Production of compressed synthesis gas from moist hydrogen

Abstract

The invention relates to the production of synthesis gas, which preferably consists substantially of N2 and H2 and is suitable for the production of NH3 in the Haber-Bosch process. The amount of N2 required for the synthesis gas is preferably provided as a first gas by air separation, wherein the first gas is typically already compressed to a pressure p1 as a result of production. The amount of H2 required for the synthesis gas is preferably provided as a second gas by water electrolysis, wherein the second gas is typically saturated with H2O and present at only low pressure p2 as a result of production. According to the invention, the second gas is first compressed by a first compression system (so-called "H2 booster compressor") to a pressure p3, which is compatible with the pressure p1 of the first gas, and then combined with the first gas, whereby a synthesis gas having a resulting pressure p4 is produced. The synthesis gas thus produced is then compressed to a pressure p5 by a second compression system (so-called "syngas compressor").

Description

Production of compressed synthesis gas from moist hydrogen

[0001] The invention relates to the production of synthesis gas, which preferably consists essentially of N2 and H2 and is suitable for the production of NH3 using the Haber-Bosch process. The amount of N2 required for the synthesis gas is preferably provided as the first gas by air separation for a so-called "green" NH3 plant without CO2 emissions, wherein the first gas is typically already compressed to a pressure p due to the production process. The amount of H2 required for the synthesis gas is preferably provided as the second gas by water electrolysis, wherein the second gas is typically saturated with H2O due to the production process and is present at a low pressure p2. According to the invention, the second gas is first compressed using a first compression system (so-called...The H2 booster compressor compresses the H2 gas to a pressure p3, which is compatible with the pressure pl of the first gas, and then combines it with the first gas, producing a synthesis gas with a resulting pressure p4. The synthesis gas thus produced is then compressed to a pressure p5 using a second compression system (the so-called "synthesis gas compressor").

[0002] The invention relates in particular to the water content of the second gas obtained during water electrolysis and its effects on compression.

[0003] The industrial production of NH3 using the Haber-Bosch process requires large quantities of N2 and H2. While centrifugal compressors are less suitable for compressing low molecular weight gases like H2 than high molecular weight gases, they have a significantly higher capacity. Therefore, for compressing large quantities of H2, it is economically advantageous to use centrifugal compressors instead of conventional positive displacement compressors. Centrifugal compressors are typically designed with multiple stages, meaning they comprise several compression stages through which the gas to be compressed passes sequentially.

[0004] Centrifugal compressors are susceptible to a condition known as "surge." If the flow rate drops below a certain threshold, brief backflows, known as pump surges, occur, which can lead to damage. Centrifugal compressors are therefore typically equipped with an anti-surge system that maintains a minimum flow rate through the compressor, preventing the unstable surge condition from occurring.

[0005] For this purpose, a portion of the flow is returned to the intake side of the centrifugal compressor via a recirculation system or discharged to the atmosphere via a line. When the centrifugal compressor approaches an unstable surge state (low flow, high delivery head), an anti-surge valve opens and initiates a temporary anti-surge measure, in which a portion of the flow is either returned to the intake side or discharged to the atmosphere. If, as a result of this temporary anti-surge measure, the flow rate through the centrifugal compressor is sufficiently high again and the condition is stable, the anti-surge valve closes again, thus ending the anti-surge measure, so that the centrifugal compressor is operated normally again.

[0006] In multi-stage compression systems, which have several compression stages, each with its own centrifugal compressor, a distinction is made between the compression ratio of the entire compression system and the compression ratio of an individual compression stage. The compression ratio of the entire compression system is the ratio of the outlet pressure from the compression system (downstream of the last compression stage) to the inlet pressure into the compression system (upstream of the first compression stage). The compression ratio of an individual compression stage is the ratio of the outlet pressure from that compression stage to the inlet pressure into that compression stage. For centrifugal compressors, the ratio of outlet pressure to inlet pressure (compression ratio of the compression stage) is a critical parameter for each compression stage, becoming increasingly sensitive as the molecular weight of the gas being compressed decreases.This applies analogously to gas mixtures, where the molecular weight of the gas mixture results from the molecular weight of the individual components in their pure form and the respective mole fractions in the mixture. For the compression of low molecular weight gases such as H₂ with centrifugal compressors, it has therefore been proposed to compress mixtures of H₂ with heavier gases in order to utilize the higher molecular weight of the mixture for compression and thereby improve the ratio of outlet pressure to inlet pressure of each compression stage (see, e.g., US 3,401,111, DE 1 792 421 Al). Such a heavier gas can be, among others, H₂O (see, e.g., EP 3 789 616 Al).

[0007] EP 4 060 089 A2 relates to a process for producing compressed hydrogen gas, comprising: electrolyzing water to generate hydrogen gas, and compressing the hydrogen gas in a multi-stage compression system to generate the compressed hydrogen gas, wherein the multi-stage compression system comprises: a centrifugal compression stage with a feed end and a product end, and a recirculation system for returning a portion of the hydrogen gas from the product end to the feed end, wherein a hydrogen gas supply is fed to the feed end at a predetermined feed temperature and a predetermined feed pressure and with a predetermined molar fraction of water, wherein a portion of the hydrogen gas is removed from the product end as required and pressure-reduced in the recirculation system to the predetermined feed pressure before a cooling step to provide a pressure-reduced hydrogen gas which is then recirculated.to form at least part of the hydrogen gas supply to the centrifugal compression stage, and wherein the process includes cooling the hydrogen gas with the pressure-reduced hydrogen gas contained therein, such that the molar fraction of water in the hydrogen gas supply is the predetermined molar fraction of water. The condensation of water in the hydrogen gas returned via the recirculation system is thereby prevented. This prevents the pressure of the hydrogen gas from decreasing before the hydrogen gas is cooled.

[0008] The method proposed in EP 4060089 A2, however, has the disadvantage that an additional heat exchanger is required to cool the compressed gas in the recirculation system (see Figures 1 and 3 of EP 4060089 A2, El 16). The heat exchangers already present in conventional multi-stage compression systems cannot be used for the method according to EP 4060089 A2 because they are usually located directly downstream of the centrifugal compressors in each centrifugal compression stage. The method proposed in EP 4060089 A2 requires, however, that the recirculation system be branched off upstream of these conventional heat exchangers, i.e., immediately after the centrifugal compressors, in order to prevent premature cooling of the recirculated hydrogen gas in these conventional heat exchangers.

[0009] It is an object of the invention to provide a method for compressing water vapor-containing H₂, which is suitable for the industrial synthesis of NH₃ according to the Haber-Bosch process and overcomes the disadvantages of the prior art. The method should be as economical as possible and not require significant additional equipment. It is a further object of the invention to provide a device for carrying out the method.

[0010] This problem is solved by the subject matter of the procedural claims.

[0011] A first aspect of the invention relates to a method for producing a compressed synthesis gas having a pressure p5, wherein the method comprises the steps: (a) Providing a compressed first gas comprising or substantially consisting of N2 and having a pressure pl; (b) Providing a second gas comprising or substantially consisting of H2 and H2O and having a pressure p2, wherein p2 < pl; (c) multi-stage compression of the second gas in a first compression system to produce a compressed second gas (i) with a pressure p3 (normal operation) or (ii) to temporarily generate a pressure p3' (anti-surge operation) if required, wherein p3' < p3; wherein the first compression system comprises several compression stages connected in series, each comprising an inlet, a centrifugal compressor and an outlet; (d) Combining the compressed first gas and the compressed second gas to produce a synthesis gas (i) with a resulting pressure p4 (normal operation) or (ii) temporarily with a resulting pressure p4' (anti-surge operation) when needed to generate where p4' < p4; and (e) multi-stage compression of the synthesis gas in a second compression system to produce the compressed synthesis gas at pressure p5; wherein, if necessary, step (c) temporarily comprises the following sub-steps: (ci) Diverting at least part of the second gas from the outlet of one of the compression stages into a recirculation system; (c2) Reducing the pressure of the second gas in the recirculation system; and (C3) Returning the second gas via the recirculation system to the inlet of the same compression stage or another upstream compression stage of the first compression system.

[0012] The condensation and separation of water from recycled hydrogen containing water vapor during anti-surge operation may lead to a reduction in the molecular weight of the hydrogen containing water vapor (H2), resulting in a reduced compression ratio of the first compression system. Surprisingly, it was found that a design reserve in the second compression system can compensate for this reduced compression ratio of the first system, ensuring that the desired pressure p5 of the compressed synthesis gas can still be achieved even during anti-surge operation.

[0013] It was also surprisingly found that the inventive method requires one less heat exchanger compared to the method according to EP 4 060 089 A2. The additional condensate separator that may be required for the inventive method (see Figures 3 and 4, condensate separator (24c)) is significantly less expensive and therefore advantageous compared to such an additional heat exchanger.

[0014] Furthermore, it was surprisingly found that the required drive power can be reduced according to the invention. The reduced suction pressure in the second compression system (synthetic gas compressor) means that, at a given volume flow rate at the surge line, the mass flow rate in the bypass is reduced, thereby lowering the power consumption. This is particularly advantageous because, with a low system load, less renewable energy is generally available to drive the compressors. The power reduction is further enhanced by the reduced amount of water during compression in the first compression system (H2Booster compressor).

[0015] For the inventive procedure, two operating states (i) and (ii) must be distinguished.

[0016] In operating state (i), which is also referred to as "normal operation" according to the invention, steps (ci) to (c3) are not performed. Accordingly, in step (c), the multi-stage compression of the second gas in the first compression system takes place to produce a compressed second gas with a pressure p3. Accordingly, in step (d), the combination of the The compressed first gas and the compressed second gas are combined to produce a synthesis gas with a resulting pressure p4. Accordingly, in step (e), the synthesis gas is then compressed in a second compression system in multiple stages, starting from pressure p4, to produce the compressed synthesis gas with pressure p5.

[0017] In operating state (ii), which according to the invention is also referred to as "anti-surge operation", steps (ci) to (C3) are temporarily carried out due to demand. Accordingly, in step (c), the second gas is then compressed in multiple stages in the first compression system to produce a compressed second gas with a pressure p3', where p3' < p3. Accordingly, in step (d), the compressed first gas and the compressed second gas are then combined to produce a synthesis gas with a resulting pressure p4', where p4' < p4. Accordingly, in step (e), the synthesis gas is then compressed in multiple stages in a second compression system starting from pressure p4' to produce the compressed synthesis gas with pressure p5.

[0018] In operating condition (ii), the second compression system must therefore ensure a higher compression ratio p5 : p4' than in operating condition (i) in order to achieve the same desired pressure p5 of the synthesis gas, starting from the lower resulting pressure p4'. According to the invention, this can be ensured by utilizing a design reserve of the second compression system.

[0019] For descriptive purposes, in the case of chemical mixtures, "essentially consisting of" means that there may be certain other components, namely those that do not significantly alter the essential characteristics of the mixture. Preferably, the total content of such other components is at most 2 wt.%, more preferably at most 1 wt.%, even more preferably at most 0.5 wt.%, and most preferably at most 0.1 wt.%, in each case based on the total weight of the mixture.

[0020] Preferably, the temporary execution of steps (ci) to (C3) requires an unstable state of the first compression system, which necessitates an anti-surge measure for re-stabilization. This unstable state can occur due to a drop in the volume flow rate of the gas to be compressed falling below or approaching a critical threshold.

[0021] Within the scope of the invention, it was recognized that a design reserve of the second compression system (synthesis gas compressor) can be used to compensate for the pressure difference p3 - p3' or a pressure difference p4 - p4' resulting after combining the compressed first gas and the compressed second gas in operating state (ii). According to the invention, such a design reserve of the second compression system (synthesis gas compressor) results from several factors. Preferably, due to its design, the second compression system can generate a greater delivery head and thus a higher compression ratio in operating state (ii) (anti-surge operation) than in Operating state (i) (normal operation). This is preferably related to the fact that the delivery head characteristic curves of centrifugal compressors (turbo compressors) increase at lower volume flows. Furthermore, according to the invention, the design of the first and second compression systems takes into account the standard API 617 of the American Petroleum Institute, according to which the maximum possible continuous speed should be 105% compared to the speed at the design point. According to the invention, the controllability of the second compression system is preferably achieved by a frequency-controlled electric motor. Since the delivery head depends quadratically on the speed, a higher pressure or a higher compression ratio can thus be achieved by increasing the speed. If this results in a slightly higher power consumption, this can preferably be covered by a power reserve of preferably 10% in the electric motor.

[0022] According to the invention, preferably the design reserve of the second compression system is sufficient to compress the synthesis gas in step (e) from pressure p4' to pressure p5 in the case of the temporary execution of partial steps (ci) to (C3).

[0023] Preferably, at least one compression stage, and preferably each compression stage, comprises a heat exchanger downstream of the respective centrifugal compressor and upstream of the respective outlet, in which the second gas is cooled. This differs from the method according to EP 4 060 089 A2, where a heat exchanger is arranged upstream of the first compressor, either in the compression channel (see Figure 2 of EP 4 060 089 A2, El 00) or in the recirculation system (see Figures 1 and 3 of EP 4 060 089 A2, El 16), and where the recirculation system branches off immediately downstream of the compressor without first passing through the heat exchanger and, if applicable, the condensate separator of the compression channel.

[0024] Preferably, at least one compression stage downstream of the respective heat exchanger and upstream of the respective outlet comprises a condensate separator in which any condensed H2O is separated from the second gas.

[0025] Preferably, a final, preferably third, compression stage downstream of its heat exchanger and upstream of its outlet does not include a condensate separator. Instead, the final, preferably third, compression stage more preferably includes a condensate separator in its recirculation system upstream of an anti-surge valve, in which any condensed H₂O is separated from the second gas.

[0026] Condensate separators can, for example, be designed as phase separators.

[0027] Preferably, each of the compression stages of the first compression system comprises its own return system for at least a part of the second gas from the respective outlet of the respective compression stage to the respective inlet of the same compression stage, wherein the return systems are each configured independently of each other, if required, for the temporary execution of the sub-steps (ci) to (C3).

[0028] Preferably, each recirculation system according to the invention comprises essentially only a pipeline, an anti-surge valve, and optionally a condensate separator along the path from the respective outlet of the compression stage to the respective inlet of the compression stage. Preferably, each recirculation system according to the invention does not include a heat exchanger along the path from the respective outlet of the compression stage to the respective inlet of the compression stage.

[0029] In step (a) of the inventive process, a compressed first gas is provided which comprises or consists substantially of N2 and has a pressure pl.

[0030] In preferred embodiments, step (a) comprises the separation of air in an air separation unit.

[0031] In other preferred embodiments, in step (a) the first gas is supplied via a pipeline.

[0032] Preferably, in step (a) the pressure pl is in the range of 4 to 9 bara, preferably 6 to 9 bara.

[0033] In step (b) of the method according to the invention, a second gas is provided which comprises or essentially consists of H2 and H2O and has a pressure p2, wherein p2 < pl.

[0034] Preferably, step (b) comprises the electrolysis of H2O in a water electrolysis unit; preferably with electric current obtained from renewable energy sources (e.g. photovoltaics, wind power, and / or hydropower).

[0035] Any suitable form of water electrolysis can be used, including alkaline water electrolysis. For example, demineralized seawater can be used.

[0036] Water electrolysis can be carried out on any suitable scale. For example, the water electrolysis unit can have a total capacity of at least approximately 240 megawatts (MW) to make compression of the H2 gas mixture with a centrifugal compressor possible and economically viable.

[0037] Preferably, the second gas provided in step (b) is hydrogen (H2) saturated with water vapor (H2O).

[0038] The gas provided in step (b) may have been temporarily stored.

[0039] Preferably, in step (b), i.e., before the first stage of the first compression system, the second gas has a molecular weight (apparent molecular weight) of at least 2.5 g / mol resulting from the molar fractions of H₂ and H₂O. In preferred embodiments, the molecular weight is in the range of 2.5 to 4 g / mol, preferably from 2.5 to 3.5 g / mol.

[0040] Preferably, in step (b) the pressure p2 of the second gas is at most 2 bara, preferably at most 1.5 bara.

[0041] Preferably in step (b) the temperature of the second gas is 10 to 80°C, preferably 20 to 60°C.

[0042] In step (c) of the method according to the invention, the second gas is compressed in a first compression system in several stages to produce a compressed second gas (i) with a pressure p3 (normal operation) or (ii) if required temporarily with a pressure p3' (anti-surge operation), wherein p3' < p3. For this purpose, the first compression system comprises several compression stages connected in series, each of which includes an inlet, a centrifugal compressor and an outlet.

[0043] In multi-stage compression systems, heat exchangers (coolers) are typically required between adjacent compressors (intercoolers) and typically after the last compressor (aftercooler) to dissipate the heat of compression from the compressed gas. A "compression stage" within the meaning of the invention preferably comprises an inlet, a centrifugal compressor with an intake side and a product side, a heat exchanger (cooler) downstream of the centrifugal compressor, and an outlet. However, more than one compression stage can be housed in a single compressor casing. The inlet and outlet need not be separate components. For descriptive purposes, these terms serve in particular to identify the location of the branch of the recirculation system (outlet) and the location of the return feed to the recirculation system (inlet). Preferably, the branch occurs at the outlet and the return feed at the inlet.According to the invention, centrifugal compressors are preferred for use in all compression stages.

[0044] Preferably in step (c) the compression ratio p3 : p2 is below a maximum compression ratio achievable with the first compression system.

[0045] In preferred embodiments, in step (c), the compressed second gas after the first compression stage and before the subsequent compression stage has a molecular weight (apparent molecular weight) of at least 2.5 g / mol, resulting from the molar fractions of H₂ and H₂O. In preferred embodiments, the molecular weight is in the range of 2.5 to 4 g / mol, preferably from 2.5 to 3.5 g / mol. In preferred embodiments, in step (c), the compressed second gas after the subsequent compression stage has a lower molecular weight (apparent molecular weight) resulting from the molar fractions of H₂ and H₂O.

[0046] In preferred embodiments, in the case of the temporary implementation of partial steps (ci) to (C3) after step (c), the compressed second gas has a molecular weight (apparent molecular weight) resulting from the molar fractions of H2 and H2O, which is below the molecular weight of the second gas provided in step (b).

[0047] Preferably, the first compression system comprises three compression stages. The number of compression stages typically depends on the manufacturer's design limitations and the Mixing pressure. The compression ratio across each compression stage is preferably in the range of 1.5 to 4, more preferably 1.5 to 3, to limit the temperature rise of the compressed second gas. A relevant design limit in this context is, for example, the permissible circumferential speed in the compression stages of the first compression system. If a manufacturer increases the maximum permissible circumferential speed, a higher pressure rise can be achieved per stage. Thus, a desired overall compression can be achieved with fewer stages. Therefore, a first compression system according to the invention can also manage with two compression stages.

[0048] Preferably, in step (c) the pressure p3 is in the range of 4 to 9 bara, preferably 6 to 9 bara.

[0049] In step (d) of the inventive process, the compressed first gas and the compressed second gas are combined to produce a synthesis gas (i) with a resulting pressure p4 (normal operation) or (ii) when required, temporarily with a resulting pressure p4' (anti-surge operation), where p4' < p4. The resulting pressure p4 or p4' is preferably obtained from the compressed first gas at pressure p1 and the compressed second gas at pressure p3 or p3', respectively, less mixing losses.

[0050] Preferably the synthesis gas comprises N2 and H2 or consists essentially of them; preferably in a molar ratio of about 1 : 3.

[0051] Preferably, in step (d) the relative difference between the pressure pl of the compressed first gas and the pressure p3 of the compressed second gas is at most 1.0 bar.

[0052] In step (e) of the process according to the invention, the synthesis gas is compressed in a second compression system in multiple stages to produce the compressed synthesis gas at pressure p5.

[0053] Preferably in step (e) the compression ratio p5 : p4 is below a maximum compression ratio achievable with the second compression system.

[0054] Preferably, in step (e) the compression ratio p5 : p4 of the second compression system is larger than in step (c) the compression ratio p3 : p2 of the first compression system.

[0055] Preferably, in step (e) the compression ratio p5 : p4' of the second compression system is larger than in step (c) the compression ratio p3' : p2 of the first compression system.

[0056] Preferably, in step (e) the pressure p5 is in the range of 130 to 250 bara.

[0057] Preferably, the second compression system comprises at least three compression stages.

[0058] Preferably, the second compression system has a controllable compression power, which is regulated as a control variable depending on the pressure p4 or p4' resulting from step (d). Preferably, the second compression system is driven by a frequency-controlled electric motor, which preferably has a power reserve of at least 5%, more preferably exhibits at least 10%. Preferably, the second compression system enables a maximum possible continuous rotational speed of at least 102%, more preferably at least 105%, compared to the rotational speed at the design point.

[0059] Another aspect of the invention relates to a process for the synthesis of a chemical product, preferably NH3, from a compressed synthesis gas comprising the inventive process described above.

[0060] Preferably, the procedure includes the additional step: (1) Synthesizing the chemical product, preferably NH3, from the compressed synthesis gas in a synthesis unit at pressure p5.

[0061] The further problem is solved by a device with the features of the independent device claim. Advantageous embodiments of the device according to the invention are specified in the dependent device claims.

[0062] With regard to the apparatus for carrying out the inventive method, the invention makes use of the fact that a design reserve of the second compression system (synthesis gas compressor) can be used to compensate for the pressure difference p3 - p3' or a pressure difference p4 - p4' resulting after combining the compressed first gas and the compressed second gas in operating state (ii). According to the invention, the design reserve of the second compression system is dimensioned such that the synthesis gas can be compressed to pressure p5 by the second compression system even if, when required, the synthesis gas temporarily (i.e., during operating state (ii)) has a pressure p4' after the mixing unit that is lower than the pressure p4 during normal operation (operating state (i)).Preferably, the second compression system includes a control for the compression power, by which the pressure p5 can be regulated as a controlled variable depending on the pressure p4 or p4' resulting in the mixing unit as a measured variable. This ensures that the synthesis gas downstream of the synthesis gas compressor always has the target pressure p5, regardless of whether the plant is operating in normal mode (operating state (i)) or temporarily in anti-surge mode (operating state (ii)).

[0063] According to one embodiment of the device according to the invention, the first compression system has a condensate separator in the return system of the last compression stage upstream of the anti-surge valve and downstream of the outlet. This condensate separator protects the anti-surge valve, which is located in the return system of the last compression stage of the first compression system, from condensate entering the anti-surge valve and causing damage (e.g., by corrosion). If, when necessary, an anti-surge measure is temporarily initiated at the last compression stage of the first compression system, the condensate separator located in the return system prevents the cooling of the water vapor-containing hydrogen in the system downstream of the centrifugal compressor of the last compression stage from causing damage (e.g., by corrosion). Condensed water from the arranged heat exchanger can enter the anti-surge valve via the return system of the last compression stage and cause damage there.

[0064] The invention is explained below with reference to the illustrations, which, however, are not to be interpreted restrictively.

[0065] Figure 1 schematically illustrates a preferred embodiment of the invention.

[0066] Figure 1A shows a flow diagram in which water (H₂O) is split into oxygen (O₂) and hydrogen vapor (H₂) in a water electrolysis unit (1), with the hydrogen vapor (H₂) leaving the electrolysis unit (1) at pressure p₂. The hydrogen vapor (H₂) is compressed to pressure p₃ or, if required, temporarily to pressure p₃' in a first compression system (2). The compression system (2) comprises several compression stages (not shown). Air (N₂ + O₂) is separated into nitrogen (N₂) at pressure p₁ and residual gases (O₂) by an air separation unit (3). The compressed hydrogen vapor (H₂) is combined with the nitrogen (N₂) in a mixing unit (4) to produce synthesis gas (H₂ + N₂) at a resulting pressure p₄ or, if required, temporarily at a resulting pressure p₄'.The synthesis gas (H2+N2) is then compressed using a second compression system (5) to produce a compressed synthesis gas (H2+N2) at pressure p5. The compressed synthesis gas (H2+N2) is then fed to a synthesis unit (6) where ammonia (NH3) is synthesized.

[0067] The first compression system (2) is equipped with a recirculation system (26) (dashed line) which can be used to temporarily initiate an anti-surge measure if necessary, preferably to restabilize or prevent an unstable state of the first compression system (2). For this purpose, at least a portion of the compressed water vapor-containing hydrogen (H2) can be temporarily recirculated from the outlet of the last compression stage of the first compression system (2) via the recirculation system (26) back to the inlet of the first compression stage of the first compression system (2) until the first compression system (2) is again in a stable state or sufficiently far from an unstable state so that the anti-surge measure can be terminated.

[0068] As a consequence of this temporary recirculation, during the temporary anti-surge measure, i.e., during anti-surge operation, the compression ratio for the first compression stage (2) is lower than without the anti-surge measure, so that the water vapor-containing hydrogen (H2) in the first compression system (2) is only compressed to pressure p3' (p3' < p3). Consequently, the combination of the compressed water vapor-containing hydrogen (H2) with the nitrogen (N2) in the mixing unit (4) also results in a synthesis gas (H2+N2) with a lower resulting pressure p4' (p4' < p4). This difference between the resulting pressure p4' (with anti-surge measure) and the resulting pressure p4 (without anti-surge measure) is However, according to the invention, this is compensated by a design reserve of the second compression stage (5), so that the compressed synthesis gas (H2+N2) can be compressed to the same pressure p5 in both cases (i.e. when pressure p4 is present and also when pressure p4' is present).

[0069] Figure 1B schematically illustrates the relative positions of the pressure levels, whereby the positions of the pressure levels relative to each other are not shown to scale (i.e., not quantitatively). The pressure profile p is shown against the spatial coordinate x along the plant's path.

[0070] Figure 2 schematically illustrates another preferred embodiment of the invention, showing only the water electrolysis unit (1) and the first compression system (2) as a detail. The first compression system (2) comprises a first compression stage (2a), a second compression stage (2b), and a third compression stage (2c), which are arranged in series and through which the hydrogen (H2) containing water vapor flows successively, whereby the hydrogen (H2) containing water vapor is compressed stepwise. Each compression stage (2a, b, c) comprises its own recirculation system (26a, b, c) with which, if required, at least a portion of the hydrogen (H2) containing water vapor can be temporarily and independently recirculated from the outlet of the respective compression stage to its inlet.

[0071] Figure 3 schematically illustrates a preferred embodiment of a first compression stage (2a) as part of the first compression system (2). The hydrogen containing water vapor (H2) is fed to the first compression stage (2a) via an inlet (21a) and compressed in a centrifugal compressor (22a). Since the hydrogen containing water vapor (H2) is heated by the compression, it is subsequently cooled in a heat exchanger (23a) located downstream of the centrifugal compressor (22a). As water (H2O) may condense during the cooling of the hydrogen containing water vapor (H2), it is separated in a condensate separator (24a) located downstream of the heat exchanger (23a).The cooled, compressed hydrogen, which typically still contains a residual amount of water vapor, leaves the first compression stage (2a) via an outlet (25a) located downstream of the condensate separator (24a). Regardless of whether an anti-surge measure is temporarily initiated as needed, the compressed hydrogen (H2) is then cooled in the heat exchanger (23a) following compression in the centrifugal compressor (22a). The water vapor content is then reduced, if necessary, by condensation and separation of water (H2O) in the condensate separator (24a).

[0072] If a temporary anti-surge measure is required, at least some of the compressed, cooled, and, if necessary, water vapor-reduced hydrogen (H2) can be returned from the outlet (25a) of the first compression stage (2a) to the inlet (21a) of the first compression stage (2a) via a recirculation system (26a) by opening an anti-surge valve (27a). As a result of the previously Following the cooling of the water vapor-containing hydrogen (H2) in the heat exchanger (23a) and the separation of condensed water (H2O) in the condensate separator (24a), the molecular weight of the recycled water vapor-containing hydrogen (H2), derived from the molar fractions of H2 and H2O, is lower than the molecular weight of the compressed water vapor-containing hydrogen (H2) previously generated in this compression stage (2a) with the centrifugal compressor (22a). Since the compression ratio of the compression stage (2a) decreases as the molecular weight of the gas to be compressed decreases, in the event of a temporarily initiated anti-surge measure, the water vapor-containing water vapor (H2) is compressed only to the pressure p3' (p3' < P 3).

[0073] Figure 4 schematically illustrates a preferred embodiment of a final, preferably third, compression stage (2c) as part of the first compression system (2). In contrast to the preferred embodiment of the first compression stage (2a) illustrated in Figure 3, in the preferred embodiment of the final, preferably third, compression stage (2c) according to Figure 4, a condensate separator (24c) is arranged within the recirculation system (26c) upstream of an anti-surge valve (27c), but not upstream of the outlet (25c). The condensate separator (24c) protects the anti-surge valve (27c) from condensed moisture.

[0074] Figure 5 schematically illustrates the serial arrangement of a first compression stage (2a), a second compression stage (2b), and a third and final compression stage (2c). The first compression stage (2a) and the second compression stage (2b) are designed analogously to the embodiment shown in Figure 3, whereas the third and final compression stage (2c) is designed analogously to the embodiment shown in Figure 4. In the return system (26c) of the final compression stage (2c), a condensate separator (24c) is arranged upstream of the anti-surge valve (27c) and downstream of the outlet (25c) of the final compression stage (2c).If, when necessary, a temporary anti-surge measure is initiated at the last compression stage (2c) of the first compression system (2), the condensate separator (24c) arranged in the return system (26c) prevents water condensed by the cooling of the water vapor-containing hydrogen (H2) in the heat exchanger (23c) located downstream of the centrifugal compressor (22c) of the last compression stage (2c) from entering the anti-surge valve (27c) via the return system (26c) of the last compression stage (2c). In this way, the anti-surge valve (27c) is effectively protected against damage and malfunctions caused by ingress of condensate.

[0075] It is understood that, according to the invention, the first compression system can also have more than three compression stages, e.g., four or five compression stages. If four or five compression stages are provided, then the first three or four compression stages are analogous to the embodiment shown in Figure 3, and the fourth or fifth compression stage is designed analogously to the embodiment shown in Figure 4. Reference symbol list: (1) Water electrolysis unit (2) first compression system (2a,b,c) first, second, third compression stage (3) Air separation unit (4) Mixing unit (5) second compression system (6) Synthesis unit (21a,b,c) Inlet of the first, second, third compression stage (22a, b, c) Centrifugal compressor of the first, second, third compression stage (23a, b, c) Heat exchangers of the first, second, third compression stage (24a, b) Condensate separator of the first, second compression stage (24c) Third compression stage condensate separator (25a, b, c) Outlet of the first, second, third compression stage (26a, b, c) Return system of the first, second, third compression stage (27a, b, c) Anti-surge valve of the first, second, third compression stage

Claims

Patent claims:

1. A method for producing a compressed synthesis gas having a pressure p5, the method comprising the steps of: (a) Providing a compressed first gas comprising or substantially consisting of N2 and having a pressure pl; (b) Providing a second gas comprising or substantially consisting of H2 and H2O and having a pressure p2, wherein p2 < pl; (c) Multi-stage compression of the second gas in a first compression system (2) to produce a compressed second gas at a pressure p3 or, if required, temporarily at a pressure p3', wherein p3' < p3; wherein the first compression system (2) comprises several compression stages (2a,b,c) connected in series, each comprising an inlet (21a,b,c), a centrifugal compressor (22a,b,c) and an outlet (25a,b,c); (d) Combining the compressed first gas and the compressed second gas to produce a synthesis gas with a resulting pressure p4 or, if required, temporarily with a resulting pressure p4', wherein p4' < p4; and (e) multi-stage compression of the synthesis gas in a second compression system (5) to produce the compressed synthesis gas at pressure p5; wherein, if necessary, step (c) temporarily comprises the following sub-steps: (ci) Diverting at least part of the second gas from the outlet (25a, b,c) of one of the compression stages (2a,b,c) into a recirculation system (26a, b,c); (c2) Reducing the pressure of the second gas in the recirculation system (26a, b, c); and (C3) Returning the second gas via the recirculation system (26a, b,c) to the inlet (21a, b,c) of the same compression stage (2a,b,c) or of another upstream compression stage (2a, b) of the first compression system (2).

2. The method according to claim 1, wherein a design reserve of the second compression system (5) is sufficient to compress the synthesis gas in step (e) from pressure p4' to pressure p5 in the case of the temporary execution of partial steps (ci) to (C3).

3. The method according to claim 1 or 2, wherein at least one compression stage (2a,b,c), preferably each compression stage (2a,b,c), comprises a heat exchanger (23a, b,c) downstream of the respective centrifugal compressor (22a, b,c) and upstream of the respective outlet (25a, b,c) in which the second gas is cooled.

4. The method according to claim 3, wherein at least one compression stage (2a,b,c) downstream of the respective heat exchanger (23a, b,c) and upstream of the respective outlet (25a, b,c) comprises a condensate separator (24a, b) in which any condensed H2O is separated from the second gas.

5. The method according to one of the preceding claims, wherein the last, preferably third, compression stage (2c) in its recirculation system (26c) upstream of an anti-surge valve (27c) comprises a condensate separator (24c) in which any condensed H2O is separated from the second gas.

6. The method according to one of the preceding claims, wherein each of the compression stages (2a,b,c) of the first compression system (2) comprises a return system (26a, b,c) for at least a part of the second gas from the respective outlet (25a, b,c) of the respective compression stage (2a,b,c) to the respective inlet (21a, b,c) of the same compression stage or of another upstream compression stage (2a, b), wherein the return systems (26a, b,c) are each configured independently of one another as required for the temporary execution of the partial steps (ci) to (c2).

7. The method according to any of the preceding claims, wherein step (a) comprises the separation of air in an air separation unit (3).

8. The method according to one of the preceding claims, wherein in step (a) the first gas is provided via a pipeline.

9. The method according to any of the preceding claims, wherein the synthesis gas comprises or consists substantially of N2 and H2; preferably in a molar ratio of about 1 :

3.

10. The method according to one of the preceding claims, wherein the compression ratio p5 : p4 is below a maximum compression ratio achievable with the second compression system (5) in step (e).

11. The method according to any one of the preceding claims, wherein - the compression ratio p5 : p4 of the second compression system is greater than the compression ratio p3 : p2 of the first compression system; and / or - the compression ratio p5 : p4' of the second compression system is greater than the compression ratio p3' : p2 of the first compression system.

12. The method according to one of the preceding claims, wherein the need for the temporary execution of partial steps (ci) to (C3) is an existing or imminent unstable state of the first compression system which requires an anti-surge measure for restabilization.

13. The method according to one of the preceding claims, wherein in step (a) the pressure pl is in the range of 4 to 9 bara, preferably 6 to 9 bara.

14. The method according to one of the preceding claims, wherein step (b) comprises electrolyzing H2O in a water electrolysis unit (1); preferably with electric current obtained from renewable energy.

15. The method according to one of the preceding claims, wherein in step (b) the pressure p2 of the second gas is at most 2 bara, preferably at most 1.5 bara.

16. The method according to one of the preceding claims, wherein in step (d) the relative difference of the pressure pl of the compressed first gas and the pressure p3 or p3' of the compressed second gas is at most 1.0 bar.

17. The method according to one of the preceding claims, wherein the second compression system (5) has a controllable compression power, which is controlled as a control variable depending on the pressure p4 or p4' resulting in step (d).

18. A device for producing a compressed synthesis gas having a pressure p5, comprising: (a) A supply line (30) for supplying a compressed first gas comprising or substantially consisting of N2 and having a pressure pl to a mixing unit (4); (b) A supply line (21a) for supplying a second gas comprising or substantially consisting of H2 and H2O and having a pressure p2 to a first compression system (2), wherein p2 < pl; (c) a first multi-stage compression system (2) for compressing the second gas to produce a compressed second gas at a pressure p3 or, if required, temporarily at a pressure p3', wherein p3' < p3; wherein the first compression system (2) comprises several comprising series-connected compression stages (2a,b,c), each comprising an inlet (21a,b,c), a centrifugal compressor (22a, b,c) and an outlet (25a, b,c); (d) a mixing unit (4) for combining the compressed first gas and the compressed second gas to produce a synthesis gas with a resulting pressure p4 or, if required, temporarily with a resulting pressure p4', wherein p4' < p4; and (e) a second multi-stage compression system (5) for compressing the synthesis gas in a second compression system (5) to produce the compressed synthesis gas at pressure p5; (ci) wherein the outlets (25a, b,c) of the first compression system (2) are configured to temporarily divert at least part of the second gas from one of the compression stages (2a,b,c) into a recirculation system (26a, b,c) when required; (C2) wherein each recirculation system (26a, b, c) has an anti-surge valve (27a, b, c) to temporarily reduce the pressure of the second gas in the recirculation system (26a, b, c) if necessary; and (C3) wherein the inlets (21 a,b,c) of the first compression system (2) are configured to allow, if required, temporary recirculation of the second gas via the respective recirculation system (26a, b,c) into the respective inlet (21a,b,c) of the same compression stage (2a,b,c) or another upstream compression stage (2a, b) of the first compression system (2), f) wherein the second multi-stage compression system (5) has a design reserve dimensioned such that the synthesis gas temporarily generated in the mixing unit (4) can be compressed from pressure p4' to pressure p5 if required.

19. Device according to claim 18, wherein the second compression system(5) has a control for the compression power by which the pressure p5 as a control variable can be controlled as a function of the pressure p4 or p4' resulting in the mixing unit (4) as a measured variable.

20. Device according to claim 18 or 19, wherein the first compression system (2) in the return system (26c) of the last compression stage (2c) has a condensate separator (24c) upstream of the anti-surge valve (27c) and downstream of the outlet (25c).

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