AMMONIA SYNTHESIS PLANT FOR FLUID PART-LOAD OPERATION AND METHOD FOR OPERATING AN AMMONIA SYNTHESIS PLANT

Description

[0001] The invention lies in the field of chemical plant engineering and relates to an ammonia synthesis plant with a hydrogen device configured to supply hydrogen and a synthesis cycle, wherein the synthesis cycle comprises a conveying device configured for the cyclic conveying of a gas mixture containing nitrogen, hydrogen, and ammonia in a synthesis cycle conveying direction, wherein the conveying device has a suction side and a pressure side, a converter configured for the catalytic conversion of nitrogen and hydrogen at least partially to ammonia, wherein the converter has an inlet and an outlet, wherein the inlet of the converter is fluidly connected to the pressure side of the conveying device and the outlet of the converter is fluidly connected to the suction side of the conveying device, and a first bypass line.which is arranged parallel to the conveying device in a flow-opposite direction from the suction side to the pressure side of the conveying device and which is designed for the shut-offable return of a first partial flow of the gas mixture from the pressure side of the conveying device to the suction side of the conveying device, wherein the first bypass line has a cooling device designed for cooling the first partial flow of the gas mixture.

[0002] The invention further relates to a method for operating an ammonia synthesis plant, in particular an ammonia synthesis plant of the aforementioned type, wherein a gas mixture comprising nitrogen, hydrogen and ammonia is cyclically conveyed in a synthesis cycle by a conveying device having a suction side and a pressure side, wherein nitrogen and hydrogen are supplied to the synthesis cycle and are at least partially converted to ammonia in a converter there, and wherein the gas mixture is divided downstream of the conveying device in the direction of the synthesis cycle conveying into a first partial stream and a first residual stream, of which the first residual stream is fed into the converter and of which the first partial stream is returned from the pressure side of the conveying device to the suction side of the conveying device, bypassing the converter, and is thereby at least partially cooled in a cooling device.

[0003] Ammonia is one of the most important industrial chemicals, with a global annual production of more than 150 million tons, the majority of which is used in the fertilizer industry. For over a century, ammonia has been produced on an industrial scale, primarily using the Haber-Bosch process, in which hydrogen and nitrogen react over a catalyst in a fixed-bed reactor. A challenge in producing ammonia from nitrogen lies in breaking the stable nitrogen-nitrogen triple bond in the nitrogen molecule and thus activating the nitrogen. In the Haber-Bosch process, this is achieved by using specifically active catalysts with iron as the main catalytically active component at high temperatures for activation. Simultaneously, the equilibrium of the ammonia formation reaction is shifted towards ammonia by applying high pressures.Typically, a reactor temperature of 350 °C should not be undercut to ensure a sufficient reaction rate for ammonia synthesis. The ammonia formation reaction is exothermic overall, which is why sufficient thermal energy is available during operation to maintain the required minimum temperature; rather, relatively large amounts of heat typically need to be dissipated to ensure stable operation and to prevent local overheating in the ammonia synthesis reactor, which could impair catalyst activity and damage the reactor.

[0004] Since this is an equilibrium reaction whose equilibrium does not lie on the side of the products, the reaction mixture, along with the unreacted reactant gases, is circulated in a synthesis loop using a conveying device. From this synthesis loop, the ammonia is separated, and the unreacted hydrogen and nitrogen are fed back to the catalyst within the synthesis loop. The amount of ammonia removed from the synthesis loop is replaced by a corresponding amount of hydrogen and nitrogen, which is supplied to the synthesis loop as fresh gas ("make-up gas"). Typically, the hydrogen required for the reaction is produced from natural gas, which is why a considerable amount of carbon dioxide is generated in the process.

[0005] To produce ammonia sustainably (so-called "green ammonia"), hydrogen is also obtained through methods other than converting natural gas to synthesis gas. Water splitting has become a particular focus in this context. Besides photocatalytic and solar thermal processes, hydrogen can be produced primarily through the electrolysis of water in an electrolysis device (an "electrolyzer"), with the necessary electrical energy being derived from renewable sources. However, the availability of renewable energy is not constant over time, meaning that electrical energy can only be generated in a time-varying manner.When generating electricity using wind turbines or photovoltaics, the amount of electrical energy produced typically varies due to changing wind conditions or solar radiation at different times. During periods of calm or storms, as well as at night or under cloudy skies, very little or no electrical energy may be available for extended periods. Even if the electrolyzer can quickly adapt to these fluctuations across a wide load range, it will then only provide the ammonia synthesis plant with a hydrogen flow that varies over time.

[0006] Of course, there are ways to mitigate the effects of fluctuating renewable energy availability by generating the required electricity from different renewable sources (for example, by combining a solar power plant with a wind or hydropower plant). Additional compensation can be achieved through intermediate storage of electricity by connecting the plant to conventional power grids (into which electricity generated from renewable sources is ideally fed) or by temporarily storing hydrogen in hydrogen tanks or electricity in energy storage systems.However, such approaches require considerable measures, meaning that a constant supply of green hydrogen to a large-scale ammonia synthesis plant cannot be easily achieved with economically justifiable effort.

[0007] If the available amount of hydrogen fluctuates, the utilization of the ammonia synthesis reactor changes accordingly. The available amount of hydrogen can even drop to zero, causing ammonia production in the reactor to cease (meaning the heat supply is no longer sufficient to maintain the minimum temperature required for the reaction). Without a sufficient supply of hydrogen or electrical energy (e.g., via external networks or a storage infrastructure), the ammonia synthesis plant can then only operate at partial load (partial utilization; the plant then operates at a utilization rate below 100%, i.e., lower than in regular production operation) or may even have to be temporarily operated without production (continuous standby, "hot standby").Once hydrogen production resumes, the reactor would first need to be brought back to a production-start state required for regular operation during such a partial standby mode. In conventional plants, the transition from one load state to another (e.g., from full load to partial load, from partial load to full load, or from one partial load to another) requires complex control intervention to ensure that hydrogen production continues (albeit on a smaller scale than at full load), while simultaneously preventing damage to the ammonia synthesis plant's components and allowing for a seamless transition to a different load state without a lengthy start-up process.

[0008] To enable operation under varying load conditions, adjustments must be made to different components of the ammonia synthesis plant. One of the most important plant components for adapting operation to the respective load condition is the conveying device, which cyclically conveys the gas mixture containing nitrogen, hydrogen, and ammonia within the synthesis cycle. Such a conveying device typically has a suction side and a pressure side. The gas mixture enters the conveying device on the suction side and exits on the pressure side, then is conveyed from the pressure side through the ammonia synthesis reactor back to the suction side within the synthesis cycle.

[0009] Turbocentrifugal compressors (turbo compressors) are frequently used as conveying devices. Almost all turbocentrifugal compressors are equipped with a surge control system ("anti-surge control") designed to prevent surge operation, i.e., intermittent pumping due to insufficient flow rate. This occurs when, at a specific pressure, the flow rate falls below the minimum mass flow required for the turbocentrifugal compressor's operation (thus exceeding the so-called "surge line"), resulting in flow separation due to an insufficient angle of attack at the compressor blades.As a result of these flow separations, the mass flow rate decreases further, leading to more flow separations and preventing the pressure differential between the suction and discharge sides from being maintained. Consequently, some of the gas being conveyed (in this case, the circulating gas mixture) flows back through the compressor. The pumping action caused by the repeated sequence of flow separations and internal backflow results in a reduction in the conveying performance and can also damage the compressor blades, or in the worst case, destroy the turbo centrifugal compressor.To prevent this, almost all turbocentrifugal compressors are equipped with a bypass line, i.e., an external bypass line to circumvent the turbo compressor. This bypass allows the pumped gas to flow back outside the turbocentrifugal compressor (in this case, bypassing the rest of the synthesis cycle, including the converter), thus maintaining the pressure differential between the suction and discharge sides. To achieve this, the bypass line is opened by the controlled opening of at least one bypass valve when the flow rate falls below a certain minimum threshold, and then closed again when the flow rate exceeds this minimum threshold.

[0010] In this operation, a portion of the gas flow is repeatedly recirculated from the compressor's pressure side to its suction side without passing through the rest of the synthesis cycle. As a result of the repeated compression, the gas heats up. Therefore, turbo centrifugal compressors typically also incorporate a cooler (recirculation cooler) in the bypass line, in which the gas recirculated directly from the pressure side to the suction side is cooled.

[0011] The pumping limit control arrangement used in many pumping devices can also be employed to implement control under varying load conditions in an ammonia synthesis plant. Typical applications of pumping limit control arrangements for regulating conventional ammonia synthesis plants include the start-up and sudden shutdown of the plant: During this process, the bypass line is opened as wide as possible, allowing almost all of the gas circulating in the synthesis cycle to bypass the converter and be routed directly from the pressure side of the pumping device to the suction side. The repeated compression of the entire gas volume within the pumping device increases the gas temperature.To prevent the gas temperature from increasing excessively ("oscillating"), the gas flow recirculated through the bypass line is cooled by water in the bypass line's cooler. Recirculating all the gas used in the synthesis cycle is therefore one of the most important applications for a bypass line in ammonia synthesis plants, which is why its components are typically designed specifically for this application. For example, the cooling capacity of the cooler in the bypass line is designed for an operating condition where the volumetric flow rate at the inlet of the conveying device corresponds approximately to the total mass flow rate during normal operation (i.e., regular operation, i.e., production operation at full capacity).In contrast, a conventional pumping limit control typically stipulates that the minimum flow rate to prevent pumping is 85% of the maximum possible flow rate - if this limit is undershot, the bypass line is opened.

[0012] If the controlled bypass line of the pumping limit control arrangement of a conventional pumping device is used to regulate different loads in ammonia synthesis plants, several disadvantages arise, which would prevent the regulation of different load states from functioning without further adjustments. This is due, among other things, to the fact that with pumping limit control, a bypass operation is initiated even with relatively small deviations from the maximum possible flow rate (typically at a flow rate that is less than 85%-90% of the maximum possible flow rate), which means that, with a classic pumping limit control, the partial gas flow that is recirculated via the bypass line is relatively small.The situation is different when bypassing a converter using a bypass line in the synthesis cycle of an ammonia synthesis plant, particularly when partial-load operation is required: The commissioning and sudden shutdown of the ammonia synthesis plant is a typical use case where the bypass line is opened. However, in this scenario, not just a small portion of the extracted gas flow is recirculated; the entire gas flow can be recirculated. Even if such operation were implemented, the bypass device would not be readily suitable for partial-load operation: The surge control is typically designed to maintain a maximum flow rate, i.e., operation as close as possible to full load, a "normal production operation."If the hydrogen required for ammonia synthesis is produced using renewable energies, the availability of this feedstock can fluctuate considerably. Therefore, to achieve stable operation, the plant must be capable of operating at any partial load. Depending on the required utilization rate, the plant must be able to recycle any portion of the cycled gas flow (synthesis cycle flow, synthesis cycle gas flow, i.e., the gas flow circulated in the synthesis cycle) – from 100% of the cycled gas flow during commissioning or shutdown to almost 0% of the cycled gas flow during regular operation with only a slightly reduced hydrogen feed-in.

[0013] At low partial loads (plant partial loads), only a small portion of the hydrogen is converted compared to full load (plant full load). Therefore, a relatively large portion of the recirculated gas flow is bypassed, bypassing the converter, and routed directly from the pressure side of the pumping device back to the suction side. This portion of the recirculated gas flow bypasses not only the converter but also the ammonia removal device – an ammonia separator in which, during normal operation, ammonia is removed from the recirculated gas, typically by condensation. If, during normal operation, some (or all) of the ammonia is discharged from the ammonia synthesis plant as a target product, further ammonia is then produced in the converter due to the re-established chemical equilibrium, in accordance with the law of mass action.However, during partial load operation, insufficient hydrogen is often available, necessitating a reduction in ammonia production and thus the removal of little or no ammonia from the cycle. Consequently, during partial load operation, the circulating gas introduced into the pumping device on the suction side has a relatively high ammonia content (often more than 20% by volume). If the circulating gas, recirculated via the bypass line, is then cooled in the recirculation cooler, it may condense outside the ammonia extraction device and be introduced into the pumping device in liquid form. Further ammonia can then condense during the compression of the circulating gas in the pumping device (while ammonia liquefaction only occurs below -33 °C under normal conditions, ammonia is already liquid at a pressure of 10 bar and a temperature of +20 °C).This can ultimately lead to damage to the conveying device. Therefore, it is desirable that ammonia is not present in liquid form within the conveying device, especially not at the inlet, i.e., on its suction side.

[0014] Stable operation is hampered by the fact that the cooler in the bypass line is designed for a cooling capacity sufficient to cool 100% of the circulated gas flow, since the entire circulated gas flow is returned via the bypass line during start-up or shutdown. During partial load operation, only a portion of the total circulated gas flow is returned, and this portion is then cooled more than necessary due to the cooler's higher cooling capacity (designed for a higher throughput). This results in (more) ammonia condensation, particularly at low partial loads with higher ammonia partial pressures.

[0015] For use in plants for the climate-neutral production of ammonia ("green ammonia plant" / plant for the production of "green ammonia" / "green ammonia synthesis"), the following optimization aspects must also be taken into account in order to be able to use the system originally intended for pumping limit control to stabilize the operation of such plants, although these aspects are not relevant for pumping limit control in conventional plants: Even at low partial loads in the plant, the flow rate in the conveying device should, on the one hand, be as close as possible to a value of 85-90% of the nominal flow rate for regular operation at full load, since a higher value would require unnecessarily large amounts of energy to operate the conveying device. On the other hand, the minimum value of 85% of the nominal flow rate for regular operation should not be undercut at full load to ensure plant safety. Typically, devices for adjusting the gas temperature of the circulating gas, such as heat exchangers (e.g., gas-to-gas heat exchangers) and heating units (e.g., electric heating units), are located downstream of the conveying device in the synthesis cycle.In heat exchangers, heat is transferred internally from a primary heat transfer medium (the circulating gas) to a secondary heat transfer medium (the heat exchanger fluid), allowing the thermal energy to be utilized in the synthesis cycle. Heating units warm any circulating gas that has cooled in the synthesis cycle, if necessary. To minimize the amount of heat required by the heating units, the outlet temperature of the gas stream on the pressure side of the conveying device should be as high as possible. Conventional conveying devices are typically designed for an outlet temperature of 200 °C. If this temperature needs to be exceeded, conventional conveying devices cannot be used; instead, custom-made solutions would be required, which would be disadvantageous because such solutions are not only expensive but would also generally require one-off designs for which no reference designs exist.For conventional conveying systems, the outlet temperature should not exceed 170 °C during normal operation, taking into account a safety margin of 30 °C to ensure safe and stable system operation.

[0016] US Patent 2022 / 388854 A1 discloses a plant and a process for the production of ammonia. The plant comprises a synthesis cycle (5) containing a conveying device (6), a bypass line (15), an ammonia reactor (7), and an ammonia separator (13). The bypass line (15) includes a control valve (17), a control unit (18), and a cooler (16). The bypass line (15) runs parallel to the conveying device (6) in the opposite direction. Hydrogen is produced electrolytically using renewable energy. The process includes the production of ammonia. During partial load operation, synthesis gas is at least partially fed downstream of the conveying device into the bypass line, cooled, and then fed back upstream of the conveying device. A bypass line with a further bypass line for at least partially bypassing the cooler of the first bypass line is not disclosed.

[0017] The object of the invention is therefore to provide a method and a device which avoids the above disadvantages and which in particular enables stable operation at different partial loads without significant condensation of ammonia at low partial loads.

[0018] This problem is solved by the ammonia synthesis plant with the features specified in claim 1 and by the method for operating an ammonia synthesis plant with the features specified in claim 8. Advantageous embodiments are described in the dependent claims, the following description, and the drawings.

[0019] Such an ammonia synthesis plant is therefore characterized by the fact that the first bypass line also has a second bypass line, which is arranged parallel to the cooling device in a flow-technical manner and which is equipped to allow a second partial flow of the first partial flow to be shut off in order to bypass the cooling device.

[0020] An ammonia synthesis plant is a facility designed to produce ammonia from hydrogen and nitrogen. Such a plant features a synthesis cycle, meaning a section that is at least partially designed to allow the reaction mixture to circulate cyclically and is configured for the synthesis of ammonia to take place within this cycle. A key functional element of the synthesis cycle is a converter (ammonia converter, reactor, synthesis reactor, ammonia synthesis reactor) configured for the catalytic conversion of nitrogen and hydrogen, at least partially, to ammonia, typically via the Haber-Bosch process. In the Haber-Bosch process, the reaction is typically carried out in the presence of an iron catalyst at temperatures ranging from approximately 350 °C to approximately 500 °C and at pressures exceeding 100 bar, according to the reaction equation 3 H₂ + N₂ The reaction is carried out with 2 NH3 + 92.28 kJ / mol. The circulating gas mixture consists mainly of nitrogen, hydrogen, and ammonia, but may also contain other components. It is introduced into the converter via an inlet, comes into contact with the catalyst, and is discharged from the converter via an outlet. During production (especially at 100% capacity), the discharged gas mixture has a higher ammonia content than the incoming gas mixture (and consequently a lower nitrogen and hydrogen content).

[0021] In the synthesis cycle, the gas mixture is circulated (cyclically conveyed) by a conveying device. This conveying device is a compressor, designed and positioned to cyclically convey the gas mixture in a single direction within the synthesis cycle. Conveying occurs through pressure differentials created by the conveying device. Therefore, the conveying device has a suction side and a pressure side. The suction side draws the gas mixture from the synthesis cycle, and the pressure side returns it to the cycle. For this purpose, the converter inlet is fluidically connected to the pressure side of the conveying device, and the converter outlet is fluidically connected to the suction side."Fluidally connected" means that there is a flowable connection between the pressure side of the conveying device and the inlet of the converter or between the outlet of the converter and the suction side of the conveying device, whereby it is not excluded that this connection in the flowable path (conveying path) in between can be diverted or otherwise regulated or even shut off via separate elements.

[0022] Downstream of the converter (the terms "downstream" and "upstream" refer here to the direction of flow in the synthesis cycle, i.e., the direction of flow of the gas mixture within the synthesis cycle and / or, if applicable, within any bypass lines), ammonia is removed from the synthesis cycle in an ammonia removal device during production (especially during operation at full load, i.e., at a capacity of 100% or close to 100%). This is typically done cryogenically as part of a low-temperature air separation process in which the gas mixture is cooled, allowing ammonia to condense out in liquid form and be separated from the gas stream. However, other selective gas separation methods are also possible, such as pressure swing adsorption.Downstream or in the ammonia extraction device, reactants (especially hydrogen and nitrogen) are added to the gas stream in the synthesis cycle via a reactant feed (as fresh gas) before the gas stream is reintroduced into the converter.

[0023] In addition to the reactant feed, conveying device, converter and ammonia extraction device, the synthesis cycle may include other elements, such as cooling devices for cooling the gas mixture after it has been heated as a result of the heat generated during the reaction (in particular coolers, waste heat steam generators or steam superheaters), heating devices to heat the gas mixture upstream of the converter to a temperature required to ensure the conversion of the reactants to the product ammonia in the converter (in particular electric heating devices) and / or combined heating / cooling devices to use excess heat energy of the gas mixture after exiting the converter to heat the gas mixture before it enters the converter (in particular gas-gas heat exchangers).

[0024] The reactant nitrogen is introduced into the synthesis cycle via a nitrogen device, in which nitrogen is typically obtained from the air, for example in a chemical or cryogenic treatment of air (for example by fractional cryogenic separation as part of a low-temperature air separation) or by selective adsorption (for example as part of a pressure swing adsorption).

[0025] The hydrogen reactant is obtained from a hydrogen generator, a device specifically designed and configured to supply hydrogen. Such a hydrogen generator serves as a hydrogen source, providing the hydrogen reactant for the reaction to form ammonia. Molecular hydrogen is introduced into the synthesis cycle via the hydrogen generator.Typical hydrogen devices may include devices for supplying hydrogen, which is then produced in the hydrogen device itself (e.g., in reactors for coal gasification, steam reforming, autothermal reforming, partial oxidation, electrolysis, pyrolysis, production from biomass, and the like), or devices for supplying hydrogen that is produced elsewhere (e.g., hydrogen pipelines connecting the ammonia synthesis plant to a hydrogen supply network, synthesis gas pipelines, hydrogen tanks, and the like).

[0026] A bypass line, the first bypass line, is provided at the conveying device. This first bypass line is arranged parallel to the conveying device, flowing in the opposite direction from the suction side to the pressure side, and is designed to allow a first partial flow of the gas mixture to be returned from the pressure side to the suction side of the conveying device, and can be shut off. This return flow is the routing of at least part or all of the gas flow from the pressure side to the suction side of the conveying device, bypassing the other functional elements of the synthesis cycle, with the exception of the conveying device itself.(i.e., most of those components of the synthesis cycle, such as the converter or any ammonia extraction device, which, unlike pipelines, branches, and the like, are intended and set up for more than just the transport of the gas flow and / or, unlike sensor devices, flow control devices such as valves and / or other shut-off devices, and the like, for more than just monitoring and / or regulating the flow of the gas flow)."Lockable return flow" refers specifically to a return flow via at least one (return) line that is designed to be partially locked (and thus partially unlocked or open / continuous) or fully locked, either manually or by a control device. Locking the line restricts the return flow of the fluid passing through it in the fully open state to a specific fraction (in the partially locked state, and therefore partially open, with the fraction depending on the degree of partial locking) or prevents / blocks the return flow altogether (in the fully locked state).

[0027] Thus, the first bypass line is designed to run parallel to the conveying device in a flow direction opposite to that of the conveying device (so that the gas flow passing through it has a flow direction that is opposite to the flow direction of the parallel pipe section between the suction side and pressure side of the conveying device), but at the same time the first bypass line is also arranged parallel to the other functional elements of the synthesis cycle (i.e. the converter and any ammonia extraction device) with the exception of the conveying device.This makes it possible for at least a partial flow or the entire gas flow to bypass the functional elements of the synthesis cycle by opening the first bypass line. These functional elements are located downstream of the pressure side of the conveying device and simultaneously upstream of the suction side of the conveying device (so that those functional elements of the synthesis cycle are bypassed which are located between the branch point of the first bypass line on the pressure side of the conveying device and the branch point of the first bypass line on the suction side of the conveying device).

[0028] The arrangement of a first element "flow-inversely parallel" to a second element means that the first element (here the first bypass line) is arranged parallel to the second element (here the conveying device) in the flow diagram, but that the first element is subjected to flow in the opposite direction compared to the second element (here the first bypass line is subjected to flow from the pressure side of the conveying direction to the suction side of the conveying direction, while the conveying device itself is subjected to flow internally from its suction side to its pressure side).Therefore, the first bypass line is set up to bypass the other functional elements of the synthesis cycle from the pressure side of the conveying device (here, the other functional elements of the synthesis cycle with the exception of the conveying device) and thus direct the gas flow from the pressure side of the conveying device to the suction side of the conveying device in order to realize operation at different partial loads.The arrangement of a first element "flow-technically parallel" to a second element therefore means that the first element (here the first bypass line) is arranged in the flow diagram parallel to the second element (here the remaining functional elements of the synthesis cycle with the exception of the conveying device), whereby the first element is subjected to the same flow direction as the second element, thus resulting in a uniform arrangement of the general flow paths through the conveying device and the general flow paths through the remaining functional elements of the synthesis cycle, each with the same general flow direction, so that a partial flow of the total gas flow is directed through the conveying device and another partial flow of the total gas flow through the remaining functional elements of the synthesis cycle.This does not preclude the possibility that the first bypass line intended for such a bypass may itself have further functional elements, for example a cooling device, which is specifically designed to stabilize the transport of the gas flow from the pressure side of the conveying direction to the suction side of the conveying direction.

[0029] The first bypass line includes a cooling device designed to cool the initial partial flow of the gas mixture. This cooling device is intended, in particular, to prevent the gas flow returned via the first bypass line from heating up due to successive compression in the conveying device. This cooling device can be any type of device designed to dissipate heat from the gas flow, such as gas coolers, liquid coolers, heat exchangers (including those for direct, semi-direct, or indirect heat transfer), recuperators, regenerators (e.g., plate coolers, tube heat exchangers, shell and tube heat exchangers), and the like. The cooling device of the bypass line is designed as a section of the entire bypass line; therefore, from a fluid dynamics perspective, it is arranged in series with the rest of the bypass line (sequentially, in series, or interlocked).With regard to cooling capacity, the cooling device of the first bypass line is preferably dimensioned for the expected gas flow under maximum full load of the entire plant, so that consequently up to 100% of the circulating gas volume can be recirculated and cooled during normal operation (i.e. for continuous "hot standby" operation, in which the temperature in the plant is largely maintained). In In this configuration, a complete shutdown would only represent a special case with 100% of the circulating gas volume.

[0030] According to the invention, the first bypass line further comprises a second bypass line, which is arranged parallel to the cooling device in a flow-consistent manner and which is configured to allow a second partial flow of the first partial flow to bypass the cooling device in a way that can be shut off. The "shut-off flow" refers in particular to a flow through at least one line that is configured to be partially shut off (and accordingly also partially open or open / continuous) or to be completely shut off, for example manually or by a control arrangement provided for this purpose.Opening the bypass line either allows a certain amount of fluid, which would not pass through the line when fully closed, to pass through (in the partially open state, and thus in the partially closed state, the amount of which depends on the degree of opening) or prevents / blocks the flow (in the fully closed state). Functionally, the second bypass line constitutes part of the first bypass line even if it is structurally separate from it.

[0031] Thus, the second bypass line is arranged parallel to the cooling device in terms of flow direction, making it possible for at least a portion or all of the gas flow to be diverted around the cooling device by opening the second bypass line (i.e., bypassing the cooling device). According to the present invention, such a second bypass line can also be arranged parallel to the entire length of the first bypass line in terms of flow direction, without branching off directly from the first bypass line.

[0032] It is particularly advantageous if the first and second bypass lines and their control arrangement, which controls or regulates the passage and shut-off of the first and second bypass lines, are set up and adapted in such a way that the volume flow on the suction side of the conveying device has a minimum value of 85% of the maximum volume flow (design flow) and does not fall below this value.Additionally or alternatively, it can be advantageous if the outlet temperature of the gas stream on the pressure side of the conveying device does not exceed a maximum value of 170 °C. However, with regard to the overall heat and energy balance of the synthesis cycle, this temperature should be as high as possible during hot standby operation so that any heating units have to supply only minimal additional heat energy to the system. A maximum value of 170 °C provides a sufficiently large safety margin against short-term temperature fluctuations for conventional compressors, which are often designed for gas with a maximum inlet temperature of 200 °C. More specific details regarding these control conditions for the system are described in the process description.

[0033] In an advantageous embodiment of the ammonia synthesis plant according to the invention, it is particularly provided that the first bypass line is arranged such that it fluidly connects a section of the synthesis circuit, which is located downstream of the at least one conveying device and upstream of the at least one converter in the direction of synthesis circuit conveyance, with a section of the synthesis circuit, which is located upstream of the at least one conveying device and downstream of the at least one converter in the direction of synthesis circuit conveyance (preferably also downstream of the ammonia extraction device), and wherein the first bypass line is configured to divide the gas mixture into the first partial flow and a first residual flow when the first bypass line is not completely shut off, and, while the first residual flow is fed to the converter,to direct the first partial flow from the pressure side of the conveying device to the suction side of the conveying device via the first bypass line, bypassing the converter, wherein the second bypass line is arranged such that it fluidly connects a section of the first bypass line which is located upstream of the cooling device in the flow direction with a section of the first bypass line which is located downstream of the cooling device in the flow direction, and wherein the second bypass line is configured to split the first partial flow in the first bypass line into the second partial flow and a second residual flow if the second bypass line is not completely shut off, and, while the second residual flow is supplied to the cooling device,to direct the second partial stream through the second bypass line, bypassing the cooling device (so that it is also not passed through the other functional elements of the synthesis cycle).

[0034] In an advantageous embodiment of the ammonia synthesis plant according to the invention, it is particularly provided that the ammonia synthesis plant further comprises a hydrogen device which is configured to supply hydrogen at least partially by means of an electrolyzer, in particular wherein the electrolyzer is operated with electrical energy obtained from renewable and at least partially fluctuating energy sources. A hydrogen device is therefore a device which is designed to supply hydrogen, in pure form or as a mixture with other gases.This includes any hydrogen source in which hydrogen is produced, stored, or simply passed through, such as a supply line of an external hydrogen network or devices for generating hydrogen in biological processes, in the pyrolysis of hydrocarbons (such as methane pyrolysis), or in thermal water splitting, for example, in a solar furnace. In the present case, the hydrogen device is specifically also a device configured to provide hydrogen, at least partially or even completely, through an electrolyzer, i.e., a device in which electrolysis takes place, meaning that hydrogen is obtained from a feedstock material using electric current. Typically, the feedstock material is water, so water electrolysis is carried out in such an electrolyzer.For water electrolysis, the water can be neutral, but it can also be water with a pH value less than 7 (acidic electrolysis) or greater than 7 (basic electrolysis), and may optionally contain other dissolved substances, such as salts. "At least partially" means that either the entire required amount of hydrogen or only a portion of the required hydrogen is obtained by electrolysis, while the remaining amount can be supplied by other means, particularly if the portion obtained by electrolysis constitutes at least 30% by volume of the hydrogen requirement, preferably at least 50% by volume, and particularly preferably at least 90% by volume or even at least 99% by volume. Typically, such an electrolyzer is directly connected to the ammonia synthesis plant, but connection via a hydrogen network is also possible.

[0035] In water electrolysis, it is particularly advantageous if the electrolyzer is operated with electrical energy derived from renewable and at least partially fluctuating energy sources (regenerative / renewable energy), i.e., with regeneratively generated electrical energy, for example, with electrical energy obtained from wind energy, solar energy, bioenergy, hydropower or geothermal energy.(In some cases, operating an electrolyzer powered by nuclear energy can also be advantageous; the resulting "pink hydrogen" (also "red hydrogen", "purple hydrogen" or "violet hydrogen") is at least more favorable in terms of carbon dioxide balance than "grey hydrogen" obtained by reforming fossil fuels or "black hydrogen" and "brown hydrogen", for whose production electrical energy derived from hard coal or lignite is used.) One of the advantages arises from the fact that the process is adapted to the specific requirements of regeneratively generated electrical energy and is therefore particularly suitable for such a combination, which is why its use here is especially advantageous: Many renewable energy sources experience fluctuations (for example, due to the day-night cycle of sunlight, changing wind conditions or the tides).As a result of these fluctuations, after the conversion of renewable energy into electrical energy, fluctuations occur in the supply of reactants produced using this electrical energy, i.e., hydrogen. The present invention is particularly suitable for compensating for such fluctuations in the supply of reactants for ammonia synthesis.

[0036] In an advantageous embodiment of the ammonia synthesis plant according to the invention, it is particularly provided that the conveying device is a centrifugal compressor and the first bypass line is a controlled shut-off and controlled opening bypass line of a surge control arrangement. A centrifugal compressor (radial compressor) is a turbo compressor (turbo-compressed compressor), i.e., a rotating compressor, in particular an axial compressor, a radial compressor, or a combined axial-radial compressor, for example, a diagonal compressor, which is designed for compressing and conveying gaseous fluids and typically has a pressure casing with corresponding guide devices, a shaft with at least one impeller or row of impellers attached to it, usually a vane, and a deceleration section (diffuser) adapted for pressure build-up.Centrifugal compressors of this type typically incorporate a surge control system to prevent unwanted surges. The bypass line of a centrifugal compressor can be used – possibly after modifications – as the first bypass line and often already includes a cooling device. This design allows for the use of standard, highly efficient compressor units with an integrated construction.

[0037] In an advantageous embodiment of the ammonia synthesis plant according to the invention, it is particularly provided that the first bypass line has a shut-off element configured to restrict and / or block the flow path through the first bypass line. The shut-off element is typically an element for shutting off or controlling the flow of gases through a line, for example, a shut-off device or a flow-diverting element, in which the shut-off or diverting effect is variable, usually manually or with the aid of a separate control arrangement.Typical shut-off elements are adapted for a two-stage control scenario (only open or closed / closed state) or a multi-stage control scenario (metering between open and closed states), for example, butterfly valves, gate valves, stopcocks, or flow deflectors; however, in principle, any other shut-off element with corresponding functionality can also be used. The shut-off element in the first bypass line is specifically positioned so that it can completely block the flow path through the first shut-off line, which is why it is located upstream or downstream of the cooling element in the flow direction of the first bypass line.

[0038] The shut-off element located directly in the first bypass line either opens or blocks the flow path through this line. When opened, a portion of the total gas flow from the synthesis cycle is (temporarily) directed through the first bypass line (this can also be the entire gas flow, as the cooling device effectively prevents any continuous temperature increase). This allows for different operating states for the system, enabling varying utilization levels, such as those required when the supply of reactants like hydrogen fluctuates over time.

[0039] In an advantageous embodiment of the ammonia synthesis plant according to the invention, it is particularly provided that the second bypass line has a shut-off element which is configured to restrict and / or block the flow path through the second bypass line. The shut-off element in the second bypass line thus allows the flow path through the second bypass line to be opened or blocked.During release, a partial flow of the gas stream in the first bypass line is (temporarily) directed through the second bypass line (depending on the flow conditions in the remaining area of ​​the first bypass line, this can also be the entire gas stream through the first bypass line, for example, if the flow path in the remaining part of the first bypass line is closed off with further shut-off elements, whereby the first bypass line remains fully functional by preventing the partial flow, which is routed past the cooling device, from being directed through the other functional elements of the synthesis cycle).In this way, as a result of at least partially bypassing the cooling device, it can be ensured that the temperature in the conveying device is not so low that ammonia condenses out of the gas stream there, even with different utilization levels and different flow rates through the first bypass line (especially with a low flow rate through the first bypass line), thus ensuring safe and low-corrosion operation of the plant even with very different utilization levels.

[0040] In an advantageous embodiment of the ammonia synthesis plant according to the invention, it is particularly provided that the ammonia synthesis plant has a measuring device and a control device connected to the measuring device, wherein the measuring device is configured to detect at least one measured variable of the gas mixture, in particular the temperature, the pressure and / or the volume flow rate of the gas mixture and / or the content / concentration of components of the gas mixture, wherein the measuring device is arranged in the synthesis circuit, and wherein the control device is configured to open or close the shut-off element of the first bypass line and / or the shut-off element of the second bypass line on the basis of the measured variable detected by the measuring device.Any standard and suitable measuring device can be used, provided it is designed to detect at least one specific parameter of the gas mixture. Examples include pressure sensors, temperature sensors, or flow rate sensors that detect either the parameter for the gas mixture in the synthesis cycle or the partial pressure / concentration of specific components of the gas mixture, such as hydrogen, ammonia, or nitrogen (meaning the sensors are substance-sensitive). The measuring device is positioned in the synthesis cycle such that it detects the measured value for the corresponding parameter of the gas flow within the gas mixture.The measured quantity is transmitted by the measuring device as a measurement signal, which represents this measured value, to a recording device and / or control device assigned to and connected with this measuring device for the transmission of the measured value (where a recording device and / or control device may also be assigned to several sensors or even all sensors).The control device is designed to actuate, depending on the respective measurement signal, the shut-off element in the first bypass line or the shut-off element in the second bypass line or both shut-off elements, the shut-off element in the first bypass line and the shut-off element in the second bypass line in a single actuation process in which the respective shut-off element is moved from its initial state to a final state determined by the control device taking into account the measured value, thereby further opening or closing the corresponding bypass line, so that the respective shut-off element is then in a fully open position, a partially open position (and thus also a partially closed position) or in a fully closed position.Depending on the quantity to be measured, the measuring device can be located at any position within the synthesis cycle. It can be particularly advantageous if more than one measured value is taken into account for the adjustment process, for example, measured values ​​from two different measuring devices that measure the same quantity at different measuring positions in the synthesis cycle, such as at a first measuring position between the pressure side of the conveying device and the inlet of the converter and at a second measuring position between the outlet of the converter and the suction side of the conveying device (where the measuring signals can be supplied to the control device as individual signals or as differential signals), or measured values ​​that are recorded at different times at the same measuring position and therefore show a temporal variation or a temporal trend.Measurement values ​​with a temporal dispersion can then be subjected to statistical analysis (allowing, for example, the monitoring of system fluctuations), while measurement values ​​with a temporal trend can be extrapolated to a target point in the future (allowing, for example, the prediction of future adjustments that will be required with sufficient probability). Such a control system offers the advantage of reacting to changes in the process at an early stage and thus enabling the system to be operated continuously at an optimal operating point, where sudden adjustments are only very rarely necessary.

[0041] The aforementioned problem is also solved by a method for operating an ammonia synthesis plant, in particular an ammonia synthesis plant of the aforementioned type, which is characterized in that the first partial stream is divided into a second partial stream and, if applicable, a second residual stream, of which the second residual stream is fed into the cooling device and cooled there, and of which the second partial stream is fed to the suction side of the conveying device, bypassing the cooling device, and of which the second residual stream (if present) is fed into the cooling device, cooled there, and from there fed to the suction side of the conveying device.

[0042] Overall, this is a process for operating an ammonia synthesis plant, specifically a process for operating an ammonia synthesis plant of the aforementioned type. During operation of the ammonia synthesis plant, a gas mixture containing nitrogen, hydrogen, and ammonia is cyclically conveyed in a synthesis cycle by a conveying device with a suction side and a pressure side. Therefore, the gas mixture containing nitrogen, hydrogen, and ammonia (and possibly other components) is conveyed in a closed loop, the synthesis cycle.

[0043] In regular operation, the reactants nitrogen and hydrogen are fed into the synthesis cycle and at least partially converted to ammonia in a converter. During regular operation, a certain amount of the ammonia produced during the cyclical operation of the synthesis cycle is also extracted as product gas at a specific point and thus removed from the synthesis cycle. To replace the missing gas, a corresponding amount of fresh gas is then added to the synthesis cycle, containing at least the reactants nitrogen and hydrogen in a suitable mixture.As a result of the circulating recirculation of the product gas mixture, during regular operation, after diverting a portion of the ammonia and replenishing the removed gas with fresh gas, a macroscopically quasi-stationary equilibrium is established when the replenished gas mixture thus obtained is converted in the converter. This equilibrium is maintained as long as the removed ammonia flow and the supplied fresh gas flow, as well as their temperature and pressure, do not change.

[0044] If the available amount of reactant gas – usually the available amount of hydrogen – is insufficient, the usual approach is to remove less ammonia from the synthesis cycle or even to forgo ammonia removal altogether. If less ammonia is removed from the synthesis cycle, less fresh gas – and therefore less reactant – needs to be added. If no ammonia is removed from the synthesis cycle, no fresh gas needs to be added, and the reactant requirement drops to zero.This can be the case, in particular, if the hydrogen device is unable to provide a sufficient quantity of hydrogen, for example, if the hydrogen device has an electrolyzer powered by electrical energy derived from renewable energy sources that have at least partially fluctuating time profiles, such as electricity from a photovoltaic system, a wind turbine, or a tidal power plant. With such hydrogen devices, hydrogen production can even cease entirely and drop to zero, making it advantageous to avoid removing ammonia from the synthesis cycle in order to avoid having to add hydrogen to it.During such "idle operation" (i.e., operation without production, corresponding to a partial load of 0%), the gas mixture is continuously circulated within the synthesis cycle for a period of time. This results in a quasi-stationary dynamic equilibrium partial pressure of ammonia, without any change in the net ammonia content of the gas mixture. Therefore, in this type of closed-loop operation, it is not necessary to completely shut down the ammonia synthesis plant. Instead, the plant remains in standby mode, where the converter maintains the required reaction temperature. This allows the ammonia synthesis plant to be switched back to regular production operation relatively quickly once the hydrogen system can again supply a sufficient quantity of hydrogen.This type of standby operation is also referred to as "hot standby." In hot standby mode, the aim is to minimize cooling of the plant—and especially the converter. Instead, the plant and converter should be maintained at temperatures that correspond to, or at least closely approximate, the respective operating temperatures during regular production, allowing for a seamless transition from hot standby to production without lengthy reheating. For this type of operation, the input of reactants (hydrogen and nitrogen) and the output of product (ammonia) are reduced or eliminated. This results in no net synthesis of ammonia (only synthesis at dynamic equilibrium occurs), thus maintaining a closed-loop gas stream with a constant equilibrium composition of product and reactants.Formally, standby operation corresponds to a special type of partial load operation, namely a partial load operation with a partial load of 0%. Since such standby operation is cost-intensive, areas of the plant that are not needed in standby mode are often shut down (with the exception, of course, of the converter). These include plant components where hydrogen and nitrogen are produced (for example, in the so-called "front end" of the plant, which can be located upstream of the synthesis cycle as a separate unit), as well as pre-compressor units, which pre-compress reactant gases in regular operation before they are fed into the synthesis cycle until they reach the system pressure required in the synthesis cycle (the conveying device of the synthesis cycle itself always remains in operation even in standby mode to maintain the circulation of the gas flow in the synthesis cycle).

[0045] From a process engineering perspective, such a hot standby operation can be facilitated by diverting a portion of the gas flow in the synthesis cycle past the converter without feeding it into the converter, thus minimizing the effort required to maintain the converter at the desired temperature. This type of operation can be implemented particularly advantageously using the first bypass line. For this purpose, the gas mixture is divided downstream of the conveying device in the direction of synthesis cycle flow into a first partial flow and, optionally, a first residual flow. The first partial flow is then recirculated from the pressure side of the conveying device to the suction side, bypassing the converter. On the recirculation path, this first partial flow is at least partially cooled in a cooling device. In such an operation, a partial flow of at least 5 vol.-% of the total gas flow is recycled; however, in the case of long-term hot standby operation, the entire gas flow can be recycled, i.e., 100 vol% of the circulating gas (circulating gas flow). Accordingly, the initial residual flow (if any) is routed to the converter via the regular synthesis cycle.

[0046] According to the invention, the first partial flow is divided into a second partial flow and, optionally, a second residual flow. The second partial flow is fed to the suction side of the conveying device, bypassing the cooling device, so that this second partial flow does not undergo any cooling. This serves to ensure that the temperature of the gas mixture upon entering the conveying device is not so low that ammonia condenses within the conveying device and thereby damages it. If the conveying device is operated at a temperature at which ammonia can condense on the suction side of the conveying device (or at least close to such a temperature, such that even slight pressure fluctuations can cause it to fall below this temperature), it is necessary to increase the inlet temperature of the gas flow at the conveying device to prevent condensation.Therefore, the overall temperature of the first partial flow must be increased. This can be easily achieved by routing at least a portion of the first partial flow as a second partial flow past the cooling device, thus preventing it from being cooled. Depending on the inlet temperature of the gas flow at the conveying device, it is quite possible for a portion of the first partial flow to be routed as a second residual flow through the cooling device, as long as the inlet temperature of the gas mixture at the conveying device is not so low that ammonia condenses out.The temperature of the gas mixture entering the conveying device can be regulated, taking into account the ratio of the first partial flow to the first residual flow and the temperature of the first residual flow, by appropriately adjusting the ratio of the second partial flow to the second residual flow using shut-off elements, so that when all partial flows are combined, the desired temperature of the gas mixture is reached at the latest on the pressure side of the conveying device.It is irrelevant whether the second residual stream is combined with the second partial stream before being fed back into the synthesis cycle as the restored first partial stream, or whether the second residual stream and the second partial stream are fed separately into the first residual stream (in principle, all process configurations are conceivable and each offers different advantages, for example, by first feeding the second partial stream into the first residual stream and introducing the second residual stream downstream, or by first feeding the second residual stream into the first residual stream and introducing the second partial stream downstream).

[0047] In an advantageous embodiment of the inventive process for operating an ammonia synthesis plant, it is particularly provided that the hydrogen is at least partially supplied by electrolysis, especially by electrolysis using electrical energy derived from renewable energy sources. Typically, the reactant material in such electrolysis is water, so it is generally water electrolysis. For water electrolysis, the water can be neutral, but it can also be water with a pH value less than 7 (acidic electrolysis) or greater than 7 (basic electrolysis), and the water may optionally also contain other dissolved substances, for example, salts."At least partially" means that either the entire required amount of hydrogen or only a portion of it is produced via electrolysis, while the remainder can be supplied by other means, such as a hydrogen network or a hydrogen storage tank. It is particularly advantageous if the remaining hydrogen is also "green" hydrogen, meaning hydrogen produced sustainably, so that no additional carbon dioxide is released into the atmosphere during its production. Ideally, this hydrogen is produced using a process where the energy required for its production is supplied by renewable energy sources. Such a process enables, above all, a particularly climate-neutral and environmentally friendly production of ammonia.

[0048] In an advantageous embodiment of the inventive method for operating an ammonia synthesis plant, it is particularly provided that the gas mixture at the suction side of the conveying device has a volume flow rate that is at least 50% of the maximum volume flow rate of the conveying device and preferably has a volume flow rate of at least 85% and at most 105% of the maximum volume flow rate of the conveying device. It can be particularly provided that the ratio of the first partial flow to the first residual flow and the ratio of the second partial flow to the second residual flow are regulated such that the gas mixture at the suction side of the conveying device has a volume flow rate of at least 85% of the maximum volume flow rate of the conveying device.A minimum suction-side flow rate of the circulating gas at the pumping device of 50%, and preferably 85%, ensures safe operation of the system without pumps ("surge"). At the same time, this value should be as close as possible to the maximum flow rate of the pumping device to utilize the energy for driving the pumping device as efficiently as possible (which is advantageously also generated using renewable energy). In particular, for reasons of system safety, the suction-side flow rate should not exceed 105%. In this way, stable and resource-efficient operation can be achieved particularly easily.

[0049] In an advantageous embodiment of the inventive method for operating an ammonia synthesis plant, it is particularly provided that the conveying device is a centrifugal compressor, the speed of the centrifugal compressor is regulated to a predetermined value, and the gas mixture at the suction side of the conveying device has a volume flow rate that is at least 50% of the maximum volume flow rate of the conveying device, preferably at least 70% and at most 105% of the maximum volume flow rate of the conveying device. In this way, the method can be implemented in a particularly energy-efficient manner.

[0050] In an advantageous embodiment of the inventive method for operating an ammonia synthesis plant, it is particularly provided that, under full plant load, the gas mixture at the pressure side of the conveying device has a temperature of at least 15 °C and at most 60 °C, and / or under partial plant load, has a temperature of at least 15 °C and at most 180 °C, particularly at a partial plant load close to 0% (i.e., at most 10% of the full plant load) of at least 150 °C and at most 180 °C. In particular, it can be provided that the ratio of the second partial flow to the second residual flow is regulated such that the gas mixture at the pressure side of the conveying device has a temperature of at least 30 °C and at most 170 °C.With a corresponding maximum pressure-side temperature, safe plant operation is ensured during "hot standby operation"—while also including a safety margin—along with the most resource-efficient operation possible, as the circulating gas only needs to be heated minimally by any downstream heating devices. The minimum temperature ensures that even at low partial loads, ammonia condensation within the conveying device (and thus premature wear or any other usage-related damage to the conveying device) is reduced or even prevented.

[0051] The inventive method can be implemented, for example, by the control device releasing the flow through the first bypass line to such an extent that the first residual flow as a circulating flow through the remaining synthesis circuit and thus through the converter corresponds to at least a minimum flow that is required to maintain the pressure, temperature and gas flow composition of the intended operation (a production operation at full load, a restricted production operation at partial load or a purely "hot" standby operation).For each partial load, the partial flows—the first partial flow through the first bypass line and, if applicable, the second partial flow through the second bypass line—as well as the final residual flow, can be adjusted so that, on the one hand, the overall volume flow on the suction side of the conveying device is close to its minimum value (thus minimizing drive energy), and on the other hand, that the outlet temperature during "hot standby operation" on the pressure side of the conveying device is close to a maximum temperature of 170 °C (which should not be exceeded). In this way, the power consumption during any heating of the circulating gas downstream of the conveying device, which is intended to compensate for any heat dissipation from the synthesis cycle, can be minimized.

[0052] In detail, there are numerous possibilities for designing and further developing the inventive system and method. Reference is made to the claims subordinate to claims 1 and 8, as well as to the following description of preferred embodiments in conjunction with the drawings, with the aid of which the invention is explained in more detail below. The drawings schematically depict... Fig. 1 a schematic representation of part of a conventional plant for the production of "green ammonia" with a coolable bypass line for the shut-offable return of a partial flow of the gas mixture from the pressure side of the conveying device to the suction side of the conveying device, Fig. 2 a schematic representation of a first embodiment of a part of a plant according to the invention for the production of ammonia, Fig. 3 a schematic representation of a second embodiment of a part of a plant according to the invention for the production of ammonia and Fig. 4 a schematic representation of a third embodiment of a part of a plant according to the invention for the production of ammonia.

[0053] Fig. 1 Figure 1 shows a schematic representation of a part of a conventional plant 1 for the production of ammonia with a coolable bypass line 6 for the shut-offable return of a partial flow 8a of the gas mixture from the pressure side 5b of the conveying device 5 to the suction side 5a of the conveying device 5.

[0054] The ammonia synthesis plant 1 has a synthesis cycle into which hydrogen and nitrogen are fed as reactants. The direction in which the gas mixture is circulated within the synthesis cycle by means of a conveying device 5 is indicated by an arrow as the synthesis cycle conveying direction d. In this case, the actual synthesis cycle runs through the converter 3, the ammonia extraction device 4, and the conveying device 5 (as well as through the intervening pipelines and other functional elements, such as coolers or heat exchangers, which are located in Fig. 1 (not shown).

[0055] Therefore, converter 3 is located in the synthesis cycle, where hydrogen and nitrogen react over a catalyst in an equilibrium reaction to form ammonia. Since the reaction takes place under equilibrium conditions in the reactor, ammonia is extracted from the gas mixture circulating in the synthesis cycle during production by an ammonia extraction device 4 as a more or less pure product stream (arrow "NH 3" in Fig. 1 ) and is replaced by a corresponding amount of fresh gas containing nitrogen and hydrogen. Hydrogen is supplied to the synthesis cycle via the hydrogen device 2, which is connected to the outlet side of the ammonia extraction device 4 (so that the hydrogen is introduced into the synthesis cycle at this point). The conveying device 5 (usually a turbo compressor) has a suction side 5a and a pressure side 5b. The gas flow to be circulated within the synthesis cycle is drawn into the conveying device 5 via the suction side 5a, and the gas flow to be circulated within the synthesis cycle is expelled from the conveying device 5 via the pressure side 5b, thus conveying the gas flow in the overall synthesis cycle conveying direction d.

[0056] The already known synthesis cycle has two bypass lines: One bypass line 16 bridges the ammonia extraction device 4, the other bypass line 6 leads from the pressure side 5b of the compressor 5 to the suction side 5a of the compressor 5.

[0057] The additional bypass line 16, used to bypass the ammonia extraction device 4, has a shut-off element 14 and a cooling device 15 and serves to divert a portion of the circulating gas flow around the ammonia extraction device 4 during partial load operation. If the shut-off element 14 is fully or partially opened for partial load operation, a portion of the circulating gas flow bypasses the ammonia extraction device 4, resulting in less ammonia being extracted from the circulating gas. Consequently, in the dynamic equilibrium of such partial load operation, less ammonia is synthesized in the converter 3, thus reducing the demand for reactant gases. Therefore, this additional bypass line 16 can serve to stabilize partial load operation.The partial flow, which is routed past the ammonia extraction device 4 (which is usually at least partially cryogenically operated) via the additional bypass line 16, is cooled by means of the cooling device 15, so that the gas flow introduced into the conveying device 5 has a sufficiently low temperature.

[0058] The bypass line 6 from the pressure side 5b of the conveying device 5 to the suction side 5a of the conveying device 5 also serves to stabilize partial load operation. For this purpose, at least a portion of the circulating gas flow bypasses the converter 3 and the ammonia extraction device 4 and is returned directly from the outlet of the conveying device 5 to the inlet of the conveying device 5; this bypass line 6 also has a shut-off element 7 and a cooling device 9. To return a portion of the circulating gas flow through this bypass line 6, the shut-off element 7 is at least partially opened, allowing a portion of the gas flow to pass through this bypass line 6. In doing so, the gas flow on the pressure side 5b of the conveying device 5 is split into a partial flow 8a and a residual flow 8b.The residual stream 8b is fed to the converter 3 and then – at least partially – enters the ammonia extraction device 4, while the partial stream 8a is directed to the suction side 5a of the compressor 5. To prevent the gas stream, which is repeatedly compressed in successive passes through the conveying device 5, from increasing its temperature in the conveying device 5, this first partial stream 8a is passed through the cooling device 9.

[0059] Fig. 2 Figure 1 shows a schematic representation of a first embodiment of a part of a plant according to the invention for the production of ammonia. The first embodiment differs from the one shown in Figure 2. Fig. 1 The conventional system depicted is characterized primarily by the fact that the Fig. 2 The depicted ammonia synthesis plant 1, as part of the first bypass line 6, has a second bypass line 10 which bridges the cooling device 9. Another difference is that the in Fig. 2 The depicted ammonia synthesis plant in the additional bypass line 16 for the ammonia extraction device 4 does not have a cooling device. Apart from these differences, the elements of the in Fig. 2 The first embodiment shown is essentially identical to the one in Fig. 1 The conventional system shown (identical reference symbols describe the respective components) is shown.

[0060] The ammonia synthesis plant 1 according to the first embodiment also has a synthesis cycle with a converter 3, an ammonia extraction device 4, and a conveying device 5, as well as pipelines. Furthermore, the synthesis cycle can include additional functional elements such as pipe branches, valves, measuring devices for monitoring process parameters, heating devices (especially electric heating devices), gas-to-gas heat exchangers (especially to use some of the thermal energy of the gas mixture from the converter 3 to preheat the gas mixture supplied to the converter 3), and waste heat steam generators or steam superheaters (to dissipate the thermal energy generated during the reaction and utilize it elsewhere; these are to be included in Fig. 2 not shown.

[0061] Hydrogen and nitrogen are fed into the synthesis cycle as reactants in proportion to the amount of ammonia removed from the synthesis cycle via the ammonia extraction device 4. The hydrogen reactant is introduced into the synthesis cycle by a hydrogen device 2. In this case, the hydrogen device 2 is a water electrolyzer powered by electrical energy (electricity) generated (converted) from renewable energy sources, in this case a photovoltaic system. However, other hydrogen devices 2 can also be used, for example, systems for the electrolysis of raw materials other than water, for pyrolysis, for production from biomass, and the like.Hydrogen devices 2 can also be devices for supplying hydrogen that is not directly produced at the ammonia synthesis plant 1, for example, hydrogen pipelines through which the ammonia synthesis plant 1 is connected to a hydrogen supply network, synthesis gas pipelines, hydrogen tanks, and the like. Preferably, hydrogen devices 2 are those in which the hydrogen is produced using renewable energies, in particular by means of wind turbines, solar power plants, plants for the use of hydropower and / or tidal power, bioenergy plants, geothermal plants, or combinations of such plants within the framework of a plant network, which increases the availability of electrical energy.In principle, conventional systems for hydrogen production can also be used (such as reactors for coal gasification, steam reforming, autothermal reforming, partial oxidation, and the like); however, these cannot produce "green hydrogen" (and therefore also not "green ammonia"), but only "grey hydrogen." Hydrogen is typically fed into the synthesis cycle into the part of the cycle that is located downstream of the ammonia extraction device 4 and upstream of the converter 3 in the direction of flow d of the synthesis cycle; in this example, at the outlet of the cycle gas stream from the ammonia extraction device 4.

[0062] The nitrogen reactant is introduced into the synthesis cycle via a suitable nitrogen device (not shown), in which nitrogen is typically obtained from the air, for example through chemical or cryogenic air treatment (e.g., by fractional cryogenic separation during low-temperature air separation) or by selective adsorption (e.g., pressure swing adsorption). The nitrogen feed into the synthesis cycle can be separate from the hydrogen feed or via a common pipeline.

[0063] The gas mixture circulating in the synthesis cycle, which contains not only the reactant gases hydrogen and nitrogen but also the product gas ammonia and, if applicable, other (gaseous) components (for example, argon, perhaps from the air, methane, perhaps from methanation, or other compounds in trace amounts, for example, as impurities), is conveyed in a circular motion by the conveying device 5 within the synthesis cycle and then – if necessary via cooling or heating sections – fed to converter 3. In converter 3, hydrogen and nitrogen react over a catalyst in an equilibrium reaction to form ammonia. In this case, converter 3 is a three-stage Haber-Bosch reactor, i.e., a reactor with three stages, in which the gas flow passes through a catalyst bed with an iron-based catalyst and a heat exchanger in each catalyst stage.In principle, converter 3 can be any single-stage or multi-stage reactor in which the corresponding catalyst is arranged (not shown). Several individual reactors connected in series or parallel in a multi-stage configuration can also serve as converter 3. Converter 3 can be a reactor for any process suitable for the production of ammonia from gaseous reactants, in particular a reactor for the Haber-Bosch process (e.g., using iron-based, ruthenium-based, osmium-based, or similar catalyst systems, optionally with promoters, supports, and other auxiliary materials), but also a reactor for electrochemical synthesis or other processes.

[0064] Since the reaction in converter 3 takes place under equilibrium conditions, ammonia is diverted from the synthesis cycle in the production plant by means of an ammonia extraction device 4 (arrow "NH 3" in Fig. 2 ) and is sent for further processing, storage, or use. In the present case, the ammonia extraction device 4 enables cryogenic ammonia separation, in which the circulating gas is cooled so much that ammonia condenses and can be separated from the gas stream in liquid form; however, other methods of ammonia separation are also possible in principle, for example, by means of pressure swing adsorption and the like. In the Fig. 2 In the illustrated system, the ammonia extraction device 4 is arranged downstream of the converter 3 and upstream of the conveying device 5, however, other arrangements are also possible in principle.

[0065] To bypass the ammonia extraction device 4, an additional bypass line 16 is also provided in the first embodiment of the present invention. This bypass line has a shut-off element 14, which serves to divert a portion of the circulating gas flow around the ammonia extraction device 4 during partial load operation. If the shut-off element 14 is fully or partially opened for partial load operation, at least a portion of the circulating gas flow bypasses the ammonia extraction device 4, resulting in less ammonia being extracted from the circulating gas. Consequently, in the dynamic equilibrium of such partial load operation, less ammonia is synthesized in the converter 3, thus reducing the demand for reactant gases.Therefore, this additional bypass line 16 can serve to stabilize part-load operation with a cryogenic ammonia extraction device 4 (this additional bypass line 16 could also be omitted, but this would result in a significantly less stable part-load operation; however, under certain circumstances, a system without such an additional bypass line 16 can also offer advantages). Additional cooling of the partial flow that bypasses the ammonia extraction device 4 via the additional bypass line 16 is not necessary, since the combination of the first bypass line 6, the second bypass line 12, the cooling device 9, and the two shut-off elements 7 and 11 allows for a defined cooling of the gas flow, so that the gas flow introduced into the conveying device 5 has a sufficiently low temperature.

[0066] In the first embodiment, a turbocentrifugal compressor (turbo compressor) is used as the conveying device 5 (compressor), but other types of compressors are also possible in principle. The conveying device 5 has a suction side 5a and a pressure side 5b; the gas flow circulating in the synthesis cycle is drawn into the conveying device 5 via the suction side 5a, and the gas flow circulating in the synthesis cycle is expelled from the conveying device 5 via the pressure side 5b, thus conveying the gas flow overall in the synthesis cycle conveying direction d. In the present arrangement, the conveying device 5 is positioned downstream of the ammonia extraction device 4 and upstream of the converter 3.

[0067] The ammonia synthesis plant 1 has a first bypass line 6, which leads from the pressure side 5b of the compressor 5 to the suction side 5a of the compressor 5. Part of the first bypass line 6 is a shut-off element 7 and a cooling device 9. In this case, the shut-off element 7 is a metering valve that can be set to a fully closed, a fully open, or a partially open position. When the shut-off element 7 is (fully or partially) open, the circulating gas flow exiting the conveying device 5 at the pressure side 5b is split into two partial flows: the first partial flow 8a and the first residual flow 8b. The first residual flow 8b is fed to the converter 3, while the first partial flow 8a is routed through the first bypass line 6.As a result of the use of a turbo centrifugal compressor, the bypass line already provided there as part of the pumping limit control arrangement can be used as the first bypass line 6, so that the bypass valve of the bypass line serves as a shut-off element 7 and the bypass cooler of the bypass line as a cooling device 9, so that conventional conveying devices can be adapted to the special requirements with simple measures.

[0068] The first bypass line 6 includes a second bypass line 10, which bypasses the cooling device 9 of the first bypass line 6. The second bypass line 10 has a shut-off element 11, which in this case is also a metering valve. This metering valve can also be set to a fully closed position, a partially open position, or a fully open position. When the shut-off element 11 is (fully or partially) open, the first partial flow 8a, which is routed through the first bypass line 6, is split into two partial flows: the second partial flow 12a and the second residual flow 12b. The second residual flow 12b is routed through the cooling device 9, while the second partial flow 12a is routed through the second bypass line 10.In the present case, the second partial flow 12a and the second residual flow 12b are recombined downstream of the cooling device 9 and fed via a common line into the portion of the circulating gas flow that has passed through the converter 3. However, other configurations are also possible; for example, the second partial flow 12a and the second residual flow 12b can be fed separately to the first residual flow 8b coming from the converter 3, or even at different points apart from each other, before the combined gas flow reaches the suction side 5a of the conveying device 5.

[0069] With the aid of the second bypass line 10, it is possible to divert a partial flow of the first partial flow 8a (namely the second partial flow 12a) past the cooling device 9, so that this second partial flow 12a is not cooled while the second residual flow 12b is cooled. Depending on the setting of the shut-off element 11, the ratio of the cooled second residual flow 12b to the uncooled second partial flow 12a can be determined – and thus the temperature at which the first partial flow 8a is recombined with the first residual flow 8b after the latter has passed through the converter 3. In this way, the inlet temperature of the circulating gas flow, which is supplied to the conveying device 5 at its suction side 5a, can be precisely controlled.By selecting a sufficiently high temperature, it is possible to prevent ammonia from condensing and damaging the conveying device 5 under the respective pressure and partial pressure conditions in the circulating gas stream. Simultaneously, the second bypass line 10, and in particular the setting of its shut-off element 11, ensures that the temperature of the gas stream entering the conveying device 5 is as high as possible (thus minimizing reheating of the gas stream before entering the converter 3), while at the same time not exceeding the maximum outlet temperature specified for the respective conveying device 5 (a maximum outlet temperature of approximately 200 °C is typically specified for turbocentrifugal compressors), allowing conventional compressors to be used as the conveying device 5.

[0070] Therefore, the use of a second bypass line 10 within the first bypass line 6 to bypass the cooling device 9 enables precise control of the temperature of the gas flow entering the conveying device 5, even during partial load operation, which was previously only possible with complicated and energy-intensive measures.

[0071] Fig. 3 Figure 1 shows a schematic representation of a second embodiment of a part of a plant according to the invention for the production of ammonia. The second embodiment differs from the one shown in Figure 2. Fig. 2 the first embodiment shown, such that the in Fig. 3 The illustrated ammonia synthesis plant 1 comprises a control device 13 and measuring devices m connected to it (automatic or non-automatic, whereas in the second embodiment no automatic control via a control device is provided). The control device 13 is connected to the measuring devices m via a common signal line or via different signal lines (in this case, two measuring devices m are shown as an example, whereby these can, in principle, be arranged at different locations or at the same location - for example, in the form of a multi-sensor - but there can also be only one measuring device m or there can be more than two measuring devices m).The control device 13 receives the signals from the measuring devices m, evaluates them, and actuates the shut-off elements 7 and 11 accordingly to ensure that the volume flow rate of the circulating gas through the conveying device 5 is sufficiently high, while simultaneously ensuring that the inlet temperature of the circulating gas flow on the suction side 5a of the conveying device 5 is within a suitable temperature range. The inlet temperature of the circulating gas flow should therefore be sufficiently high to prevent ammonia condensation upstream of or within the conveying device 5. Conversely, the inlet temperature of the circulating gas flow should be sufficiently low to ensure that the conveying device 5 operates within the temperature range specified as permissible for the conveying device 5.For hot standby operation, it is also particularly advantageous to keep the temperature at the suction side 5a of the conveying device 5 as high as possible (ideally at about 170 °C) so that the gas mixture has to be reheated as little as possible before being introduced into the converter 3. This is possible by using the interconnection of the system components and their operation according to the invention.

[0072] The control decision of the control device 13 can also take into account other aspects, such as the composition of the circulating gas. Accordingly, the measuring devices m are each configured to detect at least one measured parameter of the gas mixture, typically the temperature of the gas mixture, and optionally also its pressure, composition, or volumetric flow rate. If necessary, the partial pressure / concentration of individual components of the gas mixture and the like can also be detected and evaluated instead or additionally. Based on the measured parameters detected by the measuring devices m, the control device 13 causes the shut-off element 7 of the first bypass line 6 and / or the shut-off element 11 of the second bypass line 10 to fully or partially open or close (and optionally also the shut-off element 14).The control decision made by the control device 13 is based on predefined rules that take into account the measured value determined at the respective measuring device m; the rules may, for example, provide for measures to be initiated when certain predefined limit values ​​are exceeded or fallen below by a single measured value or by several measured values, but also measures that result from a comparison of a measured value with other measured values, for example from the comparison of measured values ​​recorded at different measuring devices m or the time course of a measured value recorded at a measuring device m (such as a trend or a dispersion); however, other rules are also possible.The acquisition of measured values ​​also allows for the creation of historical tables, which can then be used as a basis for predictive control decisions, enabling the early prevention of undesirable operating conditions. In principle, the control device 13 can also incorporate external measured values; in the case of electrolytic hydrogen production using electrical energy generated from renewable sources, these could include, for example, current data on solar irradiance or wind, or corresponding forecast data such as sunrise and sunset times or wind forecast data. These data can be used to predict the amount of hydrogen available at a later time for energy production in wind turbines or photovoltaic systems.

[0073] Fig. 4 Figure 1 shows a schematic representation of a third embodiment of a part of a plant according to the invention for the production of ammonia. The third embodiment differs from the one shown in Figure 2. Fig. 3 the second embodiment shown, such that the in Fig. 4 The illustrated ammonia synthesis plant 1 includes the additional bypass line 16 for bridging the ammonia extraction device 4 as shown in the diagram. Fig. 1The conventional system shown additionally includes a cooling device 15, with which the portion of the circulating gas flow bypassing the ammonia extraction device 4 during partial load operation can be further cooled. One of the advantages of the present invention is precisely that such a cooling device 15 can be completely dispensed with in the additional bypass line 16, since precise control of the temperature of the gas flow entering the conveying device 5 is already possible with the aid of the first bypass line 6 and the second bypass line 10, which is why the additional cooling device 15 is not required.However, the synthesis plant 1 with a first bypass line 6 and a second bypass line 10 for bypassing the cooling device 9 in the first bypass line 6 can also be operated if the cooling device 15 already exists in the additional bypass line 16 for bypassing the ammonia extraction device 4, which is why it is possible to retrofit and integrate the solution according to the invention into an already existing conventional plant. Reference symbol list

[0074] 1 Ammonia synthesis plant 2 Hydrogen device 3 Converter 4 Ammonia extraction device 5 Conveying device 5a Suction side 5b Pressure side 6 First bypass line 7 Shut-off element 8a First partial flow 8b Final flow 9 Cooling device 10 Second bypass line 11 Shut-off element 12a Second partial flow 12b Second final flow 13 Control device 14 Shut-off element 15 Cooling device 16 Additional bypass line d Synthesis cycle conveying direction m Measuring device

Claims

1. Ammonia synthesis plant (1) with a hydrogen device (2) which is designed to supply hydrogen, and a synthesis circuit, wherein the synthesis circuit comprises: - a conveying device (5) which is adapted to cyclically convey a gas mixture containing nitrogen, hydrogen and ammonia in a synthesis cycle conveying direction (d), wherein the conveying device (5) comprises a suction side (5a) and a pressure side (5b), - a converter (3) which is adapted to catalytically convert nitrogen and hydrogen at least partially to ammonia, wherein the converter (3) comprises an inlet and an outlet, wherein the inlet of the converter (3) is fluidically connected to the pressure side (5b) of the conveying device (5) and the outlet of the converter (3) is fluidically connected to the suction side (5a) of the conveying device (5), - a first bypass line (6), which is arranged parallel to the conveying device (5) from the suction side (5a) of the conveying device (5) to the pressure side (5b) of the conveying device (5) in a counterflow arrangement and which is adapted for shut-offably returning a first partial flow (8a) of the gas mixture from the pressure side (5b) of the conveying device (5) to the suction side (5a) of the conveying device (5), wherein the first bypass line (6) comprises a cooling device (9) which is adapted for cooling the first partial flow (8a) of the gas mixture, characterised in that the first bypass line (6) further comprises a second bypass line (10) which is arranged in parallel to the cooling device (9) in a cocurrent flow arrangement and which is adapted for shut-offably passing a second partial flow (12a) of the first partial flow (8a) in order to bypass the cooling device (9).

2. Ammonia synthesis plant (1) according to claim 1, wherein the first bypass line (6) is arranged such that it fluidically connects a region of the synthesis circuit which is arranged in the synthesis circuit conveying direction (d) downstream of the at least one conveying device (5) and upstream of the at least one converter (3), with a region of the synthesis circuit which is arranged in the synthesis circuit conveying direction (d) upstream of the at least one conveying device (5) and downstream of the at least one converter (3), and wherein the first bypass line (6) is adapted to divide the gas mixture into the first partial flow (8a) and a first residual flow (8b) when the first bypass line (6) is not completely shut off, and, while the first residual flow (8b) is supplied to the converter (3), to direct the first partial flow (8a) from the pressure side (5b) of the conveying device (5) through the first bypass line (6) to the suction side (5a) of the conveying device (5) by bypassing the converter (3), wherein the second bypass line (10) is arranged such that it fluidically connects a region of the first bypass line (6), which is arranged upstream of the cooling device (9) in the flow direction, to a region of the first bypass line (6), which is arranged downstream of the cooling device (9) in the flow direction, and wherein the second bypass line (10) is adapted to divide the first partial flow (8a) in the first bypass line (6) into the second partial flow (12a) and a second residual flow (12b) when the second bypass line (10) is not completely shut off, and, while the second residual flow (12b) is supplied to the cooling device (9), to direct the second partial flow (12a) through the second bypass line (10) by bypassing the cooling device (9).

3. Ammonia synthesis plant (1) according to one of claims 1 or 2, wherein the hydrogen device (2) is adapted to supply hydrogen at least partially by means of an electrolyser, in particular wherein the electrolyser is operated with electrical energy obtained from renewable and at least partially fluctuating energy.

4. Ammonia synthesis plant (1) according to one of claims 1 to 3, wherein the conveying device (5) is a centrifugal compressor and the first bypass line (6) is a controllably shut-offable and controllably openable bypass line of a anti-surge control arrangement.

5. Ammonia synthesis plant (1) according to one of claims 1 to 4, wherein the first bypass line (6) comprises a shut-off element (7) which is adapted to restrict and / or block the flow path through the first bypass line (6).

6. Ammonia synthesis plant (1) according to one of claims 1 to 5, wherein the second bypass line (10) comprises a shut-off element (11) which is adapted to restrict and / or block the flow path through the second bypass line (10).

7. Ammonia synthesis plant (1) according to one of claims 1 to 6, wherein the ammonia synthesis plant (1) comprises at least one measuring device (m) and a control device (13) connected to the measuring device (m), wherein the measuring device (m) is adapted to determine at least one quantity to be measured of the gas mixture, in particular the temperature, the pressure and / or the volume flow rate of the gas mixture or the content / concentration of components of the gas mixture, wherein the measuring device (m) is arranged in the synthesis circuit, and wherein the control device (13) is adapted to completely or partially open or close the shut-off element (7) of the first bypass line (6) and / or the shut-off element (11) of the second bypass line (10 on the basis of the quantity to be measured determined by the measuring device (m).

8. Method for operating an ammonia synthesis plant, in particular an ammonia synthesis plant (1) according to one of claims 1 to 7, wherein a gas mixture comprising nitrogen, hydrogen and ammonia is cyclically conveyed in a synthesis circuit by a conveying device (5) with a suction side (5a) and a pressure side (5b), wherein nitrogen and hydrogen are fed into the synthesis circuit and are converted there in a converter (3) at least partially to ammonia, wherein in the synthesis cycle conveying direction (d) downstream of the conveying device (5), the gas mixture is divided into a first partial flow (8a) and, if necessary, a first residual flow (8b), of which the first partial flow (8a) is returned from the pressure side (5b) of the conveying device (5) to the suction side (5a) of the conveying device (5) by bypassing the converter (3), while being at least partially cooled in a cooling device (9), and of which the first residual stream (8b), if present, is fed into the converter (3), characterised in that the first partial flow (8a) is divided into a second partial flow (12a) and, if necessary, a second residual flow (12b), of which of which the second partial flow (12a) is fed to the suction side (5a) of the conveying device (5) by bypassing the cooling device (9) and of which the second residual flow (12b), if present, is fed into the cooling device (9), cooled therein and fed from there to the suction side (5a) of the conveying device (5).

9. Method according to claim 8, wherein the hydrogen is provided at least partially by electrolysis, in particular by electrolysis using electrical energy obtained from renewable energies.

10. Method according to claim 8 or 9, wherein the gas mixture on the suction side (5a) of the conveying device (5) has a volume flow rate that does not fall below a minimum value of 50% of the maximum volume flow rate of the conveying device (5), preferably a volume flow rate of at least 85% and at most 105% of the maximum volume flow rate of the conveying device (5).

11. Method according to claim 10, wherein the ratio of the first partial flow (8a) to the first residual flow (8b) and the ratio of the second partial flow (12a) to the second residual flow (12b) is regulated in such a way that the gas mixture on the suction side (5a) of the conveying device (5) has a volume flow rate of at least 85% of the maximum volume flow rate of the conveying device (5).

12. Method according to one of claims 8 to 11, wherein the conveying device (5) is a centrifugal compressor, the rotational speed of the centrifugal compressor is controlled to a predetermined value, and the gas mixture on the suction side (5a) of the conveying device (5) has a volume flow rate that does not fall below a minimum value of 50% of the maximum volume flow rate of the conveying device (5), preferably having a volume flow rate of at least 70% and at most 105% of the maximum volume flow rate of the conveying device (5).

13. Method according to one of claims 8 to 12, wherein, under full load of the plant, the gas mixture on the pressure side (5b) of the conveying device (5) has a temperature of at least 15 °C and at most 60 °C and / or, under partial load of the plant, has a temperature of at least 25 °C and at most 180 °C.

14. Method according to claim 13, wherein the ratio of the second partial flow (12a) to the second residual flow (12b) is regulated such that the gas mixture on the pressure side (5b) of the conveying device (5) has a temperature of at least 30 °C and at most 170 °C.