Integrated process for synthesis of ammonia and nitric acid

Abstract

An integrated process for the synthesis of ammonia and nitric acid, comprising the production of hydrogen from water electrolysis, controlled by selective switching between a first mode of operation and a second mode of operation, wherein in the first mode of operation, an excess of ammonia is produced and stored in a suitable ammonia reservoir; in the second mode of operation, ammonia from the ammonia reservoir is used to provide an additional input amount of ammonia for the production of nitric acid; the switching between the first and second modes is based on the amount of power delivered to the water electrolysis.

Description

Technical Field

[0001] This invention relates to the field of ammonia and nitric acid production. In particular, this invention relates to a method for controlling an integrated process for producing ammonia and nitric acid, and to a process or apparatus for implementing said method. Background Technology

[0002] Conventional ammonia production involves reforming hydrocarbon feedstocks to produce hydrogen-containing syngas. The syngas is then purified through water-gas shift conversion, carbon dioxide removal, and optional methanation, finally converting to ammonia in a suitable catalytic converter. The makeup gas used for ammonia synthesis also includes nitrogen, which can be introduced along with combustion air, for example, in a secondary reformer or in a suitable air separation unit. Therefore, ammonia synthesis may also involve nitrogen production.

[0003] Ammonia synthesis takes place under high pressure. Compressing the ammonia makeup gas to the ammonia synthesis pressure represents the primary energy input of the process. Thermal energy is typically recovered from the process as steam, for example from thermal reforming effluents and ammonia converters. Steam can expand in a steam turbine at sufficient pressure to generate energy. Therefore, steam can be used internally within the process to at least partially satisfy the process's thermal and / or energy input.

[0004] The environmental problems associated with ammonia production are that the heat energy used to reform hydrocarbon feedstocks is usually provided by the combustion of fossil fuels (such as natural gas), which produces large amounts of carbon dioxide emissions into the atmosphere.

[0005] Emerging trends call for ammonia processes that reduce carbon footprint at an acceptable cost. Ammonia with reduced carbon footprint, particularly reduced CO2 emissions, is referred to as low-carbon ammonia. Equipment configured to produce ammonia with reduced emissions is called low-carbon ammonia equipment.

[0006] Known technologies for producing low-carbon ammonia include powering the electrolysis of water to produce hydrogen using renewable energy sources such as solar or wind power. Using this technology, some or all of the hydrogen needed for ammonia synthesis can come from renewable sources. When the total amount of hydrogen comes from renewable energy sources, the resulting low-carbon ammonia is often referred to as green ammonia.

[0007] One drawback of using renewable energy sources is the availability of that energy. Renewable energy sources (such as solar energy) are typically subject to fluctuations, which inevitably propagate throughout the process.

[0008] The processes used to produce ammonia and nitric acid involve several turbomachinery components, such as turbines and compressors, which are inherently inflexible: therefore, the entire process is inflexible and should be operated close to design conditions.

[0009] In particular, the amount of steam and power generated internally is affected by fluctuations in hydrogen production. Steam turbines are typically designed to operate close to their rated steam flow rate. When the steam flow rate decreases, the efficiency of the steam turbine can drop sharply, or it may become inoperable. If the energy produced internally decreases, the process may require external energy input, which translates to additional costs.

[0010] Current solutions to the aforementioned drawbacks include installing hydrogen storage devices as buffers to provide a stable H2 flow rate to the synthesis loop and / or battery, or other energy storage methods to provide a stable energy flow to water electrolysis and other power-consuming devices in the equipment. However, these solutions are not entirely satisfactory due to the capital costs of hydrogen and energy storage equipment.

[0011] The aforementioned drawbacks are particularly pronounced when ammonia production is integrated with the production of nitric acid and, possibly, ammonium nitrate. In such integrated facilities, fluctuations in the energy source used for hydrogen production affect ammonia production, as well as the subsequent production of nitric acid and ammonium nitrate.

[0012] Therefore, given the above considerations, there is a great need to provide greater flexibility for the integrated production of ammonia and nitric acid in order to maintain efficiency and profitability, even if hydrogen production is powered by fluctuating or intermittent power sources. Summary of the Invention

[0013] This invention addresses the problem of providing a flexible, adaptively controlled integrated ammonia-nitric acid process, wherein at least a portion of the hydrogen used for ammonia synthesis is generated via water electrolysis, thus the process is subject to the availability of the power source for the electrolysis process. In particular, this invention addresses the problem of how to follow fluctuations in the power source, which is typically the case with renewable energy sources such as solar power.

[0014] The problem was solved by using an integrated process for controlling the synthesis of ammonia and nitric acid, according to the following scheme.

[0015] This method is applied to a process in which hydrogen is generated by water electrolysis and used to produce an ammonia supplement gas; the supplement gas reacts to form ammonia; at least a portion of the ammonia is used to produce nitric acid. In some embodiments, the method is applied to a process in which ammonium nitrate is also produced.

[0016] The term "ammonia supplement gas" refers to a gas containing appropriate amounts of hydrogen and nitrogen used in the synthesis of ammonia. The gas typically has a hydrogen-to-nitrogen molar ratio of 3 or approximately 3.

[0017] The method includes a process for selectively switching between a first operating mode and a second operating mode, wherein:

[0018] In the first operating mode, the production of ammonia and nitric acid is regulated in such a way that the process has a first output of nitric acid; an excess of ammonia is produced compared to the ammonia required to produce the first output of nitric acid; and the excess ammonia is stored in a suitable ammonia storage tank.

[0019] In the second operating mode, the production of ammonia and nitric acid is regulated in such a way that the process has a second output of nitric acid; less ammonia is produced than is required to produce the second output of nitric acid, such that the production of nitric acid requires an additional input of ammonia, and ammonia from the ammonia storage tank is used to provide the additional input.

[0020] The method includes switching between a first mode and a second mode based on the amount of power delivered to the water electrolysis.

[0021] Therefore, this method allows the process to adapt to the amount of power available for the water electrolysis process. The amount of power delivered to the water electrolysis process can vary due to cost and / or the actual availability of the source. Generally, the first operating mode is selected when more power is available, and the second operating mode is selected when less power or no power is available.

[0022] As mentioned above, the choice of operating mode can be based on cost and / or availability of resources. For example, when electricity is drawn from the grid, mode one can be chosen when energy prices are low, while mode two can be chosen when prices are high.

[0023] A particularly interesting embodiment of the invention relates to a situation where water electrolysis is powered by renewable energy. In this case, a first mode can be selected when the renewable energy source is available and can generate a large amount of power; and a second mode can be selected when the source is unavailable or only available to a limited extent, such that no or a small amount of power can be supplied to the water electrolysis process.

[0024] For example, when the renewable energy source is solar energy, the first mode can be selected during the day, and the second mode can be selected at night, or more generally, when solar energy is essentially unavailable (e.g., due to cloud cover).

[0025] This invention begins with the discovery that when ammonia production relies on electricity, and especially on renewable energy sources used for hydrogen production, there may be a lack of input power depending on cost and / or the availability of sources. This invention compensates for this lack of input power by storing ammonia when sources are fully available, so that it can be used when sources are insufficient or unavailable. Therefore, this invention allows for constant or nearly constant nitric acid production, regardless of fluctuations or intermittent availability of sources.

[0026] According to certain embodiments of the invention, the aforementioned lack of input power can also be supplemented by transferring a proportionally larger amount of thermal and / or electrical energy from the nitric acid production process to the ammonia synthesis process. When available, a tied-in ammonium nitrate production process can also supply thermal and / or electrical energy to the ammonia synthesis process.

[0027] This invention opens up new possibilities for the production of low-carbon or green ammonia, as well as the production of nitric acid and, optionally, ammonium nitrate. In particular, this invention provides a more flexible process suitable for adapting to fluctuations in hydrogen production based on renewable energy sources.

[0028] Other advantages of the invention include reduced costs of green ammonia synthesis, reduced power requirements for the backup power supply to the water electrolysis and compression units, and smaller hydrogen storage units.

[0029] This invention can be applied to a process in which hydrogen production is achieved entirely through water electrolysis, or to a hybrid process in which hydrogen is partly derived from the reforming of fossil fuels and partly from water electrolysis. Detailed Implementation

[0030] Ammonia production takes place in an ammonia unit, while nitric acid production takes place in a nitric acid unit connected to the ammonia unit. The ammonia and nitric acid units can also be considered as part of an integrated system.

[0031] Ammonia production includes hydrogen production, which, according to the invention, is at least partially carried out in a water electrolyzer. If a proper hydrogen / nitrogen ratio is required in the ammonia makeup gas, ammonia production may further include the production of nitrogen in a suitable nitrogen production unit (e.g., an air separation unit).

[0032] Nitric acid production involves the catalytic oxidation of ammonia to obtain a process gas containing nitrogen oxides, which is then contacted with water in a suitable absorption tower to produce nitric acid.

[0033] This invention specifies that the loads of the ammonia and nitric acid equipment are adjusted according to the available power in the water electrolysis process. Specifically, in a first operating mode, the load of the nitric acid equipment is reduced to allow ammonia storage; in a second operating mode, the load of the ammonia equipment decreases with the reduction in the available power for water electrolysis. Therefore, this invention employs swing control, wherein the load of the ammonia equipment substantially follows the availability of renewable energy, while the load of the nitric acid equipment complements the load of the ammonia equipment.

[0034] A first operating mode can be selected when the available power for electrolysis is higher than a first threshold, and a second operating mode can be selected when the power is lower than a second threshold. The first and second thresholds can be the same or different. Preferably, the thresholds are equal to or approximately 50% of the total power consumption of the ammonia equipment including water electrolysis.

[0035] The ammonia plant has a rated ammonia output, and the nitric acid plant has a rated nitric acid output, the rated nitric acid output corresponding to the rated ammonia output that is partially or entirely transported from the ammonia plant to the nitric acid plant for the production of nitric acid.

[0036] Preferably, in the first operating mode, the ammonia plant operates at 80% or more of the rated ammonia output, and the nitric acid plant operates at 50% to 80% of the rated nitric acid output. If the plant is capable of operating at the rated capacity described above, the 80% or higher condition may include up to 100% or more, for example, 80% to 110%.

[0037] In the second operating mode, the ammonia plant can operate at 1% to 30% of the rated ammonia output, preferably 10% to 30% or 20% to 30%; the nitric acid plant can operate at 80% or more of its rated capacity.

[0038] Nitric acid production processes typically output energy as a net form of heat and / or electricity. In nitric acid plants, electricity can be generated from the tail gas of an expansion absorber and / or from the steam produced by expanding the heat released during ammonia oxidation. Heat can be output under pressure as steam (e.g., by removing heat from the catalytic oxidation of ammonia and the cooling of various process streams).

[0039] Therefore, thermal and / or electrical energy can be transferred from the nitric acid production process to the ammonia synthesis process. Here, transfer from the first process to the second process means that power generated by one or more items in the equipment performing the first process is transferred to one or more items in the equipment performing the second process.

[0040] Preferred uses of the power supplied to the connected ammonia plant include: water electrolysis, nitrogen production, and ammonia makeup gas compression. Preferably, the power is primarily used for compressing the ammonia makeup gas.

[0041] In one embodiment of the invention, the delivery of thermal and / or electrical energy from the nitric acid production process to the ammonia synthesis process is also controlled according to the operating mode. Specifically, in a second operating mode, the power delivered to the ammonia synthesis process can be proportionally greater. In particular, in one embodiment of the invention, the ratio of power input from the nitric acid production process to the total input power in the second operating mode is greater than the ratio in the first operating mode.

[0042] Thermal energy is typically output as hot steam. The thermal energy (hot steam) output from nitric acid equipment can be used, for example, to heat ammonia synthesis reactors, by providing suitable heat exchangers inside the reactor to maintain the reactor at a suitable temperature, even when operating at partial load.

[0043] The advantages of transferring energy from a nitric acid plant to an ammonia plant include avoiding or reducing the need for hydrogen storage and / or grid-connected power. A significant advantage is that the ammonia plant can operate in an “islanded” condition, meaning its electrical input is entirely generated within the integrated unit (the nitric acid plant).

[0044] Water electrolysis preferably uses renewable energy. According to various embodiments, all or some of the hydrogen in the ammonia supplement gas can be generated from renewable energy. In this case, the method involves switching between a first mode and a second mode based on the amount of available power from the renewable energy used in the electrolysis process. One embodiment of particular interest is the production of hydrogen from solar electrolysis.

[0045] During the second operating mode, a portion of the ammonia discharged from the ammonia storage can be burned to provide an additional energy source in the form of heat and / or electricity. This use of stored ammonia provides another way to compensate for energy shortages in the ammonia synthesis process.

[0046] The method of the present invention can be applied to a process that further includes the production of ammonium nitrate from at least partially generated ammonia and nitric acid. Preferably, the method includes, in a first operating mode, the ammonium nitrate production process operating at a reduced output. Generally, the ammonium nitrate production process is controlled in a manner similar to that of the nitric acid production process. More preferably, in the first operating mode, the ammonium nitrate production process can be operated at 50% to 80% of its rated output, and in a second operating mode, the ammonium nitrate production process operates at 80% or more of its rated output.

[0047] Ammonium nitrate production processes typically also output energy as a net form of heat and / or electricity. Therefore, the heat or electricity output from the ammonium nitrate production process can be used in ammonia synthesis processes, particularly in the second operating mode. The ammonium nitrate process is preferably operated in a switching mode at similar nitric acid loads. A related advantage is that, in the low-load ammonia operating mode, steam / energy from ammonium nitrate can be transferred to ammonia.

[0048] Another preferred feature of the invention is the control of the integrated process's operating mode to maintain constant or near-constant steam production. Ammonia and nitric acid production processes include various steps in which heat energy is removed from the process stream and is typically used to generate steam. This steam is either internally used for process steps requiring heat input (e.g., preheating or process stream) or expanded to generate energy for equipment (e.g., compressors and other machinery). Constant or near-constant steam generation helps maintain a stable process and reduces the need for input energy.

[0049] Therefore, one embodiment of the present invention provides:

[0050] A first amount of steam is generated from the heat energy removed from the ammonia production process, and a second amount of steam is generated from the heat energy removed from the nitric acid production process;

[0051] Control the switching between the first operating mode and the second operating mode to keep the total amount of steam (the sum of the first steam amount and the second steam amount) within the desired range.

[0052] Preferably, the process is controlled such that the total amount of steam differs from the first operating mode and the second operating mode by no more than 30%, more preferably by no more than 20%.

[0053] The mechanical and / or electrical energy obtained from the expansion of steam can be used within the process to power at least one of the following steps: generating hydrogen from water electrolysis, generating nitrogen from air, compressing ammonia makeup gas to ammonia synthesis pressure, compressing ammonia in an ammonia refrigeration section, compressing process air in a nitric acid process, and compressing nitrogen-containing oxygen gas in a nitric acid process.

[0054] The steam stream that expands in the steam turbine to recover mechanical and / or electrical energy is medium-pressure steam, and the operating pressure of the steam is preferably between 20 bar and 100 bar, more preferably between 25 bar and 60 bar.

[0055] In one embodiment, the integrated equipment for synthesizing ammonia and nitric acid may include a common vapor network between the nitric acid unit and the ammonia unit.

[0056] The complementary switching operation between the first and second operating modes allows the integrated unit to produce steam almost consistently, because when the steam produced by the ammonia unit is in a low range, the steam produced by the nitric acid unit is in a high range, and vice versa. Therefore, the efficiency of the integrated unit is maintained even during periods of fluctuation in renewable energy supply.

[0057] Therefore, this invention can combine the concept of steam integration with the insight of switching operations between alternative modes to overcome the drawbacks caused by the fluctuation of renewable energy availability.

[0058] Considering the availability of renewable energy sources, such as solar energy, the switching strategy between operating loads for ammonia and nitric acid plants can be readily understood. Typically, there is a large amount of available solar energy during the day, while little or no solar energy is available at night, resulting in a day-night cycle of renewable energy availability. Therefore, to best utilize the availability of renewable energy, the ammonia synthesis circuit is operated at or near maximum capacity during the day and at a reduced capacity at night.

[0059] The further preferred features and preferred embodiments of the present invention are as follows.

[0060] In addition to hydrogen, oxygen can be generated from the water electrolysis step and used as an oxidant stream for the catalytic oxidation of ammonia in the nitric acid production process. Preferably, the integrated process for synthesizing ammonia and nitric acid includes the following steps: a stripping step of the nitric acid solution, and supplying a portion of the oxygen obtained from the water electrolysis step to the stripping step. The stripping step is preferably carried out in a bleaching tower.

[0061] According to one embodiment of the invention, an oxygen stream is extracted from the air in the nitrogen generation step, and at least a portion of the oxygen is supplied to the stripping step and / or the catalytic oxidation of ammonia. The catalytic oxidation of ammonia is preferably carried out in a burner.

[0062] When oxygen obtained from water electrolysis and / or from the nitrogen generation unit is supplied to the ammonia burner, the amount of air required for ammonia oxidation and the amount of air supplied to the burner can be reduced. Advantageously, the amount of power required by the air compressor of the nitric acid plant is reduced, and the saved compression power can be advantageously transferred from the nitric acid plant to the ammonia plant, allowing ammonia production to be stabilized at higher loads.

[0063] When oxygen extracted from water electrolysis and / or from the nitrogen generation unit is supplied to the stripping unit (bleaching tower) of the nitric acid plant, the amount of secondary air added to the bleaching tower can be reduced, and the saved compression power can be advantageously transferred from the nitric acid plant to the ammonia plant, thereby minimizing power input requirements.

[0064] Preferably, oxygen generated in the water electrolysis step and / or oxygen extracted in the nitrogen generation step is supplied to the cooling and / or absorption steps of the ammonia combustion gas.

[0065] When oxygen is supplied to the cooling or absorption steps, the oxidation of nitrogen-containing gases in the cooling train or absorber is enhanced, resulting in increased nitric acid production under the same operating conditions of the absorber. Alternatively, with the same amount of nitric acid produced, the absorption step can be carried out at a lower pressure, requiring less compression power.

[0066] The foregoing indicates that adding oxygen from electrolysis to nitric acid is beneficial. There is another advantage when the integrated equipment produces ammonium nitrate as one of the final products: the ammonia produced is approximately twice as much as that consumed by nitric acid. Therefore, the amount of oxygen co-produced through water electrolysis is higher, and when supplied to nitric acid production, it is almost sufficient to cover all the oxidants required to oxidize ammonia to NO and further oxidize NO to NO2, thus producing nitric acid. A related advantage is that less air needs to be added to nitric acid production. Another related advantage is that more oxygen can be added to nitric acid production in any one or more of the aforementioned steps.

[0067] The integrated process may also include a step of recovering nitrogen from the exhaust gas and supplying the nitrogen to a process that catalytically converts the makeup gas into ammonia. Advantageously, at specific loads, this reduces the net power consumption of the ammonia plant.

[0068] According to one embodiment of the invention, a portion of the ammonia obtained from the catalytic conversion of the supplemental gas undergoes a combustion step, followed by an expansion step, to recover mechanical and / or electrical energy for use in an integrated ammonia-nitric acid process. When renewable energy availability is low, the energy recovered from this combustion of ammonia can be used to provide mechanical and / or electrical energy to ammonia equipment. Advantageously, this reduces the net power input from the grid or backup batteries.

[0069] The present invention is also applicable to a hybrid process in which a portion of the hydrogen is produced from renewable energy sources through water electrolysis, while a portion of the hydrogen is produced from fossil fuels, such as reforming.

[0070] This invention can also be used to modify co-located ammonia and nitric acid plants, increasing their production capacity. Modification methods may include introducing a water electrolyzer into the ammonia plant to synthesize hydrogen. The added water electrolyzer can replace the existing reforming section used for hydrogen production, or operate in parallel with it. Attached Figure Description

[0071] Figure 1 A simplified block diagram of an integrated facility for the production of ammonia, nitric acid, and ammonium nitrate is shown.

[0072] Figures 2 to 4 It shows Figure 1 A variation of the scheme.

[0073] Figure 5 A graph illustrating the typical availability of solar energy.

[0074] Figure 6 It shows the use of Figure 5 The availability of the method of the present invention allows for the use of solar energy to power the loads of the ammonia synthesis process and the nitric acid production process.

[0075] Figure 7 This illustrates another example of a variable load in the presence of a fluctuating energy source.

[0076] Figure 1 A simplified block diagram of an integrated device 1 for synthesizing ammonia 2, nitric acid 3, and ammonium nitrate 19 is shown.

[0077] Equipment 1 includes an ammonia synthesis section 41, a nitric acid synthesis section 32, and an ammonium nitrate synthesis section 18.

[0078] The ammonia synthesis section 31 includes a water electrolyzer 6 for producing hydrogen 5 from water 21; a nitrogen production unit 8 for extracting nitrogen 7 from air 30; multiple compression units 36, 37 and 9 for bringing the operating pressure of hydrogen and nitrogen to the synthesis conditions; and an ammonia catalytic converter 31 for synthesizing ammonia 2.

[0079] The water electrolyzer 6 is powered by electrical energy 110 obtained from renewable energy sources and electrical energy 15 recovered from the integrated device 1. The latter's electrical energy is recovered from the integrated device by expanding the steam flow 16 in the steam turbine 14 (which is coupled to a generator (turbine expander)). Additional electrical energy input can be supplied to the water electrolyzer from an external source.

[0080] The ammonia synthesis section 41 also includes a hydrogen storage unit 34 and an ammonia storage unit 50, configured to accumulate hydrogen 5 and ammonia 2 during a first operating mode. The compression unit 20 is connected to the ammonia catalytic converter 31 and the ammonia storage unit 50.

[0081] The nitric acid synthesis section 32 includes a burner (not shown) for catalytic oxidation of NH3 to produce a gas containing NO2, a cooling unit (heat exchanger section) for bringing the temperature of the NO2 gas to the absorption conditions, and a scrubbing tower (not shown) for reacting water with NO2 to produce nitric acid 3 and tail gas containing N2O, residual nitrogen oxides, oxygen and N2.

[0082] The integrated device 1 also includes a steam mesh 100 designed to recover first steam 12 from the ammonia catalytic converter 31 and second steam 11 from the nitric acid synthesis section 32. The steam mesh 100 is in fluid communication with a steam turbine 14 coupled to a generator to convert mechanical energy into electrical energy. The steam turbine 14 is connected to a power distribution network 35, which is intended to deliver electrical energy 15 to the nitrogen production unit 8, compression units 36, 37, 9, and 20, and the water electrolyzer 6.

[0083] In some implementations, one or more compressors can be directly coupled to a steam turbine.

[0084] Water 21 is converted into hydrogen 5 and oxygen (not shown) in water electrolyzer 6, and the first portion of hydrogen 60 extracted from water electrolyzer 6 is supplied to hydrogen storage unit 34 via compressor 36.

[0085] The second portion of hydrogen 101 extracted from the water electrolyzer is mixed with the first portion of hydrogen 102 leaving the hydrogen storage unit 34 and the nitrogen flow 103 to produce supplementary gas 4.

[0086] In the N2 generator 8, nitrogen 7 and optional oxygen 25 are extracted from air 30. The nitrogen 7 is supplied to the compressor 37 before being mixed with hydrogen streams 101 and 102 to produce supplementary gas 4.

[0087] Makeup gas 4 is supplied to syngas compressor 9 to produce makeup gas 10 ready for conversion. Makeup gas 10 is then supplied to ammonia converter 31 to produce ammonia 2. First vapor 12 is recovered from ammonia converter 32.

[0088] Ammonia 2 is supplied to NH3 feed pump 20 before being stored in ammonia storage unit 50. A first portion 104 of ammonia is fed to nitric acid synthesis section 32 to produce nitric acid 3, while a second portion 17 of ammonia is fed together with nitric acid 3 to ammonium nitrate synthesis section 18. The output of ammonium nitrate synthesis section 18 is ammonium nitrate stream 19.

[0089] In the steam recovery section (not shown), second steam 11 is recovered from the nitric acid synthesis section 32. The steam recovery section is configured to recover steam from the ammonia burner and cooling unit (heat exchanger section). The first steam 11 is combined with the second steam 12 to produce a steam stream 16, which is then supplied to a steam turbine 14 to generate electrical and / or mechanical energy 15.

[0090] Electrical energy 15 is transmitted via distribution network 35 to water electrolyzer 6, nitrogen generation unit 8, and compression units 36, 37, 9, and 20.

[0091] Figures 2 to 4 It shows Figure 1 Variations of the proposed solution. These variations can also be incorporated into other embodiments of the invention.

[0092] Figure 2 One embodiment is shown in which oxygen 22 extracted from water electrolyzer 6 is partially supplied to ammonia converter via pipeline 23 and to nitric acid synthesis section via pipeline 24.

[0093] Figure 3 One embodiment is shown in which oxygen 25 extracted from nitrogen generator 8 is supplied to nitric acid synthesis section 32.

[0094] Figure 4 One embodiment is shown in which nitrogen 27 extracted from nitric acid synthesis section 32 is recycled to ammonia converter 31. Nitrogen is recovered from the tail gas leaving the absorber.

[0095] It is understandable that the output of device 1 depends primarily on the input power 110. Figure 5 and Figure 6 An example of a control device 1 based on the availability of the power 110, according to an embodiment of the present invention, is provided.

[0096] Figure 5 The typical availability of the power input 110 when powered by solar energy (e.g., a photovoltaic (PV) field) is shown. Figure 5A typical daily cycle is shown, which includes a first period D (daytime) when the source is available and a second period N (nighttime) when the source is unavailable.

[0097] Figure 6 The corresponding operation of device 1 is shown. According to the swing load strategy, the load of the ammonia section is proportional to the renewable power generation, reaching full load (>70%) during the daytime period D and minimum load (<50%) during the nighttime period N. The nitric acid section operates at approximately 70% load during the day and approximately 100% load at night.

[0098] Obviously, Figure 6 The strategy shown can be applied to situations similar to Figure 5 Other sources for the output curve.

[0099] Figure 7 Another example is shown when the source of power 110 has a more complex curve, exhibiting, for example, the dramatic fluctuations that can be observed when power 110 originates from a wind turbine. According to the strategy of the invention, the load on the ammonia plant is high when available power is high, and decreases when available power is low or minimal. The load on the nitric acid plant is complementary to the load on the ammonia plant.

Claims

1. A method for controlling an integrated process for the synthesis of ammonia and nitric acid, wherein: in the process, hydrogen is produced by water electrolysis and used for the production of ammonia make-up gas; the make-up gas is reacted to form ammonia; at least part of the ammonia is used for the production of nitric acid; the method comprises selectively switching the process between a first mode of operation and a second mode of operation; in the first mode of operation, the production of ammonia and the production of nitric acid are adjusted in such a way that the process has a first output of nitric acid; an excess of ammonia is produced compared to the ammonia required for producing the first output of nitric acid; the excess of ammonia is stored in a suitable ammonia storage; in the second mode of operation, the production of ammonia and the production of nitric acid are adjusted in such a way that the process has a second output of nitric acid; less ammonia is produced than is required for producing the second output of nitric acid, so that an additional input of ammonia is required for the production of nitric acid, and ammonia from the ammonia storage is used to provide the additional input; the water electrolysis is powered by at least one power source, and the method comprises switching between the first mode of operation and the second mode of operation based on the amount of power delivered from the at least one power source to the water electrolysis.

2. The method according to claim 1, wherein: energy in the form of thermal and / or electrical energy is exported from the nitric acid production process to the ammonia synthesis process, so that the ammonia synthesis process has a thermal and / or electrical energy input in the form of power imported from the nitric acid production process; in the ammonia synthesis process, the ratio of power imported from the nitric acid production process to the total power input is greater in the second mode of operation than in the first mode of operation.

3. The method according to claim 2, wherein in the second mode of operation, the power imported from the nitric acid production process is used to compress the ammonia make-up gas to ammonia synthesis pressure.

4. The method according to claim 1, wherein in the first mode of operation, an excess of hydrogen is produced compared to the hydrogen required for producing the make-up gas, the excess of hydrogen is stored in a suitable hydrogen storage unit, and the excess of hydrogen accumulated during the first mode of operation is used for the production of ammonia make-up gas during the second mode of operation.

5. The method according to claim 1, wherein the at least one power source of the water electrolysis comprises at least one renewable energy source, and the method comprises switching between the first mode and the second mode based on the amount of available power provided by the renewable energy source.

6. The method according to claim 5, wherein the first mode of operation is selected when the available power provided by the at least one renewable energy source is above a first threshold value, and the second mode of operation is selected when the available power provided by the at least one renewable energy source is below a second threshold value.

7. The method according to claim 5, wherein the renewable energy source is solar energy.

8. The method according to claim 1, wherein: the production of ammonia is carried out in an ammonia plant, and the production of nitric acid is carried out in a nitric acid plant connected to the ammonia plant; the ammonia plant has a rated ammonia output, the nitric acid plant has a rated nitric acid output corresponding to the rated ammonia output delivered from the ammonia plant to the nitric acid plant for production of nitric acid; in the first mode of operation, the nitric acid plant is operated at partial load at a nitric acid output less than its rated output, and in the second mode of operation, the ammonia plant is operated at partial load at an ammonia output less than its rated output.

9. The method of claim 8, wherein in the first mode of operation, the ammonia plant is operated at 80% or more of the rated ammonia output, and the nitric acid plant is operated at 50% to 80% of the rated nitric acid output.

10. The method of claim 8, wherein in the second mode of operation, the ammonia plant is operated at 1% to 30% of the rated ammonia output, and the nitric acid plant is operated at 80% or more of the rated nitric acid output.

11. The method of claim 10, wherein the ammonia plant is operated at 10% to 30% of the rated ammonia output.

12. The method of claim 1, wherein, during the second mode of operation, a portion of the ammonia discharged from the ammonia storage is combusted to provide an additional source of energy in the form of thermal and / or electrical energy.

13. The method of claim 1, wherein the integrated process further comprises production of ammonium nitrate from at least a portion of the produced ammonia and nitric acid, the method comprising operating the ammonium nitrate production process at a reduced output in the first mode of operation.

14. The method of claim 13, wherein in the first mode of operation, the ammonium nitrate production process is operated at 50% to 80% of its rated output, and in the second mode of operation, the ammonium nitrate production process is operated at 80% or more of its rated output.

15. The method of claim 13, wherein energy is exported from the ammonium nitrate production process to the ammonia synthesis process in the form of thermal and / or electrical energy, such that the ammonia synthesis process has thermal and / or electrical power input from the ammonium nitrate production process.

16. The method of claim 1, wherein: a first amount of steam (12) is generated from heat removed from the ammonia production process, and a second amount of steam (11) is generated from heat removed from the nitric acid production process; switching between the first and second modes of operation is controlled to maintain the total amount of steam, which is the sum of the first and second amounts of steam, within a desired range.

17. The method of claim 16, wherein the total amount of steam differs by no more than 30% between the first and second modes of operation.

18. The method of claim 17, wherein the total amount of steam differs by no more than 20% between the first and second modes of operation.

19. A process for the production of ammonia and nitric acid, wherein hydrogen is produced from water electrolysis and used for the production of an ammonia make-up gas; said make-up gas is reacted to form ammonia; at least a portion of said ammonia is used for the production of nitric acid, wherein said process is controlled by the method according to claim 1.

20. The process according to claim 19, further comprising the production of ammonium nitrate from at least part of the produced ammonia and nitric acid.

21. The process of claim 19, comprising the steps of: from water electrolysis (6) and supplying at least a portion (23) of said oxygen to a catalytic conversion of ammonia (31) and / or a stripping step of a nitric acid solution.

22. An integrated plant for the synthesis of ammonia and nitric acid, comprising an ammonia synthesis section (41) and a nitric acid synthesis section (32), wherein ammonia produced in said ammonia synthesis section is used for the production of nitric acid in said nitric acid synthesis section, wherein: said ammonia synthesis section comprises a front-end section configured to produce an ammonia make-up gas containing hydrogen, said front-end section comprising a water electrolyser arranged to produce at least part of the hydrogen (5) contained in said ammonia make-up gas by water electrolysis; said plant further comprises a control system configured to control the production of ammonia and the production of nitric acid in said plant according to the method of claim 1.

23. The plant according to claim 22, comprising a common steam network, which is common between said ammonia synthesis section and said nitric acid synthesis section, wherein the production of said ammonia and said nitric acid is controlled, maintaining a stable or close to stable production of steam.

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