Method and system for producing hydrogen from ammonia cracking

Abstract

Method and system for producing a hydrogen product from ammonia, comprising: optionally at least one pre-cracking reactor, such as an adiabatic pre-cracking reactor, arranged to receive an ammonia feed stream, thereby producing a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen; an ammonia cracking reactor such as an electrically heated reactor. The reactor is arranged to receive the partly converted ammonia feed stream or the ammonia feed stream for producing an effluent gas stream comprising hydrogen and nitrogen and optionally also unconverted ammonia; and a hydrogen recovery unit arranged to receive the effluent gas stream for producing the hydrogen product and an off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia.

Description

[0001] Title: Method and system for producing hydrogen from ammonia cracking

[0002] The present invention relates to a method and system for cracking ammonia for producing hydrogen. Embodiments include passing an ammonia feed to at least one adiabatic pre-cracking reactor, subsequent cracking in an ammonia cracking reactor and hydrogen purification in a hydrogen recovery unit, as well as the recovery of unconverted ammonia in the effluent gas stream from the ammonia cracking reactor. The present invention is relevant for all technical fields using ammonia as a source of energy and / or for production of hydrogen. In particular, the present invention is relevant when ammonia is the major or only energy source, which is important in the green transition using ammonia as an energy carrier.

[0003] Liquid ammonia is an important source to produce hydrogen because it is an important energy carrier, for instance in regions with few or no fuel sources. The advantage of ammonia as energy carrier is that liquid ammonia is easier to transport and to store than for instance natural gas or hydrogen gas. Additionally, storing energy in ammonia is less expensive than e.g. in hydrogen or batteries.

[0004] It is known to use fire heated reactors comprising catalyst-filled tubes for dissociating ammonia into hydrogen and nitrogen. The firing and thus heating in such fire heated reactors is normally conducted by using natural gas so all the hydrogen in the ammonia will go to the effluent gas stream and the waste heat is recovered for steam production, which is then used to drive rotating machines in those plants.

[0005] Applicant’s patent application WO 2022189560 discloses an ammonia cracking method and system for producing hydrogen. Water in the ammonia feed gas is removed by providing a distillation column in which the reboiler duty is provided by the effluent gas from the ammonia cracker.

[0006] It would be desirable to provide a superior method (process) and system (plant) for producing a hydrogen product from ammonia with no production of steam for export or internal consumption, with no production of waste streams containing ammonia, with increased heat integration and thus high energy efficiency and reduced carbon footprint. Accordingly, in a first aspect, the invention is, in a first general embodiment, a method for producing a hydrogen product from ammonia, comprising the steps of: i) providing an ammonia feed stream; ii) optionally, passing the ammonia feed stream to at least one ammonia pre-cracking reactor for producing a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen; iii) passing the ammonia feed stream, or the optional partly converted ammonia feed stream, to an ammonia cracking reactor for producing an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia; iv) passing the effluent gas stream to a hydrogen recovery unit for producing said hydrogen product and an off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia, wherein step iv) comprises the cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the hydrogen recovery unit; wherein step iv) further comprises recovering unconverted ammonia in the effluent gas stream by a flashing step in an ammonia recovery flashing system, such as a flash column, after said cooling of the effluent gas stream by heat exchange with the ammonia feed stream, and wherein after said cooling and prior to the flashing step, the thus cooled effluent gas stream is supplied to an effluent gas separator, such as an effluent gas scrubbing unit using, i.e. being provided with, water as scrubbing medium, for generating in said effluent gas separator an overhead stream comprising nitrogen and hydrogen which is passed to said hydrogen recovery unit, and a bottom liquid stream comprising unconverted ammonia.

[0007] It would be understood that in an embodiment, step ii) and associated pre-cracking reactors) is omitted. Thereby, a simpler process and plant is provided. The ammonia feed stream may thus be a substantially pure stream of ammonia, for instance by having more than 99.5 vol.% ammonia.

[0008] In another general embodiment of the first aspect, the invention is a method for producing a hydrogen product from ammonia, comprising the steps of: i) providing an ammonia feed stream; ii) passing the ammonia feed stream to at least one ammonia pre-cracking reactor for producing a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen; iii) passing the partly converted ammonia feed stream to an ammonia cracking reactor for producing an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia; iv) passing the effluent gas stream to a hydrogen recovery unit for producing said hydrogen product and an off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia, wherein step iv) comprises the cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the hydrogen recovery unit; wherein step iv) further comprises recovering unconverted ammonia in the effluent gas stream by a flashing step in an ammonia recovery flashing system, such as a flash column, after said cooling of the effluent gas stream by heat exchange with the ammonia feed stream, and wherein after said cooling and prior to the flashing step, the thus cooled effluent gas stream is supplied to an effluent gas separator, such as an effluent gas scrubbing unit using, i.e. being provided with, water as scrubbing medium, for generating in said effluent gas separator an overhead stream comprising nitrogen and hydrogen which is passed to said hydrogen recovery unit, and a bottom liquid stream comprising unconverted ammonia.

[0009] The provision of the least one ammonia pre-cracking reactor, herein also refer to as “pre-converter”, enables the increase in the energy efficiency of the process / plant. Suitably, the at least one ammonia pre-cracking reactor is provided as a plurality of ammonia pre-cracking reactors, such as two ammonia pre-cracking reactors, i.e. two pre-con- verters.

[0010] Suitably, said unconverted ammonia in the bottom liquid stream of the effluent gas separator is a major portion such as at least 80 vol.%, or at least 90 vol.% of said unconverted ammonia present in the effluent gas from the ammonia cracking reactor in step iii). The term “first aspect” or “first aspect of the invention” means embodiments related to the method (process). The term “second aspect” or “second aspect of the invention” means embodiments related to the system (process plant i.e. plant).

[0011] The use of the term “process / plant” means interchangeably reference to the method (process) or system (plant) according to the invention.

[0012] It would be understood that a given step may comprise one or more sub-steps. It would also be understood that a given step is conducted in a corresponding unit or combination of units.

[0013] The term “suitably” means “optionally”, i.e. an optional embodiment.

[0014] The term “at least a portion” of a given stream means a portion of the stream or the entire stream.

[0015] The term “ammonia” shall be understood broadly and includes the ammonia feed stream. The term “ammonia feed stream” is to be understood as a “gaseous ammonia feed stream”, and which is for instance derived from liquid ammonia such as liquid ammonia imported from storage as it also will become apparent from the below embodiments. It would also be understood that the term partly converted ammonia feed stream is also a gas and thus the term “partly converted ammonia feed stream” has the same meaning as “partly converted gaseous ammonia feed stream”.

[0016] The term “invention” or “present invention” may be used interchangeably with “application” or “present application”, respectively.

[0017] The term “and / or” means in connection with a given embodiment any of three options. The term “and / or” may be used interchangeably with the term “at least one of” the three options.

[0018] The use of the article “a” or “an” means at least one.

[0019] Other definitions are provided in connection with one or more of below embodiments. In an embodiment, said ammonia recovery flashing system is as a flash column. The term “flash column” may be used interchangeably with “flash separation column”. The bottom liquid stream from the effluent gas separator, herein also referred to as wash water, is heated and expanded in a vessel, i.e. the flash column. The more volatile species, including a significant amount of ammonia, are released to the gas as the overhead stream of the flash column, leaving the ammonia-lean aqueous stream as a bottom liquid stream from the flash column.

[0020] In an embodiment, said effluent gas separator is an effluent gas scrubbing unit using water as scrubbing medium, i.e. water is provided as the scrubbing medium. The water may be provided as make-up water, for instance make-up water which is externally sourced. Suitably, the water is internally sourced, as it will also become apparent from a below embodiment, by which the water for the effluent gas separator at least is provided by a bottom ammonia-lean aqueous stream from the flashing step.

[0021] The provision of heat integration for electricity production purposes based on ammonia as the major or only energy source is different from the case of heat integration for hydrogen production purposes based on ammonia as the major or only energy source. For the former case heat can be recovered for steam production for additional electricity output, whereas for the latter case, which the present invention addresses, only hydrogen generation counts so waste heat should be limited i.e. minimized. The present invention enables limiting the waste heat for production of steam, where it is considered of low value or of no use. Having ammonia as the major or only energy source is important in the green transition using ammonia as an energy carrier.

[0022] The method (process) and system (plant) of the present invention is a stand-alone solution with high energy efficiency and with a high recovery in the product of the hydrogen atoms contained in the ammonia feedstock. By stand-alone solution it is meant that the ammonia cracking process or plant does not import or export steam. Heat integration is provided directly between the cold streams, e.g. ammonia feed, and hot effluent gas from the ammonia cracking unit, i.e. hot cracked gas, without producing low or medium pressure steam for internal use. Therefore, it is not necessary to have neither a boiler feed water (BFW) system nor a steam drum associated thereto. The method and system of the present invention provides also the benefit of having a low ammonia slip, namely less than 0.5 vol.%, yet this is still too high for the effluent gas from the ammonia cracking reactor to be admitted directly into the hydrogen purification system, which in an embodiment is a pressure swing adsorption (PSA) unit. More specifically, the hydrogen recovery unit, such as a PSA unit, requires less than 0.05 vol.% ammonia in the cooled effluent gas directed thereto. The effluent gas has concentrations in the order 0.2-2.0 vol.% NH3.

[0023] While the straightforward solution would be to increase the temperature of the ammonia cracking reactor to above 1000°C, as this will result in a lower ammonia slip due to the ammonia cracking reaction being endothermic and the slip thus dictated by the chemical equilibrium, the present invention elegantly and by simple means takes advantage of the still high ammonia slip for downstream hydrogen recovery, by washing out the unconverted ammonia in an effluent gas separator using water along with a flashing step. This is a much simpler solution than for instance providing a distillation step instead of the flashing step. The aqueous ammonia solution withdrawn from the effluent gas separator as bottom liquid stream and comprising unconverted ammonia, for instance 0.5-1.5 mol% NH3, is suitably heated by the effluent gas stream from the ammonia cracking reactor, depressurized and flashed in the ammonia recovery flashing system, suitably said flash column, thereby stripping part of the ammonia off from the bottom liquid steam. The ammonia-lean liquid withdrawn from the flash column is then cooled down, e.g. by the cold ammonia feed stream being introduced into the pro- cess / plant, and recycled via a recirculation pump to the effluent gas separator, where it is used again to absorb the ammonia. This strategy avoids the necessity of treating a waste aqueous ammonia stream, e.g. in a highly costly waste water treatment plant.

[0024] In the above-mentioned applicant’s patent application WO 2022189560, the issue of unconverted ammonia being present in the effluent gas stream from the ammonia cracking reactor is solved by having a distillation column with the reboiler duty being provided by the effluent gas stream. As mentioned earlier, the present invention, provides a much simpler solution by i.a. providing said flashing step in an ammonia recovery flashing system, such as a flash column. Hence, an ammonia-rich aqueous solution at high pressure, i.e. said bottom liquid stream from the effluent gas separator, again said stream herein also referred to as wash water, is heated and expanded into the flash column. As explained above, the more volatile species, including a significant amount of ammonia, are released to the gas as the overhead stream of the flash column, leaving the ammonia-lean aqueous solution that is recirculated via the recirculation pump and reused as wash stream in the effluent gas separator. In other words, the present application also provides the benefit of transferring the energy otherwise required in a reboiler of a distillation unit to said recirculation pump. This is a much simpler solution which not least also enables significant less plot size and more favorable capital expenses (CAPEX) as well as operating expenses OPEX).

[0025] In an embodiment, said bottom liquid stream comprising unconverted ammonia, i.e. the bottom liquid stream from the effluent gas separator, is provided as feed to said flashing step, and the flashing step provides an overhead stream; the method further comprising: combining said overhead stream with at least a portion of any of said off-gas from the hydrogen recovery unit, said effluent gas from step iii) i.e. the hot cracked gas, or a combination thereof, into a fuel gas, and feeding at least a portion of said fuel gas to said ammonia cracking reactor.

[0026] The mixing with the hot cracked gas enables i.a. to secure a sufficiently low temperature in ammonia cracking reactor, e.g. where this is provided as a fire heated reactor. Another benefit is that the reboiler duty of a distillation column is now instead available for pre-heating combustion air and fuel gas produced in the process or plant, thereby also decreasing the fuel consumption of the ammonia cracking reactor, for instance where this is provided as a fire heated reactor. The fire heated reactor is herein also referred to as “fired tubular cracker” or simply “fired cracker”.

[0027] In an embodiment, the at least one ammonia pre-cracking reactor and / or the ammonia cracking reactor operate(s) in the temperature range 300-700°C, and further, the at least one ammonia pre-cracking reactor and / or the ammonia cracking reactor operate^) with an ammonia cracking catalyst comprising a metal or a metal alloy selected from any of: Fe, Co, Ru, optionally Ni, or combinations thereof, such as a Fe-Co based catalyst. For instance, the method comprises the provision of two ammonia pre-cracking reactors operating in the range 500-700°C, such as two adiabatic pre-converters operating in the range 500-650°C. For instance, the at least one ammonia pre-cracking reactor is at least one adiabatic pre-cracking reactor which operates in the temperature rage 350- 600°C, for instance 350-500°C, 350-550°C or 400-550°C. For instance, the inlet temperature may be 500 or 550°C, and the outlet temperature may be 400°C.

[0028] The operation of the ammonia pre-cracking reactor in the temperature range 300- 700°C, such as 500-700°C or 500-650°C, is low compared to the standard solutions, typically requiring operating temperatures in the range 650-950°C. This is possible due to the use a catalyst that is more active than a standard monometallic Ni catalyst, which requires temperatures in the range 650-950°C. As a consequence, the process according to the invention enables also exploiting calories at lower temperatures to carry out the ammonia cracking reaction. Additionally, the milder process conditions i.e. lower operating temperatures than normal in the ammonia pre-cracking reactors, again herein also referred to as pre-converters, provide more flexibility regarding the construction materials required in and around those units.

[0029] For instance, the at least one ammonia pre-cracking reactor and / or the ammonia cracking reactor operate(s) with an ammonia cracking catalyst comprising a combination of 20-50 wt% Fe, 20-50 wt% Co and 20-50 wt% alumina, optionally promoted with an alkali metal oxide, and or oxides of Ca, Si, Al or combinations hereof. The Fe-Co catalyst may be bimetallic or an alloy.

[0030] Accordingly, in an embodiment, the at least one ammonia pre-cracking reactor operate with a catalyst comprising 20-50 wt% Fe, 20-50 wt% Co and 20-50 wt% alumina, optionally promoted with an alkali metal oxide, a lanthanide group metal oxide, and / or oxides of Ca, Si, Al or combinations thereof; and the ammonia cracking reactor operates with a Ni-catalyst; said Ni-catalyst comprising 20-60 wt% Ni, and 40-80 wt% of any oxides of Al, Ca, Mg or combinations thereof, optionally promoted with a lanthanide group metal oxide, such as La2C>3. It would be understood that that term “lanthanide” refers to any of the fifteen elements from La to Lu in the periodic table of elements. Lanthanum (La), as used herein, is also a lanthanide.

[0031] It would be understood that the wt% are with respect to the total weight of catalyst.

[0032] It would be understood that the total wt% sums up to 100%.

[0033] It is advantageous to utilize a very active catalyst such as said Fe-Co catalyst, in the pre-converter(s) which is not inhibited to a large extent by water despite operating at e.g. 500-550°C, because the pre-converter(s) have the highest water concentration. The stoichiometry of the reaction 2 NH3N2+ 3 H2(1) means that the H2O concentration is reduced in the gas stream the more ammonia is cracked. It is also advantageous to use the Ni catalyst at the operating temperatures of the downstream ammonia cracking reactor, e.g. a fired cracker, such as 800-900°C, since such high temperatures lead to lower inhibition of the Ni-catalyst than at lower temperatures.

[0034] In an embodiment, the at least one ammonia pre-cracking reactor is an adiabatic ammonia pre-cracking reactor comprising a catalytic fixed bed and having a decrease in temperature from the inlet to the outlet of the reactor, e.g. of 50-200°C.

[0035] Adiabatic reactors are well-known in the art and thus also have a well-known meaning in the art, namely a reactor, typically a reactor comprising a fixed catalyst bed, where there is an increase or decrease in temperature from the inlet to the outlet of the reactor. For an exothermic reaction there is an increase in the temperature, while for an endothermic reaction there is a decrease in the temperature.

[0036] For the purposes of the present application, the term “adiabatic ammonia pre-cracking reactor comprising a catalytic fixed bed” means a reactor where there is a decrease in temperature from the inlet to the outlet of the reactor. For instance, the reactor comprises a fixed bed of catalyst suitable for ammonia cracking and the temperature decrease is of 50-200°C or 100-200°C, such as 150°C. For instance, the inlet temperature is 550°C and the outlet temperature 400°C. In the at least one adiabatic ammonia pre-cracking reactor, the catalytic fixed bed is provided with a catalyst active in ammonia cracking, as recited above, to partially crack the ammonia feed using e.g. waste heat from the convection section of the ammonia cracking reactor. The use of the waste heat reduces the duty of the ammonia cracking reactor and hence the consumption of hydrocarbon feed gas, e.g. natural gas, thereby also reducing energy consumption. The provision of the at least one adiabatic ammonia pre-cracking reactor enables also reducing the size of the ammonia cracking reactor. Other benefits are recited below.

[0037] In an embodiment, the ammonia cracking reactor is a fire heated reactor comprising one or more catalyst-filled tubes.

[0038] The catalytic fixed-bed and catalyst-filled tubes contain a catalyst active in ammonia cracking, i.e. the ammonia cracking catalyst (the catalyst). The catalyst is suitably an ammonia synthesis catalyst.

[0039] By the invention, the ammonia cracking catalyst comprises a metal, e.g. a bimetallic catalyst, or a metal alloy selected from any of: Fe, Co, Ru, Ni, or combinations thereof, such as a Fe-Co based catalyst. For instance, the catalyst is a Fe-based catalyst in the form of a monometallic catalyst system having Fe as the metal. For instance, the catalyst is a Fe-Co-based catalyst in the form of a bimetallic catalyst system having Fe and Co as a metal alloy. Suitably the catalyst is promoted with any of K2O, CaO, SiC>2, AI2O3. The Fe-based catalyst may be supported such as Fe-Co / AhCh, or unsupported such as Fe fused with any of K2O, CaO, AI2O3. The Fe-based catalyst or Fe-Co-cata- lyst provides a much more inexpedient solution due to the lower price of iron. For instance, as earlier recited, the ammonia cracking catalyst may comprise 20-60 wt% Ni, and 40-80 wt% of any oxides of Al, Ca, Mg or combinations hereof, optionally promoted with a lanthanide group metal oxide, such as La2Os.

[0040] The selection of the catalyst is independent of the type of ammonia cracking reactor used.

[0041] In an embodiment, said fuel gas is pre-heated by said effluent gas stream prior to said cooling of the effluent gas stream by heat exchange with the ammonia feed stream in step iv). Accordingly, after exiting the ammonia cracking reactor, the effluent gas stream is provided as heat exchanging medium for pre-heating said fuel gas. Optionally, prior to this step, the effluent gas stream is provided as heat exchanging medium for pre-heating combustion air. The combustion air is provided to the ammonia cracking reactor, suitably a fire heated reactor (fired cracker), more specifically to the burners thereof. After delivering heat to said fuel gas, the effluent gas stream is further cooled by passing it to an ammonia evaporator, as it will become apparent from a below embodiment.

[0042] Hence, in an embodiment, in step iv) said cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the hydrogen recovery unit, comprises:

[0043] - passing the effluent gas stream, after delivering heat to said fuel gas, to an ammonia evaporator, thereby providing a cooled effluent gas stream;

[0044] - diverting at least a portion of said cooled effluent gas stream, as additional fuel gas, and feeding it to said ammonia cracking reactor ;

[0045] - diverting another portion of said cooled effluent gas stream, as said cooled effluent gas stream which is supplied to said effluent gas separator.

[0046] Fuel gas is thereby internally sourced as a portion of the effluent gas (cracked gas), instead of resorting to externally sources of hydrocarbon gas such as natural gas, thus significantly improving the energy consumption figures of the process / plant. Further, as the fuel gas produced in the process / plant is hydrogen-rich, significant reduction in carbon footprint is achieved, as mainly hydrogen molecules, rather than methane molecules of e.g. natural gas, are utilized for the burning in the ammonia cracking reactor. In other words, the carbon intensity (Cl) of the process or plant is significantly reduced. In connection thereto, the energy efficiency is also increased by passing the effluent gas stream to the ammonia evaporator after delivering heat to said fuel gas in a fuel gas preheater. This approach deviates from a traditional approach in which the effluent gas stream would first be cooled in an ammonia evaporator for then delivering heat to downstream heat exchangers, such as a fuel preheater. The provision of said fuel preheater upstream said ammonia evaporator enable the use of higher quality energy, i.e. effluent gas stream at higher temperature, for fuel preheating rather than for evaporation. Any of said fuel gases, such as said fuel gas resulting from the combination of the overhead stream from the flashing step and off-gas from the hydrogen recovery unit; and / or said additional fuel gas, may be also referred to as any of said fuel gases generated in the process; hence, internally sourced.

[0047] The pre-cracking step (step ii) enables to convert part of the ammonia as an initial step in the process and protects the catalyst in the downstream ammonia cracking reactor. Protection and / or prolonged lifetime of inexpensive catalysts, in particular Fe-based catalysts or Fe-Co-based catalysts, is achieved due to hydrogen presence, in particular because ammonia may react with the Fe-based catalyst and form iron nitrides, Fe2N or Fe4N. This reaction, which is undesired, is particularly pronounced at higher temperature, such as above 500°C or 600°C and in pure ammonia. Iron nitride formation leads to physical decomposition of the catalyst, which could further induce catalyst deactivation and increased pressure drop over the catalyst bed, thereby leading to increased process cost. Hydrogen in the partly converted ammonia feed stream therefore hinders the iron nitride formation. These considerations are also valid for the reactor material, by the presence of hydrogen enabling protection of the materials, e.g. catalyst filled tubes, towards nitridation.

[0048] The present invention comprises the provision of an ammonia cracking catalyst such as a Fe-Co-based catalyst, which not only is tolerant to the presence of water and other oxygen-containing species in the ammonia feed, but also enables operation of the pre-cracking reactor, suitably one or more adiabatic pre-cracking reactors (adiabatic pre-converters) operating in the low temperature range of e.g. 500-650°C, which is low compared to standard solutions, as already explained. The process of the invention enables therefore to exploit calories at lower temperatures to carry out the ammonia cracking reaction, providing thereby more flexibility in terms of construction materials required in and around those units. At the same time, there is an associated benefit in terms of not requiring water removal of the ammonia feed, thus providing a simpler process and plant, with simpler equipment and reduced plot size. For instance, a distillation column and / or electrolysis for water removal may be omitted. In an embodiment, step ii) comprises preheating the ammonia feed stream prior to passing the ammonia feed stream to the at least one ammonia pre-cracking reactor, preferably by passing the ammonia feed stream to a plurality of pre-cracking reactors, for instance two adiabatic pre-cracking reactors.

[0049] In the ammonia cracking process, either in a pre-cracking reactor or a subsequent ammonia cracking reactor, gaseous ammonia is dissociated into a mixture of hydrogen and nitrogen gases in the reversible reaction: 2 NH3 (g) N2 (g) + 3 H2 (g) (1). Reaction (1) is endothermic, requiring heat for maintaining the ammonia cracking reaction ongoing and hence the temperature will decrease across the adiabatic pre-cracking reactor, herein also referred as adiabatic reactor, as the reaction is shifted to the right. The ammonia feed stream is heated to e.g. superheated conditions, for instance up to an inlet temperature of about 500-600°C, such as about 550°C and sent to a series of adiabatic reactors with heating in between the reactors, i.e. inter-stage heating. As already explained, since the process is endothermic, a temperature decrease of e.g. about 100°C or more may also occur in the adiabatic reactor, hence the outlet temperature can for instance be about 400°C. The higher the inlet temperature e.g. 500-600°C, the higher the ammonia conversion in a given catalyst volume.

[0050] The plurality of preheating steps with adiabatic reactors, for instance when using two adiabatic reactors arranged in series with inter-stage heating, allows for a minimum of firing / heating for ammonia cracking, thus resulting in a minimum of waste heat so there is no waste heat available for steam production. Furthermore, reduction in size of the downstream ammonia cracking reactors, for instance a fire heater reactor (fired cracker) is achieved. Overall lower costs result since adiabatic reactors are less costly than the fire heated ammonia cracking reactor, which is reduced in size; furthermore, there is no need for providing steam-generation equipment.

[0051] The use of at least one pre-cracking reactor, such as adiabatic reactors as recited above, conveys also the advantage that the operating temperature in the pre-cracking reactors be gradually increased, thereby gradually generating more and more hydrogen which inhibits nitridation.

[0052] In traditional ammonia cracking, the dissociation of ammonia according to reaction (1) is normally conducted by directly i.e. with no upstream pre-cracking, subjecting an ammonia feed stream at high temperatures of e.g. 850-950°C and in the presence of nickel as catalyst in a fire heated reactor. Due to the higher temperatures required, the lifetime of the catalyst is reduced due to the thermal sintering of the catalyst. The resulting gas mixture is composed of hydrogen and nitrogen in the proportion 3:1 (75% of H2 and 25% of N2) with very little amount (20 -100 ppm) of residual undissociated ammonia with dew point -51 °C to -29°C. When performed under the conditions of the present invention, catalysts are preferably Fe-based or Fe-Co-based, particularly in the ammonia precracking reactor, and the process is performed at lower temperatures in the range 300- 700°C, as recited above. Particularly for the ammonia cracking reactor being a fire heated reactor, this reactor is for instance operated at temperatures in the range 600- 700°C, which increases conversion to hydrogen. The higher temperatures may in some instances still require the use of catalysts capable of operating at such temperatures, such as a nickel-based catalyst, as earlier recited. For instance, the temperature of a preheated partly converted ammonia feed stream, corresponding to the inlet temperature of the fire heated reactor, is suitably about 600°C, such as 580 or 590°C, while the temperature of the effluent gas stream, corresponding to the outlet temperature of the fire heated reactor, is about 800°C, such as 750, 760, 770, 780, 790, 810, or 820°C; or about 700°C such as 710, 715, 720 or 725°C.

[0053] Accordingly, in an embodiment, the ammonia cracking reactor is a fire heated reactor (fired cracker) comprising one or more catalyst-filled tubes. This reactor is the same as a tubular reformer i.e. conventional steam methane reformer (SMR), where the heat for catalytic dissociation of ammonia is transferred chiefly by radiation in a radiant furnace, and where now instead of using a typical feed stream such as natural gas or pre-re- formed natural gas, the feed stream is the partly converted ammonia feed stream.

[0054] In another embodiment, the ammonia cracking reactor is a convection heated reactor, preferably comprising one or more bayonet tubes such as an HTCR reformer i.e. Topsoe bayonet reformer, where the heat for ammonia cracking is transferred by convection along with radiation. This type of reactor enables that the effluent gas stream from the reactor be of lower temperature than in for instance a fire heated reactor, for instance at about 550°C in the convection reactor compared to about 700°C in the fire heated reactor. Thereby it is possible to operate with more inexpensive catalysts, in particular Fe based catalysts.

[0055] In another embodiment, the ammonia cracking reactor is an electrically heated reactor, where electrical resistance is used for generating the heat for catalytic dissociation of ammonia. This is for instance suitable where electricity is readily available, particularly when available from green source such as by power generated from solar or wind sources. This reactor can operate a high temperatures and pressures, for instance at 1000°C or more, as well as pressures of 100 barg or higher, such as 500 barg or even higher, which can be relevant for certain downstream applications requiring hydrogen product being recovered or delivered at high pressures, such as at about 700 barg. Despite the high pressure, the higher temperature in the reactor enables also a lower ammonia slip in the effluent gas stream of the reactor. In addition, the electrically heated reactor provides for a much lower pressure drop and a much more compact solution, thus significantly reducing plot size in the plant.

[0056] In another embodiment, the ammonia cracking reactor is an induction heated reactor, where a tube heat exchange reactor includes the use of an induction coil in order to generate an alternating magnetic field within at least a part of an inner tube comprising a bed of catalyst material susceptible for induction heating. This is for instance also suitable where electricity is readily available, particularly when available from green source such as by power generated from solar or wind sources.

[0057] Combination of these reactors is also envisaged.

[0058] For more information on these reactors, details are herein provided by direct reference to applicant’s patents and / or literature. For instance, for tubular and autothermal (ATR) reforming an overview is presented in “Tubular reforming and autothermal reforming of natural gas - an overview of available processes”, lb Dybkjaer, Fuel Processing Technology 42 (1995) 85-107; and EP 0535505 for a description of HTCR. For a description of autothermal reforming (ATR) and / or SMR for large scale hydrogen production, see e.g. the article “Large-scale Hydrogen Production”, Jens R. Rostrup-Nielsen and Thomas Rostrup-Nielsen”, CATTECH 6, 150-159 (2002). For a description of electrically heated reactors, which is a more recent technology, reference is given to particularly to applicant’s WO 2019 / 228798 A1 and co-pending patent application PCT / EP2020 / 076704 (WO 2021063795). For a description of the induction heated reactor, reference is given to applicant’s WO 2017 / 186437 A1.

[0059] For instance, the electrically heated reactor is suitably a reactor system comprising: a supply of feed gas comprising ammonia, for instance the partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen; a structured catalyst arranged for catalysing the ammonia cracking reaction of said feed gas, said structured catalyst comprising a macroscopic structure of an electrically conductive material, said macroscopic structure supporting a ceramic coating, wherein said ceramic coating supports a catalytically active material; a pressure shell housing said structured catalyst, said pressure shell comprising an inlet for letting in said feed gas and an outlet for letting out a product gas i.e. the effluent gas from the reactor comprising hydrogen, nitrogen and optionally unconverted ammonia, wherein said inlet is positioned so that said feed gas enters said structured catalyst in a first end of said structured catalyst and said product gas exits said structured catalyst from a second end of said structured catalyst; a heat insulation layer between said structured catalyst and said pressure shell; at least two conductors electrically connected to said structured catalyst and to an electrical power supply placed outside said pressure shell, wherein said electrical power supply is dimensioned to heat at least part of said structured catalyst to a temperature of at least 300°C by passing an electrical current through said macroscopic structure, wherein said at least two conductors are connected to the structured catalyst at a position on the structured catalyst closer to said first end of said structured catalyst than to said second end of said structured catalyst, and wherein the structured catalyst is constructed to direct an electrical current to run from one conductor substantially to the second end of the structured catalyst and return to a second of said at least two conductors; an outlet for the product stream.

[0060] In an embodiment, the ammonia cracking reactor is any of a fire heated reactor and convection heated reactor; and the method further comprising:

[0061] - passing a portion, e.g. another portion, of the off-gas stream from the hydrogen recovery unit to the fire heated reactor or convection heated reactor upon mixing it with: an air stream, and / or upon mixing it with a separate fuel stream, said separate fuel stream being a) an externally sourced fuel gas such as natural gas, and / or b) a portion of any of said fuel gases generated in the process; thereby generating heat required in the fire heated reactor or convection heated reactor. The majority of the off-gas stream from the hydrogen recovery unit is nitrogen and contains also hydrogen and unconverted ammonia. For instance, when operating with a hydrogen recovery unit having one Pressure Swing Adsorption (PSA) unit, in the offgas stream the nitrogen content is e.g. about 60% vol. The off-gas stream is according to this embodiment used as fuel in e.g. the fire heated reactor by mixing with a separate incoming stream of combustion air, preferably at different locations along the length of the fired heated reactor, more specifically along its wall and corresponding to the positions of burners arranged therein for generating a flame and thereby radiant heat required for the catalyst filled tubes. Hence, while normally the fuel used for the burners would be provided from an external source, typically in the form of natural gas, the use of such natural gas is now substantially reduced or omitted. Further, a portion of any of the fuel gases generated in the process such as fuel gas from the overhead stream of the flash column of the flashing step, is suitably provided as the separate fuel stream, thereby again further reducing or eliminating the use of the natural gas. A higher energy efficiency in the process is thereby achieved while at the same time enabling a lower carbon footprint of the process and plant, i.e. a lower carbon intensity is achieved. The fire heated reactor or convection heated reactor may still be designed to operate on other fuel sources, i.e. to operate with the separate fuel stream such as natural gas, if necessary.

[0062] A separate fuel stream such as natural gas may be added where the off-gas stream is mainly rich in nitrogen, and thus of less value as fuel, for the instance where two PSA- units are utilized. More specifically, when operating with a hydrogen recovery unit having two or more PSA units, the off-gas stream becomes leaner in hydrogen and richer in nitrogen compared to when operating with one PSA unit. When operating with two PSA units, the off-gas stream may have about 10% vol. hydrogen. This off-gas is suitably used as fuel in the fire heated reactor or convection heated reactor by mixing with the combustion air, while a separate fuel stream such as natural gas is also added. When utilizing a convection heated reactor, the mixture of off-gas, combustion air and separate fuel stream e.g. natural gas, is burned, for instance in a combustion chamber at the bottom of the convection heated reactor, for generating a flame and thereby radiant heat which is required for heating flue gas and thereby also the heating of bayonet tubes comprising catalyst. Each bayonet tube is surrounded by another tube that guides the heated flue gas in the vicinity of the tube.

[0063] In an embodiment, the ammonia cracking reactor is an electrically heated reactor or an induction heated reactor; and the method further comprises:

[0064] - passing a portion, e.g. another portion, of the off-gas stream to a fired heater upon mixing it with an air stream, optionally upon mixing it with a separate fuel stream, said separate fuel stream being c) an externally sourced fuel gas such as natural gas, and / or d) a portion of any of said fuel gases generated in the process; thereby preheating the ammonia feed gas stream.

[0065] When in particular utilizing these ammonia cracking reactors, the heating is powered by electricity and thus there is no need to use the off-gas for burning as for the fire heated reactor and convection heated reactor. The off-gas stream is mixed with combustion air and optionally also a separate fuel stream such as natural gas, and then burned in a fired heater for generating the heat. The fired heater, which is well known in the art, and often referred to as furnace or direct fired heater, provides thereby heat for preheating the ammonia feed gas stream prior to entering a pre-cracking adiabatic reactor, and / or prior to entering the ammonia cracking reactor.

[0066] In an embodiment, the method further comprises: electrically heating any of: the ammonia feed gas stream, any of the fuel gas streams, combustion air, or combinations thereof.

[0067] This enables to, for instance, heat up the fuel gas and optionally also the combustion air, even up to the autoignition temperature. There is an associated decrease of fuel consumption, thereby increasing the hydrogen recovery of the process, particularly when the fuel is part of the effluent gas stream from the ammonia cracking reactor, i.e. cracked gas.

[0068] The method of the present invention comprises diverting a portion of said effluent gas stream and supplying it as a portion of said separate fuel stream. The portion of said effluent gas stream may for instance be withdrawn as part of the produced effluent gas stream from the ammonia cracking reactor i.e. the effluent gas stream exiting the ammonia cracking reactor (hot cracked gas), or as part of the cooled effluent gas stream entering the hydrogen recovery unit.

[0069] Another fuel stream, such as hydrogen, in particular hydrogen produced in the process, may also be provided. Hence, in an embodiment, a hydrogen stream is provided as at least a portion of said separate fuel stream, suitably hydrogen produced by the method (process) or system (plant) of the invention.

[0070] In an embodiment, the method comprises diverting a portion of an ammonia stream, such as a portion of the ammonia feed stream, and supplying it as at least a portion of said separate fuel stream, thus suitably as said separate fuel stream.

[0071] Hence, an ammonia stream is provided as at least a portion of said separate fuel stream, suitably a portion of an ammonia gas stream produced in the method (process) or system (plant) of the invention), such as a portion of the ammonia feed stream. For instance, a portion of the ammonia feed stream is diverted and provided as fuel to the burners of a fired cracker. This has the advantage of giving a handle to control the temperature of the flue gas leaving the waste heat channel of the fired cracker.

[0072] Combinations of the above are also envisaged.

[0073] Thereby, the separate fuel stream comprises hydrogen, or a mixture of hydrogen and nitrogen, or ammonia. The provision of hydrogen, for instance hydrogen produced by the method and system of the invention, enables a burning with a significantly reduced carbon footprint, as no carbon dioxide is emitted compared to when using a carbon- containing fuel such as natural gas as the fuel stream. The separate fuel stream may also comprise ammonia, which also is suitable for burning with no generation of carbon dioxide and thus further enabling also a reduced carbon footprint.

[0074] In an embodiment, step iii) further comprises generating i.e. producing a hot flue gas stream and recovering heat thereof by at least one of:

[0075] - said preheating of the ammonia feed stream prior to passing the ammonia feed stream to the at least one adiabatic ammonia pre-cracking reactor; - preheating of the partly converted ammonia feed stream, i.e. the ammonia feed stream after passing to the at least one adiabatic ammonia pre-cracking reactor;

[0076] - preheating of the off-gas stream; or

[0077] - preheating of the air stream.

[0078] This enables achieving hydrogen production from ammonia cracking using waste heat in e.g. the fire heated ammonia cracking reactor for preheating one or more streams, including the ammonia feed stream to an adiabatic ammonia pre-cracking reactor, instead of producing steam, thereby also maximizing the yield of hydrogen and increasing process and plant efficiency. For the hydrogen business it is essential to have the maximum hydrogen output, thus any additional percent point in hydrogen yield and thereby efficiency significantly counts.

[0079] The hot flue gas stream travels through a convection section of the fire heated reactor, as is well known in the art of SMR technology. The combustion air stream is suitably preheated by heat exchange with the hot flue gas stream from e.g. 20°C to 300-350°C, while the off-gas stream, i.e. the off-gas stream from the hydrogen recovery unit, is preheated by heat exchange with the hot flue gas stream from e.g. 40°C to 150-200°C. As a particular example, the combustion air stream is indirectly heat exchanged at a portion of the convection section where the temperature of the flue gas is about 200-400°C, while the off-gas stream is indirectly heat exchanged at a portion of the convection section where the temperature of the flue gas is 150-200°C.

[0080] It is understood that the convection section, herein also referred to as “flue gas section”, is provided with one or more heat exchangers, preferably arranged as heating coils, as for instance shown by heating coils 36’, 36”, 36”’, 36IVin appended Fig. 1 , 3.

[0081] By the invention, step iv) further comprises the cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the hydrogen recovery unit.

[0082] In an embodiment, the ammonia feed stream is derived, i.e. produced, from liquid ammonia such as liquid ammonia imported from storage, for instance liquid ammonia or liquid anhydrous ammonia, and which has been subjected to: evaporation e.g. in an ammonia evaporator, in particular in the ammonia evaporator of an above embodiment of the invention, and pre-heating e.g. in a feed / effluent heat exchanger, prior to said evaporation. Accordingly, the method further comprises: providing a liquid ammonia stream imported from storage, and subjecting the liquid ammonia stream to: evaporation in said ammonia evaporator; and pre-heating prior to said evaporation in ammonia feed preheater by heat exchange with cooled effluent gas being supplied to said effluent gas separator. It would be understood that any of such steps of evaporation and pre-heating prior to said evaporation, may be part of the method according to the invention. The preheating is suitably provided by heat exchange with exhaust gas from a turbine provided in the method and system of the invention, as it will become apparent from a below embodiment.

[0083] Thereby, further heat integration and without needing to carry out water removal of the liquid ammonia is achieved, as all important waste heat available is used. The water removal from the liquid ammonia is not required, thus eliminating the need of providing expensive steps and associated units, such as electrolysis and / or distillation. Accordingly, in an embodiment, the ammonia feed stream is produced from liquid ammonia without subjecting the liquid ammonia to a water removal step, i.e. without a dedicated water removal step such as distillation and / or electrolysis.

[0084] By way of example, for preheating and evaporation, as well as for subsequent preliminary preheating of the ammonia feed stream from e.g. about 90°C to 300-350°C, the effluent gas stream is used as heat exchanging medium. For the further pre-heating of the ammonia feed stream to a temperature of about 500°C, the flue gas of e.g. the fire heated reactor is used as heat exchanging medium. When operating with e.g. an electrically heated reactor, the pre-heating of the ammonia feed is suitably provided by a fired heater, as described farther above. Particularly when operating with a plurality of pre-cracking reactors, more particularly when operating with two or more adiabatic ammonia cracking reactors, as also recited farther above, there is no available waste heat which is used for production of steam, which is highly advantageous where steam is considered as being of low value or of no use.

[0085] Suitably, the effluent gas stream from the ammonia cracking reactor, apart from providing the above mentioned preliminary preheating of the ammonia feed stream in a first feed / effluent heat exchanger, is also used to pre-heat fuel gas and to drive an ammonia evaporator for providing the evaporation of ammonia into a gaseous stream suitable for the downstream ammonia cracking, i.e. as said ammonia feed stream, as well as optionally also for preheating liquid ammonia being pumped from storage in a second feed / effluent heat exchanger.

[0086] It would be understood that the term “liquid ammonia imported from storage” has the same meaning as “liquid ammonia being pumped from storage”.

[0087] After delivering heat in said second feed / effluent heat exchanger, the effluent gas stream may be further cooled in a heat exchanger using water as cooling medium i.e. a water cooler, thereby finally bringing the temperature of the effluent gas stream from for instance about 700°C or 550°C at the outlet of, respectively, the fire heated reactor or convection heated reactor, to about 50°C before entering the hydrogen recovery unit.

[0088] Due to transport requirements, traded liquid ammonia normally contains some water, even when it is called anhydrous. For instance, by the present invention, the liquid ammonia being pumped from storage may have a water content of about 0.2 mole % or 0.5 mole %. Some of this water may be withdrawn as a water purge stream in the ammonia evaporator.

[0089] In an embodiment, the flashing step provides a bottom ammonia-lean aqueous stream which is directed to said effluent gas separator as wash-stream; optionally, the washstream is add-mixed with make-up water and then fed to the effluent gas separator.

[0090] This enables further integration as there is less need of externally sourced water as scrubbing medium for the effluent gas separator. The ammonia-lean aqueous stream is not withdrawn from the process or plant as a waste stream, thereby also eliminating the need of highly costly downstream waste-water treatment. A waste-water treatment plant is highly expensive, not only in terms of capital expenditures (CAPEX), but also in terms of operating expenditures (OPEX), normally also requiring a significant plot size of the plant. Preferably, said bottom ammonia-lean aqueous stream is directly supplied to said effluent gas separator as wash-stream.

[0091] For the purposes of the present application, the term “directly supplied” means that there is no intermediate unit or step changing the composition of a process stream.

[0092] In an embodiment, the hydrogen recovery unit comprises at least one Pressure Swing Adsorption (PSA) unit for thereby producing said hydrogen product and said off-gas stream; optionally, wherein:

[0093] - the hydrogen recovery unit comprises a first and second PSA unit for producing said hydrogen product, the method further comprising withdrawing and compressing a first off-gas stream from the first PSA unit and passing it to the second PSA unit for thereby producing said off-gas stream; or

[0094] - the hydrogen recovery unit comprises a membrane unit and a PSA unit.

[0095] At least a portion of the overhead stream from the effluent gas separator is passed to the hydrogen recovery unit. Suitably, the entire portion of the overhead stream from the effluent gas separator is passed to the hydrogen recovery unit.

[0096] According to the present invention, the hydrogen recovery unit may comprise at least one Pressure Swing Adsorption (PSA) unit for thereby producing said hydrogen product and said off-gas stream. Hence, hydrogen purification of the effluent gas stream from the ammonia cracking reactor, e.g. fire heated reactor or electrically heated reactor, is achieved by bringing in a PSA unit the hydrogen concentration from e.g. about 70% vol. in the effluent gas stream to above 99.9% vol. in the hydrogen product. From the PSA unit, the off-gas stream used as fuel in e.g. the fire heated reactor or convection heated reactor, as well as fuel in a fired heater for preheating of the ammonia feed stream when operating with e.g. an electrically heated reactor, is withdrawn. This offgas stream contains for instance about 30% vol. H2, 60% vol. N2 and 10% NH3 and some traces of H2O.

[0097] In a particular embodiment, the hydrogen recovery unit comprises a first and second PSA unit for producing said hydrogen product, the method further comprising withdrawing and compressing a first off-gas stream from the first PSA unit and passing it to the second PSA unit for thereby producing said off-gas stream. The provision of e.g. two PSA units in series conveys also the advantage of increasing the hydrogen yield and recovering a hydrogen product at high pressure in the first PSA unit. The offgas stream becomes however lean in hydrogen and ammonia, for instance by containing 8% vol. hydrogen and 92% vol. nitrogen, thus making it less feasible as fuel in the process.

[0098] This embodiment enables also saving energy in terms of hydrogen product compression that would otherwise be required for downstream applications where the necessary pressure can be high, such as 700 barg. The first PSA unit operates at higher pressure than the second PSA unit; for instance, the first PSA unit may operate at about 100 barg while the second PSA unit may operate at more normal pressures, such as 30 barg. By way of example, about 80% of the hydrogen product comes from the first PSA unit at 100 barg, which thus is highly suitable for downstream applications using hydrogen at higher pressure as described above.

[0099] In another particular embodiment, the hydrogen recovery unit comprises a membrane unit and a PSA unit, more particularly a first membrane unit and subsequently, i.e. downstream, a PSA unit. Thereby, the need of a compression stage in between consecutive PSA units is avoided. The attendant capital and operating expenses related to compression are thus saved and both hydrogen product streams, i.e. from the membrane unit and the PSA unit, are recovered at the same pressure, e.g. about 30 barg, as normally used in hydrogen plants. Furthermore, membrane units are less costly than PSA units for same capacity, as is well known in the art of ammonia technology.

[0100] In an embodiment, the method further comprises: supplying a portion of said overhead stream comprising nitrogen and hydrogen from said effluent gas separator to a turbine for generating power, said turbine producing an exhaust gas stream, and providing at least a portion of said exhaust stream as heat exchanging medium for pre-heating said ammonia feed stream.

[0101] Hence, a high synergy is achieved as the overhead gas from the effluent gas separator, this being a hydrogen-rich gas, is further used as fuel in the turbine, i.e. gas turbine, for generating power, while at the same time the exhaust gas thereof and which is waste heat, is synergistically integrated as it is used for preheating the ammonia feed stream, e.g. the liquid ammonia being pumped from storage. The overhead gas from the effluent gas separator is stripped from ammonia and by still containing a high proportion of hydrogen, it is advantageously expanded in the turbine under the production of power with low NOXgeneration and thus lower requirements on associated gas treatment such as SCR (Selective Catalytic Reduction). The temperature of the overhead gas is about 30-60°C, hence low temperatures at the inlet of the turbine are provided, which also enables having a turbine and associated equipment with less costly materials than when operating at much higher temperatures.

[0102] Furthermore, the power generated in the turbine may be used as part of the electrical heating in the method of the invention, such as where the ammonia cracking reactor is provided as an electrically heated reactor and / or for the electrical heating of any of the ammonia feed gas stream, any of the fuel gas streams, and combustion air. Furthermore, where power is generated from renewable sources such as wind or solar, there are huge variations in power output due to the inherent intermittency of these sources. The power from the turbine may be used for e.g. electrical heating of the above mentioned streams, where there is no power available from renewable sources, e.g. where there is no wind.

[0103] The exhaust gas from the turbine is withdrawn at 500-500°C, or at 80-120°C such as 90-100°C, thus enabling high flexibility in connection with the pre-heating of the ammonia feed stream. Accordingly, in an embodiment, said pre-heating of the ammonia feed stream comprises:

[0104] - pre-heating of the ammonia feed stream from the ammonia evaporator, i.e. in the ammonia feed stream being passed to the at least one ammonia pre-cracking reactor; and / or

[0105] - pre-heating of the ammonia feed stream prior to said evaporation, i.e. for pre-heating of liquid ammonia.

[0106] In yet another general embodiment according to the first aspect of the invention, the entire overhead gas stream from the effluent gas separator is supplied to a turbine for generating power. Accordingly, there is also provided a method for producing a hydro- gen-rich gas from ammonia, comprising the steps of: i) providing an ammonia feed stream; ii) passing the ammonia feed stream to at least one ammonia pre-cracking reactor for producing a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen; iii) passing the partly converted ammonia feed stream to an ammonia cracking reactor for producing an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia; iv) passing the effluent gas stream to an effluent gas separator for producing said hydrogen-rich gas;, wherein step iv) comprises the cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the effluent gas separator; wherein step iv) further comprises recovering unconverted ammonia in the effluent gas stream by a flashing step in an ammonia recovery flashing system, such as a flash column, after said cooling of the effluent gas stream by heat exchange with the ammonia feed stream, and wherein after said cooling and prior to the flashing step, the thus cooled effluent gas stream is supplied to said effluent gas separator, such as an effluent gas scrubbing unit using water as scrubbing medium, for generating in said effluent gas separator an overhead stream comprising nitrogen and hydrogen as said hydro- gen-rich gas, and a bottom liquid stream comprising unconverted ammonia; optionally, wherein said bottom liquid stream comprising unconverted ammonia is provided as feed to said flashing step, and the flashing step provides an overhead stream; optionally, wherein the flashing step provides a bottom ammonia-lean aqueous stream which is directed to said effluent gas separator as wash-stream; optionally, the method further comprising: combining said overhead stream with at least a portion of said effluent gas from step iii) into a fuel gas, and feeding at least a portion of said fuel gas to said ammonia cracking reactor; the method further comprising: supplying at least a portion of said hydrogen-rich gas to a turbine for generating power, said turbine producing an exhaust gas stream, and providing at least a portion of said exhaust stream as heat exchanging medium for pre-heating said ammonia feed stream. In an embodiment, the method further comprises:

[0107] - passing at least a portion of said off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia, from the hydrogen recovery unit to a nitrogen recovery unit selected from any of a PSA unit, cryogenic separation unit, membrane unit, and combinations thereof, for producing a hydrogen-rich gas stream and a nitrogenrich gas stream;

[0108] - feeding at least a portion of said hydrogen-rich gas stream as a separate fuel gas to said ammonia cracking reactor; preferably said ammonia cracking reactor being a fire heated reactor.

[0109] Thereby the nitrogen-rich gas stream may be withdrawn as a valuable product. Nitrogen is traditionally produced by supercooling an atmospheric air to its liquefaction point followed by distillation of its fractions at their different boiling points. The process takes place in a multi-column cryogenic distillation process to produce gaseous oxygen and nitrogen at above atmospheric pressure and near ambient temperature; for instance, in an air separation unit (ASU). The present invention further enables producing valuable nitrogen from the e.g. PSA off-gas, by supplying at least a portion of the off-gas, i.e. a portion of the off-gas or the entire off-gas, to said PSA, cryogenic air separation unit, membrane or combination hereof. Furthermore, the hydrogen-rich gas stream being withdrawn is advantageously utilized as fuel gas in the ammonia cracking reactor, thereby further providing synergistic integration of process streams and significantly reducing the requirement of external sources of fuel gas, such as natural gas. The content of CO2 emissions in the flue gas from the ammonia cracking reactor is thereby also significantly reduced.

[0110] In an embodiment, step iii) further comprises:

[0111] - producing a hot flue gas stream and recovering heat thereof by at least one of: preheating of the ammonia feed stream prior to passing the ammonia feed stream to the at least one adiabatic ammonia pre-cracking reactor; and preheating of the partly converted ammonia feed stream, i.e. the ammonia feed stream after passing to the at least one adiabatic ammonia pre-cracking reactor; - injecting ammonia to the hot flue gas stream before said heat recovery for conducting a selective non-catalytic removal (SNCR) of nitrogen oxides (NOx), preferably the hot flue gas stream having a temperature in the range of 800-1000°C, such as 850-950°C;

[0112] - injecting ammonia to the hot flue gas after said heat recovery and passing the hot flue gas to a selective catalytic reduction (SCR) unit for further removal of NOXand N2O, preferably the hot flue gas having a temperature in the range of 300-500°C, such as 325-475°C.

[0113] The hot flue gas stream travels through the convection section, i.e. flue gas section, of said ammonia cracking reactor, preferably a fire heated reactor, and is utilized for the pre-heating of streams, such as an ammonia feed stream, suitably by means of one or more of the heating coils arranged in the flue gas section. The hot flue gas enters the flue gas section at e.g. 800-1000°C, such as 850-950°C. Ammonia is injected into the flue gas section at a point where the flue gas is within these temperature ranges, thus preferably before any heat recovery with e.g. an ammonia feed stream, thereby enabling the SNCR.

[0114] After heat recovery from the hot flue gas, hence after the temperature of the hot flue gas has been reduced to 300-500°C, such as 325-475°C, ammonia is injected to this hot flue gas and passed to the SCR unit, thereby enabling the removal of NOXand N2O.

[0115] NOXis traditionally removed by Selective Catalytic Reduction (SCR) with ammonia. Selective Non-Catalytic Reduction (SNCR) with ammonia is also frequently used to reduce NOX. It is understood that in SNCR, a catalyst such as catalyst bed is not provided. The present invention combines SCR and SNCR, preferably in a single step as recited above, thereby enabling a less expensive solution i.e. lower capital expenditures, since at least the SCR unit and associated ammonia injection device(s) is reduced in size.

[0116] In an embodiment, the method further comprises:

[0117] - passing the hot flue gas after said SCR unit to a N2O catalytic unit for further removal of N2O. In an embodiment:

[0118] - the SCR unit comprises: (a) a catalyst comprising an iron (Fe)-promoted zeolite, preferably an iron-promoted-beta zeolite (Fe-Beta zeolite); or (b) a catalyst comprising vanadium (V), optionally wolfram (W), on a carrier selected from at least one of: titania (TiC>2), alumina (AI2O3), and silica (SiCh);

[0119] - the N2O catalytic unit comprises: a catalyst comprising cobalt (Co).

[0120] A traditional SCR unit comprises a vanadium-based catalyst stabilized with wolfram on a titanium carrier. N2O is a very potent greenhouse gas and can be removed either downstream the SCR or in combination with NOX. The latter is achieved by addition of ammonia to an iron promoted zeolite, Fe-Beta. N2O can also be catalytically decomposed to N2 on a cobalt based catalyst.

[0121] In an embodiment, the ammonia is injected to the hot flue gas to the SCR in a molar ratio of >1 with respect to the NOx-content in the hot flue gas, and excess ammonia is decomposed to NOXin on a noble metal catalyst ,such as a catalyst comprising any of silver (Ag), platinum (Pt), palladium (Pd), ruthenium (Ru) and rhodium (Rh).

[0122] Hence, in connection with the injection of ammonia for the SCR, the catalytic removal of NOXis accompanied by catalytic destruction of excess ammonia, The ammonia is injected, e.g. dosed, in the molar ratio of >1 with respect to the NOx-content in the hot flue gas in order to achieve an acceptable low NOXemission. In order to avoid emitting ammonia, the excess ammonia is decomposed to NOXon the noble metal catalyst.

[0123] In an embodiment, the method further comprises:

[0124] - diverting a portion of an ammonia stream, such as a portion of the ammonia feed stream, as said ammonia to the hot flue gas stream.

[0125] Thereby, further synergistic integration is achieved, as available ammonia streams are incorporated not only with the purpose of producing hydrogen, but advantageously also for eliminating or reducing NOXand N2O carried over in the hot flue gas.

[0126] In a second aspect, the invention provides also a system, i.e. plant, for producing a hydrogen product from ammonia, comprising: -at least one pre-cracking reactor, such as an adiabatic pre-cracking reactor, arranged to receive an ammonia feed stream, said optional at least one pre-cracking reactor preferably having arranged therein a catalytic fixed-bed, and provide a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen;

[0127] - an ammonia cracking reactor arranged to receive the partly converted ammonia feed stream and provide an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia;

[0128] - a hydrogen recovery unit, arranged to receive the effluent gas stream and provide the hydrogen product, and an off-gas stream comprising: hydrogen, nitrogen and optionally unconverted ammonia; wherein the system comprises at least one heat exchanger arranged upstream the hydrogen recovery unit for cooling said effluent gas stream by heat exchange with the ammonia feed stream; wherein the system further comprises:

[0129] - an effluent gas separator, arranged to receive the thus cooled effluent gas stream, and to provide: an overhead stream comprising nitrogen and hydrogen and a conduit for passing said overhead stream comprising nitrogen and hydrogen to said hydrogen recovery unit, and a bottom liquid stream comprising the unconverted ammonia;

[0130] - an ammonia recovery flashing system, such as a flash column, arranged to receive said bottom liquid stream comprising the unconverted ammonia, and to provide an overhead stream.

[0131] In another general embodiment of the second aspect of the invention, i.e. system (plant), there is provided a system for carrying out the method according to the first aspect of the invention.

[0132] Accordingly, there is provided a system for conducting the method according to any of the above method (process) embodiments, the system comprising:

[0133] - at least one pre-cracking reactor, such as an adiabatic pre-cracking reactor, arranged to receive an ammonia feed stream, said optional at least one pre-cracking reactor preferably having arranged therein a catalytic fixed-bed, and provide a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen;

[0134] - an ammonia cracking reactor arranged to receive the ammonia feed stream and provide an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia; - a hydrogen recovery unit, arranged to receive the effluent gas stream and provide a hydrogen product, and an off-gas stream comprising: hydrogen, nitrogen and optionally unconverted ammonia; wherein the system comprises at least one heat exchanger arranged upstream the hydrogen recovery unit for cooling said effluent gas stream by heat exchange with the ammonia feed stream; wherein the system further comprises:

[0135] - an effluent gas separator, arranged to receive the thus cooled effluent gas stream, and to provide: an overhead stream comprising nitrogen and hydrogen and a conduit for passing said overhead stream comprising nitrogen and hydrogen to said hydrogen recovery unit, and a bottom liquid stream comprising the unconverted ammonia;

[0136] - an ammonia recovery flashing system, such as a flash column, arranged to receive said bottom liquid stream comprising the unconverted ammonia, and to provide an overhead stream.

[0137] In an embodiment, the ammonia recovery flashing system is further arranged to provide a bottom ammonia-lean aqueous stream, and the system further comprises a conduit for directing said bottom ammonia-lean aqueous stream as a wash-stream to said effluent gas separator.

[0138] It is understood that the term “conduit” means a process line, such as a pipe, carrying a given process stream.

[0139] In an embodiment, the system further comprises: a mixing point for combining said overhead stream from the ammonia recovery flashing system with at least a portion of any of said off-gas from the hydrogen recovery unit, said effluent gas stream from the ammonia cracking reactor, or a combination thereof, into a fuel gas, and a conduit for feeding at least a portion of said fuel gas to said ammonia cracking reactor.

[0140] In an embodiment, the at least one ammonia pre-cracking reactor and / or the ammonia cracking reactor comprising an ammonia cracking catalyst comprising a metal or a metal alloy selected from any of: Fe, Co, Ru, optionally Ni, or combinations thereof. In an embodiment, the at least one ammonia pre-cracking reactor comprises a catalyst comprising 20-50 wt% Fe, 20-50 wt% Co and 20-50 wt% alumina, optionally promoted with an alkali metal oxide, a lanthanide group metal oxide, and / or oxides of Ca, Si, Al or combinations thereof; and wherein the ammonia cracking reactor comprises a Ni-cata- lyst, said Ni-catalyst comprising 20-60 wt% Ni, and 40-80 wt% of any oxides of Al, Ca, Mg or combinations hereof, optionally promoted with a lanthanide group metal oxide, such as La2C>3.

[0141] In an embodiment, the system further comprises:

[0142] - a turbine arranged to receive a portion of said overhead stream comprising nitrogen and hydrogen from the effluent gas separator, for generating power, and to provide an exhaust gas stream;

[0143] - a heat exchanger arranged to receive at least a portion of said exhaust stream as heat exchanging medium for pre-heating said ammonia feed stream.

[0144] In an embodiment, said at least one heat exchanger arranged upstream the hydrogen recovery unit for cooling said effluent gas stream by heat exchange with the ammonia feed stream comprises an ammonia evaporator; said heat exchanger arranged to receive the at least a portion of said exhaust stream as heat exchanging medium, is provided downstream said ammonia evaporator for pre-heating the ammonia feed stream upstream the at least one ammonia pre-cracking reactor; and / or said heat exchanger arranged to receive the at least a portion of said exhaust stream as heat exchanging medium, is provided upstream said ammonia evaporator for preheating liquid ammonia.

[0145] Suitably, the system further comprises:

[0146] - a conduit for providing said liquid ammonia, such as liquid ammonia imported from a storage tank.

[0147] In an embodiment, the system further comprises:

[0148] - a nitrogen recovery unit selected from any of a PSA unit, cryogenic separation unit, membrane unit, and combinations thereof, arranged to receive said at least a portion of said off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia, from the hydrogen recovery unit, and provide a hydrogen-rich gas stream and a nitrogen-rich gas stream;

[0149] - a conduit arranged for feeding at least a portion of said hydrogen-rich gas stream as a separate fuel gas to said ammonia cracking reactor, preferably said ammonia cracking reactor being a fire heated reactor.

[0150] In an embodiment,

[0151] - the ammonia cracking reactor, preferably a fire heated reactor, comprises a convection section i.e. a flue gas section, and the reactor is further arranged to provide a hot flue gas stream and recovering heat therefrom by means of one or more heat exchangers, preferably arranged as heating coils in said flue gas section;

[0152] - the ammonia cracking reactor is further arranged to receive a conduit for injecting ammonia to the hot flue gas upstream said one or more heat exchangers of the flue gas section and conducting a selective non-catalytic removal (SNCR) of nitrogen oxides (NOX), preferably the ammonia cracking reactor being arranged to provide the hot flue gas stream at a temperature in the range of 800-1000°C, such as 850-950°C;

[0153] - the ammonia cracking reactor is further arranged to receive a conduit for injecting ammonia to the hot flue gas downstream stream said one or more heat exchangers of the flue gas section and conducting a selective catalytic reduction (SCR) in a SCR unit for further removal of NOXand N2O, preferably the ammonia cracking reactor being arranged to provide the hot flue gas at a temperature in the range of 300-500°C, such as 325-475°C.

[0154] In an embodiment, the ammonia cracking reactor is further comprises a N2O catalytic unit arranged downstream said SCR unit, for further removal of N2O.

[0155] In an embodiment,

[0156] - the SCR unit comprises: (a) a catalyst comprising an iron (Fe)-promoted zeolite, preferably an iron-promoted-beta zeolite (Fe-Beta zeolite); or (b) a catalyst comprising vanadium (V), optionally wolfram (W), on a carrier selected from at least one of: titania (TiC>2), alumina (AI2O3), and silica (SiCh);

[0157] - the N2O catalytic unit comprises: a catalyst comprising cobalt (Co).

[0158] In an embodiment, - the SCR unit is arranged to receive said ammonia in a molar ratio of >1 with respect to the NOx-content in the hot flue gas, and further there is provided a noble metal catalyst, such as a catalyst comprising any of silver (Ag), platinum (Pt), palladium (Pd), ruthenium (Ru) and rhodium (Rh), for decomposing excess ammonia to NOX.

[0159] In an embodiment, the system further comprises a conduit arranged for diverting a portion of an ammonia stream, such as a portion of the ammonia feed stream, as said ammonia to the hot flue gas stream.

[0160] It would be understood that any of the embodiments and associated technical advantages (benefits) according to the first aspect (method) of the invention may be combined with the second (system) aspect of the invention, and vice versa.

[0161] In general, the present invention provides at least the following advantages:

[0162] - High energy efficiency and high recovery (in the product) of the hydrogen atoms contained in the NH3 feedstock.

[0163] - Stand-alone solution without import or export of steam to the plant.

[0164] - Heat integration done directly between the cold streams and the hot cracked gas, without producing low or medium pressure steam for internal use.

[0165] - Exploitation of calories at lower temperature to carry out the ammonia cracking reaction, while at the same time eliminating the need for dedicated units for removal of water and / or oxygen containing species in the ammonia feed.

[0166] - The milder temperatures in the optional pre-cracking reactors give more flexibility regarding the construction materials required in and around those units.

[0167] - No waste streams from the process.

[0168] - Simpler and more energy efficient method and system than prior art requiring distillation for removal of water from liquid ammonia feed.

[0169] - Integration of a gas turbine providing additional flexibility by generating power useful for driving e.g. an ammonia cracking reactor provided as an electrically heated reactor, as well as the gas turbine providing an exhaust gas stream that is used for pre-heating of the ammonia feed stream. - Production of valuable nitrogen, while at the same time producing hydrogen-rich gas which is utilized as fuel source in ammonia cracking, thereby significantly reducing CC>2-emissions.

[0170] - Synergistically combining selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) of NOXvia ammonia, along with the removal of the potent greenhouse gas N2O.

[0171] The present application, having ammonia as the major or only energy source is important in the green transition using ammonia as an energy carrier.

[0172] Fig. 1 shows a schematic layout of the process and plant according to an embodiment of the present invention including ammonia pre-cracking, ammonia cracking in a fire heated reactor (fired cracker) for producing an effluent gas stream (cracked gas), and provision of fuel gas produced in the process and plant supplied to the fired cracker.

[0173] Fig. 2 shows a schematic layout of the process and plant downstream the fired cracker cracking unit of Fig. 1 , including effluent gas stream cooling, ammonia recovery and preparation of the ammonia feed gas stream, as well as hydrogen recovery.

[0174] Fig. 3 shows a schematic layout as in Fig. 1 , along with selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) with ammonia of NOXand N2O.

[0175] Fig. 4 shows a schematic layout as in Fig. 2, along with a nitrogen recovery unit for producing an ammonia product and a hydrogen-rich gas.

[0176] With reference to both Fig. 1 and Fig. 2, liquid ammonia 1 (Fig. 2) is received from battery limits, pumped as liquid ammonia stream T and preheated in ammonia feed preheater 10 by cooled effluent gas stream 13’ from fired cracker 34 (Fig. 1), thus forming preheated liquid ammonia stream 1”. The preheated liquid ammonia stream 1” is then further preheated in recirculation cooler 12 by ammonia-lean aqueous stream (wash stream) 23, 23’ being pumped from flash column 22. Subsequently, the thus preheated ammonia stream T” is vaporized in ammonia evaporator 14 by exchanging heat with effluent gas stream 7iv. It would be understood that the effluent gas stream from the fired cracker until the ammonia evaporator 14 is herein provided with the reference numbers 7 such as 7, 7’, 7” etc., while the effluent gas stream after passing the ammonia evaporator 14 and until the effluent gas separator 18 is provided with the reference numbers 13 such as 13’, 13”. It would also be understood that the effluent gas stream, for instance stream 7 or 7’ is also referred to as “cracked gas”. A fuel gas pre-heater 26 is advantageously provided upstream the ammonia evaporator 14, thereby enabling the use of higher quality energy by virtue of the effluent gas stream 7’, 7” from the fired cracker 34 being at a high temperature, e.g. 600-650°C, for the preheating of fuel gas 11 , rather than for evaporation of the ammonia. From the ammonia evaporator 14, ammonia vapor 3 is produced as the ammonia feed stream to the fired cracker 34.

[0177] Turning now specifically to Fig. 1 , the ammonia feed stream 3 which is provided as ammonia vapor is superheated to e.g. 600-700°C by flue gas 27 in first heating coil 36’ of the convection section 34’” of the fired cracker 34. The convection section is also referred to as flue gas section. Where ammonia is used as fuel, it is suitably provided at an adequate temperature by withdrawing and mixing portions of the streams before and after this first heating coil 36’. For instance, Fig. 1 shows a portion 3” of the ammonia feed stream 3 being diverted and provided as fuel to the burners 34” of the fired cracker 34. This has the advantage of giving a handle to control the temperature of the flue gas 27 leaving the waste heat channel. The ammonia feed stream 3’ then enters a first adiabatic pre-converter 28 where the ammonia feed stream cools down as the cracking reaction proceeds. The gas leaves the first pre-converter at a temperature of e.g. 450-550°C, such as 480-500°C. In a second heating coil 36”, the gas, i.e. the partly converted ammonia feed stream, is reheated to e.g. 600-700°C by flue gas and enters a second adiabatic pre-converter 30. Again, the outlet therefrom will have a temperature of e.g. 450- 550°C, such as 480-500°C. Finally, the partly converted ammonia feed stream is reheated in a third coil 36’” which brings the temperature to e.g. 550-650°C before entering as partly converted ammonia feed stream 5 to the fired cracker 34. The catalyst in the adiabatic pre-converters 28, 30 is tolerant to the trace amounts of water contained in the raw ammonia 3, 3’ being fed and has higher activity than conventional Ni-based formulations.

[0178] The fired cracker 34 comprises an array of tubes 34’ packed with catalyst. The catalyst is suitably a conventional Ni-based catalyst, or more active catalysts like alloyed formulations. The temperature of the effluent gas stream 7 (cracked gas) is in the range of e.g. 750-850°C, such as 800°C, thus withdrawn as a hot cracked gas. The fired cracker 34 is provided with said burners, herein illustrated as item 34”. The fuel gas to the burners can be hydrocarbons such as natural gas, hydrogen, cracked gas, ammonia as explained above, or a mixture thereof. Suitably, fuel gas 11 which is at least partly derived from the overhead stream 25 from said flash column 22 (Fig. 2), is provided as fuel gas to the fired cracker 34, as illustrated in Fig. 1. The provision of internal streams as fuel reduces or eliminates the need for the use of natural gas, which is normally externally sourced. The effluent gas stream 7 from the fired cracker 34 exchanges heat with air preheater 24 located immediately downstream the fired cracker 34, thus providing effluent gas stream 7’. The combustion air 9”, had already been conditioned in heating coil 36ivinto preheated combustion air 9’. The combustion air 9 is provided at for instance 20°C and preheated to close to about 90°C in said heating coil 36iv.

[0179] Turning now to Fig. 2, after the air preheater 24 of Fig. 1 , the effluent gas 7’ is optionally split into stream 7”’ which is combined with overhead gas 25 of flash column 22, while effluent gas stream 7” provides heat to the thus derived fuel gas 11 . The fuel gas 11 is derived from the overhead gas stream 25 and combines the portion 7”’ of the effluent gas stream, as well as off-gas 19 from hydrogen recovery unit 20, e.g. PSA unit. The cooled effluent gas stream 7iventers the ammonia evaporator 14 at a temperature within the range of e.g. 580-650°C. Where the fired cracker 34 requires cracked gas as fuel, a portion 13 of the cooled effluent gas stream is withdrawn, e.g. as additional fuel gas, immediately downstream the ammonia evaporator 14, as shown in the figure. The other portion of the effluent gas stream 13 enters heat exchanger 16 where it exchanges heat with the bottom liquid stream 21 comprising unconverted ammonia from effluent gas separator 18. The cooled effluent gas stream 13’ is further cooled down by the liquid ammonia feed T in ammonia feed preheater 10, as explained above. The thus cooled effluent gas stream 13” enters the effluent gas separator 18, which then provides overhead stream 15 comprising nitrogen and hydrogen, as a hydrogen-rich gas stream, as well as the bottom liquid stream 21 comprising the unconverted ammonia. The overhead stream 15 from the effluent gas separator 18 is passed to the hydrogen recovery unit 20, thereby providing a hydrogen product 17 and the off-gas stream 19.

[0180] The streams that enter the effluent gas separator 18 have temperatures in the range 15- 35°C; these streams being the effluent gas stream 13”, recirculating water 23”and make- up water 23”’. It would be understood that the recirculating water 23, 23’, 23” refers to the bottom ammonia-lean aqueous stream from the flash column 22. The unreacted ammonia in the effluent gas stream 13” is absorbed by the liquid water, leaving said overhead stream 15 that contains less than 500 ppm vol. NH3 which can be fed to the hydrogen recovery unit 20, e.g. PSA. The bottom liquid stream 21 comprising the unconverted ammonia. is then preheated by the effluent gas stream 13 in the earlier mentioned heat exchanger 16 to around 150°C as stream 2T and then depressurized. In this way the more volatile compounds (H2, N2 and part of the NH3) are stripped off from the liquid in the flash column 22. The gas phase, i.e. the overhead stream 25 from the flash column 22, is mixed with the off-gas 19 from the PSA 20, suitably also with portion 7’” of the effluent gas stream from the fired cracker 34, and then sent to the fuel system as fuel gas 11 , as explained above. The bottom ammonia-lean aqueous stream 23, 23’ from the flash column 22 is cooled down in said recirculation cooler 12, optionally also in a recirculation water cooler (not shown), and recirculated as a wash-stream 23” to the effluent gas separator 18. Suitably, this wash-stream 23” is add-mixed with make-up water 23’” and fed to the effluent gas separator 18.

[0181] A portion of the overhead stream 15 from the effluent gas separator 18, said overhead stream 15 being a hydrogen-rich gas, may also be diverted (not shown) and supplied to a gas turbine (not shown) for generating power as well as an exhaust gas. Where the exhaust gas is withdrawn at for instance 90-100°C it is suitably used for pre-heating the liquid ammonia stream T. Where the exhaust gas is withdrawn at for instance 500- 550°C, it is suitably used for pre-heating ammonia feed stream 3 from the ammonia evaporator 14.

[0182] Now with reference to Fig. 3, a schematic layout as in Fig. 1 is shown, further including selective catalytic reduction (SCR) 34IV, 34vand selective non-catalytic reduction (SNCR) with ammonia for removal of NOXand N2O. Ammonia 29 is injected to hot flue gas stream in the flue gas section 34’” before heat recovery for conducting the selective non-catalytic removal (SNCR) of nitrogen oxides (NOx), the hot flue gas stream preferably having a temperature in the range of 800-1000°C, such as 850-950°C. Ammonia 29' is also injected via injecting device 34IVto the hot flue gas after heat recovery, the hot flue gas now preferably having a temperature in the range of 300-500°C, such as 325-475°C. This hot flue gas is passed to a selective catalytic reduction (SCR) unit 34vfor further removal of NOXand N2O. After the SCR unit 34v, the hot flue gas is passed to a N2O catalytic unit 34VIfor further removal of N2O.

[0183] With reference to Fig. 4, a schematic layout as in Fig. 2 is shown, further including the provision of nitrogen recovery unit 38 which as arranged to receive at least a portion 19’ of the off-gas 19 from the hydrogen recovery unit 20, e.g. PSA unit 20, for producing a valuable ammonia product 33 and a hydrogen-rich gas 31 which is advantageously utilized as separate fuel gas source, for instance for addition along with fuel gas 11 (Fig. 1 , 3) to the ammonia cracking reactor.

Claims

CLAIMS1 . Method for producing a hydrogen product from ammonia, comprising the steps of: i) providing an ammonia feed stream; ii) passing the ammonia feed stream to at least one ammonia pre-cracking reactor for producing a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen; iii) passing the partly converted ammonia feed stream to an ammonia cracking reactor for producing an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia; iv) passing the effluent gas stream to a hydrogen recovery unit for producing said hydrogen product and an off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia, wherein step iv) comprises the cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the hydrogen recovery unit; wherein step iv) further comprises recovering unconverted ammonia in the effluent gas stream by a flashing step in an ammonia recovery flashing system, such as a flash column, after said cooling of the effluent gas stream by heat exchange with the ammonia feed stream, and wherein after said cooling and prior to the flashing step, the thus cooled effluent gas stream is supplied to an effluent gas separator, such as an effluent gas scrubbing unit using water as scrubbing medium, for generating in said effluent gas separator an overhead stream comprising nitrogen and hydrogen which is passed to said hydrogen recovery unit, and a bottom liquid stream comprising unconverted ammonia.

2. Method according to claim 1 , wherein said bottom liquid stream comprising unconverted ammonia is provided as feed to said flashing step, and the flashing step provides an overhead stream; the method further comprising: combining said overhead stream with at least a portion of any of said off-gas from the hydrogen recovery unit, said effluent gas from step iii), or a combination thereof, into a fuel gas, and feeding at least a portion of said fuel gas to said ammonia cracking reactor.

3. Method according to any of claims 1-2, wherein the at least one ammonia pre-crack- ing reactor and / or the ammonia cracking reactor operate(s) in the temperature range 300-700°C, and further wherein the at least one ammonia pre-cracking reactor and / or the ammonia cracking reactor operate(s) with an ammonia cracking catalyst comprising a metal or a metal alloy selected from any of: Fe, Co, Ru, optionally Ni, or combinations thereof, such as a Fe-Co based catalyst.

4. Method according to any of claims 1-2, wherein the at least one ammonia pre-crack- ing reactor operate with a catalyst comprising 20-50 wt% Fe, 20-50 wt% Co and 20-50 wt% alumina, optionally promoted with an alkali metal oxide, a lanthanide group metal oxide, and / or oxides of Ca, Si, Al or combinations thereof; and wherein the ammonia cracking reactor operates with a Ni-catalyst, said Ni-catalyst comprising 20-60 wt% Ni, and 40-80 wt% of any oxides of Al, Ca, Mg or combinations hereof, optionally promoted with a lanthanide group metal oxide, such as La2C>3.

5. Method according to any of claims 2-4, wherein said fuel gas is pre-heated by said effluent gas stream prior to said cooling of the effluent gas stream by heat exchange with the ammonia feed stream in step iv).

6. Method according to any of claims 1-5, wherein: in step iv) said cooling of the effluent gas stream by heat exchange with the ammonia feed stream prior to passing the effluent gas stream to the hydrogen recovery unit, comprises:- passing the effluent gas stream, after delivering heat to said fuel gas, to an ammonia evaporator, thereby providing a cooled effluent gas stream;- diverting at least a portion of said cooled effluent gas stream as additional fuel gas, and feeding it to said ammonia cracking reactor;- diverting another portion of said cooled effluent gas stream, as said cooled effluent gas stream which is supplied to said effluent gas separator.

7. Method according to any of claims 1-6, wherein the ammonia cracking reactor is: a fire heated reactor comprising one or more catalyst-filled tubes, a convection heated reactor, an electrically heated reactor, an induction heated reactor, or combinations thereof.

8. Method according to claim 7, wherein the ammonia cracking reactor is any of a fire heated reactor and convection heated reactor; the method further comprising:- passing a portion of the off-gas stream from the hydrogen recovery unit to the fire heated reactor or convection heated reactor upon mixing it with an air stream, and / or upon mixing it with a separate fuel stream, said separate fuel stream being a) an externally sourced fuel gas such as natural gas; and / or b) a portion of any of said fuel gases, thereby generating heat required in the fire heated reactor or convection heated reactor.

9. Method according to claim 7, wherein the ammonia cracking reactor is an electrically heated reactor or an induction heated reactor; the method further comprising:- passing a portion, e.g. another portion, of the off-gas stream to a fired heater upon mixing it with an air stream, optionally upon mixing it with a separate fuel stream, said separate fuel stream being c) an externally sourced fuel gas such as natural gas, and / or d) a portion of any of said fuel gas streams; thereby preheating the ammonia feed gas stream.

10. Method according to any of claims 1-9, wherein the method further comprises: electrically heating any of: the ammonia feed gas stream, any of said fuel gas streams, combustion air, or combinations thereof.

11. Method according to any of claims 8-10, comprising:- diverting a portion of an ammonia stream, such as a portion of the ammonia feed stream, and supplying it as at least a portion of said separate fuel stream.

12. Method according to any of claims 1-11 , wherein the ammonia feed stream is produced from liquid ammonia such as liquid ammonia imported from storage, and which has been subjected to: evaporation and pre-heating prior to said evaporation.

13. Method according to any of claims 1-12, wherein the flashing step provides a bottom ammonia-lean aqueous stream which is directed to said effluent gas separator as wash-stream; optionally, the wash-stream is add-mixed with make-up water and then fed to the effluent gas separator.

14. Method according to any of claims 1-13, wherein the hydrogen recovery unit comprises at least one Pressure Swing Adsorption (PSA) unit for thereby producing said hydrogen product and said off-gas stream; optionally, wherein:- the hydrogen recovery unit comprises a first and second PSA unit for producing said hydrogen product, the method further comprising withdrawing and compressing a first off-gas stream from the first PSA unit and passing it to the second PSA unit for thereby producing said off-gas stream; or- the hydrogen recovery unit comprises a membrane unit and a PSA unit.

15. Method according to any of claims 12-14, further comprising: supplying a portion of said overhead stream comprising nitrogen and hydrogen from said effluent gas separator to a turbine for generating power, said turbine producing an exhaust gas stream, and providing at least a portion of said exhaust stream as heat exchanging medium for pre-heating said ammonia feed stream.

16. Method according to claim 15, wherein said pre-heating of the ammonia feed stream comprises:- pre-heating of the ammonia feed stream from the ammonia evaporator, i.e. in the ammonia feed stream being passed to the at least one ammonia pre-cracking reactor; and / or- pre-heating of the ammonia feed stream prior to said evaporation, i.e. for pre-heating of liquid ammonia.

17. Method according to any of claims 1-16, further comprising:- passing at least a portion of said off-gas stream comprising hydrogen, nitrogen and optionally unconverted ammonia, from the hydrogen recovery unit to a nitrogen recovery unit selected from any of a PSA unit, cryogenic separation unit, membrane unit, and combinations thereof, for producing a hydrogen-rich gas stream and a nitrogenrich gas stream;- feeding at least a portion of said hydrogen-rich gas stream as a separate fuel gas to said ammonia cracking reactor, preferably said ammonia cracking reactor being a fire heated reactor.

18. Method according to any of claims1-17, wherein step iii) further comprises:- producing a hot flue gas stream and recovering heat thereof by at least one of: preheating of the ammonia feed stream prior to passing the ammonia feed stream to the at least one adiabatic ammonia pre-cracking reactor; and preheating of the partly converted ammonia feed stream, i.e. the ammonia feed stream after passing to the at least one adiabatic ammonia pre-cracking reactor;- injecting ammonia to the hot flue gas stream before said heat recovery for conducting a selective non-catalytic removal (SNCR) of nitrogen oxides (NOX), preferably the hot flue gas stream having a temperature in the range of 800-1000°C, such as 850-950°C;- injecting ammonia to the hot flue gas after said heat recovery and passing the hot flue gas to a selective catalytic reduction (SCR) unit for further removal of NOXand N2O, preferably the hot flue gas having a temperature in the range of 300-5000C, such as 325-4750C.

19. Method according to claim 18, further comprising:- passing the hot flue gas after said SCR unit to a N2O catalytic unit for further removal of N2O.

20. Method according to any of claims 18-19; wherein:- the SCR unit comprises: (a) a catalyst comprising an iron (Fe)-promoted zeolite, preferably an iron-promoted-beta zeolite (Fe-Beta zeolite); or (b) a catalyst comprising vanadium (V), optionally wolfram (W), on a carrier selected from at least one of: titania (TiC>2), alumina (AI2O3), and silica (SiCh);- the N2O catalytic unit comprises: a catalyst comprising cobalt (Co).

21. Method according to any of claims 18-20, wherein the ammonia is injected to the hot flue gas to the SCR in a molar ratio of >1 with respect to the NOx-content in the hot flue gas, and wherein excess ammonia is decomposed to NOXin on a noble metal catalyst ,such as a catalyst comprising any of silver (Ag), platinum (Pt), palladium (Pd), ruthenium (Ru) and rhodium (Rh).

22. Method according to any of claims 18-21, further comprising- diverting a portion of an ammonia stream, such as a portion of the ammonia feed stream, as said ammonia to the hot flue gas stream.

23. System for producing a hydrogen product from ammonia, comprising:- at least one pre-cracking reactor, such as an adiabatic pre-cracking reactor, arranged to receive an ammonia feed stream, said optional at least one pre-cracking reactor preferably having arranged therein a catalytic fixed-bed, and provide a partly converted ammonia feed stream comprising ammonia, hydrogen and nitrogen;- an ammonia cracking reactor arranged to receive the partly converted ammonia feed stream and provide an effluent gas stream comprising hydrogen, nitrogen and unconverted ammonia;- a hydrogen recovery unit, arranged to receive the effluent gas stream and provide the hydrogen product, and an off-gas stream comprising: hydrogen, nitrogen and optionally unconverted ammonia; wherein the system comprises at least one heat exchanger arranged upstream the hydrogen recovery unit for cooling said effluent gas stream by heat exchange with the ammonia feed stream; wherein the system further comprises:- an effluent gas separator, arranged to receive the thus cooled effluent gas stream, and to provide: an overhead stream comprising nitrogen and hydrogen and a conduit for passing said overhead stream comprising nitrogen and hydrogen to said hydrogen recovery unit, and a bottom liquid stream comprising the unconverted ammonia;- an ammonia recovery flashing system, such as a flash column, arranged to receive said bottom liquid stream comprising the unconverted ammonia, and to provide an overhead stream.

24. System according to claim 23, wherein the ammonia recovery flashing system is further arranged to provide a bottom ammonia-lean aqueous stream, and the system further comprises a conduit for directing said bottom ammonia-lean aqueous stream as a wash-stream to said effluent gas separator.

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