Method and system for determining an operating point of a system for synthesizing ammonia, having a power supply for providing hydrogen, said power supply comprising at least one renewable power source

Abstract

The invention relates to a method and a system (1) for determining an operating point, in particular a hydrogen flow into an ammonia synthesis unit (40), of a system (1) for synthesizing ammonia, having a power supply (10) for providing hydrogen, said power supply comprising at least one renewable power source (11, 12, 13), wherein the determining process involves the process of determining a hydrogen flow supplied to or discharged from a hydrogen store (33) of the system (1). The invention further relates to a control program, to a computer-readable medium, and to the use of the method according to the invention, the system (1) according to the invention, or the control program according to the invention in order to produce ammonia and / or urea.

Description

[0001] Method and system for determining an operating point of an ammonia synthesis plant with a power supply for hydrogen production comprising at least one renewable power source

[0002] The present invention relates to a method and a system for determining an operating point of an ammonia synthesis plant with a power supply for the provision of hydrogen comprising at least one renewable power source.

[0003] State of the art

[0004] In light of global population growth, the development of flexible and efficient fertilizers is of great and increasing importance. A very large proportion of global fertilizer production consists of urea-based fertilizers. These water-soluble fertilizers decompose in the soil into ammonium salts or nitrates and represent an important base fertilizer. These urea-based fertilizers can be combined with other elements such as potassium, manganese, phosphates, sulfur, sulfur compounds, selenium, and calcium.

[0005] Urea can be produced according to the simplified equations [1] and [2]:

[0006] 2 NH3+ CO2H2N-COONH4[1]

[0007] H2N-COONH4(NH2)2C0 + H2O [2]

[0008] The two starting materials, ammonia and carbon dioxide, can be provided in ammonia synthesis based on the Haber-Bosch process. Ammonia is the second most produced synthetic chemical worldwide (Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, DOI: IO.IOO2 / 14356OO7.OO2_OII, hereinafter referred to as "Ullmann's").

[0009] Ammonia is produced primarily from hydrogen and nitrogen in the presence of an iron catalyst. Temperatures are often between 400 °C and 500 °C at pressures exceeding 100 bar. The main factor influencing process costs is the supply of hydrogen from synthesis gas production (Ullmann's, page 139).

[0010] Accordingly, ammonia is preferably produced in principle as described, for example, in Holleman, Wiberg, Textbook of Inorganic Chemistry, 102nd edition, 2007, pages 662-665 (ISBN 978-3-11-017770-1), based on the “Haber-Bosch process” from the elements according to equation [3]:

[0011] 3 H2+ N22 NH3+ 92.28 kJ [3]

[0012] The reactant nitrogen (N2) can be obtained, for example, by low-temperature air separation from ambient air.

[0013] The hydrogen is preferably obtained via the “steam reforming process” according to equation [4]:

[0014] C n H 2m + n H2O (n+m) H2+ n CO [4]

[0015] In the subsequent “carbon dioxide conversion”, a further conversion takes place according to equation [5]:

[0016] CO + H2O CO2 + H2[5]

[0017] The carbon dioxide (CO2) produced according to equation [5] is preferably used as a carbon dioxide source for urea synthesis according to equations [1] and [2]. According to equation [4], fossil fuels, usually methane from natural gas, serve as a feedstock for hydrogen production. Due to limited resources and the numerous consequences of climate change, a reduction in the consumption of fossil fuels, such as natural gas, is being pursued worldwide.

[0018] One approach regarding ammonia and urea synthesis is the construction of "green" ammonia plants ("gNH3 plants") that are at least partially powered by "green" hydrogen ("gH2") produced using renewable (regenerative) electricity sources. While these gNH3 plants are desirable and relevant for the future, their high operating costs currently prevent a complete switch to such plants.

[0019] A further challenge lies in the fluctuating energy feed-in from renewable sources such as wind or solar power plants. The operating point of a gNH3 plant cannot be directly adjusted to these fluctuations, as this could lead to pressure fluctuations within the plant and consequently, damage to the system. It is standard practice to design a green ammonia plant to accommodate several operating point changes per day. The following steps are performed to select the desired operating points:

[0020] - Collecting weather data, taking into account past time periods and forecasts

[0021] - Based on the collected weather data, forecasts of operational parameters for the hydrogen storage, the nitrogen storage, the battery and the ammonia storage

[0022] - Based on the predicted operating parameters, create state variables for the ammonia plant in an optimization model.

[0023] - Based on the generated state variables, determine target values ​​to maximize ammonia plant production

[0024] - Transferring the setpoint values ​​to a control system for controlling the ammonia plant

[0025] A disadvantage of this approach is the need for an optimization model for the entire ammonia plant that can reliably simulate various plant conditions. This results in a high computational effort. Furthermore, extensive input data is required to generate the state variables for the optimization model. Finally, this method is characterized by a high degree of complexity, as determining the setpoints and controlling the ammonia plant are combined in a single process or model.

[0026] US Patent 11,656,612 B2 concerns a method for controlling an industrial gas production plant using a model predictive method. This method has the disadvantage that a detailed model of the ammonia plant is required. In particular, a model predictive model is used to determine control variables for the ammonia plant. This results in a very high computational and data overhead.

[0027] US 11,626,730 B2 also concerns a method for controlling an industrial gas production plant, but in this case, it uses machine learning. Therefore, extensive datasets are required for training and validating the model, resulting in significant computational and data costs. Furthermore, the determined control variables include the ammonia production rate of the ammonia plant, for which a model of ammonia synthesis is necessary.

[0028] US Patent 11,625,020 B2 also concerns a method for controlling an industrial gas production plant, but here using an optimization model, preferably a system of non-linear equations. This method also encompasses the control of the entire ammonia plant, including ammonia synthesis. The optimization model used is therefore again very complex, resulting in extensive computational and data processing requirements.

[0029] The present invention aims to control a gNH3 plant without an optimization model, with the goal of ensuring maximum and safe ammonia production. Furthermore, the amount of data required for this control task should be minimal.

[0030] Solution according to the invention: The problem of the invention is surprisingly solved by a method for determining an operating point of an ammonia synthesis plant according to claim i. Further advantageous embodiments are found in the dependent claims.

[0031] The invention further comprises a plant for ammonia synthesis according to claim 16. Further advantageous embodiments are found in the respective dependent claims.

[0032] The invention further comprises a control program for executing the method according to the invention by a control unit according to claim 19. Further advantageous embodiments can be found in the respective dependent claims.

[0033] The invention further comprises a computer-readable medium on which the control program according to the invention is stored, according to claim 23, and the use of the method, the apparatus or the control program according to the invention for the production of ammonia and / or urea according to claim 24.

[0034] By determining the operating point through the determination of the hydrogen flow supplied to or removed from the hydrogen storage system, the invention enables the system operation to be adapted to fluctuating energy supplies without requiring intervention in the control of the entire system, particularly the ammonia synthesis process. Operating point determination and ammonia synthesis control can thus be decoupled. Furthermore, the amount of required input data can be significantly reduced compared to methods known from the prior art, since the acquisition of input data only includes reliably predicted weather data, the fill level of a hydrogen storage system, the charge level of an electrical battery in the system, and the current operating point of the system.

[0035] The method according to the invention thus enables the control or regulation of the gNH3 plant, adapted to the electrical energy supplied from at least one renewable electricity source, taking into account the states of an electricity storage system and the hydrogen storage and electrolysis. However, complex modeling, in particular an optimization model, of the ammonia synthesis and a combination of setpoint determination and control of the ammonia synthesis itself can be dispensed with.

[0036] Finally, the method according to the invention is characterized by a reduced degree of complexity compared to methods known from the prior art, since the determination of the setpoints and the control or regulation of the, in particular the entire, ammonia plant are not combined in a single model. The method according to the invention enables the control of a gNH3 plant without an optimization model, in particular for the ammonia synthesis of the gNH3 plant. In other words, the method according to the invention can be used without an optimization model for controlling a gNH3 plant.

[0037] A further advantage of the method according to the invention lies in the minimization or at least reduction of the hydrogen flow supplied to or removed from the hydrogen storage system, so that the hydrogen storage system can be made smaller compared to the use of known methods, which can lead to a reduction in costs. Preferably, the ammonia plant can be operated at a different utilization rate than the electrolysis plant in order to minimize the hydrogen flow supplied to or removed from the hydrogen storage system.

[0038] Determining the plant's operating point is understood here specifically as determining the hydrogen input flow rate into the plant's ammonia synthesis process. This allows for an advantageous decoupling between operating point determination and the control of the ammonia synthesis.

[0039] The provision of hydrogen here refers to the chemical process of water electrolysis, which is preferably powered exclusively, or preferably at least to more than 50%, by renewable energies.

[0040] Here, a renewable electricity source is understood as the provision of electrical energy using renewable energy sources. At least one renewable electricity source could be, for example, a wind or solar power plant. However, other renewable energy sources are also conceivable. The at least one renewable electricity source could also be an interconnected or islanded grid that is itself powered by renewable energy sources.

[0041] Data acquisition refers to providing information for use in the process. Reliable weather forecasts are defined here as those weather data that provide a forecast for a few hours. Specifically, reliable weather forecasts are defined as those data that provide a forecast for a maximum of the next four hours.

[0042] In particular, controlling or regulating the operating point of the plant (the actuation of the plant to control or regulate the operating point of the plant) based on the determined operating point can be carried out in such a way that a hydrogen inlet flow supplied to an ammonia synthesis process in the plant is controlled or regulated. This can be done, in particular, by actuating a valve. For example, it may preferably be provided that a first controller or a first control program sets the hydrogen inlet flow based on the determined operating point. Particularly preferably, a second controller or a second control program may be provided which regulates the ammonia synthesis based on the set hydrogen inlet flow, in particular based on a measurement of an actual hydrogen inlet flow into the ammonia synthesis process.

[0043] Preferably, the determination process can additionally include determining the expected generated electrical current from the renewable energy source, the hydrogen current generated in the electrolysis process of the system, the charging or discharging of the system's battery, and / or the fill level of the hydrogen storage. This enables a more precise determination of the operating point, and in particular, allows the determined hydrogen current to be more accurately adapted to the system's operating condition.

[0044] Furthermore, the determination can preferably be carried out in such a way that the ammonia production of the plant is maximized, while fluctuating loads on plant components resulting from the determined operating point are minimized or at least remain below a threshold value. The invention thus enables the optimal utilization of the plant's capacity, ensuring that, on the one hand, the largest possible quantity of ammonia is provided, and on the other hand, wear and tear on the plant is minimized.

[0045] Maximum ammonia production is defined as the amount of hydrogen supplied by electrolysis, such that the utilization rate of ammonia synthesis corresponds to the utilization rate of electrolysis. One or more threshold values ​​can be predefined and stored, for example, in a database. This allows for consideration of maximum permissible pressure fluctuations or maximum temperatures of pipe connections and other components.

[0046] In a preferred embodiment, the determination of the hydrogen flow supplied to or removed from the hydrogen storage system can be carried out in such a way that changes to the system's operating point are avoided as far as possible, a new operating point is as close as possible to the current operating point, and / or the pressure or pressure change in the hydrogen storage system remains within limit values. The determination is thus performed in such a way that an operating point is only changed when this is actually necessary. This is because every change in the operating point can lead to pressure oscillations in the system and thus increases wear. For example, it can be provided that if a change in the operating point is necessary, the change is as small as possible relative to the current operating point. Furthermore, it can be provided that a change in the operating point only occurs after a specific time interval.For example, a change in the operating point may be limited to 12 changes per day, preferably 6 changes per day, and most preferably four changes per day.

[0047] Preferably, the hydrogen flow rate supplied to or removed from the hydrogen storage system can be determined based on a predicted hydrogen production rate and a sliding, cumulative mass of hydrogen in the storage system. This allows the state of the hydrogen storage system and the electrolysis process to be taken into account when determining the hydrogen flow rate. Preferably, the predicted hydrogen production rate can be determined based on a predicted electrical energy supplied by at least one renewable power source. This allows the available electrical energy to be considered when determining the operating point, making the operating point adaptable to external conditions.

[0048] Preferably, the conversion of predicted electrical energy into the predicted hydrogen production rate can be achieved using hydrogen supply efficiency curves. These efficiency curves can, for example, be stored in a control unit and indicate the relationship between the hydrogen supply efficiency and the initial or boundary conditions of the hydrogen supply process. The efficiency curves can exist for different initial or boundary conditions. In particular, the efficiency curves can characterize hydrogen electrolysis under different operating conditions.

[0049] Preferably, the data acquisition can include current weather data, forecasted weather data (as a trend), the maximum capacity, pressure and / or temperature of the hydrogen storage system, the flow rate of a hydrogen storage system compressor, the maximum battery capacity, and / or the battery charging rate. This allows additional external influences and / or system-internal conditions to be considered when determining the operating point.

[0050] Furthermore, based on the determination of the operating point, the operating point can be predefined, whereby the operating point is either predefined to a control system for the ammonia synthesis process of the plant or the operating point is detected by the control system, and the control system then regulates the ammonia synthesis based on the predefined or detected operating point. Thus, the invention enables, on the one hand, the decoupling of the operating point determination from the regulation of the ammonia synthesis itself, but on the other hand, allows the regulation of the ammonia synthesis based on the operating point determination. In this case as well, the operating point determination only interferes with the regulation of the ammonia synthesis insofar as the operating point is predefined. The adjustment of the ammonia synthesis, however, is carried out by the control system.Determining the operating point does not directly affect the states of the ammonia synthesis process, such as valve positions or compression rates, and information about the states within the ammonia synthesis process is not required for determining the operating point. Adjusting the ammonia synthesis process can, for example, involve adjusting the flow rate of the circulating gas and / or the ammonia concentration at the inlet of a synthesis reactor.

[0051] In particular, it may be provided that the operating point is set by adjusting or regulating a hydrogen inlet flow rate into the ammonia synthesis process of the plant. Furthermore, the control or regulation of the ammonia synthesis process may be designed and configured to measure the set or regulated hydrogen inlet flow rate and to control or regulate the ammonia synthesis process based on this measured hydrogen inlet flow rate.

[0052] The acquisition and determination processes can be performed repeatedly, preferably continuously, and / or the determination can be carried out over a time horizon. This time horizon comprises at least one future point in time, preferably at least two future points in time, and most preferably at least four future points in time. For example, the time horizon could be four hours and include four points in time. The determination process then predicts the operating point for a four-hour time horizon, taking into account time intervals of one hour defined by the points in time. The latter is particularly advantageous because influencing factors, such as the weather, typically change over the course of the considered time interval.

[0053] Both the time horizon and the number of time points can be varied. The time horizon can be longer, for example 6 or 10 hours, or shorter, for example 3 or 2 hours. This depends in particular on how frequently the operating point of the system can or should be changed during the course of a day.

[0054] Preferably, the method after determination includes a correction of the operating point, wherein the correction is based on a minimum and maximum ammonia production rate of the plant and / or on a minimum and maximum hydrogen storage pressure. This prevents operating points from being set that exceed the plant's capacity or no longer allow for sensible operation of the plant. Safety limits can also be maintained in this way.

[0055] Furthermore, the plant's operating point can be controlled or regulated based on a specific operating point such that the hydrogen input flow supplied to the plant's ammonia synthesis is partially fed from the hydrogen storage and hydrogen generated in the plant's electrolysis process. The proportional supply of the hydrogen input flow corresponds to the determined hydrogen flow rate supplied to or removed from the hydrogen storage. This minimizes the hydrogen flow rate supplied to or removed from the hydrogen storage, thus minimizing fluctuations in the hydrogen storage level.

[0056] The hydrogen can be provided predominantly, preferably to more than 75%, and particularly preferably exclusively, by at least one renewable electricity source, preferably by alkaline water electrolysis powered by electricity from renewable energy sources. Alternatively, the hydrogen can be provided by proton exchange membrane electrolysis (PEM) or a solid oxide electrolyzer cell (SOEC).

[0057] In a preferred embodiment, the ammonia synthesis plant of the facility is controlled independently of an optimization model.

[0058] The invention further comprises an ammonia synthesis plant comprising at least one renewable power source, a hydrogen storage system, an electric battery and means adapted to perform the steps of the inventive process.

[0059] In a preferred embodiment, the hydrogen can be provided by at least one renewable electricity source, preferably by water electrolysis powered by electricity from renewable energy sources. In particular, the hydrogen can be provided by an alkaline water electrolysis device (ALED). In another preferred embodiment, the hydrogen is provided by renewable sources, preferably by water electrolysis powered by renewable energy. In principle, other water electrolysis technologies can also be used.

[0060] The system according to the invention further comprises an ammonia synthesis unit. For the purposes of this invention, the term "unit" encompasses devices and apparatus known to those skilled in the art for the stated purpose. The ammonia synthesis unit comprises the actual ammonia synthesis reactor for the reaction of hydrogen and nitrogen according to equation [3]. The nitrogen supply can preferably be provided in an attached air separation unit. Examples of suitable reactors can also be found in EP 345 504 Ai and DE 35 22 308 Ai, Examples 1 to 7 and the description. Preferably, the ammonia synthesis unit is connected to devices for purification, compression, and / or liquefaction.

[0061] The invention further relates to a control program comprising commands which, when the method is executed by a control unit, cause the control unit to execute the method according to the invention.

[0062] The control program can include, in particular, commands for controlling the fill level of the hydrogen storage system. This makes it possible to achieve a low fluctuation in the fill level of the hydrogen storage system and to implement the hydrogen storage system with a smaller volume compared to state-of-the-art systems.

[0063] Furthermore, the control program can include commands for controlling or regulating ammonia synthesis, with the regulation of the ammonia synthesis being based on the defined operating point. This means that commands for determining the operating point and controlling or regulating the ammonia synthesis are, on the one hand, stored in a control program, but on the other hand, remain decoupled, so that no knowledge of the states within the ammonia synthesis is required for determining the operating point. For example, the operating point determination and the control or regulation of the ammonia synthesis can be executed as separate subroutines of the control program, with the defined operating point then being passed from the operating point determination via an interface. In particular, the control or regulation of the ammonia synthesis can be carried out by an independent control device.This independent control device can then adjust ammonia production to the specific operating point, in particular depending on a measured hydrogen input current into the ammonia synthesis.

[0064] The invention further relates to a computer-readable medium on which the control program according to the invention is stored.

[0065] Furthermore, the invention includes the use of the inventive method, the inventive plant or the inventive control program according to a process for the production of ammonia and / or urea.

[0066] Furthermore, the invention is explained in more detail with reference to the following figures. The figures do not limit the scope of protection of the invention, but serve only as examples.

[0067] They show:

[0068] Figure 1 shows a schematic flow diagram of an ammonia synthesis plant according to the invention, including means for determining a hydrogen flow supplied to or removed from a hydrogen storage unit of the plant.

[0069] Figure 2 shows a schematic representation of a method according to the invention for determining an operating point of an ammonia synthesis plant.

[0070] Figure 3 shows a comparison of storage mass and storage pressure in a hydrogen storage system of an ammonia synthesis plant using a method according to the invention and without using a method according to the invention.

[0071] Fig. 1 shows a schematic representation of a plant 1 according to the invention and the implementation of a process according to the invention for the production of green ammonia (gNH3) by providing renewable energy. The plant comprises a power supply 10, an electrolysis unit 20, a hydrogen storage unit 30, and an ammonia synthesis unit 40. The power supply 10 is fed at least partially from renewable energy sources such as wind power 11 and solar energy 12. Electricity can also be drawn partially from a grid or island grid 13, which is preferably supplied entirely from renewable energy sources. To ensure a sufficient power supply to the plant 1 during periods of insufficient power from wind power 11, solar energy 12, and / or the grid or island grid 13, a battery 14 is provided.The battery 14 also makes it possible to store the surplus electricity in the battery 14 for later use during phases with excess electricity from wind power 11, solar energy 12 and / or grid connection or island grid 13.

[0072] The electricity provided by the power supply 10 powers the electrolysis unit 20. Here, hydrogen is produced in an alkaline hydrogen electrolysis unit 21.

[0073] The hydrogen produced is fed into the hydrogen storage system 30. Here, the hydrogen is compressed in a first H2 compressor 31 and a second H2 compressor.

[0074] The hydrogen is compressed by the hydrogen storage compressor 32 and fed into a hydrogen storage tank 33. The hydrogen storage tank also includes valves 34 and 35, which allow for the regulation of hydrogen supply to and withdrawal from the hydrogen storage tank 33. Thus, depending on demand, the hydrogen produced in the electrolysis unit 20 can also be bypassed via valve 35 bypassing the hydrogen storage tank 33. The amount of hydrogen produced in the electrolysis unit 20 that is not bypassed by the hydrogen storage tank 33 is compressed by the hydrogen storage compressor 32 and pumped into the hydrogen storage tank 33.

[0075] From the hydrogen storage facility 30, the hydrogen from the hydrogen storage facility is used.

[0076] The hydrogen is fed to the ammonia synthesis unit 40 via valve 33 and / or directly from the electrolysis unit 20 via valve 35. Here, nitrogen from an air separation unit 41 is first added to the hydrogen. The hydrogen-nitrogen mixture is then compressed again. Optionally, oxygen can be removed in a de-oxo reactor (not shown). The actual ammonia synthesis 40 takes place in a synthesis reactor 42, which, as shown in Fig. 1, includes numerous other components. The ammonia obtained in the synthesis reactor 42 is condensed by cooling in several heat exchangers, separated from the recycle gas, and freed from dissolved recycle gases by one or more pressure reductions. At the end of this complex process, the ammonia is made available at a discharge point 43. The ammonia can then be used, for example, for urea production.

[0077] In the state of the art, a control system is typically used to regulate such gNH3 plants, adapting the operating point of the ammonia synthesis 40 to the available energy. However, this involves coupling the complex control of the entire ammonia synthesis 40 process, including internal state variables, with the determination and adjustment of the operating point. This results in a very high computational effort and a large amount of data.

[0078] To reduce these costs, the system shown in Fig. 1 includes means 51, 52 to determine an operating point of the system, thereby enabling decoupling from the control of the ammonia synthesis 40. This allows for simpler calculations and reduced data requirements.

[0079] The means 51, 52 are adapted to perform the following steps of a method according to the invention:

[0080] - Acquisition of input data, here comprehensively and reliably predicted weather data 61, a fill level of the hydrogen storage 33 of the system 1, a charge of the electrical battery 14 of the system 1 and a current operating point of the system 1 and

[0081] - Determining the operating point of plant 1, here a hydrogen inlet stream into the ammonia synthesis 40, based on the recorded input data.

[0082] Determining the hydrogen inlet flow rate into the ammonia synthesis 40 comprises determining the hydrogen flow rate supplied to or removed from the hydrogen storage 33. For example, the means 51 can be configured as a control unit with a control program comprising commands that, when executed by the control unit 51, cause it to carry out the process according to the invention. The means 52, on the other hand, can be configured as a control element and set up to regulate the hydrogen inlet flow rate specified by the control unit 51 and possibly corrected as described below. Based on the determined operating point, the control element 52 opens or closes the valves 34, 35 such that a hydrogen flow rate is supplied to or removed from the hydrogen storage 33 according to the determined hydrogen inlet flow rate into the ammonia synthesis 40.

[0083] In particular, the control program can include commands for controlling the fill level of the hydrogen storage tank 33. For example, a predetermined fill level in the hydrogen storage tank 33 can be set based on the determined hydrogen flow, especially within desired limits. This prevents the fill level from falling below a minimum value or exceeding a maximum value. Preferably, the commands for controlling the fill level are designed to minimize changes in the fill level.

[0084] Furthermore, the control program can include commands for controlling or regulating the ammonia synthesis 40, whereby the regulation of the ammonia synthesis 40 is based on the determined operating point. Here, the commands for controlling or regulating the ammonia synthesis 40 are stored on a control unit of the ammonia synthesis 40 (not shown), a master controller. The master controller is configured to measure the hydrogen input flow regulated by the control element 521 and to automatically adjust the ammonia synthesis 40 to the determined hydrogen input flow. Compared to prior art methods, however, the advantage remains that the control of the ammonia synthesis 40 is decoupled from the determination of the operating point, so that the determination can still be carried out independently of the complex control of the ammonia synthesis 40.

[0085] A method according to the invention is schematically illustrated in detail in Figure 2, which is carried out by the control unit 51 for an arbitrary time interval, in this case, by way of example, a 4-hour interval. In a first step, Si performs an initialization. For this purpose, a continuously calculated hydrogen storage mass (Running Cumulative Hydrogen Storage Mass - RCHSM) is set to zero.

[0086] In a second step S2, the control program determines a hydrogen storage mass m H2 for the current time t and the time t-4 four hours earlier. The control program has data on the temporal progression of the pressure p available for this purpose. H2 and the temperature T H2 available in hydrogen storage 33.

[0087] This allows the control program to recalculate the cumulative hydrogen storage mass RCHSM in step 3 by adding the current hydrogen storage mass to a cumulative hydrogen storage mass RCHSM at time t-4 and subtracting the hydrogen mass from time t-4.

[0088] The cumulative hydrogen storage mass RCHSM thus represents the excess or deficit of hydrogen within the considered time interval, here 4 hours. To maintain a largely constant storage state of the hydrogen storage system 33, the RCHSM should therefore be close to zero. The RCHSM can be positive or negative. If the RCHSM is positive, there is an excess of hydrogen. Therefore, more hydrogen can be supplied to the ammonia synthesis 40. If, on the other hand, the RCHSM is negative, there is a deficit of hydrogen, and the supply to the ammonia synthesis must be reduced.

[0089] To determine the hydrogen flow to be supplied or removed, the control program calculates hydrogen production rates (rh) in step S4. H2 electrolysis for the time intervals At ; Here, each time interval corresponds to one hour, so that Ab corresponds to the interval from time t to time t plus one hour, At2 corresponds to the interval from time t+1 to time t+1 plus one hour, and so on. For a prediction horizon of four hours, the control program thus determines four hydrogen production rates.

[0090] The hydrogen production rates are determined based on the recorded weather data 61, which it uses to determine the available amount of electricity. The reliably predicted weather data 61 includes a forecast for the following four hours. Using the amount of electricity available for the following four hours and efficiency curves for the hydrogen electrolysis unit 21, the control program can then determine the hydrogen production rates.

[0091] The determined hydrogen production rates are used by the control program in step S5 to calculate a hydrogen production quantity m. H2 ,ges5 which is composed of the individual hydrogen production rates as well as the cumulative hydrogen storage mass RCHSM at time t.

[0092] The hydrogen production quantity corresponds to the determined hydrogen flow, which is to be discharged to the hydrogen storage tank 33 if the value is positive and supplied if the value is negative. Accordingly, the actuator 52 can be configured to receive the hydrogen production quantity as a data input and to control the valves 34 and 35 accordingly, so that the determined hydrogen flow is supplied to or discharged from the hydrogen storage tank 33.

[0093] The process shown in Fig. 2 comprises the further steps S6, S7 and S8. In step S6, the determined hydrogen production quantity is first converted into an ammonia production quantity rh. NH3 The total value has been converted. This is done taking into account stoichiometric relationships and losses estimated at 1%. In other embodiments, other assumptions, in particular other loss estimates, may be used.

[0094] In step S7, the ammonia production quantity is corrected. If the calculated ammonia production quantity is greater than a capacity rh NH3j If the ammonia plant's cap is reached, the calculated ammonia production quantity is limited to the capacity. If the calculated ammonia production quantity is less than a minimum ammonia production quantity rh NH3 ,td of the ammonia plant, the calculated ammonia production quantity is set to the minimum ammonia production quantity.

[0095] In the final step S8 of the described process, the determined ammonia production quantity is passed as a control variable S to a controller of the ammonia synthesis for the next four hours. Thus, the ammonia synthesis 40 can be operated according to the amount of hydrogen available.

[0096] Instead of the respective hydrogen storage mass, other corresponding quantities can also be used to describe the amount of hydrogen stored. In other embodiments, the time horizon can cover a period other than four hours. Furthermore, the intermediate intervals can be greater or less than one hour.

[0097] The process can include an additional correction. For example, the system shown in Fig. 1 has a correction agent 53 that detects a hydrogen storage pressure and a current operating point of the ammonia synthesis 40. A control program for the correction agent 53 can perform the following case distinctions, preferably between steps S5 and S6:

[0098] - The hydrogen storage pressure reaches or falls below a minimum operating pressure: the calculated hydrogen production quantity is reduced, so that the amount of hydrogen to be discharged from the hydrogen storage is reduced or the amount of hydrogen to be supplied is increased and the hydrogen storage pressure can be rebuilt.

[0099] - The hydrogen storage pressure reaches or exceeds a maximum pressure and the current operating point of the ammonia synthesis is below the maximum load: the calculated amount of hydrogen to flow to the ammonia plant 40 is increased, so that the amount of hydrogen to be discharged from the hydrogen storage is increased or the amount of hydrogen to be supplied is reduced and the hydrogen storage pressure can be reduced again.

[0100] - The hydrogen storage pressure reaches or exceeds a maximum pressure, and the current operating point of ammonia synthesis corresponds to the maximum load: the hydrogen electrolysis unit 21 is throttled so that the amount of hydrogen produced is adapted to the operating point of ammonia synthesis. Alternatively or additionally, it can be provided to store any additional available electrical energy in the battery 14. Fig. 3 shows a comparison of a system without the application of the inventive method and a system with the inventive method. The left side shows results for the system without the inventive method, and the right side shows results for the system with the inventive method. The quantities shown are the stored hydrogen mass (upper curves) and the storage pressure (lower curves) in the hydrogen storage unit 33.

[0101] The basic boundary conditions are identical for both cases. The ammonia plant has a capacity of 3600 tons per day, the electricity supply from solar and wind power is 3000 MW, and the hydrogen electrolysis unit 21 has a capacity of 1520 MW. The operating point of the plant is adjusted every 4 hours in both cases.

[0102] For the system without the inventive process, the storage mass varies widely between 40 and 140 tons. In contrast, the storage mass using the inventive process ranges between 10 and 60 tons. This allows the hydrogen storage tank to be significantly smaller. The storage pressure fluctuates less in the system without the inventive process; however, in the event of a heavy discharge, a significantly larger fluctuation can occur, leading to faster wear of the hydrogen storage tank. Conversely, the pressure fluctuation cycles are shorter when using the inventive process, with five complete cycles between 50 and 150 barg per year, which is within acceptable limits.

[0103] Overall, the invention thus makes it possible to flexibly adjust the operating point of plant 1 several times a day when hydrogen storage requirements are reduced.

[0104] Reference symbol list

[0105] 1 Ammonia synthesis plant

[0106] 10 Power supply

[0107] 11 Wind power Solar energy

[0108] interconnected or islanded network

[0109] battery

[0110] electrolysis

[0111] Hydrogen electrolysis unit

[0112] Hydrogen storage

[0113] H2 compressor

[0114] Hydrogen storage compressor

[0115] Hydrogen storage, 35 valves

[0116] Ammonia synthesis

[0117] Air separation plant

[0118] Synthesis reactor

[0119] Ammonia removal, 52 agents

[0120] Correction agents

Claims

Patent claims 1. Method for determining an operating point of an ammonia synthesis plant (1) with a power supply (10) for hydrogen provision comprising at least one renewable power source (11, 12, 13), comprising the following steps: - Acquisition of input data, comprehensively reliable forecasted weather data, a fill level of a hydrogen storage (33) of the plant (1), a charge of an electric battery (14) of the plant (1) and a current operating point of the plant (1), - Determining the operating point of the plant (1), in particular (1), based on the recorded input data, and - Controlling or regulating the operating point of the plant (1) based on the determined operating point, characterized in that the determination includes determining a hydrogen flow supplied to or removed from the hydrogen storage (33).

2. Method according to claim 1, characterized in that the control or regulation of the operating point of the plant (1) is carried out based on the determined operating point in such a way that a hydrogen inlet stream supplied to an ammonia synthesis (40) of the plant (1) is controlled or regulated.

3. Method according to claim 1 or 2, characterized in that the determination additionally comprises determining an expected generated electric current of the renewable electricity source (11, 12, 13), a hydrogen current generated in an electrolysis (20) of the plant (1), a charging or discharging of the battery (14) of the plant (1) and / or a fill level of the hydrogen storage.

4. Method according to one of the preceding claims, characterized in that the determination is carried out in such a way that the ammonia production of the plant (1) is maximized, wherein a fluctuating The stress on plant components resulting from the specific operating point is minimized or at least lies below a threshold value. 5- Method according to one of the preceding claims, characterized in that the determination of the hydrogen flow supplied to or removed from the hydrogen storage (33) is carried out in such a way that a change in an operating point of the system (1) can be avoided as far as possible, a new operating point of the system (1) is as close as possible to a current operating point and / or a pressure or a change in pressure in the hydrogen storage (33) is within limit values.

6. Method according to one of the preceding claims, characterized in that the determination of the hydrogen flow supplied to or removed from the hydrogen storage (33) is based on a predicted hydrogen production rate and a sliding, cumulative mass of hydrogen in the hydrogen storage (33).

7. Method according to claim 6, characterized in that the predicted hydrogen production rate is determined based on a predicted electrical energy provided by at least one renewable electricity source (11, 12, 13).

8. Method according to claim 7, characterized in that the predicted electrical energy is converted into the predicted hydrogen production rate by means of efficiency curves for the provision of hydrogen.

9. Method according to one of the preceding claims, characterized in that the acquisition includes current weather data, weather data predicted as a trend, a maximum capacity, a pressure and / or a temperature of the hydrogen storage (33), a flow rate of a compressor of the hydrogen storage (33), a maximum capacity of the battery (14) and / or a charging speed of the battery (14).

10. Method according to one of the preceding claims, characterized in that, based on the determination of the operating point, the operating point is specified, in particular by adjusting or regulating a hydrogen inlet flow into an ammonia synthesis (40) of the plant (1), wherein the operating point is specified to a control or regulation of the ammonia synthesis (40) or the operating point is detected by the control or regulation and wherein the control or regulation controls or regulates the ammonia synthesis (40) based on the specified or detected operating point.

11. Method according to one of the preceding claims, characterized in that the detection and determination are carried out repeatedly, preferably continuously, and / or the determination is carried out over a time horizon, wherein the time horizon comprises at least one future point in time, preferably at least two future points in time, and particularly preferably at least four future points in time.

12. Method according to one of the preceding claims, characterized in that the method after determination comprises a correction of the operating point, wherein the correction is based on a minimum and maximum ammonia production rate of the plant and / or on a minimum and maximum hydrogen storage pressure.

13. Method according to one of the preceding claims, characterized in that the operating point of the plant (1) is controlled or regulated based on the determined operating point in such a way that a hydrogen inlet flow supplied to an ammonia synthesis (40) of the plant (1) is supplied proportionally from the hydrogen storage (33) and hydrogen generated in an electrolysis (20) of the plant (1) in accordance with the determined hydrogen flow supplied to or removed from the hydrogen storage (33).

14. Method according to one of the preceding claims, characterized in that the provision of the hydrogen is predominantly, preferably to more than 75%, particularly preferably exclusively by electricity from which is supplied by at least one renewable electricity source (11, 12, 13), the provision preferably being carried out by alkaline water electrolysis. 15- Method according to one of the preceding claims, characterized in that the ammonia synthesis (40) of the plant (1) is controlled free from an optimization model.

16. Plant (1) for ammonia synthesis with a power supply (10) comprising at least a renewable power source (11, 12, 13), a hydrogen storage (33), an electric battery (14) and means (51, 52, 53) adapted to perform the steps of the method according to any one of claims 1 to 15.

17. Plant (1) according to claim 16, characterized in that the provision of the hydrogen is predominantly, preferably to more than 75%, particularly preferably exclusively supplied by electricity from the at least one renewable electricity source (11, 12, 13).

18. Plant (1) according to claim 16 or 17, characterized in that the provision of the hydrogen is designed as an alkaline water electrolysis device (AWE), a proton exchange membrane electrolysis device (PEM) or a solid oxide electrolyzer cell (SOEC).

19. Control program comprising commands which, when executed by a control unit, cause the control unit to execute the method according to any one of claims 1 to 15.

20. Control program according to claim 19, comprising commands for controlling a hydrogen inlet stream into an ammonia synthesis (40) of the plant (1), in particular relating to a partial supply of the hydrogen inlet stream from the hydrogen storage (33) and hydrogen generated in an electrolysis (20) of the plant (1).

21. Control program according to claim 19 or 20, comprising commands for controlling the fill level of the hydrogen storage (33).

22. Control program according to one of claims 19 to 21, comprising commands for controlling or regulating an ammonia synthesis (40), characterized in that the regulating of the ammonia synthesis (40) is based on the determined operating point.

23. Computer-readable medium on which the control program according to one of claims 19 to 22 is stored.

24. Use of the method according to any one of claims 1 to 15, the apparatus (1) according to any one of claims 16 to 18 and / or the control program according to any one of claims 19 to 22 for the production of ammonia and / or urea.

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