Method for producing ammonia

Abstract

A method of producing ammonia (2) in an ammonia synthesis converter (19) and co-producing steam (40) by recovering process heat generated in the synthesis converter, the method comprising generating power (44) by expansion of the steam (40) in a steam turbine (42), the steam turbine (42) being mechanically connected to a reversible motor / generator (43) and to a compressor, the reversible motor / generator (43) is driven by the steam turbine (42) so as to form an assembly that is selectively operable in a first operating mode in which mechanical power (44) is transmitted from the steam turbine (42) to the reversible motor / generator (43) and to the compressor, and a second operating mode in which mechanical power (44) is transmitted from the steam turbine (42) to the reversible motor / generator (43). And in the second mode, mechanical power (44) is transmitted from the steam turbine (42) and the reversible motor / generator to the compressor.

Description

Technical Field

[0001] The present invention belongs to the field of ammonia synthesis. In particular, the present invention relates to a process and a method for controlling an ammonia plant which is subject to fluctuations in steam production. Background Art

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

[0003] The cooling of the gaseous effluent of the catalytic converter is usually carried out in a shell and tube heat exchanger, wherein the gaseous effluent is cooled by indirect heat transfer with water to produce cooling gas and steam. In contrast, the condensation of ammonia is carried out in a suitable condensation section comprising a refrigerator system equipped with a gas compressor.

[0004] In general, the steam produced in the coolant process can be advantageously used in an ammonia plant as a driving force for utility machines, such as to operate a feed gas compressor or a catalytic converter circulator. In some plants, the steam can also be used to drive a steam turbine generator, which typically includes a steam turbine mechanically coupled to an alternator, for generating electrical energy.

[0005] Unfortunately, the production of steam is not constant with respect to time, especially in those ammonia plants that utilize renewable energy to produce hydrogen and meet the energy needs of the plant. In fact, during operation, fluctuations in steam production are observed due to the time dependency of the availability of renewable energy, forcing ammonia plants to operate in very short time frames during renewable energy peaks and shortages.

[0006] Especially in the case of a shortage of renewable energy, the plant may be forced to operate at reduced capacity, resulting in low ammonia production and low steam generation. When the steam produced is below the threshold, it cannot be used to operate the plant's utility machines and in most cases the steam must be condensed, resulting in a significant waste of energy.

[0007] On the contrary, during peaks in renewable energy production, additional steam production is available. In conventional ammonia plants, this is not a problem, because the steam balance of the plant can be regulated by means of an external auxiliary boiler supplied with fossil fuels, and the excess steam production can be exported to other processes. In contrast, in green ammonia plants, it is crucial to maintain a closed-loop steam balance, because auxiliary boilers are usually not provided, and in most cases there is no demand for steam outside the process, and in some cases, exporting steam is not even feasible. Therefore, the additional steam produced is once again wasted.

[0008] Therefore, in view of the above considerations, it is highly desirable to provide processes and methods for controlling and utilizing fluctuating steam production in an efficient manner. Summary of the invention

[0009] The present invention aims to overcome the above-mentioned drawbacks of the prior art. In particular, the present invention aims to solve the steam production fluctuations in an ammonia plant driven by renewable energy.

[0010] The present invention is based on the insight that an assembly comprising a steam turbine, a compressor and a reversible motor / generator can be effectively used to accommodate excess or deficiency in steam production which may result in excess or deficiency in mechanical power in the plant.

[0011] Therefore, one aspect of the present invention is a method for producing ammonia according to claim 1.

[0012] The method comprises producing ammonia in an ammonia synthesis converter and producing steam by recovering process heat generated in the ammonia synthesis converter.

[0013] The method further includes generating power from expansion of the steam in a steam turbine, the steam turbine being mechanically connected to a reversible motor / generator and a compressor to form an assembly, the assembly being selectively operable in a first mode of operation and a second mode of operation depending on the steam generated from process heat recovery and the power consumed by the compressor.

[0014] Specifically, in the first mode, mechanical power is transmitted from the steam turbine to the reversible motor / generator acting as a generator and the compressor; and in the second mode, mechanical power is transmitted from the steam turbine and the reversible motor / generator acting 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 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 turbine is less than the power required by the compressor.

[0016] Another aspect of the invention is a method for controlling an ammonia plant according to the claims. Another aspect of the invention is a plant for synthesizing ammonia according to the claims.

[0017] The present invention has the following advantages:

[0018] The invention allows addressing the intermittent availability of renewable energy sources that results in fluctuations in steam production.

[0019] The present invention provides a more flexible way to operate and control an ammonia plant. In particular, when the amount of mechanical power generated from the expansion of steam in the turbine exceeds the power required by the compressor in the assembly, the generator can use the excess power to generate electricity.

[0020] Conversely, when the amount of mechanical power generated by the steam turbine is insufficient to meet the power required by the compressor, additional mechanical power may be provided by an electric motor.

[0021] During plant start-up, another advantage can be foreseen: no dedicated steam generator or steam boiler is required to generate additional steam and additional mechanical power, since the mechanical power required for compressor start-up can be fully provided by the electric motor in the assembly.

[0022] Furthermore, all steam generated within the device can be utilized within the device, with no net export of steam or condensation of steam.

[0023] In addition, since the reversible motor / generator supports power balance, smooth operation of the equipment under transient conditions can be obtained.

[0024] Detailed description of the invention

[0025] The method of the present invention comprises the following steps: producing an ammonia feed gas containing hydrogen from renewable energy, reacting the feed gas in an ammonia synthesis converter to form ammonia, producing steam by recovering process heat generated during the exothermic reaction of the feed gas, and producing power by expanding the steam.

[0026] The expansion of the steam takes place in a steam turbine which is mechanically connected to a reversible electric motor / generator and a compressor. The steam turbine, the reversible electric motor / generator and the compressor form an assembly which can be selectively operated in a first operating mode and in a second operating mode.

[0027] In a first operating mode, mechanical power is transferred from the steam turbine to the reversible motor / generator and to the compressor, the reversible motor / generator acting as a generator driven by the steam turbine.

[0028] In the second operating mode, mechanical power is transmitted from the steam turbine and the reversible motor / generator to the compressor, and accordingly, the reversible motor / generator acts as a motor driving the compressor.

[0029] The method further includes selecting a first operation mode or a second operation mode based on steam generated by recovering the process heat and power required by the compressor.

[0030] In particular, when the power available from the expansion of the steam in the steam turbine is greater than the power required by the compressor, the first operating mode is selected. Conversely, when the power available from the expansion of the steam in the steam turbine is less than the power required by the compressor, the second operating mode is selected.

[0031] According to a particularly interesting application of the invention, the hydrogen in the ammonia feed gas is partially or completely produced by water electrolysis. For this purpose, a water electrolyzer powered by renewable energy sources is preferably used.

[0032] The method may further include the steps of extracting a portion of the hydrogen produced from the renewable energy, compressing the portion of the hydrogen in an H2 compressor to obtain compressed H2 gas, and storing the compressed H2 gas in a hydrogen storage tank. Advantageously, when the hydrogen produced from the renewable energy exceeds the amount of hydrogen required for producing the make-up gas, the excess hydrogen can be stored in the storage tank after compression and used for further production of the gas when needed. In a specific preferred application, the compressed hydrogen can be used to produce make-up gas when the available amount of renewable energy is low to non-available.

[0033] The compressor section in the assembly with a steam turbine and a reversible motor / generator is preferably one of the following: a compressor configured to increase the pressure of the feed gas from the pressure at which the feed gas is produced to the ammonia synthesis pressure; a compressor configured to maintain gas circulation in the ammonia synthesis converter; a compressor of a refrigeration system configured to cool the gaseous effluent of the ammonia synthesis converter; an H2 compressor configured to increase the pressure of the portion of hydrogen extracted from the main hydrogen portion generated by renewable energy.

[0034] Preferably, the compressor configured to increase the feed gas pressure and the compressor configured to maintain the gas circulation in the ammonia synthesis converter are two independent units. However, according to an alternative embodiment of the present invention, the compressor configured to increase the feed gas pressure and the compressor configured to maintain the gas circulation in the ammonia synthesis converter are part of a single-geared unit, which is configured to receive mechanical power from the steam turbine and / or the reversible motor / generator.

[0035] Preferably, in said first mode of operation, the electric power generated by said reversible motor / generator can be exported out of the process or can also be utilized within the plant. Advantageously, any steam generated in said process can be utilized to generate mechanical power via a steam turbine or to generate electric power via an electric motor in a component that receives the mechanical power generated by the steam turbine.

[0036] According to the present invention, steam is generated by recovering process heat generated during the exothermic conversion of feed gas into ammonia. Preferably, the steam is generated 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 conducted to the steam turbine is generated completely by recovering process heat in the reformer and no additional steam is added to the steam turbine.

[0038] The method of the invention may also include an operating mode in which the power produced by the steam turbine is completely balanced with the power absorbed by the compressor. Thus, the steam produced by recovering process heat is used to generate mechanical power, which is fully transmitted to the compressor in the assembly without the need for additional production of mechanical power.

[0039] Preferably, the steam generated by recovering process heat is superheated steam.

[0040] The present invention also discloses a method for controlling an ammonia plant, wherein the plant comprises a front-end configured for producing an ammonia feed gas comprising hydrogen from renewable energy, and an ammonia synthesis section arranged for producing ammonia by catalytic conversion of the feed gas.

[0041] The apparatus further comprises a steam system configured to produce steam by recovering process heat generated during the feed gas conversion process and to generate power by expansion of the steam.

[0042] The steam system comprises a steam turbine, which is part of an assembly comprising the steam turbine, a reversible motor / generator and at least one compressor, wherein the reversible motor / generator and the compressor are mechanically connected to the steam turbine. The steam turbine, the motor / generator and the compressor may be mounted on a common shaft. In some embodiments, a gearbox may be provided between the compressor and the motor / generator. It may be noted that the steam turbine and the motor / generator may operate as drivers for the compressor. However, the motor / generator may also operate as a generator driven by the steam turbine.

[0043] The motor / generator is connected to the grid, and when the motor / generator acts as a motor (i.e., an additional drive device for the compressor), it uses electricity from the grid. When it acts as a generator (driven by a steam turbine), it outputs the generated electricity to the grid. In some embodiments, the electricity generated by the generator can be used internally in the process. For example, in a chemical device that is isolated from the grid and equipped with a rechargeable battery, the electricity generated in the device can be used to charge the battery.

[0044] The method for controlling an apparatus includes selectively controlling the steam turbine, the reversible motor / generator, and the compressor in a first operating mode and a second operating mode.

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

[0046] In the second operating mode, mechanical power is transmitted from the steam turbine and the reversible motor / generator to the compressor, with the reversible motor / generator acting as a motor driving the compressor.

[0047] The method comprises selecting a first operating mode or a second operating mode depending on the steam generated by recovering process heat and on the power required for a compressor in the assembly.

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

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

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

[0051] The present invention also discloses an apparatus for synthesizing ammonia, comprising: a front end for producing a feed gas, the front end being at least partially powered by renewable energy; and a compressor for the feed gas; an ammonia synthesis section comprising a compressor acting as a circulator for the feed gas and an ammonia synthesis converter for generating a gaseous effluent containing ammonia.

[0052] The apparatus further comprises a heat recovery section comprising a steam system configured to cool the gaseous effluent containing ammonia and generate steam; a condensing section comprising a refrigeration system comprising a gas compressor of a refrigerator system, and an assembly comprising a steam turbine, a reversible motor / generator and at least one compressor, wherein the reversible motor / generator and the compressor are mechanically connected to the steam turbine.

[0053] In an interesting application of the present invention, the equipment used further includes a buffering section, which includes an H2 compressor connected to the front fluid of the equipment, a hydrogen storage tank connected to the H2 compressor, and a recycling line, which is configured to connect the hydrogen storage tank to the suction fluid of the supply gas compressor.

[0054] When the synthesis section produces excess hydrogen, the buffer section can be used to accumulate hydrogen; and when the available amount of renewable resources is less or even zero, the buffer section can be used to provide the accumulated hydrogen to the synthesis section of the equipment.

[0055] Advantageously, the possibility of operating a reversible motor / generator together with a buffer section provides great flexibility in the operation of the plant. In particular, the intermittent availability of renewable energy power and fluctuations in H2 production can be handled extremely well.

[0056] Preferably, the compressor of the component is one of the following: the compressor of the make-up gas, the compressor acting as a make-up gas circulator, the compressor of the refrigerator system or the H2 compressor of the buffer section.

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

[0058] The apparatus preferably comprises a control system configured for controlling the components according to the method disclosed above.

[0059] According to one embodiment, the heat recovery section comprises a boiler feed water pre-heater, a waste heat boiler, a steam superheater and a demi-water pre-heater.

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

[0061] Preferably, the refrigeration system is an ammonia refrigerator system, and the ammonia refrigerator system further comprises an ammonia receiver and an ammonia chiller. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0063] Figure 1 The ammonia plant 1 comprises a front end 100 for producing a make-up gas 11, an ammonia synthesis section 400 for producing an ammonia-containing gaseous effluent 20, a heat recovery section 500, a condensation section 600, a separation section 700 for separating an ammonia product 2, and a buffer section 800 for accumulating hydrogen.

[0064] In more detail, the front end 100 comprises a hydrogen generation section 200 for producing a hydrogen gas stream 7 , a nitrogen production section 300 for producing a nitrogen feed 10 , and a make-up gas compressor 12 .

[0065] The hydrogen generation section 200 comprises a water electrolyser 4 for generating a hydrogen feed 5 from a water stream 3 and co-producing oxygen 30. The water electrolyser 4 is powered by electricity E provided by a renewable energy source 59. Figure 1 In the embodiment, the renewable energy 59 is a solar energy S. The solar energy S can be, for example, a photovoltaic field. In other embodiments, the electric power E can be obtained from any of the following energy sources: wind energy, biomass, hydropower, geothermal power, or a mixture thereof.

[0066] The hydrogen generation section 200 further comprises a deoxygenation unit 6, which is configured to remove trace amounts of oxygen from the hydrogen feed 5. The output of the deoxygenation unit is a hydrogen stream 7.

[0067] The nitrogen production section 300 comprises a nitrogen generation unit 9 for extracting nitrogen 10 from an air feed 8. The nitrogen generation unit 9 may be an air separation unit (ASU) which also produces oxygen or oxygen-enriched air.

[0068] The buffer section 800 is used to accumulate a portion 52 of the hydrogen 7 produced in the front end 100, and the section includes an H2 compressor 53 fluidly connected to the front end 100, a hydrogen storage tank 55 connected to the H2 compressor 53, and a recirculation pipeline 56 configured to enable the hydrogen storage tank 55 to be fluidly connected to the suction end of the supply gas compressor 12.

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

[0070] As can be seen from the figure, the hydrogen stream 7 and the nitrogen feed 10 are mixed together to produce a feed gas 11, which is delivered to the ammonia synthesis section 400 through a feed gas compressor 12 and a circulator 15. The outflow of the feed gas compressor 12 is the compressed feed gas 30. A valve 13 is provided downstream of the feed gas compressor 12 and upstream of the ammonia synthesis section 400 for adjusting the flow rate of the compressed feed gas 30 delivered to the ammonia synthesis section 400.

[0071] The ammonia synthesis section 400 comprises an ammonia converter 19 and a circulator 15 equipped with a bypass line 16. The circulator 15 receives the compressed feed gas 30 effluent from the compressor 12, and it also receives the tail gas 24 effluent from the separation section 700. Figure 1 In the embodiment of FIG. 1 , the tail gas 24 and the compressed make-up gas 30 are mixed together at the outlet of the compressor 12 to generate a mixed stream 14 , which is then supplied to the circulator 15 .

[0072] The effluent of the circulator 15 is a reagent gas feed 17 which is passed to an ammonia converter 19. The ammonia converter 19 comprises one or more reaction zones, such as one or more catalytic beds.

[0073] The bypass line 16 can be used to recover a portion of the reaction gas feed 17 of the circulator 15 so as to keep the operating pressure of the ammonia converter 19 within a preset range under partial load conditions, such as due to a shortage of renewable energy power. To this end, the system disclosed in WO2021 / 089276 can be used.

[0074] In the ammonia converter 19, the reaction gas feed 17 reacts 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 fed by water 21, which is converted into the steam 40 after recovering heat from the gaseous effluent 20.

[0075] The cooling gas 50 effluent of the heat recovery section is passed to the condensing section 600 comprising the condenser 22 and the ammonia chiller system 41 .

[0076] The ammonia refrigerator system 41 uses ammonia as a coolant to remove heat from the condenser 22. The ammonia refrigerator system adopts a standard design, including an ammonia compressor, an ammonia receiver, and a chiller.

[0077] The outflow of the condenser is a condensed stream 23, which is separated into an ammonia product 2 and a tail gas 24 in the ammonia separation section 700. Preferably, the tail gas 24 is completely recovered by the suction end of the circulator 15. Alternatively, an embodiment can also be envisioned in which most of the tail gas is recovered by the suction end of the circulator 15, and a portion of the tail gas 24 is discharged from the device 1 through a valve 26. As can be seen from the figure, the amount of ammonia 2 extracted from the separator 700 is adjusted by a valve 27.

[0078] The apparatus also includes components including a steam turbine 42 , a compressor, and a reversible electric motor / generator 43 .

[0079] according to Figure 1 The compressor in the components of the embodiment is one of the following: a compressor of the refrigeration system 41, a circulator 15 of the ammonia synthesis section 400, an H2 compressor of the buffer section 800, or a make-up gas compressor 12.

[0080] The reversible motor / generator 43 is configured to function as a motor, which converts electrical input into mechanical energy, or as a generator, which converts power (mechanical energy) into electrical energy.

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

[0082] Now refer to Figure 1 The method of the present invention is explained.

[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 generated in the heat recovery section 500 and the amount of power 44 required by the compressor of the assembly.

[0084] In the first operation mode, the steam 40 is at least partially expanded in the steam turbine 42 to generate mechanical power 44, which is transmitted to the circulator 15 through the pipeline 48, to the compressor of the ammonia refrigerator system 41 through the pipeline 49, to the H2 compressor 53 of the buffer section 800 through the pipeline 57, or to the feed gas compressor 12 through the pipeline 60. In addition, the excess power not used to drive the above compressor is transmitted to the reversible motor / generator 43 to generate electricity. In the first operation mode, the reversible motor / generator acts as a motor.

[0085] The first operating mode is selected when the power available from the expansion of the steam 40 in the turbine 42 is greater than the power required by the above-mentioned compressor of the assembly, such as a circulator.

[0086] Conversely, when the power available from the expansion of the steam 40 in the turbine 42 is less than the power required by the compressor, the plant operates in a second operating mode.

[0087] In the second operating mode, the mechanical power 44 obtainable from the expansion of the steam 40 in the steam turbine 42 is transferred to the circulator 15 via line 48, or to the compressor of the ammonia refrigerator system 41 via line 49, or to the H2 compressor 53 via line 57, or to the make-up gas compressor 12, and the balance of the mechanical power required to operate the compressor is provided by the reversible motor / generator 43 via line 51. In the second operating mode, the reversible motor / generator 43 operates as a generator.

Claims

1. A method for producing ammonia (2), comprising: Producing an ammonia feed gas (11) containing hydrogen (5) from a renewable energy source (59) and reacting the feed gas (11) in an ammonia synthesis converter (19) to form ammonia (2); producing steam (40) by recovering process heat generated by the feed gas (11) during an exothermic reaction; producing power (44) by expansion of the steam (40); wherein the expansion of the steam (40) is carried out in a steam turbine (42) which is mechanically connected to a reversible electric motor / generator (43) and to at least one compressor; The steam turbine, the reversible motor / generator and the compressor constitute an assembly that can be selectively operated in a first operating mode and a second operating mode, wherein: In the first mode, mechanical power (44) is transmitted from the steam turbine (42) to the reversible motor / generator (43) and the compressor, and the reversible motor / generator (43) acts as a generator under the drive of the steam turbine (42); In the second mode, mechanical power (44) is transmitted from the steam turbine (42) and the reversible motor / generator to the compressor, the reversible motor / generator acting as a motor driving the compressor; The method comprises selecting a first operating mode or a second operating mode according to the production of steam (40) and the power required by the compressor, wherein: selecting a first operating mode when the power available from expansion of the steam (40) in the turbine (42) is greater than the power required by the compressor; and The second operating mode is selected when the power available from the expansion of the steam (40) in the turbine (42) is less than the power required by the compressor.

2. The method according to claim 1, wherein the hydrogen (5) in the ammonia feed gas (11) is partially or completely produced by water electrolysis (4).

3. The method according to claim 1 or 2, further comprising the steps of extracting a portion (52) of the hydrogen (5) generated from the renewable energy (59), compressing the portion (52) of the hydrogen in an H2 compressor (53) to obtain compressed H2 gas (54), and storing the compressed H2 gas (54) in a hydrogen storage tank (55).

4. A method according to any one of the preceding claims, wherein the compressor is one of the following: a compressor (12) configured to increase the pressure of the feed gas (11) from the pressure at which the feed gas (11) is produced to the ammonia synthesis pressure; a compressor (15) configured to maintain gas circulation in the ammonia synthesis converter (19); a compressor of a refrigeration system (41) configured to cool the gaseous effluent of the ammonia synthesis converter (19); an H2 compressor (53) configured to increase the pressure of the hydrogen in the portion (52).

5. The method according to any of the preceding claims, wherein in the first operating mode the reversible motor / generator (43) generates electrical energy (45) which is output outside the process.

6. A method according to claim 4 or 5, wherein the steam (40) is generated by cooling the gaseous effluent of the ammonia synthesis converter (19) and / or by directly cooling the catalyst contained in the ammonia synthesis converter (19).

7. The method according to any of the preceding claims, wherein during operation, the steam (40) directed to the steam turbine (42) is generated entirely by recovering process heat without additional steam generation in a fuel boiler.

8. The method according to any of the preceding claims, further comprising an operating mode in which the power produced by the steam turbine (42) is completely balanced with the power absorbed by the compressor.

9. The method according to any one of the preceding claims, wherein the steam (40) is superheated.

10. A method for controlling an ammonia plant (1), wherein: The plant (1) comprises a front end (100) configured to produce an ammonia feed gas (11) containing hydrogen (5) from a renewable energy source (59); and an ammonia synthesis section (400) configured to produce ammonia (2) by catalytic conversion of the feed gas (11); The apparatus (1) comprises a steam system configured to produce steam (40) by recovering process heat generated during the conversion of the feed gas (11), and to generate power (44) by expansion of the steam (40); wherein the steam system comprises a steam turbine (42), the steam turbine (42) being part of an assembly comprising the steam turbine (42), a reversible motor / generator (43) and at least one compressor, the reversible motor / generator (43) and the compressor being mechanically connected to the steam turbine (12); The method for controlling the device (1) comprises: The steam turbine (12), the reversible motor / generator (43) and the compressor are selectively controlled in a first operating mode and a second operating mode, wherein: In the first operating mode, mechanical power (44) is transmitted from the steam turbine (42) to the reversible motor / generator (43) and the compressor, the reversible motor / generator (43) acting as a generator driven by the steam turbine (42); In the second operating mode, mechanical power (44) is transmitted from the steam turbine (42) and the reversible motor / generator (43) to the compressor, and the reversible motor / generator (43) acts as a motor to drive the compressor; The method comprises selecting the first operating mode or the second operating mode according to the production of the steam (40) and the power required by the compressor, wherein: selecting the first operating mode when the power obtainable by expansion of the steam (40) in the steam turbine (42) is greater than the power required by the compressor; and The second operating mode is selected when the power (44) obtainable by expansion of the steam (40) in the steam turbine (42) is less than the power required by the compressor.

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

12. An apparatus (1) for synthesizing ammonia (2), comprising: A front end (100) for generating a supply gas (11), the front end (100) being powered at least in part by a renewable energy source (59); and a compressor (12) for the supply gas (11); an ammonia synthesis section (400) comprising a compressor (15) acting as a circulator for said feed gas (11) and an ammonia synthesis converter (19) for generating a gaseous effluent (20) containing ammonia; a heat recovery section (500) comprising a steam system configured to cool the gaseous effluent (20) containing ammonia and generate steam (40); A condensation section (600) comprising a refrigeration system (41), wherein the refrigeration system (41) comprises a gas compressor of the refrigerator system (41); An assembly comprising a steam turbine (42), a reversible electric motor / generator (43) and at least one compressor, the reversible electric motor / generator and the compressor being mechanically connected to the steam turbine.

13. The apparatus (1) according to claim 12, further comprising a buffer section (800), the buffer section (800) comprising an H2 compressor (53) connected to the front end (100) fluid, a hydrogen storage tank (55) connected to the H2 compressor (53), and a recirculation line (56), the recirculation line (56) being used to connect the hydrogen storage tank (55) to the compressor (12) of the make-up gas (11) fluid.

14. The apparatus (1) according to claim 12 or 13, wherein the compressor of the component is one of the following: 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 chiller system (41) or the H2 compressor (53) of the buffer section (800).

15. Apparatus according to any of the preceding claims, wherein the front end comprises a water electrolyser (4) for producing hydrogen (5), the water electrolyser (4) being at least partly powered by a renewable energy source (59).

16. Apparatus according to any preceding claim, further comprising a control system configured for controlling the components according to the method of claim 10 or 11.

17. The apparatus according to any one of the preceding claims, wherein the heat recovery section (500) comprises a boiler feed water preheater, a waste heat boiler, a steam superheater and a desalted water preheater.

18. The apparatus according to any one of the preceding claims, further comprising a separation section (700) for separating the ammonia product (2) from the ammonia-containing gaseous effluent (20), and further comprising a recirculation pipeline (24) connecting the separation section (700) to the suction end of the circulator (15).

19. The apparatus according to any one of the preceding claims, wherein the refrigeration system (41) is an ammonia refrigeration system, the ammonia refrigeration system further comprising an ammonia receiver and an ammonia cooler.

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