Processes for the production of ammonia

Abstract

A process for producing ammonia (2) in an ammonia synthesis converter (19) using co-production of steam (40) through recovery of process heat generated in the ammonia synthesis converter is provided, comprising producing power (44) from the expansion of steam (40) in a steam turbine (42) mechanically coupled to a reversible electric motor / generator (43) and a compressor to form an assembly selectively operable in a first mode and a second mode of operation, wherein in the first mode mechanical power (44) is transferred from the steam turbine (42) to the reversible electric motor / generator (43) and compressor, and in the second mode mechanical power (44) is transferred from the steam turbine (42) and the reversible electric motor / generator to the compressor.

Description

[Technical Field]

[0001] The present invention relates to the field of ammonia synthesis, and in particular to a process and method for controlling an ammonia plant exposed to fluctuations in steam output. [Background technology]

[0002] Ammonia is synthesized by reacting hydrogen and nitrogen-containing makeup gas in a catalytic converter to produce an ammonia-containing gaseous effluent, which is separated into a liquid ammonia product after cooling and condensation.

[0003] Typically, cooling of the catalytic converter gaseous effluent is performed in a shell-and-tube heat exchanger, where the gaseous effluent is cooled by indirect heat transfer with water to produce cooled gas and steam. In contrast, condensation of ammonia is performed in a suitable condenser, which includes a cooling system with a gas compressor.

[0004] Overall, the steam produced during the cooling process can be advantageously used to drive utility machines in the ammonia plant, for example, to operate make-up gas compressors or catalytic converter circulators. In some plants, the steam may also be used to drive a steam turbine generator, which typically includes a steam turbine mechanically coupled to an alternator to produce electrical energy.

[0005] Unfortunately, especially in ammonia plants that utilize renewable energy to produce hydrogen and meet the plant's energy needs, steam production is not constant over time. In fact, fluctuations in steam production are observed during operation. This is due to the inherent time-dependent availability of renewable resources, forcing plants to operate within very short time frames during peak times and renewable power shortages.

[0006] In particular, during times of renewable power shortages, plants may be forced to operate at lower capacity, resulting in lower ammonia output and steam production. If the steam produced falls below a threshold, it cannot be used to run the plant's utility machines and in most cases the steam must be condensed, resulting in significant energy waste.

[0007] Conversely, during peak renewable power production, excess steam production is obtained. In conventional ammonia plants, this is not an issue because they rely on external auxiliary boilers supplied with fossil fuels and can adjust the steam balance of the plant by exporting excess steam production to other processes. In contrast, green ammonia plants often do not have auxiliary boilers, and in most cases there is no demand for steam outside the process, and in some cases it is even not possible to export steam, so it is essential to have a self-sufficient steam balance. As a result, excess steam production is again wasted.

[0008] Therefore, in light of the above considerations, it would be highly desirable to provide processes and methods for efficiently controlling and utilizing fluctuating steam output. Summary of the Invention

[0009] The present invention aims to overcome the above-mentioned drawbacks of the prior art, and in particular to address fluctuating steam production in ammonia plants powered by renewable energy sources.

[0010] The present invention is based on the enlightened insight that an assembly including a steam turbine, compressor, and reversible motor / generator can be effectively used to address steam over- and under-production, which can lead to excess or shortage of mechanical power within a plant.

[0011] Therefore, one aspect of the present invention is a process for producing ammonia as defined in claim 1.

[0012] The process includes producing ammonia in an ammonia synthesis converter and producing steam from recovery of process heat generated in the ammonia synthesis converter.

[0013] The process further includes producing electrical power from the expansion of the steam in a steam turbine mechanically coupled to the reversible electric motor / generator and the compressor to form an assembly selectively operable in a first mode of operation and a second mode of operation in response to steam produced from the process heat recovery and to electrical power consumed by the compressor.

[0014] Specifically, in the first mode, mechanical power is transferred from the steam turbine to the reversible electric motor / generator, which acts as a generator, and to the compressor. In the second mode, mechanical power is transferred from the steam turbine and from the reversible electric motor / generator, which acts as a motor, to the compressor.

[0015] The first operating mode is selected when the power obtainable from the expansion of the steam in the steam turbine is greater than the power consumed by the compressor, and the second operating mode is selected when the power obtainable from the expansion of the steam in the steam turbine is less than the power required by the compressor.

[0016] Another aspect of the invention is a method for controlling an ammonia plant as claimed.A further aspect of the invention is a plant for the synthesis of ammonia as claimed.

[0017] The present invention has the following advantages:

[0018] The present invention makes it possible to address the intermittent availability of renewable energy sources, which leads to fluctuations in steam production.

[0019] The present invention provides a more flexible approach to operating and controlling an ammonia plant. In particular, if the amount of mechanical power generated from the expansion of steam in the turbine exceeds the power demand of the compressor of the assembly, this excess power can be used to generate electricity using a generator.

[0020] Conversely, if the amount of mechanical power produced by the steam turbine is insufficient to meet the power demands of the compressor, additional mechanical power can be provided via an electrical motor.

[0021] During start-up of the plant, further advantages can be envisaged, since all the mechanical power required to start the compressors can be provided by the electric motors of the assembly, eliminating the need for dedicated steam generators or steam boilers to generate additional steam and additional mechanical power.

[0022] Additionally, all steam produced within the plant is usable within the plant and there is no net steam export or steam condensation.

[0023] Additionally, reversible motor / generators support power balance, allowing for smooth operation during plant transients.

[0024] The process of the present invention comprises the steps of producing ammonia makeup gas comprising hydrogen from a renewable energy source and reacting the makeup gas in an ammonia synthesis converter to form ammonia, producing steam from recovery of process heat generated during the exothermic reaction of the makeup gas, and producing power from the expansion of the steam.

[0025] The expansion of the steam is accomplished in a steam turbine mechanically coupled to a reversible motor / generator and a compressor, the steam turbine, the reversible motor / generator, and the compressor selectively operating in a first mode and a second mode of operation.

[0026] In a first mode of operation, mechanical power is transferred from the steam turbine to the reversible motor / generator and the compressor, with the reversible motor / generator functioning as a generator driven by the steam turbine.

[0027] In a second mode of operation, mechanical power is transferred from the steam turbine and the reversible motor / generator to the compressor, with the reversible motor / generator thus acting as an electric motor driving the compressor.

[0028] The process further includes selecting a first mode of operation or a second mode of operation in response to steam produced from the recovery of process heat and in response to a power requirement for the compressor.

[0029] In particular, the first operating mode is selected when the power obtainable from the expansion of the steam in the steam turbine is greater than the power required for the compressor, and conversely, the second operating mode is selected when the power obtainable from the expansion of the steam in the steam turbine is less than the power required for the compressor.

[0030] According to a particularly interesting application of the present invention, the hydrogen in the ammonia make-up gas is partially or fully produced by electrolysis of water, preferably using a water electrolysis device powered by a renewable energy source for this purpose.

[0031] The process may further comprise the steps of removing a portion of the hydrogen produced from the renewable energy source, compressing the portion of the hydrogen in an H compressor to obtain compressed H gas, and storing the compressed H gas in a hydrogen storage tank. Advantageously, if the hydrogen produced from the renewable energy source exceeds the amount of hydrogen required to produce make-up gas, the excess hydrogen can be stored in the storage tank after compression and used as needed for further production of the gas. In a particularly preferred application, the compressed hydrogen can be used to produce make-up gas when the availability of renewable energy sources is low or non-existent.

[0032] The compressor part of the assembly comprising the steam turbine and the reversible electric motor / generator is preferably one of the following: a compressor configured to increase the pressure of the make-up gas from the pressure at which the make-up gas is produced to the ammonia synthesis pressure; a compressor configured to maintain the circulation of gas in the ammonia synthesis converter; a compressor of a cooling system configured to cool the gaseous effluent of the ammonia synthesis converter; an H2 compressor configured to increase the pressure of a portion of the hydrogen extracted from the main portion of the hydrogen produced from renewable energy sources.

[0033] Preferably, the compressor configured to increase the pressure of the make-up gas and the compressor configured to maintain circulation of gas within the ammonia synthesis converter are two separate units. However, according to an alternative embodiment of the invention, the compressor configured to increase the pressure of the make-up gas and the compressor configured to maintain circulation of gas within the ammonia synthesis converter are part of a single-geared unit configured to receive mechanical power from a steam turbine and / or the reversible electric motor / generator.

[0034] Preferably, in the first operating mode, the reversible motor / generator produces electrical power that can be exported outside the process or, alternatively, used within the plant. Advantageously, all steam produced within the process can be used to generate mechanical power via a steam turbine or to generate electrical energy via an electric motor in an assembly that receives the mechanical power produced by the steam turbine.

[0035] In accordance with the present invention, steam is produced by recovering process heat generated by the exothermic conversion of make-up gas to ammonia.

[0036] Preferably, steam is produced by cooling the gaseous effluent of the ammonia synthesis converter and / or by directly cooling the catalyst contained in the ammonia synthesis converter.

[0037] Particularly preferably, during operation, all steam delivered to the steam turbine is produced by process heat recovery within the converter, with no further steam being added to the converter.

[0038] The process of the present invention also includes an operating mode in which the power produced by the steam turbine is fully balanced by the power absorbed by the compressor, and therefore no additional mechanical power production is required, since the steam produced by the process heat recovery is used to generate mechanical power that is fully transferred to the compressor of the assembly.

[0039] Preferably, the steam produced by the recovery of process heat is superheated steam.

[0040] The present invention also discloses a method for controlling an ammonia plant, the plant comprising a front end configured to produce ammonia makeup gas comprising hydrogen from a renewable energy source, and an ammonia synthesis section configured to produce ammonia from catalytic conversion of the makeup gas.

[0041] The plant further comprises a steam system configured to produce steam from the recovery of process heat generated during the conversion of the makeup gas and to produce power from the expansion of the steam.

[0042] The steam system includes a steam turbine, part of an assembly including the steam turbine, a reversible electric motor / generator, and at least one compressor, the reversible electric motor / generator, and the compressor mechanically coupled to the steam turbine. The turbine, electric motor / generator, and compressor may be mounted on a common shaft. In some embodiments, a gearbox may be provided between the compressor and the electric motor / generator. The turbine and electric motor / generator may operate as a drive for the compressor. However, the electric motor / generator may also operate as a generator driven by the turbine.

[0043] The motor / generator is connected to the grid such that when it functions as an electric motor (i.e., an additional drive for the compressor), it uses electrical energy from the grid. When it functions as a generator (driven by a turbine), it may export the energy it produces to the grid. In some embodiments, the electrical energy produced by the generator can be used internally in the process. For example, in a chemical plant that is isolated from the grid and equipped with rechargeable batteries, the electrical energy produced within the plant can be used to charge the batteries.

[0044] A method for controlling a plant includes selectively controlling the turbine, the reversible motor / generator, and the compressor in a first mode of operation and a second mode of operation.

[0045] In the first mode of operation, mechanical power is transferred from the steam turbine to the reversible motor / generator and the compressor, and in the first mode of operation, the reversible motor / generator functions as a generator driven by the steam turbine.

[0046] In the second operating mode, mechanical power is transferred from the steam turbine and the reversible motor / generator to the compressor, with the reversible motor / generator acting as an electric motor to drive the compressor.

[0047] The method includes selecting a first or second operating mode in response to steam produced by process heat recovery and in response to a power requirement for a compressor of the assembly.

[0048] A first operating mode is selected when the power available from the expansion of the steam in the steam turbine is greater than the power required by the compressor.

[0049] A second operating mode is selected when the power available from the expansion of the steam in the steam turbine is less than the power required by the compressor.

[0050] According to a preferred embodiment, the reversible motor / generator is used as the motor to drive the compressor during start-up.

[0051] The present invention also discloses a plant for the synthesis of ammonia, comprising: a front end for the production of makeup gas, at least partially powered by a renewable energy source and a compressor for the makeup gas; an ammonia synthesis section including the compressor acting as a circulator for the makeup gas; and an ammonia synthesis converter for producing an ammonia-containing gaseous effluent.

[0052] The plant further comprises a heat recovery section including a steam system configured to cool the ammonia-containing gaseous effluent to produce steam, a condensation section including the cooling system including a cooling system gas compressor, and an assembly including a steam turbine, a reversible electric motor / generator, and at least one compressor, the reversible electric motor / generator and the compressor being mechanically coupled to the steam turbine.

[0053] In an interesting application of the present invention, the plant further comprises a buffering section including an H2 compressor in fluid communication with the front end of the plant, a hydrogen storage tank in communication with said H2 compressor, and a recycle line arranged to fluidly connect said hydrogen storage tank with the suction of the make-up gas compressor.

[0054] The buffering section can be used to store hydrogen when excess hydrogen is produced in the synthesis section, and can be used to provide stored hydrogen to the synthesis section of the plant when renewable resources are less or not available.

[0055] As an advantage, the possibility of using a reversible motor / generator in conjunction with a buffering unit allows for great flexibility in the operation of the plant, especially in adapting very well to intermittent renewable power use and fluctuations in H2 production.

[0056] Preferably, the compressor of the assembly is one of the make-up gas compressor, the compressor acting as a circulator for make-up gas, the compressor of the cooling system, or the H2 compressor of the buffering section.

[0057] Particularly preferably, the front end comprises a water electrolysis unit for producing hydrogen, which is at least partly powered by a renewable energy source.

[0058] The plant preferably comprises a control system configured to control said assembly in accordance with the method disclosed above.

[0059] According to one embodiment, the heat recovery section includes a boiler feedwater preheater, a waste heat boiler, a steam superheater, and a demi-water preheater.

[0060] The plant preferably comprises a separation section configured to separate an ammonia product from said ammonia-containing gaseous effluent, and further comprises a recycle line connecting said separation section to the suction of the circulator.

[0061] Preferably, the cooling system is an ammonia cooling system further comprising an ammonia receiver and an ammonia chiller. [Brief explanation of the drawings]

[0062] [Figure 1] 1 is a schematic diagram of an ammonia plant according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0063] The ammonia plant 1 of Figure 1 includes a front end 100 for the production of makeup gas 11, an ammonia synthesis section 400 for the production of an ammonia-containing gaseous effluent 20, a heat recovery section 500, a condensation section 600, a separation section 700 for separating the ammonia output 2, and a buffering section 800 for the storage of hydrogen.

[0064] More specifically, the front end 100 includes a hydrogen production section 200 for the production of a hydrogen stream 7 , a nitrogen production section 300 for the output of a nitrogen feed 10 , and a make-up gas compressor 12 .

[0065] The hydrogen production section 200 includes a water electrolysis device 4 for the generation of hydrogen feed 5 from a water stream 3 and the co-production of oxygen 30. The water electrolysis device 4 is powered by electricity E provided by a renewable source 59, which in FIG. 1 is a solar source S. The solar source S can be, for example, a photovoltaic field. In other embodiments, the electricity E is obtained from any one of wind, biomass, hydroelectric, geothermal, or a combination thereof.

[0066] The hydrogen generation section 200 further includes a deoxygenation unit 6 configured to remove remaining traces of oxygen from the hydrogen feed 5. The output of the deoxygenation unit is a hydrogen stream 7.

[0067] Nitrogen production section 300 includes a nitrogen generation unit 9 for extracting nitrogen 10 from an air supply 8. Nitrogen generation unit 9 may be an air separation unit (ASU) that also produces oxygen or oxygen-enriched air.

[0068] The buffering section 800 is used to store a portion 52 of the hydrogen 7 produced in the front end 100. The buffering section includes an H2 compressor 53 in fluid communication with the front end 100, a hydrogen storage tank 55 in communication with the H2 compressor 53, and a recycle line 56 positioned to fluidly connect the hydrogen storage tank 55 with the suction of the make-up gas compressor 12.

[0069] In practice, a portion 52 of hydrogen stream 7 is compressed in H2 compressor 53 to obtain compressed hydrogen gas 54 which is subsequently stored in hydrogen storage tank 55. Preferably, compressed hydrogen gas 54 is fed to the suction of compressor 12 when the availability of renewable energy sources is low or absent. The amount of hydrogen fed to the suction of compressor 12 is regulated by valve 58.

[0070] It can be seen from the drawing that hydrogen stream 7 and nitrogen feed 10 are mixed together to produce makeup gas 11 which is sent to ammonia synthesis section 400 via makeup gas compressor 12 and circulator 15. The output of makeup gas compressor 12 is compressed makeup gas 30. A valve 13 is located downstream of makeup gas compressor 12 and upstream of ammonia synthesis section 400 to regulate the flow of compressed makeup gas 30 sent to ammonia synthesis section 400.

[0071] The ammonia synthesis section 400 includes an ammonia converter 19 and a circulator 15 with a bypass line 16. The circulator 15 receives compressed makeup gas 30, which is the discharge of the compressor 12, and also receives tail gas 24, which is the discharge of the separation section 700. In the embodiment of FIG. 1, the tail gas 24 and compressed makeup gas 30 are mixed together at the discharge of the compressor 12 to generate a mixed stream 14 prior to being fed to the circulator 15.

[0072] The output of circulator 15 is a reagent gas feed 17 that is sent to an ammonia converter 19. The ammonia converter 19 includes one or more reactive zones, for example, one or more catalyst beds.

[0073] A bypass line 16 may be used to recycle a portion of the reagent gas feed 17 of the circulator 15 to keep the operating pressure of the ammonia converter 19 within a predetermined range, for example, during a part-load event due to a lack of renewable power. For this purpose, the system disclosed in WO 2021 / 089276 may be used.

[0074] In the ammonia converter 19, the reagent gas feed 17 is reacted over a suitable catalyst to form an ammonia-containing gaseous effluent 20. The ammonia-containing gaseous effluent 20 is then indirectly cooled in a heat recovery section 500 to produce cooled gas 50 and steam 40. The heat recovery section is supplied with water 21 which is converted to said steam 40 after heat recovery from the gaseous effluent 20.

[0075] The output of the heat recovery section, cooled gas 50, is sent to a condensation section 600 which includes a condenser 22 and an ammonia cooling system 41.

[0076] An ammonia refrigeration system 41 is used to remove heat in the condenser 22 using ammonia as a refrigerant. The ammonia refrigeration system is of standard design and includes an ammonia compressor, an ammonia receiver, and a chiller.

[0077] The output of the condenser is a condensed stream 23 which is separated in an ammonia separation section 700 into an ammonia product 2 and tail gas 24. Preferably, all of the tail gas 24 is returned to the suction of the circulator 15. Alternatively, an embodiment is envisaged in which most of the tail gas is returned to the suction of the circulator 15 and part of the tail gas 24 is discharged outside the plant 1 via a valve 26. It is noted in the drawing that the amount of ammonia 2 removed from the separator 700 is regulated by a valve 27.

[0078] The plant further includes an assembly comprising a steam turbine 42 , a compressor, and a reversible motor / generator 43 .

[0079] The compressor of the assembly according to the embodiment of FIG. 1 is either the compressor of the refrigeration system 41, the circulator 15 of the ammonia synthesis section 400, the H2 compressor of the buffering section 800, or one of the make-up gas compressors 12.

[0080] The reversible motor / generator 43 is configured to function as an electrical motor, converting electrical input into mechanical power, or as a generator, converting prime mover (mechanical power) into electrical power.

[0081] The steam turbine 42 is connected to a heat recovery section 500, a reversible motor / generator 43, and any one of the following: an H2 compressor 53, a circulator 15, a compressor of the ammonia refrigeration system 41, and a make-up gas compressor 12. The reversible motor / generator 43 is further connected to the circulator 15, a compressor of the ammonia refrigeration system 41, the H2 compressor 53, and the make-up gas compressor 12.

[0082] The method of the present invention will now be described with reference to FIG.

[0083] The method includes switching the operability of the plant between a first operating mode and a second operating mode based on the amount of steam 40 produced in the heat recovery section 500 and the amount of power 44 required by the compressor of the assembly.

[0084] In the first operating mode, steam 40 is at least partially expanded in steam turbine 42 to generate mechanical power 44, which is transmitted to one of the following: circulator 15 via line 48, a compressor of ammonia refrigeration system 41 via line 49, H2 compressor 53 of buffering section 800 via line 57, or make-up gas compressor 12 via line 60. Additionally, excess power not used to operate the compressors is transmitted to reversible motor / generator 43 to generate electrical power. In the first operating mode, reversible motor / generator functions as an electric motor.

[0085] A first operating mode is selected when the power available from the expansion of the steam 40 in the steam turbine 42 is greater than the power required by one of the compressors of the assembly, for example a circulator.

[0086] Conversely, if the power available from the expansion of the steam 40 in the steam turbine is less than the power required for the compressor, the plant operates according to a second operating mode.

[0087] In the second mode of operation, mechanical power 44 available from the expansion of the steam in the steam turbine 42 is transferred to the circulator 15 via line 48, or to the compressor of the ammonia refrigeration system 41 via line 49, or to the H2 compressor 53 via line 57, or to the make-up gas compressor 12. The balance of the mechanical power required to operate the compressors is provided by the reversible motor / generator 43 via line 51. In the second mode of operation, the reversible motor / generator 43 is operated as a generator.

Claims

1. 1. A process for producing ammonia (2), said process comprising: producing an ammonia make-up gas (11) comprising hydrogen (5) from a renewable energy source (59) and reacting the make-up gas (11) in an ammonia synthesis converter (19) to form the ammonia (2); producing steam (40) from the recovery of process heat generated during the exothermic reaction of said make-up gas (11); and producing power (44) from the expansion of said steam (40); The expansion of the steam (40) takes place in a steam turbine (42) mechanically coupled to a reversible electric motor / generator (43) and at least one compressor; the turbine, the reversible motor / generator, and the compressor form an assembly selectively operable in a first mode of operation and a second mode of operation; In the first mode, mechanical power (44) is transferred from the steam turbine (42) to the reversible electric motor / generator (43) and the compressor, and the reversible electric motor / generator (43) acts as a generator driven by the steam turbine (42); in the second mode, mechanical power (44) is transferred from the steam turbine (42) and the reversible motor / generator to the compressor, with the reversible motor / generator acting as the motor driving the compressor; The process further comprises: selecting the first or second operating mode depending on the steam (40) production and depending on the power required by the compressor; the first operating mode is selected when the power available from the expansion of the steam (40) in the steam turbine (42) is greater than the power required by the compressor; The process wherein the second operating mode is selected when the power available from the expansion of the steam (40) in the steam turbine (42) is less than the power required by the compressor.

2. 2. The process of claim 1, wherein the hydrogen (5) in the ammonia make-up gas (11) is partially or fully produced by electrolysis of water (4).

3. Removing a portion (52) of the hydrogen (5) produced from the renewable energy source (59); 2 A portion of the hydrogen (52) is reacted with H to obtain a gas (54). 2 compressing in a compressor (53); 2 3. The process of claim 1 or 2, further comprising storing the gas (54) in a hydrogen storage tank (55).

4. The compressor is a compressor (12) configured to increase the pressure of the makeup gas (11) from the pressure at which the makeup gas (11) is produced to an ammonia synthesis pressure; a compressor (15) configured to maintain gas circulation in the ammonia synthesis converter (19); a compressor of a cooling system (41) configured to cool the gaseous effluent of the ammonia synthesis converter (19); a compressor of a cooling system (41) configured to increase the pressure of a portion of the hydrogen (52); 2 The process according to any one of claims 1 to 3, wherein the compressor (53) is any one of the compressors (53).

5. The process of any one of claims 1 to 4, wherein in the first operating mode, the reversible motor / generator (43) produces electrical energy (45) that is exported outside the process.

6. 6. The process of claim 4 or 5, wherein the steam (40) is produced by cooling the gaseous effluent of the ammonia synthesis converter (19) and / or by directly cooling a catalyst contained in the ammonia synthesis converter (19).

7. 7. The process of any one of claims 1 to 6, wherein in operation, all of the steam (40) delivered to the steam turbine (42) is produced by process heat recovery without producing additional steam in a fuel-fired boiler.

8. The process of any one of claims 1 to 7, further comprising an operating mode in which the power produced by the steam turbine (42) is substantially balanced by the power absorbed by the compressor.

9. The process of any one of claims 1 to 8, wherein the steam (40) is superheated.

10. A method for controlling an ammonia plant (1), comprising: The plant (1) a front end (100) configured to produce an ammonia make-up gas (11) comprising hydrogen (5) from a renewable energy source (59); and an ammonia synthesis section (400) configured to produce ammonia (2) from catalytic conversion of the make-up gas (11), The plant (1) a steam system configured to produce steam (40) from the recovery of process heat generated during the conversion of the make-up gas (11) and to produce power (44) from the expansion of the steam (40); the steam system comprises a steam turbine (42), the steam turbine (42) being part of an assembly including the steam turbine (42), a reversible electric motor / generator (43), and at least one compressor, the reversible electric motor / generator (43) and the compressor being mechanically coupled to the steam turbine (12); The method for controlling the plant (1) comprises: selectively controlling the turbine (12), the reversible electric motor / generator (43), and the compressor in a first mode of operation and a second mode of operation, In the first operating mode, mechanical power (44) is transferred from the steam turbine (42) to the reversible electric motor / generator (43) and the compressor, and the reversible electric motor / generator (43) acts as a generator driven by the steam turbine (42); in the second operating mode, mechanical power (44) is transferred from the steam turbine (42) and the reversible electric motor / generator (43) to the compressor, the reversible electric motor / generator (43) acting as an electric motor to drive the compressor; The method comprises: selecting the first or second operating mode depending on the steam (40) production and the power required by the compressor, the first operating mode is selected when the power available from the expansion of the steam (40) in the steam turbine (42) is greater than the power required by the compressor; the second operating mode is selected if power available from expansion of the steam in the steam turbine is less than the power required by the compressor.

11. 11. The method of claim 10, wherein the reversible motor / generator (43) is used as a motor to drive the compressor during start-up.

12. A plant (1) for the synthesis of ammonia (2), comprising: a front end (100) for the production of make-up gas (11), at least partially driven by a renewable energy source (59) and a compressor (12) for said make-up gas (11); an ammonia synthesis section (400) including a compressor (15) acting as a circulator for the make-up gas (11) and an ammonia synthesis converter (19) for producing an ammonia-containing gaseous effluent (20); a heat recovery section (500) including a steam system configured to cool the ammonia-containing gaseous effluent (20) and generate steam (40); a condenser (600) including a cooling system (41), the cooling system (41) including a gas compressor of the cooling system (41); an assembly including a steam turbine (42), a reversible electric motor / generator (43) and at least one compressor, said reversible electric motor / generator and said compressor being mechanically coupled to said steam turbine; A plant (1) comprising:

13. H in fluid communication with said front end (100) 2 Compressor (53) and the H 2 13. The plant (1) of claim 12, further comprising a buffering section (800) including: a hydrogen storage tank (55) in communication with the compressor (53); and a recycle line (56) arranged so that the hydrogen storage tank (55) is in fluid communication with the compressor (12) of the makeup gas (11).

14. The compressor of the assembly may be the compressor (12) of the make-up gas (11), the compressor (15) acting as a circulator for the make-up gas (11), the compressor of the cooling system (41), or the H of the buffering section (800). 2 14. The plant (1) according to claim 12 or 13, being one of the compressors (53).

15. The plant according to any one of claims 12 to 14, wherein the front end comprises a water electrolysis device (4) for the production of hydrogen (5) powered at least in part by a renewable energy source (59).

16. A plant according to any one of claims 12 to 15, further comprising a control system configured to control the assembly according to the method of claim 10 or 11.

17. The plant of any one of claims 12 to 16, wherein the heat recovery section (500) includes a boiler feedwater preheater, a waste heat boiler, a steam superheater, and a pure water preheater.

18. 18. The plant of any one of claims 12 to 17, further comprising a separation section (700) configured to separate an ammonia product (2) from the ammonia-containing gaseous effluent (20), and further comprising a recycle line (24) connecting the separation section (700) to the suction of the circulator (15).

19. The plant according to any one of claims 12 to 18, wherein the cooling system (41) is an ammonia cooling system further comprising an ammonia acceptor and an ammonia chiller.

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