Method for controlling ammonia plant using renewable energy

Abstract

The invention provides a novel control method, so that the ammonia equipment can be randomly changed between 5% and 100% of hydrogen feeding rate. The method includes adjusting a temperature controller setpoint (quench TC) of an inlet gas into a first reactor catalyst bed, and adjusting controller tuning parameters for feed hydrogen and nitrogen flow and reactor loop pressure, all based on a hydrogen feed rate.

Description

Technical Field

[0001] This invention relates to a process for controlling the operation of ammonia equipment. Background Technology

[0002] The Haber process is a well-established industrial method for ammonia production. Ammonia plants typically operate under steady-state conditions with minimal variation in the feed rate. However, there is a growing emphasis on abandoning fossil fuels as the hydrogen source for ammonia production.

[0003] A popular alternative is to produce the required hydrogen through electrolysis powered by renewable electricity. Unlike fossil fuels, renewable electricity fluctuates, sometimes significantly, depending on the availability of wind and solar power. Therefore, hydrogen production from renewable electricity is expected to be highly volatile. This will impact the operation of ammonia processes, which require stable operation with variable feed rates.

[0004] To supply hydrogen obtained from electrolysis to ammonia equipment at a range of low to high loads, several steps are typically involved.

[0005] First, the hydrogen is compressed and purified to remove any impurities that may be present. This is crucial to ensuring that the hydrogen meets the quality standards required in the ammonia production process.

[0006] Next, the purified hydrogen is fed into the ammonia plant at the rate it was produced. In some cases, intermediate hydrogen storage is preferred to decouple hydrogen production from the ammonia synthesis section. In hydrogen storage, hydrogen is stored in high-pressure tanks until needed. These tanks can hold large quantities of hydrogen and provide a convenient way to transport the gas from the electrolysis unit to the ammonia plant. However, storage is an expensive investment and should be avoided or at least minimized.

[0007] When an ammonia plant requires hydrogen, high-pressure hydrogen is supplied to the plant via pipeline from a storage tank. The gas is typically metered and controlled to ensure that the correct amount of hydrogen is delivered to the plant.

[0008] Once hydrogen arrives at the ammonia plant, it is used as a feedstock for ammonia production. The ammonia production process typically involves mixing hydrogen and nitrogen in the presence of a catalyst at high pressure and high temperature. This produces ammonia, which is then processed and purified to remove any impurities before being stored or transported for various applications.

[0009] EP381261 A1 discloses the use of recirculation around a recirculation compressor to control ammonia equipment under partial load.

[0010] US9463983 B2 discloses a method for load regulation by controlling reactor pressure using a flow containing inert material by increasing or decreasing the amount of inert material present.

[0011] US10995009 B2 discloses the use of energy storage to allow ammonia plants to operate nearly continuously under variable renewable power generation conditions.

[0012] EP3426601 B1 discloses adjusting production based on power availability by using a bypass that bypasses the first reactor bed, by changing the flow rate through the bypass.

[0013] WO2021 / 060985 A1 discloses the use of a three-way valve to control the amount of ammonia extracted from the reactor loop based on the availability of renewable electricity. Most of the product is removed at a smaller recirculation flow rate in operating mode 1, while most of the product is recycled in operating mode 2. The variability between the two modes is not discussed.

[0014] WO2021 / 233780 A1 discloses a loop pressure controller that uses a dedicated control valve acting on an anti-surge valve in a recirculation compressor or a reactor loop to maintain loop pressure when hydrogen availability is reduced due to variability in renewable electricity.

[0015] Reference: Morud (1998) Analysis of Instability in an Industrial Ammonia Reactor compared a dynamic model of an ammonia reactor with equipment data during periods of temperature instability caused by a sudden drop in reactor pressure.

[0016] The applicant hereby presents a control scheme that differs from typical control schemes for steady-state operating equipment, in order to help overcome some of the problems associated with variable feed operation. This includes adding pressure control and other modified control loops to the reactor circuit.

[0017] Several methods can be used to control the pressure in the ammonia circuit under variable hydrogen load conditions. Recently, the use of renewable energy sources in ammonia synthesis has become more feasible. As an example, it has been envisioned to mix hydrogen produced by water electrolysis driven by renewable energy sources (such as wind and solar power) with nitrogen produced by an air separation unit to prepare ammonia syngas. The resulting hydrogen and nitrogen are mixed in stoichiometric proportions to form syngas for ammonia production.

[0018] The problem with using renewable energy in ammonia synthesis is that the energy supply depends on natural variations (such as wind and sunlight). Therefore, the flow rate of fresh ammonia syngas produced using renewable energy can vary significantly.

[0019] Due to balance constraints, the single-pass conversion rate of ammonia synthesis gas in the ammonia reactor is relatively low, therefore a large amount of unconverted synthesis gas loop recirculation flow is required in the loop.

[0020] To replace the converted hydrogen and nitrogen in the unconverted syngas, fresh ammonia syngas must be continuously added to the loop recirculation gas. Under conditions of significant and frequent load variations due to changes in the flow rate of fresh syngas into the synthesis loop, the pressure fluctuations caused by these load variations will lead to mechanical stress conditions (not disclosed here), potentially causing mechanical failures in pressure-bearing equipment. However, temperature variations will be limited.

[0021] These operating conditions are particularly relevant when production depends on variable flow rates of feedstock (e.g., in the case of renewable ammonia production).

[0022] Traditionally, ammonia loops lack dedicated pressure control. A decrease in feed flow into the loop causes a drop in loop pressure. Consequently, the conversion rate decreases until it eventually matches the makeup gas flow rate. An increase in feed flow rate increases both pressure and conversion rate. Because the load on conventional ammonia plants tends to remain stable over long periods, the lack of pressure control is usually not a problem.

[0023] For a given ammonia reactor / loop configuration, one possible way to control loop pressure is to change the H / N ratio in the fresh ammonia synthesis gas. In some cases, the inert content in the loop can also be altered by reducing the purge stream, but this is less relevant to renewable ammonia production because the inert content in its makeup gas is very low, and the emission of valuable renewable hydrogen is undesirable. However, in practice, it is difficult to control loop pressure using this method.

[0024] The method described in WO2021 / 233780 utilizes the compressor's anti-surge control valve and / or compressor flow regulating valve to recirculate the ammonia loop recirculation gas when the fresh ammonia synthesis gas flow rate changes. As stated, the feed gas rate to the ammonia reactor can be controlled by the anti-surge controller of the recirculator (loop recirculation compressor). Anti-surge or reflux valves are typically fast-responding control elements used to prevent surge-induced vibrations that could damage the compressor.

[0025] In ammonia plants, a setpoint is a fixed target value used to control various process parameters in ammonia production. These setpoints remain constant over a period of time and are input into the plant's control system to ensure the process operates under safe and efficient conditions. By using static setpoints, ammonia plants can operate safely and efficiently, ensuring product quality and minimizing any negative environmental impacts. Some common examples of static setpoints in ammonia plants include: a) Temperature setpoints for each stage of the ammonia synthesis process are set to maintain optimal conditions for the reaction to occur. These setpoints are typically based on the specific reaction kinetics of the process. b) Pressure setpoints for different stages of the ammonia production process are set to maintain the conditions required for the reaction to occur. These setpoints are typically based on the specific pressure requirements of the process. c) Flow rate setpoints for different process flows (such as feed and product flows), which are set to maintain optimal conditions for the reaction to occur. These setpoints are typically based on the specific flow rate requirements of the process; d) Component setpoints for various process streams (such as feed streams and product streams), which are set to maintain the required proportions of different components. These setpoints are typically based on the specific chemical requirements of the process.

[0026] In this invention, a feedback control system is used to set the hydrogen flow rate in the ammonia loop based on the available renewable hydrogen flow rate. Feedback control involves continuously monitoring process variables, comparing them to desired setpoints, and using the error (i.e., the difference between the process value and its setpoint) to adjust the control action, bringing the process variables closer to the setpoints. PID (Proportional-Integral-Derivative) control is one of the most common and well-known algorithms for feedback control; it uses the current error, historical error accumulation, and error rate of change to adjust the control output and regulate the process variables. The feedback mechanism in PID control ensures that the system continuously adjusts its action based on the deviation between the desired setpoint and the actual process variables.

[0027] Cascade control is used to control an ammonia loop with a variable hydrogen feed. The main control loop controls the pressure entering the ammonia reactor by sending a flow setpoint to the secondary control loop, which in turn controls the syngas flow rate circulating back to the ammonia reactor.

[0028] Feedforward control is used to control ammonia loops with variable hydrogen feed. The feedforward controller calculates the required syngas flow rate to be recirculated to the ammonia reactor inlet based on the measured feed flow rate.

[0029] Proportional control is used to control ammonia loops with variable hydrogen feed. The controller maintains a constant hydrogen-to-nitrogen ratio in the ammonia synthesis process. The nitrogen flow rate is adjusted based on the hydrogen flow rate to provide the required proportion in the loop.

[0030] Controller tuning parameters are settings for the PID control algorithm that determine how the controller operates. These parameters are used to adjust the controller's behavior to ensure it maintains desired process conditions and improves process stability. These controller tuning parameters are adjusted by process control engineers to ensure the controller maintains the desired setpoints and meets process requirements. The tuning process typically involves testing the system to determine the optimal combination of tuning parameters for achieving best performance.

[0031] The main controller tuning parameters used in ammonia equipment are: Proportional gain (Kp): The proportional gain parameter determines the sensitivity of the controller output to error signals. Increasing Kp can make the controller respond more quickly, but it can also make the control loop less stable.

[0032] Integral Gain (Ki): The integral gain parameter determines how the controller responds to changes in the process over time. Increasing Ki can reduce steady-state error, but if set too high, it can also lead to overshoot and instability. The integral time is the reciprocal of the integral gain and is used to replace the integral gain in Table 1.

[0033] Differential gain (Kd): The differential gain parameter determines the controller's response to changes in the rate of change of process variables. Increasing Kd can improve the controller's response to sudden process changes, but it may also lead to instability.

[0034] This invention provides a novel control method that enables ammonia equipment to vary arbitrarily between 5% and 100% of the hydrogen feed rate or load, preferably 3% per minute or faster, for example 5% per minute or faster.

[0035] The method includes adjusting the temperature controller setpoint (cold shot TC) of the inlet gas entering the reactor catalyst bed 1, as well as controller tuning parameters for the feed hydrogen flow rate, reactor loop H2 / N2 ratio and reactor loop pressure, all of which are based on the hydrogen feed rate. Summary of the Invention

[0036] This invention relates to a method, apparatus, and computer-implemented method for controlling the operation of an ammonia plant to prevent downtime and adjust operation, for example, to adjust for the availability and / or price of renewable energy.

[0037] Rapid increases or decreases in the feed rate of an ammonia plant can cause several controllers to become unstable, because PID controllers are typically tuned for conditions close to 100% capacity, while at lower productivity rates (e.g., below about 30%), small disturbances in production can lead to relatively large production changes.

[0038] Different controllers need to be tuned when operating at low capacity. Therefore, in order to ensure that the control of the equipment remains stable, these PID controllers need to have tuning parameters that vary with the feed rate.

[0039] A typical configuration of an ammonia reactor is as follows: Figure 2As shown, the reactor comprises three adiabatic catalyst beds with interstage cooling to maximize ammonia production, which is limited by chemical equilibrium. The inlet temperature of the reactor catalyst beds is typically optimized to achieve maximum ammonia production with the minimum catalyst volume. Lower inlet temperatures allow for higher ammonia conversion of hydrogen and nitrogen before further conversion is inhibited by chemical equilibrium. However, higher temperatures favor faster reaction rates, thus requiring a larger catalyst volume to reach chemical equilibrium at lower inlet temperatures. Furthermore, if the inlet temperature of the ammonia reactor is too low or the catalyst volume is too small at a given feed rate, there is a risk of reactor shutdown because the heat generated by the chemical reaction is less than the heat required to heat the feed gas. When the ammonia unit rapidly increases from a low hydrogen feed rate (or load) to a high hydrogen feed rate, the outlet temperature of reactor catalyst bed 1 drops significantly more than when it begins to decrease from full load operation. This results in temperature oscillations in reactor catalyst beds 2 and 3. As the temperature distribution within the reactor catalyst beds changes, the degree of reaction shifts, which in turn leads to loop pressure variations. The control system is unable to suppress these oscillations, which become increasingly severe over time until the entire loop control becomes unstable. Eventually, the discharge temperature of bed 3 drops to a low point, indicating that the reaction in the reactor is beginning to stop. As the reaction stops, nitrogen and hydrogen accumulate in the loop, causing the loop pressure to rise, or necessitating the restriction of the hydrogen feed rate.

[0040] The first key difference in the disclosed novel control scheme is that the controller tuning parameters for the hydrogen feed flow controller, the reactor loop hydrogen / nitrogen ratio controller, and the reactor loop pressure controller are adjusted based on the hydrogen feed flow rate. This means that as the hydrogen feed decreases, the controller tuning parameters continuously change, and the control scheme does not become unstable at any point. System dynamics change with the hydrogen feed rate. These changes need to be reflected in the controller tuning parameters to maintain the same performance level at different feed rates.

[0041] Furthermore, the inlet temperature setpoint of reactor catalyst bed 1 is controlled by adjusting the flow rate through the quench bypass. The quench temperature controller setpoint increases with increasing hydrogen feed. This raises the temperature at the inlet of reactor catalyst bed 1. As the increased gas throughput absorbs the heat of reaction, the temperature distribution in the rest of the bed decreases. Similar behavior was observed in reactor catalyst beds 2 and 3, and a new temperature distribution was quickly established after the load increase. More details are included in the accompanying figures and examples below.

[0042] The advantage of making these modifications to the controller tuning parameters and setpoints is that the necessary changes are automatically calculated as hydrogen flow changes, requiring no operator intervention. They also maintain stable operation of the ammonia process under rapidly changing load rates and a wide range of feed rates.

[0043] definition

[0044] "Atmospheric pressure" refers to 1.01325 bar, or approximately 1 bar.

[0045] A "reactor catalyst bed" refers to a catalyst bed capable of achieving the catalytic conversion (synthesis) of N2(g) + 3H2(g) = 2NH3(g) + heat (Q). The reactor catalyst bed is a key component of an ammonia plant, where ammonia synthesis occurs. It is a container filled with catalyst that converts the reactants hydrogen and nitrogen into ammonia. The reactor catalyst bed is designed with a high surface area to maximize reactant contact with the catalyst. It operates at high temperatures and pressures, typically around 400-500°C and 100-200 bar. Reactants, hydrogen, and nitrogen are fed into the reactor catalyst bed in appropriate proportions to ensure maximum conversion to ammonia. The reaction occurring in the reactor catalyst bed is exothermic, meaning it releases heat. A cooling system removes heat from the reactor catalyst bed to maintain the desired operating temperature. The effluent gas from the reactor catalyst bed is cooled, and a series of condensers and separators separate the ammonia from unreacted hydrogen and nitrogen. The ammonia is then further purified and stored for use or transport. In summary, the reactor catalyst bed is a key component of an ammonia plant, where ammonia synthesis takes place. Its proper design, operation, and maintenance are essential to ensuring efficient production of high-quality ammonia.

[0046] "Cold scalding TC" or "cold scalding bypass" refers to cold scalding temperature control, which means that cold gas (cold scalding flow) bypasses the interbed heat exchanger in the ammonia reactor and mixes with heated gas from the interbed heat exchanger before entering the catalyst bed inlet of the first reactor, thereby controlling the inlet temperature of the catalyst bed in the first reactor.

[0047] The "cold shock valve" is the actual control valve used in the aforementioned cold shock temperature control circuit.

[0048] "Dynamic ammonia production" refers to the ability of an ammonia plant to adjust its productivity according to changes in demand or process conditions. In other words, it refers to the ability of the equipment to operate at different productivity levels based on constantly changing market conditions, customer demand, or other factors. Dynamic ammonia production typically involves adjusting equipment capacity and process conditions to accommodate available feedstock flow rates or desired ammonia production rates. This may involve adjusting the temperature, pressure, and feed ratios of various parts of the equipment, such as reformers, shift reactors, and ammonia synthesis loops. In particular, it can refer to ammonia production where the load varies based on the availability of renewable electricity.

[0049] "Fractional hydrogen required rate" refers to the expected hydrogen feed rate relative to the maximum capacity of the ammonia plant.

[0050] The "hydrogen (demand) flow setpoint" refers to the hydrogen production output in the upstream hydrogen production unit (including electrolysis, deoxygenation, drying, compression, and optional hydrogen storage), and defines the equipment load and the hydrogen flow rate to be fed into the ammonia synthesis loop. Hydrogen flow rate is typically measured using a flow meter or other instrument, and the data is fed back to the control system to ensure that the actual flow rate matches the setpoint. The control system then adjusts the flow rate as needed to accommodate the actual hydrogen production rate in the hydrogen production unit. In some cases, due to demands originating outside the ammonia loop, it may be necessary to limit hydrogen consumption; in these cases, external control can be used to limit the hydrogen flow rate into the synthesis loop. However, the rest of the system will operate as described above.

[0051] "Loop pressure controller" refers to the operating pressure in the ammonia loop, which is usually controlled by a PID control loop at the inlet or outlet of the ammonia reactor.

[0052] "Hydrogen increase / decrease" refers to increasing / decreasing the hydrogen flow rate entering the ammonia synthesis circuit.

[0053] "Renewable electricity or energy" refers to electricity generated from renewable sources, primarily wind and solar power in this context.

[0054] The "set value of the quench temperature control loop" refers to the desired inlet temperature of the catalyst bed in the first reactor. The specific set value of the quench temperature control loop is determined during the equipment design phase and can be adjusted during operation according to specific process conditions.

[0055] "Temperature controller setpoint" refers to the setpoint that the temperature PID controller is required to achieve.

[0056] "Tuning parameters" refer to the tuning constants specified in the PID control loop. According to the form of the PID algorithm, they are: proportional gain (Kp), integral reset time (Ti), and derivative time (Td).

[0057] Example 1

[0058] One embodiment of the invention is illustrated by a dynamic ammonia device configured to receive hydrogen produced by electrolysis driven by renewable energy sources such as solar or wind power.

[0059] The ammonia plant is equipped with an ammonia reactor containing three adiabatic reactor catalyst beds, such as... Figure 1 and Figure 2 As shown. Figure 1 The ammonia synthesis circuit is shown. Figure 2 The synthesis reactor is shown.

[0060] Hydrogen feed gas (50) is received from the hydrogen production unit. The hydrogen flow rate is measured and controlled by the hydrogen feed flow control loop (51). Nitrogen (52) is added to the hydrogen at a ratio of 1:3. The nitrogen flow rate is controlled by the flow control loop (53), which receives the flow setpoint calculated from the measured hydrogen feed flow rate and corrects it based on the actual hydrogen-nitrogen ratio (61) measured in the synthesis loop.

[0061] The mixed supplemental gas is compressed in the supplemental gas compressor (56). Then, it is mixed with the recirculated gas from (70) and sent to the recirculator compressor (80).

[0062] The synthesis loop pressure is controlled by a loop pressure controller (62), which regulates the flow rate of the process gas circulating in the ammonia loop (63).

[0063] The mixed syngas is preheated in (60) before entering the ammonia synthesis reactor.

[0064] like Figure 2As shown, the partially preheated syngas (10) is split into three streams. One stream (16) is directed to the second interbed heat exchanger (IHE) (28) to cool the converted gas (27) leaving the reactor catalyst bed 2 (26) and proceeding to bed 3 (30). The second stream (14) is directed to the first IHE (24) to cool the converted gas leaving the reactor catalyst bed 1 (23). The third stream (12) is a cold slug that bypasses the two IHEs and is used to control (17) the inlet temperature of the first reactor catalyst bed (21). The mixed unconverted gas from the two IHEs and the cold slug is sent to reactor catalyst bed 1 (22), where the main part of ammonia synthesis occurs. The partially converted gas (23) is then cooled in the first IHE (24) before entering reactor catalyst bed 2 (26) for further conversion. The further converted gas from reactor catalyst bed 2 is cooled in the second IHE (28) before being sent to reactor catalyst bed 3 (30) for final conversion. In this configuration, the hot gas (31) leaving the catalyst bed 3 of the reactor exits the ammonia reactor and proceeds to a gas cooling roller assembly consisting of steam generating equipment (such as a steam superheater, waste heat boiler, and boiler feedwater preheater). Starting from the boiler feedwater preheater, the gas enters a series of gas / gas heat exchangers (heat exchangers and cold exchangers) to exchange heat with cold, unconverted syngas from the ammonia separator, water cooler, and ammonia chiller, before entering the ammonia separator, where the condensed ammonia is separated from the syngas.

[0065] The vapor from the ammonia separator (containing unconverted hydrogen and nitrogen, as well as some ammonia) is then sent to the recirculation gas compressor and mixed with freshly introduced hydrogen and nitrogen from the makeup gas compressor. From there, the mixed recirculation and makeup gas is preheated in a cold exchanger and a heat exchanger, and exits the heat exchanger as partially heated unconverted gas.

[0066] The liquid ammonia leaving the ammonia separator undergoes a process step where dissolved gases are removed, and then it is discharged as a liquid ammonia product.

[0067] The main control loops in the ammonia synthesis circuit include: Hydrogen make-up gas flow controller (51), Loop pressure controller (62), and Loop hydrogen-nitrogen ratio controller (61).

[0068] In this embodiment, these control loops remain in an automatic control state with variable tuning parameters. The tuning parameters are shown in Table 1: Table 1: Load-based PID controller tuning parameters used in the two examples.

[0069]

[0070] The dynamic simulation model of the ammonia plant configured as described above has been used to test the design and operability of the ammonia plant under transient conditions.

[0071] Figure 3A / B / C displays the simulated temperatures at 20 different locations in catalyst beds 1, 2, and 3 of the reactor under a scenario where the hydrogen feed rate increases from 10% load to 100% at a rate of 3% / min. Throughout the simulation, the setpoint of the quench temperature controller (17), which controls the inlet temperature, remains constant. Figure 3A As shown, temperature oscillations begin to occur after the hydrogen feed load has increased. These oscillations propagate to catalyst beds 2 and 3 in reactors, where they intensify and the bed temperatures trend downward, indicating that the reaction is slowing down. Such temperature oscillations are unacceptable because they could lead to premature fatigue and mechanical failure of the ammonia reactor and other high-pressure equipment in the synthesis loop.

[0072] Example 2

[0073] This embodiment is similar to Embodiment 1, except that in this simulation, the setpoint of the quench temperature controller (17) controlling the inlet temperature of the reactor catalyst bed 1 is load-dependent. The actual temperature setpoint for the quench temperature control is calculated according to the following formula: TIC.SP = 389°C + 10°C Fractional hydrogen required rate TIC.SP is the setpoint for the cold shock temperature control loop.

[0074] This means that if the equipment is operating at 10% load, the setpoint for the cold shock temperature control loop is 390°C; at 100% load, the setpoint for the cold shock temperature control is 399°C.

[0075] Figure 4A / B / C shows the temperatures at 20 different locations in each of the simulated reactor catalyst beds 1, 2, and 3, under the scenario where the hydrogen feed rate increases from 10% load to 100% at a rate of 3% / min.

[0076] like Figure 4A As shown in / B / C, the temperature oscillations found in Example 1 have now been eliminated, and the temperature quickly stabilizes to the new steady-state conditions.

Claims

1. A method for controlling ammonia production by raising or lowering of the hydrogen feed flow, wherein the behavior of the controller is adjusted by varying the controller tuning parameters with the change in the plant, wherein: a) compressed hydrogen feed gas (50) is received from a hydrogen production unit; b) hydrogen flow is measured and controlled by a hydrogen feed flow control loop (51); c) nitrogen (52) is added to the hydrogen in a desired ratio; d) the mixed make-up gas is compressed in a make-up gas compressor (56) and then mixed with the recycle gas from (70) and sent to a recycle compressor (80); e) the mixed synthesis gas is preheated in (60) before entering the ammonia synthesis reactor; f) the ammonia synthesis reactor is configured with at least two adiabatic catalytic reactor beds with inter-bed cooling, and wherein the partially preheated synthesis gas (10) is split into two or more streams, wherein the first stream is a quench stream (12) which is controlled by a quench temperature controller (17); the first stream is added to control the inlet temperature to reactor catalyst bed 1; the second stream (14) and optionally more streams (16) are further heated by cooling the reforming gas in inter-bed or effluent gas heat exchangers (24 etc.) and the mixed gas is fed to the inlet of the first reactor catalyst bed (22); g) hot gas (31) leaves the ammonia reactor; h) the produced gas is cooled before entering the ammonia separator where condensed ammonia is separated from the synthesis gas which is recycled and mixed with the make-up gas in step d); i) the liquid ammonia leaving the ammonia separator is passed through process steps where dissolved gases are separated and then the liquid ammonia is discharged as a liquid ammonia product; wherein the main control loops in the ammonia synthesis loop include: wherein the ammonia synthesis loop has load dependent controller tuning parameters and the set point of the quench temperature controller (17) controlling the inlet temperature of reactor catalyst bed 1 is load dependent.

2. The method according to claim 1, wherein in step c) the nitrogen flow is controlled by a flow control loop (53) which receives a flow set point calculated from the measured hydrogen feed flow and is corrected according to the actual measured (61) hydrogen to nitrogen ratio in the synthesis loop.

3. The method according to any one of claims 1 or 2, wherein in step c) the nitrogen is added to the hydrogen in a ratio of about 1:

3.

4. The method according to any one of claims 1 to 3, wherein during step f) in the adiabatic three-bed reactor: (i) stream (16) is directed to the second IHE (28) for cooling of the reforming gas (27) leaving reactor catalyst bed 2 (26) and going to reactor catalyst bed 3 (30); (ii) stream (14) is directed to the first IHE (24) for cooling of the reforming gas leaving reactor catalyst bed 1 (22); (iii) stream (12) is the quench temperature controller which bypasses both IHEs and is sent to reactor catalyst bed 1 (22) with the mixed unconverted gas from both IHEs and the quench temperature controller where the major part of the ammonia synthesis takes place. ​ ​ ​ ​ ​ ​ ​ hydrogen make-up gas flow controller (51), a circuit pressure controller (62), and Loop hydrogen to nitrogen ratio controller (61), ​ ​ ​ ​ ​ ​ ​ (iv) The partially converted gas (23) is then cooled in a first IHE (24) before entering reactor catalyst bed 2 (26) for further conversion; and (v) The further converted gas from reactor catalyst bed 2 is cooled in a second IHE (28) before being sent to reactor catalyst bed 3 (30) for final conversion.

5. The method according to any one of claims 1 to 4, wherein the hot gas from the ammonia reactor (31) is passed through a series of gas / gas heat exchangers exchanging heat with cold unconverted syngas from the ammonia separator, water cooler and ammonia chiller.

6. The method according to any one of claims 1 to 5, wherein the set value of the inlet temperature controller of the quenched reactor catalyst bed 1 is increased with an increase in the set value of the hydrogen demand flow rate.

7. The method according to any one of claims 1 to 5, wherein the set value of the inlet temperature controller of the quenched reactor catalyst bed 1 is decreased with a decrease in the set value of the hydrogen demand flow rate.

8. The method according to any one of claims 1 to 7, wherein the hydrogen is ramped up or down in the range of 5% to 100% load.

9. The method according to claim 8, wherein the ramping up or down rate is approximately faster than 1% per minute.

10. The method according to any one of the preceding claims, wherein the set value of the cold shock temperature controller (17) controlling the inlet temperature of the reactor catalyst bed 1 is load dependent and calculated according to the formula TIC.SP = A°C + B°C the required rate of hydrogen gas, wherein A is about the cold shock temperature at the lowest production, and B is the temperature increment between the lowest and the highest production.

11. The method according to any one of the preceding claims, wherein the synthesis loop pressure is controlled by a loop pressure controller (62).

12. An ammonia plant controlled by the method according to claims 1 to 11, the plant being configured to receive a variable hydrogen flow rate, wherein the ammonia loop pressure is controlled by a pressure controller (62), and wherein the adiabatic ammonia reactor comprises at least two adiabatic reactor catalyst beds located after a quench valve, such that the hot gas (31) leaving the final reactor catalyst bed exits the ammonia reactor and enters a gas cooling train comprising a steam superheater, a waste heat boiler and a boiler feed water preheater.

13. The ammonia plant according to claim 12, wherein the variable hydrogen flow rate is produced by electrolysis driven by renewable energy.

14. The ammonia plant according to any one of claims 12 or 13, wherein the adiabatic ammonia reactor comprises three adiabatic reactor catalyst beds.

15. The ammonia plant according to any one of claims 12 to 14, wherein the loop pressure controller (62) is an anti-surge control valve of a compressor and / or a compressor flow regulation valve for recycling of ammonia loop recycle gas in case of changes in fresh ammonia synthesis gas flow rate.

16. A computer-implemented method for dynamically operating the method of claims 1 to 11 in a plant according to claims 12-15-14, wherein the PID tuning parameters and variable controller set values are automatically calculated within the plant’s distributed control system (DCS).

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