Integrated process for the synthesis of ammonia and nitric acid

Abstract

The integrated process for synthesis of ammonia and nitric acid, including the production of hydrogen from the electrolysis of water, is controlled by selectively switching between a first mode of operation and a second mode of operation, in which in the first mode of operation, ammonia is produced in excess and stored in a suitable ammonia storage; in the second mode of operation, ammonia from the ammonia storage is used to provide additional ammonia input for the production of nitric acid; and the switching between the first mode and the second mode is based on the amount of power transferred to the electrolysis of water.

Description

[Technical Field]

[0001] The present invention relates to the field of ammonia and nitric acid production. In particular, the present invention relates to a method for controlling an integrated process for the production of ammonia and nitric acid, and to a process or plant for implementing said method. [Background technology]

[0002] Conventional ammonia production involves reforming a hydrocarbon feedstock to produce a hydrogen-containing synthesis gas, water-gas shift conversion, synthesis gas purification with carbon dioxide removal and optionally methanation, and finally conversion to ammonia in a suitable catalytic converter. The make-up gas for ammonia synthesis also contains nitrogen, which, along with combustion air, can be introduced, for example, into a secondary reformer or produced in a suitable air separation unit. Thus, ammonia synthesis can also involve the production of nitrogen.

[0003] Ammonia synthesis occurs at high pressure. Compression of ammonia make-up gas to ammonia synthesis pressure is the primary energy input for the process. Heat is typically recovered from the process in vapor form, for example, from high-temperature reforming wastewater and from the ammonia converter. Steam at sufficient pressure can be expanded in a steam turbine to produce energy. Thus, steam can be used internally in the process to at least partially meet the heat and / or energy input of the process.

[0004] An environmental problem associated with the production of ammonia is that the heat for the reforming of hydrocarbon feedstocks is traditionally provided by the combustion of fossil fuels (e.g., natural gas), which results in significant carbon dioxide emissions into the atmosphere.

[0005] According to new trends, it is desirable to provide an ammonia process with a reduced carbon footprint at an acceptable cost. Ammonia produced with a reduced carbon footprint, particularly with a reduced carbon dioxide emission, is called low-carbon ammonia. A plant configured to produce ammonia with reduced emissions is called a low-carbon ammonia plant.

[0006] Known approaches for the production of low-carbon ammonia include the production of hydrogen from the electrolysis of water, powered by renewable energy sources (e.g., solar or wind energy). Using this approach, some or all of the hydrogen needed for ammonia synthesis can come from renewable energy. When all of the hydrogen comes from renewable energy, the resulting low-carbon ammonia is usually called green ammonia.

[0007] The drawback of using renewable energy is represented by the availability of the energy source: renewable energy sources such as solar energy are usually subject to fluctuations that inevitably propagate through the entire process.

[0008] The process for the production of ammonia and nitric acid involves several turbomachinery such as turbines and compressors that are inherently inflexible: as a result, the entire process is inflexible and must operate near design conditions.

[0009] In particular, the amount of steam and power that can be produced internally is affected by fluctuations in hydrogen production. Steam turbines are typically designed to operate near their nominal steam flow rate. If the steam flow rate drops, the turbine may suffer a dramatic reduction in efficiency or may not be able to operate. If the internal production of energy drops, the process may require external energy input, which means additional costs.

[0010] Current solutions to the above drawbacks include hydrogen storage to act as a buffer and provide a steady H flow to the synthesis loop, and / or the installation of batteries or other energy storage means to provide a steady flow of energy to the water electrolysis and other electricity consumers within the plant. However, these solutions are not fully satisfactory due to the capital costs of the hydrogen and energy storage means.

[0011] The above drawbacks are particularly felt when the production of ammonia is integrated with the production of nitric acid, and possibly ammonium nitrate, in such integrated plants, where fluctuations in the energy source for the production of hydrogen affect the production of ammonia and the subsequent production of nitric acid and ammonium nitrate.

[0012] Therefore, in light of the above considerations, it is highly desirable to provide more flexibility to the integrated production of ammonia and nitric acid to maintain efficiency and profitability even when hydrogen production is powered by variable or intermittent power sources. Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention addresses the problem of how to provide flexible, adaptive control of an integrated ammonia-nitric acid process in which at least a portion of the hydrogen for the synthesis of ammonia is produced by water electrolysis, and as a result, the process is dependent on the availability of the power source used for the electrolysis process. In particular, the present invention addresses the problem of how to follow the fluctuations of the power source, which is generally the case for renewable energy sources such as solar energy. [Means for solving the problem]

[0014] The above problem is solved by a method for controlling an integrated process for the synthesis of ammonia and nitric acid according to claim 1.

[0015] The method applies to a process in which hydrogen is produced from the electrolysis of water and used to produce ammonia make-up gas; the make-up gas is reacted to form ammonia; and at least a portion of the ammonia is used to produce nitric acid. In some embodiments, the method applies to a process in which ammonium nitrate is also produced.

[0016] The term ammonia make-up gas refers to a gas containing hydrogen and nitrogen in amounts suitable for the synthesis of ammonia. Typically, the gas has a hydrogen to nitrogen molar ratio of 3 or just around 3.

[0017] the method includes 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 regulated such that: the process has a first output of nitric acid; ammonia is produced in excess relative to the ammonia required to produce the first output of nitric acid; and the excess 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 such that: the process has a second output of nitric acid; the ammonia produced is less than the ammonia required to produce the second output of nitric acid, so that the production of nitric acid requires an additional input of ammonia, and ammonia from the ammonia store is used to provide the additional input.

[0018] The method includes switching between a first mode and a second mode based on the amount of power transferred to the electrolysis of water.

[0019] The method thus allows for adaptation of the process to the amount of power available for the water electrolysis process. The amount of power transferred to the water electrolysis may vary depending on the cost and / or actual availability of the power source. Generally, the first mode of operation is selected when more power is available, and the second mode of operation is selected when less power or no power is available.

[0020] As mentioned above, the selection of the mode of operation may follow the cost and / or availability of the power source. For example, if electric power is obtained from the grid, a first mode may be selected when the price of energy is low, while a second mode may be selected when the price is high.

[0021] A particularly interesting embodiment of the present invention relates to the case of renewable energy-powered water electrolysis, where the first mode may be selected when renewable energy sources are available and capable of generating significant power; the second mode may be selected when renewable energy sources are not available or are available only to a limited extent, and therefore no or little power is transferred to the water electrolysis process.

[0022] For example, if the renewable energy is solar energy, the first mode may be selected during the day, and the second mode may be selected at night, or more generally when solar energy is substantially unavailable, for example due to cloud cover.

[0023] The present invention is based on the discovery that ammonia production, when dependent on electrical energy for hydrogen production, and particularly on renewable energy, may suffer from a shortage of input power due to the cost and / or availability of the power source. The present invention compensates for this shortage by storing ammonia when the power source is sufficiently available, to be used when the power source is in short supply or unavailable. Thus, the present invention allows for constant or near-constant production of nitric acid despite variable or intermittent availability of the power source.

[0024] According to certain embodiments of the invention, the input power deficit may be compensated for by transferring a proportionately greater amount of thermal and / or electrical power from the nitric acid production process to the ammonia synthesis process. If provided, the associated ammonium nitrate production process may also export thermal and / or electrical power to the ammonia synthesis process.

[0025] The present invention opens new possibilities for the production of low-carbon or green ammonia in combination with the production of nitric acid, and optionally ammonium nitrate. In particular, the present invention provides a more flexible process adapted to follow fluctuations in the renewable energy-based production of hydrogen.

[0026] Other advantages of the present invention include reduced synthesis costs for green ammonia, reduced backup power required to power water electrolysis and compression units, and reduced size of hydrogen storage units.

[0027] Further aspects of the invention include the processes and plants set forth in the claims.

[0028] The invention can be applied to processes in which hydrogen production is entirely by electrolysis of water, or to hybrid processes in which hydrogen is produced partly from the reforming of fossil fuels and partly from the electrolysis of water. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 shows a simplified schematic block diagram of an integrated plant for the production of ammonia, nitric acid, and ammonium nitrate. [Figure 2] 1. A variation of the schematic diagram of FIG. [Figure 3] 1. A variation of the schematic diagram of FIG. [Figure 4] 1. A variation of the schematic diagram of FIG. [Figure 5] 1 is a plot showing the general availability of solar energy sources. [Figure 6] FIG. 5 shows the load of an ammonia synthesis process and a nitric acid production process powered by a solar energy source with the availability and using the method of the present invention. [Figure 7] 1 illustrates another example of a variable load in the presence of a variable energy source. DETAILED DESCRIPTION OF THE INVENTION

[0030] The production of ammonia occurs in an ammonia plant, and the production of nitric acid occurs in a nitric acid plant connected to the ammonia plant, which may be considered sections of an integrated plant.

[0031] The production of ammonia includes the generation of hydrogen, which, according to the present invention, is carried out at least in part in a water electrolysis device, and may further include the generation of nitrogen in a suitable nitrogen generation unit, for example an air separation unit, if necessary to reach the correct hydrogen / nitrogen ratio in the ammonia make-up gas.

[0032] The production of nitric acid involves the catalytic oxidation of ammonia to obtain a process gas containing nitric oxide, which is contacted with water in a suitable absorption column to produce nitric acid.

[0033] The present invention provides that the loads of the ammonia plant and the nitric acid plant are adjusted in response to the power available for the water electrolysis process. Specifically, in a first mode of operation, the load of the nitric acid plant is reduced to allow for ammonia storage; in a second mode of operation, the load of the ammonia plant is reduced in response to the reduced amount of power available for water electrolysis. Thus, the present invention employs variable control where the load of the nitric acid plant is complementary to the load of the ammonia plant, while the load of the ammonia plant substantially tracks the availability of renewable energy sources.

[0034] A first mode of operation may be selected when the power available for electrolysis is above a first threshold, and a second mode of operation may be selected when the power is below a second threshold. The first and second thresholds may be the same or different. Preferably, the thresholds are equal to or about 50% of the total power consumption of the ammonia plant, including water electrolysis.

[0035] The ammonia plant has a nominal ammonia output and the nitric acid plant has a nominal nitric acid output, and the nominal nitric acid output corresponding to the ammonia output is transferred in part or in whole from the ammonia plant to the nitric acid plant for the production of nitric acid.

[0036] Preferably, in the first mode of operation, the ammonia plant is operated at 80% or more of its nominal ammonia output and the nitric acid plant is operated at 50% to 80% of its nominal nitric acid output, where 80% or more can include up to or greater than 100%, provided the plants are capable of operating above nominal capacity, e.g., 80% to 110%.

[0037] In a second mode of operation, the ammonia plant may be operated at 1% to 30%, preferably 10% to 30%, or 20% to 30% of the nominal ammonia output, and the nitric acid plant may be operated at 80% or more of its nominal capacity.

[0038] The nitric acid production process generally has a net energy export in the form of heat and / or electrical energy. Electrical energy can be produced within the nitric acid plant by expanding the tail gas of the absorption column and / or by expanding steam generated from the heat released in the oxidation of ammonia. Heat can be exported in the form of steam under pressure, produced, for example, by the removal of heat from the catalytic oxidation of ammonia and by cooling various process streams.

[0039] Thus, thermal and / or electrical power can be transferred from the nitric acid production process to the ammonia synthesis process, where transfer from a first process to a second process means that one or more items of the plant performing the first process generate power that is transferred to one or more items of the plant performing the second process.

[0040] Preferred uses for the electrical power exported to the associated ammonia plant include: water electrolysis, nitrogen generation, and ammonia make-up gas compression. Preferably, the power is used primarily for ammonia make-up gas compression.

[0041] In an embodiment of the present invention, the transfer of thermal and / or electrical power from the nitric acid production process to the ammonia synthesis process is also controlled according to the mode of operation. In particular, the power transferred to the ammonia synthesis process may be proportionally greater in the second mode of operation. Specifically, in an embodiment of the present invention, the ratio of power transferred from the nitric acid production process to the total input power is greater in the second mode of operation than in the first mode of operation.

[0042] Heat is usually exported by hot steam. The heat exported by the nitric acid plant (hot steam) can be used to heat, for example, an ammonia synthesis reactor, for example by providing a suitable heat exchanger inside the reactor to keep the reactor at a suitable temperature even when operating at part load.

[0043] Advantages of transferring energy from the nitric acid plant to the ammonia plant include avoiding or reducing the need to provide hydrogen storage and / or import electricity from the grid. A notable advantage is that the ammonia plant can operate in an "island" state, i.e., with all of its input of electrical energy generated internally within the integrated plant, i.e., within the nitric acid plant.

[0044] The electrolysis of water preferably uses renewable energy. According to various embodiments, all or part of the hydrogen in the ammonia make-up gas can be produced from renewable energy. In that case, the method includes switching between the first and second modes based on the amount of power made available by the renewable energy source(s) used in the electrolysis process. An embodiment of particular interest is the production of hydrogen from solar-powered electrolysis.

[0045] During the second mode of operation, a portion of the ammonia removed from the ammonia storage may be combusted to provide an additional source of energy in the form of heat and / or electrical energy. This use of stored ammonia may provide a further means for making up the energy deficit of the ammonia synthesis process.

[0046] The method of the present invention can be applied to a process further comprising the production of ammonium nitrate from at least a portion of the produced ammonia and nitric acid. The method preferably includes operating the ammonium nitrate production process at a reduced output in a first mode of operation. Generally, the ammonium nitrate production process is controlled similarly to the nitric acid production process. More preferably, in the first mode of operation, the ammonium nitrate production process can be operated at 50% to 80% of its nominal output, and in the second mode of operation, the ammonium nitrate production process is operated at 80% or more of its nominal output.

[0047] Furthermore, the ammonium nitrate production process is typically the ultimate exporter of energy in the form of heat and / or electricity. Therefore, the heat or electrical power exported from the ammonium nitrate production process can be used within the ammonia synthesis process, particularly in the second mode of operation. The ammonium nitrate process is preferably operated in a switching mode, with a similar load to the nitric acid. A related advantage is that steam / energy from the ammonium nitrate can be transferred to the ammonia during the low-load mode of operation.

[0048] Yet another preferred feature of the present invention is managing the mode of operation of the integrated process to maintain a constant or near-constant production of steam. Ammonia and nitric acid production processes involve various steps in which heat is removed from process streams and typically used to generate steam. The steam is used internally for process steps requiring heat input, such as preheating or process streams, or expanded to generate energy for equipment such as compressors and other machinery. A constant or near-constant production of steam contributes to maintaining a stable process and reduces the need to import energy.

[0049] Thus, embodiments of the present invention include: a first amount of steam is generated from heat removed from the ammonia production process, and a second amount of steam is generated from heat removed from the nitric acid production process; Switching between the first mode of operation and the second mode of operation is controlled to maintain a total steam flow rate, which is the sum of the first steam flow rate and the second steam flow rate, within a desired range. It stipulates that:

[0050] Preferably, the process is controlled so that the total steam flow between the first mode of operation and the second mode of operation differs by no more than 30%, and more preferably by no more than 20%.

[0051] The mechanical and / or electrical energy obtained from the expansion of the steam can be used internally within the process to power at least one of the following steps: production of hydrogen from water electrolysis; production of nitrogen from air; compression of ammonia make-up gas to ammonia synthesis pressure; compression of ammonia in the ammonia refrigeration section; compression of process air in the nitric acid process; compression of NOx-containing gas in the nitric acid process.

[0052] The steam stream expanded in the steam turbine to recover mechanical and / or electrical energy is medium-pressure steam, preferably the working pressure of said steam is comprised between 20 and 100 bar, more preferably between 25 and 60 bar.

[0053] In one embodiment, an integrated plant for the synthesis of ammonia and nitric acid may comprise a common steam network between the nitric acid plant and the ammonia plant.

[0054] The complementary switching between the first and second modes of operation results in a nearly stable production of steam from the integrated plant because when the steam produced from the ammonia plant is in a low range, the steam produced from the nitric acid plant is in a high range, and vice versa, so that the efficiency of the integrated plant is maintained even during fluctuations in the supply of renewable energy sources.

[0055] The present invention may therefore combine the concept of steam integration with the insight of switching between alternative modes of operation to overcome the drawbacks posed by fluctuations in renewable power availability.

[0056] The switching policy between the operating loads of the ammonia and nitric acid plants can be easily understood by considering a scenario in which renewable energy sources, for example, solar energy, are supplied. Typically, solar energy is available at high levels during the day, while availability is low or nonexistent at night, resulting in a cyclical availability of renewable power. Therefore, to best utilize the availability of renewable power, the ammonia synthesis loop is operated at or near full capacity during the day, while at night it is operated at a reduced capacity.

[0057] Further preferred features and preferred embodiments of the present invention are as follows:

[0058] In addition to hydrogen, oxygen can be produced 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 the synthesis of ammonia and nitric acid includes subjecting the nitric acid solution to a stripping step and feeding a portion of the oxygen obtained from the water electrolysis step to the stripping step. Preferably, the stripping step is carried out in a bleaching column.

[0059] According to an embodiment of the invention, an oxygen stream is extracted from the air in the nitrogen production step, and at least a portion of said oxygen is supplied to the stripping step and / or to the catalytic oxidation of ammonia, which preferably takes place in a burner.

[0060] When oxygen obtained from water electrolysis and / or oxygen obtained from a nitrogen generation unit is supplied to the ammonia burner, the amount of air required for ammonia oxidation and 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 exported from the nitric acid plant to the ammonia plant, so that ammonia production can be stabilized at higher loads.

[0061] If oxygen extracted from water electrolysis and / or from the nitrogen generation unit is fed to the stripping unit (bleach column) of the nitric acid plant, the amount of secondary air added to the bleach may be reduced, and the saved compression power can advantageously be exported from the nitric acid plant to the ammonia plant to minimize electricity import requirements.

[0062] Preferably, oxygen produced from the water electrolysis step and / or oxygen extracted from the nitrogen production step is supplied to the ammonia combustion gas cooling step and / or absorption step.

[0063] When oxygen is supplied to the cooling step or the absorption step, the oxidation of NOx-containing gases in the cooling train or in the absorbent is enhanced, and as a result, the productivity of nitric acid is increased under the same operating conditions of the absorption column. Alternatively, the absorption step can be carried out at a lower pressure so that less compression power is required for the same amount of nitric acid produced.

[0064] The above discussion demonstrates the benefits of adding oxygen from electrolysis to nitric acid. When an integrated plant produces ammonium nitrate as one of several end products, there is an additional benefit in that more ammonia is produced than is consumed for nitric acid, i.e., approximately twice as much. Consequently, the amount of oxygen co-produced by water electrolysis is greater, and when fed to nitric acid production, is nearly sufficient to cover all of the oxidant needed for the oxidation of ammonia to NO and the further oxidation of NO to NO for the production of nitric acid. One related advantage is that less air needs to be added to nitric acid production. Another related advantage is that more oxygen is available to be added to nitric acid production in any one or more of the above steps.

[0065] The integrated process may further comprise the steps of recovering nitrogen from the tail gas and feeding said nitrogen to the catalytic conversion of make-up gas to ammonia. Advantageously, the net power consumption of the ammonia plant at a specific load is reduced.

[0066] According to one embodiment of the present invention, a portion of the ammonia obtained from the catalytic conversion of the make-up gas is subjected to a combustion step followed by an expansion step to recover mechanical and / or electrical energy for use in the integrated ammonia-nitric acid process. The energy recovered from such combustion of ammonia can be used to provide mechanical and / or electrical power to the ammonia plant when the availability of renewable energy sources is low. Advantageously, the net import of electricity from the electric grid or from backup batteries is reduced.

[0067] The invention is also applicable to hybrid processes in which some of the hydrogen is produced from renewable energy sources via water electrolysis, while some of the hydrogen is produced from fossil fuels, for example from reforming.

[0068] The present invention can also be applied to retrofitting adjacent ammonia and nitric acid plants to increase their ammonia and nitric acid production capacity. The retrofit method can include the introduction of a water electrolysis unit within the ammonia plant to synthesize hydrogen. The added water electrolysis unit can replace or operate in parallel with the existing reforming section for the production of hydrogen.

[0069] FIG. 1 shows a simplified schematic block diagram of an integrated plant 1 for the synthesis of ammonia 2, nitric acid 3, and ammonium nitrate 19.

[0070] The plant 1 includes an ammonia synthesis section 41, a nitric acid synthesis section 32, and an ammonium nitrate synthesis section 18.

[0071] The ammonia synthesis section 31 includes a water electrolysis device 6 for generating hydrogen 5 from water 21, a nitrogen generation unit 8 for extracting nitrogen 7 from air 30, a plurality of compression units 36, 37 and 9 for bringing the operating pressures of hydrogen and nitrogen to synthesis conditions, and an ammonia catalytic converter 31 for synthesizing ammonia 2.

[0072] The water electrolysis device 6 is powered by electrical energy 110 obtained from renewable energy sources and electrical energy 15 recovered from the integrated plant 1 by expanding a steam flow 16 in a steam turbine 14 connected to a generator (turboexpander). Additional electrical energy input may be provided to the water electrolysis device from an external source.

[0073] The ammonia synthesis section 41 further includes a hydrogen storage unit 34 and an ammonia storage unit 50 configured to store hydrogen 5 and ammonia 2 during the first mode of operation. The compression unit 20 is in communication with the ammonia catalytic converter 31 and with the ammonia storage unit 50.

[0074] The nitric acid synthesis section 32 includes a burner (not shown) for catalytically oxidizing NH to obtain a NO-containing gas, a cooling train (heat exchanger section) for bringing the temperature of the NO gas to absorption conditions, and a scrubbing column (not shown) for reacting water with NO to produce nitric acid and a tail gas containing N2O, residual NOx, oxygen, and N2.

[0075] The integrated plant 1 further comprises a steam network 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 network 100 is in fluid communication with a steam turbine 14 connected to a generator for converting mechanical energy to electrical energy, and the steam turbine 14 is in communication with a distribution grid 35 which is considered to supply electrical energy 15 to the nitrogen generation unit 8, to the compression units 36, 37, 9 and 20, and to the water electrolysis unit 6.

[0076] In some embodiments, one or more compressors may be directly coupled to the steam turbine.

[0077] Water 21 is converted into hydrogen 5 and oxygen (not shown) in the water electrolysis device 6, and a first portion 60 of the hydrogen extracted from the water electrolysis device 6 is passed through a compressor 36 and supplied to a hydrogen storage unit 34.

[0078] The second portion of hydrogen 101 extracted from the water electrolysis device is mixed with the first portion of hydrogen 102 exiting the hydrogen storage unit 34 and with a nitrogen stream 103 to obtain the make-up gas 4 .

[0079] Nitrogen 7, and optionally oxygen 25, are extracted from air 30 in N2 generator 8. Nitrogen 7 is fed to compressor 37 and then mixed with hydrogen streams 101 and 102 to obtain make-up gas 4.

[0080] The make-up gas 4 is fed to a synthesis gas compressor 9 to obtain make-up gas 10 ready for conversion, which is then fed to an ammonia converter 31 to obtain ammonia 2. A first vapor 12 is recovered from the ammonia converter 32.

[0081] The ammonia 2 is fed to an NH3 feed pump 20 and then stored in an ammonia storage unit 50. A first portion of the ammonia 104 is fed to a nitric acid synthesis section 32 to obtain nitric acid 3, while a second portion 17 of the ammonia is fed together with nitric acid 3 to an ammonium nitrate synthesis section 18. The output of the ammonium nitrate synthesis section 18 is an ammonium nitrate stream 19.

[0082] The second steam 11 is recovered from the nitric acid synthesis section 32 in a steam recovery section (not shown) configured to recover steam from the ammonia burner and from the refrigeration train (heat exchanger section). The first steam 11 is mixed with the second steam 12 to obtain a steam stream 16, which is then fed to a steam turbine 14 to generate electrical and / or mechanical energy 15.

[0083] Electrical energy 15 is transmitted via a power distribution grid 35 to the water electrolysis device 6 , to the nitrogen generation unit 8 , and to the compression units 36 , 37 , 9 and 20 .

[0084] Figures 2 to 4 show variations of the schematic diagram of Figure 1, which may be combined with further embodiments of the invention.

[0085] FIG. 2 shows an embodiment in which oxygen 22 extracted from the water electrolysis unit 6 is partially fed via line 23 to the ammonia converter and via line 24 to the nitric acid synthesis section.

[0086] FIG. 3 shows an embodiment in which oxygen 25 extracted from nitrogen generator 8 is fed to nitric acid synthesis section 32 .

[0087] Figure 4 shows an embodiment in which nitrogen 27 extracted from the nitric acid synthesis section 32 is recycled to the ammonia converter 31. Nitrogen is recovered from the tail gas exiting the absorption column.

[0088] It can be seen that the output of the plant 1 depends primarily on the input power 110. Figures 5 and 6 describe examples of controlling the plant 1 according to embodiments of the present invention based on the availability of said power 110.

[0089] Figure 5 illustrates the availability of the power input 110 when supplied by a solar energy source, such as a photovoltaic (PV) electric field. Figure 5 illustrates a typical daily cycle that includes a first period D (daytime) when the energy source is available, and a second period N (nighttime) when the energy source is not available.

[0090] Figure 6 shows the corresponding operation of plant 1. According to the variable load policy, the load of the ammonia section is proportional to the renewable energy generation, reaching full capacity (>70%) during the daytime period D and minimum load (<50%) during the nighttime period N. The nitric acid section is operated at approximately 70% load during the day and approximately 100% load during the night.

[0091] Obviously, the above policy shown in FIG. 6 can also be applied to other energy sources with output profiles similar to that of FIG.

[0092] 7 shows another example where the source of power 110 has a more complex profile with rapid fluctuations, such as may be seen when power 110 comes from a wind turbine. According to the policy of the present invention, the load on the ammonia plant is high when the available power is also high, and the load on the ammonia plant is reduced when the 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 described above, hydrogen is produced from the electrolysis of water and used to produce a supply gas for ammonia; the supply gas is reacted to form ammonia; and at least a portion of the ammonia is used to produce nitric acid; The method includes selective switching of 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 nitric acid is: the process has a first output of nitric acid; ammonia is produced in excess of the ammonia required to produce the first output of nitric acid; and the excess ammonia is stored in an ammonia storage unit; In the second mode of operation, the production of ammonia and nitric acid is adjusted such that: the process has a second output of nitric acid; the amount of ammonia produced is less than the amount of ammonia required to produce the second output of nitric acid, and thus the production of nitric acid requires a further input of ammonia, and ammonia from the ammonia storage unit is used to supply the further input; The electrolysis of water is powered by at least one power source, and the method includes switching between the first mode and the second mode based on the amount of power transmitted from the at least one power source to the electrolysis of water. method.

2. Energy in the form of heat and / or electrical energy is transferred from the nitric acid production process to the ammonia synthesis process, and thus the ammonia synthesis process has a heat and / or electrical power input represented by the power transferred from the nitric acid production process; In the ammonia synthesis process, the ratio of the power transferred from the nitrate production process to the total power input is greater in the second mode of operation than in the first mode of operation. The method according to claim 1.

3. The method according to claim 2, wherein the power supplied from the nitric acid production process is used in a second mode of operation for compressing the ammonia supply gas to the ammonia synthesis pressure.

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

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

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

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

8. Ammonia is produced in an ammonia plant, and nitric acid is produced in a nitric acid plant connected to the ammonia plant; The ammonia plant has a nominal ammonia output, and the nitrate plant has a nominal nitrate output, the nominal nitrate output corresponding to the nominal ammonia output that is partially or completely transferred from the ammonia plant to the nitrate plant for the production of nitrate; In the first mode of operation, the nitric acid plant is operated at a partial load with a nitric acid output lower than its nominal output, and in the second mode of operation, the ammonia plant is operated at a partial load with an ammonia output lower than its nominal output. The method according to claim 1.

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

10. The method according to claim 8, wherein in the second mode of operation, the ammonia plant is operated at 1% to 30% of the nominal ammonia output.

11. The method according to claim 10, wherein in the second mode of operation, the ammonia plant is operated at 10% to 30% of the nominal ammonia output.

12. The method according to claim 10, wherein in the second mode of operation, the nitric acid plant is operated at 80% or more of the nominal nitric acid output.

13. The method according to claim 1, wherein in a second mode of operation, a portion of the ammonia removed from the ammonia storage unit is burned to provide an additional energy source in the form of heat and / or electrical energy.

14. The method according to claim 1, wherein the integrated process further comprises the production of ammonium nitrate from at least a portion of the ammonia and nitric acid produced, and in a first mode of operation, the ammonium nitrate production process is operated at reduced power.

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

16. The method according to claim 14, wherein energy is transferred from the ammonium nitrate production process to the ammonia synthesis process in the form of heat and / or electrical energy, and the ammonia synthesis process thus has a heat and / or electrical power input from the ammonium nitrate production process.

17. A first amount of vapor (12) is produced from the heat removed from the ammonia production process, and a second amount of vapor (11) is produced from the heat removed from the nitric acid production process; The method according to claim 1, wherein the switching between the first mode of operation and the second mode of operation is controlled to maintain the total amount of steam, which is the sum of the first amount of steam and the second amount of steam, within a desired range.

18. The method according to claim 17, wherein the switching between the first mode of operation and the second mode of operation is controlled such that the total amount of steam, which is the sum of the first amount of steam and the second amount of steam, differs between the first mode of operation and the second mode of operation by 30% or less.

19. The method according to claim 18, wherein the switching between the first mode of operation and the second mode of operation is controlled such that the total amount of steam, which is the sum of the first amount of steam and the second amount of steam, differs between the first mode of operation and the second mode of operation by 20% or less.

20. A process for the production of ammonia and nitric acid, wherein hydrogen is produced from the electrolysis of water and used to produce a supplement gas for ammonia; the supplement gas is reacted to form ammonia; and at least a portion of the ammonia is used to produce nitric acid, the process being controlled by the method according to any one of claims 1 to 19.

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

22. The process according to claim 20, comprising the steps of generating oxygen (22) from water electrolysis (6) and supplying at least a portion (23) of the oxygen to a catalytic conversion of ammonia (31) and / or a stripping step of a nitric acid solution.

23. 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 the ammonia produced in the ammonia synthesis section is used to produce nitric acid in the nitric acid synthesis section: The ammonia synthesis section includes a front-end section configured to produce a hydrogen-containing ammonia supply gas, the front-end section includes a water electrolyzer configured to produce at least a portion of the hydrogen (5) contained in the ammonia supply gas by water electrolysis; The plant further comprises a control system configured to control the production of ammonia and nitrate within the plant by the method described in any one of claims 1 to 19.

24. The plant according to claim 23, comprising a common steam network between the ammonia synthesis section and the nitrate synthesis section, wherein the production of ammonia and nitrate is controlled to maintain a stable or near-stable production of steam.

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