Process for operating an ammonia synthesis with varying plant utilization

Abstract

The present invention relates to a process for operating an ammonia synthesis plant, wherein the ammonia synthesis plant has a recirculation circuit (10), wherein the recirculation circuit (10) comprises a converter (20), a first heat exchanger (30), a second heat exchanger (40), an ammonia separator (50), a compressor (60) and a reactant feed (80), characterized in that the recirculation circuit (10) comprises a heating element (70), wherein in case of partial plant utilization the heating power of the heating element (70) is subjected to closed-loop control according to the reactant gas amount supplied via the reactant feed (80).

Description

[0001] Method for operating an ammonia synthesis with fluctuating capacity utilization

[0002] The invention relates to a process and a plant for the synthesis of ammonia under fluctuating load conditions.

[0003] For decades, ammonia has been produced primarily using the Haber-Bosch process. In most cases, hydrogen is first generated from natural gas, which is then reacted with nitrogen at high pressure and high temperature over a catalyst. Since this is an equilibrium reaction whose equilibrium is not shifted toward the products, the ammonia is separated in a recirculation circuit, and any unconverted hydrogen and nitrogen are returned to the catalyst. However, the use of natural gas produces a corresponding amount of carbon dioxide.

[0004] In order to produce ammonia sustainably, the focus today is on the electrolysis of water using renewable energy. However, this represents a major difference to the previous process. If solar power is used, for example, the day-night cycle results in a period in which no renewable energy is available. By combining solar and wind power, for example, this effect can be mitigated somewhat, but the fundamental problem remains. While it is theoretically possible in some regions to draw electrical energy from the general power grid, it will also be difficult to supply it with renewable energy at these times. Furthermore, plants are also planned that will be located in locations suitable for energy generation and that do not have access to an electrical supply grid.The electrolysis of water to produce hydrogen for an ammonia synthesis plant is known, for example, from US 9 463 983 B2.

[0005] A converter for ammonia synthesis cannot simply be switched on and off. For example, a temperature of at least 350 °C is necessary for the reaction to take place on the catalyst. During operation, the necessary energy (to compensate for thermal losses) is generated by the energy released during the reaction. To compensate for these fluctuations, corresponding systems have energy storage devices (batteries) and / or hydrogen storage. However, these are also limited to a certain size, or rather, economically viable.

[0006] The object of the invention is to adapt the operation of the ammonia synthesis plant in such a way that it can compensate for these general fluctuations in the supply of reactants for ammonia synthesis – especially fluctuations in the supply of hydrogen. For example, the operation of an ammonia synthesis plant should be adapted so that it can still compensate for fluctuations in the generation of renewable energy while using the smallest possible storage capacity.

[0007] This object is achieved by the method having the features specified in claim 1 and the ammonia synthesis plant having the features specified in claim 13. Advantageous further developments emerge from the subclaims, the following description, and the drawings.

[0008] The method according to the invention is used to operate an ammonia synthesis plant. The ammonia synthesis plant has a recirculation circuit, as is conventional. As is known from the prior art, the recirculation circuit comprises a converter, a first heat exchanger, a second heat exchanger, an ammonia separator, a compressor, and a reactant feed. The hydrogen-nitrogen mixture is fed via the reactant feed, passed through the second heat exchanger, heated, fed to the converter, and converted in the converter. The mixture exiting the converter is passed through the first heat exchanger, where it releases the heat generated by the reaction to a heat transfer medium.(In particular, the first heat exchanger can serve to transfer the thermal energy of the gas mixture from the converter to a heat transfer medium for utilizing the thermal energy outside the recirculation circuit, for which purpose it is arranged in the recirculation circuit downstream of the converter and upstream of the second heat exchanger; in particular, the first heat exchanger can be a waste heat boiler, so that the heated heat transfer medium is then hot water, steam, wet steam, saturated steam, superheated steam or the like.) The gas mixture is then passed through the second heat exchanger and cooled (wherein, in return, the stream flowing to the converter is heated).(In particular, the second heat exchanger can be used to release the thermal energy of the gas mixture from the converter to preheat the gas mixture before it is introduced into the converter. For this purpose, it is arranged - at full load - in the recirculation circuit downstream of the first heat exchanger and upstream of the ammonia separator (heat energy releasing side) and downstream of the ammonia separator and upstream of the converter (heat absorbing side). After the second heat exchanger, the mixture enters the ammonia separator, where ammonia is separated. From the ammonia separator, the unreacted hydrogen-nitrogen mixture is fed back to the converter via the second heat exchanger. The ammonia separator can be complex and, for example, have a cooling section and / or additional heat exchangers.

[0009] According to the invention, the recirculation circuit has a heating element. The heating output of the heating element is regulated depending on the amount of reactant gas supplied through the reactant feed. While during normal operation, i.e. typically at 80% to 100% of maximum load, so much thermal energy is generated by the process that it must be removed via the first heat exchanger, this is no longer the case, especially at low partial loads. In fact, the energy generated by the chemical reaction is sometimes no longer sufficient to compensate for the thermal losses. This creates the risk that the converter will cool down. If the converter cools below a critical temperature, for example 350 °C, the chemical reaction can come to a complete standstill (it becomes too kinetically slow). This would then result in further cooling, with the consequence that the plant would first have to be slowly heated up and started up again.To avoid this, the invention involves heating the gases in the recirculation circuit, whereby the converter is kept at the right temperature and thus ready for use at all times, regardless of the load.

[0010] Although appropriate heating elements are known for starting up such systems (as mentioned, for example, by P. Schmitz et al. in “Mechanical integrity of process installations: Barrier alarm management based on bowties” on pages 139-147 in volume 138 of Process Safety and Environmental Protection), what is new is having these permanently in the recirculation circuit and thus compensating for the thermal losses of the system at low partial loads. This process makes it possible to operate the system even at low partial loads without shutting it down. For example, in a purely solar-powered system, the day-night cycle can be better accommodated because very low partial loads can then be run at night without the need for extremely large energy storage and hydrogen storage.

[0011] Full load (maximum load) is the operation of the plant at the maximum supply of reactant gas mixture and thus the production of the maximum possible amount of ammonia (maximum possible capacity).

[0012] Partial load, compared to full load, is the operation of the plant with a feedstock gas mixture below the maximum feedstock gas mixture, with a percentage that utilizes the plant's maximum possible capacity. At 50% partial load, for example, only half the ammonia is produced compared to full load.

[0013] In standby mode, no synthesis takes place; however, the converter and adjacent components are kept at the right temperature to quickly restart the plant. Standby therefore corresponds to a partial load of 0%. In standby mode, the plant components upstream of the recirculation circuit are switched off preferentially. This affects the production of hydrogen and, if necessary, nitrogen. One of the key points for standby mode at a partial load of 0% is the shutdown of the compressors that bring the reactant gases to the pressure of the recirculation circuit (one compressor, which maintains the flow of cycle gas within the recirculation circuit, should be kept running). Even at small partial loads, the energy required for this compression is only slightly lower than in full-load operation.Therefore, a significant amount of energy can be saved by completely shutting down the system components upstream of the recirculation circuit and only maintaining the converter at the right temperature through closed-loop operation. A complete shutdown completely shuts down the system, and the converter also cools down. This is necessary, for example, for maintenance or repair work.

[0014] In a further embodiment of the invention, the recirculation circuit has a first heat exchanger bypass connection (first heat exchanger bypass line). The first heat exchanger bypass connection is arranged to bypass the first heat exchanger. The first heat exchanger bypass connection is switched to bypass the first heat exchanger (for example, by opening a valve of a line which connects the inlet of the first heat exchanger to the outlet of the first heat exchanger, bypassing the first heat exchanger), provided that the amount of reactant gas supplied through the reactant supply falls below a proportion of 25% of the maximum amount, preferably 20% of the maximum amount, or in other words, when the partial load is reduced to 25% of the maximum load of the system, preferably to 20% of the maximum load of the system.To minimize the energy input via the heating element, it is therefore advantageous to eliminate heat loss via the first heat exchanger. Furthermore, this reduces the flow resistance and thus the pressure loss that the compressor must overcome, thus saving further energy.

[0015] In a further alternative embodiment of the invention, the ammonia synthesis plant has a heat transfer medium bypass connection (heat transfer medium bypass line). The heat transfer medium bypass connection is arranged to bypass the first heat exchanger by routing the heat transfer medium around the first heat exchanger. The heat transfer medium bypass connection is switched to bypass the first heat exchanger if the amount of reactant gas supplied through the reactant supply falls below 25% of the maximum amount, preferably 20% of the maximum amount, or in other words, if the partial load is reduced to 25% of the maximum load of the plant, preferably to 20% of the maximum load of the plant. In order to minimize the energy to be introduced via the heating element, it is therefore advantageous to exclude heat loss via the first heat exchanger.Unlike the previously described embodiment, the first heat exchanger is not bypassed, but rather the feed of the heat transfer medium into the first heat exchanger, so that no heat exchange takes place there.

[0016] In a further embodiment of the invention, the heating power Q of the heating element is additionally regulated as a function of the amount of recycle gas flowing through the recirculation circuit. In short: the faster the gas mixture is transported through the converter, the more heat can be removed from the converter. Therefore, the heating power of the heating element is preferably higher when the amount of recycle gas flowing through the recirculation circuit is larger. For example, and preferably, the heating power is therefore regulated proportionally (in a linear relationship) to the amount of recycle gas flowing through the recirculation circuit as a percentage V of the maximum amount.

[0017] Q oc

[0018] In the context of the invention, the recycle gas quantity is to be understood as a material flow (molar flow) and not as a volume flow or mass flow.

[0019] In a further embodiment of the invention, the heating power Q is chosen proportional to the exponential function of the negative percentage T of the reactant gas quantity supplied through the reactant feed in relation to the maximum quantity. Empirically, the following relationship has been found:

[0020] T

[0021] Q oc e const 2 where const2 is a constant to be determined for the respective system (see below).

[0022] In a further embodiment of the invention, for a constant partial load, the heating power Q is selected to be proportional to the maximum system capacity K. Empirically, the following relationship was found:

[0023] QC

[0024] In a further embodiment of the invention, the heating power is set to 0 if the amount of reactant gas supplied through the reactant feed exceeds 20% of the maximum amount. At partial loads of more than 20%, the energy generated by the chemical reaction is sufficiently large that supply via the heating element is not necessary. Therefore, to simplify process control, the value is set to zero for higher partial loads; only below a partial load of 20% is the heating power according to the invention introduced via the heating element.

[0025] For a maximum system capacity K, an upper limit and a lower limit for the heating output can be determined using the above-mentioned relations as a function of the maximum recirculation quantity V and the supplied reactant gas quantity T, in particular as follows:

[0026] In a further embodiment of the invention, the upper limit for the heating power Q of the heating element is therefore generally chosen as where K is the maximum system capacity, V is the amount of cycle gas flowing through the recirculation circuit (given as a percentage of the maximum recirculation volume), and T is the amount of reactant gas supplied (given as a percentage of the maximum volume). The proportionality constants consti and const2 can be determined for each system. For example, the constants can be determined by determining the actually required heating output as a function of the amount of reactant gas supplied (determined as a percentage of the maximum volume) for more than one system size (corresponding to at least two different system capacities), and then determining the proportionality constants consti and const2 based on the above formula by curve fitting.

[0027] Particularly preferably, the upper limit for the heating power Q of the heating element is selected as

[0028] Here, an upper limit of 7- 10 -5 MW / tato and used as const22.5. The capacity K is used in daily tons (tato), based on the mass of ammonia produced in the plant, and T and V are used as percentages, resulting in the heating capacity in MW. This value has proven to be a good approximation for an upper limit for a wide variety of plants. The actually required heating capacity Q will therefore be lower than the specified value, for example, if the outside temperature is comparatively high or other influences reduce heat dissipation.

[0029] In a further embodiment of the invention, the lower limit for the heating power Q of the heating element is selected as

[0030] Q > const3- K ' T v— . econst2

[0031] The proportionality constants consts and const2 can be determined, particularly for the respective system, in an analogous manner to the proportionality constants consti and const2.

[0032] Particularly preferably, the lower limit for the heating power Q of the heating element is selected as

[0033] Q > 0.07

[0034] Here, a lower limit of 0.07- 10' is used as consti 5 MW / tato and const2 2.5 are used, and the capacity K in daily tons (tato), relative to the mass of ammonia produced in the plant, and K and V are used as percentages, so that the heating capacity is then calculated in MW. This value has proven to be a good approximation for a lower limit for a wide variety of plants.

[0035] In a further embodiment of the invention, the lower limit for the heating power Q of the heating element is selected as

[0036] Q > 0.1 kW / ta to K at 0% reactant gas supply (e.g., during standby operation). This represents the usual lower limit even under optimal conditions.

[0037] Particularly preferably, the heat quantity Q between this upper limit and this lower limit at a partial load between 20% and 0% is selected such that the temperature in the converter does not fall below a target temperature, for example 370 °C. In a further embodiment of the invention, the recirculation circuit has an ammonia separator bypass connection (ammonia separator bypass line). The ammonia separator bypass connection is arranged to bridge the ammonia separator. The ammonia separator bypass connection is switched to completely bypass the ammonia separator, for example if the amount of reactant gas supplied through the reactant feed falls below a proportion of 10% of the maximum amount, preferably 5% of the maximum amount, particularly preferably if this is reduced to 0%, i.e. no further conversion takes place.Bridging the ammonia separator with simultaneous further supply of reactant gas mixture is therefore particularly useful during transfer to standby mode (0% partial load) and during restart.

[0038] In a further embodiment of the invention, the recirculation circuit has an ammonia separator bypass connection. The ammonia separator bypass connection is arranged to bypass the ammonia separator. The ammonia separator bypass connection is switched to partially bypass the ammonia separator if the amount of reactant gas supplied through the reactant feed falls below 80% of the maximum amount, preferably 50% of the maximum amount. As a result, less or no ammonia is removed from the recirculation circuit during partial load operation, so that, due to equilibrium, less or no new ammonia is produced in the converter and, consequently, less or no reactant gas needs to be supplied.

[0039] As already explained, the invention can compensate for general fluctuations in the supply of reactants for ammonia synthesis, especially fluctuations in the supply of nitrogen and hydrogen. It is fundamentally irrelevant where the reactants originate and which chemical or physical processes (e.g., during production or processing) are used to provide them. These reactants can be provided, for example, using conventionally generated energy (e.g., electrical energy obtained from nuclear energy or fossil fuels) or using renewably generated energy (e.g., electrical energy obtained from wind energy, solar energy, bioenergy, hydropower, or geothermal energy).Furthermore, the reactants can also be obtained directly from corresponding processes, for example, in the case of hydrogen, from biological processes, from the pyrolysis of hydrocarbons (such as methane pyrolysis), or from thermal water splitting in a solar furnace. In a further embodiment of the invention, the hydrogen supplied to the reactant feed is produced by electrolysis using renewably generated energy. This avoids the CCh emissions caused by hydrogen production, for example, from natural gas ("green ammonia"). The disadvantage of fluctuating hydrogen production can be particularly well compensated for by the process according to the invention.

[0040] In a further embodiment of the invention, the decision regarding the amount of reactant gas supplied is made as a percentage of the maximum amount depending on the forecast of energy generation and the available storage amount of electrical energy and / or hydrogen. Accordingly, according to this further embodiment of the invention, the amount of reactant gas supplied to the converter is determined / specified, in particular, as a percentage of the maximum amount based on a forecast of energy generation and the available storage amount of electrical energy and / or hydrogen. A minimum amount of energy is required to operate the compressor and maintain the temperature of the converter.For example, if we consider the (hypothetical) case of energy generation using solar technology and a comparatively small energy storage system, it may be sensible to stop hydrogen synthesis in the afternoon and store the energy in order to have sufficient energy for standby operation (0% partial load) until sunrise. With a very large solar field and a very large battery, operation could also be carried out at night, either at full load or only at a less reduced partial load of, for example, 50%. If we consider another hypothetical case of energy generation using wind power in the offshore area, for example, if a lull in wind is predicted for, say, 3 days, operation can be put into standby mode (0% partial load) in good time, so that the energy from the energy storage system is then sufficient to bridge the standby operation for the period of the lull.

[0041] In a further embodiment of the invention, the other electrical consumers, in particular the compressor, are taken into account for the decision. Accordingly, according to this further embodiment of the invention, the amount of reactant gas supplied to the converter is determined / specified, in particular as a percentage of the maximum amount, taking into account the other electrical consumers, in particular the compressors. This primarily concerns the energy required by these consumers during the time period to be bridged.

[0042] In a further embodiment of the invention, the plant components of the ammonia synthesis plant arranged upstream of the recirculation circuit (and thus outside the recirculation circuit) are switched off when 0% of the feed gas quantity is supplied.

[0043] In a further embodiment of the invention, a deep standby is defined as a further operating state. In deep standby, the temperature in the converter is reduced, for example, to 250 °C to 300 °C. In contrast to (regular) standby, direct start-up is no longer possible. First, the converter must be reheated at, for example, 50 °C per hour. This means that 2 hours are lost, for example, to bring the converter back up to temperature so that the reaction on the catalyst can resume. For this purpose, energy radiation is greatly reduced, so that the energy requirement is massively lower than in standby mode, and thus a longer period can be bridged with reduced energy production.

[0044] In a further aspect, the invention relates to an ammonia synthesis plant for carrying out the process according to the invention. The ammonia synthesis plant has a recirculation circuit, as is typical for prior art ammonia synthesis plants. The recirculation circuit comprises a converter, a first heat exchanger, a second heat exchanger, an ammonia separator, a compressor, and a reactant feed. The hydrogen-nitrogen mixture is fed via the reactant feed, passed through the second heat exchanger and heated, fed to the converter, and converted in the converter. The mixture exiting the converter is passed through the first heat exchanger, where it transfers the heat generated by the reaction to a heat transfer medium. In particular, the first heat exchanger can be a waste heat boiler (so that the heated heat transfer medium is then hot water, steam, wet steam, saturated steam, superheated steam, or the like).The gas mixture is then passed through the second heat exchanger and cooled (while, in turn, the stream flowing to the converter is heated). After the second heat exchanger, the mixture enters the ammonia separator, where further cooling takes place and ammonia is separated. From the ammonia separator, the unreacted hydrogen-nitrogen mixture is fed back to the converter via the second heat exchanger.

[0045] According to the invention, the recirculation circuit has a heating element. The ammonia synthesis plant further comprises a control device. The ammonia synthesis plant has a reactant flow detection device and a recycle gas quantity detection device. The control device is connected to the reactant flow detection device for transmitting the reactant flow rate (the volume flow of the supplied reactant) and to the recycle gas quantity detection device for transmitting the recycle gas quantity. The control device is connected to the heating element for regulating the heating element. The control device thereby knows the percentage partial load with the aid of the reactant flow detection device and can thus adjust the heating output of the heating element accordingly according to the method according to the invention.

[0046] The term "reactant flow detection device" is to be understood broadly within the meaning of the invention. On the one hand, the gas flow can, of course, be detected directly, for example, via the flow velocity and pressure. However, the detection can also be done indirectly, for example, via the power consumption of a hydrogen electrolysis system and the resulting hydrogen flow flowing from the electrolysis device to the recirculation circuit.

[0047] In a further embodiment of the invention, the recirculation circuit has a first heat exchanger bypass connection, wherein the first heat exchanger bypass connection is arranged to bypass the first heat exchanger. This allows the first heat exchanger to be bypassed initially when partial load decreases, with the aforementioned advantages.

[0048] In a further embodiment of the invention, the recirculation circuit has an ammonia separator bypass connection, wherein the ammonia separator bypass connection is arranged to bypass the ammonia separator. As explained above, the ammonia separator bypass connection is used at low partial loads, particularly during standby operation (0% partial load).

[0049] In a further embodiment of the invention, the heating element is arranged between the second heat exchanger and the converter.

[0050] In a further alternative embodiment of the invention, the heating element is arranged in the second heat exchanger.

[0051] In a further alternative embodiment of the invention, the heating element is arranged in the converter.

[0052] In a further embodiment of the invention, the heating element is an electric heating element.

[0053] In another alternative embodiment of the invention, the heating element is an ammonia burner. While an ammonia burner makes little economic sense, since the energy generated by burning ammonia is less than that required for synthesis, it can still be useful, particularly when connection to a public power grid is not possible, for example, in an offshore application. Furthermore, it naturally makes it easier to bridge longer periods of time, such as a lull in wind, without the need for extremely large batteries. This can therefore also be a decisive factor in offshore applications, for example, where space is also a crucial consideration.

[0054] In a further embodiment of the invention, the recirculation circuit has a second heat exchanger bypass connection (second heat exchanger bypass line), wherein the second heat exchanger bypass connection is arranged to bridge the second heat exchanger between the ammonia separator bypass connection and the converter.

[0055] The following example illustrates the process. The decision (determination / specification) as to how the ammonia synthesis plant is operated is primarily based on the state of charge of an energy storage device (batteries) and / or the state of charge of a hydrogen storage device. The energy content of the battery is EB. The content of a hydrogen storage device can be specified as a quantity of substance (mol, kg); to simplify the calculation, however, this quantity can also be converted into the equivalent energy that would be required for its production or that was expended in its manufacture, i.e., the energy equivalent EH. Furthermore, the power requirement for standby (PS, minimum energy consumption while shutting down all components outside the recirculation circuit, in particular an optional hydrogen electrolysis plant), i.e., the minimum energy consumption of the plant, is taken into account.Furthermore, the power requirement PO for operation at the lowest possible throughput plus the power requirement PE for hydrogen electrolysis at the lowest possible throughput is specified. In addition, there is the forecast for the expected renewably generated energy. This is considered in two time intervals. The first forecast concerns a first time window T1 of, for example, and in particular, 4 hours. The first time window can be adjusted, in particular, depending on the local and / or temporal forecast accuracy. This is considered to be comparatively reliable. In addition, a second time window T2 of approximately 4 to 72 hours is considered, although the forecast accuracy is correspondingly lower here. A first energy quantity E1 is expected / forecast for the first time interval T1 and a second energy quantity E2 for the second time interval T2.To estimate the uncertainty in the energy production forecast, a safety factor S can be introduced, which is preferably between 0.7 (cautious) and 1 (confident). Furthermore, it is useful to define a minimum battery state of charge (EBC) at which the battery is normally charged. This can prevent, for example, deep discharge. If a time interval T is considered, the energy requirement is calculated by multiplying the power requirement by time. Thus, the energy requirement EO for operation at the lowest possible throughput is the product of PO and T, and the energy requirement EE for hydrogen electrolysis at the lowest possible throughput is the product of PE and T.

[0056] Some special cases are considered below. First, we assume that the battery and hydrogen storage are either empty or not present. Two subcases are distinguished for this case. If energy production decreases, the system is switched to standby mode as soon as the energy production falls below the sum of PO and PE in the forecast window T1. If the value falls further below the value ES, a complete shutdown must occur. If energy production increases while the system is in standby mode, it is switched back to normal operation as soon as the energy production is always greater than EO plus EE for the entire period T1.

[0057] In a second case, the situation is considered where a battery is present (and at least partially charged), but no hydrogen storage is available or the storage is empty. Here, too, the two subcases are differentiated by whether the expected energy production is increasing or decreasing. If energy production decreases, the system switches to standby mode as soon as the sum of E1 and EB is less than the product of time T1 and the sum of PO and PE. Fluctuations within the time interval can then no longer be absorbed by the battery.

[0058] E1 + EB < (PO + PE) * T1

[0059] If the period T2 is also to be considered, it is advantageous to consider the safety factor S. This is applied to the expected energy production.

[0060] E2 * S + EB < (PO + PE) * T2

[0061] If the voltage falls below this level, the system switches to standby mode.

[0062] When energy production increases again, this is reversed accordingly and it switches back to normal operation as soon as the sum of E1 and EB is greater than the product of time T1 and the sum of PO and PE.

[0063] E1 + EB > (PO + PE) * T1

[0064] The analysis can be carried out analogously for the second time window T2: E2 * S + EB > (PO + PE) * T2

[0065] Here, too, the safety factor is given priority.

[0066] In a third case, both a battery and a hydrogen storage unit are present, and each is at least partially charged or filled. Here, too, a distinction is made between the two subcases: decreasing or increasing energy production. In this case, if energy production decreases, the system switches to standby mode as soon as the sum of E1, EB, and EH is less than the product of time T1 and the sum of PO and PE. Fluctuations within the time interval can then no longer be absorbed by the battery.

[0067] E1 + EB + EH < (PO + PE) * T1

[0068] If the period T2 is also to be considered, it is advantageous to consider the safety factor S. This is applied to the expected energy production.

[0069] E2 * S + EB + EH < (PO + PE) * T2

[0070] If the voltage falls below this level, the system switches to standby mode.

[0071] When energy production increases again, this is reversed accordingly and it switches back to normal operation as soon as the sum of E1, EB and EH is higher than the product of the sum of PO and PE multiplied by the time T1.

[0072] E1 + EB + EH > (PO + PE) * T1

[0073] The second time window T2 can be considered in a similar way:

[0074] E2 * S + EB + EH > (PO + PE) * T2

[0075] Here, too, the safety factor is given priority. If the minimum battery charge level (EBC) is to be taken into account, EB can be replaced by (EB - EBC).

[0076] The ammonia synthesis plant according to the invention is explained in more detail below using an embodiment shown in the drawings.

[0077] Fig. 1 Schematic representation of a recirculation circuit

[0078] Fig. 1 shows a simplified schematic of the recirculation circuit 10. A hydrogen-nitrogen mixture is fed to the recirculation circuit for conversion via the reactant feed 80. This flow is subject to significant fluctuations and can fluctuate between 100% (maximum load) and 0% (standby). The gas flow is fed to the converter 20 via the compressor 60 and the second heat exchanger 40. During normal operation, the gas mixture leaving the converter 20 is fed via the first heat exchanger 30 for removing the reaction heat and the second heat exchanger 40 into the ammonia separator 50. There, the ammonia is separated and removed from the circuit via the product discharge 90.

[0079] If the partial load drops below 70%, for example, the ammonia separator bypass connection 110 is partially opened so that less ammonia condenses in the ammonia separator 50 and the recycle gas has a higher ammonia content. This reduces the conversion in the converter 20 accordingly. As the partial load continues to decrease, the ammonia separator bypass connection 110 is opened further and further. Preferably, the gas flow is directed completely through the ammonia separator bypass connection 110 in standby mode.

[0080] If the partial load continues to drop below 25%, for example, the first heat exchanger bypass connection 100 is opened and thus the energy dissipation via the first heat exchanger 30 is prevented.

[0081] If the partial load drops further below, for example, 20%, heating power is added to the system via the heating element 70. For example, the heating power is adjusted accordingly:

[0082] Purely as an example, for a partial load of 10%, a maximum plant capacity of 600 daily tonnes (tato), based on the mass of ammonia produced in the plant, and a value of 50% of the cycle gas flowing through the recirculation circuit as a percentage of the maximum recirculation quantity, the value is:

[0083] 600 - 50

[0084] Q = 7 ■ IO“ 5 - MW = 2.1 ■ e -4 MI / !Z = 3.8 ■ 1O- 2 Motor vehicles « 40W

[0085] Purely as an example, for a partial load T of 0% (standby operation), a maximum plant capacity K of 600 daily tonnes (tato) and a value V of 50 of the cycle gas quantity flowing through the recirculation circuit as a percentage of the maximum recirculation quantity, an upper value of 2.1 MW results.

[0086] At very low partial loads, for example, below 6%, this is reduced to 0%, meaning no operation between 6% and 0%, and the recirculation circuit is placed in standby mode. For this purpose, the ammonia separator 50 is bridged with the ammonia separator bypass connection 110. The minimum heating power provided by the heating element 70 is given by:

[0087] <2 = 1 kW / tato ■ K

[0088] For example, for an exemplary plant with a maximum plant capacity of 600 tonnes per day (tato), this results in a minimum value of 600 kW corresponding to 0.6 MW of heating power to keep the plant in standby mode.

[0089] Thus, for the aforementioned plant with a capacity of 600 tpd in standby mode (T = 0), the aforementioned upper limit of 2.1 MW and a lower limit of 600 kW are achieved. The actual value then depends, for example, on ambient weather conditions and the like and is preferably finely controlled via temperature sensing in the converter. Likewise, the second heat exchanger 40 can be at least partially bypassed with the second heat exchanger bypass connection.

[0090] The invention therefore makes it possible to adapt the operation of an ammonia synthesis plant so that it can compensate for fluctuations in the generation of renewable energy while using the smallest possible storage capacity. Furthermore, the invention makes it possible to adapt the operation of an ammonia synthesis plant so that these fluctuations in the supply of reactants for ammonia synthesis can generally be compensated.For example, it can be used to counteract fluctuations in the supply of hydrogen that can occur if the supply of hydrogen via tank systems or pipelines is uneven or interrupted, or if the supply of hydrogen via reformer plants upstream of ammonia synthesis is uneven, for example due to repair work, maintenance work or operational disruptions in these reformer plants or due to irregular availability of reactants from these reformer plants, for example hydrocarbons such as methane.

[0091] Reference symbol

[0092] 10 Recirculation circuit

[0093] 20 converters

[0094] 30 first heat exchanger

[0095] 40 second heat exchanger

[0096] 50 ammonia separators

[0097] 60 compressors

[0098] 70 heating element

[0099] 80 reactant feed

[0100] 90 Product delivery

[0101] 100 First heat exchanger bypass connection

[0102] 110 Ammonia separator bypass connection

[0103] 120 Second heat exchanger bypass connection

[0104] V valve

Claims

Patent claims 1. Method for operating an ammonia synthesis plant, wherein the ammonia synthesis plant has a recirculation circuit (10), wherein the recirculation circuit (10) has a converter (20), a first heat exchanger (30), a second heat exchanger (40), an ammonia separator (50), a compressor (60) and a reactant feed (80), characterized in that the recirculation circuit (10) has a heating element (70), wherein at partial load the heating power of the heating element (70) is regulated as a function of the amount of reactant gas supplied by the reactant feed (80).

2. Method according to claim 1, characterized in that the recirculation circuit (10) has a first heat exchanger bypass connection (100), wherein the first heat exchanger bypass connection (100) is arranged to bypass the first heat exchanger (30), wherein the first heat exchanger bypass connection (100) is switched to bypass the first heat exchanger (30) if the amount of reactant gas supplied by the reactant supply (80) falls below 25% of the maximum amount, preferably 20% of the maximum amount.

3. Method according to claim 1, characterized in that the ammonia synthesis plant has a heat transfer medium bypass connection, wherein the heat transfer medium bypass connection is arranged to bypass the first heat exchanger (30), wherein the heat transfer medium is routed around the first heat exchanger through the heat transfer medium bypass connection, wherein the heat transfer medium bypass connection is switched to bypass the first heat exchanger (30) if the amount of reactant gas supplied by the reactant feed (80) falls below 25% of the maximum amount, preferably 20% of the maximum amount.

4. Method according to one of the preceding claims, characterized in that the heating power of the heating element (70) is additionally regulated depending on the amount of circulating gas flowing through the recirculation circuit (10). A method according to any one of the preceding claims, characterized in that the heating power is selected proportionally to the exponential function of the negative percentage of the reactant gas quantity supplied by the reactant feed (80) relative to the maximum quantity. A method according to any one of the preceding claims, characterized in that the heating power is selected proportionally to the maximum system capacity. A method according to any one of the preceding claims, characterized in that the heating power is set to 0 if the reactant gas quantity supplied by the reactant feed (80) exceeds 20% of the maximum quantity. A method according to any one of the preceding claims, characterized in that the heating power Q of the heating element (70) is selected as with K as plant capacity, V as the amount of circulating gas flowing through the recirculation circuit (10) as a percentage of the maximum recirculation quantity, T as the amount of reactant gas supplied as a percentage of the maximum quantity, where in particular consti can be chosen as 7 10' 5 MW / tato and const2 can be selected as 2.

5. Method according to one of the preceding claims, characterized in that the heating power Q of the heating element (70) is selected as K - V Q > const3- — g const2 with K as plant capacity, V as the amount of circulating gas flowing through the recirculation circuit (10) as a percentage of the maximum recirculation quantity, T as the amount of reactant gas supplied as a percentage of the maximum quantity, where in particular consts can be chosen as 0.07- 10' 5MW / tato and const2 can be selected as 2.

5. Method according to one of the preceding claims, characterized in that the heating power Q of the heating element (70) is selected as Q > 0.1 kW / tato- K at 0% of the reactant gas supplied. Method according to one of the preceding claims, characterized in that the recirculation circuit (10) has an ammonia separator bypass connection (110), wherein the ammonia separator bypass connection (110) is arranged to bypass the ammonia separator (50), wherein the ammonia separator bypass connection (110) is switched to completely bypass the ammonia separator (50) if the reactant gas supplied by the reactant supply (80) falls below 10% of the maximum quantity, preferably 5% of the maximum quantity.A method according to any one of the preceding claims, characterized in that the recirculation circuit (10) has an ammonia separator bypass connection (110), wherein the ammonia separator bypass connection (110) is arranged to bypass the ammonia separator (50), and wherein the ammonia separator bypass connection (110) is switched to partially bypass the ammonia separator (50) if the amount of reactant gas supplied by the reactant feed (80) falls below 80%, preferably 50%, of the maximum amount. A method according to any one of the preceding claims, characterized in that the hydrogen supplied to the reactant feed (80) is produced by electrolysis using regeneratively generated energy.The method of claim 13, characterized in that the amount of reactant gas supplied to the converter is determined as a percentage of the maximum amount based on a forecast of energy generation and the available storage quantity of electrical energy and / or hydrogen. The method of claim 14, characterized in that the amount of reactant gas supplied to the converter is determined as a percentage of the maximum amount, taking into account the other electrical consumers, in particular the compressor (60). Method according to one of the preceding claims, characterized in that the plant components of the ammonia synthesis plant arranged upstream of the recirculation circuit (10) are switched off when 0% of the amount of reactant gas supplied is zero. Ammonia synthesis plant for carrying out the process according to one of the preceding claims, wherein the ammonia synthesis plant comprises a recirculation circuit (10) has a converter (20), a first heat exchanger (30), a second heat exchanger (40), comprising an ammonia separator (50), a compressor (60) and a reactant feed (80), characterized in that the recirculation circuit (10) comprises a heating element (70), wherein the ammonia synthesis plant comprises a control device, wherein the ammonia synthesis plant comprises a reactant current feed detection device, wherein the ammonia synthesis plant comprises a comprising a circulating gas quantity sensing device, wherein the control device is connected to the reactant current supply sensing device for transmitting the reactant current intensity, wherein the control device is connected to the circulating gas quantity sensing device for transmitting the The circulating gas quantity is connected, with the control device for regulating the heating element (70) being connected to it. Ammonia synthesis plant according to claim 17, characterized in that the recirculation circuit (10) has a first heat exchanger bypass connection (100), wherein the first heat exchanger bypass connection (100) is arranged to bypass the first heat exchanger (30). Ammonia synthesis plant according to one of claims 17 to 18, characterized in that the recirculation circuit (10) has an ammonia separator bypass connection (110), wherein the ammonia separator bypass connection (110) is arranged to bypass the ammonia separator (50). An ammonia synthesis plant according to any one of claims 17 to 19, characterized in that the heating element (70) is arranged between the second heat exchanger (40) and the converter (20) downstream of the second heat exchanger (40). An ammonia synthesis plant according to any one of claims 17 to 19, characterized in that the heating element (70) is arranged in the second heat exchanger (40). An ammonia synthesis plant according to any one of claims 17 to 19, characterized in that the heating element (70) is arranged in the converter (20). An ammonia synthesis plant according to any one of claims 17 to 22, characterized in that the heating element (70) is an electric heating element. An ammonia synthesis plant according to any one of claims 17 to 22, characterized in that the heating element (70) is an ammonia burner.Ammonia synthesis plant according to one of claims 17 to 24, characterized in that the recirculation circuit (10) has a second heat exchanger bypass connection (120), wherein the second heat exchanger bypass connection (120) is arranged to bridge the second heat exchanger (40) between the ammonia separator bypass connection (110) and the converter (20).

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