Method of managing an ammonia synthesis reactor during fluctuating feed rates

Abstract

The reaction rate of a catalyst in an ammonia synthesis reactor can be managed during a period of variable feed flow in order to regulate outlet temperature of the reactor; the reactor has an initial feed ratio prior to onset of the variable feed flow period, which is initial H2 flow to initial N2 flow (H:N1); the method comprises inter alia reducing H:N1 to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or increasing H:NI to a transition feed ratio H:NTr2, if the catalyst is operating in Productivity Regime 2; the reaction rate of the catalyst is managed and reactor outlet temperature is regulated.

Description

[0001]METHOD OF MANAGING AN AMMONIA SYNTHESIS REACTOR DURINGFLUCTUATING FEED RATES STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with government support under DE-AR-0000811 awarded by USDepartment of Energy Advanced Research Projects Agency Energy (ARPA-E). The government has certain rights in the invention. BACKGROUND OF THE INVENTION Hydrogen (H2) and nitrogen (N2) react in the presence of a catalyst at relatively high pressures (80-150 bar) and temperatures (300-475°C) to form ammonia (NH3) in a well-known and industrially practiced process. N2is typically supplied to the process in the form of air fed directly into the process or purified in an air separation unit before introduction into the process.The source of H2 in industrial processes is often a hydrocarbon that can be supplied using a varietyof processes including steam methane reforming (SMR), autothermal reforming (ATR), partialoxidation (POX), or a combination thereof. H2 can also be supplied by non-hydrocarbons,traditionally, but not limited to, electrolysis of water. Catalysts often used for NH3 production arebased on iron (Fe) or ruthenium (Ru). After the NH3 synthesis reactor, NH3 is separated out, andmost of the unreacted gases are recycled back to the reactor, while a small amount is purged. In several scenarios, the availability of electrical energy can vary at short (seconds, minutes), medium (hourly or daily), or long (monthly and seasonal) timescales. Renewableelectricity, for example from wind and solar power, is inherently intermittent. Other sources, suchas nuclear and hydro power can be curtailed depending on market demand. As more variable energy generation sources are integrated into grids, there is an increasing need for fossil-fuel powered generation assets such as natural gas or coal-powered plants to develop flexibility to maintain grid integrity. Energy storage provides the desired flexibility while potentially increasing energy efficiency and offering higher reliability of energy production systems. Storing excess energy in the form of H2, produced by a process such as water electrolysis, is popular since the process can respond quickly to changing loads. However, the exorbitant cost of storing H2formedium to long amounts of time weighs against using it as an ideal energy storage medium. Incontrast, NH3 has a high energy density (4.25 kWh / L) and is a liquid at moderate conditions (15bar and ambient temperatures), so it can be cost-effectively stored in tanks, making it a very attractive energy (and H2) carrier. Thus, for use as an energy storage medium, as well as for production of renewable NH3, there is a need for the NH3 production process to be flexible. For flexible NH3production, H2supplied by the electrolysis of water is a commonly used process configuration. In certain configurations, an NH3production process will have N2and H2storage to provide a buffer for variable availability of these gases. When available electrical energy or load varies, the amount of fresh N2 and H2 available to the NH3 synthesis reactor changes. A decrease in fresh N2 and H2 due to partial energy loads can result in increased rate of reaction, which can cause increased temperatures in the reactor. In certain configurations, the feed of N2 and H2 supplied to the NH3 synthesis reactor is pre-heated in a heat exchanger using the reactor effluent as the heating media. In operating scenarios where available load increases, leading to an increase in feed flow to the reactor, the feed cannot be pre-heated adequately due to the increasedheat capacity of the feed flow compared with the available hot reactor effluent. In these and otherscenarios, the NH3 synthesis reaction could be undesirably quenched and NH3 production cannot be sustained. The ammonia synthesis reactor can contain one or more catalytic beds. In case of more than one catalytic beds, these are connected in series flow. The first catalyst bed is the one crossed by the feed with highest concentration of reactants, hence is the one manifesting the highest exotherm. Exotherms on the catalytic bed may harm the mechanical resistance of the reactor internalsif temperatures approach the design limits of the construction materials of the reactor internal parts.An even more important concern of exotherms in the catalyst beds, is when the selectedammonia synthesis catalysts become thermally unstable in a temperature range which partlyoverlaps with the typical operating conditions of the industrial ammonia synthesis. Iron fused (Fe) ammonia synthesis catalyst, are very well known for their high thermal stability and can operate at 500°C or more. As such, the iron fused ammonia synthesis catalyst is thermally stable in therange of operating conditions of the industrial ammonia synthesis. However other ammoniasynthesis catalysts known in literature, are known to deteriorate due to high temperature, attemperatures lower than iron catalyst. The sensitivity to higher temperature depends on theindividual catalysts, and is per se known from the prior art. A non-limiting example for rutheniumcatalyst supported on carbon is Catal. Sci. Technol., 2015,5, 2829-2838, which reports the damaging of the catalyst support at temperature of 500°C. If one of such, non-iron fused ammonia synthesis catalysts is adopted for the production of ammonia, the temperature at which the catalystbecomes thermally deteriorated may be overcome in case of uncontrolled exotherms in theoperation of the ammonia reactor, which could happen as a consequence of the variable feed fluctuations. One known method to handle possible exotherms includes lowering operating pressures todepress the rate of reaction. However, frequent fluctuating pressures can result in fatigue failureof process vessels. Another method for controlling the NH3 synthesis process when variable loadis present is to vary the purge rate of the processing plant, which enables accumulation of inerts(including argon and helium). This action allows for maintenance of nominal operating pressureswhile operating at partial energy loads. This method is described in EP2589574. A drawback ofvarying purge rate is that increasing the concentration of inerts in the loop by varying purge alonecan take a long time, thus limiting efficacy in responding to shorter timescale variability. Moreover, the availability of inerts in the process often depends on the feedstock and imposing minimum inert requirements can be expensive in certain scenarios. A method to handle scenarios where inadequate pre-heating can occur is to provide the additional heat by means of a separategas heater that could be powered by electricity or other means. DE102016203753 A1 describes amethod to optimize the energy usage and maximize productivity of a NH3 synthesis reactor underconditions of low energy supply: this is achieved by changing the reagent gases composition inresponse to a low energy supply and forming gas mixtures with determined composition which arerecycled to specific parts of the plant to support plant productivity; however the recycling of gasmixtures requires expensive constructive requirements; further in this method, the composition of the reagent gases is modified independently from the current productivity regime of the catalystbed: this operation, while contributing to the plant productivity if associated to the above describedrecycling, is not suited to control the temperature of the catalyst bed and of the overall plant, animportant factor which also affects the plant productivity; in order to control the temperature, themethod includes a separate measure, consisting in reducing the total gas flow supplied to the firstcatalyst bed, which is the one most exposed to temperature increase; however, this operation reduces the plant productivity, complicates the process management, and generates oscillations of pressure within the plant which may cause structural fatigue. An efficient and relatively inexpensive method for process control of an NH3production plant during periods of variable energy load without damaging processing vessels is needed. Themethod described herein, based on an efficient temperature control, can safely and effectivelycontrol the output of an NH3 synthesis reactor in response to changes in feed flow. SUMMARY OF THE INVENTION The present method stems from Applicant’s observation that a reduction of energy supply / feed flow to the ammonia synthesis plant, as may accidentally occur during the service lifeof the plant, causes an overheating of the catalytic bed, with possible heat-related damages to thecatalyst and plant, and connected reduction of productivity / functionality; alternatively, anexcessive energy supply / feed flow results in an undesired cooling of the catalytic bed andundesired reduction of productivity. The Applicant has conceived a handy method aimed at a controlling the temperature of the catalyst bed as key factor for ensuring and maintaining high plant productivity. The method teaches to modify the hydrogen:nitrogen ratio fed to the plant, from the initiallevel prior to the variation of energy supply (defined herein as H:NI) to transition values H:NTr1 orH:NTr2, being respectively lower or higher than H:NI. This transition modifies the activity level ofthe catalyst, causing a modified temperature of the catalytic bed; the temperature change of the catalyst bed is conveyed to the outlet of the catalytic bed and ultimately to the outlet of the reactor.Whether to reduce H:NI to H:NTr1 or to increase H:NI to H:NTr2 is decided in function of theongoing Productivity Regime of the catalyst, as further defined herein: the corresponding transitionof H:NI is guided by the aim of preventing an excessive temperature increase of the catalyst bed ifthe reactor is in accidental condition of reduced feed flow (or promoting a temperature increase ofthe catalyst bed if the reactor is in accidental condition of increased feed flow). In both cases,catalyst / plant productivity and efficiency are advantageously preserved. Also advantageously, themethod is entirely managerial, i.e. it can be performed on standard existing plants, without requiring any structural modifications thereof, e.g. providing complex recycling loops, etc., such as provided e.g. by DE102016203753 A1. A further advantage consists in the process capabilityto react to a loss of supplied energy while keeping constant the total gas flow in the plant, since only the H:N ratio is modified, not quantity / pressure of the overall gas fed to the plant: gas pressure excursions are thus avoided which would cause fatigue of the plant vessels: in particular, there is no need to reduce the gas pressure fed to the catalytic bed(s), as required by e.g. DE102016203753 A1 to control the catalyst bed temperature. Based on the above criteria, a first aspect of the invention concerns a method of managingreaction rate of a catalyst, such as e.g. a ruthenium catalyst, in an ammonia synthesis reactor duringa period of reduced feed flow, where said managing lies in regulating the temperature of catalyticbed and, consequently, the outlet temperature of the catalytic beds and of the reactor. The reactor has an initial feed ratio prior to onset of the period of variable feed flow, which is the ratio of initial H2 flow to initial N2 flow (H:NI). When the variability results in a lower available feed flow, the method comprises reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or increasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalyst is operating in Productivity Regime 2, or performing any of these actions if the catalyst is operating at the Maximum Productivity Regime. The terms “Productivity Regime 1”, “Productivity Regime 2” and “Maximum Productivity Regime” are defined further in the description. The reaction rate of the catalyst is accordinglymanaged by preventing an excessive temperature increase of the catalyst bed, and the outletstemperature is accordingly regulated. Conversely, when the variability results in an increased available feed flow or decreasedfeed pre-heat, the initial feed ratio H:NIcan be increased to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or the initial feed ratio H:NIcan be decreased to atransition feed ratio H:NTr2, if the catalyst is operating in Productivity Regime 2, or any of theseactions can be performed if the catalyst is operating at the Maximum Productivity Regime. Theincrease in specific heat capacity and hence heat transferred brought about by the increase in feed ratio from H:NI to a transition feed ratio H:NTr1, is advantageously used if the catalyst is operating in Productivity Regime 1. The increased enhancement of ammonia production rate will need to be balanced against the decreased heat transfer arising from the decrease in H:NI to H:NTr2. Thereaction rate of catalyst is managed, and NH3 production is regulated.In a second aspect, the invention concerns a method of managing an ammonia synthesisreactor having an ammonia synthesis catalyst during a period of variable feed flow, where said managing lies in regulating the temperature of the one or more catalytic beds and, consequently,the outlet temperature of catalytic beds and of the reactor.The reactor has an initial feed ratio immediately prior to the period of variable feed flow of initial H2 to initial N2 (H:NI). When the variability results in a lower available feed flow, the method comprises reducing H:NI to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or increasing H:NI to a transition feed ratio H:NTr2, if the catalyst isoperating in Productivity Regime 2, or performing any of these actions if the catalyst is operatingat the Maximum Productivity Regime. An excessive temperature increase of the catalyst bed isthus prevented and the outlets temperature is accordingly regulated.Conversely, when the variability results in an increased available feed flow or decreasedfeed pre-heat, the method comprises increasing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if the ammonia synthesis catalyst is operating in Productivity Regime 1, or decreasing the initial feed ratio H:NI to a transition feed ration H:NTr2, if the ammonia synthesis catalyst isoperating in Productivity Regime 2, or performing any of these actions if the catalyst is operatingat the Maximum Productivity Regime. Additionally, the method advantageously uses the increase in specific heat capacity and hence heat transferred brought about by the increase in feed ratio from H:NI to a transition feed ratio H:NTr1, if the ammonia synthesis catalyst is operating in Productivity Regime 1. The ammonia production rate and reactor outlet temperature is regulated. In a third aspect, the invention concerns a method of managing outlet temperature of anammonia synthesis reactor during a period of variable feed flow, where said managing lies inregulating the temperature of the one or more catalytic beds and, consequently, the outlettemperature of the catalytic beds and of the reactor. The reactor has an initial feed ratio prior toonset of the period of variable feed flow of initial H2to initial N2(H:NI). When the variabilityresults in a lower available feed flow, the method comprises reducing the initial feed ratio H:NI toa transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or increasingthe initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalyst is operating in ProductivityRegime 2, or performing any of these actions if the catalyst is operating at the MaximumProductivity Regime. An excessive temperature increase of the catalyst bed is thus prevented, andthe outlets temperature is accordingly managed to reduce exotherm.Conversely, when the variability results in an increased available feed flow or decreasedfeed pre-heat, the initial feed ratio H:NI can be increased to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or the initial feed ratio H:NIcan be decreased to a transition feed ration H:NTr2, if the catalyst is operating in Productivity Regime 2, or any of these actions can be performed if the catalyst is operating at the Maximum Productivity Regime. The increase in specific heat capacity and hence heat transferred brought about by the increase in feed ratio from H:NI to a transition feed ratio H:NTr1 is used if the catalyst is operating in Productivity Regime 1. The ammonia production rate and reactor outlet temperature is regulated. In a fourth aspect, the invention concerns a method of supporting efficiency andproductivity of an ammonia synthesis reactor during a period of variable feed flow. The reactor has an initial feed ratio prior to onset of the period of variable feed flow of initial H2to initial N2(H:NI). When the variability results in a lower available feed flow, the method comprises reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or increasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalyst is operating in Productivity Regime 2, or performing any of these actions if the catalyst is operating at the Maximum Productivity Regime. An excessive temperature increase of the catalyst bed is thus prevented and the efficiency and productivity of the reactor are accordingly maintained. Thismethod can have the consequence, for example, of regulating the reaction rate of the catalyst,and / or managing the outlet temperature of the catalytic beds or of the reactor, and / or managing theammonia synthesis reactor. Conversely, when the variability results in an increased available feed flow or decreased feed pre-heat, the initial feed ratio H:NIcan be increased to a transition feed ratio H:NTr1, if the catalyst is operating in Productivity Regime 1, or the initial feed ratio H:NIcan be decreased to a transition feed ration H:NTr2, if the catalyst is operating in Productivity Regime 2, or any of these actions can be performed if the catalyst is operating at the Maximum Productivity Regime. The increase in specific heat capacity and hence heat transferred brought about by the increase in feed ratio from H:NI to a transition feed ratio H:NTr1 is used if the catalyst is operating in Productivity Regime 1. The ammonia production rate and reactor outlet temperature is regulated. Advantageously, all the present methods can be performed at constancy of the overall flowrate (H+N) fed to the plant, thus without generating oscillations of pressure within the plant whichcan cause fatigue of the plant structure. It is to be understood that both the foregoing general description of the invention and the following detailed description are exemplary, but are not restrictive of the invention. BRIEF DESCRIPTION OF THE FIGURES A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: FIG. 1 is a line chart generated from experiments carried out in a microreactor apparatuswith the NH3synthesis reactor operating in an isothermal mode showing an exemplary embodiment of how NH3production rate can vary as a function of H:N ratio for a Ru catalyst. FIG. 2 is a line chart generated from experiments carried out in a microreactor apparatus with the NH3 synthesis reactor operating in an isothermal mode showing an exemplaryembodiment of how N2 conversion rate can vary as a function of H:N ratio for an Fe catalyst.FIGS. 3A and 3B are line charts showing the effect of flow turndown on reactor temperature and H:N ratio. FIGS. 4A and 4B are line charts showing the detrimental effects of increased H2in this scenario. FIGS.4C and 4D are line charts showing the advantageous effects of increased N2 in this scenario. FIGS. 5A, 5B, 5C, and 5D are line charts showing the advantageous effects of increased H2in this example. DETAILED DESCRIPTION OF THE INVENTION Described herein is a method for managing an ammonia (NH3) production plant duringperiods of variable energy load, by regulating the temperature of the one or more catalytic bedsand, consequently, the outlet temperature of the catalytic beds and of the reactor. Variable loadscan occur when electricity is supplied to the NH3 plant from renewable electricity sources, whichare inherently intermittent. Additionally, fossil-based energy generation, which is subjected topeaking, requires the ability to store energy over time in order to maintain flexibility. Moreover,generated power, such as nuclear power, is at times intentionally curtailed. Varying feed flowcaused by the decrease and increase of available power can result in undesirable effects on theoperation of the NH3 synthesis reactor. The methods described herein control the detrimentaleffects caused by transitions in available feed flow during periods of variable energy load.In embodiments, the methods described herein safely control the output of the NH3synthesis reactor in response to changes in feed flow. Advantageously, H2 and N2 are readilyavailable in the production system, enabling fast response time to changes and not requiringpurchase of additional fresh feed materials. Moreover, in contrast to some conventional methods used during periods of variable feed flow, the described methods can be implemented at nominal reactor design pressures. The methods described herein relate to using the ratio of H2 to N2 (H:N ratio) in thesynthesis reactor feed to control the rate of reaction, and thus the reactor temperature, as the reactoris subjected to variable fresh feeds due to fluctuation in available energy load. The H:N ratio in the feed to the reactor can be used to counter expected exothermic behavior when the synthesisreactor is subjected to partial loads or prevent quenching when the synthesis reactor is subjectedto conditions where available pre-heat is limited, such as increased loads. Unlike inert gases, H2and N2are readily present in the system. For example, feed for a H2stream can come from any number of known sources, e.g. water electrolysis, SMR, ATR, POX, etc., and feed for a N2stream can come from any number of known sources, e.g., pressure swing adsorption, cryogenic separation, pipeline supplies, bulk liquid supply, etc. The H:N feed ratio and the type of catalyst affect the rate of reaction. Catalysts often used for NH3 production are based on iron (Fe) or ruthenium (Ru). For these catalysts, three distinct catalyst productivity regimes are observed as a functionof H:N ratio. The H:N ratio that demarcates productivity regime 1 from productivity regime 2 isthe H:N ratio that provides maximum catalyst productivity, where the catalyst productivity isexpressed as quantity of ammonia produced per quantity catalyst per unit time.Therefore, the catalyst is meant to “operate in the Productivity Regime 1” when the H:N ratio fed to the reactor is below the ratio providing the maximum catalyst productivity; conversely,the catalyst is meant to “operate in the Productivity Regime 2” when the H:N ratio fed to the reactoris above the ratio providing the maximum catalyst productivity. Lastly, the catalyst is meant to “operate at the Maximum Productivity Regime” when the H:N ratio fed to the reactor correspondsto the maximum catalyst productivity. In common practice, the ammonia production plants operatein the Productivity Regime 1 or 2. The H:N ratio considered for determining the Productivity Regime is the one applied to the plant in operation prior to the variation of energy supply and before the application of the present method, herein expressed as H:NI. The determination of the maximum catalyst productivity and the Productivity Regimes isperformed according to standard general knowledge by the person having ordinary skill in the art.In particular, the catalyst productivity as a function of the H:N ratio is typically represented by abell-shaped curve, with the maximum productivity set at the apex of the bell. Prior to performingthe present method, the absolute value of H:N ratio corresponding to the maximum productivitycan be determined via a calibration phase: this can done by step-wise feeding the catalyst withincreasing H:N ratios at constancy of all other reaction conditions, measuring the catalystproductivity at each of said ratios and building the corresponding calibration curve: the maximumproductivity level and the corresponding H:N ratio can be read at the apex of the curve; the valueof this ratio can then be taken in the present method as demarcation value for defining the differentProductivity Regimes. The calibration phase is best performed in the plant intended for productionand at the conditions intended therefor (operating temperature, operating pressure, and spacevelocity in the NH3 synthesis reactor, etc.); however, it can also be performed on a smaller scale,e.g. on a pilot plant or in laboratory scale, at conditions representative of those meant for theproduction plant; otherwise, in alternative to performing a calibration procedure, the H:N ratiocorresponding to the maximum productivity for the catalyst in use can be taken from standard literature, insofar as available. In operation, each of the above referred Productivity Regimes is applicable for ammoniaproduction: the person skilled in the art chooses the suitable regime according to conventional knowledge in function of the circumstances (type of plant, environmental conditions, etc.) and industrial needs (required production volume, operative costs, etc.). When the catalyst is operating in Regime 1, if H:N ratio decreases, catalyst productivitydecreases due to the absence of a reactant (H2). In contrast, when the catalyst is operating inRegime 2, catalyst productivity decreases as H:N ratio increases towards stoichiometric amounts (H:N = 3:1). This behavior in Regime 2 occurs due to “H2 poisoning,” where H2 in the reactant mixture adsorbs preferentially on the catalyst surface, thereby not allowing surface adsorption ofN2 and conversion to NH3. This behavior is reversible since the H2 desorbs with a decrease inpartial pressure that occurs when H:N ratio decreases. This mechanism is well-understood inliterature and has been described in Kammert et al. Lastly, when the catalyst is operating at theMaximum Regime, its productivity decreases either due to the absence of a reactant (H2) or as H:Nratio increases towards stoichiometric amounts (H:N = 3:1). The H:N ratio that demarcates Regime 1 from Regime 2 for the present catalysts varies anddepends on the particular catalyst, operating temperature, operating pressure, and space velocityin the NH3 synthesis reactor, among other variables. Figure 1 is a line chart generated from experiments carried out in a microreactor apparatus with the NH3 synthesis reactor operating in an isothermal mode showing an exemplary embodiment of how NH3production rate can vary as afunction of H:N ratio for a Ru catalyst. The dotted line is the demarcation line between Regime 1and Regime 2. Regime 1 is to the left of the line and Regime 2 is to the right of the line. As can be seen in Figure 1, NH3 production rate varies based on reactor temperature andH / N ratio. The Ru catalysts used for NH3 synthesis at both temperatures operated in twoproductivity regimes: Regime 1 and Regime 2. As can be seen, the demarcating H:N ratio was different for the different operating temperatures. For the reaction taking place around 400°C, thedemarcating (or maximum production) H:N ratio was about 0.5. For the reaction taking placearound 370°C, the demarcating (or maximum production) H:N ratio was about 0.45.Fe catalysts can also be used for NH3synthesis. In Fe catalysts, the variation of catalyst productivity with H:N ratio resembles behavior seen for Ru catalysts and is highest atstoichiometric ratios of H:N = 3:1. Figure 2 is a line chart generated from experiments carried outin a microreactor apparatus with the NH3 synthesis reactor operating in an isothermal modeshowing an exemplary embodiment of how N2 conversion rate can vary as a function of H:N ratiofor an Fe catalyst. Other ammonia synthesis catalysts suitable for the conversion of reactants to ammonia areknown in the art, which are neither iron nor ruthenium catalysts. It will be understood that themethod of the invention can be applied also for the ammonia synthesis catalysts which exhibit the behaviour of Ru or Fe catalysts of Production Regimes 1 and / or 2 as described in the invention. Furthermore, other ammonia synthesis catalysts known in literature are known to thermallydeteriorate at temperatures of <500 °C, for example 475 °C or lower, which may be experiencedin case of uncontrolled exotherms as a consequence of the variable feed fluctuations. The thermalstability temperature of such catalyst is per se known from the art. The methods of the inventionare to be considered for these catalysts as well which are sensitive to temperature <500°C during the operation. In larger scale NH3production processes such as those seen in bench-, pilot-, and commercial-scale plants, the NH3synthesis reactor typically operates in an adiabatic mode.Accordingly, in a preferred embodiment, the present process is performed in an adiabatic reactor.Since NH3 synthesis is an exothermic reaction, the temperatures at the outlet of the catalyst bedare typically higher than the temperatures at the inlet of the bed. A decrease in reactor feed flowrates due to partial energy loads relative to the amount of catalyst in the reactor can result in anincreased rate of reaction, which can cause increased temperatures in the reactor. In certain plantconfigurations and operational scenarios, including an increase in reactor feed flow, the lack ofadequate pre-heating of the feed gases can result in quenching of the reactor. The methodsdescribed herein use an understanding of the physical phenomena shown in Figure 1 and Figure 2,i.e., varying catalyst productivity (or rate of reaction) at varying H:N ratios, to suppress reactionrate as a counter to increase of reaction rate expected due to decreased feed flow.During operation, an NH3 synthesis reactor has an initial feed ratio immediately prior to a period of variable feed flow. As used herein the term “immediately prior” is intended to mean the steady state operating feed ratio prior to onset of feed flow variability or disruption to feed flow. Minor variations in feed flow rate that are within the ordinary course of operation for an NH3synthesis reactor are not considered to be feed flow variability or disruption. A person having ordinary skill in the art will understand whether a change in feed flow rate is a minor variation within the ordinary course of operation or whether it is variability or disruption to feed flow as described herein. The initial feed ratio is determined using the initial H2 feed flow and the initial N2 feedflow. The initial feed ratio is represented as H:NI.In an embodiment, a method of managing the NH3synthesis reactor having an NH3synthesis catalyst during a period of lower feed flow, comprises reducing H:NI to a transition feed ratio H:NTr1, if the catalyst is operating in ProductivityRegime 1. H:NTr1 is the feed ratio of the feed flow to the reactor during the transition period whenthe catalyst was operating in Productivity Regime 1 prior to onset of the period of lower feed flow.If the catalyst was operating in Productivity Regime 2 prior to onset of the period of lower feedflow, the feed ratio H:NI is increased to a transition feed ratio H:NTr2. H:NTr2 is the feed ratio ofthe feed flow to the reactor during the transition period when the catalyst was operating in Productivity Regime 2 immediately prior to the period of lower feed flow. If the catalyst is operating at the Maximum Productivity Regime, the H:NIcan either be reduced to the transitionfeed ratio H:NTr1, or increased to the transition feed ratio H:NTr2The described method can regulate the reactor outlet temperature thus avoiding damagingtemperature increases and uncontrolled exotherm. The method can be used for Ru- and Fe- basedNH3 synthesis catalysts. The method can be advantageously used for other catalysts having anupper limit to the allowable temperature before they deteriorate lower than 500C. Conversely, in an embodiment, a method of managing the NH3synthesis reactor having an NH3synthesis catalyst during a period of higher feed flow or lower pre-heat, comprises increasing H:NIto a transition feed ratio of H:NTr1, if the catalyst is operating in Productivity Regime 1. H:NTr1 is the feed ratio of the feed flow to the reactor during the transition period when the catalyst was operating in Productivity Regime 1 prior to onset of the period of higher feed flow or lower pre-heat. If the catalyst was operating in Productivity Regime 2 prior to onset of the period of higher feed flow or lower pre-heat, the feed ratio H:NI is decreased to a transition feed ratio H:NTr2. H:NTr2is the feed ratio of the feed flow to the reactor during the transition period when the catalyst was operating in Productivity Regime 2 immediately prior to the period of higher feed flow or lower pre-heat. If the catalyst is operating at the Maximum Productivity Regime, the H:NIcan either be increased to the transition feed ratio H:NTr1, or reduced to the transition feed ratio H:NTr2. The described method can regulate NH3 production and reactor outlet temperature thus avoidingreactor quenching and decreased NH3 production. The method can be used, in particular, for Ru-and Fe-based NH3synthesis catalysts. In embodiments, a Ru catalyst is used in the NH3synthesis reaction. A method of managing reaction rate of a Ru catalyst in an NH3synthesis reactor during a period of lower feed flow in order to regulate reactor outlet temperature comprises reducing the initial feed ratio H:NIto a transition feed ratio H:NTr1, if the Ru catalyst is operating in Productivity Regime 1, or increasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the Ru catalyst is operating in Productivity Regime 2. A method of managing reaction rate of a Ru catalyst in an NH3 synthesis reactor during a period of higher feed flow or lower pre-heat in order to regulate reactor outlettemperature comprises increasing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if theRu catalyst is operating in Productivity Regime 1, or decreasing the initial feed ratio H:NIto atransition feed ratio H:NTr2, if the Ru catalyst is operating in Productivity Regime 2, or performingany of these actions if the catalyst is operating at the Maximum Productivity Regime. The methodcan manage the reaction rate of the Ru catalyst and regulate the reactor outlet temperature and NH3production. In an exemplary embodiment, when the initial feed ratio H:NI is less than or equal to 0.5and a Ru catalyst is being used, the Ru catalyst is operating in Productivity Regime 1. In an exemplary embodiment, when the initial feed ratio H:NI is greater than 0.5 and a Ru catalyst isbeing used, the Ru catalyst is operating in Productivity Regime 2. Ru catalysts tend to be moreactive and produce more NH3 at lower temperatures and pressures. Fe-based catalysts are generallymore conventionally used. In an exemplary embodiment, when the initial feed ratio H:NI is 3:1and an Fe-based catalyst is being used, the Fe catalyst is operating in Productivity Regime 1. Themethod can be used for other catalysts having an upper limit to the allowable temperature before they deteriorate lower than 500C. In embodiments, the ruthenium catalyst may be prepared from a precursor metal organic framework (MOF), wherein the metal of the MOF comprises ruthenium. Metal organic frameworks (MOFs) have been widely used as versatile precursors for the preparation ofcatalytically active materials upon applying certain conditions. The versatility of MOFs asprecursors is mainly due to their unique and highly tunable features, such as well-defined metal sites spaced by organic struts displayed along a crystalline structure with permanent porosity, which can play two simultaneous roles acting as template and precursor. Upon transformation, MOFs can lead to well defined nanostructured catalytically active species, which are monodispersed within hierarchical scaffolds, depending on the conversion conditions, i.e., microporous metal oxide under oxidant conditions or microporous carbonaceous matrix under inert conditions. The resulting nanostructured catalysts can be composed by metals, metal oxides, heteroatom-doped carbon and combinations thereof (Wei, J.; Ge, Q.; Yao, R.; Wen, Z.; Fang, C.;Guo, L.; Xu, H.; Sun, J.: Directly converting CO2 into a gasoline fuel Nat. Commun 2017, 8, 15174doi: 10.1038 / ncomms15174). A method to prepare nano-sized catalyst via controlled transformation of MOFnanocrystals is described in commonly owned International Publication No. WO2019191034. Asdescribed, the catalysts can be optionally decorated with additional organometallic metalcomplexes or metal salts previously or afterwards confined within mesoporous materials and or optionally decorated with polymers, organometallic ligand precursors, nitrogen-containing organic compounds, phosphorous-containing organic compounds, sulfur-containing organic compounds,boron-containing organic compounds, halide salts, organic halides, metal atoms added via atomiclayer deposition or chemical vapor deposition or other compounds previously or afterwardsconfined within mesoporous materials. The method preserves the dispersion, nano-sizeddimension, and 3-D distribution along the mesoporous matrix of the support precursor into the resulting catalysts, thus favoring the formation of nanometric and sub-nanometric active species (such as metals, metal oxides, N-doped carbons, P-doped carbons, S-doped carbons, B-doped carbons, halide-doped carbons, and combinations thereof) with high precision by using proper selection of the hybrid precursors, (i.e., organometallic metal complex, metal salt, polymer, organometallic ligand precursor, nitrogen-containing organic, phosphorous-containing organic, sulfur-containing organic, boron-containing organic, halide salts, organic halides, MOF and mesoporous scaffold). Examples of the production of ruthenium-based nanocatalysts for use in ammonia synthesisare described in WO2019191034. For example, Ru / SiO2 was synthesized. The ruthenium MOFprecursor Ru-HKUST-1 was provided. Ru-HKUST-1 was then converted into rutheniumnanoparticles using a 900 °C heat treatment with a slow temperature ramp. At temperatures above400 °C, the high surface area and long-range structure of the MOF broke down as certaincomponents of the organic linker were gasified and released as CO2. Monoatomic ruthenium wasreleased from complexation and deposited on the surface among the residual organic fragments. Ruthenium atom agglomeration occurs at high temperature, and small, well-dispersed, rutheniumnanoparticles were formed on the surface of the support. A promotion procedure was followedfrom the literature using barium and cesium nitrates, which have been shown to promote ammonia synthesis with ruthenium catalysts. The promotion was accomplished by wet deposition of barium and cesium nitrate salts from aqueous solutions onto the surface of Ru / SiO2, resulting in thebarium- and cesium-promoted Ru / SiO2 catalyst.Ru-based catalysts can also be also prepared by other techniques that have been describedin literature. A non-exhaustive list of exemplary Ru-based catalysts include those described in: Kowalczyk, Z., Jodzis, S., Sentek, J., Studies on kinetics of ammonia synthesis over ruthenium catalyst supported on active carbon, Applied Catalysis A: General 1996, 138, 83-91; Bielawa, H.; Hinrichsen, O.; Birkner, A.; Muhler, M.: The ammonia-synthesis catalyst of the next generation:Barium-promoted oxide-supported ruthenium. Angewandte Chemie-International Edition 2001,40, 1061-1063; Kowalczyk, Z., Krukowski, M., Rarog-Pilecka, W., Szmigel, D., Zielinski, J., Carbon-based ruthenium catalyst for ammonia synthesis Role of the barium and caesiumpromoters and carbon support, Applied Catalysis A: General 2003, 248, 67-73; Zardi, M.,Catalysts for Ammonia Synthesis, European Patent EP1451107B1, 2008; Li, Y., Pan, C., Han, W., Chai, H., Liu, H., An efficient route for the preparation of activated carbon supported ruthenium catalysts with high performance for ammonia synthesis, Catalysis Today, 2011, 174, 97-105; Saadatjou, N, Jafari, A, Sahebdelfar, S., Ruthenium Nanocatalysts for Ammonia Synthesis: A Review, Chemical Engineering Communications 2014, 202, 4, 420-448 and others. Fe catalysts are commercially available from several vendors but can also be prepared by several established techniques, including MOF-based approaches as described in Luz-Minguez, I., Parvathikar, S., Carpenter, M., Carpenter, J., Lail, M. Snowflake Porous Multi-Metal Oxide Nanocatalysts from Metallocene@Metal Organic Framework Precursors, submitted to CrystEngComm, 2020. When the catalyst is operating in Productivity Regime 1 immediately prior to the period oflower feed rate, the process management method comprises reducing H:NI to H:NTr1. H:NI can bereduced by increasing the amount of N2being fed to the reactor and / or by decreasing the amountof H2 being fed to the reactor. Increasing injection of N2 to the reactor can decrease H:NI to H:NTr1and lower the rate of reaction along with onset of decreasing load, for the duration of load variability. If the onset of decreasing load is planned or expected, N2 injection rate can be increased prior to decrease in load to counter expected temperature increase. Decreasing the amount of H2 fed to the reactor can decrease H:NIto H:NTr1and lower the rate of reaction along with onset of decreasing load, for the duration of load variability. If the onset of decreasing load is planned or expected, H2feed flow rate can be decreased prior to decrease in load to counter expectedtemperature increase. A combination of increased injection of N2 and decreased supply of H2 candecrease H:NI to H:NTr1 and lower the rate of reaction along with onset of decreasing load, for the duration of load variability. In embodiments where a Ru catalyst is used, the transition feed ratio H:NTr1 can be loweredto 0.1 if needed. Thus, H:NTr1 ≥ 0.1. For example, 0.1 ≤ H:NTr1 < 0.5. In embodiments, H:NTr1 maybe one of 0.1, 0.2, 0.3, 0.4, or 0.45. In additional embodiments, H:NTr1 may be about 10% to about80% less than H:NI. For example, H:NTr1 may be one of 10%, 20%, 30%, 40%, 50%, 60%, 70%,or 80% less than H:NI. In embodiments where an Fe catalyst used, the transition feed ratio H:NTr1can be lowered to 0.1 if needed. Thus, H:NTr1≥ 0.1. For example, 0.1 ≤ H:NTr1< 3.0. In embodiments, H:NTr1may be one of 0.1, 0.5, 1.0, 1.5, 2.0, or 2.5. In additional embodiments, H:NTr1may be about 3% to about 95% less than H:NI. For example, H:NTr1 may be one of 3%, 5%, 10%, 20%, 30%, 40%,50%, 60%, 70%, 80%, 90% or 95% less than H:NI.When the catalyst is operating in Productivity Regime 2 immediately prior to the period oflower feed rate, H:NI is increased to H:NTr2. The increase in feed ratio can be achieved byincreasing the amount of H2being fed to the reactor and / or by decreasing the amount of N2being fed to the reactor. Increasing injection of H2to the reactor can increase H:NIto H:NTr2and lower the rate of reaction along with onset of decreasing load, for the duration of load variability. If the onset of decreasing load is planned or expected, H2 injection rate can be increased prior to decrease in load to counter expected temperature increase. Decreasing the amount of N2 fed to the reactor can increase H:NI to H:NTr2 and lower the rate of reaction along with onset of decreasing load, for the duration of load variability. If the onset of decreasing load is planned or expected, N2feed flow rate can be decreased prior to decrease in load to counter expected temperature increase. A combination of increased injection of H2and decreased supply of N2can increase H:NIto H:NTr2and lower the rate of reaction along with onset of decreasing load, for the duration of load variability. In embodiments where Ru catalysts are used, the transition feed ratio H:NTr2 can beincreased up to 3:1 if needed. Thus, H:NTr2 ≤ 3:1. For example, 0.5 ≤ H:NTr2 ≤ 3:1. In embodiments,H:NTr2may be one of 1:1, 1.5:1, 2.0:1, 2.5:1, or 3:1. In additional embodiments, H:NTr2may be about 100% to about 500% greater than H:NI. For example, H:NTr2may be one of 100%, 200%, 300%, 400%, or 500% greater than H:NI.Advantageously, when the process management methoddescribed herein is used, increase in reactor outlet temperature and reactor operating temperaturegenerally, can be reduced or moderated. Thus, the method described herein is also a method ofmanaging outlet temperature of the NH3 synthesis reactor during a period of variable feed flow. For example, the reactor outlet temperature may increase by less than 100°C, less than 75°C, or less than 50°C during a period of variable feed flow. In embodiments, the reactor outlet temperature may only increase by about 10°C to about 100°C. When the catalyst is operating in Productivity Regime 1 immediately prior to the period ofhigher feed rate or lower pre-heat, it is possible to increase H:NI to H:NTr1. H:NI by decreasing the amount of N2being fed to the reactor and / or by increasing the amount of H2being fed to the reactor. Decreasing injection of N2to the reactor can increase H:NIto H:NTr1and enhance the rate of reaction along with onset of increasing load or decreasing pre-heat, for the duration of load variability. If the onset of increasing load is planned or expected, N2 injection rate can be decreased prior to increase in load to counter expected quenching. Increasing the amount of H2 fed to the reactor can increase H:NI to H:NTr1 and enhance the rate of reaction along with onset of increasing load, for the duration of load variability. If the onset of increasing load is planned or expected, H2feed flow rate can be increased prior to increase in load to counter expected temperature decrease. A combination of decreased injection of N2and increased supply of H2can increase H:NIto H:NTr1and enhance the rate of reaction along with onset of increasing load, for the duration of loadvariability. The increase in specific heat capacity and hence heat transferred brought about by theincrease in feed ratio from H:NI to a transition feed ratio H:NTr1 is used when the catalyst is operating in Productivity Regime 1. In embodiments where Ru catalysts are used, the transition feed ratio H:NTr1 can beincreased to 0.5 if needed. Thus, H:NTr1≤ 0.5. For example, 0.1 ≤ H:NTr1< 0.5. In embodiments, H:NTr1may be one of 0.1, 0.2, 0.3, 0.4, 0.45 or 0.5. In additional embodiments, H:NTr1may be about 10% to about 80% more than H:NI. For example, H:NTr1 may be one of 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80% more than H:NI. In embodiments where Fe catalysts are used, the transition feed ratio H:NTr1 can be ≥ 3.0.For example, 3.0 ≤ H:NTr1 ≤ 4.0. In embodiments, H:NTr1 may be one of 3.1, 3.2, 3.3, 3.4, 3.5, 3.75or 4.0. When the catalyst is operating in Productivity Regime 2 immediately prior to the period ofhigher feed rate or decreased available preheat, H:NI is decreased to H:NTr2. The increasedenhancement of ammonia production rate from the decrease in H:NI to H:NTr2 will need to beoptimized against the decreased heat transfer from the increase in N2 and / or decrease in H2. Thedecrease in feed ratio can be achieved by decreasing the amount of H2 being fed to the reactor and / or by increasing the amount of N2 being fed to the reactor. Decreasing injection of H2 to the reactor can decrease H:NIto H:NTr2and enhance the rate of reaction along with onset of increasing load or reduced pre-heat, for the duration of load variability. If the onset of increasing load or reduced pre-heat is planned or expected, H2injection rate can be decreased prior to increase in load to counter anticipated quenching. Increasing the amount of N2 fed to the reactor can decrease H:NIto H:NTr2and enhance the rate of reaction along with onset of increasing load or reduced pre-heat conditions, for the duration of load variability. If the onset of increasing load or reduced pre-heat is planned or expected, N2feed flow rate can be increased prior to increase in load or reduced pre-heat to counter anticipated quenching. A combination of decreased injection of H2 and increased supply of N2 can decrease H:NI to H:NTr2 and enhance the rate of reaction along with onset of increasing load or decreasing pre-heat, for the duration of load variability. In embodiments, the transition feed ratio H:NTr2 can be decreased up to 1:2 if needed. Thus,H:NTr2≥ 1:2. For example, 0.5 ≤ H:NTr2≤ 3:1. In embodiments, H:NTr2may be one of 0.5:1, 0.75:1, 1:1, 1.5:1, 2.0:1, 2.5:1, or 3:1. In additional embodiments, H:NTr2may be about 100% to about500% lower than H:NI. For example, H:NTr2 may be one of 100%, 200%, 300%, 400%, or 500%lower than H:NI.In embodiments, the transition feed ratio H:NTr1 or H:NTr2 is maintained for an amount oftime T. During the period of lower feed flow, the reactor outlet temperature will initially increase.However, after the transition feed ratio H:NTr1 or H:NTr2 is implemented and feed is introduced tothe reactor at the transition feed ratio for a period of time T, the reactor outlet temperature will reach a new relatively constant or consistent value. Once the reactor outlet temperature returns to a relatively consistent temperature, the feed ratio can be decreased or increased, depending onwhether the transition feed ratio is H:NTr1 or H:NTr2, to an adjusted feed ratio H:NA. If the catalystwas operating in Productivity Regime 1 prior to onset of feed rate variability, to achieve an adjusted feed ratio H:NA, feed rate of N2can be decreased, feed rate of H2can be increased, or acombination of both to increase the feed ratio from H:NTr1 to H:NA. If the catalyst was operatingin Productivity Regime 2 prior to onset of feed rate variability, to achieve an adjusted feed ratio H:NA, feed rate of N2can be increased, feed rate of H2can be decreased, or a combination of bothto decrease the feed ratio from H:NTr2 to H:NA.Similarly, during periods of higher feed flow or lower available pre-heat, NH3 production will initially decrease. However, after the transition feed ratio of H:NTr1 or H:NTr2 is implemented and introduced into the reactor for a period of time T, the pre-heat temperature will increase, theNH3 production rate will increase and avoid quenching due to decreased pre-heat. Once thetransition is complete, the transition feed ratio can be adjusted to an adjusted feed ratio H:NA. The H:NA will generally be a value that is closer to the initial feed ratio H:NI than the valueof the transition feed ratio H:NTr1 or H:NTr2. In embodiments, the H:NA is within 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1% or 0.5% of the H:NI. In embodiments, the H:NAis the same as the initial feed ratio H:NI. While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter. Throughout the present specification, all the given H:N ratios, e.g. any H:NI, H:NTr1, H:NTr2, or H:NA, are meant as molar ratios, unless differently specified. Throughout the present specification, the terms “about” and / or “approximately” may be used in conjunction with numerical values and / or ranges. The term “about” is understood to mean those values near to a recited value. For example, “about 40 [units]” may mean within ± 25% of 40 (e.g., from 30 to 50), within ± 20%, ± 15%, ± 10%, ± 9%, ± 8%, ± 7%, ± 6%, ± 5%, ± 4%, ± 3%, ± 2%, ± 1%, less than ± 1%, or any other value or range of values therein or there below. Furthermore, the phrases “less than about [a value]” or “greater than about [a value]” should be understood in view of the definition of the term “about” provided herein. The terms “about” and “approximately” may be used interchangeably. Throughout the present specification, numerical ranges are provided for certain quantities. It is to be understood that these ranges comprise all subranges therein. Thus, the range “from 50 to 80” includes all possible ranges therein (e.g., 51-79, 52-78, 53-77, 54-76, 55-75, 60-70, etc.). Furthermore, all values within a given range may be an endpoint for the range encompassed thereby (e.g., the range 50-80 includes the ranges with endpoints such as 55-80, 50-75, etc.). As used herein, the verb “comprise” as is used in this description and in the claims and its conjugations are used in its non-limiting sense to mean that items following the word are included,but items not specifically mentioned are not excluded. Throughout the specification the word“comprising,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The present disclosure may suitably “comprise”, “consist of”, or “consist essentially of”, the steps, elements, and / or reagents described in the claims. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as "solely", "only" and the like in connection with the recitation of claim elements, or the use of a "negative" limitation. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Preferred methods, devices, and materials are described, although any methods andmaterials similar or equivalent to those described herein can be used in the practice or testing ofthe present disclosure. All references cited herein are incorporated by reference in their entirety. The following Examples further illustrate the disclosure and are not intended to limit the scope. In particular, it is to be understood that this disclosure is not limited to particular embodiments described. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. EXAMPLES Example 1. Turndown Operation in Productivity Regime 1 An adiabatic fixed-bed reactor NH3 synthesis reactor with a Ru catalyst (Rutheniumsupported on graphitic carbon) was initially operated at 100 barg with a GHSV of 30,000 h-1(corresponding to 100% load and feed flows conditions) and system and had an initial feed ratioH:NI= 0.45.100% load refers to a plant operating condition wherein the reactant gas flow rate in the reactor is at a value that corresponds to the flow rate needed to produce ammonia at the nominaldesign production capacity: as an example, if the design capacity of a plant is 500 tons of ammoniaper day, the amount of reactant flowing through the reactor is equal to the amount needed to produce 500 tons per day of ammonia. A10% turndown in load was simulated by a 10% reduction of total flow to the reactor, asgraphically represented in Figure 3A, which shows the reduction from the standard operative flowrate (“100% of design flow rate”), to 90% of such value. No other changes were implemented. Forexample, the H:N ratio in the fresh feed was not changed. Figure Figure 3B is a line chart showingthe effect of said flow turndown on reactor temperature and H:N ratio. As can be seen, a largeexotherm, up to 40°C temperature increase was seen at the bed outlet. An accompanying increasein reaction rate consumed the H2 in the reactor loop, naturally lowering the H:N. It is expected thatlarger changes in load, i.e., > 10% decrease, would lead to higher exotherms and potentiallytemperature runaway and dangerous conditions. While the NH3 synthesis reaction is self-limiting,i.e., H2consumption in the loop will eventually decrease reaction rate, it is desirable to control exotherms caused by increased reaction rates. In a scenario where the NH3 synthesis catalyst is operating in Regime 1, increasing H:Nratio by adding of H2 while beginning a 10% turndown is not advised since it increases the rate ofreaction causing high exotherms. Figures 4A and 4B are line charts showing the detrimental effects of increased H2in this scenario. However, in a scenario where the NH3synthesis catalyst is operating in Regime 1, addition of N2 prior to or at the same time as beginning a 10% turndown to rapidly decrease H:N ratio results in a more manageable exotherm with a modest temperature increase of 20-25°C at the bed outlet. Figures 4C and 4D are line charts showing the advantageous effects of increased N2 in this scenario. The absolute temperatures the reactor bed reaches in these scenarios are less important than the magnitude of change in those temperatures. A larger increase in fresh N2or a lower H2to affect a sharper decrease in H:N ratio is expected to further lower the observed exotherm. Example 2: Turndown Operation in Regime 2 The NH3synthesis reactor and system of Example 1 is operating in Productivity Regime2 and the initial feed ratio H:NI = 1:1. An injection of H2 at the beginning of a 10% turndown,increased the H:N ratio to H:NTr2 and limited the exothermic behavior to a temperature increase ofabout 20°C. After the change to 90% flow (or equivalently 10% turndown) was complete, the H:NTr2 ratio was adjusted to an adjusted feed ratio H:NA, which was equivalent to the initial feedratio H:NI of 1:1. Operations can resume at the new set-point. Figures 5A, 5B, 5C, and 5D are linecharts showing the advantageous effects of increased H2 in this example.

Claims

Claims1. A method of managing reaction rate of a catalyst in an ammonia synthesis reactor whichcontains one or more catalytic beds during a period of reduced feed flow, wherein thereactor has an initial feed ratio H:NI prior to onset of the period of variable feed flow,wherein said initial feed ratio H:NI is the ratio of initial H2 flow to initial N2 flow, whereinthe reaction rate is managed by regulating the temperature of the one or more catalytic beds and, consequently, the outlet temperature of the catalytic beds and of the reactor, themethod comprising: ^reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if the catalystis operating in Productivity Regime 1, or ^increasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalystis operating in Productivity Regime 2, ^either reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1 orincreasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalyst is operating at the Maximum Productivity Regime,wherein the catalyst operates: -in the Productivity Regime 1 if the H:N ratio fed to the reactor is below the ratioproviding the maximum catalyst productivity; -in the Productivity Regime 2 if the H:N ratio fed to the reactor is above the ratioproviding the maximum catalyst productivity; -at the Maximum Productivity Regime if the H:N ratio fed to the reactor correspondsto the maximum catalyst productivity, and whereby the temperature of the one or more catalytic beds and, consequently, the outlet temperature of the catalytic beds and of the reactor is regulated.

2. The method of claim 1, wherein the transition feed ratio H:NTr1 ≥ 0.1.

3. The method of claim 2, wherein 0.1 ≤ H:NTr1 < 0.5.

4. The method of claim 2, wherein H:NTr1 is one of 0.1, 0.2, 0.3, 0.4, or 0.45.

5. The method of claims 1-4, wherein H:NTr1 is about 10% to about 80% less than H:NI.

6. The method of claim 5, wherein H:NTr1 is one of 10%, 20%, 30%, 40%, 50%, 60%, 70%,or 80% less than H:NI.

7. The method of claims 1-6, wherein H:NI is reduced to H:NTr1 by increasing the amount ofN2being fed to the reactor and / or decreasing the amount of H2being fed to the reactor.

8. The method of claims 1-7, wherein the transition feed ratio H:NTr2 ≤ 3:1.

9. The method of claim 8, wherein 0.5 ≤ H:NTr2 ≤ 3:1.

10. The method of claim 8, wherein H:NTr2 is one of 1:1, 1.5:1, 2.0:1, 2.5:1, or 3:1.

11. The method of claims 1-10, wherein H:NTr2 is about 100% to about 500% greater thanH:NI.

12. The method of claim 11, wherein H:NTr2 is one of 100%, 200%, 300%, 400%, or 500%greater than H:NI.

13. The method of claims 1-12, wherein H:NI is increased to H:NTr2 by increasing the amountof H2 being fed to the reactor and / or decreasing the amount of N2 being fed to the reactor.

14. The method of claims 1-13, further comprising, after an amount of time T, adjusting H:NTr1or H:NTr2 to an adjusted feed ratio H:NA, which is the same as or within 20% of H:NI.

15. The method of claim 14, wherein H:NA = H:NI.16 The method of claims 1-15, wherein the ammonia synthesis catalyst comprises rutheniumor iron.

17. The method of claim 16, wherein the catalyst comprises a supported Ru catalyst or asupported iron catalyst, wherein the support comprises carbon, or Al2O3, or another oxide, or another material, and wherein if the support is carbon, the carbon support is optionally activated or graphitic.

18. The method of claims 1-17, wherein the reactor outlet temperature or the outlet temperatureof one of the catalyst beds preferably the first catalytic bed increases less than 100 °C, lessthan 75 °C, or less than 50 °C.

19. The method of claims 1-17, wherein the reactor outlet temperature or the outlet temperatureof one of the catalyst beds preferably the first catalytic bed increases by about 10 °C toabout 100 °C.

20. The method of claims 1-19, wherein the catalyst is operating in Productivity Regime 1 ifH:NI< 0.5.

21. The method of claims 1-19, wherein the catalyst is operating in Productivity Regime 2 ifH:NI > 0.5.

22. A method of managing an ammonia synthesis reactor having an ammonia synthesis catalystduring a period of reduced feed flow, wherein the reactor contains one or more catalyticbeds and has an initial feed ratio immediately prior to the period of variable feed flow ofinitial H2 to initial N2 (H:NI), wherein the ammonia synthesis is managed by regulating thetemperature of the one or more catalytic beds and, consequently, the outlet temperature of the catalytic beds and of the reactor, the method comprising:^ reducing H:NI to a transition feed ratio H:NTr1, if the catalyst is operating inProductivity Regime 1, or ^increasing H:NI to a transition feed ratio H:NTr2, if the catalyst is operating inProductivity Regime 2, or^ either reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1 orincreasing the initial feed ratio H:NIto a transition feed ratio H:NTr2, if the catalyst is operating at the Maximum Productivity Regime, whereby the temperature of the one or more catalytic beds and, consequently, the outlet temperature of the catalytic beds and of the reactor is regulated.

23. The method of claim 22, wherein the ammonia synthesis catalyst comprises ruthenium oriron.

24. A method of managing outlet temperature of an ammonia synthesis reactor which containsone or more catalytic beds during a period of reduced feed flow, wherein the reactor hasan initial feed ratio prior to onset of the period of variable feed flow of initial H2 to initial N2 (H:NI), wherein the outlet temperature is managed by regulating the temperature of the one or more catalytic beds and, consequently, the outlet temperature of the catalytic beds and of the reactor, the method comprising:^ reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if the catalystis operating in Productivity Regime 1, or ^increasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalystis operating in Productivity Regime 2, ^either reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1 orincreasing the initial feed ratio H:NIto a transition feed ratio H:NTr2, if the catalyst is operating at the Maximum Productivity Regime, whereby the temperature of the one or more catalytic beds and, consequently, the outlet temperature of the catalytic beds and of the reactor is regulated.

25. The method of claims 1-24, wherein the ammonia synthesis catalyst comprises an ammoniasynthesis catalyst which deactivates or deteriorates performances or loses durability at a temperature of less than 500°C, preferably at a temperature of less than 450°C.

26. A method of supporting efficiency and productivity of an ammonia synthesis reactor duringa period of reduced feed flow, by regulating the temperature of the one or more catalyticbeds and, consequently, the outlet temperature of the catalytic beds and of the reactor,wherein the reactor has an initial feed ratio H:NI prior to onset of the period of variablefeed flow, wherein said initial feed ratio H:NI is the ratio of initial H2 flow to initial N2flow, the method comprising:^ reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1, if the catalystis operating in Productivity Regime 1, or^ increasing the initial feed ratio H:NI to a transition feed ratio H:NTr2, if the catalystis operating in Productivity Regime 2,^ either reducing the initial feed ratio H:NI to a transition feed ratio H:NTr1 orincreasing the initial feed ratio H:NIto a transition feed ratio H:NTr2, if the catalyst is operating at the Maximum Productivity Regime. whereby the temperature of the one or more catalytic beds and, consequently, the outlettemperature of the catalytic beds and of the reactor is regulated.

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