: a third phase separator comprising: an inlet for a two-phase fluid comprising a nitrogen-enriched liquid and a hydrogen-enriched gas in fluid flow communication with the outlet of the pressure reducing valve; a first outlet for the nitrogen-enriched liquid; and a second outlet for the hydrogen-enriched gas in fluid flow communication with an inlet of an exhaust gas compression system.

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