Synthesizing green ammonia with a variable throughput

Abstract

The invention relates to a method for synthesizing NH3 with a variable throughput on a system comprising multiple synthesis units connected in parallel. A reactant gas stream comprises H2 which is provided by electrolyzing water with an electric current from a renewable energy. The currently available quantity of H2 varies on the basis of the currently available quantity of renewable energy. On the basis of the currently available quantity of H2 as such, the reactant gas stream is introduced into an individual synthesis unit of the synthesis units or into a plurality of synthesis units or all of the synthesis units in a divided manner in independent sub-streams, NH3 then being synthesized from H2 and N2 in said synthesis unit(s). The invention additionally relates to a system which is configured for carrying out the method.

Description

__________________________________________________________________________________ Synthesis of green ammonia at variable throughput __________________________________________________________________________________

[0001] Priority is claimed from Luxembourg patent application No. LU103199, filed on 4 October 2023.

[0002] The invention relates to a process for the synthesis of NH3 at variable throughput in a plant comprising several synthesis units connected in parallel. A reactant gas stream comprises H2, which is provided by electrolysis of water using electrical power from renewable energy. The currently available amount of H2 varies depending on the currently available amount of renewable energy. Depending on the currently available amount of H2, the reactant gas stream is introduced as such into a single synthesis unit or divided into independent substreams into several or all of the synthesis units, where NH3 is subsequently synthesized from H2 and N2. The invention also relates to a plant configured to carry out the process.

[0003] In the conventional synthesis of NH3 from H2 and N2 according to the Haber-Bosch process, H2 is often obtained by steam reforming hydrocarbons. The hydrocarbons can be safely stored temporarily for extended periods, ensuring they are always available in sufficient quantities. Therefore, a sufficient amount of H2 can be obtained from them at any time through steam reforming. This enables conventional synthesis of NH3 over extended periods at maximum utilization of the synthesis plant under continuous process control (full-load operation). Variable utilization of the synthesis plant under continuous process control is also possible. This allows the throughput to be temporarily reduced (partial load operation) without completely interrupting the process.Interruptions in synthesis are usually only necessary after longer periods of synthesis, often only after months or even years, e.g. for maintenance work.

[0004] As a result of general efforts to reduce or completely avoid the use of fossil fuels, alternative processes for the synthesis of NH3 from H2 and N2 according to the Haber-Bosch process have been developed. These processes produce H2 not by steam reforming hydrocarbons, but by electrolysis of water. The electricity used for the electrolysis is generated from renewable energy sources, particularly wind power, hydropower, solar energy, or combinations thereof.

[0005] Renewable energy is not continuously available in constant quantities. The availability of wind and solar power, in particular, is subject to considerable fluctuations, caused primarily by the weather and the day-night cycle. As the availability of renewable energy fluctuates, so does the availability of renewable energy. generated electrical power. For the electrolysis of water, such fluctuations are a minor problem, because the performance of modern electrolysis cells can be adjusted promptly to such fluctuations. As a result, the availability of H2, which is generated by electrolysis of water with electrical power from renewable energy, fluctuates simultaneously (or slightly delayed) with the fluctuation in the availability of renewable energy.

[0006] Plants for the synthesis of NH3 from H2 and N2 using the Haber-Bosch process are comparatively slow and cannot compensate for short-term fluctuations in the availability of H2, or only to a limited extent.

[0007] In order to ensure a sufficient amount of H2 is available at all times so that the plants can operate continuously, it would be necessary to temporarily store the renewable energy, the electricity generated from it, or the H2 obtained through the electrolysis of water. The respective buffer could then be accessed during times of low renewable energy availability. The size of the buffer would have to be sufficient to bridge typical periods of low renewable energy availability, i.e., possibly several days.

[0008] Renewable energy as such is difficult to store temporarily. The electricity generated from renewable energy can also hardly be stored in batteries in the quantities required for the large-scale synthesis of NH3. The required storage capacity of the batteries would be so large that the investment costs for the batteries would not allow for a cost-effective process. While H2 produced by electrolysis of water can in principle be stored temporarily, this poses a significant safety risk, especially considering the quantity required for the large-scale synthesis of NH3.

[0009] There is a need for processes and plants for the synthesis of NH3 using H2, which is obtained by electrolysis of water with electrical power from renewable energy, whereby the processes and plants tolerate a temporarily reduced or interrupted availability of renewable energy (and thus of electrical power generated therefrom and of H2 obtained by electrolysis of water) without the need to temporarily store large quantities of renewable energy, electrical power generated therefrom, or H2 obtained by electrolysis of water.

[0010] EP 2589574 A1 relates to a method for controlling an NH3 plant in which a purge gas containing inert substances is taken from the NH3 synthesis circuit and in which the NH3 plant is operated at partial load by maintaining the NH3 synthesis circuit at a nominal high pressure and reducing the purge rate in order to increase the concentration of inert substances in the NH3 synthesis circuit and to avoid overheating of the reactor.

[0011] US 7892511 relates to systems and methods for producing one or more products from synthesis gas.

[0012] WO 2017153304 A1 relates to a process and a plant for synthesizing a product gas from a first reactant gas and a second reactant gas, wherein product gas is discharged and unconverted reactant gas is circulated, and wherein the volume flow of the first reactant gas, the second reactant gas, and / or the discharged product gas is varied during the process. In this way, the amount of product gas formed per unit of time can be temporarily throttled (partial load operation) or its synthesis can be temporarily completely stopped (standby operation), without the plant on which the process is carried out having to be completely shut down.

[0013] WO 2021060985 A1 relates to a process for the production of NH3, wherein switching between a first operating mode and a second operating mode occurs depending on the availability of H2.

[0014] WO 2021089276 A1 relates to a process for the synthesis of NH3, including the generation of make-up gas in a front-end and the conversion of the make-up gas in an NH3 synthesis loop. When the loop is operated at part load and the make-up gas flow rate is reduced, the loop is controlled by separating a gas stream from a converter feed line at a point upstream of a converter, thus forming a bypass stream, which is reintroduced into the loop at the suction side of a circulator or at a point in a loop downstream of a separation section.

[0015] WO 2021151672 A1 relates to a process for NH3 synthesis in a synthesis circuit, wherein a gas mixture comprising N2, H2, and NH3 is circulated in the synthesis circuit by means of a conveying device, wherein N2 and H2 are at least partially converted to NH3 in a converter, and wherein the gas mixture is cooled in a cooling device such that NH3 condenses out of the gas mixture.

[0016] WO 2022173794 A1 relates to a process for the synthesis of renewable ammonia.

[0017] WO 2022256907 A1 relates to a container system for producing anhydrous ammonia from air, water and an energy source.

[0018] WO 2023006291 A1 relates to an integrated process for the synthesis of NH3 and nitric acid, including the production of H2 from the electrolysis of water. The process is controlled by selectively switching between a first operating mode and a second operating mode, wherein, in the first operating mode, excess NH3 produced is used and stored in a suitable NH3 storage facility; and wherein, in the second operating mode, the NH3 from the NH3 storage facility is used to provide an additional supply of NH3 for nitric acid production. Switching between the first mode and the second mode is based on the amount of energy transferred to the electrolysis of water.

[0019] WO 2023036560 A1 relates to a method for controlling an ammonia plant comprising an ammonia synthesis section with an ammonia converter and a hydrogen generation section connected to a hydrogen storage unit.

[0020] The processes and systems for synthesizing NH3 known from the prior art are not satisfactory in all respects, and it is an object of the invention to provide improved processes and systems. The processes and systems should use H2 obtained by electrolysis of water with electrical power from renewable energy, wherein the processes and systems tolerate a temporarily reduced or interrupted availability of renewable energy (and thus of the electrical power generated therefrom and of the H2 obtained by electrolysis of water) without the need to temporarily store large quantities of renewable energy, the electrical power generated therefrom, or the H2 obtained by electrolysis of water.

[0021] This problem is solved by the subject matter of the patent claims.

[0022] A first aspect of the invention relates to a process for the synthesis of NH3 at variable throughput in a plant comprising a plurality of NH3 synthesis units connected in parallel, the process comprising the steps of: (a) providing H2 by electrolysis of H2O using electrical power from renewable energy; (b) providing a reactant gas stream comprising the H2; preferably in a mixture with N2; (c) introducing the reactant gas stream, depending on the currently available amount of H2, (i) as such into a single one of the NH3 synthesis units; or divided into independent substreams (ii) into a plurality of the NH3 synthesis units or (iii) into all of the NH3 synthesis units, wherein (ii) one of the substreams is introduced independently of one another into each of the plurality of NH3 synthesis units or (iii) into all of the NH3 synthesis units; and (d) synthesizing NH3 from H2 and N2 (i) in the one, (ii) in the plurality of, respectively.(iii) in all of the NH3 synthesis units into which reactant gas stream or a partial stream thereof is introduced in step (c).

[0023] During the course of the process according to the invention, the instantaneous availability of H2 changes, preferably due to external influences such as day-night cycle, weather, etc. During one time interval, the instantaneous availability of H2 is high, during another time interval, the availability of H2 is moderate, and during another time interval, the instantaneous availability of H2 is low. Depending on this instantaneous availability of H2, step (c) takes place, ie the process reacts to fluctuations in the availability of H2 with a modified process control in Step (c), and consequently also step (d). The change in process control due to fluctuations in H2 availability results in variable throughput.

[0024] Step (c) addresses the following three alternative possibilities for introducing the reactant gas stream: Alternative (i): the reactant gas stream is introduced as such (i.e. completely) into a single one of the NH3 synthesis units; or Alternative (ii): the reactant gas stream is divided into independent substreams and introduced into several of the NH3 synthesis units, with one of the substreams being introduced independently of one another into each of the several NH3 synthesis units; or Alternative (iii): the reactant gas stream is divided into independent substreams and introduced into all of the NH3 synthesis units, with one of the substreams being introduced independently of one another into each of the NH3 synthesis units.

[0025] The introduction of the reactant gas stream according to one of the three alternatives depends on the currently available amount of H2. If the (current) availability of H2 changes sufficiently, a change also occurs from one of the alternative possibilities for introducing the reactant gas stream (i), (ii), or (iii) to another of the alternative possibilities for introducing the reactant gas stream (i), (ii), or (iii). This change depends on the current availability of H2.

[0026] Preferably, each time interval comprises at least 15 minutes, more preferably at least 30 minutes, even more preferably at least 45 minutes, most preferably at least 1 hour. The maximum length of the time interval depends on the ratio of heating rate to cooling rate under the given conditions. Preferably, each time interval comprises at most 24 hours, more preferably at most 18 hours, even more preferably at most 12 hours, most preferably at most 6 hours.

[0027] It was surprisingly found that plant configuration and flexibility can be improved under temporarily limited H2 availability by replacing conventional multi-bed reactors with simplified NH3 synthesis units connected in parallel.

[0028] Preferably, the parallel-connected NH3 synthesis units are designed as single-bed reactors, with each NH3 synthesis unit preferably being arranged in its own pressure vessel. For this purpose, the system preferably comprises at least two parallel-connected NH3 synthesis units, preferably single-bed reactors; more preferably, at least three parallel-connected NH3 synthesis units, preferably single-bed reactors; even more preferably, exactly three parallel-connected NH3 synthesis units, preferably single-bed reactors.

[0029] It was surprisingly found that flexibility can be increased in partial load operation by sequentially shutting down individual NH3 synthesis units. Synthesis units cool down slowly and are also preferably insulated. Towards the end of the temporary shutdown, process heat from at least one still-active NH3 synthesis unit is then preferably used to warm up the not-yet-active NH3 synthesis units.

[0030] Assuming a nominal plant load of 100%, with three parallel NH3 synthesis units, temporarily shutting down the first NH3 synthesis unit reduces the total plant load by 33% to 67% of the plant's nominal load. If the second NH3 synthesis unit (reactor) is also shut down, the total plant load is reduced by a further 33% to just 33% of the plant's nominal load.

[0031] Alternatively or additionally, according to the invention, individual NH3 synthesis units are preferably throttled independently of the other NH3 synthesis units by reducing the individual throughput on this NH3 synthesis unit (partial load operation). Thus, it is not necessary for each NH3 synthesis unit to always be operated at the maximum possible throughput (full load operation). Rather, conventional NH3 synthesis units are perfectly capable of maintaining NH3 synthesis even at a throughput lower than the maximum (partial load operation). According to the invention, preference is given to using NH3 synthesis units in which the individual partial load can be continuously reduced to approximately 30% of the maximum possible throughput by reducing the throughput, without the synthesis of NH3 from H2 and N2 coming to a standstill.

[0032] It was surprisingly discovered that the shutdown of individual NH3 synthesis units and the individual throttling of individual NH3 synthesis units can be advantageously combined. For example, if two of the NH3 synthesis units in a plant with three parallel NH3 synthesis units are shut down (reducing the total plant load to 33% of its nominal load), a further reduction can be achieved by throttling the third, non-shutdown NH3 synthesis unit by reducing its throughput, for example, to an individual partial load of 30%. The total plant load is then reduced to approximately 10% of its nominal load.

[0033] It was surprisingly found that in a plant with three parallel NH3 synthesis units, the total plant load can be significantly reduced from 100% of its nominal load, e.g., down to 40% of its nominal load or even 30% of its nominal load, by simultaneously throttling all three parallel NH3 synthesis units (partial load operation), without having to temporarily shut down any of the NH3 synthesis units. However, if the temporarily low availability of H2 makes it necessary to further reduce the total plant load, the temporary shutdown of individual NH3 synthesis units has proven to be useful.

[0034] In the case of a temporary shutdown of individual NH3 synthesis units, it was surprisingly found that a revolving process is particularly favorable and allows a reduction of the total load of the plant even over longer periods.

[0035] If the supply of renewable energy is interrupted and individual NH3 synthesis units are shut down accordingly, they cool down. To prevent cooling below the catalyst light-off temperature, the parallel NH3 synthesis units are preferably operated in a revolving manner, i.e., after a suitable operating period of one of the NH3 synthesis units, the reactant gas stream is preferably fed as such to another of the NH3 synthesis units. The previously operated NH3 synthesis unit is preferably no longer flowed through, i.e., shut down, and the newly supplied NH3 synthesis unit is preferably reheated by the exothermic reaction up to a predetermined temperature. Another parallel NH3 synthesis unit can be reheated in the same way. For example, if three NH3 synthesis units are connected in parallel, the total load of the system can be reduced to only approximately 10% of its nominal load, even over longer periods of time.

[0036] The NH3 synthesis units can be operated within a temperature range. In this mode of operation, the temperature in none of the NH3 synthesis units preferably falls below the minimum start-up temperature. It has been found that the heating rate can be 50 K / h, with the cooling rate being significantly slower. Therefore, according to the invention, two NH3 synthesis units can preferably always be switched off and cooled down, while one NH3 synthesis unit is heated by its reaction heat (process heat). Preferably, none of the NH3 synthesis units cools below the start-up temperature. All NH3 synthesis units then preferably have a different temperature at a given time. The temperature of the reactors is preferably monitored, e.g., by thermocouples.

[0037] Surprisingly, it was discovered that further improvements and even greater flexibility can be achieved if the NH3 synthesis units are in heat exchange with each other. If the NH3 synthesis units are each arranged in their own pressure vessels, three different pressure vessels are required for three NH3 synthesis units. This results in increased costs.

[0038] It was surprisingly discovered that the three NH3 synthesis units can be housed together in a pressure vessel in such a way that they can be subjected to uniform but separate flow. The separation of the NH3 synthesis units is preferably not thermally insulated, so that the NH3 synthesis units that are temporarily not subjected to flow, i.e., are switched off, can be kept at least at the start-up temperature.

[0039] The method according to the invention comprises steps (a) to (d), which are preferably performed in alphabetical order. In addition, the method according to the invention can comprise any additional steps before, after, or between the steps, which can be performed independently of one another in sequence or at least partially simultaneously.

[0040] For the purpose of description, a distinction is made between the total load of the plant on the one hand and the individual load of a single NH3 synthesis unit on the other. The load of an individual NH3 synthesis unit is further differentiated between full load operation and partial load operation.

[0041] For the purpose of description, the nominal load of the plant means the maximum load when all NH3 synthesis units are operated at full load without any throttling, ie the maximum possible throughput for which the plant as a whole is designed.

[0042] For the purposes of this description, "NH3 synthesis unit" in the simplest case means a spatially defined collection of catalyst material suitable for catalyzing the conversion of H2 and N2 to NH3. This can be, for example, a catalyst bed or a reactor. If each of the NH3 synthesis units is arranged in its own pressure vessel, this pressure vessel can be regarded as a reactor. This pressure vessel can optionally comprise several catalyst beds connected in series, which are then preferably regarded together as one NH3 synthesis unit. If the several NH3 synthesis units are arranged together in a pressure vessel, this pressure vessel can be regarded as a reactor in which the several NH3 synthesis units are preferably present as catalyst beds connected in parallel, which preferably exchange heat with one another.It is possible for the multiple NH3 synthesis units, which are present as parallel catalyst beds, to be followed in series by additional catalyst beds, each independently of one another, so that each of the NH3 synthesis units can, in turn, possibly comprise several catalyst beds connected in series. Preferably, however, each of the NH3 synthesis units comprises only a single catalyst bed.

[0043] Preferably, each of the NH3 synthesis units comprises at least one catalyst bed, preferably only a single catalyst bed, through which the reactant gas stream preferably flows axially. Preferably, each catalyst bed independently of one another has a substantially cylindrical shape, so that in this context, "axial" means in a direction substantially parallel to the cylinder jacket. Alternatively, each catalyst bed can also be independently subjected to radial flow, although this is less preferred according to the invention.

[0044] The multiple NH3 synthesis units are connected in parallel, i.e., not in series. The parallel connection of the NH3 synthesis units is used when the reactant gas stream is divided into independent substreams and fed into several of the NH3 synthesis units or into all of the NH3 synthesis units in parallel. In this case, each substream is fed into its own NH3 synthesis unit independently of the others.

[0045] The conversion of H2 and N2 to NH3 is not complete in large-scale ammonia production plants, so the process gas is usually recycled, recompressed if necessary, and passes through the NH3 synthesis units several times. Fresh reactant gas is then introduced into the cycle. For the sake of simplicity, the terms "reactant gas stream" and "partial stream" refer to both recycled process gas and fresh reactant gas (make-up gas).

[0046] In preferred embodiments, step (d) of the process according to the invention comprises - synthesizing NH3 from H2 and N2 in the one, in the several or in all of the NH3 synthesis units into which the reactant gas stream or a substream thereof is introduced in step (c), to obtain a product gas stream or product gas substream which contains NH3 and optionally unreacted H2 and N2; and - recycling the product gas stream or product gas substream to the one, the several or all of the NH3 synthesis units.

[0047] During recycling, the product gas stream or partial product gas stream is preferably recycled only to those NH3 synthesis units into which reactant gas stream or a partial stream thereof was previously introduced.

[0048] The plant preferably comprises three NH3 synthesis units connected in parallel; preferably no more than three NH3 synthesis units connected in parallel.

[0049] Preferably, the NH3 synthesis units each have essentially the same structure.

[0050] In preferred embodiments, each of the NH3 synthesis units is arranged separately in its own pressure vessel.

[0051] In other preferred embodiments, the NH3 synthesis units are arranged in a common pressure vessel.

[0052] Preferably, the NH3 synthesis units are in heat exchange with each other.

[0053] Preferably, each of the NH3 synthesis units contains at least one catalyst bed.

[0054] Preferably, each of the NH3 synthesis units contains only a single catalyst bed.

[0055] In step (a) of the process according to the invention, H2 is provided by electrolysis of H2O with electrical power from renewable energy.

[0056] In preferred embodiments, in step (a), the electrical power is generated from wind power; preferably, the currently available amount of H2 depends on the current availability of wind power.

[0057] In preferred embodiments, in step (a), the electrical power is generated from hydropower; preferably, the currently available amount of H2 depends on the current availability of hydropower.

[0058] In preferred embodiments, in step (a), the electrical power is generated from solar energy; preferably, the currently available amount of H2 depends on the current availability of solar energy.

[0059] Combinations of the above-mentioned sources of renewable energy are also possible according to the invention.

[0060] Preferably, step (a) comprises the intermediate storage of electrical power from renewable energy, preferably in an accumulator.

[0061] Preferably, step (a) comprises the intermediate storage of H2, preferably in a tank.

[0062] In step (b) of the process according to the invention, a reactant gas stream is provided which comprises the H2 provided in step (a).

[0063] Preferably, in step (b), the reactant gas stream is provided with a throughput depending on the currently available amount of H2.

[0064] Preferably, the reactant gas stream provided in step (b) comprises N2 in addition to H2.

[0065] In preferred embodiments, the reactant gas stream provided in step (b) consists essentially of H2 and N2.

[0066] In other preferred embodiments, the reactant gas stream provided in step (b) comprises H2, N2 and NH3.

[0067] Preferably, step (b) comprises compressing the reactant gas stream to elevated pressure, preferably to a pressure of at least 150 bar.

[0068] Preferably, step (b) comprises heating the reactant gas stream to an elevated temperature, preferably to a temperature of at least 300°C.

[0069] In step (c) of the process according to the invention, the reactant gas stream is introduced into NH3 synthesis unit(s) depending on the currently available amount of H2. In particular, three alternative operating modes are distinguished: (1) the reactant gas stream is not divided into substreams, but is introduced as such into a single NH3 synthesis unit; then, neither the reactant gas stream nor a substream thereof is introduced into any of the remaining NH3 synthesis units; or (2) the reactant gas stream is divided into independent substreams, and the substreams are introduced into several, but not all, of the NH3 synthesis units, with one of the substreams being introduced independently into each of the several NH3 synthesis units; then, neither the reactant gas stream nor a substream thereof is introduced into the remaining NH3 synthesis units.or (3) the reactant gas stream is divided into independent substreams, and the substreams are introduced into all of the NH3 synthesis units, with one of the substreams being introduced into each of the NH3 synthesis units independently of one another; there are then no NH3 synthesis units remaining into which neither reactant gas stream nor a substream thereof is introduced.

[0070] In step (d) of the process according to the invention, NH3 is synthesized from H2 and N2 in one, in several or in all of the NH3 synthesis units into which reactant gas stream or a partial stream thereof is introduced in step (c).

[0071] Here, too, a distinction is made between three alternative operating modes: (1) in each of the NH3 synthesis units into which the reactant gas stream is introduced as such, NH3 is synthesized; in all other NH3 synthesis units into which neither reactant gas stream nor a partial stream thereof is introduced, no NH3 is synthesized, i.e. all other NH3 synthesis units are (temporarily) switched off; or (2) in the several NH3 synthesis units into which the reactant gas stream is introduced divided into partial streams, NH3 is synthesized in each case; in the other NH3 synthesis units into which neither reactant gas stream nor a partial stream thereof is introduced, no NH3 is synthesized, i.e.the remaining NH3 synthesis units are (temporarily) switched off; or (3) in all of the NH3 synthesis units into which the reactant gas stream is divided into partial streams, NH3 is synthesized; there are then no NH3 synthesis units left in which no NH3 is synthesized, ie which are (temporarily) switched off.

[0072] In step (c) of the process according to the invention, the feed gas stream is introduced depending on the currently available amount of H2. "Depending on" means that the currently available amount of H2 is monitored, either directly as such, and / or indirectly via the currently available amount of electrical power and / or via the currently available amount of renewable energy. Monitoring may also include forecasts, for example, forecasts of the day-night cycle or weather forecasts that predict the expected precipitation, the expected wind, and / or the expected hours of sunshine. The feed gas stream is then introduced according to one of the three alternative operating modes (1), (2), and (3).

[0073] "Currently" refers to a current state that lasts only for a certain period of time and then passes. For example, at night, in the absence of sunlight, the current availability of solar energy is low (or nonexistent), and thus also the availability of H2, which is produced by electrolysis of H2O using solar power. In this case, the total load of the system is preferentially reduced. During the day, however, due to sunlight, the current availability of solar energy is high, and thus also the availability of H2, which is produced by electrolysis of H2O using solar power. In this case, the total load of the system is preferentially increased. As a result of the change in the total load of the system depending on the fluctuating current availability of H2, the synthesis of NH3 occurs at a variable throughput.When H2 availability is currently high, the total load of the plant is preferably higher than when H2 availability is currently low.

[0074] In addition to the currently available amount of H2, step (c) of the process according to the invention can also be carried out depending on the expected future availability of H2. The current availability of H2 is then not the only parameter depending on which step (c) is carried out. The expected future availability of H2 is preferably derived from forecasts.

[0075] With a known day-night cycle, for example, the onset of the next dusk can be predicted very precisely and reliably. The change in the availability of solar energy that accompanies dusk, in turn, influences the availability of electrical power generated from solar energy and thus of H2 obtained by electrolysis of H2O using this electrical current. In this case, a time lag may need to be taken into account, which the electrolysis of H2O using this electrical current requires before the H2 thus obtained can be made available. In this case, in addition to the currently available amount of H2, the expected future availability of H2 is also preferably taken into account for controlling the process, with the future 4 hours being given priority.

[0076] In weather forecasts, changes in the availability of renewable energy are less reliable. The shorter the future time interval additionally considered for process control, the more likely the predicted change will actually occur, and thus the more stable the process control. In this case, too, in addition to the currently available amount of H2, the expected future available amount of H2 is preferably also taken into account for process control, with at least the future 4 hours being considered, more preferably the future 6 hours, and even more preferably the future 12 hours.

[0077] Preferably, the method according to the invention is controlled as a function of the currently available amount of H2, wherein the control preferably selects one of the three alternative operating modes (1), (2) and (3) as a function of the currently available amount of H2 and comparison with a predetermined threshold value or several predetermined threshold values.

[0078] Depending on whether the currently available amount of H2 is decreasing or increasing, different thresholds may be relevant. The change from operating mode (1) to operating mode (2) ((1)->(2)) can thus occur at a different set threshold than the converse change from operating mode (2) to operating mode (1) ((2)->(1)).

[0079] In preferred embodiments, the control is carried out as a function of both the currently available amount of H2 and the expected future available amount of H2, which results from predictions.

[0080] If one of the three alternative operating modes (1), (2) and (3) is selected, then control of the method within this selected alternative operating mode (1), (2) or (3) is also preferred, wherein this control is preferably also dependent on the current available amount of H2, whereby preferably a comparison of the currently available amount of H2 with a specified threshold value or several specified threshold values ​​is also carried out.

[0081] According to the invention, the introduction preferably takes place according to the alternative operating mode (3) when H2 is available in large quantities. In this case, all NH3 synthesis units can each be operated at full load, i.e. at maximum throughput, so that the maximum achievable total load of the plant in this operating mode is 100% of its nominal load. Alternatively, all NH3 synthesis units can also be operated independently of one another at partial load, i.e. at reduced throughput, so that in this operating mode the total load of the plant can also be less than 100% of its nominal load. It is also possible for one or more of the NH3 synthesis units to be operated at full load and the remaining NH3 synthesis units to be operated at partial load, so that in this operating mode the total load of the plant can also be less than 100% of its nominal load.

[0082] According to the invention, the introduction preferably takes place according to the alternative operating mode (2) when H2 is available in medium quantities. The plurality of NH3 synthesis units can each be operated at full load, i.e. at maximum throughput, in which case the total load of the plant is already less than 100% of its nominal load because at least one of the NH3 synthesis units is switched off. Alternatively, the plurality of NH3 synthesis units can also be operated independently of one another at partial load, i.e. at reduced throughput, so that the total load of the plant is further reduced. It is also possible for one or more of the plurality of NH3 synthesis units to be operated at full load and the remaining plurality of NH3 synthesis units to be operated at partial load.

[0083] According to the invention, introduction according to alternative operating mode (1) is preferred when H2 is available in small quantities. The individual NH3 synthesis unit can be operated at full load, i.e., at maximum throughput, whereby the total load of the plant is then already less than 100% of its nominal load because the remaining NH3 synthesis units are shut down. Alternatively, the individual NH3 synthesis unit can also be operated at partial load, i.e., at reduced throughput, so that the total load of the plant is reduced even further.

[0084] During the process according to the invention, a change from one of the alternative operating modes to another of the alternative operating modes preferably occurs. This change preferably occurs depending on a corresponding change in the availability of H2.

[0085] According to the invention, in particular the following nine states of the NH3 synthesis units can be distinguished: (0) no reactant gas stream is introduced into any of the NH3 synthesis units, neither as such nor divided into independent partial streams; (1a) the reactant gas stream is introduced as such into a single one of the NH3 synthesis units, which is operated at reduced throughput (partial load operation); (1b) the reactant gas stream is introduced as such into a single one of the NH3 synthesis units, which is operated at maximum throughput (full load operation); (2a) the reactant gas stream is divided into independent substreams and introduced into several, but not all, of the NH3 synthesis units, each of which is operated independently of one another at reduced throughput (partial load operation); (2b) the reactant gas stream is divided into independent substreams and introduced into several, but not all, of the NH3 synthesis units, of which at least one of the NH3 synthesis units is operated at reduced throughput (partial load operation) and at least one of the NH3 synthesis units is operated at maximum throughput (full load operation);(2c) the reactant gas stream is divided into independent substreams and introduced into several, but not all, of the NH3 synthesis units, each of which is operated at maximum throughput (full load operation); (3a) the reactant gas stream is divided into independent substreams and introduced into all of the NH3 synthesis units, each of which is operated independently of one another at a reduced throughput (partial load operation); (3b) the reactant gas stream is divided into independent substreams and introduced into all of the NH3 synthesis units, of which at least one of the NH3 synthesis units is operated at a reduced throughput (partial load operation) and all of the remaining NH3 synthesis units are operated at maximum throughput (full load operation);or (3c) the reactant gas stream is divided into independent partial streams and introduced into all of the NH3 synthesis units, each operating at maximum throughput (full-load operation). In this condition, the plant's nominal load of 100% is reached, ie, the total load corresponds to the nominal load.

[0086] In preferred embodiments, the plant according to the invention comprises exactly three NH3 synthesis units, which are set to the following states depending on the current availability of H2, expressed in % based on the amount of H2 possible or required for full-load operation (100% of the nominal load of the plant) (=100%): H2 Preferred embodiments 100% 3c 90% 3a or 3b 80% 3a or 3b 70% 3a or 3b 67% 3a or 3b or 2c 60% 3a or 3b or 2b 50% 3a or 2a or 2b 40% 3a or 2a 33% 3a or 2a or 1b 30% 3a or 2a or 1a 20% 2a or 1a 10% 1a 0% 0

[0087] In order to reduce the total load of the system, depending on the current availability of H2, in preferred embodiments [1] to

[0016] according to the invention, the following states are passed through one after the other starting from 100% of the nominal load (3c), wherein a threshold value Ssinkt is preferably defined for the transition from one state to the next state (according to the table above): [1] (3c) -> Ssinkt -> (3b); [2] (3c) -> Ssinkt -> (3b) -> Ssinkt -> (1a); [3] (3c) -> Ssinkt -> (3b) -> Ssinkt -> (3a); [4] (3c) -> Ssinkt -> (3b) -> Ssinkt -> (3a) -> Ssinkt -> (2b); [5] (3c) -> Ssinkt -> (3b) -> Ssinkt -> (3a) -> Ssinkt -> (1a); [6] (3c) -> Ssinks -> (3b) -> Ssinks -> (2b); [8] (3c) -> Ssinks -> (3a); [9] (3c) -> Ssinks -> (3a) -> Ssinks -> (2a);

[0010] (3c) -> Ssinks -> (3a) -> Ssinks -> (2a) -> Ssinks -> (1a);

[0011] (3c) -> S sinkt -> (3a) -> S sinkt -> (1a);

[0012] (3c) -> S sinkt -> (3a) -> S sinkt-> (2b);

[0013] (3c) -> Ssinks -> (3a) -> Ssinks -> (2b) -> Ssinks -> (1a);

[0014] (3c) -> S sinks -> (2b);

[0015] (3c) -> Ssinks -> (2b) -> Ssinks -> (1a); or

[0016] (3c) -> Sink -> (1a).

[0088] For the purpose of description, the subscript suffix "decreases" means that the respective threshold is relevant for the case in which the instantaneous availability of H2 is decreasing, ie the temporal progression of the instantaneous availability of H2 has a negative slope.

[0089] To increase the total load of the system, depending on the current availability of hydrogen, the aforementioned states are preferably run through successively, but in reverse order, starting from state (1a). The relevant threshold values ​​determined for this purpose can be quantitatively the same as those used to reduce the total load, but they can also be higher or lower independently of one another.

[0090] To increase the total load of the system, depending on the current availability of H2, according to the invention in preferred embodiments

[0017] to

[0032] starting from a reduced nominal load (e.g. (1a), (2b) or (3a)), the following states are passed through one after the other, wherein a threshold value Ssteigt is preferably set for the transition from one state to the next state (according to the table above):

[0017] (3b) -> Ssteigt -> (3c);

[0018] (1a) -> Ssteigt -> (3b) -> Ssteigt -> (3c);

[0019] (3a) -> Ssteigt -> (3b) -> Ssteigt -> (3c);

[0020] (2b) -> Ssteigt -> (3a) -> Ssteigt -> (3b) -> Ssteigt -> (3c);

[0021] (1a) -> Srises -> (3a) -> Srises -> (3b) -> Srises -> (3c);

[0022] (2b) -> Srises -> (3b) -> Srises -> (3c);

[0023] (1a) -> Srises -> (2b) -> Srises -> (3b) -> Srises -> (3c);

[0024] (3a) -> S rises -> (3c);

[0025] (2a) -> Srises -> (3a) -> Srises -> (3c);

[0026] (1a) -> Srises -> (2a) -> Srises -> (3a) -> Srises -> (3c);

[0027] (1a) -> Srises -> (3a) -> Srises -> (3c);

[0028] (2b) -> Srises -> (3a) -> Srises -> (3c);

[0029] (1a) -> Srises -> (2b) -> Srises -> (3a) -> Srises -> (3c);

[0030] (2b) -> S rises -> (3c);

[0031] (1a) -> Srises -> (2b) -> Srises -> (3c); or

[0032] (1a) -> S rises -> (3c).;

[0091] For the purpose of description, the superscript suffix "increases" means that the respective threshold is relevant for the case in which the instantaneous availability of H2 is increasing, ie the temporal course of the instantaneous availability of H2 has a positive slope.

[0092] In preferred embodiments of the process according to the invention, in step (c), the reactant gas stream is introduced - during a first time interval, divided into independent partial streams, into all of the NH3 synthesis units, so that NH3 is synthesized in each of the NH3 synthesis units (alternative operating mode (3)); and - during a second time interval, which immediately follows the first time interval, divided into independent partial streams, into several of the NH3 synthesis units, but not into all of the NH3 synthesis units, so that NH3 is synthesized in each of the several of the NH3 synthesis units, but not in all of the NH3 synthesis units (alternative operating mode (2)).

[0093] In this case, the availability of H2 is preferably lower during the second time interval than during the first time interval.

[0094] In other preferred embodiments, the order of the two aforementioned time intervals is exactly the opposite. In this case, the availability of H2 is preferably greater during the second time interval than during the first time interval.

[0095] In preferred embodiments of the process according to the invention, in step (c), the reactant gas stream is introduced - during a first time interval, divided into independent partial streams, into all of the NH3 synthesis units, so that NH3 is synthesized in each of the NH3 synthesis units (alternative operating mode (3)); and - during a second time interval, which immediately follows the first time interval, as such, into a single one of the NH3 synthesis units, so that NH3 is synthesized only in the single one of the NH3 synthesis units (alternative operating mode (1)).

[0096] In this case, the availability of H2 is preferably lower during the second time interval than during the first time interval.

[0097] In other preferred embodiments, the order of the two aforementioned time intervals is exactly the opposite. In this case, the availability of H2 is preferably greater during the second time interval than during the first time interval.

[0098] In preferred embodiments of the process according to the invention, in step (c) the reactant gas stream is introduced - during a first time interval divided into independent partial streams - into several of the NH3 synthesis units, but not into all of the NH3 synthesis units, so that in the several of the NH3 synthesis units, but not in all of the NH3 synthesis units NH3 is synthesized (alternative operating mode (2)); and - during a second time interval, which immediately follows the first time interval, as such, is introduced into a single one of the NH3 synthesis units, so that NH3 is synthesized only in the single one of the NH3 synthesis units (alternative operating mode (1)).

[0099] In this case, the availability of H2 is preferably lower during the second time interval than during the first time interval.

[0100] In other preferred embodiments, the order of the two aforementioned time intervals is exactly the reverse. In this case, the availability of H2 is preferably greater during the second time interval than during the first time interval.

[0101] Preferably, the first time interval and the second time interval each independently comprise at least 15 minutes, more preferably at least 30 minutes, even more preferably at least 45 minutes, most preferably at least 1 hour. Preferably, the first time interval and the second time interval each independently comprise at most 24 hours, more preferably at most 18 hours, even more preferably at most 12 hours, most preferably at most 6 hours.

[0102] In preferred embodiments, step (c) comprises the substeps: (c1) determining the currently available amount of H2; (c2) comparing the determined currently available amount of H2 with a specified threshold value for the amount of H2 (e.g., threshold value As decreases when the current availability of H2 decreases, threshold value A increases when the current availability of H2 increases).

[0103] Determining the currently available amount of H2 in sub-step (c1) preferably comprises determining the currently available amount of H2 as such, and / or determining the currently available amount of electrical power, and / or determining the currently available amount of renewable energy. Forecasts can also be taken into account, for example, forecasts of the day-night cycle or weather forecasts that predict the expected precipitation, the expected wind, and / or the expected hours of sunshine.

[0104] Based on the comparison of the determined currently available amount of H2 with the specified threshold value for the amount of H2 (e.g. threshold value As decreases with a decrease in the current availability of H2 or threshold value As increases with an increase in the current availability of H2) in sub-step (c2), the process is then preferably controlled, in particular the division of the reactant gas stream into two or more sub-streams, and the introduction of the reactant gas stream as such or divided into sub-streams into a single one, into several or into all of the NH3 synthesis units.

[0105] In preferred embodiments, step (c) comprises the substep: (c3) Determine the temporal change of the currently available amount of H2, ie whether the currently available amount of H2 is decreasing or increasing.

[0106] In preferred embodiments, in step (c) a threshold value B is set for the amount of H2 sinktand a threshold value B increases; where - first, the reactant gas flow is divided into independent sub-flows and the sub-flows are introduced into several or all of the NH3 synthesis units; and where, in the event of a decrease in the instantaneous availability of H2 and falling below the threshold value B sinkt the reactant gas stream is introduced as such into a single one of the NH3 synthesis units; or - firstly, the reactant gas stream is introduced as such into a single one of the NH3 synthesis units; and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value B, the reactant gas stream is divided into independent sub-streams and the sub-streams are introduced into several or all of the NH3 synthesis units.

[0107] Preferably, the threshold values ​​Bsinkt and Bsteigt are different from one another. In preferred embodiments, B > Bsteigt applies. In other preferred embodiments, Bsinkt < B applies.

[0108] The plant according to the invention preferably comprises n NH3 synthesis units, of which each NH3 synthesis unit is designed for 1 / n of the nominal load of the plant at maximum throughput (full load operation), with n = 2, 3, 4, 5 or 6, more preferably 2 or 3, even more preferably 3. Preferably, the n NH3 synthesis units can each be throttled independently of one another by reducing the individual throughput (partial load operation), wherein the individual partial load can preferably be continuously reduced to about 30% of the maximum possible throughput (throttling) without the synthesis of NH3 from H2 and N2 coming to a standstill.

[0109] If none of the n NH3 synthesis units are temporarily shut down, but all n NH3 synthesis units are supplied with reactant gas flow divided into independent partial flows, the minimum possible total load of the plant in this operating mode (ie without shutting down at least one of the NH3 synthesis units) is preferably 30% of the nominal load of the plant (all NH3 synthesis units are then throttled to an individual throughput of 30% of the maximum possible throughput in partial load operation).

[0110] Within this operating mode (alternative operating mode (3)), any reduction in the instantaneous availability of H2 can be compensated by throttling the individual throughput on one, several or all of the n NH3 synthesis units in the range between - the maximum possible total load of the plant (100% of the nominal load of the plant), and - the minimum possible total load of the plant in this operating mode, ie without switching off at least one of the NH3 synthesis units (e.g. 30% of the nominal load of the plant), without the need for a temporary shutdown of one or more NH3 synthesis units.

[0111] Within this operating mode (alternative operating mode (3)), starting from full load operation (100% of the nominal load of the plant), a first threshold value for the instantaneous availability of H2 is preferably set for the start of the throughput throttling (transition from state (3c) to state (3b) or state (3a)), preferably the amount of H2 possible or required for full load operation (100% of the nominal load of the plant). If this first threshold value is undershot, i.e. the amount of H2 possible or required for full load operation (100% of the nominal load of the plant) is no longer available, the individual throughput is initially throttled on at least one of the NH3 synthesis units, preferably uniformly on all of the NH3 synthesis units simultaneously.However, the operating mode as such (alternative operating mode (3)) remains fundamentally unchanged for the time being; the change consists in the individual throttling of the throughput for individual NH3 synthesis units (transition from state (3c) to state (3b) or state (3a)).

[0112] However, if the current availability of H2 continues to decrease, i.e., below the minimum possible total plant load achievable with the aid of throttling for this operating mode (alternative operating mode (3), e.g., 30% of the plant's nominal load), then not all NH3 synthesis units can be supplied with reactant gas divided into independent partial streams; instead, the temporary shutdown of at least one of the NH3 synthesis units is then required (alternative operating mode (2)), or if necessary, the temporary shutdown of all NH3 synthesis units except for a single NH3 synthesis unit (alternative operating mode (1)). This is due to the fact that throttling of an individual NH3 synthesis unit is not possible to an indefinite extent; rather, throttling to approximately 30% of the maximum possible throughput reaches a limit below which the flow cannot be reduced any further.A change of operating mode then preferably occurs, starting from alternative operating mode (3) either to alternative operating mode (2) or directly to alternative operating mode (1).

[0113] Starting from the alternative operating mode (3), if necessary by exhausting all possibilities of throttling the individual throughput, a second threshold value for the instantaneous availability of H2 is preferably set for the transition to the alternative operating mode (2) or to the alternative operating mode (1), preferably the amount of H2 at which, for the alternative operating mode (3), it is just possible to supply all NH3 synthesis units when throttling (e.g. 30% of the nominal load of the plant).

[0114] If all NH3 synthesis units except for one single NH3 synthesis unit, ie n-1 NH3 synthesis units, are temporarily switched off, so that only one single NH3 synthesis unit is supplied with the reactant gas stream as such (alternative operating mode (1)), the minimum possible total load of the plant for this example is 30% / n (the only NH3 synthesis unit not switched off Each synthesis unit contributes only 1 / n to the maximum possible total load of the plant and is additionally throttled to an individual throughput of, for example, 30% of its maximum possible throughput. For three NH3 synthesis units (n=3), the minimum possible total load of the plant for this operating mode (alternative operating mode (1)) is then preferably 10% of its nominal load.

[0115] The temporary shutdown of at least one NH3 synthesis unit (alternative operating mode (2)) or all but one NH3 synthesis unit (alternative operating mode (1)) is therefore particularly relevant when the current availability of H2 falls below the second threshold value, up to which, in alternative operating mode (3), all NH3 synthesis units can still be supplied with throttling, e.g., 30% of the nominal load of the plant.

[0116] In preferred embodiments, this aforementioned second threshold value (e.g., threshold value Bsinkt) is 20±15%, more preferably 20±10%, even more preferably 20±5%, most preferably 20% of the maximum possible amount of H2 for full-load operation (100% of the nominal load of the plant). The possible or required amount of H2 for full-load operation is limited by the design of the plant, resulting in a maximum value.

[0117] The synthesis of NH3 from H2 and N2 is exothermic, meaning that the NH3 synthesis units heat up as a result of the synthesis, provided they have not (yet) reached their respective normal operating temperatures, at which the inflow of heat (process heat) due to the synthesis and the outflow of heat are in equilibrium. However, conventional catalysts for the Haber-Bosch process require a minimum temperature (light-off temperature) to be catalytically effective. Once this temperature is reached, synthesis takes place, and the NH3 synthesis unit continues to heat itself.

[0118] According to the invention, the following temperatures or temperature ranges are distinguished in particular, which are independent for each of the NH3 synthesis units: (i) temperatures below the light-off temperature: if the reactant gas stream or a partial stream thereof is introduced into an NH3 synthesis unit at such temperatures, practically no synthesis of NH3 from H2 and N3 takes place; (ii) light-off temperature: at this temperature the synthesis of NH3 from H2 and N3 starts and subsequently heats up the NH3 synthesis unit as a result of the reaction heat (process heat) formed; typical light-off temperatures can, for example, be in the range of approx. 300-350°C, but can also be lower or higher; and (iii) usual operating temperature: at this temperature, at the maximum possible throughput (full load operation), the inflow of heat as a result of the synthesis and the outflow of heat are in equilibrium with one another; typical usual operating temperatures can, for example, be in the range of approx.420-500°C, but also below or above.

[0119] Unless explicitly stated otherwise, temperatures are measured inside the NH3 synthesis units, preferably by suitable thermocouples. The temperature is preferably measured at one or more locations (as an average value) which is indicative of the thermal state of the respective NH3 synthesis device, preferably in the center of the respective NH3 synthesis device.

[0120] The respective light-off temperature and typical operating temperature depend on the type and age of the catalyst used and other factors, such as the design of the NH3 synthesis unit, its insulation, etc., and can be determined for a given NH3 synthesis unit through standard routine tests. Since the NH3 synthesis units preferably have essentially the same design, they preferably also have essentially the same light-off temperature and typical operating temperature.

[0121] The advantages of the process and system according to the invention are particularly evident in the temperature range between the start-up temperature and the usual operating temperature. If the NH3 synthesis units are in heat exchange with each other, temperatures below the start-up temperature can also be relevant.

[0122] With three NH3 synthesis units, in preferred embodiments according to the invention, the following immediately successive time intervals #1, #2 and #3 are run through one after the other in order to realize a revolving operation: first NH3 synthesis unit second NH3 synthesis unit third NH3 synthesis unit synthesis temperature synthesis temperature synthesis temperature #1 yes ↑ heats up no ↓ cools down no ↓ cools down #2 no ↓ cools down yes ↑ heats up no ↓ cools down #3 no ↓ cools down no ↓ cools down yes ↑ heats up #1 yes ↑ heats up no ↓ cools down no ↓ cools down #2 no ↓ cools down yes ↑ heats up no ↓ cools down #3 no ↓ cools down no ↓ cools down yes ↑ heats up etc.

[0123] In preferred embodiments, at least one of the NH3 synthesis units is permanently maintained at a temperature above its start-up temperature. This prevents the respective temperature in all NH3 synthesis units from simultaneously falling below the respective start-up temperature, which is relevant for the respective NH3 synthesis unit. Otherwise, it would no longer be possible to start the synthesis of NH3 from H2 and N2 without the external supply of heat, e.g., from a heater.

[0124] According to the invention, the process is preferably controlled or regulated such that at any given time at least one of the NH3 synthesis units, preferably several of the NH3 synthesis units independently of one another, more preferably all NH3 synthesis units independently of one another have or have a temperature above their respective start-up temperature.

[0125] The appropriate process control, in particular the time for the revolving change from one operating state to the next operating state, depends, among other things, on the total number of NH3 synthesis units, the relative temperature difference ΔT between the operating temperature at full load (T B ) and the light-off temperature (T A ) (ie ΔT = T B - T A ), the heating rate at full load operation, the heating rate at partial load operation, and the cooling rate.

[0126] According to the invention, it is not always absolutely necessary to permanently and continuously introduce the reactant gas stream as such or divided into partial streams into at least one of the NH3 synthesis units. Accordingly, it is also not always absolutely necessary for NH3 to be permanently and continuously synthesized from H2 and N2 in at least one of the NH3 synthesis units, thereby generating reaction heat. Rather, it is entirely possible according to the invention for the reactant gas stream to be temporarily and completely interrupted. This is preferred according to the invention when at least one of the NH3 synthesis units has a temperature that is significantly above its start-up temperature, so that it is acceptable to temporarily and completely interrupt the reactant gas stream, whereby this NH3 synthesis unit cools down somewhat.It is only important, and preferred according to the invention, that the introduction of the reactant gas stream or a partial stream thereof is started again before the temperature of this NH3 synthesis unit falls below its start-up temperature (and unless there is another NH3 synthesis unit instead whose temperature is above its start-up temperature).

[0127] In preferred embodiments, however, the reactant gas flow is not temporarily completely interrupted, ie at any time the reactant gas flow is either introduced as such into a single one of the NH3 synthesis units or divided into several sub-flows and introduced into several or all of the NH3 synthesis units.

[0128] In preferred embodiments according to the invention, with three NH3 synthesis units, the following immediately successive time intervals #1, #2 and #3 are run through one after the other to realize a revolving operation, wherein in each of the three NH3 synthesis units the temperature is kept above the respective light-off temperature: first NH3 synthesis unit second NH3 synthesis unit third NH3 synthesis unit synthesis temperature synthesis temperature synthesis temperature #1 yes ↑ TB ≥ T1 > TA no ↓ TB > T2 > TA no ↓ TB > T3 > TA #2 no ↓ T B > T1> T A yes ↑ T B ≥ T2> T A no ↓ T B > T3> T A #3 no ↓ TB > T1 > TA no ↓ TB > T2 > TA yes ↑ TB ≥ T3 > TA #1 yes ↑ T B > T1> T A no ↓ T B > T2> T A no ↓ T B > T3> T A #2 no ↓ TB ≥ T1 > TA yes ↑ TB ≥ T2 > TA no ↓ TB > T3 > TA #3 no ↓ T B > T1> T A no ↓ TB > T2> T A yes ↑ T B ≥ T3> T A etc.

[0129] This means: "↑" = heats up "↓" = cools down "T A " = respective light-off temperature "T B " = respective operating temperature at full load "T1" = current temperature in the first synthesis unit "T2" = current temperature in the second synthesis unit "T3" = current temperature in the third synthesis unit.

[0130] A preferred system according to the invention, schematically illustrated in Figure 2, is particularly suitable for carrying out such a revolving operation.

[0131] For this purpose, a plurality of NH3 synthesis units, preferably exactly two NH3 synthesis units, more preferably exactly three NH3 synthesis units, are preferably arranged in a common pressure vessel. The plurality of NH3 synthesis units are preferably in heat exchange with one another. The common pressure vessel preferably has a substantially circular cross-sectional area and thus a substantially cylindrical shape. The reactant gas stream can preferably be introduced into the pressure vessel in the axial direction, wherein targeted introduction into a single, several, or all of the NH3 synthesis units is possible. The interior of the common pressure vessel is preferably divided into a plurality of cylinder sectors, which preferably have substantially the same shape and size. One of the NH3 synthesis units is preferably arranged in each of the cylinder sectors.The number of cylinder sectors therefore preferably corresponds to the number of NH3 synthesis units in the common pressure vessel.

[0132] The cylinder sectors are preferably defined by walls that separate the NH3 synthesis units from one another. These walls are preferably substantially gas-tight. Heat can preferably flow through these walls from one NH3 synthesis unit into an adjacent NH3 synthesis unit, thereby enabling preferential heat exchange between the NH3 synthesis units.

[0133] In the case of exactly two NH3 synthesis units, the interior of the common pressure vessel is preferably divided into two preferably essentially equal-sized semicircular cylinder halves (cylinder sectors), each of which defines an angle of 180° and each of which extends over the entire length of the interior of the common pressure vessel. The boundary between the two semicircular cylinder halves runs as the diameter of the preferably circular cross-sectional area through its center (cylinder sector with an angle of 180°).

[0134] In the case of exactly three NH3 synthesis units, the interior of the common pressure vessel is preferably divided into three cylinder thirds (cylinder sectors), each of which preferably has essentially the same size and which each describe an angle of 120° and which each extend over the entire length of the interior of the common pressure vessel or the cylindrical part of the common pressure vessel. The boundary between the three cylinder thirds runs as three-pointed star in the circular cross-sectional area through its center (cylindrical sector with an angle of 120°).

[0135] In the case of exactly four NH3 synthesis units, the interior of the common pressure vessel is preferably divided into four cylinder quarters (cylinder sectors), each of which preferably has essentially the same size, each defining an angle of 90° and each extending over the entire length of the interior of the common pressure vessel or the cylindrical part of the common pressure vessel. The boundary between the four cylinder quarters runs as a four-pointed star in the circular cross-sectional area through their center (cylinder sector with an angle of 90°).

[0136] In preferred embodiments, each of the NH3 synthesis units is characterized independently of one another by a maximum possible throughput of the reactant gas stream or the partial stream and is operable either at full load or at partial load, wherein the throughput of the reactant gas stream or the partial stream thereof is - undiminished at full load and - reduced at partial load compared to the maximum possible throughput.

[0137] In preferred embodiments, in step (c) a threshold value C decreases and a threshold value C increases are defined for the amount of H2, wherein - firstly the throughput of the reactant gas stream or the partial stream thereof which is passed into at least one of the NH3 synthesis units is undiminished compared to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units with undiminished throughput (full load operation);and wherein, in the event of a decrease in the instantaneous availability of H2 and the threshold value C being undershot, the throughput of the reactant gas stream or the partial stream thereof which is introduced into said at least one of the NH3 synthesis units is reduced compared to the maximum possible throughput for said at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in said at least one of the NH3 synthesis units at a reduced throughput (partial load operation); or - initially the throughput of the reactant gas stream or the partial stream thereof which is introduced into at least one of the NH3 synthesis units is reduced compared to the maximum possible throughput for said at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in said at least one of the NH3 synthesis units at a reduced throughput (partial load operation);and wherein in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value C, the throughput of the reactant gas stream or the partial stream thereof which is fed into at least one of the NH3 synthesis units is undiminished compared to the maximum possible throughput for said at least one of the NH3 synthesis units, so that in; Step (d) in which at least one of the NH3 synthesis units synthesizes NH3 with undiminished throughput (full load operation).

[0138] The preferred threshold values ​​are C sinkt and C rises differently from each other. In preferred embodiments, C sinkt > Cincreases. In other preferred embodiments, C sinkt < C rises.

[0139] Depending on the alternative operating mode (1), (2) or (3), this is at least one of the NH3 synthesis units which changes from full load operation to partial load operation, - the only loaded NH3 synthesis unit (alternative operating mode (1)), or - one of several but not all loaded NH3 synthesis units (alternative operating mode (2)), or - one of all loaded NH3 synthesis units (alternative operating mode (3)).

[0140] The above-mentioned threshold value Csinkt or Csinkt is then preferably decisive according to the invention for the transition of this at least one of the NH3 synthesis units from full load operation to partial load operation, ie for the transition of the following states with decreasing instantaneous availability of H2: - in alternative operating mode (1): - (1b) -> Csinkt -> (1a); - in alternative operating mode (2): - (2c) -> Csinkt -> (2b); - (2c) -> Csinkt -> (2a); or - (2b) -> Csinkt -> (2a); - in alternative operating mode (3): - (3c) -> Csinkt -> (3b); - (3c) -> Csinkt -> (3a); or - (3b) -> Csinkt -> (3a).

[0141] In preferred embodiments, below the threshold values ​​(e.g. below the threshold values ​​Csinkt and Csteigert), the throughput of the reactant gas stream, which is introduced into several of the NH3 synthesis units divided into independent partial streams, is reduced in each case independently of one another compared to the respective maximum possible throughput for the several of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the several of the NH3 synthesis units with a reduced throughput (partial load operation).

[0142] In preferred embodiments, below the threshold values ​​(e.g. below the threshold C sinkt and Cincreases) the throughput of the reactant gas stream, which is divided into independent Partial streams are introduced into all of the NH3 synthesis units, each independently reduced compared to the maximum possible throughput for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all NH3 synthesis units with reduced throughput (partial load operation).

[0143] In preferred embodiments, in step (c) a threshold value D decreases and a threshold value D increases are defined for the amount of H2; wherein - firstly, the reactant gas stream is divided into independent partial streams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and wherein in the event of a decrease in the current availability of H2 and falling below the threshold value D sinktthe reactant gas flow is interrupted for at least one of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the at least one of the NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units; or - initially the reactant gas flow is interrupted for at least one of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the at least one of the NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units;and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value D rises, the reactant gas stream is divided into independent partial streams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units. ;

[0144] Preferably, the threshold values ​​D rises falls and D are different from one another. In preferred embodiments, D rises > D t. In other preferred embodiments, D rises falls < D .

[0145] In preferred embodiments, these aforementioned threshold values ​​Dsinkt and Dsteigt are independently 67±15%, more preferably 67±10%, even more preferably 67±5%, most preferably 67% of the maximum possible amount of H2 for full load operation (100% of the nominal load of the plant).

[0146] In other preferred embodiments, these above-mentioned threshold values ​​Dsinkt and Dsteigt are independently 50±15%, more preferably 50±10%, even more preferably 50±5%, most preferably 50% of the maximum possible amount of H2 for full load operation (100% of the nominal load of the plant).

[0147] In further preferred embodiments, these above-mentioned threshold values ​​D sinkt and D increases independently of each other 20±15%, more preferably 20±10%, even more preferably 20±5%, preferably 20% of the maximum possible amount of H2 for full load operation (100% of the nominal load of the plant).

[0148] In preferred embodiments, in step (c) a threshold value D for the amount of H2 sinktand a threshold value D rises; where - first, the reactant gas stream is divided into independent substreams and fed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and where, in the event of a decrease in the current availability of H2 and falling below the threshold value D sinktthe reactant gas flow is interrupted for several of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the several NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units; or - initially the reactant gas flow is interrupted for several of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the several NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units;and wherein in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value D rises, the reactant gas stream is divided into independent partial streams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units. ;

[0149] In preferred embodiments, in step (c) a threshold value D increases and decreases for the amount of H2; wherein - firstly the reactant gas stream is divided into independent partial streams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and wherein in the event of a decrease in the instantaneous availability of H2 and the threshold value D falls below, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; and wherein the reactant gas stream is interrupted for all other NH3 synthesis units, so that in step (d) no NH3 is synthesized in any of the other NH3 synthesis units;or - initially the reactant gas flow is interrupted for all but one of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in all but one of the NH3 synthesis units; and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value D, the reactant gas flow is divided into independent partial flows and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units.

[0150] In preferred embodiments, below the threshold value (e.g. the threshold value D sinkt) the reactant gas flow is interrupted for several of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the several NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units. Preferably, the above-mentioned threshold values ​​(e.g. the threshold values ​​D u increases decreases and D ) are then independently of one another 20±15%, more preferably 20±10%, even more preferably 20±5%, most preferably 20% of the maximum possible amount of H2 for full-load operation (100% of the nominal load of the plant).

[0151] In preferred embodiments, below the threshold value (e.g. A sinkt , A rises, B sinkt , B rises, C sinkt , C rises, D sinktor Dincreases) the reactant gas stream is introduced as such into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; and wherein the reactant gas stream is interrupted for all the remaining NH3 synthesis units, so that in step (d) no NH3 is synthesized in any of the remaining NH3 synthesis units. Preferably, the above-mentioned threshold values ​​(e.g. the threshold values ​​Dincreases and Dincreases) are then independently 20±15%, more preferably 20±10%, even more preferably 20±5%, most preferably 20% of the maximum possible amount of H2 for full-load operation (100% of the nominal load of the plant).

[0152] In preferred embodiments, the throughput of the reactant gas stream, which is introduced as such into the individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the individual NH3 synthesis units with a reduced throughput (partial load operation).

[0153] In preferred embodiments, below the threshold value (e.g., A rises or falls, A , B falls, B rises, C falls, C rises, D falls or D rises), the reactant gas flow for all of the NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in any of the NH3 synthesis units.

[0154] In preferred embodiments of the method according to the invention, at least one of the above-mentioned pairs of threshold values, e.g. A rises rises rises falls and A , B falls and B , C falls and C , or D rises falls d D is fixed for the amount of H2 and the control of the method according to the invention is carried out on the basis of these two threshold values, which are preferably each independently of one another (i) 20±15%, more preferably 20±10%, even more preferably 20±5%, most preferably 20%; (ii) 25±15%, more preferably 25±10%, even more preferably 25±5%, most preferably 25%; (iii) 33±15%, more preferably 33±10%, even more preferably 33±5%, most preferably 33%; (iv) 50±15%, more preferably 50±10%, even more preferably 50±5%, most preferably 50%; or (v) 67±15%, more preferably 67±10%, even more preferably 67±5%, most preferably 67% the maximum possible amount of H2 for full load operation (100% of the nominal load of the plant).

[0155] In preferred embodiments - during a first time interval, the reactant gas stream is introduced as such or as a partial stream thereof into at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the at least one of the NH3 synthesis units; wherein the reactant gas stream is interrupted for at least one other of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the at least one other of the NH3 synthesis units, as a result of which the at least one other of the NH3 synthesis units cools; - during a second time interval, which immediately follows the first time interval, process heat is transferred from the at least one of the NH3 synthesis units to the at least one other of the NH3 synthesis units, as a result of which the at least one other of the NH3 synthesis units is heated;and - during a third time interval, which immediately follows the second time interval, the reactant gas stream is divided into independent partial streams and introduced into the at least one of the NH3 synthesis units and into the at least one other of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the at least one of the NH3 synthesis units and in the at least one other of the NH3 synthesis units. ;

[0156] In preferred embodiments, the first time interval ends and the second time interval begins as soon as the temperature of the at least one other of the NH3 synthesis units falls below a specified first threshold value; and wherein the second time interval ends and the third time interval begins as soon as the temperature of the at least one other of the NH3 synthesis units exceeds a specified second threshold value.

[0157] In preferred embodiments - during a first time interval, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; wherein the reactant gas stream is interrupted for all the remaining NH3 synthesis units, so that in step (d) no NH3 is synthesized in any of the remaining NH3 synthesis units, as a result of which all the remaining NH3 synthesis units cool down; - during a second time interval, which immediately follows the first time interval, process heat is transferred from the single one of the NH3 synthesis units to all the remaining NH3 synthesis units, as a result of which all the remaining NH3 synthesis units are heated;and - during a third time interval, which immediately follows the second time interval, the reactant gas stream is divided into independent partial streams and introduced into the individual NH3 synthesis units as well as into all the remaining NH3 synthesis units, so that in step (d) in the individual; of the NH3 synthesis units as well as in all other NH3 synthesis units.

[0158] In preferred embodiments, the first time interval ends and the second time interval begins as soon as the temperature of all the remaining NH3 synthesis units falls below a predetermined first threshold value (e.g., a threshold value E); and wherein the second time interval ends and the third time interval begins as soon as the temperature of all the remaining NH3 synthesis units exceeds a predetermined second threshold value (e.g., a threshold value F).

[0159] In preferred embodiments, the multiple NH3 synthesis units connected in parallel are operated in a revolving manner.

[0160] In preferred embodiments - during a first time interval, the reactant gas stream is introduced as such into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; wherein the reactant gas stream is interrupted for all the remaining NH3 synthesis units, so that in step (d) no NH3 is synthesized in the all the remaining NH3 synthesis units, as a result of which all the remaining NH3 synthesis units cool down; and - during a second time interval, which immediately follows the first time interval, the reactant gas stream is introduced as such into another one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the other one of the NH3 synthesis units, as a result of which the other one of the NH3 synthesis units is heated;wherein the reactant gas flow for all remaining NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, whereby all remaining NH3 synthesis units cool down. ;

[0161] Preferably, during a third time interval, which immediately follows the second time interval, the reactant gas stream as such is introduced into a further individual one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the further individual one of the NH3 synthesis units, whereby the further individual one of the NH3 synthesis units is heated; wherein the reactant gas stream for all the remaining NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in any of the remaining NH3 synthesis units, whereby all the remaining NH3 synthesis units cool down.

[0162] In preferred embodiments - during the first time interval, the throughput of the reactant gas stream, which is introduced as such into the individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the individual NH3 synthesis units with reduced throughput (partial load operation); and / or - during the second time interval, the throughput of the reactant gas stream, which is introduced as such into the other individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the other individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the other individual NH3 synthesis units at a reduced throughput (partial load operation); and / or - optionally during the third time interval, the throughput of the reactant gas stream, which is introduced as such into the further individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the further individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the further individual NH3 synthesis units at a reduced throughput (partial load operation).

[0163] Preferably, the first time interval, the second time interval and, if applicable, the third time interval are selected such that the temperature in none of the NH3 synthesis units falls below the minimum start-up temperature for the synthesis of NH3 from H2 and N2.

[0164] Preferably, the NH3 synthesis units are arranged in a common pressure vessel.

[0165] Preferably, the NH3 synthesis units are subjected to uniform flow from the reactant gas stream as such, separately and one after the other.

[0166] Preferably, the NH3 synthesis units are in heat exchange with one another, so that - during the first time interval, a heat flow flows from the individual NH3 synthesis units into one or more of the remaining NH3 synthesis units; and / or - during the second time interval, a heat flow flows from the other individual NH3 synthesis units into one or more of the remaining NH3 synthesis units; and / or - optionally during the third time interval, a heat flow flows from the further individual NH3 synthesis units into one or more of the remaining NH3 synthesis units.

[0167] In preferred embodiments, the plurality of NH3 synthesis units comprise a first NH3 synthesis unit and a second NH3 synthesis unit; wherein - during a first time interval, the reactant gas flow for the first NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d); and - during a second time interval, which immediately follows the first time interval, the reactant gas flow for the second NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d).

[0168] Preferably, during the first time interval and during the second time interval, the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units.

[0169] Preferably, during the first time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the second NH3 synthesis unit, so that in step (d) NH3 is synthesized in the second NH3 synthesis unit.

[0170] Preferably, the throughput of the reactant gas stream, which is introduced as such or as a partial stream thereof into the second NH3 synthesis unit, is reduced compared to the maximum possible throughput for the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit with a reduced throughput (partial load operation).

[0171] Preferably, during the second time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit.

[0172] Preferably, the throughput of the reactant gas stream, which is introduced as such or as a partial stream thereof into the first NH3 synthesis unit, is reduced compared to the maximum possible throughput for the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit with a reduced throughput (partial load operation).

[0173] In preferred embodiments - during the first time interval, the first NH3 synthesis unit cools down; wherein the first time interval ends and the second time interval begins as soon as the temperature of the first NH3 synthesis unit falls below a specified threshold value (e.g. a threshold value G); and - during the second time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit and the temperature of the first NH3 synthesis unit rises again.

[0174] In preferred embodiments, the plurality of NH3 synthesis units comprise a first NH3 synthesis unit, a second NH3 synthesis unit, and a third NH3 synthesis unit; and - during a first time interval, the reactant gas flow for the first NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d); and - during a second time interval, which immediately follows the first time interval, the reactant gas flow for the second NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d); and - during a third time interval, which immediately follows the second time interval, the reactant gas flow for the third NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the third NH3 synthesis unit in step (d).

[0175] Preferably, during the first time interval, during the second time interval and during the third time interval, the reactant gas flow is not simultaneously for all of the NH3 synthesis units are interrupted, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units.

[0176] In preferred embodiments, the reactant gas stream is introduced alternately into an individual NH3 synthesis unit during the first time interval, the second time interval, and the third time interval, so that none of the NH3 synthesis units cools down too much, preferably so that the temperature in none of the NH3 synthesis units drops below the respective start-up temperature. By introducing the reactant gas stream into an individual NH3 synthesis unit, the temperature rises again, whereas in the remaining NH3 synthesis units, into which no reactant gas stream is then temporarily introduced, the temperature drops.

[0177] In the case of alternating introduction of the reactant gas stream into a single one of the NH3 synthesis units, the change preferably takes place starting from the one of the NH3 synthesis units which has the highest temperature at the time of the change to the one of the NH3 synthesis units which has the lowest temperature at the time of the change.

[0178] Preferably, the NH3 synthesis units are each configured such that the short-term heating rate when the reactant gas flow is introduced is significantly faster than the cooling rate when the reactant gas flow is interrupted. The heating rate is preferably at least twice as fast as the cooling rate, more preferably at least three times as fast. The heating preferably lasts very briefly, typically only a few minutes, after which the temperature preferably remains constant.

[0179] In preferred embodiments, the reactant gas stream is introduced into the second NH3 synthesis unit as such or as a partial stream thereof during the first time interval, so that NH3 is synthesized in the second NH3 synthesis unit in step (d). In other preferred embodiments, the reactant gas stream for the second NH3 synthesis unit is interrupted during the first time interval, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d).

[0180] In preferred embodiments, the reactant gas stream is introduced into the third NH3 synthesis unit as such or as a partial stream thereof during the first time interval, so that NH3 is synthesized in the third NH3 synthesis unit in step (d). In other preferred embodiments, the reactant gas stream for the third NH3 synthesis unit is interrupted during the first time interval, so that no NH3 is synthesized in the third NH3 synthesis unit in step (d).

[0181] In preferred embodiments, during the second time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit in step (d). In other preferred embodiments, the reactant gas stream for the first NH3 synthesis unit is interrupted during the second time interval, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d).

[0182] In preferred embodiments, during the second time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the third NH3 synthesis unit, so that in step (d) NH3 is synthesized in the third NH3 synthesis unit. In other preferred embodiments, the reactant gas flow for the third NH3 synthesis unit is interrupted during the second time interval, so that no NH3 is synthesized in the third NH3 synthesis unit in step (d).

[0183] In preferred embodiments, during the third time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit in step (d). In other preferred embodiments, the reactant gas stream for the first NH3 synthesis unit is interrupted during the third time interval, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d).

[0184] In preferred embodiments, during the third time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit in step (d). In other preferred embodiments, the reactant gas stream for the second NH3 synthesis unit is interrupted during the third time interval, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d).

[0185] In preferred embodiments - during the first time interval, the reactant gas flow for the first NH3 synthesis unit and for the second NH3 synthesis unit is interrupted in each case, so that in step (d) no NH3 is synthesized in the first NH3 synthesis unit and in the second NH3 synthesis unit; wherein the reactant gas flow as such is introduced into the third NH3 synthesis unit, so that NH3 is synthesized in the third NH3 synthesis unit; - during the second time interval, the reactant gas flow for the second NH3 synthesis unit and for the third NH3 synthesis unit is interrupted in each case, so that in step (d) no NH3 is synthesized in the second NH3 synthesis unit and in the third NH3 synthesis unit; wherein the reactant gas stream as such is introduced into the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit;and - during the third time interval, the reactant gas flow for the third NH3 synthesis unit and for the first NH3 synthesis unit is interrupted, so that in step (d) no NH3 is synthesized in the third NH3 synthesis unit and in the first NH3 synthesis unit; wherein the reactant gas flow as such is introduced into the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit. ;

[0186] In preferred embodiments - during the first time interval, the throughput of the reactant gas stream, which is introduced as such into the third NH3 synthesis unit, is reduced compared to the maximum possible throughput for the third NH3 synthesis unit, so that NH3 is synthesized in the third NH3 synthesis unit with a reduced throughput (partial load operation); and / or - during the second time interval, the throughput of the reactant gas stream, which is introduced as such into the first NH3 synthesis unit, is reduced compared to the maximum possible throughput for the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit at a reduced throughput (partial load operation); and / or - during the third time interval, the throughput of the reactant gas stream, which is introduced as such into the second NH3 synthesis unit, is reduced compared to the maximum possible throughput for the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit at a reduced throughput (partial load operation).

[0187] In preferred embodiments - during the first time interval, the first NH3 synthesis unit and the second NH3 synthesis unit cool down; wherein the first time interval ends and the second time interval begins as soon as the temperature of the first NH3 synthesis unit falls below a specified threshold value (e.g., a threshold value H); - during the second time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit and the temperature of the first NH3 synthesis unit rises again; wherein during the second time interval, the second NH3 synthesis unit and the third NH3 synthesis unit cool down; and wherein the second time interval ends and the third time interval begins as soon as the temperature of the second NH3 synthesis unit falls below a specified threshold value (e.g.,a threshold value I); and - during the third time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the second NH3 synthesis unit, so that in step (d) NH3 is synthesized in the second NH3 synthesis unit and the temperature of the second NH3 synthesis unit rises again; wherein during the third time interval, the third NH3 synthesis unit and the first NH3 synthesis unit cool down; and wherein the third time interval ends as soon as the temperature of the third NH3 synthesis unit falls below a specified threshold value (e.g. a threshold value J).

[0188] In preferred embodiments of the method according to the invention, the above-mentioned threshold value H is defined for the temperature of the first NH3 synthesis unit, the above-mentioned threshold value I is defined for the temperature of the second NH3 synthesis unit and the above-mentioned threshold value J is defined for the temperature of the third NH3 synthesis unit, wherein the control of the method according to the invention is carried out on the basis of these threshold values, and wherein each of these threshold values ​​is preferably each independently of one another at least 10°C, more preferably at least 20°C, even more preferably at least 30°C, most preferably at least 40°C above the respective light-off temperature of the first, second or third NH3 synthesis unit.

[0189] Preferably, the first time interval, the second time interval, and the third time interval each independently comprise at least 15 minutes, more preferably at least 30 minutes, even more preferably at least 45 minutes, and most preferably at least 1 hour. Preferably, the first time interval, the second time interval, and the third time interval each independently comprise at most 24 hours, more preferably at most 18 hours, even more preferably at most 12 hours, and most preferably at most 6 hours.

[0190] A further aspect of the invention relates to a plant for the synthesis of NH3 at variable throughput, the plant comprising: - a device configured to provide H2 by electrolysis of H2O with electrical power from renewable energy; - a device configured to provide a reactant gas stream comprising the H2; preferably in a mixture with N2; - a plurality of parallel-connected NH3 synthesis units configured to synthesize NH3 from H2 and N2; and - a device configured to introduce the reactant gas stream, depending on the currently available amount of H2 - as such into a single one of the NH3 synthesis units; or - divided into independent partial streams into a plurality of the NH3 synthesis units or into all of the NH3 synthesis units.

[0191] Preferably, the plant comprises three NH3 synthesis units connected in parallel, preferably not more than three NH3 synthesis units connected in parallel.

[0192] Preferably, the NH3 synthesis units have essentially the same structure.

[0193] Preferably, each of the NH3 synthesis units is arranged separately in its own pressure vessel.

[0194] Preferably, the NH3 synthesis units are arranged in a common pressure vessel.

[0195] Preferably, the NH3 synthesis units are in heat exchange with each other.

[0196] Preferably, each of the NH3 synthesis units contains at least one catalyst bed; preferably, the catalyst bed can be axially flowed against by the reactant gas stream.

[0197] Preferably, each of the NH3 synthesis units contains only a single catalyst bed; preferably, the catalyst bed can be flowed against axially by the reactant gas stream.

[0198] The system according to the invention is preferably configured to carry out the method according to the invention described above.

[0199] Particularly preferred embodiments of the invention are summarized below as Sentence 1 to Sentence 81: Sentence 1: A process for the synthesis of NH3 at variable throughput in a plant comprising a plurality of NH3 synthesis units connected in parallel, the process comprising the steps of: (a) providing H2 by electrolysis of H2O using electrical current from renewable energy; (b) providing a reactant gas stream comprising the H2; (c) introducing the reactant gas stream as a function of the currently available amount of H2 as such into a single one of the NH3 synthesis units; or - divided into independent partial streams into a plurality of the NH3 synthesis units or into all of the NH3 synthesis units, wherein a plurality of NH3 synthesis units orone of the partial streams is introduced into each of the NH3 synthesis units independently of one another; and (d) synthesizing NH3 from H2 and N2 in one, in several or in all of the NH3 synthesis units into which the reactant gas stream or a partial stream thereof is introduced in step (c). Sentence 2: The process according to sentence 1, wherein the plant comprises three NH3 synthesis units connected in parallel; preferably no more than three NH3 synthesis units connected in parallel. Sentence 3: The process according to one of the preceding sentences, wherein the NH3 synthesis units each have essentially the same structure. Sentence 4: The process according to one of the preceding sentences, wherein each of the NH3 synthesis units is arranged separately in its own pressure vessel. Sentence 5: The process according to one of sentences 1 to 3, wherein the NH3 synthesis units are arranged in a common pressure vessel.Sentence 6: The process according to one of the preceding sentences, wherein the NH3 synthesis units are in heat exchange with one another. Sentence 7: The process according to one of the preceding sentences, wherein each of the NH3 synthesis units contains at least one catalyst bed; preferably wherein the reactant gas stream flows axially against the catalyst bed. Sentence 8: The process according to one of the preceding sentences, wherein each of the NH3 synthesis units contains only a single catalyst bed; preferably wherein the reactant gas stream flows axially against the catalyst bed. Sentence 9: The process according to one of the preceding sentences, wherein in step (a) the electrical power is generated from wind power; preferably wherein the currently available amount of H2 depends on the current availability of wind power.Sentence 10: The process according to any one of the preceding sentences, wherein in step (a) the electrical power is generated from hydropower; preferably wherein the currently available amount of H2 depends on the current availability of hydropower. Sentence 11: The process according to one of the preceding sentences, wherein in step (a) the electrical power is generated from solar energy; preferably wherein the currently available amount of H2 depends on the current availability of solar energy. Sentence 12: The process according to one of the preceding sentences, wherein step (a) comprises the temporary storage of electrical power from renewable energy; preferably in an accumulator. Sentence 13: The process according to one of the preceding sentences, wherein step (a) comprises the temporary storage of H2; preferably in a tank. Sentence 14: The process according to one of the preceding sentences, wherein in step (b) the reactant gas stream is provided with a throughput depending on the currently available amount of H2. Sentence 15: The process according to one of the preceding sentences, wherein the reactant gas stream provided in step (b) comprises N2 in addition to H2; preferably consists essentially of H2 and N2, or preferably comprises H2, N2 and NH3.Sentence 16: The process according to any one of the preceding sentences, wherein step (b) comprises compressing the reactant gas stream to elevated pressure, preferably to a pressure of at least 150 bar. Sentence 17: The process according to any one of the preceding sentences, wherein step (b) comprises heating the reactant gas stream to elevated temperature, preferably to a temperature of at least 300°C. Sentence 18: The process according to any one of the preceding sentences, wherein step (c) comprises the substeps: (c1) determining the currently available amount of H2; (c2) comparing the determined currently available amount of H2 with a specified threshold value for the amount of H2.Sentence 19: The method according to one of the preceding sentences, wherein in step (c) a threshold value Bsinkt and a threshold value Bsteigt are specified for the amount of H2; wherein - firstly the reactant gas stream is divided into independent sub-streams and the sub-streams are introduced into several or all of the NH3 synthesis units; and wherein in the event of a decrease in the instantaneous availability of H2 and the threshold value Bsinkt being undershot, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units; or - firstly the reactant gas stream as such is introduced into a single one of the NH3 synthesis units; and wherein in the event of an increase in the instantaneous availability of H2 and the threshold value B is exceeded, the reactant gas stream is divided into independent sub-streams and the sub-streams are introduced into several or all of the NH3 synthesis units.Sentence 20: The process according to any one of the preceding sentences, wherein each of the NH3 synthesis units is independently characterized by a maximum possible throughput of the reactant gas stream or of the partial stream and is operable either at full load or at part load, wherein the throughput of the reactant gas stream or of the partial stream thereof is - undiminished at full load and - reduced at part load compared to the maximum possible throughput. Sentence 21: The method according to any one of the preceding sentences, wherein in step (c) a threshold value C sinktand a threshold value C rises are defined, wherein - initially the throughput of the reactant gas stream or the partial stream thereof, which is fed into at least one of the NH3 synthesis units, is undiminished compared to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units with undiminished throughput (full load operation); and wherein in the event of a decrease in the instantaneous availability of H2 and falling below the threshold value C sinktthe throughput of the reactant gas stream or the partial stream thereof, which is introduced into this at least one of the NH3 synthesis units, is reduced compared to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units at a reduced throughput (partial load operation); or - initially the throughput of the reactant gas stream or the partial stream thereof, which is introduced into at least one of the NH3 synthesis units, is reduced compared to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units at a reduced throughput (partial load operation); and wherein in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value C, the throughput of the reactant gas stream or the partial stream thereof increases,which is fed into at least one of the NH3 synthesis units, is reduced in comparison to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units with an unreduced throughput (full load operation). Sentence 22: The method according to sentence 21, wherein below the threshold values ​​C increases decreases and C the throughput of the reactant gas stream, which is divided into independent partial streams and is introduced into a plurality of the NH3 synthesis units, is reduced in each case independently of one another compared to the respective maximum possible throughput for the plurality of NH3 synthesis units, so that in step (d) NH3 is synthesized in the plurality of NH3 synthesis units with a reduced throughput (partial load operation). Sentence 23: The process according to sentence 21 or 22, where below the threshold values ​​C increases decreases and C is the throughput of the reactant gas stream,which is introduced into all the NH3 synthesis units, divided into independent partial streams, is reduced independently of each other compared to the maximum possible throughput for all the NH3 synthesis units, so that in step (d) NH3 is synthesized in all NH3 synthesis units with reduced throughput (partial load operation). Sentence 24: The method according to one of the preceding sentences, wherein in step (c) a threshold value D is set for the amount of H2, sinkt and a threshold value D rises are specified; wherein - first, the reactant gas stream is divided into independent substreams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and wherein in the event of a decrease in the current availability of H2 and falling below the threshold value D sinkt the The reactant gas flow for at least one of the NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in the at least one of the NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units; or - initially the reactant gas flow for at least one of the NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in the at least one of the NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units;and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value D, the reactant gas stream is divided into independent substreams and passed into all of the NH3 synthesis units, so that NH3 is synthesized in all of the NH3 synthesis units in step (d). Sentence 25: The process according to sentence 24, wherein in step (c) a threshold value is set for the amount of H2; and a threshold value D rises are specified; wherein - firstly, the reactant gas stream is divided into independent partial streams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and wherein in the event of a decrease in the instantaneous availability of H2 and the threshold value D sinks, the reactant gas stream is interrupted for several of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the several of the NH3 synthesis units; preferably with the proviso that the reactant gas stream is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units; or - initially the reactant gas flow for several of the NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in the several of the NH3 synthesis units;preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units; and wherein in the event of an increase in the instantaneous availability of H and exceeding the threshold value D, the reactant gas flow is divided into independent substreams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units. Sentence 26: The process according to sentence 24 or 25, wherein - firstly the reactant gas flow is divided into independent substreams and passed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and wherein in the event of a decrease in the instantaneous availability of H2 and falling below the threshold value D; sinktthe reactant gas stream is introduced as such into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; and wherein the reactant gas stream is interrupted for all the remaining NH3 synthesis units, so that in step (d) no NH3 is synthesized in all the remaining NH3 synthesis units; or - initially the reactant gas stream is interrupted for all but one of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in all but one of the NH3 synthesis units NH3 is synthesized; and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value D, the reactant gas stream is divided into independent partial streams and fed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units. Sentence 27: The method according to sentence 26, wherein the throughput of the reactant gas stream, which is introduced as such into the individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the individual NH3 synthesis units, so that in step (d) NH3 is synthesized with a reduced throughput in the individual NH3 synthesis units (partial load operation). Sentence 28: The method according to one of sentences 24 to 27, wherein below the threshold values ​​D sinktand D rises, the reactant gas flow is interrupted for all of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in any of the NH3 synthesis units. Sentence 29: The process according to one of the preceding sentences, wherein - during a first time interval, the reactant gas flow as such or as a partial flow thereof is introduced into at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the at least one of the NH3 synthesis units; wherein the reactant gas flow is interrupted for at least one other of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the at least one other of the NH3 synthesis units, whereby the at least one other of the NH3 synthesis units cools down;- during a second time interval, which immediately follows the first time interval, process heat is transferred from the at least one of the NH3 synthesis units to the at least one other of the NH3 synthesis units, whereby the at least one other of the NH3 synthesis units is heated; and - during a third time interval, which immediately follows the second time interval, the reactant gas stream is divided into independent partial streams and introduced into the at least one of the NH3 synthesis units and into the at least one other of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the at least one of the NH3 synthesis units and in the at least one other of the NH3 synthesis units. Sentence 30: The method according to sentence 29, wherein the first time interval ends and the second time interval begins as soon as the temperature of the at least one other of the NH3 synthesis units falls below a specified first threshold value;and wherein the second time interval ends and the third time interval begins as soon as the temperature of the at least one other of the NH3 synthesis units exceeds a specified second threshold value. Sentence 31: The method according to one of the preceding sentences, wherein - during a first time interval, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; wherein the reactant gas stream for all remaining NH3 synthesis units is interrupted so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, as a result of which all remaining NH3 synthesis units cool down; - during a second time interval which immediately follows the first; time interval follows, process heat is transferred from the individual NH3 synthesis units to all the remaining NH3 synthesis units, whereby all the remaining NH3 synthesis units are heated; and - during a third time interval, which immediately follows the second time interval, the reactant gas stream is divided into independent substreams and introduced into the individual NH3 synthesis units and into all the remaining NH3 synthesis units, so that in step (d) NH3 is synthesized in the individual NH3 synthesis units and in all the remaining NH3 synthesis units. Sentence 32: The method according to sentence 31, wherein the first time interval ends and the second time interval begins as soon as the temperature of all the remaining NH3 synthesis units falls below a specified first threshold value;and wherein the second time interval ends and the third time interval begins as soon as the temperature of all the remaining NH3 synthesis units exceeds a specified second threshold value. Sentence 33: The method according to one of the preceding sentences, wherein the plurality of parallel-connected NH3 synthesis units are operated in a revolving manner. Sentence 34: The method according to one of the preceding sentences, wherein - during a first time interval, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; wherein the reactant gas stream for all the remaining NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in all the remaining NH3 synthesis units, whereby all the remaining NH3 synthesis units cool down;- during a second time interval, which immediately follows the first time interval, the reactant gas stream as such is introduced into another individual one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the other individual one of the NH3 synthesis units, whereby the other individual one of the NH3 synthesis units is heated;wherein the reactant gas flow for all remaining NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, whereby all remaining NH3 synthesis units cool down. Sentence 35: The process according to sentence 34, wherein - during a third time interval, which immediately follows the second time interval, the reactant gas flow as such is introduced into a further individual one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the further individual one of the NH3 synthesis units, whereby the further individual one of the NH3 synthesis units is heated;wherein the reactant gas flow for all remaining NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, whereby all remaining NH3 synthesis units cool down. Sentence 36: The process according to one of sentences 33 to 35, wherein - during the first time interval, the throughput of the reactant gas flow, which is introduced as such into the individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the individual NH3; synthesis units, so that in step (d) NH3 is synthesized at a reduced throughput in the individual NH3 synthesis units (partial load operation); and / or - during the second time interval, the throughput of the reactant gas stream, which is introduced as such into the other individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the other individual NH3 synthesis units, so that in step (d) NH3 is synthesized at a reduced throughput in the other individual NH3 synthesis units (partial load operation); and / or - if necessary.during the third time interval, the throughput of the reactant gas stream, which is introduced as such into the further individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the further individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the further individual NH3 synthesis units at a reduced throughput (partial load operation). Sentence 37: The process according to one of sentences 33 to 36, wherein the first time interval, the second time interval and optionally the third time interval are selected such that the temperature in none of the NH3 synthesis units falls below the minimum light-off temperature for the synthesis of NH3 from H2 and N2. Sentence 38: The process according to one of sentences 33 to 37, wherein the NH3 synthesis units are arranged in a common pressure vessel.Sentence 39: The process according to sentence 38, wherein the NH3 synthesis units are uniformly flowed over by the reactant gas stream as such, separately and one after the other. Sentence 40: The process according to one of sentences 33 to 39, wherein the NH3 synthesis units are in heat exchange with one another, so that - during the first time interval, a heat flow flows from the individual NH3 synthesis units into one or more of the remaining NH3 synthesis units; and / or - during the second time interval, a heat flow flows from the other individual NH3 synthesis units into one or more of the remaining NH3 synthesis units; and / or - optionally during the third time interval, a heat flow flows from the further individual NH3 synthesis units into one or more of the remaining NH3 synthesis units.Sentence 41: The method according to any one of the preceding sentences, wherein the plurality of NH3 synthesis units comprise a first NH3 synthesis unit and a second NH3 synthesis unit; and wherein - during a first time interval, the reactant gas flow for the first NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d); and - during a second time interval, which immediately follows the first time interval, the reactant gas flow for the second NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d). Sentence 42: The process according to sentence 41, wherein during the first time interval and during the second time interval the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units. Sentence 43: The process according to sentence 41 or 42, wherein during the first time interval, the reactant gas stream is introduced as such or as a partial stream thereof into the second NH3 synthesis unit, so that in step (d) NH3 is synthesized in the second NH3 synthesis unit. Sentence 44: The process according to sentence 43, wherein the throughput of the reactant gas stream, which is introduced as such or as a partial stream thereof into the second NH3 synthesis unit, is reduced compared to the maximum possible throughput for the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit at a reduced throughput (partial load operation). Sentence 45: The process according to any one of sentences 41 to 44, wherein during the second time interval the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit.Sentence 46: The process according to sentence 45, wherein the throughput of the reactant gas stream which is introduced as such or as a partial stream thereof into the first NH3 synthesis unit is reduced compared to the maximum possible throughput for the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit with a reduced throughput (partial load operation).Sentence 47: The method according to one of sentences 41 to 46, wherein - during the first time interval the first NH3 synthesis unit cools down; wherein the first time interval ends and the second time interval begins as soon as the temperature of the first NH3 synthesis unit falls below a specified threshold value; and - wherein during the second time interval the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit and the temperature of the first NH3 synthesis unit rises again.Sentence 48: The method according to any one of the preceding sentences, wherein the plurality of NH3 synthesis units comprise a first NH3 synthesis unit, a second NH3 synthesis unit, and a third NH3 synthesis unit; and wherein - during a first time interval, the reactant gas flow for the first NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d); and - during a second time interval, which immediately follows the first time interval, the reactant gas flow for the second NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d); and - during a third time interval, which immediately follows the second time interval, the reactant gas flow for the third NH3 synthesis unit is interrupted, so that in step (d) no NH3 is synthesized in the third NH3 synthesis unit.Sentence 49: The process according to sentence 48, wherein during the first time interval, during the second time interval and during the third time interval the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units. Sentence 50: The process according to sentence 48 or 49, wherein during the first time interval the reactant gas stream is introduced as such or as a partial stream thereof into the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit in step (d). Sentence 51: The process according to sentence 49 or 49, wherein during the first time interval the reactant gas stream for the second NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the second NH3 synthesis unit in step (d). Sentence 52: The process according to one of sentences 48 to 51, wherein during the first time interval the reactant gas stream is introduced as such or as a partial stream thereof into the third NH3 synthesis unit, so that NH3 is synthesized in the third NH3 synthesis unit in step (d).Sentence 53: The process according to any one of sentences 48 to 51, wherein during the first time interval the reactant gas flow for the third NH3 synthesis unit is interrupted, so that in step (d) no NH3 is synthesized in the third NH3 synthesis unit. Sentence 54: The process according to any one of sentences 48 to 53, wherein during the second time interval the reactant gas flow as such or as a partial flow thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit. Sentence 55: The process according to any one of sentences 48 to 53, wherein during the second time interval the reactant gas flow for the first NH3 synthesis unit is interrupted, so that in step (d) no NH3 is synthesized in the first NH3 synthesis unit.Sentence 56: The process according to any one of sentences 48 to 55, wherein during the second time interval the reactant gas stream is introduced as such or as a partial stream thereof into the third NH3 synthesis unit, so that NH3 is synthesized in the third NH3 synthesis unit in step (d). Sentence 57: The process according to any one of sentences 48 to 55, wherein during the second time interval the reactant gas stream for the third NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the third NH3 synthesis unit in step (d). Sentence 58: The process according to any one of sentences 48 to 57, wherein during the third time interval the reactant gas stream is introduced as such or as a partial stream thereof into the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit in step (d).Sentence 59: The process according to any one of sentences 48 to 57, wherein during the third time interval, the reactant gas stream for the first NH3 synthesis unit is interrupted, so that no NH3 is synthesized in the first NH3 synthesis unit in step (d). Sentence 60: The process according to any one of sentences 48 to 59, wherein during the third time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit in step (d). Sentence 61: The method according to any one of sentences 48 to 59, wherein during the third time interval, the reactant gas flow for the second NH3 synthesis unit is interrupted, so that in step (d) no NH3 is synthesized in the second NH3 synthesis unit. Sentence 62: The method according to any one of sentences 48 to 61, wherein - during the first time interval, the reactant gas flow for the first NH3 synthesis unit and for the second NH3 synthesis unit is interrupted, so that in step (d) no NH3 is synthesized in the first NH3 synthesis unit and in the second NH3 synthesis unit; and wherein the reactant gas flow as such is introduced into the third NH3 synthesis unit, so that NH3 is synthesized in the third NH3 synthesis unit;- during the second time interval, the reactant gas flow for the second NH3 synthesis unit and for the third NH3 synthesis unit is interrupted in each case, so that in step (d) no NH3 is synthesized in the second NH3 synthesis unit and in the third NH3 synthesis unit; and wherein the reactant gas flow as such is introduced into the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit; and - during the third time interval, the reactant gas flow for the third NH3 synthesis unit and for the first NH3 synthesis unit is interrupted in each case, so that in step (d) no NH3 is synthesized in the third NH3 synthesis unit and in the first NH3 synthesis unit;and wherein the reactant gas stream is introduced as such into the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit. Sentence 63: The method according to sentence 62, wherein - during the first time interval, the throughput of the reactant gas stream, which is introduced as such into the third NH3 synthesis unit, is reduced compared to the maximum possible throughput for the third NH3 synthesis unit, so that NH3 is synthesized in the third NH3 synthesis unit with a reduced throughput (partial load operation); and / or - during the second time interval, the throughput of the reactant gas stream, which is introduced as such into the first NH3 synthesis unit, is reduced compared to the maximum possible throughput for the first NH3 synthesis unit, so that NH3 is synthesized in the first NH3 synthesis unit with a reduced throughput (partial load operation);and / or - during the third time interval, the throughput of the reactant gas stream, which is introduced as such into the second NH3 synthesis unit, is reduced compared to the maximum possible throughput for the second NH3 synthesis unit, so that NH3 is synthesized in the second NH3 synthesis unit at a reduced throughput (partial load operation). Sentence 64: The method according to sentence 62 or 63, wherein - during the first time interval, the first NH3 synthesis unit and the second NH3 synthesis unit cool down; wherein the first time interval ends and the second time interval begins as soon as the temperature of the first NH3 synthesis unit falls below a specified threshold value; - during the second time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the first NH3 synthesis unit, so that in step (d) NH3 is synthesized in the first NH3 synthesis unit and the temperature of the first NH3 synthesis unit rises again;wherein during the second time interval, the second NH3 synthesis unit and the third NH3 synthesis unit cool down; and wherein the second time interval ends and the third time interval; begins as soon as the temperature of the second NH3 synthesis unit falls below a specified threshold value; and - during the third time interval, the reactant gas stream as such or as a partial stream thereof is introduced into the second NH3 synthesis unit, so that in step (d) NH3 is synthesized in the second NH3 synthesis unit and the temperature of the second NH3 synthesis unit rises again; wherein during the third time interval, the third NH3 synthesis unit and the first NH3 synthesis unit cool down; and wherein the third time interval ends as soon as the temperature of the third NH3 synthesis unit falls below a specified threshold value.Sentence 65: A plant for the synthesis of NH3 at variable throughput, the plant comprising: - a device configured to provide H2 by electrolysis of H2O using electrical power from renewable energy; - a device configured to provide a reactant gas stream comprising the H2; - several NH3 synthesis units connected in parallel, configured to synthesize NH3 from H2 and N2; and - a device configured to introduce the reactant gas stream, depending on the currently available amount of H2, - as such into a single one of the NH3 synthesis units; or - divided into independent partial streams into several of the NH3 synthesis units or into all of the NH3 synthesis units. Sentence 66: The plant according to Sentence 65, which comprises three NH3 synthesis units connected in parallel. Sentence 67: The plant according to sentence 65 or 66, where the NH3 synthesis units have essentially the same structure.Sentence 68: The plant according to one of sentences 65 to 67, wherein each of the NH3 synthesis units is arranged separately in its own pressure vessel. Sentence 69: The plant according to one of sentences 65 to 68, wherein the NH3 synthesis units are arranged in a common pressure vessel. Sentence 70: The plant according to one of sentences 65 to 69, wherein the NH3 synthesis units are in heat exchange with one another. Sentence 71: The plant according to one of sentences 65 to 70, wherein each of the NH3 synthesis units contains at least one catalyst bed; preferably wherein the reactant gas stream can flow axially against the catalyst bed. Sentence 72: The plant according to one of sentences 65 to 71, wherein each of the NH3 synthesis units contains only a single catalyst bed; preferably wherein the reactant gas stream can flow axially against the catalyst bed.Clause 73: The plant according to any one of clauses 65 to 72, wherein a plurality of NH3 synthesis units, preferably exactly two NH3 synthesis units, more preferably exactly three NH3 synthesis units, are arranged in a common pressure vessel; wherein the plurality of NH3 synthesis units are preferably in heat exchange with one another. Sentence 74: The system according to sentence 73, wherein the common pressure vessel has a substantially circular cross-sectional area and thus a substantially cylindrical shape. Sentence 75: The system according to sentence 73 or 74, wherein the reactant gas flow can be introduced into the pressure vessel in the axial direction; preferably wherein targeted introduction into a single, several or all of the NH3 synthesis units is possible. Sentence 76: The system according to one of sentences 73 to 75, wherein the interior of the common pressure vessel is divided into several cylinder sectors, which preferably have substantially the same shape and size. Sentence 77: The system according to sentence 76, wherein one of the NH3 synthesis units is arranged in each of the cylinder sectors; preferably wherein the number of cylinder sectors corresponds to the number of NH3 synthesis units in the common pressure vessel.Sentence 78: The system according to sentence 76 or 77, wherein the cylinder sectors are delimited by walls that separate the NH3 synthesis units from one another. Sentence 79: The system according to sentence 78, wherein the walls are essentially gas-tight. Sentence 80: The system according to sentence 78 or 79, wherein heat can flow through the walls from one NH3 synthesis unit into an adjacent NH3 synthesis unit. Sentence 81: The system according to one of sentences 65 to 80, which is configured to carry out the method according to one of sentences 1 to 64.

[0200] Preferred embodiments are explained in more detail below with reference to Figures 1, 2, and 3. However, these explanations are not to be interpreted in a restrictive manner.

[0201] Figure 1 schematically shows a preferred embodiment of a plant according to the invention with a device (1) which is configured to introduce the reactant gas stream (H2 + N2) depending on the currently available amount of H2. Starting from the device (1), the reactant gas stream can be introduced as such or as a partial stream thereof via a first line (2) into a first NH3 synthesis unit (3), in which, in the case of such an introduction, the synthesis of NH3 from H2 and N2 takes place on a suitable catalyst. Starting from the device (1), the reactant gas stream can be introduced as such or as a partial stream thereof alternatively or additionally via a second line (4) into a second NH3 synthesis unit (5), in which, in the case of such an introduction, the synthesis of NH3 from H2 and N2 takes place on a suitable catalyst.Starting from the device (1), the reactant gas stream, as such or as a partial stream thereof, can alternatively or additionally be introduced via a third line (6) into a third NH3 synthesis unit (7), in which, in the case of such introduction, the synthesis of NH3 from H2 and N2 takes place over a suitable catalyst. The first NH3 synthesis unit (3), the second NH3 synthesis unit (5), and the third NH3 synthesis unit (7) are connected in parallel and, according to this embodiment, are each arranged in a separate pressure vessel.

[0202] Figure 2 schematically shows a preferred development of the embodiment according to Figure 1, wherein the first NH3 synthesis unit (3), the second NH3 synthesis unit (5), and the third NH3 synthesis unit (7) are also connected in parallel, but, unlike Figure 1, are arranged in a common pressure vessel. Figure 2A shows a perspective view, and Figure 2B a top view. The first NH3 synthesis unit (3), the second NH3 synthesis unit (5), and the third NH3 synthesis unit (7) are preferably in heat exchange with one another. Preferably, in the case of reduced availability of H2, the reactant gas stream as such is always introduced into only one of the NH3 synthesis units (3), (5) and (7) and after a certain time is changed by revolving operation from one of the NH3 synthesis units (3), (5) and (7) to the next of the NH3 synthesis units (3), (5) and (7).

[0203] Figure 3 schematically shows another preferred embodiment of a plant according to the invention with a first NH3 synthesis unit (3), a second NH3 synthesis unit (5), and a third NH3 synthesis unit (7), which are connected in parallel. As long as all three NH3 synthesis units (3), (5), and (7) are producing NH3, the gas mixture leaving the three NH3 synthesis units (3), (5), and (7) is cooled in one or more heat exchangers (11), then in a gas-gas heat exchanger (8) and in a further cooling section (9), after which the NH3 is subsequently condensed and removed. The remaining cycle gas together with the fresh gas (H2 + N2) is compressed in a compressor (10) and, after warming up in the gas-gas heat exchanger (8), is fed to the NH3 synthesis units (3), (5) and (7) via valves (12a-c).

[0204] If, for example, the two valves (12a) and (12c) are closed and the valve (12b) remains open, the reactant gas stream is introduced as such into the NH3 synthesis unit (5). The heat generated in the NH3 synthesis unit (5) can be used to warm up the other two NH3 synthesis units (3) and (7), which would otherwise cool down. For this purpose, the gas mixture leaving the NH3 synthesis unit (5) can be recirculated, optionally as a partial stream, via the valves (13a-c) and (14a-c) to the NH3 synthesis units (3) and (7), which are not currently receiving a reactant gas stream.

[0205] List of reference symbols: 1 Device configured to introduce the reactant gas flow depending on the currently available amount of H2 2 First line 3 First NH3 synthesis unit 4 Second line 5 Second NH3 synthesis unit 6 Third line third NH3 synthesis unit gas-gas heat exchanger cooling section compressor heat exchanger ac valves ac valves ac valves

Claims

Patent claims:

1. A process for the synthesis of NH3 at variable throughput in a plant comprising a plurality of NH3 synthesis units connected in parallel, preferably three NH3 synthesis units connected in parallel, the process comprising the steps of: (a) providing H2 by electrolysis of H2O using electrical power from renewable energy; (b) providing a reactant gas stream comprising the H2; (c) introducing the reactant gas stream, depending on the currently available amount of H2 as such, into a single one of the NH3 synthesis units; or - divided into independent sub-streams into a plurality of the NH3 synthesis units or into all of the NH3 synthesis units, wherein one of the sub-streams is introduced independently of one another into each of the plurality of NH3 synthesis units or into all of the NH3 synthesis units; and (d) synthesizing NH3 from H2 and N2 in the one, in the plurality orin all of the NH3 synthesis units into which reactant gas stream or a partial stream thereof is introduced in step (c).

2. The process according to claim 1, wherein in step (a) the electrical power is generated from (i) wind power; preferably, the currently available amount of H2 depends on the current availability of wind power; and / or (ii) hydropower; preferably, the currently available amount of H2 depends on the current availability of hydropower; and / or (iii) solar energy is generated; preferably, the currently available amount of H2 depends on the current availability of solar energy. 3.The method according to claim 1 or 2, wherein in step (c) a threshold value B decreases and a threshold value B increases are defined for the amount of H2; wherein - firstly the reactant gas stream is divided into independent sub-streams and the sub-streams are introduced into several or all of the NH3 synthesis units; and wherein in the event of a decrease in the instantaneous availability of H2 and falling below the threshold value B. sinkt the reactant gas stream as such is introduced into a single NH3 synthesis unit; or - first, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units; and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value B, the reactant gas stream is divided into independent substreams and the substreams are introduced into several or all of the NH3 synthesis units.

4. The process according to one of the preceding claims, wherein in step (c) a threshold value C is set for the amount of H2. sinktand a threshold value C rises are specified, wherein - initially the throughput of the reactant gas stream or the partial stream thereof which is fed into at least one of the NH3 synthesis units is undiminished compared to the maximum possible throughput for said at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in said at least one of the NH3 synthesis units with undiminished throughput (full load operation); and wherein in the event of a decrease in the instantaneous availability of H2 and the threshold value C falls below, the throughput of the reactant gas stream or the partial stream thereof which is introduced into said at least one of the NH3 synthesis units is reduced compared to the maximum possible throughput for said at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in said at least one of the NH3 synthesis units with reduced throughput (partial load operation);or - initially the throughput of the reactant gas stream or the partial stream thereof which is introduced into at least one of the NH3 synthesis units is reduced compared to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units with a reduced throughput (partial load operation);and wherein in the event of an increase in the instantaneous availability of H and exceeding the threshold value C, the throughput of the reactant gas stream or the partial stream thereof which is fed into at least one of the NH3 synthesis units remains undiminished compared to the maximum possible throughput for this at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in this at least one of the NH3 synthesis units with undiminished throughput (full load operation).

5. The method according to one of the preceding claims, wherein in step (c) a threshold value D is set for the amount of H2; sinktand a threshold value D rises are specified; wherein - first, the reactant gas stream is divided into independent partial streams and fed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units; and wherein in the event of a decrease in the current availability of H2 and falling below the threshold value D sinkt the reactant gas flow for at least one of the NH3 synthesis units is interrupted, so that in step (d) in the at least one of the NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units; or - initially the reactant gas flow is interrupted for at least one of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in at least one of the NH3 synthesis units; preferably with the proviso that the reactant gas flow is not interrupted simultaneously for all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in at least one of the NH3 synthesis units;and wherein, in the event of an increase in the instantaneous availability of H2 and exceeding the threshold value D increases, the reactant gas stream is passed, divided into independent substreams, into all of the NH3 synthesis units, so that NH3 is synthesized in all of the NH3 synthesis units in step (d).

6. The method according to claim 5, wherein - first, the reactant gas stream is passed, divided into independent substreams, into all of the NH3 synthesis units, so that NH3 is synthesized in all of the NH3 synthesis units in step (d); and wherein, in the event of a decrease in the instantaneous availability of H2 and falling below the threshold value D falls, the reactant gas stream as such is introduced into an individual one of the NH3 synthesis units, so that NH3 is synthesized in the individual one of the NH3 synthesis units in step (d);and wherein the reactant gas flow is interrupted for all remaining NH3 synthesis units, so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units; or - initially the reactant gas flow is interrupted for all but one of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in all but one of the NH3 synthesis units;and wherein, in the event of an increase in the instantaneous availability of H2 and the exceeding of the threshold value D rises, the reactant gas stream is divided into independent partial streams and fed into all of the NH3 synthesis units, so that in step (d) NH3 is synthesized in all of the NH3 synthesis units.

7. The method according to claim 6, wherein the throughput of the reactant gas stream which is introduced as such into the individual NH3 synthesis units is reduced compared to the maximum possible throughput for the individual NH3 synthesis units, so that in step (d) NH3 is synthesized at a reduced throughput in the individual NH3 synthesis units (partial load operation).

8. The method according to any one of the preceding claims, wherein; - during a first time interval, the reactant gas stream as such or as a partial stream thereof is introduced into at least one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the at least one of the NH3 synthesis units; wherein the reactant gas stream is interrupted for at least one other of the NH3 synthesis units, so that in step (d) no NH3 is synthesized in the at least one other of the NH3 synthesis units, whereby the at least one other of the NH3 synthesis units cools; - during a second time interval, which immediately follows the first time interval, process heat is transferred from the at least one of the NH3 synthesis units to the at least one other of the NH3 synthesis units, whereby the at least one other of the NH3 synthesis units is heated;and - during a third time interval, which immediately follows the second time interval, the reactant gas stream is introduced, divided into independent partial streams, into the at least one of the NH3 synthesis units and into the at least one other of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the at least one of the NH3 synthesis units and in the at least one other of the NH3 synthesis units.

9. The process according to one of the preceding claims, wherein - during a first time interval, the reactant gas stream as such is introduced into a single one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the single one of the NH3 synthesis units; wherein the reactant gas flow for all remaining NH3 synthesis units is interrupted so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, whereby all remaining NH3 synthesis units cool down;- during a second time interval, which immediately follows the first time interval, the reactant gas stream as such is introduced into another individual one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the other individual one of the NH3 synthesis units, whereby this other individual one of the NH3 synthesis units is heated;wherein the reactant gas flow is interrupted for all remaining NH3 synthesis units, so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, whereby all remaining NH3 synthesis units cool down.

10. The method according to claim 9, wherein - during a third time interval, which immediately follows the second time interval, the reactant gas flow as such is introduced into a further individual one of the NH3 synthesis units, so that in step (d) NH3 is synthesized in the further individual one of the NH3 synthesis units, whereby this further individual one of the NH3 synthesis units is heated; whereby; the reactant gas flow for all remaining NH3 synthesis units is interrupted, so that in step (d) no NH3 is synthesized in all remaining NH3 synthesis units, whereby all remaining NH3 synthesis units cool down. 11.The method according to one of claims 9 or 10, wherein - during the first time interval, the throughput of the reactant gas stream, which is introduced as such into the individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the individual NH3 synthesis units with a reduced throughput (partial load operation); and / or - during the second time interval, the throughput of the reactant gas stream, which is introduced as such into the other individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the other individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the other individual NH3 synthesis units with a reduced throughput (partial load operation); and / or - if necessary.During the third time interval, the throughput of the reactant gas stream, which is introduced as such into the further individual NH3 synthesis units, is reduced compared to the maximum possible throughput for the further individual NH3 synthesis units, so that in step (d) NH3 is synthesized in the further individual NH3 synthesis units at a reduced throughput (partial load operation).

12. The method according to one of claims 9 to 11, wherein the first time interval, the second time interval, and optionally the third time interval are selected such that the temperature in none of the NH3 synthesis units falls below the minimum light-off temperature for the synthesis of NH3 from H2 and N2. 13.The process according to any one of claims 9 to 12, wherein the NH3 synthesis units (i) are arranged in a common pressure vessel; and / or (ii) are separated and uniformly supplied with the reactant gas stream as such in succession; and / or (iii) are in heat exchange with one another, so that - during the first time interval, a heat flow flows from the individual NH3 synthesis units into one or more of the remaining NH3 synthesis units; and / or. - during the second time interval, a heat flow flows from the other individual NH3 synthesis unit into one or more of the remaining NH3 synthesis units; and / or - optionally, during the third time interval, a heat flow flows from the further individual NH3 synthesis unit into one or more of the remaining NH3 synthesis units. 14.A plant for synthesizing NH3 at variable throughput, the plant comprising: - a device configured to provide H2 by electrolysis of H2O using electrical power from renewable energy; - a device configured to provide a reactant gas stream comprising the H2; - a plurality of parallel-connected NH3 synthesis units configured to synthesize NH3 from H2 and N2; and - a device configured to introduce the reactant gas stream, depending on the currently available amount of H2, - as such into a single one of the NH3 synthesis units; or - divided into independent substreams into several of the NH3 synthesis units or into all of the NH3 synthesis units.

15. The plant according to claim 14, which is configured to carry out the method according to any one of claims 1 to 13.

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