Process for ammonia synthesis using green hydrogen and method for renovating an ammonia plant

Description

1 / 40 “PROCESS FOR AMMONIA SYNTHESIS USING GREEN HYDROGEN AND METHOD FOR RENOVATING AN AMMONIA PLANT DESCRIPTION Field of application

[0001] The present invention relates to the field of ammonia synthesis. Previous technique

[0002] Ammonia is produced industrially by the reaction of a makeup gas containing hydrogen and nitrogen in a suitable molar ratio. The makeup gas is conventionally produced by reforming a hydrocarbon source, such as natural gas.

[0003] MUG production typically involves a reforming process and purification of the reformed gas. Purification typically includes conversion of CO to CO2; CO2 removal and methanation. The purified gas obtained is fed to a high-pressure ammonia synthesis circuit via a main compressor.

[0004] In the ammonia synthesis circuit, the makeup gas reacts to form ammonia in a suitable ammonia converter. The hot effluent containing ammonia from the ammonia converter undergoes a cooling and separation step, yielding liquid ammonia and a side stream containing unreacted hydrogen and impurities. Typically, a portion of said side stream undergoes a hydrogen recovery process, and the recovered hydrogen is sent to a suction line of said main compressor. Another portion of said side stream is reintroduced into the ammonia converter, typically with a circulator, thus forming the ammonia synthesis circuit. Petition 870250091085, dated 06 / 10 / 2025, page 10 / 74 2 / 40 mentioned above.

[0005] The nitrogen required for ammonia synthesis can be introduced during the reforming process, typically in a secondary air reforming. In some cases, nitrogen can be added separately, for example, when an air separation unit (ASU) is used.

[0006] In summary, industrial ammonia production depends on hydrocarbon reforming to produce the necessary hydrogen. Reforming is typically a fuel-fed process that involves a considerable amount of CO2 emissions.

[0007] There is a growing interest in reducing the carbon footprint of ammonia production. Applicable standards and regulations may introduce additional taxation related to CO2 emissions, for example, considering the amount of CO2 per ton of ammonia produced. The CO2 contained in combustion fumes can be captured, but the related techniques are costly and, more importantly, carbon dioxide capture does not prevent the generation of CO2 emissions in process gases, but only represents ex post remediation. A promising way to achieve this goal is the production of hydrogen from renewable energy sources.

[0008] Hydrogen produced with renewable energy is called “green” hydrogen because it does not cause CO2 emissions, in contrast to conventional production fueled by reforming. Hydrogen produced by burning fossil fuels is often called “grey” hydrogen. The advantage of using green hydrogen is that no CO2 is formed and therefore, Petition 870250091085, dated 06 / 10 / 2025, page 11 / 74 3 / 40 there is no need for expensive carbon dioxide capture and sequestration.

[0009] An example of a process of practical interest for producing green hydrogen is represented by water electrolysis. Water electrolysis requires electricity which can be produced from a renewable source, leading to the production of green hydrogen without releasing CO2 into the atmosphere.

[0010] The green hydrogen thus produced can be injected into an existing plant, typically into the suction of the synthesis gas compressor machine, or directly into the synthesis circuit, in addition to grey hydrogen, increasing the plant's output, decreasing the plant's specific hydrocarbon consumption and reducing the relevant CO2 footprint.

[0011] The production of green hydrogen from renewable energy sources, however, is normally subject to fluctuations. For example, solar-powered hydrogen production obviously depends on the availability of sunlight. To compensate for such fluctuations, green hydrogen storage can be provided. Storage can totally or partially replace green hydrogen production when the energy source is totally or partially unavailable, in order to maintain a certain minimum flow of green hydrogen for ammonia production. Hydrogen storage is carried out in the form of a fixed-volume reservoir whose hydrogen stock is often controlled by gas pressure. Hydrogen storage in this form presents a certain rigidity, thus imposing a minimum and maximum stock of Petition 870250091085, dated 06 / 10 / 2025, page 12 / 74 4 / 40 hydrogen and, consequently, capital and operational costs.

[0012] One disadvantage of a rigid storage system of the type mentioned above is that its capacity must be high enough to guarantee the aforementioned contribution of green hydrogen for as long as the process requires it. However, the supply of high-capacity storage is usually critical in terms of cost, especially when fluctuations in green hydrogen are wide and frequent.

[0013] Fluctuations in green hydrogen production are undesirable events because they abruptly alter the load on the ammonia converter. This load change is considered potentially harmful to the converter itself and other equipment in the high-pressure synthesis circuit if the fluctuations exceed the mechanical and process limits for controlled and safe operation. For example, a rapid load change can cause high gas velocity, which can damage internal converter components or other circuit items. A sudden pressure drop can result in shock (“hammering”) and damage to the equipment. Furthermore, if pressure changes are frequent and large enough, the equipment may wear out due to fatigue cycles. Similar phenomena can also occur in the case of significant fluctuations in operating temperatures.

[0014] EP 4 148 020 A1 discloses a method for controlling an ammonia plant according to the prior art. Petition 870250091085, dated 06 / 10 / 2025, page 13 / 74 5 / 40 Summary of the invention

[0015] The invention aims to overcome the aforementioned disadvantages of the prior art. In particular, the present invention aims to provide a process for the synthesis of ammonia in which the use of so-called green hydrogen, i.e., hydrogen made from at least one renewable energy source, becomes more attractive compared to the prior art.

[0016] The objective is achieved with an ammonia synthesis process in which: (a) Ammonia makeup gas containing hydrogen and nitrogen is reacted in an ammonia converter under ammonia-forming conditions, thus obtaining an effluent containing ammonia; (b) a first portion of hydrogen contained in the ammonia replacement gas is produced by reforming a hydrocarbon source in a reforming process; (c) a second portion of hydrogen contained in the ammonia replacement gas is produced separately from said reforming process, using at least one renewable energy source, preferably a variable renewable energy source; (d) a portion of said hydrogen produced (i.e., being produced or that has been produced) in step (c) is stored in a hydrogen storage facility; (e) the hydrogen from said hydrogen storage is used for Petition 870250091085, dated 06 / 10 / 2025, page 14 / 74 6 / 40 replace all or part of the hydrogen produced in step (c) when said renewable energy source is totally or partially unavailable; The aforementioned process comprises the following steps: (f) evaluate an expected flow rate of hydrogen produced in step (c); (g) adjust a hydrocarbon source flow rate in step (b) so that a flow rate of the first portion of hydrogen in the said ammonia replacement gas is at a desired ratio to the said expected flow rate of step (f); (h) detect an actual quantity, for example, a fill level, of said hydrogen in said hydrogen storage; (i) detect an actual flow rate of hydrogen produced in step (c); (j) adjust the hydrogen flow rate of said hydrogen storage depending on said actual quantity detected in step (h) and said actual flow rate detected in step (i).

[0017] The invention arises from the observation that a flexible operation of the process – in particular, adjusting the flow rate of the hydrocarbon source and the flow rate of hydrogen from said hydrogen storage based on selected criteria – allows achieving surprising advantages in terms of reduced storage space for the hydrogen storage and reduced mechanical stresses on the equipment. Petition 870250091085, dated 06 / 10 / 2025, page 15 / 74 7 / 40 of the installation.

[0018] A reduced storage volume involves lower capital costs compared to traditional hydrogen storage facilities which, operating with rigid parameters, must be designed to store considerable quantities of hydrogen.

[0019] On the other hand, infrequent variations in front parameters prevent the installed equipment from being operated in cyclic mode, which would affect its mechanical reliability. By way of example, without introducing significant changes in temperature and pressure in the reforming process, in the flow rate through air or gas compressors and in the pressure of the ammonia synthesis circuit, the present process can reduce overall mechanical stresses and therefore achieve safe and long-term operation of the equipment.

[0020] These advantages are possible despite the wide and frequent fluctuations in green hydrogen flow that are unavoidable in hydrogen production with renewable energy sources, specifically with variable renewable energy sources. In the present description, “variable” means that the renewable energy source(s) provide(s) amounts of energy that may be subject to change over time.

[0021] Also within the scope of the present invention is a method for renovating an ammonia synthesis plant. The plant to be renovated comprises a reforming front end for generating an ammonia makeup gas by reforming a hydrocarbon source and an ammonia synthesis circuit, including a converter. Petition 870250091085, dated 06 / 10 / 2025, page 16 / 74 8 / 40 of ammonia. The aforementioned method for renovating the installation comprises the following steps: (I) provide a green hydrogen producing device, such as a water electrolyzer, using a renewable energy source, and a line arranged to supply green hydrogen from said green hydrogen producing device to the pressurized ammonia converter; (II) provide a hydrogen storage facility, an inlet line arranged to supply the hydrogen storage facility with green hydrogen, and an outlet line arranged to supply the hydrogen from said hydrogen storage facility to the ammonia converter; (III) update a process management system of said facility to implement said process. Description of preferred embodiments of the present invention

[0022] The hydrocarbon source 1 can be natural gas.

[0023] According to one embodiment, the said reforming process 100 includes a hydrocarbon source desulfurization step 1 followed by a primary reforming step 3 in a lit furnace and a secondary reforming step 4 with air, both in the presence of steam.

[0024] According to another embodiment, the aforementioned reforming process 100 includes a desulfurization step of the hydrocarbon source 1 followed by an autothermal reforming (ATR) step, possibly without pre- Petition 870250091085, dated 06 / 10 / 2025, page 17 / 74 9 / 40 reforming, in an adiabatic reactor. A typical steam-to-carbon ratio in the ATR may be less than 2, preferably between 1.4 and 1.95. According to another embodiment, the steam / carbon ratio in the ATR may be equal to or greater than 2, for example, between 2 and 3.5.

[0025] The aforementioned autothermal reforming step is preferably fed with oxygen or oxygen-enriched air. For this purpose, an oxygen (O2) stream obtained – together with hydrogen 19 – in step (c) by electrolysis of water W can be used. An additional oxygen source for autothermal reforming, for example, an air separation unit (ASU; 31), can also be used in the present process.

[0026] Preferably, a purification 6 of the reformed gas may include CO displacement, CO2 removal and methanation.

[0027] A particularly preferred process for producing hydrogen 19 in step (c) is water electrolysis W. Preferably, water electrolysis W, more preferably pressurized alkaline electrolysis, is operated by solar energy SE and / or wind energy WE, in particular such energy being produced by means of a photovoltaic power plant 104 and / or a wind power plant 105, respectively, connected to the electrolyzer. The photovoltaic power plant 104 and / or the wind power plant 105 may be stand-alone installations or may be connected to an electrical grid.

[0028] According to a preferred embodiment, the aforementioned process additionally comprises the following steps: Petition 870250091085, dated 06 / 10 / 2025, page 18 / 74 10 / 40 (k) store part of the electrical energy produced by said renewable energy source (SE, WE) in an electrical storage battery 4 6; and (l) produce said second portion of hydrogen 19 with electricity stored in said electrical storage battery 46, when said renewable energy source SE, WE is totally or partially unavailable.

[0029] According to another embodiment, an oxygen (O2) stream obtained – together with hydrogen 19 in step (c) by electrolysis of water W – can be fed to an ATR 32 or to a secondary reformer 4 from the reforming front end 100 via an oxygen feed line 42. Preferably, said oxygen (O2) stream is compressed in an oxygen compressor 44 and fed to an oxygen storage 106. The oxygen from said oxygen storage 106 is fed to the ATR 32 or to the secondary reformer 4, preferably in an amount that does not exceed the design temperature of the ATR or the secondary reformer, or of the cooling stage heat recovery exchanger(s) 5 that is / are positioned downstream of said ATR 32 or secondary reformer 4.

[0030] According to one embodiment, the renewable energy source is or comprises biomass. Preferably, said hydrogen 19 is produced in step c) by a conversion step of said biomass into a hydrogen-containing gas, followed by a step of Petition 870250091085, dated 06 / 10 / 2025, page 19 / 74 11 / 40 purification of said hydrogen-containing gas.

[0031] Biomass is widely considered a renewable form of energy because its energy comes from the sun. Biomass can be converted into hydrogen through a thermochemical or biological process, such as fermentation. Preferred thermochemical processes include gasification, partial oxidation, and steam reforming. The source biomass is preferably plant biomass, more preferably lignocellulosic biomass. In a preferred embodiment, a process for converting biomass into hydrogen includes the gasification of this biomass, preferably plant biomass.

[0032] An oxygen gasification process converts biomass into a hydrogen-containing gas, followed by purification of the hydrogen-containing gas into hydrogen and separation of CO2. H2 from biomass creates CO2 emissions, but these CO2 emissions are acceptable because they are carbon neutral. This is because the plant material used as a biomass source captures almost the same amount of CO2 through photosynthesis as it grows as is released when the biomass is burned.

[0033] Biomass gasification is related to the logistics of collecting biomass – the raw material for gasification – from one or more locations and transporting it to a gasification site. Furthermore, biomass storage requires significant storage space (land), therefore only a limited amount of biomass can be stored where gasification is carried out. As a consequence of these logistical and space constraints, the availability of raw material for the Petition 870250091085, dated 06 / 10 / 2025, page 20 / 74 12 / 40 gasification can be affected and gasification can suffer temporal variation in biomass flow rate to the gasifier. Consequently, the hydrogen flow rate produced can also vary over time.

[0034] Preferably, a step adjustment frequency (g) is less than a step adjustment frequency (j). More preferably, the step adjustment frequency (g) can be at least ten times, more preferably at least fifty times, even more preferably at least one hundred times, less than the step adjustment frequency (j).

[0035] Even more preferably, step (g) is a long-term adjustment and step (j) is a short-term adjustment.

[0036] A long-term adjustment can be performed in time intervals ranging from 4 days to 7 weeks, preferably ranging from 5 days to 6 weeks, more preferably ranging from 6 days to 4 weeks (e.g., 1 week, 2 weeks or 3 weeks).

[0037] Short-term adjustment can be performed in time intervals ranging from 1 minute to 28 hours, preferably ranging from 10 minutes to 26 hours, more preferably ranging from 20 minutes to 24 hours (e.g., 30 minutes, 1 hour, 12 hours or 18 hours).

[0038] In step (g), the said adjustment is preferably performed with a slight change in ramp, i.e., over a period of time of at least 3 hours, for example, from 3 hours to 24 hours, preferably from 4 hours to 18 hours, more Petition 870250091085, dated 06 / 10 / 2025, page 21 / 74 13 / 40 preferably from 5 to 12 hours, even more preferably from 6 to 10 hours, for example, from 7 to 9 hours. The airflow rates for optional secondary reforming and fuel flow rates for optional primary reforming can also be varied with the same ramp change to maintain the necessary operating parameters.

[0039] The desired ratio in step (g) is preferably such that the flow rate of the first portion of hydrogen in the ammonia replacement gas is inversely proportional to the expected flow rate of step (f).

[0040] According to one embodiment, step (f) is or comprises a calculation of said expected flow rate from the detected flow rates of said hydrogen 19 produced in step (c) in a past performance of said process. Said calculation is or comprises an average, a weighted average, or a moving average (or moving average) of said detected flow rates over a predetermined time span. A moving average is particularly preferred. The predetermined time span may cover the same time intervals as the long-term adjustment defined above.

[0041] According to one possible approach, the moving average can be calculated using weighted detected flow rates. For example, detected flow rates from a more recent past performance of the process in question (e.g., the previous day or two days prior) may have a greater weight compared to detected flow rates from a less recent past performance of the process in question (e.g., one or two weeks prior). Petition 870250091085, dated 06 / 10 / 2025, p. 22 / 74 14 / 40 before).

[0042] According to another modality, stage (f) comprises a forecast based on the estimated electrical energy 21 generated through the renewable energy source SE, WE in a given geographical area, in particular the geographical area where the process is carried out. As an example, such an estimate of the electrical energy generated 21 can be based on previous or historical exploration of the renewable energy source SE, WE and / or on previous or historical meteorological data (solar irradiance, wind speeds, ...) in the given geographical area. Meteorological data do, in fact, have a direct influence on the generation of electrical energy.

[0043] According to another embodiment, step (f) comprises a forecast based on electricity costs in relation to production costs. Preferably, said step (f) is a trigger / signal based on an available electricity market price with a forecasting mechanism (e.g., short-term, such as 1 to 3 days, or long-term, such as 1 to 3 weeks).

[0044] Preferably, additional nitrogen may be mixed with the ammonia makeup gas 7 upstream of the ammonia converter 15 to adjust a hydrogen to nitrogen (H / N) molar ratio for ammonia synthesis. Preferably, said additional nitrogen 22 is mixed with the hydrogen produced in step (c) at a mixing point or area 30 along a green hydrogen feedline 25, where the green hydrogen feedline 25 connects an electrolyzer 102 and / or hydrogen storage 103 to the reforming front end 100, to the main compressor 11 or to Petition 870250091085, dated 06 / 10 / 2025, page 23 / 74 15 / 40 Ammonia synthesis circuit 101. The aforementioned H / N molar ratio is preferably between 2.9 and 3.1. At least part (e.g., all) of the additional nitrogen 22 can be obtained by cryogenic air separation, or pressure swing absorption (PSA), or by a dedicated air separation unit based on selective adsorption (an N2 PSA unit), followed by a purification step to remove residual oxygen.

[0045] According to a preferred embodiment, said additional nitrogen 22 is mixed with an air stream 9 feeding the reforming front end 100 upstream of an air compressor 10 to adjust a hydrogen to nitrogen molar ratio for ammonia synthesis. Said H / N molar ratio is preferably between 2.9 and 3.1. The hydrogen 19 produced in step (c) can be fed to the ammonia converter 15 via a main compressor 11 or via a dedicated compressor 29. More preferably, at least part (e.g., all) of said additional nitrogen 22 is or comprises a waste gas from a nitric acid production process.

[0046] Preferably, the said additional nitrogen 22 or the said residual gas is compressed by the said air compressor 10. According to another embodiment, the additional nitrogen 22 or the residual gas is compressed by the dedicated compressor 23.

[0047] According to one embodiment, the electrolyzer 102 and / or the hydrogen storage 103 can be connected to an inlet line (suction side) of the main compressor 11, through a line of Petition 870250091085, dated 06 / 10 / 2025, page 24 / 74 16 / 40 green hydrogen feed 25.

[0048] According to other possible embodiments, the electrolyzer 102 and / or the hydrogen storage 103 may be connected to the reforming front end 100 (preferably downstream of the reforming stage(s) and upstream of the reformed gas purification 6), to an outlet line (discharge side) of the main compressor 11 or to the ammonia synthesis circuit 101 by means of a green hydrogen feed line 25. In the latter cases, additional compression may be required to bring the green hydrogen fed by the green hydrogen feed line 25 to an ammonia synthesis pressure.

[0049] According to another embodiment, the electrolyte 102 is connected to the hydrogen storage 103 via an inlet line 24 arranged to supply green hydrogen under pressure to the hydrogen storage 103 by means of a hydrogen compressor 29. The hydrogen storage 103 has an outlet line 20 connected to a suction side of the hydrogen compressor 29.

[0050] With this circuit connection between hydrogen compressor 29 and hydrogen storage 103 it is possible to maintain the desired pressure values ​​(which may be subject to changes over time, inter alia due to the actual or current quantity of hydrogen stored in hydrogen storage) in hydrogen storage 103, and to feed green hydrogen along the green hydrogen feed line 25 with the same hydrogen compressor 29, without making use of a Petition 870250091085, dated 06 / 10 / 2025, page 25 / 74 17 / 40 additional compressor.

[0051] According to other possible embodiments, the electrolyzer 102 and the hydrogen storage 103 can be connected to a suitable location at the reforming front end to feed green hydrogen, preferably upstream of the reformed gas purification 6, even more preferably upstream of a methanator, upstream of a CO2 removal section or upstream of a CO displacement converter.

[0052] According to another embodiment, the hydrogen obtained in step (c) is fed directly under pressure to the ammonia synthesis circuit 101, without passing through a compression step performed by the hydrogen compressor 29. In this embodiment, a hydrogen compressor 29 can be located on a dedicated side line to feed the hydrogen storage 103.

[0053] According to another embodiment, nitrogen required to adjust a hydrogen to nitrogen (H / N) molar ratio for ammonia synthesis can be obtained by adjusting an air flow rate 9 to an air compressor 10 that feeds the reforming front end 100. According to this embodiment, an excess of nitrogen relative to the hydrogen / nitrogen (H / N) ratio required by the stoichiometry of ammonia synthesis is introduced into the reforming process 100. The air flow rate 9 is chosen so that this excess nitrogen results in the stoichiometric H / N molar ratio for ammonia synthesis once the hydrogen produced in step (c) is mixed with the ammonia makeup gas 7.

[0054] Preferably, the first portion of Petition 870250091085, dated 06 / 10 / 2025, page 26 / 74 18 / 40 hydrogen is introduced into the ammonia synthesis circuit 101 with at least one of the hydrogen 19 produced in step (c) and the hydrogen 20 from the hydrogen storage 103.

[0055] According to a preferred embodiment, said reforming process includes reforming the hydrocarbon source 1 and purifying 6 the reformed gas thus obtained, thereby obtaining ammonia replacement gas; feeding said ammonia converter 15 with the ammonia replacement gas via the main compressor 11; said second portion of hydrogen 19 being fed to the ammonia converter 15 via the same main compressor 11 or via a dedicated compressor 29. Additional nitrogen 22 (optional) may be fed to the ammonia converter 15 via one or more dedicated compressors 23, or first via an air compressor 10 and then via the main compressor 11.

[0056] Preferably, the hydrogen storage 103 is maintained at a pressure of at least 50 bar, preferably at a pressure between 50 bar and 250 bar, more preferably between 60 bar and 200 bar. Hydrogen can be stored under pressure in one or more suitable hydrogen storage vessels. Therefore, a hydrogen compressor 29 can be provided to raise the hydrogen pressure from electrolysis above the minimum storage pressure.

[0057] According to a preferred embodiment, a portion of the hydrogen produced in step (c) is sent to hydrogen storage 103 via a hydrogen compressor 29. The hydrogen stored in Petition 870250091085, dated 06 / 10 / 2025, page 27 / 74 19 / 40 hydrogen storage 103 feeds one suction side of hydrogen compressor 29 so that said compressor maintains the desired pressure values ​​in hydrogen storage 103 and feeds hydrogen 19 to be contained in ammonia replacement gas 7.

[0058] According to another preferred embodiment, a hydrogen compressor 29 is positioned downstream of the electrolyzer 102 and upstream of the hydrogen storage 103. Preferably, a green hydrogen outlet line 20 feeds part of the hydrogen stored in the hydrogen storage 103 to a suction side of the hydrogen compressor 29. The desired pressure values ​​in the hydrogen storage 103 are therefore maintained. Consequently, hydrogen is stored economically and in terms of space, as well as being supplied at a higher pressure than the initial operating pressure.

[0059] According to one embodiment, the hydrogen storage 103 has a maximum average production capacity of 1 week, preferably an average production of 2 days, more preferably an average production of 1 day, of hydrogen 19 produced in step (c).

[0060] In a typical embodiment, the second portion of hydrogen 19 produced with renewable energy accounts for up to 50% of the hydrogen contained in the ammonia replacement gas 7, preferably from 1% to 50%, more preferably from 2% to 35%, even more preferably from 3% to 25%, even more preferably from 5% to 15%. However, in some embodiments, green hydrogen may represent a larger share (more than 50%) of the total hydrogen. Petition 870250091085, dated 06 / 10 / 2025, page 28 / 74 20 / 40

[0061] In one possible embodiment, the ammonia converter 15 is part of an ammonia synthesis circuit 101. The ammonia synthesis circuit 101 may include the ammonia converter 15, a makeup gas preheater, a cooling and separation stage 16, and a circulator 13. Preferably, the green hydrogen feed line 25 is connected to the ammonia synthesis circuit 101 between the circulator 13 and the converter 15, more preferably at a discharge from the circulator 13.

[0062] In another embodiment, the green hydrogen feed line 25 is fed downstream of the ammonia converter 15, for example, between the ammonia converter 15 and the cooling-separation stage 16 or between the cooling-separation stage 16 and the circulator 13.

[0063] Preferably, in the renewal method, said step (III) comprises loading a computer program into an internal memory of a process management system 26 of said installation, said computer program comprising portions of software code suitable for implementing said process, wherein said portions of software code are executed by said process management system 26.

[0064] According to another embodiment of the method for reforming, said green hydrogen producing device is a water electrolyzer, and said method comprises providing a line 42 arranged to feed a flow of oxygen (O2) obtained by said water electrolyzer from said water electrolyzer to a reforming front end 100, preferably Petition 870250091085, dated 06 / 10 / 2025, page 29 / 74 21 / 40 for an ATR 32 or a secondary reformer 4 from the reforming end 100. Advantages of the present invention

[0065] According to an advantageous aspect, the process of the present invention makes it possible to reduce the size of hydrogen storage and avoid the waste or release of a significant portion of floating green hydrogen.

[0066] Advantageously, a hydrogen storage tank used in the process of the present invention can be scaled up to 10 times, preferably up to 20 times, more preferably up to 30 times, smaller than a hydrogen storage tank in a rigid installation.

[0067] Advantageously, the present method for renovation preserves the use of an existing front end. Possible hardware modifications to the ammonia synthesis section are less impactful and costly.

[0068] Furthermore, the present method for refurbishment advantageously allows existing equipment of an ammonia plant to operate within the constraints of the original design, avoiding any cyclic operation and therefore mechanical fatigue problems, despite having to accommodate a significant additional amount of variable green hydrogen.

[0069] Advantageously, the nitrogen required to obtain a stoichiometric hydrogen-to-nitrogen (H / N) ratio for ammonia synthesis can be obtained by modifying the air flow rate to the air compressor, so that an excess of nitrogen in the ammonia makeup gas is obtained relative to the H / N ratio required by Petition 870250091085, dated 06 / 10 / 2025, page 30 / 74 22 / 40 stoichiometry of ammonia synthesis. The air flow rate is chosen so that this excess nitrogen results in a stoichiometric H / N ratio when green hydrogen is mixed with the ammonia makeup gas through the feedline. In this way, the costs associated with an additional nitrogen source are reduced or eliminated.

[0070] Advantageously, the supply of green hydrogen and, optionally, additional nitrogen to the suction of the main compressor allows for a reduction in investment costs for newly installed compressors.

[0071] Advantageously, the presence of a hydrogen compressor allows for economical and space-saving hydrogen storage, as well as delivering hydrogen at a pressure higher than the front operating pressure. In some embodiments, the hydrogen compressor can be configured to deliver green hydrogen at the pressure of the ammonia synthesis circuit, or at a pressure higher than the pressure of the ammonia synthesis circuit.

[0072] Advantageously, the presence of an additional nitrogen source causes this additional nitrogen not to pass through the reformer front end 100 and therefore avoids fluctuations in the reformer outlet temperatures. This is because the air flow rate to the air compressor must not change to maintain the desired H / N ratio according to the fluctuating amount of hydrogen produced in step (c).

[0073] Advantageously, feeding green hydrogen and, optionally, additional nitrogen directly into the ammonia synthesis circuit leads to smaller variations in operating conditions due to fluctuations in Petition 870250091085, dated 06 / 10 / 2025, page 31 / 74 23 / 40 green hydrogen (since the mass flow of gas circulating in the circuit is typically 2 to 4 times the mass flow delivered by the front end), lower energy consumption of the main compressor and therefore lower CO2 emissions (if the synthesis gas compressor is driven by steam generated at the front end using fossil feedstock).

[0074] Advantageously, feeding green hydrogen and, optionally, additional nitrogen into the circulator discharge avoids burdening the cooling section of the ammonia synthesis circuit with additional cooling tasks. Furthermore, temperature levels in the circuit can be maintained, while simultaneously limiting the heat exchange area to be installed in the circuit's gas-gas heat exchangers, thus limiting their cost.

[0075] Advantageously, the variation of green hydrogen input into the ammonia synthesis circuit is chosen so that the ammonia production rate is maintained within a maximum deviation range from the required overall average production.

[0076] Advantageously, pressurized alkaline electrolysis involves lower investment costs compared to other electrolysis technologies, as well as lower energy consumption and investment costs by avoiding the compression of green hydrogen from atmospheric pressure.

[0077] Advantageously, pressure swing absorbers (PSAs) are more flexible and more expensive units than alternative air separation technologies, leading to lower energy consumption and investment costs. Petition 870250091085, dated 06 / 10 / 2025, page 32 / 74 24 / 40

[0078] The advantages of single-train cryogenic air separation units are higher ammonia production rates and lower investment cost compared to other air separation units at the higher production rates mentioned.

[0079] Advantageously, the use of moving average values ​​allows obtaining a useful set point for the initial production rate, which avoids loss of ammonia production when the storage is empty or reduced energy consumption when the storage is completely full. Furthermore, these values ​​as set points require only information that is available to the plant operators.

[0080] Advantageously, a portion of the green hydrogen can be used as fuel in the reforming process. Any fluctuations in the availability of green hydrogen can be resolved by the reformer adjusting the relative amount of green hydrogen fuel compared to natural gas fuel, while maintaining a constant reforming temperature. As a result, there are no fluctuations in the process gas undergoing steam reforming, despite the use of fluctuating green hydrogen as fuel.

[0081] Advantageously, a hybrid process according to the present invention replaces at least part of the gray hydrogen with green hydrogen, so that CO2 emissions are reduced. This reduction is twofold: on the one hand, small amounts of CO2 are generated in the combustion gases from the reformer front end and, on the other hand, a general process gas from the reformer (process synthesis gas) and, consequently, also the CO2 contained therein. Petition 870250091085, dated 06 / 10 / 2025, page 33 / 74 25 / 40 are reduced.

[0082] It is worth mentioning that another known technical strategy for reducing CO2 emissions is electric reforming, in which the fuel for generating reforming heat at the reforming front end is replaced by electrical energy, so that no combustion gas containing carbon dioxide is generated. However, the amount of CO2 in the process, the synthesis gas (mostly) remains unchanged if the productivity of the reforming front end remains the same. This is because green hydrogen is not used to partially replace the grey hydrogen produced through electrical energy, so the same amounts of CO2 are contained in the process synthesis gas.

[0083] Advantageously, the process of the present invention allows decoupling the green hydrogen feed from the hydrogen storage and the ammonia synthesis process. This is because ammonia synthesis does not depend solely on the hydrogen flow rate feeding the storage, so the synthesis is carried out independently of the hydrogen storage filling process.

[0084] Advantageously, feeding an air compressor with additional nitrogen results in more stable operation in terms of flow rate, compared to a dedicated compressor.

[0085] More precisely, when green hydrogen is available and added, additional nitrogen is usually required and fed to the air compressor along with the air required by the front end load. Petition 870250091085, dated 06 / 10 / 2025, page 34 / 74 26 / 40 reforming. However, when green hydrogen is not available, additional nitrogen is not required and only the air needed for the front end reforming is fed into the suction side of the compressor. In both conditions, the air compressor is fed with air and / or additional nitrogen with a gas flow rate greater than 50% of the air flow rate required for front end reforming operating at 100% load.

[0086] This leads to a preferred embodiment, in which the flow of gas fed to the air compressor may comprise 50% to 115%, preferably comprising 70% to 110%, more preferably comprising 85% to 105%, and even more preferably comprising 97.5% to 102.5%.

[0087] According to another embodiment, when green hydrogen is available, additional nitrogen 22 may be required and may be fed to the dedicated compressor 23 with a flow rate of up to 100% of a maximum nitrogen flow rate. When green hydrogen is not available, additional nitrogen may not be required and there may be no gas flow to the dedicated compressor (flow: 0%). Therefore, a dedicated compressor 23 may be subject to a flow rate variation of 0% to 100%. Description of the Figures

[0088] Figure 1: Simplified diagram of a first embodiment of the present invention;

[0089] Figure 2: Simplified diagram of a second embodiment of the present invention;

[0090] Figure 3: Simplified diagram of a third embodiment of the present invention; Petition 870250091085, dated 06 / 10 / 2025, page 35 / 74 27 / 40

[0091] Figure 4: energy availability of a photovoltaic power installation over a period of approximately 200 hours, as discussed in the example;

[0092] Figure 5: a means moving average, calculated over a predetermined period of two weeks, of the power profile shown in Figure 4;

[0093] Figure 6: Hydrogen storage capacity of a rigid installation according to the prior art;

[0094] Figure 7: Required adjustments of a front load during the year according to the process of the present invention;

[0095] Figure 8: Filling profile resulting from a hydrogen storage tank used in the process of the present invention;

[0096] Figure 9: enlargement of the dashed area shown in Figure 8 at a time between 3000 h and 4000 h;

[0097] Figure 10: Simplified diagram of a fourth embodiment of the present invention;

[0098] Figure 11: Simplified diagram of a fifth embodiment of the present invention. Detailed description of the invention

[0099] Figure 1 is a simplified schematic of a preferred embodiment of the present invention, in which the main items are represented according to the following list of reference signs: Hydrocarbon source, such as natural gas, ammonia makeup gas, effluent containing ammonia, air, feed for the reforming process. Petition 870250091085, dated 06 / 10 / 2025, page 36 / 74 28 / 40 main compressor for ammonia makeup gas 7 recirculated gas circulator ammonia converter cooling-separation stages makeup gas from the reforming process (reforming makeup gas) hydrogen produced in stage (c) or second portion of hydrogen or green hydrogen green hydrogen outlet lines from hydrogen storage electrical power additional nitrogen (optional) dedicated compressors (optional) green hydrogen inlet lines to hydrogen storage green hydrogen feed line process management system first portion (purge gas) second portion hydrogen compressors mixing points or areas valve media management line management line management line management line management line management line management line oxygen feed line from electrolyzer Petition 870250091085, dated 06 / 10 / 2025, page 37 / 74 29 / 40 (optional) oxygen compressor oxygen outlet line 100 reform process or front end reform 101 Ammonia synthesis circuit 102 electrolyzer for hydrogen production 103 hydrogen storage 104 photovoltaic energy installation 105 wind turbine power installation 106 Oxygen storage (optional) SE is a renewable energy source, particularly solar energy. WE is a source of renewable energy, particularly wind energy. Water O2 oxygen

[00100] With reference to Figure 1, a hydrocarbon source 1 is desulfurized and steam reformed at a reforming front end 100. The desulfurized and reformed gas thus obtained is purified to obtain a purified synthesis gas.

[00101] The required quantity of nitrogen can be introduced with an air feed 9 directed to the front end of reforming 100 through an air compressor 10 to obtain an ammonia replacement gas 7 containing the purified synthesis gas.

[00102] Ammonia makeup gas 7 is fed to an ammonia synthesis circuit 101 by a main compressor 11. After preheating in a heat exchanger, the preheated ammonia makeup gas Petition 870250091085, dated 06 / 10 / 2025, page 38 / 74 30 / 40 reacts in an ammonia converter 15.

[00103] An effluent from the converter goes to a cooling and separation stage 16. From here, an effluent containing ammonia 8 and a recycling gas 12 are separated.

[00104] The recycling gas 12 is divided into a first portion 27 (purge gas) and a second portion 28. The first portion 27 is sent to a hydrogen recovery unit (HRU), where the hydrogen is separated from other impurities, such as non-condensable gases. The second portion 28 is recycled back into the ammonia synthesis circuit 101 via a circulator 13. The circulator 13 compensates for pressure drops by maintaining circulation in the ammonia synthesis circuit 101. The HRU can use a cryogenic system, a membrane-based system, or a PSA.

[00105] An electrolyzer 102 is powered by at least one renewable energy source – namely, solar energy SE and / or wind energy WE – producing electrical energy 21 to perform the electrolysis of water W. The electrical energy 21 is produced by means of a photovoltaic energy installation 104 and / or a wind energy installation 105. The electrolysis of water W produces hydrogen 19 and oxygen O2. This oxygen can be exported to the reforming front end 100 via an oxygen supply line from the electrolyzer 42. The said oxygen stream O2 can be compressed in an oxygen compressor 44, fed to an oxygen storage 106 and then to the reforming front end 100 in an appropriate quantity. The oxygen storage 106 has an oxygen outlet line 45 connected to a suction side. Petition 870250091085, dated 06 / 10 / 2025, page 39 / 74 31 / 40 of the oxygen compressor 44.

[00106] The electrolyzer 102 can be connected to an inlet line of the main compressor 11, via a green hydrogen feed line 25. Alternatively (see dashed arrows), a green hydrogen feed line 25 can connect the electrolyzer 102 to the reforming front end 100, to an outlet line of the main compressor 11, or directly to the ammonia synthesis circuit 101. In these latter alternatives, an additional compressor (not shown) may be required to bring the green hydrogen fed by the electrolyzer 102 to an ammonia synthesis pressure, or alternatively, the hydrogen compressor 29 can be used for this purpose (see below).

[00107] The electrolyzer 102 is additionally connected to a hydrogen storage tank 103 via an inlet line 24 designed to supply green hydrogen under pressure to the hydrogen storage tank 103 by means of a hydrogen compressor 29. The hydrogen storage tank 103 has an outlet line 20 connected to a suction side of the hydrogen compressor 29. With this circuit connection between the hydrogen compressor 29 and the hydrogen storage tank 103, it is possible to maintain the desired pressure values ​​in the hydrogen storage tank 103 and supply green hydrogen along the green hydrogen supply line 25 with the same hydrogen compressor 29, without using an additional compressor.

[00108] Additional nitrogen 22 can be fed into the hydrogen feed line 25 by a dedicated compressor 23 to adjust a molar ratio of Petition 870250091085, dated 06 / 10 / 2025, page 40 / 74 32 / 40 hydrogen to nitrogen for ammonia synthesis. This additional nitrogen 22 can be obtained with an air separation unit 31 (see, for example, Figure 3) or pressure swing absorption (PSA).

[00109] A process management system 26 is functionally connected to the reforming front end 100, to the electrolyzer 102, to the hydrogen storage 103, optionally to the hydrogen compressor 29, to the photovoltaic power plant 104 and / or to the wind power plant 105 via respective process management lines 36, 37, 38, 39, 40, 41 to manage the process for ammonia synthesis as follows.

[00110] The ammonia synthesis circuit 101 receives the conventionally produced ammonia makeup gas 7 at the reforming front end 100 along with green hydrogen 19 from line 25. For example, the hydrogen from the electrolyzer 102 may be about 10% of the total hydrogen contained in the ammonia makeup gas 7.

[00111] Based on the availability (e.g., energy generated) of the renewable energy source of electrolyzer 102, hydrogen from storage 103 can be used to partially or totally replace the production of said electrolyzer 102. For example, assuming that electrolyzer 102 uses SE solar energy, the stored hydrogen (withdrawn from storage 103 via line 20) can be used during the night and / or in cloudy conditions when solar energy drops.

[00112] The use of hydrogen storage is beneficial in terms of carbon dioxide emissions because Petition 870250091085, dated 06 / 10 / 2025, page 41 / 74 33 / 40 stores only green hydrogen.

[00113] According to the present process, firstly an expected flow rate of green hydrogen produced by the electrolyzer 102 is evaluated. This evaluation may involve a calculation (e.g., a mathematical average) from the detected flow rates of said green hydrogen 19 in a past performance of said process and / or a prediction based on an estimated electrical energy 21 generated by means of the renewable energy source in a given geographical area.

[00114] A flow rate from the hydrocarbon source 1 is subsequently adjusted (e.g., by means of valve means 35 functionally connected to the process management system 26), so that a flow rate of the first portion of hydrogen in the said ammonia makeup gas 7 (and, more precisely, in the reforming makeup gas 18) is at a desired ratio in relation to the said expected flow rate.

[00115] An actual quantity, for example, a fill level, of said green hydrogen in said hydrogen storage 103 and an actual flow rate of hydrogen produced in step (c) are also detected, and a flow rate of green hydrogen 20 from hydrogen storage 103 is adjusted depending on said actual quantity and said actual flow rate. The air 9 and fuel flow rates for the reforming process may be varied correspondingly or may be kept constant.

[00116] More precisely, the flow rate of green hydrogen fed to the ammonia synthesis circuit 101 can be defined between a minimum and a maximum value, of Petition 870250091085, dated 06 / 10 / 2025, page 42 / 74 34 / 40 according to the actual quantity (e.g., fill level) of the hydrogen storage 103. If the actual quantity is greater than an upper limit, a maximum quantity of green hydrogen is fed. If the actual quantity is less than a lower limit, a minimum quantity of green hydrogen is fed. If the fill level is between these limits, an intermediate quantity of green hydrogen – between the minimum and maximum quantities – is fed to the ammonia synthesis circuit 101.

[00117] If, however, the amount of green hydrogen to be fed to the ammonia synthesis circuit 101 is greater, or respectively less, than the amount produced in step (c), the difference is withdrawn, or respectively directed to, the hydrogen storage 103.

[00118] Figure 2 shows another embodiment of the present process. The same reference signs as in Figure 1 denote identical or corresponding technical attributes. In addition, the following references are used: desulfurization primary reformer, such as a combustion furnace secondary reformer cooling purification of the reformed gas, preferably displacement converter(s) and carbon dioxide removal air compressors

[00119] The front end of reforming 100 is shown in more detail. Hydrocarbon source 1 Petition 870250091085, dated 06 / 10 / 2025, page 43 / 74 35 / 40 passes – in sequence – through the desulfurization stage 2, primary reformer 3 and secondary reformer 4. The air feed 9 is directed to the secondary reformer 4 after compression in the air compressor 10.

[00120] An effluent from the secondary reformer 4 is then subjected to a cooling stage 5, and this cooled effluent passes through displacement converters and carbon dioxide removal stages 6. One or more displacement converters may be provided, for example, a high-temperature displacement converter followed by a low-temperature displacement converter. Carbon dioxide removal may be performed, for example, by scrubbing with amine or carbonate solution, pressure swing adsorption (PSA) or another technique for removing CO2 from a gas. The reforming makeup gas 18 is then obtained.

[00121] Figure 3 shows another embodiment of the present process. The same reference signs from Figure 1 and Figure 2 denote identical or corresponding technical attributes. In addition, the following references are used: Air separation unit (ASU) autothermal reforming (ATR) oxygen supply line from ASU to ATR nitrogen supply line from ASU to effluent ATR nitrogen feed line from ASU for point or area mixing.

[00122] An alternative front end of the 100 reform is shown in more detail. A source of Petition 870250091085, dated 06 / 10 / 2025, page 44 / 74 36 / 40 desulfurized hydrocarbon 1 is reformed in an autothermal reforming stage 32. An effluent from the ATR then goes through a reformed gas purification stage 6 to obtain a reforming replacement gas 18.

[00123] An air feed 9 is directed to an air separation unit 31, in which the air is separated into an oxygen stream and a nitrogen stream. The oxygen stream is fed to the ATR 32 via line 33, and the nitrogen stream is fed via line 34 between the ATR 32 and the reformed gas purification stage 6 to supply the required amounts of nitrogen for ammonia synthesis.

[00124] Oxygen 2 produced in electrolyzer 102 can also be fed to ATR 32 via an oxygen supply line from electrolyzer 42.

[00125] A portion of the nitrogen flow separated in the air separation unit 31 can be fed to the mixing point or area 30 with a nitrogen feed line 43, preferably through the dedicated compressor 23, to provide additional nitrogen 22 to adjust the hydrogen to nitrogen molar ratio (H / N) for ammonia synthesis.

[00126] Figure 10 shows an alternative embodiment of Figure 1 comprising an electrical storage battery 46 electrically connected to the renewable energy source(s) SE, WE, such that part of the electrical energy produced by said source(s) can be stored in the electrical storage battery 46. In other words, the electrical storage battery 46 is charged by the renewable energy source(s) SE, WE, Petition 870250091085, dated 06 / 10 / 2025, page 45 / 74 37 / 40 for example, when there is an overproduction of electrical energy produced by the aforementioned source(s) in relation to the energy required for the production of the second portion of hydrogen 19.

[00127] The electrical storage battery 46 is electrically connected to the electrolyzer 102 so that the said second portion of hydrogen 19 can be produced with electricity stored in said electrical storage battery 46, for example, when said renewable energy source SE, WE is totally or partially unavailable. This means that the electrolyzer 102 can be powered by the electrical storage battery 46, if required.

[00128] Figure 11 shows an alternative embodiment of Figure 2, wherein additional nitrogen 22 is mixed into the air stream 9 feeding the reforming front end 100 at a position upstream of the air compressor 10. At least part of this additional nitrogen 22 may be or comprise a waste gas from a nitric acid production process.

[00129] Figure 11 also shows another additional flow of nitrogen 22 compressed in the dedicated compressor 23 and directed to the mixing point or area 30. The dashed lines of the dedicated compressor 23 and the connecting pipes mean that these parts are optional, so that the additional nitrogen 22 can only be fed by mixing with the air flow 9.

[00130] The present invention will now be described in view of the following non-limiting examples. Example Petition 870250091085, dated 06 / 10 / 2025, page 46 / 74 38 / 40

[00131] This example refers to an ammonia plant as shown in Figure 1, where a second portion of hydrogen (green hydrogen) corresponding to 10% of the hydrogen required for a total ammonia production of 1,000 tons per day is used.

[00132] Green hydrogen is produced by the electrolysis of water using renewable energy. In this example, this energy is supplied only by a photovoltaic solar power plant 104. However, other tests (not shown) performed using wind power or a combination of solar and wind power provided results that are consistent with the evidence obtained using only a photovoltaic solar power plant 104.

[00133] A representative sample of approximately 200 hours (approximately 8 days) of the energy availability of the photovoltaic power plant 104 is given in Figure 4.

[00134] The moving average (calculated over 337 h, i.e., two weeks) for this power profile is shown in Figure 5. The resulting curve shows the average availability of green hydrogen during the year and therefore the seasonality of the energy profile. As can be seen, the energy availability and therefore the production of green hydrogen is about 2.5 times greater in summer (about 4,000 hours) than in winter (about 0 and 9,000 hours).

[00135] As a result, a traditional hybrid plant (a rigid plant) designed to accommodate the same green hydrogen input, but not Petition 870250091085, dated 06 / 10 / 2025, page 47 / 74 39 / 40 applying the flexible operation of the present invention would require a very large and impractical hydrogen storage facility, with a maximum storage capacity of up to 825 tons of hydrogen required between the 6,000th and 7,000th hours of plant operation, to operate at a constant ammonia production rate and achieve the same overall goal of 10% green hydrogen input. This H2 storage fill profile is shown in Figure 6. Figure 6 demonstrates that a large storage capacity is essential due to the seasonal imbalance in the availability of green hydrogen for a rigid plant.

[00136] In contrast, a hybrid installation operated according to the process of the present invention can use the same total amount of green hydrogen, delivered with the same profile as the case above, with a hydrogen storage size of only 24 tons of hydrogen, corresponding to 32 hours of average green hydrogen production.

[00137] The adjustments required - in step (g) of the front load during the year are shown in Figure 7.

[00138] Adjustments are made in this case on a weekly basis, where the new setpoint is determined to be equal to the moving average of green hydrogen availability over the previous 2 weeks. The resulting curve reflects the seasonality of the power profile, and the average annual load of the front end is, as expected, around 90%.

[00139] Thanks to the variability compensation provided by the front end, the synthesis section of Petition 870250091085, dated 06 / 10 / 2025, page 48 / 74 The 40 / 40 ammonia system only needs to operate with a flexibility in the ammonia production rate of 5% of the total production, which is within the variability that the existing equipment can tolerate. The resulting fill profile from hydrogen storage is shown in Figure 8 and Figure 9. Figure 9 is a zoom of the interval between 3000h and 4000h from Figure 8. As can be seen, hydrogen storage, in this case, is only buffering short-term fluctuations (hours to days) in the availability of green hydrogen, which the relatively small flexibility used in the ammonia synthesis circuit is unable to absorb by adapting its load and ammonia production.

[00140] Overall, when comparing the production cost of the ammonia fraction produced with the input of 10% green hydrogen, considering the investment cost of the green hydrogen production section and its operating costs (mainly electricity to power the electrolyzer(s)), the hybrid plant managed with the process of the present invention presents a production cost more than three times more economical than a rigid hybrid plant. This large difference is, in fact, mainly caused by the large capacity of expensive hydrogen storage to be installed in the case of a rigid plant. Petition 870250091085, dated 06 / 10 / 2025, page 49 / 74

Claims

1 / 9 CLAIMS 1. Process for the synthesis of ammonia, characterized in that: (a) ammonia makeup gas (7) containing hydrogen and nitrogen is reacted in an ammonia converter (15) under ammonia-forming conditions, thereby obtaining an effluent containing ammonia (8); (b) a first portion of hydrogen contained in the ammonia makeup gas (7) is produced by reforming a hydrocarbon source (1) in a reforming process (100); (c) a second portion of hydrogen (19) contained in the ammonia makeup gas (7) is produced separately from said reforming process, using at least one renewable energy source (SE, WE); (d) a portion of said hydrogen produced in step (c) is stored in a hydrogen storage facility (103);(e) Hydrogen (20) from said hydrogen storage (103) is used to replace wholly or partially said hydrogen produced in step (c) when said renewable energy source (SE, WE) is wholly or partially unavailable; said process comprising the following steps: Petition 870250091085, 06 / 10 / 2025, p. 50 / 74 2 / 9 (f) assess an expected flow rate of hydrogen (19) produced in step (c); (g) adjust a flow rate of the hydrocarbon source (1) in step (b) so that a flow rate of the first portion of hydrogen in the ammonia replacement gas (7) is at a desired ratio to said expected flow rate of step (f); (h) detect an actual quantity, for example, a fill level, of said hydrogen in said hydrogen storage (103); (i) detect an actual flow rate of hydrogen produced in step (c);(j) adjust the hydrogen flow rate (20) of said hydrogen storage (103) depending on said actual quantity detected in step (h) and said actual flow rate detected in step (i).; 2. Process, according to claim 1, characterized in that a step adjustment frequency (g) is less than a step adjustment frequency (j), preferably the step adjustment frequency (g) being at least ten times, more preferably at least fifty times, even more preferably at least one hundred times, less than the step adjustment frequency (j).

3. Process, according to any of the preceding claims, characterized in that Petition 870250091085, dated 06 / 10 / 2025, page 51 / 74 3 / 9 step (g) is a long-term adjustment and step (j) is a short-term adjustment: - said long-term adjustment being performed in time intervals ranging from 4 days to 7 weeks, preferably ranging from 5 days to 6 weeks, more preferably ranging from 6 days to 4 weeks; and - said short-term adjustment being performed in time intervals ranging from 1 minute to 28 hours, preferably ranging from 10 minutes to 26 hours, more preferably ranging from 20 minutes to 24 hours.

4. Process, according to any of the preceding claims, characterized in that step (f) is or comprises a calculation of said expected flow rate from the detected flow rates of said hydrogen (19) produced in step (c) in a past performance of said process.

5. A process, according to the preceding claim, characterized in that the calculation is or comprises a moving average of the flow rates detected over a predetermined period of time.

6. Process according to any of the preceding claims, characterized in that step (f) comprises a forecast based on the estimated electrical energy Petition 870250091085, dated 06 / 10 / 2025, page 52 / 74 4 / 9 (21) generated through the renewable energy source (SE, WE) in a given geographical area.

7. Process, according to any of the preceding claims, characterized in that additional nitrogen (22) is mixed with the ammonia makeup gas (7) upstream of the ammonia converter (15) to adjust a hydrogen to nitrogen molar ratio for ammonia synthesis; said hydrogen (19) produced in step (c) being fed to the ammonia converter (15) by means of a main compressor (11) or by means of a dedicated compressor (29); at least part of said additional nitrogen (22) being obtained by cryogenic air separation or pressure swing absorption (PSA).

8. Process, according to any of the preceding claims, characterized in that additional nitrogen (22) is mixed with an air stream (9) feeding the reforming front end (100) upstream of an air compressor (10) to adjust a hydrogen to nitrogen molar ratio for ammonia synthesis; said hydrogen (19) produced in step (c) being fed to the ammonia converter (15) by means of a main compressor (11) or by means of a dedicated compressor (29); at least part of said additional nitrogen (22) being or comprising a waste gas from a nitric acid production process; preferably said waste gas being compressed by said air compressor (10).

9. Process according to any of the preceding claims, characterized in that the hydrogen (19) of step (c) is produced by electrolysis of water (W), preferably by pressurized alkaline electrolysis.

10. Process, according to the preceding claim, characterized in that said water electrolysis (A), preferably pressurized alkaline electrolysis, is operated by solar energy (ES) and / or by wind energy (E), in particular through a photovoltaic power plant (104) and / or a wind power plant (105).

11. Process, according to any of the preceding claims, characterized in that it further comprises the following steps: (k) storing part of the electrical energy produced by said renewable energy source (SE, WE) in an electrical storage battery (46); and (l) producing said second portion of hydrogen (19) with electricity stored in said electrical storage battery (46), when said renewable energy source (SE, WE) is totally or partially unavailable. Petition 870250091085, dated 06 / 10 / 2025, page 54 / 74 6 / 9 12. Process, according to any of the preceding claims, characterized in that the renewable energy source is or comprises biomass, said hydrogen (19) being produced in step c) by a conversion step of said biomass into a hydrogen-containing gas with a thermochemical process, for example, gasification, or a biological process, for example, fermentation, followed by a purification step of said hydrogen-containing gas.

13. Process, according to any of the preceding claims, characterized in that a portion of the hydrogen (19) produced in step (c) is sent to the hydrogen storage (103) by means of a hydrogen compressor (29), hydrogen stored in the hydrogen storage (103) feeding a suction side of the hydrogen compressor (29) so that such compressor maintains the desired pressure values ​​in the hydrogen storage (103) and feeds the hydrogen to be contained in the ammonia replacement gas (7).

14. Process, according to any of the preceding claims, characterized in that said hydrogen storage (103) is maintained at a pressure of at least 50 bar, preferably at a pressure between 50 bar and 250 bar, preferably Petition 870250091085, dated 06 / 10 / 2025, page 55 / 74 7 / 9 between 60 bar and 200 bar.

15. Process, according to any of the preceding claims, characterized in that said hydrogen storage (103) has a maximum average production capacity of 1 week, preferably an average production capacity of 2 days, more preferably an average production capacity of 1 day, of the hydrogen (19) produced in step (c).

16. Process, according to any of the preceding claims, characterized in that said hydrogen (19) produced with renewable energy represents up to 50% of the hydrogen contained in the ammonia replacement gas (7), preferably from 1% to 50%, more preferably from 2% to 35%, even more preferably from 3% to 25%, even more preferably from 5% to 15%.

17. Process, according to any of the preceding claims, characterized in that said reforming process (100) includes reforming a hydrocarbon source (1) and purifying (6) the reformed gas thus obtained, thereby obtaining said ammonia replacement gas; feeding the ammonia replacement gas to said ammonia converter (15) by means of a compressor (11); said hydrogen (19) produced in step (c) being fed to the ammonia converter (15) by means of the same compressor (11); wherein optional additional nitrogen (22) Petition 870250091085, dated 06 / 10 / 2025, p. 56 / 74 8 / 9 is fed to the ammonia converter (15) by means of one or more dedicated compressors (23) or by means of an air compressor (10) and then by the main compressor (11).

18. Method for renovating an ammonia synthesis plant, characterized in that said plant comprises: a reforming front end (100) for generating an ammonia replacement gas (7) by reforming a hydrocarbon source (1); an ammonia synthesis circuit (101) including an ammonia converter (15); wherein said method for renovating the plant comprises the following steps: (I) providing a green hydrogen producing device, such as a water electrolyzer (102), using a renewable energy source (SE, WE), and a line (25) arranged to supply green hydrogen from said green hydrogen producing device to the ammonia converter (15) under pressure;(II) providing a hydrogen storage (103), an input line (24) arranged to feed green hydrogen into the hydrogen storage (103), and an output line (20) arranged to feed hydrogen from said hydrogen storage (103) to the ammonia converter (15); (III) upgrading a process management system (26) of said facility to implement the process defined in any of the preceding claims; wherein step (III) comprises loading a computer program into an internal memory of the process management system (26) of said facility; said computer program comprising portions of software code suitable for implementing said process, wherein said portions of software code are executed by said process management system (26). Petition 870250091085, dated 06 / 10 / 2025, pp. 58 / 74;

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