Method and system for producing a process product

Abstract

The invention relates to a method (200) for producing a process product in which a reactant mixture (1) is fed to a reactor (10) and reacted in the reactor (10) in an exothermic reaction having an activation energy, the method comprising a start-up operation (210) in which at least part of the activation energy is provided using one or more start-up heaters (17), wherein the method comprises a production operation (220) carried out after the start-up operation (210), in which at least part of the activation energy is provided using thermal energy generated in the exothermic reaction, and wherein a load is reduced (222) during the production operation (220), in which an amount of the process product produced per unit time in the reactor (10) is reduced. According to the invention, the start-up heater (17) or at least one of the plurality of start-up heaters (17) is operated during the load reduction (222). The invention also relates to a corresponding system (100).

Description

[0001] Description

[0002] Process and plant for the production of a process product

[0003] The present invention relates to a process and a plant for producing a process product, in particular ammonia, according to the preambles of the independent patent claims.

[0004] background

[0005] In order to reduce greenhouse gas emissions and dependence on fossil fuels in the long term, renewable energy sources are advantageously used for the production of energy and various chemicals.

[0006] In contrast to conventional or fossil fuels such as natural gas, liquid hydrocarbons, and coal, these energy sources, especially solar and wind energy, are notoriously subject to hourly, daily, and seasonal fluctuations in availability. Therefore, processes powered by such renewable energy sources must be able to follow these fluctuations to a certain extent or have extensive means of energy storage, for example, in the form of electrochemical or hydrogen storage. In general, the more flexible a process is, the less storage is required, which can improve the process's economic performance.

[0007] Although the present invention is explained below mainly with reference to ammonia synthesis, its embodiments are also suitable for other processes and plants for the production of process products in which comparable problems occur, in particular for exothermic reactions in corresponding reactors.

[0008] There is a need for improvements in corresponding processes and systems, particularly with regard to more flexible operation using fluctuating energy sources. Disclosure of the invention

[0009] Against this background, a method and a system with the respective features of the independent patent claims are proposed. Further embodiments are the subject of the dependent claims and the following description.

[0010] The proposed process serves to produce a process product and comprises feeding a reactant mixture to a reactor and reacting it in the reactor in an exothermic reaction with an activation energy, wherein the process comprises a start-up operation in which at least part of the activation energy is provided using one or more start-up heaters (hereinafter, only for the sake of simplicity, "a" start-up heater is sometimes referred to in the singular), wherein the process comprises a production operation carried out after the start-up operation in which at least part of the activation energy is provided using thermal energy which is generated during the exothermic reaction, and wherein a load reduction, i.e. a reduction in the amount of process product produced per unit time in the reactor, is carried out during the production operation.It is proposed that the start-up heater or at least one of the several start-up heaters be operated during load reduction.

[0011] The amount of process product produced can be reduced, for example, by reducing the reactant mixture fed to the reactor. The same amount of reactant mixture can also be fed in, but less reacted (e.g., by increasing the temperature). Unreacted reactants can then be recycled to the reactor in a cycle. In this case, less reactant mixture is fed to the cycle, but not to the reactor itself.

[0012] As mentioned, the process can be used in the production of ammonia, but is not limited to this. The following explanations are therefore for illustrative purposes only.

[0013] Large-scale ammonia synthesis in Haber-Bosch cycles is both efficient and cost-effective. Various designs exist, including the so-called Linde ammonia concept, which uses high-purity hydrogen and nitrogen. In most conventional plants, ammonia formation takes place in a reactor consisting of several adiabatic catalyst beds, between which the respective material streams are cooled by mixing with fresh feed or by indirect heat exchange.

[0014] The reaction products downstream of a corresponding reactor are cooled and the ammonia is condensed and removed from the cycle, while the gaseous, unreacted reactants are returned to the reactor together with fresh feedstock.

[0015] Corresponding processes can, in principle, be operated with "green" hydrogen, i.e., hydrogen produced by water electrolysis using renewable energy sources. However, conventional ammonia plants based on a corresponding Haber-Bosch cycle can only operate at partial load to a limited extent and react only slowly to load changes, which, as mentioned above, are to be expected when using renewable energy sources.

[0016] The solution proposed here involves using a start-up heater primarily provided for start-up operation during load reduction in order to increase the load change rate of the reactor and avoid exceeding a minimum pressure in the reactor.

[0017] In this way, embodiments of the present invention can particularly address the limited load flexibility of conventional ammonia plants based on a Haber-Bosch cycle, or plants producing other process products. This limited load flexibility is therefore no longer the limiting factor for the overall flexibility of a corresponding "green" plant to the extent that it is in conventional concepts.

[0018] When shutting down the feed to the ammonia cycle, a significant pressure drop occurs in corresponding reactors. This pressure drop can be limited by changing the conditions in the reactor to reduce conversion. Such changes can also include changes in the reactor temperature. When the reactor temperature is increased, the reaction equilibrium allows for less ammonia production, so that less material is discharged from the cycle in the form of liquid product and therefore less pressure reduction occurs. However, the process of increasing the reactor temperature is comparatively slow, so that during rapid shutdowns the pressure in the cycle can temporarily fall below a certain minimum value established for normal operation. The same applies to other processes using exothermic reactions.

[0019] The measures proposed within the scope of embodiments of the present invention, however, enable significantly faster load changes.

[0020] The term "start-up heater" is used here in the usual sense. For example, in this context, and especially regarding applicable start-up heaters, reference can be made to articles such as Rasmussen, CV, "Converter start-up heater: electric or fired?", Nitrogen 194: 30-35, 1991. For the sake of completeness, the function of start-up heaters will be briefly discussed below.

[0021] Ammonia production plants typically operate for long periods without shutdown near their optimal operating point. Nevertheless, special devices in the form of start-up heaters are installed for the few start-up operations that occur during the lifetime of a plant. For example, US 2011 / 123404 A1 proposes the use of an electric start-up heater in the pressure jacket of an ammonia reactor.

[0022] The ammonia synthesis reaction, in which nitrogen and hydrogen react in the presence of a catalyst, is exothermic and self-sustaining. However, the reaction can only start at elevated temperatures. When starting up an ammonia plant from a cold state, the ammonia reactor and its catalyst mass must therefore be preheated by appropriate start-up heaters. During each start-up or reheating, the heater is in continuous operation for an extended period. During normal operation, it is shut down in conventional processes. The most commonly used start-up heater is the direct-fired type, but electric heaters are also used. The measures proposed here can include reducing a load from a first operating point to a second operating point during production mode. When using a reactor with multiple catalyst beds, the feed temperature of at least the last catalyst bed is increased.In certain embodiments, it may also be provided to increase the flow temperatures of all catalyst beds downstream of a respective intercooler during load changes. This temperature increase is achieved at least partially by the use of the start-up heater. Thus, in corresponding embodiments, the reactor may have several reaction beds arranged in series, with heat transfer or a portion of the heat transfer taking place downstream of one or more of these reaction beds. A change in the amount of heat transferred during heat transfer can be made during load reduction. In this way, a controlled and targeted influence can be achieved.

[0023] A temperature of the gas leaving the reactor can be increased by directing a larger portion of the feed to one or more intercoolers or feed-effluent heat exchangers, thereby reducing the intercooling or final cooling.

[0024] At part load, reaction equilibrium is reached or nearly reached due to the reduced flow rate in the reactor. The higher the equilibrium temperature, the less ammonia is present at equilibrium conditions. Therefore, increasing the outlet temperature of the last catalyst bed reduces the ammonia content in the reactor effluent. This, in turn, reduces the amount of material discharged from the loop, thus helping to maintain a higher loop pressure than would otherwise be possible.

[0025] One way to increase the outlet temperature of the last catalyst bed is to reduce intercooling. In an extreme case, intercooling is eliminated altogether, and the existing catalyst beds act as a single unit.

[0026] In embodiments of the invention, provision of at least one component of the reactant mixture, in the case of ammonia synthesis in particular hydrogen, can be provided using renewably generated electrical energy from an isolated grid in which an energy generation unit for the renewably generated electrical energy is provided. The load reduction can then be carried out when the amount of renewably generated electrical energy decreases or falls below a predetermined threshold. The term "isolated grid" refers to an electrical grid that is not connected to a supra-regional, transnational, or transcontinental power grid, so that only the electrical energy provided by the energy generation unit, for example comprising one or more photovoltaic or wind turbines, must be used. An isolated grid does not necessarily have to have further components in addition to the components mentioned.

[0027] In alternative embodiments, at least one component of the reactant mixture can be provided using electrical energy from a long-distance grid, with the load reduction being implemented when the availability of electrical energy decreases and / or the price of electrical energy rises above a predetermined threshold. The "long-distance grid" can, in particular, be a supra-regional, transnational, or transcontinental power grid that comprises a plurality of energy generation facilities, in particular of different types, and a plurality of consumers, e.g., industrial facilities, residential buildings, office buildings, electromobility facilities, etc.

[0028] In embodiments, the operation of the start-up heater or at least one of the plurality of start-up heaters can be carried out, in particular, on the basis of one or more variables detected in the method. In this way, an adaptive adjustment of the output of the start-up heater(s) can take place. A corresponding variable detected in the method or at least one of the plurality of variables detected in the method can comprise one or more pressure values ​​in the reactor, so that a pressure drop can be directly counteracted. In addition, in embodiments of the invention, it can be provided and advantageous to detect one or more temperature values, specifically in the reactor beds, in the streams leaving the reactor beds, and / or in the streams entering the reactor beds, wherein in particular an exit stream of the last bed and an inlet stream of the first bed provide meaningful values.In embodiments of the proposed method, the provision of at least part of the activation energy in the production operation can comprise an adjustable heat transfer from one or more material streams formed using the reactor to the reactant mixture and / or to one or more partial streams of the reactant mixture.

[0029] In embodiments of the invention, the start-up heater can be installed inside or outside a pressure jacket of the reactor. The heat can be generated electrically or by the combustion of a fuel, e.g., natural gas, ammonia, or hydrogen. Alternatively, the heat can be extracted from a heat storage device, e.g., a molten salt storage device, which has been previously charged with electricity, one of the aforementioned fuels, the heat released in the ammonia reactor, or a combination thereof.

[0030] The provision of at least part of the activation energy during start-up operation and during the other operating phases of the start-up heater can comprise adjustable heating of the reactant mixture and / or one or more partial streams of the reactant mixture. The start-up heater can be fed with preheated or fresh feedstock.

[0031] Within the scope of embodiments of the invention, one or more additional adjustable operating parameters of the process can be changed during load reduction. The one or more operating parameters can be or include a speed of a cycle compressor and / or an operating parameter of a valve or other blocking device arranged in parallel with the cycle compressor. The invention can thus be combined with other advanced control methods that are not available in conventional Haber-Bosch cycles.

[0032] For example, the pressure can be regulated within limits by changing the speed of the cycle compressor in the Haber-Bosch cycle or by switching a valve in a line parallel to the cycle compressor. However, this alone does not necessarily allow the pressure to be kept within the permissible range without violating other operational constraints. However, such measures can be useful for fine-tuning the pressure near the desired operating point.

[0033] Embodiments of the proposed process can be used to produce ammonia, methane or methanol as process product.

[0034] The reactor system described above is exemplary, and the basic concept of the invention can be applied to other reactor types. Thus, in addition to ammonia synthesis, the invention can also be used in other chemical processes involving equilibrium-limited exothermic reactions. These include, for example, methanol and methane synthesis.

[0035] In addition to using the start-up heater to reduce load, in further embodiments of the invention it can also be used to expand the process's load range. Continuous operation of the start-up heater at low load allows for a lower partial load due to the higher equilibrium temperature at the reactor outlet.

[0036] In addition to a start-up heater that directly heats the reactor inlet, a heat buffer system that stores electrical energy in the form of heat can also be used. To achieve the required inlet temperature, systems with thermal oil or molten salt, for example, can be used. In this case, the heat in these systems can be stored during periods of low electricity costs and released during phases of low ammonia production when electrolysis is costly or impossible.

[0037] The advantages of using start-up heating during load changes in an ammonia plant include an increase in the achievable load change rate by reducing pressure fluctuations and the addition of a control variable for reactor control.

[0038] The proposed plant for producing a process product has a reactor and a start-up heater and is designed to feed a reactant mixture to the reactor and to react it in the reactor in an exothermic reaction with an activation energy, to carry out a start-up operation in which at least part of the activation energy is provided using one or more start-up heaters, and after the start-up operation to carry out a production operation in which at least part of the activation energy is provided using thermal energy generated in the exothermic reaction, and to carry out a load reduction during the production operation in which a reduction in the amount of process product formed in the reactor per unit time is carried out.It is intended that the system is designed to operate the start-up heater or at least one of the several start-up heaters during load reduction.

[0039] For further features and advantages of a corresponding system and embodiments thereof, reference is expressly made to the above explanations concerning the method proposed according to the invention and its embodiments, since these apply equally to this.

[0040] The same applies to a system which, according to an embodiment of the invention, is designed to carry out a method according to any embodiment of the present invention.

[0041] Short description of the drawing

[0042] Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings, in which

[0043] Figure 1 illustrates a plant for the production of ammonia,

[0044] Figure 2 illustrates aspects of a method not according to the invention,

[0045] Figure 3 illustrates aspects of a method according to one embodiment, and

[0046] Figure 4 illustrates a method according to one embodiment.

[0047] Embodiments of the Invention The embodiments described below are provided solely for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting with regard to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures and / or other aspects described above and below are not to be considered as limitations on the scope of the invention as defined in the claims or as limitations of equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention.

[0048] Different embodiments of the invention may include, comprise, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein. Furthermore, the disclosure may encompass other inventions that are not currently claimed but that may be claimed in the future, particularly if they are encompassed within the scope of the independent claims.

[0049] Explanations relating to devices, apparatus, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to the embodiments of the present invention, and vice versa. Elements, method steps, etc. that are identical, have the same effect, are functionally equivalent, are structurally identical, or are comparable may be identified by identical reference numerals.

[0050] The present invention and embodiments thereof are explained below with reference to ammonia synthesis. However, as mentioned several times, the invention is not limited to this.

[0051] Figure 1 shows a plant for producing ammonia, which may form the basis of an embodiment of the invention, and is designated overall by 100. Plant 100 comprises a reactor 10, which in the example shown has three catalytic beds 11, 12, 13, downstream of which intermediate or aftercoolers 14, 15, 16 are arranged. Furthermore, a start-up heater 17 is provided. Reactor 10 is suitable for operation at low partial load.

[0052] A reactant mixture 1 is fed to the reactor 10, which is divided into partial streams 1a, 1b, 1c via a valve arrangement not specifically designated.

[0053] Aftercoolers 14, 15, 16 are supplied. Bypasses 1d, 1e can be provided in any manner, and a remaining residue 1f of the reactant mixture 1 can be supplied to the start-up heater 17. The example illustrated here does not limit the invention, and any desired connections can be provided.

[0054] The feed mixture is again designated 1 at the point where it is recombined and fed to the first catalyst bed 11. Its temperature at this point depends on the conditions in the intercoolers and aftercoolers 14, 15, 16 and the corresponding distribution between them and the operation and supply of the start-up heater 17.

[0055] Figure 1 shows that the effluent from the start-up heater 17 is fed directly into the first catalyst bed 11 without further indirect heat exchange. Alternatively, the corresponding reactant mixture can pass through one or more intercoolers before entering one of the catalyst beds 11, 12, 13. A product mixture flowing out of the reactor 10 is designated by 2, and the respective intermediate streams upstream of the intercoolers or aftercoolers 14, 15, 16 are indicated by 2a, 2b, 2c, respectively.

[0056] Figure 2 illustrates aspects of a process not according to the invention in the form of a diagram in which a time in seconds is indicated on the horizontal axis, a mass flow of hydrogen used in kg / h on a vertical axis 101, a temperature in °C on a second vertical axis 102, and a pressure in kPa on a third vertical axis 103. The corresponding values ​​shown are obtained, for example, in the system 100 according to Figure 1.

[0057] 104 represents a temperature downstream of the first catalyst bed 11, 105 a temperature downstream of the second catalyst bed 12, and 106 a temperature downstream of the third catalyst bed 13. A pressure in the reactor 10 or a corresponding circuit is indicated by 107, a permissible minimum pressure by 108, and the mass flow of hydrogen by 109.

[0058] Figure 2 thus illustrates the relative temperature profiles of the three catalyst beds 11, 12, 13 shown, for example, in Figure 1 for a selected load reduction process without the use of a start-up heater. As can be seen from the bed temperatures, it can be seen that the desired state of high outlet temperatures of the three beds is not reached within the period shown. Due to the slow temperature change, the pressure 107 temporarily drops below the marked permissible minimum pressure 108.

[0059] Figure 3 illustrates aspects of a method according to an embodiment of the invention, wherein the axes or curves 102 to 109 correspond to the axes or curves 102 to 109 already explained in relation to Figure 2. However, the first vertical axis 101a shown here also indicates a heating output of the start-up heater 17 in kW; the corresponding curve is indicated by 110.

[0060] Figure 3 illustrates the same load reduction process with the exact same hydrogen supply ramp as shown in Figure 2. In this case, however, the load change is supported by the start-up heater 17. This allows for a more favorable bed temperature profile and prevents the pressure 107 from falling below the specified minimum pressure 108.

[0061] Figure 4 illustrates a method according to one embodiment of the invention in a simplified block diagram, designated overall by 200. The corresponding method steps will now be explained again with reference to Figure 1 and the elements shown therein.

[0062] In process 200, the reactant mixture 1 is generally fed to reactor 10 and reacted in reactor 10 in an exothermic reaction with activation energy. A first process step refers to a start-up operation 210, in which at least a portion of the activation energy is provided using the start-up heater 17. Once sufficient heating has occurred and the reaction has begun, a production operation 220 can be carried out in a next step, in which at least a portion of the activation energy is provided using thermal energy.

[0063] In the production operation, operation at a first load point can occur in a first step 221. A further step comprises a load reduction 222, wherein, as proposed here, a reduction in the amount of the respective process product, in this case ammonia, formed per unit time in the reactor 10 is carried out until a second, lower load point is reached in a next step 223. During the load reduction 222, as shown in particular with reference to Figure 3, the start-up heater 17 is operated to prevent an excessive pressure drop.

Claims

Patent claims 1 . Method (200) for producing a process product, in which a reactant mixture (1) is fed to a reactor (10) and is reacted in the reactor (10) in an exothermic reaction with an activation energy, wherein the method comprises a start-up operation (210) in which at least part of the activation energy is provided using one or more start-up heaters (17), wherein the method comprises a production operation (220) carried out after the start-up operation (210), in which at least part of the activation energy is provided using thermal energy which is generated during the exothermic reaction, and wherein during the production operation (220) a load reduction (222) is carried out, in which reduction of a per unit time in the reactor (10) produced quantity of the process product, characterized in that during the load reduction (222) operation of the start-up heater (17) or at least one of the plurality of start-up heaters (17) is carried out.

2. The method (200) according to claim 1, which comprises providing at least one component of the reactant mixture (1) using regeneratively generated electrical energy from an island grid in which an energy generation unit is provided for providing the regeneratively generated electrical energy, wherein the load reduction is carried out when the regeneratively generated electrical energy decreases.

3. Method (200) according to claim 1 or 2, which comprises providing at least one component of the reactant mixture (1) using electrical energy from a long-distance network, wherein the load reduction is carried out when an availability of the electrical energy decreases and / or a price of the electrical energy rises above a predetermined threshold.

4. Method (200) according to one of the preceding claims, in which the operation of the start-up heater (17) or at least one of the plurality of start-up heaters (17) is carried out on the basis of one or more variables detected in the method (200).

5. The method (200) according to claim 4, wherein the variable detected in the method (200) or at least one of the plurality of variables detected in the method (200) comprises one or more pressure values ​​in the reactor (10) and / or one or more temperature values.

6. The method (200) according to any one of the preceding claims, wherein the provision of at least part of the activation energy in the production plant (220) comprises an adjustable heat transfer from one or more material streams (2a-2c) formed using the reactor (10) to the reactant mixture (1) and / or to one or more partial streams (1a-1f) of the reactant mixture (1).

7. The process (200) according to claim 6, wherein the reactor (10) comprises a plurality of serially arranged reaction beds (11-13), wherein the heat transfer or a portion of the heat transfer is carried out downstream of one or more of these reaction beds (11-13).

8. The method (200) of claim 6 or claim 7, wherein a change in an amount of heat transferred during heat transfer is made during load reduction (222).

9. Method (200) according to one of the preceding claims, wherein the provision of at least part of the activation energy in the start-up operation (210) comprises an adjustable heating of the reactant mixture (1) and / or one or more partial streams (1 a-1 f) of the reactant mixture (1 ).

10. Method (200) according to one of the preceding claims, in which one or more further adjustable operating parameters of the method (200) is or are changed during the load reduction (222).

11. Method (200) according to claim 10, wherein the one or more operating parameters is or comprise a speed of a cycle compressor and / or an operating parameter of a valve arranged in parallel with the cycle compressor.

12. A process (200) according to any one of the preceding claims, which is used to produce ammonia, methane or methanol as a process product.

13. Plant (100) for producing a process product, comprising a reactor (10) and a start-up heater (17), wherein the plant (100) is configured to supply a reactant mixture (1) to the reactor (10) and to react it in the reactor (10) in an exothermic reaction with an activation energy, to carry out a start-up operation (210) in which at least part of the activation energy is provided using one or more start-up heaters (17), and after the start-up operation (210), to carry out a production operation (220) in which at least part of the activation energy is provided using thermal energy generated during the exothermic reaction, and to carry out a load reduction (222) during the production operation (220), in which a reduction in the amount of the process product produced per unit time in the reactor (10) is carried out, characterized in thatthat the system (100) is designed to operate the start-up heater (17) or at least one of the plurality of start-up heaters (17) during the load reduction (222).

14. Plant (100) according to claim 11, which is arranged to carry out a method according to one of claims 1 to 10.

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