Production of ammonia from syngas with wide range of plant loads

Abstract

The present invention relates to the operation of exothermic reactors, such as ammonia synthesis converters in ammonia synthesis plants operating with a wide range of plant loads. Embodiments include a method of operating an ammonia synthesis converter, a method of retrofitting an ammonia synthesis converter, and an ammonia synthesis converter.

Description

[0001] The present invention relates to the operation of an exothermic reactor, such as an ammonia synthesis converter in an ammonia synthesis plant. Embodiments include a method of operating an ammonia synthesis converter, a method of modifying an ammonia synthesis converter, and an ammonia synthesis converter.

[0002] In an ammonia synthesis plant (hereinafter also referred to as a "plant") that produces ammonia from a conventional hydrocarbon feed source (e.g., natural gas) by the Haber-Bosch process, the load in the ammonia synthesis section (e.g., ammonia synthesis loop) of the plant (i.e., ammonia synthesis gas feed) is typically close to full capacity (normal load), varying with a very narrow margin of ±15% or ±10% relative to the design value. In contrast, the load of plants producing ammonia from renewable raw material sources (e.g., those in which hydrogen in the ammonia synthesis gas is produced by electrolysis of water or steam) varies greatly, typically between 5 and 115% or between 5 and 110% relative to the design value, for example, 5-80% of the design value, or 120% or 125% of the design value. These large variations are related to the intermittency of the renewable energy (e.g., solar, wind, or hydro) required for the electrolysis of water and / or steam to obtain the reactants (in particular, hydrogen) for the ammonia synthesis gas. The ammonia synthesis gas comprises a mixture of hydrogen and nitrogen, suitably in a molar ratio of 3:1. Therefore, an ammonia synthesis converter (hereinafter also referred to as "ammonia converter" or simply "converter") designed for conditions where the renewable electricity input is mainly at its maximum when, for example, only 5% of electricity is available, will be oversized by a large margin. An oversized converter means that the space velocity in the converter is very low, so the gas mixture approaches equilibrium after passing through a small portion of the catalyst bed arranged in the converter.

[0003] In an adiabatic converter, this means that the entire heat of reaction is released near the inlet, so most of the catalyst volume is exposed to the highest temperature, i.e. the equilibrium temperature. In a non-adiabatic catalyst bed of an ammonia converter, the ammonia synthesis gas (i.e. the feed gas) is used to cool the catalyst bed, for example in the applicant's WO 2019121949A1, where the temperature is also higher when the load is reduced compared to full load (and therefore relative to the design value). This is partly because the feed gas is preheated to a higher temperature at low flow rates, and partly because the lower linear velocity leads to a lower cooling efficiency of the catalyst bed, i.e. a low heat transfer coefficient. For example, in the case of exothermic ammonia synthesis, high temperatures in the catalyst bed mean low conversion rates to ammonia and high catalyst deactivation rates due to generally irreversible thermal sintering. In fact, the main reason for the irreversible deactivation of industrial ammonia synthesis catalysts is sintering, i.e. the heat-driven growth of the metal nanoparticles that constitute the catalyst. Promoted iron catalysts obtained from magnetite, which are the most widely used catalysts in industry, show significant sintering when exposed to temperatures close to 500°C for a long time (e.g., several months). Iron-based catalysts obtained from wüstite (FeO) are more susceptible to sintering and show significant deactivation after exposure to temperatures above 450°C for a few days. Sintering can also affect support materials, such as ruthenium-based catalysts.

[0004] US2004 / 0096370 discloses a split-flow vertical ammonia converter.

[0005] WO 2019121949 A1 of the above-mentioned applicant also discloses the use of a split-flow ammonia converter, in which the fixed bed catalyst zone is configured into two or more mechanically separated catalyst volumes and two or more gas streams operated in parallel. WO 2019121951 of the applicant discloses an adiabatic axial flow converter, in which the process gas flows from an outer ring through a catalyst bed (wherein the process gas is converted into products) to an inner central tube, and the catalyst bed includes at least one module, which includes one or more catalyst layers.

[0006] However, these references do not mention at least how to control superheating of the catalyst bed in the converter, nor more generally how to cope with large reductions or increases in the load of the plant and, therefore, the load of the process gas passing through the converter.

[0007] WO 200907018, US1704214, US2512586, US 4180543 and US 3186935 describe reactors with quench designs that operate by turning some quench streams on or off to control space velocity. These references do not address the problem of large load reductions or increases in the equipment and thus in the process gas passing through the reactor (e.g. converter). Furthermore, these references do not at least mention providing catalyst modules (catalyst baskets) without fluid communication therebetween.

[0008] Therefore, the present application provides a method that can alleviate the excessive temperature of the catalyst bed of an ammonia converter under varying loads, particularly at low loads, such as 40% load or less relative to full capacity (i.e., normal load), such as 30%, 20%, 10% or 5% load.

[0009] More generally, the present application provides a method of operating a reactor for performing an exothermic catalytic reaction, a method of modifying an ammonia synthesis converter, and an ammonia synthesis converter.

[0010] The present invention also provides a simple solution to the challenges of producing ammonia synthesis gas using an intermittent source.

[0011] Other advantages of the present application will become apparent from the following description.

[0012] Thus, in a general embodiment of a first aspect of the present invention, there is provided a method of operating a reactor for conducting an exothermic catalytic reaction, the reactor comprising within a single pressure-resistant shell: at least two catalyst modules, the at least two catalyst modules being arranged in a stacked order with no fluid communication between the at least two catalyst modules, the total number of catalyst modules defining the number "N", and each catalyst module comprising one or more catalyst zones arranged in series;

[0013] The method comprises:

[0014] i) at normal load, which is defined by the continuous operation of the reactor, wherein the process gas led through varies with a margin of ±15% relative to the design value of the reactor:

[0015] supplying a process gas stream by directing all or a portion of the process gas through a number "n" of catalyst modules, wherein "n" is equal to or less than "N" (n≤N);

[0016] and

[0017] ii) under a variable load, defined by the instantaneous or continuous operation of the process gas, wherein the process gas directed through varies with a margin of more than ±15% relative to the design value of the reactor, by interrupting or allowing, i.e. directing, the flow of process gas into at least one catalyst module by:

[0018] ii-1) supplying a process gas stream by directing all or a portion of the process gas through a number "m" of catalyst modules, where "m" is less than "n" and greater than 0 (0 <m<n);

[0019] or

[0020] ii-2) Supplying a process gas flow by directing all or a portion of the process gas through an "m" number of catalyst modules, wherein "m" is equal to or greater than "n" (m≥n) when "n" is less than "N".

[0021] As used herein, the term “comprising” may also include “consisting of”.

[0022] As used herein, the terms "suitable" or "suitably" are used interchangeably with the terms "optional" or "optionally" to indicate optional embodiments.

[0023] As used herein, the term "first aspect of the present invention" or "first aspect" for short refers to a method of operating a reactor for performing an exothermic catalytic reaction. The term "second aspect of the present invention" or "second aspect" for short refers to a method of modifying an ammonia synthesis converter. The term "third aspect of the present invention" or "third aspect" for short refers to an ammonia synthesis converter.

[0024] As used herein, the terms "invention" or "present invention" may be used interchangeably with the terms "application" or "this application," respectively.

[0025] It should be understood that the catalyst modules are arranged in a stacked order without fluid communication therebetween. Thus, there is no flow from a catalyst module (e.g., a first catalyst module) to another catalyst module (e.g., a second catalyst module); optionally, the catalyst modules share only one common outlet, e.g., Figure 1 Thus, the present application provides a mechanism to, for example, completely stop the influent flow (ie, the process gas flow) through the catalyst module.

[0026] It should be understood that under normal load, the reactor operates at a load essentially equivalent to full capacity, which varies with respect to the design value of the reactor within a very narrow margin of ±15%, for example ±10%, that is, the process gas directed through the reactor is 85-115% of the design value of the reactor, for example 90%, 95%, 100%, 105%, 110% of the design value of the reactor.

[0027] It should be understood that under varying loads, the load at which the reactor operates is significantly different from the normal load and thus significantly different from full capacity, varying with a margin of more than ±15%, that is to say, the process gas guided through the reactor is, for example, 5 - 80% of the design value of the reactor or, for example, 120% or 125% of the design value of the reactor.

[0028] It should be understood that although "n" and "N" in i), ii - 1) and ii - 2) are the same, "m" in ii - 1) may be different from "m" in ii - 2).

[0029] For example, referring to the appendix illustrating the present invention Figure 1 , N = 3. In step i), under normal load, the process gas is supplied to two catalyst modules, so n = 2 (n < N). Thus, for illustrative purposes, it is assumed here that two catalyst modules are sufficient for normal operation. A sudden increase in load occurs, and it is necessary to introduce the process gas flow into all catalyst modules to restore normal operation, so ii - 2) is carried out, where m = 3 (m > n).

[0030] More frequently encountered is a sudden decrease in load. For example, referring to the appendix Figure 1 , three catalyst modules are provided, so N = 3. In step i), under normal load, the process gas can be supplied to three catalyst modules, so n = 3 (n = N). A sudden decrease in load occurs, so in ii - 1), under varying load, the process flow is interrupted and the process gas is supplied to one catalyst module, so m = 1 (0 < m < n).

[0031] There has also been a situation where the load suddenly decreases and then increases. For example, referring to the appendix Figure 1 , three catalyst modules are provided, so N = 3. In step i), under normal load, the process gas can be supplied to three catalyst modules, so n = 3 (n = N). A sudden decrease in load occurs, so in ii - 1), under varying load, the process flow is interrupted and the process gas is supplied to one catalyst module, so m = 1 (0 < m < n). Then, an increase in load occurs, and it is necessary to introduce the process gas flow into all catalyst modules to restore normal operation, so ii - 2) is carried out, where m = 3 (m = n = N).

[0032] For example, referring to the appendix Figure 1, three catalyst modules are provided, so N = 3. In step i), under normal load, the process gas is supplied to two catalyst modules, so n = 2 (n < N). Therefore, for the sake of illustration, it is assumed here that two catalyst modules are sufficient for normal operation. A sudden decrease in load occurs, so in step ii-1), under the varying load, the process gas flow is interrupted and the process gas is supplied to one catalyst module, so m = 1 (0 < m < n). Then, an increase in load occurs and it is necessary to introduce the process gas flow into all catalyst modules to resume normal operation, so m = 3 (m > n).

[0033] Therefore, in one embodiment, ii-2) is carried out after ii-i); ii-1) is carried out when the reactor changes from the normal load (i) to a lower load, i.e., a load lower than the normal load; ii-2) is carried out when the reactor changes from the lower load to the normal load (i) or a high load, where the high load is defined as more than 15% higher than the normal load, and where when "n" is equal to or less than "N" (n ≤ N), "m" is equal to or greater than "n" (m ≥ n), more specifically, where when "n" is equal to "N", "m" is equal to "n" (m = n = N).

[0034] Therefore, ii-1) and ii-2) are carried out in sequence so as to cover the case where m = n = N in ii-2). Thus, another general embodiment according to the first aspect of the present invention can be described as a method of operating a reactor for carrying out an exothermic catalytic reaction, the reactor comprising, within a single pressure-resistant shell: at least two catalyst modules, the at least two catalyst modules being arranged in a stacked order and having no fluid communication between the at least two catalyst modules, the total number of catalyst modules defining the number "N", and each catalyst module comprising one or more catalyst zones arranged in series;

[0035] The method comprises:

[0036] i) at normal load, which is defined by the continuous operation of the reactor, where the process gas being directed therethrough varies within a margin of ±15% relative to the design value of the reactor:

[0037] supplying a process gas flow by directing all or a portion of the process gas through a number "n" of catalyst modules, where "n" is equal to or less than "N" (n ≤ N);

[0038] and

[0039] ii) under a variable load, defined by the transient or continuous operation of the process gas, wherein the process gas directed through varies with a margin exceeding ±15% relative to the design value of the reactor, by interrupting or allowing, i.e. directing, the process gas through at least one catalyst module by:

[0040] ii-1) supplying a process gas stream by directing all or a portion of the process gas through a number "m" of catalyst modules, where "m" is less than "n" and greater than 0 (0 <m<n);

[0041] and

[0042] ii-2) supplying a process gas flow by directing all or a portion of the process gas through a number "m" of catalyst modules, wherein "m" is equal to or greater than "n" (m≥n) when "n" is equal to or less than "N" (n≤N).

[0043] In one embodiment, in ii), the process gas is at 5% to 115% or more of the design value of the reactor under varying load. Thus, the process gas may also be 85%-115%, such as 90%-110%, of the design value of the reactor under varying load and transient operation of the process gas. For example, the process gas may be in a transient state, where it increases rapidly from a low load of, for example, 10% to full capacity (normal load), so that the process gas reaches, for example, 90%, 95%, 100% of the design value of the reactor.

[0044] The design value of the reactor is suitably expressed in terms of space velocity (SV), for example the design value of the reactor is the space velocity on the first catalyst bed of the catalyst module, which is in the range of 20,000 to 50,000 Nm 3 / h / m 3 Between, for example, 25000-45000Nm 3 / h / m 3 So, for example, a 10% lower load means that the SV is, for example, 2500-4500Nm 3 / h / m 3 That is 2500-4500h -1 within the range.

[0045] A catalyst module, ie a catalyst basket, is an assembly comprising one or more catalyst beds. A catalyst module is also referred to herein as a "module".

[0046] As used herein, the term "low load" refers to 70% or less, such as 60%, 50%, 40%, 30%, 20%, 10% or 5% of full capacity (normal load). These percentages are relative to the design value of the reactor.

[0047] As used herein, the term "high load" means +15% or more, for example +20%, relative to full capacity (normal load); thus, the process gas directed through the reactor is, for example, 120% of the design value of the reactor. For example, if the SV is 25000 Nm 3 / h / m 3 , then +20% high load means 30000Nm 3 / h / m 3 It should be understood that ±15% means within 15%, thus including 15%, while +15% means above 15%, thus excluding 15%. Therefore, it should be understood that +20% means 20% or higher, that is, +20% here includes 20%.

[0048] Therefore, the load between "low load" and "high load" can be regarded as an intermediate load, i.e., a medium load. For example, a medium load is a load of 75%, 80% relative to full capacity (normal load). It should be understood that loads of 85%, 90%, 95%, 100%, 105%, 110%, 115% are normal loads. These percentages are relative to the design values ​​of the reactor.

[0049] As used herein, the term "lower load" refers to a lower load relative to full capacity (normal load), so for example, 80%, 75%, and for example 70% or less, such as 60%, 50%, 40%, 30%, 20%, 10% or 5% relative to full capacity (normal load). Therefore, the term "lower load" encompasses any of the lower or lower loads described. The percentages provided herein are relative to the design values ​​of the reactor.

[0050] For the purposes of this application, when loading percentages are provided, these are relative to the design values ​​for the reactor unless expressly stated otherwise.

[0051] Accordingly, the present invention provides a method for alleviating excessive temperatures in a catalyst bed at particularly low loads by using two or more catalyst modules (also referred to herein as catalyst baskets), which can be operated in parallel within the same pressure-resistant shell, the method being by supplying a process gas stream through some or all of the catalyst modules according to load conditions (i.e., at normal load or varying load). For example, in i), the supplying of the process gas stream is by allowing i.e., guiding the process gas stream through all of the catalyst modules (n = N) at normal load; in ii-1), the supplying of the process gas stream is by interrupting (e.g., stopping) the process gas stream when the reactor changes from normal load to low load (e.g., drops to 10% or 5% load), such that it only passes through some of the catalyst modules (e.g., m < n); and / or in ii-2), the supplying of the process gas stream is by again allowing i.e., guiding the process gas stream through all of the catalyst modules (e.g., m > n) when the reactor changes from low load to normal or high load.

[0052] In one embodiment, the reactor is an ammonia synthesis converter and the process gas is ammonia synthesis gas.

[0053] At low loads, the process gas stream can be stopped from passing through some of the modules, forcing the feed gas (e.g., the ammonia synthesis gas being fed) to only pass through the modules that remain open. In this way, the space velocity through the converter can be adjusted according to the equipment load and overheating of the catalyst can be controlled. More specifically, the total flow rate of the ammonia synthesis gas is distributed among the catalyst modules such that they operate in parallel; then the flow through one or more of the catalyst modules is stopped, forcing the process gas to pass through those catalyst modules that remain open, thereby increasing the space velocity.

[0054] For the purposes of the present application, the terms "feed gas", "process gas" and "ammonia synthesis gas" can be used interchangeably.

[0055] For example, a modular converter can consist of a fixed catalyst bed placed in catalyst modules, which are housed within a single pressure-resistant shell. The volume of the catalyst in the modules can be the same or different, and the modules can be stacked on top of each other in a vertical configuration or placed side by side in a horizontal configuration. The catalyst bed can be adiabatic, gas-cooled or a combination of both. The inlet gas to the converter can be split such that a portion of the flow passes through each module (i.e., the modules operate in parallel). An example of a modular converter is the converter in the applicant's WO 2019121949 A1 mentioned above.

[0056] A notable feature of the present application is that the process gas flow through one or more catalyst modules can be stopped by blocking the inlet or outlet of the module. Thus, the gas is forced to flow through the modules that remain open, thereby increasing the space velocity. Consequently, the average temperature in the open catalyst modules is lower than the temperature observed if the process gas at the same inlet flow rate were to flow through all the catalyst modules. Similarly, the catalyst modules that remain closed will be exposed to a temperature lower than the highest temperature they would obtain when they are in the on-line state. The operating mode described here alleviates overheating of the catalyst charge, thereby extending its service life.

[0057] In one embodiment, in i), n = N, so that all or a portion of the process gas passes through all the catalyst modules in i). Thus, at normal load, the reactor operates at full capacity and thus has a very narrow margin of ±15%, for example ±10% relative to the design value of the reactor, and the process gas is allowed to enter by flowing the process gas through all the catalyst modules. For example, the converter is equipped with a total of six (6) catalyst modules (N = 6), and when the process gas enters all the catalyst modules at varying loads, then n = N = 6.

[0058] The above represents an example of the normal operation of a reactor (such as an ammonia synthesis converter) where all the catalyst beds are used, for example when there is a +5% change relative to the design value of the reactor, but there may be a situation where the reactor operates at normal load but the process gas is not allowed to enter all the catalyst modules and thus n < N. For example, if the reactor operates at a load of -10% relative to the design value of the reactor, i.e., 90% of the load (90% of the design value of the reactor), and the reactor may be equipped with six catalyst modules (N = 6), then the process gas may only be allowed to enter five catalyst modules, so n = 5.

[0059] At varying loads, the change in operation can be sudden, i.e., abrupt, for example within a few minutes, such as changing 2 - 5% per minute within the 5 - 100% load range. The sudden change in load can not only result in a low load, such as 10% or 5% relative to the design value of the reactor, but also in a load significantly higher than the design value, such as 115% or higher. The former is the case, for example, when there is no wind or solar power generation, and the latter is the case when there is an excess of wind or solar power generation.

[0060] Thus, in a particular embodiment, when the so-called varying load suddenly changes, N = 6, n = 6, and m = 1, so that only one catalyst module is used (opened), while five catalyst modules are not used (closed), where, for example, the process gas guided through the reactor is 10% of the design value. Example 1 below further illustrates this embodiment.

[0061] In another specific embodiment, when the so-called variable load suddenly changes, N = 6, n = 5 and m = 1. Thus, again, only one catalyst module is used, where, for example, the process gas guided through the reactor is 5% of the design value. However, under normal operation, the reactor can be operated with one less catalyst module (n = 5) instead of using all catalyst modules (N = 6).

[0062] In another specific embodiment, when the so-called variable load suddenly changes, N = 6, n = 5 and m = 6. Thus, again, when changing from normal operation (n < N, m = 5, N = 6) using one less catalyst module than all the catalyst modules provided in the reactor, all catalyst modules (m = 6) are now used, where, for example, the process gas guided through the reactor is 115% of the design value.

[0063] Other specific embodiments can be envisaged, such as N = 3, n = 3, m = 1, as shown in connection with Example 2.

[0064] The solution provided by the present application is superior to the prior art for at least the following reasons:

[0065] - In traditional ammonia synthesis equipment, the inlet temperature of the catalyst bed of the ammonia synthesis converter is controlled by adjusting the bypass ratio in the heat exchanger for preheating the feed. According to this patent application, this feature can also be achieved in the ammonia synthesis converter. However, there is a limit to the extent to which the inlet temperature of the catalyst bed can be reduced, which is determined by the onset of catalytic activity (usually not less than 350 °C). For very low loads, such as 10% or 5%, the applicant has found that this control of the inlet temperature is not sufficient to avoid overheating of a large part of the catalyst, as further explained in the Examples section below.

[0066] - Another straightforward option is to change the composition of the feed gas by increasing the amount of nitrogen in the reactor, so that the ratio of H 2 :N 2 is lower than the normal ideal ratio of 3. In this way, the reactivity of the feed gas becomes lower and overheating in the catalyst bed is also reduced. However, this poses a risk of tripping the feed gas compressor, as the compressor is typically designed to operate within a very narrow range of the H 2 :N 2 = 3. In addition, this also makes the response of the ammonia synthesis loop sluggish, because if the ideal H 2 :N 2 ratio of 3 is suddenly required, it takes some time to purge the excess nitrogen present in the loop.

[0067] Thus, the present application is able to cope with a wider range of loads, in particular very low loads, such as 10%, 5% or even lower relative to the design value of the reactor. This is important because the load can easily change from one extreme to another, for example, on one day the load may be close to 100%, and therefore close to normal load, for example when there is strong wind driving the wind turbine to produce the electricity required for electrolysis of water or steam into hydrogen, while later in the same day or the next day, the wind may be very light or even absent, so that the wind turbine does not produce any electricity, thus significantly reducing the load, for example to 5%. The next day, wind or solar power may return and the load will change from a low load, such as 5%, to a high load, such as 115% or 120% relative to the design value of the reactor (with a margin of +15% or +20%).

[0068] Another alternative used in the industry is to install two or more converters operating in parallel and bring them online and offline depending on the available load in the ammonia synthesis loop. This solution involves a number of converters, each housed in its own pressure-resistant housing. The converters usually comprise one or more fixed beds of catalyst arranged in series with inter-bed cooling.

[0069] - According to the invention, the space velocity through the catalyst bed can be adjusted to reduce irreversible deactivation of the catalyst charge when the plant load is reduced, thereby allowing the converter to be operated at varying loads. This is because the overheated area that undergoes faster sintering is confined to a smaller volume within the catalyst module that remains open. The catalyst in the module that is offline is exposed to lower temperatures and deactivation due to sintering is not significant.

[0070] The present application provides a mechanism to completely stop flow through one or more catalyst modules when the load is reduced.

[0071] The present application allows parallel operation of catalyst modules (catalyst baskets) placed in a single pressure shell, regardless of the type of converter used, and therefore whether the converter is of the type described in the applicant's WO 2019121949A1, in which the process gas is provided in parallel with the catalyst basket; or a converter in which the process gas is provided in series with the catalyst basket, and the typical solution is to provide reactors arranged in parallel, each with its own pressure shell. The present invention makes it possible to have only one pressure shell, which is the most expensive component in the ammonia converter.

[0072] Therefore, the present invention provides a high degree of flexibility in the operating process and significantly reduces the investment cost and operating cost of the customer.

[0073] The ammonia converter is capable of operating in continuous operation, i.e. steady state or near steady state, referred to herein as transient or continuous operation, where normal load exists, and is capable of operating in transient conditions or continuous conditions, where the load suddenly changes to, for example, as low as 10% load, and the load is maintained at this 10% load for a considerable number of hours or days - thus the reactor is in continuous operation.

[0074] In one embodiment, the process gas is passed through at least two catalyst modules, for example through the first catalyst group, in an axial and / or radial flow direction. In another embodiment, at least two catalyst modules are operated in parallel, i.e. in parallel with respect to the process gas. Thus, the operation of the reactor has a high degree of flexibility.

[0075] The present application unexpectedly provides a method of parallel operation in an already parallel operation, i.e., operating catalyst modules in parallel. For example, a first catalyst module is operated by directing a portion of the process gas to flow therethrough, while a second catalyst module is operated independently, wherein another portion of the process gas is directed therethrough. This is significantly different from the parallel method in, for example, the applicant's WO 2019121949A1, in which the catalyst modules are operated in parallel with respect to the process gas, but not independently.

[0076] In one embodiment, the catalyst module is operated in an adiabatic manner; or the catalyst module is operated in a non-adiabatic manner, for example by being gas cooled, for example by being cooled with a process gas directed to the reactor; or the first catalytic zone of the catalyst module is operated in a non-adiabatic manner and subsequent catalytic zones of the catalyst module arranged in series are operated in an adiabatic manner.

[0077] This can further reduce catalyst degradation because the number of modules used for different process gas flow rates can be adjusted and keep exothermic reactions (such as the conversion of hydrogen and nitrogen in ammonia synthesis gas (process gas) into ammonia) close to equilibrium because the space velocity of the module in use is kept high and the temperature is kept low to favor the thermodynamics of the exothermic reaction.

[0078] Throughout the ammonia converter, the high temperatures that prevail at particularly low loads can reduce the catalyst life in conventional converter designs, where catalyst life is typically 15 years. Thus, the present invention can extend the life of the catalyst because the catalyst is less susceptible to sintering due to exposure to high temperatures.

[0079] The present application is also very useful for retrofitting ammonia converters, as relatively minor modifications can be made to existing converters, but have a significant impact in coping with varying loads and attendant problems, as described above.

[0080] Therefore, in a second aspect of the present invention, there is provided a method for modifying an ammonia synthesis converter, the ammonia synthesis converter comprising in a pressure-resistant shell:

[0081] at least two catalyst modules arranged in a stacked order and operated in parallel, each catalyst module comprising one or more catalyst zones connected in series, the one or more catalyst zones having catalyst layers adapted for axial and / or radial flow;

[0082] an outer annular space located between the at least two catalyst modules operating in parallel and the pressure housing, wherein the outer annular space is fluidly connected to the at least two catalyst modules operating in parallel;

[0083] an inlet disposed within the pressure housing for directing the ammonia synthesis gas through the outer annular space;

[0084] an outlet arranged to receive product gas from at least two parallel catalyst modules, the outlet being optionally arranged in a space formed at the center within the at least two stacked catalyst modules (i.e., a central space);

[0085] The method includes:

[0086] - installing one or more seals in the outer annular space, the one or more seals being in direct contact with the pressure shell and one or more of the at least two catalyst modules operating in parallel, respectively; wherein a first seal is installed between the pressure shell and the first of the at least two catalyst modules in parallel, thereby defining a first outer annular space; and a second seal is installed between the pressure shell and the second of the at least two catalyst modules in parallel, thereby defining a second outer annular space;

[0087] - installing a plurality of inlets for independently directing the ammonia synthesis gas through the first or second outer annular space; wherein the first inlet is arranged to be in fluid communication with the first outer annular space, optionally in direct fluid communication with the first outer annular space; and the second inlet is arranged to be in fluid communication with the second outer annular space, optionally in direct fluid communication with the second outer annular space.

[0088] It should be understood that there is no fluid communication between the at least two catalyst modules.

[0089] In one embodiment, the method comprises installing one or more seals on the top of the first and second of at least two catalyst modules operated in parallel. Thus, process gas can enter the entire catalyst module, and the seals can be installed in a simple manner to align with the top (e.g., lid) of each catalyst module.

[0090] The seal is gas-tight so that the corresponding catalyst module (if required) is completely closed.

[0091] In one embodiment, the seal is an annular plate.The seal is gas-tight and fits into the outer annular space of the converter, thus enabling easy installation.

[0092] In a third aspect of the present invention, there is also provided an ammonia synthesis converter, comprising:

[0093] - at least two catalyst modules arranged in a stacked order and operated in parallel, each catalyst module comprising one or more catalyst zones connected in series, the one or more catalyst zones having catalyst layers suitable for axial and / or radial flow;

[0094] - an outer annular space located between the at least two catalyst modules operated in parallel and the pressure-resistant housing, wherein the outer annular space is fluidically connected to the at least two catalyst modules operated in parallel;

[0095] - one or more seals arranged in the outer annular space, the one or more seals being in direct contact with the pressure shell and one or more of the at least two catalyst modules operating in parallel, respectively; wherein a first seal is arranged between the pressure shell and the first of the at least two catalyst modules in parallel, thereby defining a first outer annular space; and a second seal is arranged between the pressure shell and the second of the at least two catalyst modules in parallel, thereby defining a second outer annular space;

[0096] - a plurality of inlets for independently directing the ammonia synthesis gas through the first or second outer annular space; wherein the first inlet is arranged in direct fluid communication with the first outer annular space and the second inlet is arranged in fluid communication with the second outer annular space;

[0097] - an outlet for receiving product gas from one or more of the at least two parallel catalyst modules.

[0098] It should be understood that there is no fluid communication between the at least two catalyst modules.

[0099] In modern adiabatic ammonia converters, the space velocity (SV) on the first catalyst bed is between 25000 Nm 3 / h / m 3 Up to 45000Nm 3 / h / m 3The typical inlet temperature is between 350°C and 385°C. The equilibrium temperature is between 495°C and 540°C, depending on the loop pressure (typically 120 bar g-250 bar g) and the ammonia concentration in the gas (typically 3.0 vol.%-10.0 vol.%). The minimum inlet temperature of the converter is limited by the significant reaction rate that must be present on the catalyst bed. The space velocity is usually selected to obtain an outlet temperature 5°C to 15°C lower than the thermodynamic equilibrium.

[0100] Thus, as with the first or second aspect of the invention, under varying loads, for example under low loads, the process gas flow can be stopped through some catalyst modules, forcing the feed gas to pass only through the catalyst modules that remain open. In this way, the space velocity through the converter can be adjusted according to the plant load, thereby according to the amount of process gas directed through the converter, and the overheating of the catalyst can be controlled. Thus, the converter of the present invention is able to control the space velocity in the converter by allowing or stopping the gas flow through some catalyst modules.

[0101] In one embodiment, the outlet is arranged in a space formed at the center of at least two stacked catalyst modules; that is, the outlet is arranged in the central space of the ammonia synthesis converter. Thus, the product gas (ammonia-containing gas) is collected in a simple manner and allowed to leave the converter from a single outlet arranged in the converter pressure shell, and can be used to preheat the process gas entering the converter. Preheating can be performed by a feed / effluent heat exchanger arranged inside the pressure shell of the converter (internal heat exchanger) or outside the pressure shell (external heat exchanger).

[0102] In one embodiment, the one or more seals are annular plates and are arranged on the top of the first and second of at least two catalyst modules operated in parallel. As previously described, process gas can thereby enter the entire catalyst module, and the seal can be installed in a simple manner to align with the top (e.g., lid) of each catalyst module.

[0103] In one embodiment, the converter further comprises:

[0104] - a cover, such as a lid, which closes at least two catalyst modules operated in parallel;

[0105] - an intra-bed heat exchanger for cooling the catalyst layer in at least one catalyst zone; the intra-bed heat exchanger comprises an inlet and an outlet; and

[0106] In at least one cooled catalyst zone, the ammonia synthesis converter comprises a feed device for directing the ammonia synthesis gas to the inlet of an intra-bed heat exchanger, wherein the inlet fluid of the intra-bed heat exchanger is connected to the first outer annular space or the second outer annular space; the outlet of the intra-bed heat exchanger is optionally fluidly connected to a feed device (e.g. a pipeline) for directing the thus preheated ammonia synthesis gas together with fresh ammonia synthesis gas to the inlet of at least one catalyst zone.

[0107] In one embodiment, at least one of the catalyst zones in series is an adiabatic catalyst zone, and a single cooled catalyst zone is connected in series with a single adiabatic catalyst zone. Thus, within a single catalyst basket, first a cooled zone is provided, which is therefore non-adiabatic, and subsequently an adiabatic zone is provided, in which there is no heat exchange. In this way, the reaction temperature can be better controlled.

[0108] It should be understood that any embodiment and associated benefits of the first aspect of the present invention may be used with any embodiment and associated benefits of the second or third aspects of the present invention, and vice versa.

[0109] Figure 1 is a simplified cross-sectional view of an ammonia converter according to the present invention showing three catalyst modules operating in parallel within a single (common) pressure housing.

[0110] Figure 2 Corresponding to Example 1, the performance of an ammonia converter according to the prior art consisting of a single adiabatic bed (e.g., applicant's ammonia converters named S-100 and S-50, as known in the art) is shown, compared with the performance of a modular reactor according to one embodiment of the present invention having six catalyst baskets operated in parallel.

[0111] Figure 3 Corresponding to Example 2, the performance of an ammonia converter consisting of three modules with in-bed gas cooling according to one embodiment of the present invention is shown.

[0112] refer to Figure 1, the ammonia converter 10 with a pressure-resistant shell 16 also includes three catalyst modules 12 (12', 12", 12'") operated in parallel, which are arranged in a stacked order. Each catalyst module contains one or more catalyst regions in series, which have catalyst layers suitable for radial flow of, for example, process gas (here, ammonia synthesis gas). An outer annular space 22 (22', 22", 22'") is defined between the catalyst modules 12 (12', 12", 12'") operated in parallel and the pressure-resistant shell 16. The outer annular space 22 is fluidly connected to the catalyst modules 12 operated in parallel. The seal 14 (14', 14", 14'") is arranged in the outer annular space 22, for example as an annular plate at the top of the catalyst module 12. The seal 14 is in direct contact with the pressure-resistant shell 16 and the corresponding catalyst module 12 operated in parallel. Thus, for example, the seal 14' is arranged to be in direct contact with the pressure shell 16 and the catalyst module 12', as shown. Thereby, a first external annular space 22' is defined. The second seal 14" is arranged between the pressure shell 16 and the second 12" of the parallel catalyst modules, thereby defining a second external annular space 22". The third seal 14"' is arranged between the pressure shell 16 and the third 12"' of the parallel catalyst modules, thereby defining a third external annular space 22"'. The converter 10 includes multiple inlets 18 (18', 18", 18"'), for example via nozzles on the pressure shell 16 and corresponding valves 20 (20', 20", 20"'), which are used to independently guide the ammonia synthesis gas 1, 3 (3', 3", 3"') through the first (22') or second (22") or third (22"') external annular space. The first inlet 18' is arranged to be in direct fluid communication with the first 22' outer annular space, the second inlet 18" is arranged to be in fluid communication with the second 22" outer annular space, and the third inlet 18"' is arranged to be in fluid communication with the third 22"' outer annular space. The converter 10 also includes an outlet, such as a conduit 24, which is arranged to receive product gas 5', 5", 5"' from the catalyst module 12 as a product gas flow 5 iv The outlet 24 is arranged in the space formed at the center of the catalyst module 12, that is, in the central space. By first using the hot product gas (ammonia product) 5 iv The ammonia synthesis gas 1 is preheated in an external feed / effluent heat exchanger 26 as a heat exchange medium, and the ammonia synthesis gas 1 is introduced into the converter 10, while the hot product gas (ammonia product) 5 ivIt is therefore cooled and leaves as stream 7. The preheated ammonia synthesis gas 3 is then split into 3', 3", 3"' and introduced into the converter 10. The flow of the ammonia synthesis gas 3 can be allowed or interrupted depending on the load of the plant. Under normal load, all valves 18', 18", 18"' can be opened so that the ammonia synthesis gas 3 passes through all (here three) catalyst modules 12. When the load changes, in particular at low loads, such as at 10% load, the flow of the ammonia synthesis gas 3 to the first 12' and second 12" catalyst modules is interrupted, and it is only allowed to enter the third 12"' catalyst module as stream 3"' through the inlet 18"'. It should therefore be understood that the catalyst modules 12 (12', 12", 12"') are arranged in a stacked order without fluid communication therebetween. As shown in the figure, the corresponding sections 12' and 22'; 12" and 22"; 12"' and 22"', share only one common outlet 24. There is no fluid communication between the catalyst modules. Furthermore, the catalyst modules, and therefore the corresponding stages, can be operated independently. The present application provides a mechanism to completely stop flow through one or more catalyst modules. Example

[0113] Example 1

[0114] exist Figure 2 In the Figure, the performance of an ammonia converter consisting of a single adiabatic bed (and therefore not a modular adiabatic bed converter) (e.g., Applicant's S-100 or S-50 as described above; left side of the figure) is compared with the performance of a modular adiabatic converter having six catalyst modules (catalyst baskets) operated in parallel according to one embodiment of the present invention (right side of the figure). The ammonia synthesis gas, i.e., the feed gas, contains 70.40 vol.% H 2 、23.46vol.%N 2 、4.13vol.%NH 3 and 2.01 vol.% inert gas, and the converter was operated at 138.1 bar g, with a space velocity (SV) of 45000 Nm at full capacity (100% load). 3 / h / m 3 Therefore, the design value of the converter here is SV = 45000Nm 3 / h / m 3 These process conditions are representative of a facility for producing ammonia from renewable sources.

[0115] At 100% load, the performance of a single non-modular adiabatic bed converter and a modular adiabatic converter is identical, with the converter (reactor) temperature exceeding 490°C only in the last approximately 20% of the catalyst volume. However, at 10% load, i.e. at 10% of the design capacity (so now SV = 4500 Nm 3 / h / m3 ) and still using all catalyst modules, the large excess of catalyst in a single adiabatic bed results in 95% of the catalyst volume being exposed to temperatures above 490°C. If low load cycles occur repeatedly and / or continuously, a large and irreversible loss of catalytic activity will become apparent after just a few years of operation. Figure 2 on the left side.

[0116] In contrast, Figure 2 As shown on the right, in a converter with six catalyst baskets in parallel (N=6, n=6), when the equipment load is 10%, flow can be allowed to pass through only one module (m=1). If the six modules are the same size, the space velocity on the open basket is 27000Nm 3 / h / m 3 Then the volume of the catalyst heated to above 490°C is only 50% of one bed, ie about 8% of the total catalyst charge.

[0117] Example 2

[0118] Figure 3 The performance of a converter according to the applicant's WO 2019121949 is shown, which consists of three modules with in-bed gas cooling (N=3). Two cases are compared: 1) at high and low load, all three modules (N=3) are online and therefore open; 2) the flow through two modules can be stopped (N=3, m=1), so that at low load (here 10% load), the inlet passes only over one third of the available catalyst. The feed gas contains 61.28 vol.% H 2 、21.21vol.%N 2 、6.26vol.%NH 3 and 11.25 vol.% inert gas. The converter was operated at 224.0 bar g and the space velocity at full capacity, i.e. normal load, was 37750 Nm 3 / h / m 3 Therefore, the design value of the converter here is SV = 37750Nm 3 / h / m 3 The inlet temperature of the cooling plates used for in-bed gas cooling was 297° C. These process conditions are representative of a plant for the production of ammonia from renewable sources.

[0119] At 100% load, when all three modules are on (so N=3, n=3, m=0), the reactor temperature throughout the catalyst volume is well below 490°C, as shown by the lower solid line in the figure. However, at a load change of 10% of the design capacity (so now SV=3775Nm 3 / h / m 3), if all modules are in operation (so N=3, n=3, m=0), about 85% of the catalyst volume (bed volume) is exposed to temperatures above 490°C, as shown by the top line in the figure. Now, in the converter at a 10% load variation, flow is allowed through only one module (so N=3, n=3, m=1), and if the volumes of the three modules are the same, then at 10% load, the space velocity on the open basket is 11325 Nm 3 / h / m 3 The volume of catalyst heated to above 490°C then accounts for only 75% of one bed, which corresponds to about 25% of the total catalyst charge.

Claims

1. A method of operating a reactor for performing an exothermic catalytic reaction, the reactor comprising within a single pressure-resistant shell: at least two catalyst modules, the at least two catalyst modules being arranged in a stacked order with no fluid communication between the at least two catalyst modules, the total number of catalyst modules defining the number "N", and each catalyst module comprising one or more catalyst zones arranged in series; The method comprises: i) at normal load, which is defined by the continuous operation of the reactor, wherein the process gas led through varies with a margin of ±15% relative to the design value of the reactor: supplying a process gas stream by directing all or a portion of the process gas through a number "n" of catalyst modules, wherein "n" is equal to or less than "N" (n≤N); and ii) under a variable load, defined by a transient or continuous operation of the process gas, wherein the process gas directed through varies with a margin exceeding ±15% relative to the design value of the reactor, interrupting or allowing the flow of process gas into at least one catalyst module by: ii-1) supplying a process gas stream by directing all or a portion of the process gas through a number "m" of catalyst modules, where "m" is less than "n" and greater than 0 (0 <m<n); or ii-2) supplying a process gas flow by directing all or a portion of the process gas through a number "m" of catalyst modules, wherein when "n" is less than "N", "m" is equal to or greater than "n" (m≥n).

2. The method according to claim 1, wherein: - after ii-i), ii-2) is performed; - when the reactor is switched from the normal load (i) to a lower load, i.e. a load lower than the normal load, ii-1) is performed; and When the reactor is switched from a lower load to the normal load (i) or high load, ii-2) is carried out, wherein the high load refers to a load that is more than 15% higher than the normal load, and when "n" is equal to or less than "N" (n≤N), "m" is equal to or greater than "n" (m≥n).

3. The method according to any one of claims 1 to 2, wherein in ii), the process gas is 5% to 115% or more of the design value of the reactor under varying loads.

4. The method according to any one of claims 1 to 3, wherein the design value of the reactor is the space velocity (SV) on the first catalyst bed of the catalyst module, and the SV is 20000-50000 Nm 3 / h / m 3 , e.g. 25000-45000Nm 3 / h / m 3 .

5. The method according to any one of claims 1 to 4, wherein the reactor is an ammonia synthesis converter and the process gas is ammonia synthesis gas.

6. The method according to any one of claims 1 to 5, wherein in i) n=N, so that in i) all of the process gas or a portion thereof is passed through all catalyst modules.

7. The method according to any one of claims 1 to 6, wherein: N=6, n=6 and m=1; or N=6, n=5 and m=1; or N=6, n=5 and m=6; or N=3, n=3, m=1.

8. The method according to any one of claims 1 to 7, wherein the process gas passes through at least two catalyst modules in an axial and / or radial flow direction; and / or at least two catalyst modules are operated in parallel.

9. The method according to any one of claims 1 to 8, wherein: - The catalytic module is operated adiabatically; or - the catalyst module is operated in a non-adiabatic manner, for example by being gas-cooled, for example by being cooled with a process gas which is led to the reactor; or - A first catalytic zone of the catalyst module is operated in a non-adiabatic manner and subsequent catalytic zones of the catalyst module arranged in series are operated in adiabatically.

10. A method for modifying an ammonia synthesis converter, the ammonia synthesis converter comprising: at least two catalyst modules arranged in a stacked order and operated in parallel, each catalyst module comprising one or more catalyst zones connected in series, the one or more catalyst zones having catalyst layers adapted for axial and / or radial flow; an outer annular space located between the at least two catalyst modules operating in parallel and the pressure housing, wherein the outer annular space is fluidly connected to the at least two catalyst modules operating in parallel; an inlet disposed within the pressure housing for directing ammonia synthesis gas through the outer annular space; an outlet arranged to receive product gas from at least two parallel catalyst modules, the outlet optionally being arranged in a space formed at the center within the at least two stacked catalyst modules; The method comprises: - one or more seals are installed in the outer annular space, the one or more seals are in direct contact with the pressure shell and one or more of the at least two catalyst modules operated in parallel, respectively; wherein a first seal is installed between the pressure shell and the first of the at least two catalyst modules in parallel, thereby defining a first outer annular space; and a second seal is installed between the pressure shell and the second of the at least two catalyst modules in parallel, thereby defining a second outer annular space; - installing a plurality of inlets for independently directing the ammonia synthesis gas through the first or second outer annular space; wherein the first inlet is arranged in fluid communication with the first outer annular space and the second inlet is arranged in fluid communication with the second outer annular space.

11. The method of claim 10, comprising installing one or more seals at the top of first and second of at least two catalyst modules operating in parallel.

12. The method according to any one of claims 10-11, wherein the seal is an annular plate.

13. An ammonia synthesis converter (10), comprising: - at least two catalyst modules (12', 12", 12'") arranged in a stacked order and operated in parallel, each catalyst module comprising one or more catalyst zones connected in series, the one or more catalyst zones having catalyst layers suitable for axial and / or radial flow; - an outer annular space (22, 22', 22", 22'") located between at least two catalyst modules (12', 12", 12'") operated in parallel and the pressure-resistant housing (16), wherein the outer annular space (22, 22', 22", 22'") is fluidically connected to the at least two catalyst modules (12', 12", 12'") operated in parallel; - one or more seals (14', 14", 14'"), which are arranged in the outer annular space (22, 22', 22", 22'"), the one or more seals (14', 14", 14'") being in direct contact with the pressure shell (16) and one or more of the at least two catalyst modules (12', 12", 12'") operated in parallel, respectively; wherein the first seal (14') is arranged between the pressure shell (16) and the first (12') of the at least two parallel catalyst modules, thereby defining a first outer annular space (22'); and the second seal (14") is arranged between the pressure shell (16) and the second (12") of the at least two parallel catalyst modules, thereby defining a second outer annular space (22"); a plurality of inlets (18', 18", 18'"') for independently directing the ammonia synthesis gas (1, 3) through the first (22') or second (22") outer annular space; wherein the first inlet (18') is arranged in direct fluid communication with the first (22') outer annular space and the second inlet (18") is arranged in fluid communication with the second (22") outer annular space; an outlet (24) for receiving product gas (5', 5", 5'", 5'"', 5'"') from one or more of the at least two parallel catalyst modules (12', 12", 12'"); iv ).

14. An ammonia synthesis converter (10) according to claim 13, wherein the outlet (24) is arranged in a space formed at the center within at least two stacked catalyst modules (12', 12", 12'").

15. An ammonia converter (10) according to any one of claims 13-14, wherein the one or more seals (14', 14", 14'") are annular plates and are arranged on top of the first and second of at least two catalyst modules (12', 12", 12'") operated in parallel.

16. The ammonia synthesis converter (10) according to any one of claims 13 to 15, further comprising: - a cover which closes at least two catalyst modules (12', 12", 12'") operating in parallel; - an intra-bed heat exchanger for cooling the catalyst layer in at least one catalyst zone, thereby defining at least one cooled catalyst zone; the intra-bed heat exchanger comprising an inlet and an outlet; as well as In at least one cooled catalyst zone, the ammonia synthesis converter comprises a feed device for directing the ammonia synthesis gas to the inlet of an intra-bed heat exchanger, wherein the inlet fluid of the intra-bed heat exchanger is connected to the first (22') outer annular space or the second (22') outer annular space; the outlet of the intra-bed heat exchanger is optionally fluidly connected to a feed device such as a pipeline for directing the thus preheated ammonia synthesis gas together with fresh ammonia synthesis gas to the inlet of at least one catalyst zone.

17. An ammonia converter according to any one of claims 13 to 16, wherein at least one of the catalyst zones in series is an adiabatic catalyst zone, and wherein a single cooled catalyst zone is connected in series with a single adiabatic catalyst zone.

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