EP3969433A1

EP3969433A1 - Method and system for the synthesis of methanol

Info

Publication number: EP3969433A1
Application number: EP20724793.3A
Authority: EP
Inventors: Alexander Schulz; Nicolas VON WINNING; Sina KUNZ
Original assignee: ThyssenKrupp AG; ThyssenKrupp Industrial Solutions AG
Current assignee: ThyssenKrupp AG; ThyssenKrupp Industrial Solutions AG
Priority date: 2019-05-16
Filing date: 2020-05-06
Publication date: 2022-03-23
Also published as: CN113840818A; US20220162143A1; AU2020274854A1; WO2020229261A1; CA3140518A1; DE102019113003A1; JP2022533602A; AU2020274854B2

Abstract

The invention relates to a method for the synthesis of methanol (1), wherein: a CO2 stream (2), predominantly consisting of carbon dioxide, and a H stream (3), predominantly consisting of hydrogen, is supplied to a methanol reactor assembly (7) for conversion into methanol; a residual gas stream (9) containing unreacted hydrogen is recovered from the methanol reactor assembly (7); and the unreacted hydrogen is fed back, at least in part, to the methanol reactor assembly (7). The method is characterised in that the residual gas stream (9) is supplied to a hydrogen recovery assembly (8) for recovering a return stream (4) containing the unreacted hydrogen, and in that the molar hydrogen proportion in the return stream (4) is greater than in the residual gas stream (9). The invention also relates to a corresponding system for the synthesis of methanol (1).

Description

Process and plant for the synthesis of methanol

The invention relates to a method for the synthesis of methanol according to the preamble of claim 1 and a plant for the synthesis of methanol according to the preamble of claim 15.

The production of methanol takes place through an exothermic reaction, which provides hydrogen and carbon oxides as starting materials, which are fed as a gas stream to a corresponding reactor for the methanol synthesis. These substances can be obtained from various sources.

A first possibility consists in subjecting a carbon-containing energy carrier stream to steam reforming or, for example, catalytic partial oxidation, so that a synthesis gas is obtained that essentially contains hydrogen and carbon oxides. Depending on the type of energy source and the way the synthesis gas is generated, different proportions of hydrogen and the carbon oxides - and thus different stoichiometry - are achieved in the synthesis gas. The resulting stoichiometry can then be adapted by various measures such as subjecting a water-gas shift reaction. One advantage of this approach is that the energy source itself - e.g. B. natural gas - can be provided regularly at a high pressure, so that after the synthesis gas has been obtained, only a comparatively small pressure increase is necessary to achieve the pressure required for the methanol synthesis.

Another possibility for providing the starting materials for the synthesis of methanol is to use a gas stream with a high carbon dioxide content and without hydrogen. Such a gas flow can be obtained from a flue gas, that is, from an exhaust gas from a combustion. Such a gas flow could also be obtained from a plant for the production of bioethanol. Since such a flue gas does not contain any hydrogen, in this variant the hydrogen has to be provided from another source, for example from electrolysis. For the methanol synthesis, the gas with the starting materials is regularly circulated in a circuit, since usually a single passage of this gas through the reactor does not lead to a sufficiently extensive conversion into methanol. The converted methanol is regularly removed from the circulating gas by condensation. At the same time, however, inert substances also accumulate through the circulation, which cannot be sufficiently removed by this condensation. To remove these substances from the cycle, it is necessary to discharge part of the circulating gas as purge gas, which purge gas can then be burned, for example.

WO 2014/173452 A1, from which the present invention is based, describes such a method and a corresponding plant for the synthesis of methanol from a carbon dioxide stream and a separate hydrogen stream.

WO 2018/019875 A1 also shows such a method and a corresponding system.

It is a disadvantage of this prior art that hydrogen is always removed when gas is discharged. This discharged hydrogen is therefore lost for the methanol synthesis.

Based on this prior art, the object of the invention is therefore to reduce the proportion of hydrogen in the purge gas and thus to minimize the loss of hydrogen, which is relatively valuable for methanol synthesis.

In relation to a method for the synthesis of methanol according to the preamble of claim 1, this object is achieved by the features of the characterizing part of claim 1. In relation to a plant for the synthesis of methanol according to the preamble of claim 15, this object is achieved by the features of the characterizing part of claim 15.

The invention is based on the knowledge that hydrogen can be recovered from a residual gas of a methanol reactor before it is discharged and the recovered hydrogen is then returned to the methanol synthesis can be. In this way, the hydrogen can be used for the synthesis of methanol and is not just burned.

The proposed method is used for the synthesis of methanol, a C02 stream consisting predominantly of carbon dioxide and an H stream consisting predominantly of hydrogen being fed to a methanol reactor arrangement for conversion into methanol. The fact that the C02 stream consists predominantly of carbon dioxide means that the molar proportion of carbon dioxide in the C02 stream is at least 50%. The molar proportion of carbon dioxide in the CO 2 stream is preferably at least 95% and in particular at least 99%. The fact that the H stream consists mainly of hydrogen means that the molar proportion of hydrogen in the H stream is at least 50%. The molar proportion of hydrogen in the H stream is preferably at least 95% and in particular at least 99%. The conversion of the supplied substances into methanol is usually not complete.

In the method according to the proposal, a residual gas stream with unreacted hydrogen is obtained from the methanol reactor arrangement and the unreacted hydrogen is at least partially returned to the methanol reactor arrangement. In addition to the unreacted hydrogen, the residual gas stream can also contain unreacted carbon dioxide and carbon monoxide formed in the methanol reactor arrangement in particular as a result of the reverse water gas shift reaction. Likewise, the residual gas flow for the methanol synthesis can contain components such as nitrogen, methane and noble gases and by-products such as dimethyl ether. It is preferred that the methanol reactor arrangement is encompassed by a plant for the synthesis of methanol.

The proposed method is characterized in that the residual gas stream is fed to a hydrogen recovery arrangement for recovering a recycle stream with the unreacted hydrogen. The proposed method is further characterized in that the recycle stream consists predominantly of hydrogen. This means that the molar proportion of hydrogen in the recycle stream is at least 50%. The molar proportion of hydrogen in the recycle stream is preferably at least 95% and in particular at least 99%. It is also preferred that the molar proportion of hydrogen in the recycle stream is higher than in the residual gas stream. An enrichment of hydrogen takes place through the hydrogen recovery arrangement. The plant for the synthesis of methanol preferably comprises the hydrogen recovery arrangement.

It is preferred that a purge flow is also obtained from the hydrogen recovery arrangement, which purge flow preferably has a lower molar hydrogen content than the residual gas flow. In this way, proportionally more hydrogen is fed back than is removed by the purge flow. In principle, the purge flow can be discharged for any further use. The purge flow can be directed to a flare or to a catalytic post-combustion.

It is preferred that the purge stream is fed as fuel to a combustion device of a chemical plant for obtaining a substance. The substance obtained is a different substance than methanol. This chemical plant is preferably an additional plant compared to the plant for the synthesis of methanol. This chemical plant can, however, have devices in common with the proposed plant for the synthesis of methanol, in particular the hydrogen recovery arrangement. Likewise, this chemical plant is preferably a plant for extracting a substance from an output stream containing hydrocarbons. As an alternative or in addition, the chemical plant is set up to obtain a hydrocarbon-containing product stream. The energy from the chemical plant combustor can be used for virtually any purpose. It is preferred that the energy from the combustion device is used in the chemical plant for heating up a process stream and / or for generating steam. The chemical plant can in particular be a steameracker, a hydrogen plant or a dehydrogenation plant.

A preferred embodiment of the proposed process is characterized in that the recycle stream is fed as an H stream to the methanol reactor arrangement. In this way, the recycle stream can use the hydrogen for the methanol synthesis predominantly or even completely provide. This is particularly possible when the

Hydrogen recovery arrangement is not only supplied to the residual gas flow, but also one or more other hydrogen-containing flows. The

Recycle stream can then include the hydrogen of any of these hydrogen-containing streams. Here it may be that the hydrogen recovery arrangement is included in the chemical plant. In such a case, a relatively small proportion of hydrogen can be diverted from the hydrogen recovery arrangement of the chemical plant, which serves a purpose other than the synthesis of methanol, for the synthesis of methanol.

In particular, it can be the case that a hydrogen-containing fresh gas stream is fed to the hydrogen recovery arrangement for recovering the recycle stream. The hydrogen-containing fresh gas flow can in particular be obtained from a hydrogen production arrangement, that is to say a system for producing a hydrogen flow. The hydrogen production arrangement can be included in the chemical plant. In this way, there is also a double use for the production of hydrogen.

However, it can also be the case that, in addition to the hydrogen from the recycle stream, a fresh gas stream of hydrogen is fed to the methanol reactor arrangement. A corresponding further preferred embodiment of the proposed method is characterized in that the H stream is a fresh gas stream from a hydrogen recovery arrangement and that the recycle stream is recycled in addition to the H stream to the methanol reactor arrangement for conversion into methanol. This approach reduces the processing capacity requirements of the hydrogen recovery arrangement. The hydrogen production arrangement can comprise a system for producing hydrogen by electrolysis. The plant for the synthesis of methanol preferably comprises the hydrogen production arrangement. However, the chemical plant can also include the hydrogen generation arrangement.

Basically, the hydrogen recovery arrangement can recover hydrogen according to any technical principle carry out. According to a preferred embodiment of the proposed method it is provided that the hydrogen recovery arrangement has a pressure swing adsorption device (PSA). In particular, it can be that the hydrogen recovery arrangement has a pressure swing adsorption device for obtaining the recycle stream from the residual gas stream. The pressure swing adsorption device can likewise be set up to obtain the purge flow. Such a pressure swing adsorption device achieves a very high degree of purity in the recycle stream and is associated with a comparatively low pressure drop, so that the recycle stream for the methanol synthesis only has to be pressure increased again to a small extent. A further preferred embodiment of the proposed method provides that the hydrogen recovery arrangement has a further pressure swing adsorption device (PSA) and that the further pressure swing adsorption device is process-related downstream of the pressure swing adsorption device. In this case, an effluent from the pressure swing adsorption device of the further pressure swing adsorption device can be set up to obtain a further recycle stream with hydrogen from the effluent, the further recycle stream being fed to the methanol reactor arrangement for conversion into methanol

According to a further preferred embodiment of the proposed method, it is provided that the hydrogen recovery arrangement has a membrane device. In particular, the hydrogen recovery arrangement can have a membrane device for recovering the recycle stream from the residual gas stream. The membrane device is preferably set up to separate hydrogen.

However, it is also possible to combine different types of hydrogen recovery in the hydrogen recovery arrangement. A preferred variant provides that the residual gas flow is fed to the membrane device to generate a membrane hydrogen flow and a membrane residual flow and that the membrane residual flow is fed to the pressure swing adsorption device to generate a PSA hydrogen flow. In such a case it can either the membrane hydrogen stream or the PSA hydrogen stream form the recycle stream and the respective other stream forms the further recycle stream, the further recycle stream being fed to the methanol reactor arrangement for conversion to methanol. It is also possible for both recycle streams to be fed to the methanol reactor arrangement for conversion to methanol. However, the membrane hydrogen stream and the PSA hydrogen stream can also be combined to form the recycle stream.

According to a further preferred embodiment of the proposed method it is provided that the membrane hydrogen flow is obtained from a low pressure side of the membrane device and that the membrane residual flow is obtained from a high pressure side of the membrane device. It is therefore possible that the membrane hydrogen flow is obtained at a lower pressure than the membrane residual flow.

In addition to the recycle stream, further streams can also be returned to the methanol reactor arrangement. A preferred embodiment of the proposed method is characterized in that a recycle stream with further unreacted residual gas from the methanol reactor arrangement is returned to the methanol reactor arrangement for partial conversion into methanol. This is unreacted residual gas in addition to the unreacted residual gas of the residual gas flow. It is preferred that the recycle stream is increased in pressure by a recycle compressor assembly before it is returned to the methanol reactor arrangement. In this way, there is also a recirculation of the carbon dioxide and, if necessary, of the carbon monoxide produced in the methanol reactor arrangement. The plant for the synthesis of methanol preferably comprises the recycle compressor arrangement.

The recycle compressor arrangement can also be used to pressurize the recycle stream. Another preferred embodiment of the proposed method is therefore characterized in that the recycle stream is fed to the recycle stream. In particular, the recycle stream can be fed to the recycle stream before the pressure is increased by the recycle compressor arrangement. According to a preferred embodiment of the proposed method it is provided that the methanol reactor arrangement comprises a methanol separation arrangement for recovering the residual gas flow and a raw methanol flow. It is also preferred that the recycle stream is obtained from the methanol separation arrangement. The residual gas flow can be obtained from the methanol separation arrangement in that the residual gas flow is branched off from the recycle flow.

A preferred embodiment of the proposed method provides that the raw methanol stream is fed to a distillation for recovering the methanol. The plant for the synthesis of methanol preferably comprises the distillation.

In principle, it can be the case that the methanol reactor arrangement comprises only a single reactor stage or only a single reactor for the methanol synthesis. Several reactors for the methanol synthesis can be connected in parallel within a single reactor stage. According to a further preferred embodiment of the proposed method, it is provided that the methanol reactor arrangement has a plurality of reactor stages for methanol synthesis which are connected in series in terms of process technology. It is not necessary here for the reactor stages to follow one another directly in terms of process technology.

In correspondence with the large number of reactor stages, the methanol separating arrangement can also be designed in several stages. It is thus preferred that the methanol separation arrangement has a plurality of methanol separation devices, one methanol separation device being connected downstream of the plurality of methanol separation devices of a reactor stage of the plurality of reactor stages in terms of process technology. In other words, in terms of process technology, each methanol separating device is connected after a single one of the reactor stages and, if it is not the last reactor stage in terms of process technology, before the subsequent reactor stage. By removing methanol and water after each individual reactor stage, the reaction equilibrium can be improved for the respective subsequent reactor stage. A preferred embodiment of the proposed method is characterized in that a raw methanol partial flow and a staged residual gas flow with unreacted hydrogen are obtained from the methanol separation devices of the plurality of methanol separation devices. The stage residual gas stream can also contain carbon monoxide, nitrogen, methane, noble gases and / or other constituents. Likewise, the stage residual gas stream can also contain unreacted carbon dioxide. In particular, it can be the case that up to a last switched reactor stage of the plurality of reactor stages, the stage residual gas stream is fed to a reactor stage which is in each case downstream of the methanol separation device in terms of process technology. In other words, after each reactor stage, methanol is first separated off and the remaining residual gas is fed to the next reactor stage in each case, provided that such a next reactor stage is present. It is further preferred that the raw methanol substreams are combined to form the raw methanol stream.

In principle, the reactor stages can have reactors of any type. Another preferred embodiment of the proposed method is characterized in that at least one of the reactor stages for methanol synthesis has an isothermal reactor or consists of an isothermal reactor. In particular, it can be that all reactor stages for methanol synthesis each have an isothermal reactor or each consist of an isothermal reactor.

According to a further preferred embodiment of the proposed method, it is provided that the CO 2 stream and the H stream, preferably also the recycle stream, are fed to a first reactor stage of the plurality of reactor stages. It is also preferred that the increased pressure recycle stream is fed to the first reactor stage.

A preferred embodiment of the proposed method is characterized in that the residual gas stream is obtained from a methanol separation device which, in terms of process technology, is connected downstream of a residual gas recovery reactor stage, the residual gas recovery stage being connected in process technology to the first reactor stage. Put another way is here provided that the residual gas stream is obtained after a certain reactor stage, which is referred to here as the residual gas recovery reactor stage. This residual gas recovery reactor stage is connected downstream of the first reactor stage, so it is a different than the first reactor stage. In particular, the residual gas stream is obtained from the methanol separating device which, in terms of process technology, exactly follows this residual gas recovery reactor stage. In terms of process technology, the residual gas recovery reactor stage is preferably the last one of the plurality of reactor stages. In other words, the last reactor stage is the residual gas recovery reactor stage.

A further preferred embodiment of the proposed method is characterized in that the CO 2 flow and the H flow, preferably also the recycle flow, are increased in pressure by a feed gas compressor arrangement before being fed to the methanol reactor arrangement. In principle, the feed gas compressor arrangement can be designed in one stage, so that the feed gas compressor arrangement has only a single compressor stage. The CO 2 stream and the H stream, preferably also the recycle stream, are preferably increased to a synthesis pressure of between 50 bar and 80 bar by the feed gas compressor arrangement.

It is preferred that the feed gas compressor arrangement has a multiplicity of compressor stages connected in series in terms of process technology for increasing pressure. The feed gas compressor arrangement preferably has four compressor stages. Such a multistage makes it possible that certain flows, which can be provided with a higher pressure, do not have to pass through all compressor stages. The plurality of compressor stages can be a plurality of compressor stages of a single compressor, so that the plurality of compressor stages have a common shaft. Likewise, the multitude of compressor stages can also be formed by a multitude of individual compressors.

It is particularly preferred that the H-flow is fed between other compressor stages of the plurality of compressor stages of the feed gas compressor arrangement to increase the pressure than the CO 2 flow. This is useful if the H-stream with a different pressure is provided as the C02 stream. It is also possible, however, for the H flow to be supplied between those compressor stages of the multiplicity of compressor stages for increasing the pressure, between which the CO 2 flow is also supplied. This is advantageous if the H flow is provided at the same pressure as the CO 2 flow. It can also be the case that the recirculation flow between other compressor stages of the plurality of compressor stages of the feed gas compressor arrangement is fed to the pressure increase as the further recirculation flow. The plant for the synthesis of methanol preferably comprises the feed gas compressor arrangement.

According to a preferred embodiment of the proposed method, it is provided that the CO 2 stream consists essentially of carbon dioxide. Alternatively or in addition, it can be that the H stream consists essentially of hydrogen.

The proposed plant is used for the synthesis of methanol and has a methanol reactor arrangement to which a C02 stream consisting predominantly of carbon dioxide and an H stream consisting predominantly of hydrogen are fed for partial conversion into methanol.

In the proposed plant, a residual gas stream with unreacted hydrogen is obtained from the methanol reactor arrangement and the unreacted hydrogen of the residual gas flow is at least partially returned to the methanol reactor arrangement.

The proposed system is characterized in that the system has a hydrogen recovery arrangement to which the residual gas stream is fed to recover a recycle stream with the unreacted hydrogen and that the molar hydrogen content in the recycle stream is higher than in the residual gas stream.

Features, advantages and properties of the proposed system correspond to the features, advantages and properties of the proposed method and vice versa. Further details, features, objectives and advantages of the present invention are explained below with reference to the drawing, which only shows exemplary embodiments. In the drawing shows

1 schematically shows the flow diagram of a plant for carrying out the proposed method according to a first one

Embodiment,

2 schematically shows the flow diagram of a plant for carrying out the proposed method according to a second exemplary embodiment,

3 schematically shows the flow diagram of a plant for carrying out the proposed method according to a third

Embodiment,

4 schematically shows the flow diagram of a plant for carrying out the proposed method according to a fourth embodiment,

5 schematically shows the flow diagram of a plant for carrying out the proposed method according to a fifth embodiment and

6 schematically shows the flow diagram of a plant for carrying out the proposed method according to a sixth embodiment.

The plant shown in FIG. 1 according to a first exemplary embodiment of the proposed plant is used for the synthesis of methanol 1 and can be operated according to the proposed method.

A C02 stream 2 consisting essentially of carbon dioxide, an H stream 3 consisting essentially of hydrogen and a recycle stream 4 also consisting essentially of hydrogen are passed through a feed gas compressor arrangement 5 increased in pressure and then fed to a first reactor stage 6a of a methanol reactor arrangement 7.

This feed gas compressor arrangement 5 is designed in several stages. For the sake of simplicity, the feed gas compressor arrangement 5 is shown here with three compressor stages 21a-c of an individual compressor connected one behind the other in terms of process technology, wherein a feed gas compressor arrangement 5 can regularly have four compressor stages. It can be seen that the CO 2 flow 2, the H flow 3 and the recirculation flow 4 are supplied upstream of a respective different compressor stage 21a-c. The C02 stream 2 is supplied without pressure, which is why it should be increased in pressure through all compressor stages 21a-c of the feed gas compressor arrangement 5 in order to achieve the pressure aimed at for the methanol synthesis and it is consequently already supplied to the first compressor stage 21a. The H stream 3 is supplied at a slightly higher pressure and is therefore supplied in terms of process technology after the first compressor stage 21a and before the second compressor stage 21b. Finally, the recirculation stream 4 is supplied with the highest pressure and therefore, in terms of process technology, between the second compressor stage 21b and the third compressor stage 21c.

A recycle stream 13 is also fed to the first reactor stage 6a. In this first reactor stage 6a, which consists of a single isothermal reactor, a partial conversion of the carbon dioxide and hydrogen into methanol takes place.

The C02 stream 2 is obtained from the flue gas of a power plant, not shown here. The H-stream 3 is obtained from an electrolysis plant, likewise not shown here, for the production of hydrogen, the H-stream 3 also being able to occur without pressure in this example. However, it is also conceivable that the H flow 3 is provided with a lower pressure than the CO 2 flow 2, in which case the feed to the compressor stages 21a-c would be swapped. The recycle stream 4 is obtained from a hydrogen recovery arrangement 8 of the plant, to which a residual gas stream 9 from the methanol reactor arrangement 7 is fed for this purpose, which has unreacted starting materials of the methanol synthesis and therefore in particular unreacted hydrogen.

Downstream of the first reactor stage 6a in terms of process technology, although not immediately, is a second reactor stage 6b of the methanol reactor arrangement 7, which second reactor stage 6b here also consists of a single isothermal reactor. The methanol reactor arrangement 7 has a methanol separating arrangement 10, which is set up by condensation of raw methanol to obtain the residual gas flow 9 and a raw methanol flow 12. The methanol separation arrangement 10 in turn consists of a first methanol separation device 11a, which is connected in terms of process technology between the first reactor stage 6a and the second reactor stage 6b, and a second methanol separation device 11b, which in terms of process technology is connected downstream of the second reactor stage 6b.

The gas mixture with methanol and unreacted residual gas from the first reactor stage 6a is fed to the first methanol separation device 11a and from this methanol separation device 11a a first raw methanol substream 14a, essentially consisting of raw methanol, and a first stage residual gas flow 15a with the unreacted Residual gases obtained from the first reactor stage 6a. The first stage residual gas stream 15a is fed to the second reactor stage 6b for the synthesis of methanol. Correspondingly, the gas mixture from the second reactor stage 6b is fed to the second methanol separation device 11b and a second raw methanol substream 14b and a second stage residual gas stream 15b are obtained from this. The first raw methanol substream 14a and the second raw methanol substream 14b are combined to form the raw methanol stream 12, which in turn is fed to a distillation 16 to obtain the methanol 1.

The second stage residual gas flow 15b is divided into the residual gas flow 9, which is fed to the hydrogen recovery arrangement 8, and the recycle flow 13. In this way, both the residual gas stream 9 and the recycle stream 13 are obtained from the methanol separation arrangement 10. The recycle stream 13 is fed to a recycle compressor arrangement 17 to increase the pressure and then to the first reactor stage 6a. Since the residual gas flow 9 is obtained immediately downstream of the second reactor stage 6b, the second reactor stage 6b can be referred to as the residual gas acquisition reactor stage 20.

In the exemplary embodiment in FIG. 1, the hydrogen recovery arrangement 8 is a pressure swing adsorption device 18 which extracts the recycle stream 4 from the residual gas stream 9. A purge stream 19 is also obtained, which is fed to a combustion device (not shown here) of a separate chemical plant and is burned there. The composition of the purge stream 19 essentially corresponds to the composition of the residual gas stream 9 minus the recycle stream 4. The hydrogen returned to the methanol reactor arrangement 7 through the recycle stream 4 is not burned with the purge stream 19, but is available for the methanol synthesis.

The system shown in FIG. 2 according to a second exemplary embodiment of the proposed system can be operated according to the proposed method. This embodiment basically corresponds to the first embodiment of FIG. 1, but the recycle stream 4 from the hydrogen recovery arrangement 8 is not passed through

Feed gas compressor arrangement 5 increased in pressure before being fed to the first reactor stage 6a. Rather, the recycle stream 4 is fed to the recycle stream 13. This feed takes place upstream of the recycle compressor arrangement 17 in terms of process technology, so that the return flow 4 is increased in pressure together with the recycle flow 13 through the recycle compressor arrangement 17. Compared to the exemplary embodiment of FIG. 1, this firstly relieves the load on the feed gas compressor arrangement 5. It can also be the case that the pressure of the recycle stream 4 is close to the pressure of the recycle stream 13, so that it only needs to be relaxed slightly, and therefore merging the recycle stream 4 with the recycle stream 13 is more favorable than feeding the recycle stream to the feed gas compressor arrangement 5.

The system shown in FIG. 3 according to a third exemplary embodiment of the proposed system can according to the proposed method operate. This exemplary embodiment also basically corresponds to the first exemplary embodiment in FIG. 1, but here the hydrogen recovery arrangement 8 consists of a membrane device 22 for recovering the recycle stream 4 and the purge stream 19. In particular if a greater pressure drop in the recycle stream 4 compared to the residual gas stream 9 is accepted - which in principle can be compensated for by the pressure increase of the feed gas compressor arrangement 5 - a particularly high proportion of the hydrogen in the residual gas stream 9 can be recovered by the recycle stream 4. Accordingly, the loss of hydrogen in the purge stream 19 is low.

The system shown in FIG. 4 according to a fourth exemplary embodiment of the proposed system is based on the third exemplary embodiment in FIG. 3 and can also be operated in accordance with the proposed method. Here the hydrogen recovery device 8 comprises both a membrane device 22 and a pressure swing adsorption device 18. The residual gas flow 9 is specifically fed to the membrane device 22. A membrane hydrogen stream 23 enriched with hydrogen and a correspondingly hydrogen-poor membrane residual stream 24 are obtained from the membrane device 22. The membrane residual flow 24 is fed to the pressure swing adsorption device 18, so that a PSA-hydrogen flow 25 essentially consisting of hydrogen and the purge flow 19 are obtained therefrom. The PSA hydrogen stream 25 is here combined with the membrane hydrogen stream 23 to form the recycle stream 4. However, it would also be possible to conduct only the membrane hydrogen stream 23 as recycle stream 4 and the PSA hydrogen stream 25 separately as a further recycle stream to the feed gas compressor arrangement 5. In this case, the membrane hydrogen stream 23 and the PSA hydrogen stream 25 could be fed in upstream of different compressor stages 21a-c because of their different pressures. Because the membrane device 22 is connected upstream of the pressure swing adsorption device 18 in this manner described for the fourth exemplary embodiment, the pressure swing adsorption device 18 is relieved to such an extent that it can be designed to be smaller. Overall, a very high proportion of the hydrogen can thus be returned in the residual gas flow 9. The system shown in FIG. 5 according to a fifth exemplary embodiment of the proposed system can be operated according to the proposed method and is based in principle on the first exemplary embodiment in FIG. 1, whereby - as will be described in more detail - the H-stream 3 does not originate electrolysis is obtained. However, here the hydrogen recovery arrangement 8, which is designed as a pressure swing adsorption device 18, is also used for the hydrogen-containing fresh gas flow 26, which fresh gas flow 26 is obtained from a hydrogen recovery arrangement 27. The hydrogen production arrangement 27 consists of a steam reformer 28, to which a natural gas stream 31 is fed and from which a synthesis gas stream 32 with carbon oxides and hydrogen is obtained. This synthesis gas stream 32 is fed to a reactor 29 of the hydrogen recovery arrangement 27 for the water-gas shift reaction to increase the hydrogen content, from which reactor 29 the fresh gas stream 26 is then obtained. The purge gas 19 from the pressure swing adsorption device 18 can then be used together with a fuel gas 30 to operate the steam reformer 28. Deviating from the embodiment of FIGS. 1 to 4, the pressure swing adsorption device 18 and the hydrogen recovery arrangement 27 added in this embodiment are also part of a chemical plant 33, the pressure swing adsorption device 18 being part of this chemical plant 33 and part of the proposed plant for the synthesis of Is methanol.

Through the joint use of the pressure swing adsorption device 18, the recycle stream 4 from the hydrogen recovery arrangement 8 forms the H stream 3, so that the recycle stream 4 is thus fed as H stream 3 to the methanol reactor arrangement 7. As shown in FIG. 5, only part of the hydrogen obtained from the hydrogen recovery arrangement 8 forms the recycle stream 4 and the further hydrogen can be fed to a use in the chemical plant 33.

Finally, the system shown in FIG. 6 according to a sixth embodiment of the proposed system can also be operated according to the proposed method and starts with the fifth Embodiment from. However, here, similar to the fourth exemplary embodiment, the hydrogen recovery arrangement 8 has a membrane device 22 and a pressure swing adsorption device 18. According to the fourth embodiment, the membrane residual flow 24 is also fed to the pressure swing adsorption device 18 here, together with the fresh gas flow 26. The PSA hydrogen flow 25 now forms the recycle flow 4, which as H flow 3 emulates the methanol reactor arrangement 7 Pressure increase is supplied by the feed gas compressor arrangement 5. The membrane hydrogen stream 23 forms a further recycle stream 34, which is fed to the methanol reactor arrangement 7 after the pressure has been increased by the feed gas compressor arrangement 5.

Claims

1. A process for the synthesis of methanol (1), wherein a predominantly carbon dioxide (2) stream (2) and a hydrogen (3) predominantly hydrogen stream are fed to a methanol reactor arrangement (7) for conversion into methanol, wherein a residual gas stream (9) with unreacted hydrogen is obtained from the methanol reactor arrangement (7) and wherein the unreacted hydrogen is at least partially returned to the methanol reactor arrangement (7), characterized in that the residual gas flow (9) to a hydrogen recovery arrangement (8) Obtaining a recycle stream (4) is fed with the unreacted hydrogen and that the recycle stream (4) consists predominantly of hydrogen.

2. The method according to claim 1, characterized in that the recycle stream (4) is fed as H-stream (3) of the methanol reactor arrangement (7), in particular that a hydrogen-containing fresh gas stream (26) of the hydrogen recovery arrangement (8) to recover the Recycle stream (4) is supplied.

3. The method according to claim 1 or 2, characterized in that the H stream (3) is a fresh gas stream (26) from a hydrogen recovery arrangement (27) and that the recycle stream (4) in addition to the H stream (3) to the methanol Reactor arrangement (7) is recycled for conversion into methanol.

4. The method according to any one of claims 1 to 3, characterized in that the hydrogen recovery arrangement (8) has a pressure swing adsorption device (18) (PSA), in particular that the hydrogen recovery arrangement (8) has a pressure swing adsorption device (18) (PSA) for recovering the recycle stream (4) from the residual gas stream (9).

5. The method according to any one of claims 1 to 4, characterized in that the hydrogen recovery arrangement (8) has a membrane device (22), in particular that the Hydrogen recovery arrangement (8) has a membrane device (22) for obtaining the recycle stream (4) from the residual gas flow (9), preferably that the residual gas flow (9) of the membrane device (22) for obtaining a membrane hydrogen flow (23) and a Membrane residual flow (24) is fed and that the membrane residual flow (24) is fed to the pressure swing adsorption device (18) for obtaining a PSA-hydrogen flow (25).

6. The method according to any one of claims 1 to 5, characterized in that a recycle stream (13) with further unreacted residual gas of the methanol reactor arrangement (7) to the methanol reactor arrangement (7) is recycled for partial conversion into methanol, preferably that the Recycle stream (13) is increased in pressure by a recycle compressor arrangement (17) before being returned to the methanol reactor arrangement (7).

7. The method according to claim 6, characterized in that the recycle stream (4) is fed to the recycle stream (13), in particular before the pressure is increased by the recycle compressor arrangement (17).

8. The method according to any one of claims 1 to 7, characterized in that the methanol reactor arrangement (7) comprises a methanol separation arrangement (10) for recovering the residual gas stream (9) and a raw methanol stream (12), in particular that the recycle stream ( 13) is obtained from the methanol separation arrangement (10).

9. The method according to any one of claims 1 to 8, characterized in that the methanol reactor arrangement (7) has a plurality of process technology in series reactor stages (6a, b) for methanol synthesis, preferably that the methanol separation arrangement (10) a plurality of methanol separation devices (11a, b), one methanol separation device (11a, b) of the plurality of methanol separation devices (11a, b) of a reactor stage (6a, b) of the plurality of reactor stages (6a, b) in process engineering is downstream.

10. The method according to claim 9, characterized in that from the methanol separation devices (11a, b) of the plurality of methanol separation devices each have a raw methanol substream (14a, b) and a staged residual gas stream (15a, b) with unreacted hydrogen is obtained, in particular that up to a last connected reactor stage (6b) of the plurality of reactor stages (6a, b) the stage residual gas stream (15a, b) of one of the methanol separation devices (11a, b) in each case process technology downstream reactor stage (6a, b) is supplied, preferably that the raw methanol substreams (14a, b) are combined to form the raw methanol stream (12).

11. The method according to claim 9 or 10, characterized in that the C02 stream (2) and the H stream (3), preferably also the recycle stream (4), a first reactor stage (6a) of the plurality of reactor stages (6a, b) are fed, preferably that the pressure-increased recycle stream (13) is fed to the first reactor stage (6a).

12. The method according to any one of claims 9 to 11, characterized in that the residual gas stream (9) is obtained from a methanol separating device (11a, b) which, in terms of process technology, is connected downstream of a residual gas recovery reactor stage (20), the residual gas recovery reactor stage (20) downstream of the first reactor stage (6a) in terms of process technology, preferably that the residual gas recovery reactor stage (20) among the plurality of reactor stages (6a, b) is connected last in terms of process technology.

13. The method according to any one of claims 1 to 12, characterized in that the CO 2 stream (2) and the H stream (3), preferably also the recycle stream (4), before being fed to the methanol reactor arrangement (7) a feed gas compressor arrangement (5) can be increased in pressure, preferably that the feed gas compressor arrangement (5) has a plurality of compressor stages (21a-c) connected in series in terms of process technology for increasing the pressure, in particular that the H-flow (3) is between other compressor stages (21a-c) the plurality of compressor stages (21a-c) of the feed gas compressor arrangement (5) is fed to the pressure increase as the CO 2 flow (2).

14. The method according to any one of claims 1 to 13, characterized in that the C02 stream (2) consists essentially of carbon dioxide and / or that the H stream (3) consists essentially of hydrogen.

15. Plant for the synthesis of methanol with a methanol reactor arrangement (7), soft a C02 stream (2) consisting predominantly of carbon dioxide and an H stream consisting predominantly of hydrogen (3) for conversion into methanol, with a residual gas stream (9) is obtained with unreacted hydrogen from the methanol reactor arrangement (7) and the unreacted hydrogen of the residual gas stream (9) is at least partially returned to the methanol reactor arrangement (7), characterized in that the system has a hydrogen recovery arrangement (8), to which the residual gas stream (9) is fed to obtain a recycle stream (4) with the unreacted hydrogen and that the recycle stream (4) consists predominantly of hydrogen.