Method for controlling an ammonia or methanol converter - Patents.com

Abstract

1. A method for controlling an ammonia synthesis converter or a methanol synthesis converter during intermittent availability of a renewable power dependent hydrogen supply, wherein when power availability is limited or absent, converter effluent (20) is collected in a loop back to an inlet of the converter and heated to maintain the converter in a hot standby mode where the temperature in a reaction space remains within a target range.

Description

[Technical field]

[0001] The present invention is in the field of chemical plants. In particular, the present invention relates to a method for operating an ammonia or methanol synthesis converter during intermittent availability of renewable energy sources. [Background technology]

[0002] Industrial production of ammonia and methanol relies on hydrogen-containing make-up gas, which is typically produced by reforming hydrocarbons such as natural gas.

[0003] A common feature of ammonia and methanol plants is that the make-up gas is reacted in a so-called synthesis loop. The main items of the synthesis loop include a catalytic converter where the make-up gas reacts to produce a reaction effluent, a product cooler where the hot reaction effluent is cooled, a separator where the liquid phase containing the product (ammonia or methanol) is removed, and a recycle line where at least a portion of the gas phase withdrawn from the separator is recovered so as to return to the converter via a circulator.

[0004] Reforming equipment such as combustion primary reformer and secondary reformer, and CO 2 At the front end, a make-up gas is produced, with further equipment for synthesis gas processing and purification, such as shift conversion and removal of . The make-up gas thus obtained is generally compressed to synthesis pressure in a main compressor. The above-mentioned circulator of the synthesis loop may be integrated into the main compressor, i.e. the main compressor and the circulator share the same shaft.

[0005] The converter is essentially a catalytic reactor with a reaction space (or reaction zone) containing one or more catalyst beds, possibly with a heat exchanger immersed in the catalyst bed or with an adiabatic catalyst bed equipped with an interbed heat exchanger. In normal operation, the make-up gas supply is preheated to a suitable reaction temperature by the heat of the exothermic reaction, e.g., by flushing the pressure vessel of the converter and / or in a gas-gas heat exchanger where heat is transferred from the hot reaction effluent to the gas supply. The converter generally comprises a start-up heat exchanger that is used to heat the make-up gas during start-up when the heat of reaction is not available or is insufficient to adequately pre-heat the feed.

[0006] Reforming-based ammonia or methanol plants can emit significant amounts of carbon dioxide into the atmosphere, especially due to the fuel-burning primary reformer. There is growing interest in finding environmentally friendly processes for the generation of the necessary hydrogen supplies. In this respect, techniques for producing hydrogen from renewable energies, such as water electrolysis, offer a very interesting solution. For example, water electrolysis can be powered by solar or wind energy and emits virtually no CO 2 This can result in the production of hydrogen that is free of hydrogen (green hydrogen).

[0007] However, renewable energy-dependent hydrogen feed is subject to variability. Renewable energy sources are commonly referred to as variable renewable energy sources (VRE) due to their inherent variability. Solar energy, for example, is subject to day-night cycles and weather conditions, and wind energy typically has high frequency fluctuations.

[0008] The problem with ammonia or methanol plants that are fed in whole or in part by such green hydrogen is that the synthesis loops are traditionally designed to operate at or near maximum capacity and are generally not flexible to operate at part load. This is especially true for ammonia and methanol converters, which are generally not designed to operate at low part loads. The loops and converters may require 12-24 hour start-ups to reach nominal synthesis pressures and temperatures, so it is economically unacceptable to shut down the plant when the energy source is unavailable.

[0009] Plant shutdowns and subsequent startups should be avoided, as they not only lead to economic losses but can also induce fatigue stresses in the converter due to temperature and / or pressure cycling. Furthermore, a drop in the operating temperature and / or pressure in the converter can result in condensation of one or more products on the catalyst, causing its degradation.

[0010] Producers often use energy imported from the grid to compensate for fluctuations in renewable energy when available, however, grid energy is typically expensive, making this solution economically unattractive.

[0011] Certain solutions proposed in the art rely on the principle of storing hydrogen and / or heat to cope when renewable electricity is mostly available, and then using it when little or no electricity is available. These solutions have the drawback of requiring expensive storage means.

[0012] For example, Patent Document 1 describes a method for storing hydrogen (H ) in a buffer tank to supply to an ammonia converter in the event of a shortage of renewable electricity. 2 The required hydrogen tanks are expensive and pose safety concerns in the event of a leak. Furthermore, to reduce the size of the storage tanks, 2must be stored under pressure, which requires a dedicated compressor, which is an additional cost and consumes power.

[0013] US Patent No. 5,399,633 discloses a solution in which a heat carrier, e.g., molten salt, is stored in a dedicated tank and used to supply heat to an ammonia converter to keep it at a suitable temperature for synthesis while the availability of renewable electricity is limited. This solution requires the addition of an expensive tank, which is large and needs to be properly insulated to store the heat. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] European Patent Application Publication No. 3957772 [Patent Document 2] International Publication No. 2021 / 060985 Brochure Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention aims to overcome the above-mentioned shortcomings of the prior art. The present invention addresses the problem of how to control an ammonia synthesis loop during a shortage of renewable power-dependent hydrogen feed to ensure that the loop can quickly resume production of ammonia when the hydrogen supply is restored, avoiding shutting down the loop and avoiding the use of expensive storage / buffer equipment. The same problem is addressed for the methanol synthesis loop. [Means for solving the problem]

[0016] This problem is solved by the method according to claim 1.

[0017] When the flow rate of the renewable energy dependent hydrogen supply falls below a threshold value, the method includes recovering at least a portion of the converter effluent after passing through a separator back to an inlet of the converter, and heating the recovered converter effluent to maintain the converter in a standby mode with a temperature within a reaction space within a target range.

[0018] The method of the present invention maintains the synthesis loop in a hot standby mode, where the reaction space is continuously pressurized at an appropriate temperature for rapid restart as soon as renewable power and hydrogen supply are returned.

[0019] The present invention is based on the finding that such a hot standby mode can be maintained for a relatively long period of time at the expense of a limited amount of energy.

[0020] In a very interesting embodiment of the invention, the heating of the recovered effluent is performed by the start-up heater of the converter. The invention therefore provides an innovative use of the start-up heater, which is not utilized temporarily for start-up, but to keep the converter in standby mode. The heat input provided by the start-up heater is cleverly used to compensate for the heat loss or the heat removed by the cooling medium, which in some cases cannot be completely stopped in hot standby mode, and to keep the loop, and in particular the reaction space of the converter, in a hot and pressurized state for a quick resumption of production, for example in just one hour or less.

[0021] For example, in an ammonia plant supplied with hydrogen from the electrolysis of water, a suitable hot standby mode is often maintained at a power as low as about 2%, or 1%, or even about 0.5% of the power required to operate at nominal capacity (nominal output of ammonia).

[0022] In a preferred embodiment, during the hot standby of the invention, the reaction space is maintained below the minimum reaction temperature so that no or negligible synthesis of ammonia or methanol occurs. Thus, there is no substantial removal of products from the loop and no introduction of fresh gas into the loop. The loop is maintained in a substantially close to mass transfer state. Pressure and heat remain in the loop apart from the heat losses or heat removed in the process, which are compensated for by the start-up heater. For this purpose, the start-up heater can be suitably controlled, preferably with an on / off control and / or with the adjustment of its heat output. Pressure losses in the goods and piping are compensated for by compressors or circulators.

[0023] In a preferred embodiment, the start-up heater is an electric heater, although various embodiments such as a fuel-fired heater or a heat exchanger may be used.

[0024] In the standby mode of the present invention, the flow rate circulating in the loop may, according to preferred embodiments, be 50% or less, or 25% or less, or 10% or less of the flow rate at nominal capacity.

[0025] The invention will be further illustrated with reference to an ammonia plant.

[0026] The method of the present invention is applicable to plants where the production of hydrogen is at least partially powered by one or more renewable energy sources, which may include at least one of solar, wind, hydro, geothermal and biomass.

[0027] In standby mode, the temperature in the reaction space is preferably below the activation temperature of the catalyst. In particular for ammonia synthesis, the temperature is preferably below 330° C., preferably below 300° C., more preferably below 260° C. In all the above cases, the minimum temperature of the reaction space may be set, for example, at 150° C. or 200° C. Temperatures closer to the lower end of the range, such as 150° C. to 160° C. or about 150° C., are preferred for methanol synthesis.

[0028] The method of the present invention includes maintaining the converter and loop in a standby mode when the renewable power available for hydrogen production falls below a threshold value. The method may be implemented when the power remains below the threshold value for a given period of time, for example, one hour or more.

[0029] The threshold may correspond to a capacity for hydrogen supply that can be generated from renewable electricity that is 50% or less, or 25% or less, or 10% or less of the nominal output of the loop, i.e. the nominal hydrogen supply corresponding to the nominal amount of ammonia or methanol drawn from the loop. The renewable electricity dependent hydrogen supply may be the only hydrogen supply of the loop, which is a preferred embodiment, or may form part of the hydrogen supply.

[0030] The renewable power dependent hydrogen supply may be generated using renewable electricity, preferably by water electrolysis.

[0031] The threshold for hydrogen supply may correspond to the renewable power being less than 50%, or less than 25%, or less than 10% of the nominal power corresponding to the nominal output of the product.

[0032] In a preferred embodiment, the temperature of the reaction space is dynamically controlled by controlling the heat power transferred to the collected converter effluent. Particularly preferably, the collected converter effluent is heated by an electrically-started heater of said converter, and the dynamic control of the heat power transferred to the collected effluent may include controlling the start-up heater on / off and / or adjusting its heat power.

[0033] The temperature within the reaction space may be controlled by suitable controls that dynamically adjust the heat power delivered to the recirculating gas, for example, by turning on or off a start-up heater and / or by adjusting the power output of the start-up heater.

[0034] The control unit may be operatively connected to one or more temperature sensors, such as thermocouples, configured to sense temperature at one or more locations within the reaction space, and based on the temperature detected by the sensor, the control unit provides an output signal to a start-up heater.

[0035] In a preferred embodiment, standby conditions are maintained by a start-up heater and by circulation of recovered converter effluents which collectively absorb less than 2.0% of the power required for nominal plant operation.

[0036] Further preferred features of the present invention are as follows:

[0037] The loop typically includes a composite converter, a separator, a circulator, and a converter start-up heater, which may be mounted inside the converter or may be a separate item.

[0038] The method may include recovering at least a portion of the converter gaseous effluent back to the inlet of the converter after passing through a separator and a start-up heater. Recovery may be performed in a loop including at least the circulator, the start-up heater, the catalytic converter, and the separator.

[0039] In standby mode, the reaction space is maintained within a target temperature range, which may be below a minimum reaction temperature such that no or negligible synthesis of said product occurs in the reaction space during standby, which may be equal to or close to the activation temperature of the catalyst used for the synthesis.

[0040] According to one embodiment, ammonia or methanol is not synthesized in the converter, so that the gaseous stream is continuously withdrawn in the loop and no mass transfer outside the loop is performed. According to an alternative embodiment, the supply of fresh make-up gas and the withdrawal of ammonia or methanol from the loop are performed periodically to maintain a constant pressure in the loop itself.

[0041] The loop may further include a condenser disposed downstream of the catalytic converter and upstream of the separator.

[0042] The start-up heater may be located upstream of the converter. According to a preferred embodiment, the start-up heater is part of the converter and is located upstream of the reaction zone, e.g., above the catalyst bed.

[0043] According to a less preferred embodiment, the start-up heater may be a firing heater or a shell-and-tube heat exchanger.

[0044] The plant typically includes a make-up gas compressor configured to raise the make-up gas to synthesis pressure.

[0045] In some embodiments, the loop circulator operates independently of the make-up gas compressor, hi certain embodiments, the circulator and compressor are part of a single geared machine.

[0046] According to an interesting application, the recovery of the gas returning to the circulator is carried out via a dedicated recovery line, which in particular can be arranged to take the gaseous flow downstream of the converter and to reintroduce the gas at a suitable position upstream of said circulator.

[0047] A dedicated recovery line can provide a short recovery path, reducing pressure drop and heat loss; for example, the gaseous effluent does not have to pass through a condenser and separator, and can be returned directly to the suction section of the circulator for recovery.

[0048] The recovery line may be provided with a heat exchanger for cooling the gas. Preferably, the gas is cooled to a temperature of about 50 to 60° C. before being conveyed to the circulator.

[0049] Preferably, the plant does not include a hydrogen buffer tank and / or a utility tank used to store the heat transfer medium. Thus, in a preferred embodiment, the method of the present invention does not include hydrogen storage and / or heat storage. While storage may be provided in some embodiments, the present invention remains advantageous in significantly reducing storage size and cost compared to solutions that rely entirely on storage to deal with renewable power fluctuations.

[0050] In a particularly interesting application, the method of the invention cooperates with a method for controlling a loop at partial load according to the disclosure of WO 2021 / 089276, which comprises separating a gas flow from the converter supply line at a point upstream of the converter to form a bypass flow, and reintroducing the bypass flow into the synthesis loop at the suction side of the circulator or at a point downstream of the separation section.

[0051] Therefore, when renewable electricity fluctuates, the method of the present invention may include:

[0052] a) If the renewable power remains above a predetermined threshold, the loop is controlled at part load by separating the gas flow from the converter supply line at a point upstream of the converter to form a bypass flow and reintroducing the bypass flow into the synthesis loop at the suction side of the circulator or at a point downstream of the separation section, as the case may be, in accordance with further details disclosed in WO 2021 / 089276. b) If the renewable power falls below a minimum value, the loop transitions to the hot standby mode of the present invention.

[0053] Under condition a), the loop continues to produce ammonia (or methanol), but at a reduced capacity that can be as low as 10% of the nominal capacity. Under condition b), synthesis is preferably stopped or nearly stopped as the loop is maintained below the catalyst activation temperature.

[0054] Preferably, under hot standby condition b), no or substantially no product is drawn from the loop. The term substantially no product may mean that the amount of product removed from the loop in standby mode is less than 5%, preferably less than 1%, of the amount removed during normal operation.

[0055] The plant may be controlled to switch from a) to b) at a given percentage of nominal load. In mode a), the loop may follow the fluctuations until the load on the converter is equal to or greater than said percentage of nominal load, and if the hydrogen supply and load tend to drop further, the loop enters hot standby mode b) until the power returns above said percentage. The control system may include that the switch from a) to b) is performed at a first percentage of nominal load and the switch from b) to a) is performed at a second percentage of nominal load. The second percentage may be the same as the first percentage or may be different. The second percentage may be greater than the first percentage to provide stable operation. The first load percentage at which the system enters hot standby mode b) is preferably in the range of 5% to 50%, for example 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%. The second load percentage at which the system returns to normal mode a) may be, for example, any of the values ​​listed above.

[0056] The combination of the variable load control method of WO2021 / 089276 with the hot standby control of the present invention is particularly synergistic for optimizing the use of renewable energy sources in ammonia or methanol production.

[0057] As a practical example, an ammonia plant rated at 53 MTD (metric tons per day) of ammonia supplied with green hydrogen from a solar-powered electrolyser requires about 21,000 kW for operation at nominal capacity. Assuming that the reaction space is maintained at a temperature of about 250°C, it is calculated that the start-up heater would require about 85 kW and the circulation would require an additional 40 kW. Thus, the hot standby mode could be maintained with an input of 125 kW, which is equal to about 0.6% of the nominal power.

[0058] Yet another aspect of the present invention is as follows. 1) A method for controlling a process for producing ammonia or methanol from a make-up gas containing hydrogen produced from renewable electricity, wherein said production of ammonia or methanol comprises conversion of said make-up gas in a catalytic reactor, and during periods when said renewable electricity availability is limited or unavailable, the reactor is maintained in a hot standby mode by continuous loop recirculation of a gas stream that is heated to maintain the reactor under pressure and within a given temperature range, the temperature range being below an activation temperature of the catalyst such that substantially no ammonia or methanol is produced during standby. 2) The method according to point 1 above, wherein said gas stream is heated in a start-up heater of the reactor. 3) The method according to point 1 or 2 above, wherein the hot standby mode is implemented when the renewable power falls below a minimum power corresponding to the minimum allowable load of the reactor. 4) The method according to any one of points 1 to 3 above, wherein no hydrogen storage is carried out. 5) The method according to any one of points 1 to 4 above, wherein the loop circulation in standby mode is maintained by a make-up gas compressor and / or by a synthesis loop circulator. The invention will now be further explained with reference to the drawings. [Brief description of the drawings]

[0059] [Figure 1] FIG. 1 is a schematic diagram of an ammonia synthesis plant according to one embodiment. [Diagram 2] FIG. 2 is a schematic diagram of an ammonia synthesis plant according to an alternative embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] The ammonia plant 1 of FIG. 1 includes a hydrogen production section 100 for producing a hydrogen stream 7, a nitrogen production section 200 for producing a nitrogen feed 10, and an ammonia synthesis section 300 in which said hydrogen stream 7 and said nitrogen feed 10 are reacted to form an ammonia product 23.

[0061] More specifically, the hydrogen production section 100 includes a water electrolyser 4 for producing a hydrogen supply 5 from a water stream 3 and an oxygen stream 30. The electrolyser 2 is powered by electricity E provided by a renewable energy source 2, which in Figure 1 is a solar source S. The solar source S may for example be a photovoltaic field.

[0062] The hydrogen section 100 further includes a deoxygenation unit 6 configured to remove trace amounts of oxygen from the hydrogen supply 5. The output of the deoxygenation unit is a hydrogen stream 7.

[0063] The nitrogen production section 200 includes a nitrogen production unit 9 for extracting nitrogen 10 from an air supply 8. The nitrogen production unit 9 may be an air separation unit (ASU) that also produces oxygen or oxygen-enriched air.

[0064] The hydrogen stream 7 and the nitrogen feed 10 are mixed together to produce a make-up gas 11 that is delivered to the ammonia synthesis section 300 via a make-up gas compressor 12. The output of the make-up gas compressor 12 is compressed make-up gas 30. A valve 13 is positioned downstream of the make-up gas compressor 12 and upstream of the ammonia synthesis section 300 to regulate the flow of compressed make-up gas delivered to the ammonia synthesis section.

[0065] The ammonia synthesis section 300 includes an ammonia converter 19 and a circulator 15 with a bypass line 16. The circulator 15 receives the compressed make-up gas 30 effluent of the compressor 12 and the stripping gas 24 effluent of the separator 22. The stripping gas 24 and the compressed make-up gas 30 may be mixed together to generate a mixed stream 14 before being fed to the circulator 15. In other embodiments, the stripping gas 24 and the compressed make-up gas 30 may be fed to the circulator 15 as separate streams, or the make-up gas 30 may be fed directly downstream of the circulator 15.

[0066] The effluent of the circulator 15 is a reagent gas supply 17 that is delivered to an ammonia converter 19. The ammonia converter 19 includes one or more reaction zone(s), e.g., one or more catalyst bed(s), and a start-up heater 18 disposed upstream of the reaction zone(s). For simplicity, in Figure 1, the start-up heater 18 is shown as a separate item in front of the ammonia converter 19, but preferably the start-up heater 18 is part of the converter 19, e.g., mounted inside the top of the converter's pressure vessel.

[0067] The bypass line 16 can be used to recover a portion of the reagent gas supply 17 of the circulator 15 to maintain the operating pressure of the ammonia converter 19 within a pre-established range, particularly during part load events such as those disclosed in WO 2021 / 089276. According to various embodiments, other means can be provided to maintain the loop pressure approximately constant, such as throttling the suction circulator valve.

[0068] In the ammonia converter, the reagent gas supply 17 is reacted over a suitable catalyst to form an ammonia-containing gaseous effluent 20. The ammonia-containing gaseous effluent 20 is then cooled in a condenser 21 and the condenser effluent is then conveyed to a separator 22 where the ammonia 23 is separated from the stripping gas 24. The amount of ammonia 23 withdrawn from the separator 23 is regulated via a valve 27.

[0069] At least a portion of the withdrawn gas 24 is withdrawn via line 35 to the suction section of the circulator 15 where it is mixed with the compressed make-up gas 30 .

[0070] The converter 19 is part of a loop 400 that includes the circulator 15 , the start-up heater 18 and converter 19 , the condenser 21 , the separator 22 , and the return line 35 .

[0071] A portion of the stripping gas 24 may be vented through valve 26 to avoid accumulation of inert materials within the loop 400 . The method of the present invention will now be described with reference to FIG.

[0072] In the event that renewable electricity E is limited or unavailable, the water electrolysis device 4 cannot provide the hydrogen supply 7. To prevent a complete shutdown of the plant, the gas delivered by the circulator 15 and passing through the converter 19, the condenser 21 and the separator 22 is continuously withdrawn via line 35 into the suction of said circulator 15, i.e. in a loop 400.

[0073] The continuously withdrawn gas is heated by a start-up heater 18, which is preferably an electric heater operatively connected to a control system (not shown) which is connected to a temperature sensing device. The temperature sensing device measures one or more temperature(s) in the reaction zone(s) of the converter 19 and provides a signal to a control unit. When the temperature(s) measured in said reaction zone(s) are lower than a threshold(s), the control unit activates the start-up heater and adjusts the power output of the heater to maintain the temperature in said reaction zone(s) at a standby temperature below the activation temperature of the catalyst in the converter 19, preferably between 200°C and 330°C, more preferably between 200°C and 260°C, with the set temperature preferably close to 150°C for a methanol thin loop.

[0074] The loop is maintained in a hot standby mode in which substantially no ammonia is synthesized. The gaseous effluent 20 of the circulator 19, which is continuously recovered in the loop 400, comprises primarily hydrogen and nitrogen. In such a standby mode, substantially no ammonia is condensed in the condenser 21 and is separated in the separator 22.

[0075] During the standby mode, loop 400 is substantially a closed loop, so valves 13, 26, and 27 may be closed.

[0076] 2 shows an alternative embodiment of the invention in which a dedicated recovery line 28 is provided. Said line 28 connects a point downstream of the converter 19 and upstream of the condenser 21 to the suction side of the circulator 15. In standby conditions, the gas is recovered via said line 28, avoiding the passage through the condenser 21 and the separator 22.

[0077] Preferably, a heat exchanger 29 is provided in line 28 to cool the gas. According to this embodiment, a closed loop is obtained by closing valve 13, located after the make-up compressor 12, and valve 36 before the condenser.

Claims

1. A method for controlling an ammonia synthesis converter (19 ) or a methanol synthesis converter during intermittent availability of renewable power-dependent hydrogen supply, comprising: reacting a reagent gas containing a catalyst and said hydrogen supply to form ammonia (23) or methanol, said reaction space being included in said ammonia synthesis converter ( 19), wherein, under the condition that the renewable power available for the production of said hydrogen supply is below a threshold value, said method comprises: returning at least a part of the converter effluent (20) to the inlet of the ammonia synthesis converter (19) and recovering it in a loop; and heating the recovered converter effluent (20) to maintain the ammonia synthesis converter in standby mode, wherein the temperature in said reaction space is within a target range, steps; and, wherein the recovered converter effluent is heated in a start-up heater of the ammonia synthesis converter Method.

2. The temperature of the target range is below the minimum reaction temperature so that the synthesis of the product occurs not at all or negligibly in the reaction space during the standby mode, according to claim 1 The method described.

3. 、 In the standby mode, no product is removed from the loop, or substantially no product is removed, and no fresh reaction gas is introduced into the loop, according to the method of claim 2

4. In the standby mode, the temperature in the reaction space is in the range of 150°C to 330°C, preferably 150°C to 300°C, more preferably 150°C to 260°C, according to the method of claim 1

5. The threshold value is 50% or less, or 25% or less, or 10% or less, or 5% or less of the nominal hydrogen supply corresponding to the nominal output capacity of the ammonia synthesis converter, corresponding to the capacity of the hydrogen obtained from the renewable power The method described in claim 1.

6. The hydrogen supply is preferably generated by renewable power, preferably by water electrolysis, according to claim 1 The method described.

7. The threshold value corresponding to the renewable power is less than 50%, or less than 25%, or less than 10%, or less than 5% of the nominal power corresponding to the nominal output of the ammonia synthesis converter The method described in claim 6.

8. The renewable power is generated by one or more renewable energy sources, preferably solar energy The method described in claim 1.

9. ​ ​ ​ ​ ​ ​ ​ ​ ​ During the standby mode, the temperature of the reaction space is dynamically controlled by controlling the heat output transferred to the recovered converter effluent The method according to claim 1, wherein the heat output transferred to the recovered converter effluent is dynamically controlled by controlling the heat output transferred to the recovered converter effluent

10. The starting heater is disposed upstream of the ammonia synthesis converter (19) or is part of the ammonia synthesis converter (19) described above, and is disposed upstream of the reaction zone, for example, above the catalyst bed The method according to claim 1, wherein the starting heater is disposed upstream of the ammonia synthesis converter (19) or is part of the ammonia synthesis converter (19) described above, and is disposed upstream of the reaction zone, for example, above the catalyst bed The method according to claim 1, wherein the starting heater is disposed upstream of the ammonia synthesis converter (19) or is part of the ammonia synthesis converter (19) described above, and is disposed upstream of the reaction zone, for example, above the catalyst bed

11. The method according to claim 1, wherein the starting heater (18) is electrically powered

12. The method according to claim 11, including on / off control of the starting heater (18) for controlling the temperature in the reaction space The method according to claim 11, including on / off control of the starting heater (18) for controlling the temperature in the reaction space

13. The standby mode is maintained by the starting heater and the circulation of the recovered converter effluent that absorbs 2.0% or less of the power required for the nominal operation of the plant The method according to claim 11, wherein the standby mode is maintained by the starting heater and the circulation of the recovered converter effluent that absorbs 2.0% or less of the power required for the nominal operation of the plant The method according to claim 11, wherein the standby mode is maintained by the starting heater and the circulation of the recovered converter effluent that absorbs 2.0% or less of the power required for the nominal operation of the plant

14. The ammonia synthesis converter further includes a circulator (15), a starting heater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a recovery gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a tail gas line The ammonia synthesis converter further includes a circulator (15), a starting heater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a recovery gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a tail gas line The ammonia synthesis converter further includes a circulator (15), a starting heater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a recovery gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a tail gas line The ammonia synthesis converter further includes a circulator (15), a starting heater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a recovery gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a tail gas line The method according to claim 1, wherein the ammonia synthesis converter further includes a circulator (15), a starting heater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a recovery gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a tail gas line The method according to claim 1, wherein the ammonia synthesis converter further includes a circulator (15), a starting heater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a recovery gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a tail gas line

15. The ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The method according to claim 1, wherein the ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The method according to claim 1, wherein the ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The method according to claim 1, wherein the ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator The method according to claim 1, wherein the ammonia synthesis converter further includes a circulator (15), a preheater (18) for converter supply, a condenser (21) downstream of the ammonia synthesis converter, a separator (22) downstream of the condenser, and a tail gas line connecting the separator (22) to a point upstream of the circulator, and is part of a synthesis loop (400). During the standby mode of the ammonia synthesis converter, the converter effluent is recovered to the ammonia synthesis converter via a dedicated line connecting a point downstream of the ammonia synthesis converter but upstream of the condenser to a point upstream of the circulator

16. During the standby mode, the flow rate of the gas circulating through the loop is 50% or less, preferably 20% or less, more preferably, of the total flow rate passing through the ammonia synthesis converter (19) at nominal capacity During the standby mode, the flow rate of the gas circulating through the loop is 50% or less, preferably 20% or less, more preferably, of the total flow rate passing through the ammonia synthesis converter (19) at nominal capacity The method according to claim 1, wherein it is 10% or less, or more preferably 5% or less.

17. The method according to claim 1, wherein the method is carried out without buffer storage of hydrogen and without buffer storage of heat. The method according to claim 1.

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