Method and system for synthesizing methanol

Abstract

The invention relates to a method and a system for synthesizing methanol (1), wherein: a hydrogen stream (35) including external hydrogen is supplied to a synthesis gas stream (2); part of a remaining gas stream (15) discharged from a methanol reactor assembly (4), and / or of a recovery stream (6) optionally supplied to a hydrogen recovery assembly (5), and / or of a stream (71) downstream of the hydrogen recovery assembly (5) is branched off and is supplied to a synthesis gas reactor assembly (13) as return stream (40). This concept allows the efficiency of methanol production to be significantly increased. Furthermore, undesired emissions can be reduced and thus the ecobalance of the method or the system improved.

Description

[0001] Process and plant for the synthesis of methanol

[0002] The invention relates to a process for the synthesis of methanol according to the preamble of claim 1 and to a plant for the synthesis of methanol according to the preamble of claim 21.

[0003] Methanol is an important basic chemical used in the synthesis of higher or functionalized hydrocarbon compounds and as a solvent. Methanol serves, for example, as a starting material for the production of formaldehyde, formic acid, and acetic acid.

[0004] Methanol is typically produced in a reactor assembly within a methanol synthesis plant (methanol reactor assembly). A synthesis gas stream containing hydrogen and carbon oxides is fed to the methanol reactor assembly, and an (exothermic) chemical reaction takes place to produce methanol. Synthesis gas can be generated in a synthesis gas reactor assembly located upstream of the methanol reactor assembly. Primarily, carbon-containing gases (i.e., carbon-containing energy sources) such as natural gas or biogas are converted into synthesis gas. Such carbon-containing energy sources often contain methane. The synthesis gas reactor assembly and the methanol reactor assembly can together form a methanol synthesis plant.

[0005] To convert the carbon-containing energy source into synthesis gas, the aforementioned synthesis gas reactor arrangement can be based, for example, on the principle of autothermal reforming or partial oxidation and comprise corresponding reactors (e.g., a reforming reactor or oxidation reactor, respectively). Likewise, the synthesis gas reactor arrangement can comprise a steam reformer. The use of a steam reformer can be advantageous when adding CO2 or using a CO2-rich carbon-containing energy source such as biogas. This is generally known in the art.

[0006] Processes for the synthesis of methanol are described, for example, in those publications WO 2020 / 058859 Al, WO 2007 / 108014 Al, DE 10 2016 213 668 Al, WO 2013 / 144041 Al, WO 2020 / 048809 Al, DE 10 2019 124 078 Al, US 2019 / 0185887 Al and WO 2020 / 249923 Al, which form the technological background of the present invention.

[0007] Depending on how the synthesis gas stream is produced and the energy source used for the synthesis gas, the proportion of hydrogen in the resulting synthesis gas stream may be lower than originally desired. For example, the proportion of hydrogen may be substoichiometric. To improve the stoichiometry, it is therefore often advisable to recover unreacted hydrogen from a residual gas of the reactor assembly using a hydrogen recovery system and return this hydrogen to the reactor assembly. Such a hydrogen-rich stream returned to the reactor assembly can, to a certain extent, compensate for the aforementioned hydrogen deficiency caused by the substoichiometry.

[0008] Likewise, it is known that a hydrogen deficiency occurring during methanol synthesis can be (at least partially) compensated by adding external hydrogen. The external hydrogen can come from fossil sources or be generated renewably and added to the synthesis gas stream.

[0009] Both methanol synthesis plants with integrated hydrogen recovery and plants with an external hydrogen supply generate purge gas, which must be removed from the synthesis or recovery circuit to prevent excessive accumulation of inert components such as nitrogen and methane. Such purge gas is typically burned off as fuel gas. To ensure a satisfactory environmental impact of such synthesis plants, it is desirable to keep the amount of purge or fuel gas generated as low as possible.

[0010] The invention is based on the object of providing a process and a plant for the synthesis of methanol, which, on the one hand, can compensate for a substoichiometric presence of hydrogen and, on the other hand, can reduce the proportion of purge or fuel gas generated. A particular object of the invention is therefore, on the one hand, to increase the efficiency and yield in methanol synthesis and, on the other hand, to improve the environmental friendliness and ecological balance. This object is achieved by a process having the features of claim 1 and a plant having the features of claim 21.

[0011] First, the invention relates to a process for the synthesis of methanol, wherein a carbon-containing energy carrier stream is fed to a synthesis gas reactor arrangement to obtain a synthesis gas stream containing hydrogen and carbon oxides. Optionally, the synthesis gas stream can be fed to a synthesis gas compressor to increase the pressure. According to the invention, the synthesis gas stream, optionally the pressurized synthesis gas stream, is fed at least partially to a first reactor stage of a methanol reactor arrangement for at least partial conversion into methanol. Optionally, unreacted residual gas from the first reactor stage is subsequently fed to a second reactor stage of the methanol reactor arrangement for at least partial conversion into methanol. A residual gas stream containing unreacted carbon oxides is obtained from the methanol reactor arrangement. This residual gas stream is fed to a recycle compressor to increase the pressure of the residual gas stream.wherein the pressure-increased residual gas stream is fed to the methanol reactor arrangement for at least partial conversion into methanol, wherein optionally a recovery stream comprising unreacted residual gas from the first and / or second reactor stage is fed to a hydrogen recovery arrangement for obtaining an H2 recycle stream, which H2 recycle stream comprises unreacted hydrogen from the unreacted residual gas from the first reactor stage and / or from the unreacted residual gas from the second reactor stage, wherein the unreacted hydrogen of the H2 recycle stream is again fed to the first reactor stage for at least partial conversion into methanol. The process is characterized in that upstream or downstream of the synthesis gas reactor arrangement, a hydrogen stream with external hydrogen is fed to one of the streams, and that a portion of the residual gas stream and / or the optional recovery stream,and / or a stream downstream of the hydrogen recovery arrangement and fed to the synthesis gas reactor arrangement as a recycle stream. A preferred embodiment may be one in which the water stream with external hydrogen is fed to the synthesis gas stream (downstream of the synthesis gas reactor arrangement). The proposed process serves to synthesize methanol. In the proposed process, a carbon-containing energy carrier stream is fed to a synthesis gas reactor arrangement to obtain a synthesis gas stream containing hydrogen and carbon oxides. The synthesis gas stream thus comprises hydrogen, carbon monoxide, and carbon dioxide and may also contain other components, such as, in particular, nitrogen and noble gases. The synthesis gas stream can also be referred to as a fresh gas stream.

[0012] The synthesis gas stream can be fed to a synthesis gas compressor for pressure increase. The designated synthesis gas compressor can be designed with one or more stages. The (optionally pressurized) synthesis gas stream is fed at least partially to a first reactor stage of a methanol reactor arrangement for at least partial conversion to methanol. It is preferred that the (optionally pressurized) synthesis gas stream be fed essentially entirely to the first reactor stage. However, it is also possible for a portion of the synthesis gas stream to be diverted beforehand. The characteristic of "at least partial conversion to methanol" is based on the fact that an unreacted residue of reactants escapes from the methanol reactor arrangement, and therefore the conversion cannot proceed completely. The methanol reactor arrangement can have several (in particular two, but also more than two) reactor stages or only a single reactor stage.If the methanol reactor arrangement does not have multiple reactor stages, the first reactor stage is the only reactor stage in the methanol reactor arrangement. The first reactor stage of the methanol reactor arrangement is the reactor stage in the methanol reactor arrangement to which the synthesis gas stream is at least partially fed before it or a remaining residual gas stream is fed to another, e.g., a second, reactor stage. In this respect, the first reactor stage is the reactor stage in the methanol reactor arrangement that is located first in terms of process technology. This circumstance corresponds to the possible designation of the synthesis gas stream as a fresh gas stream. Each individual reactor stage in the methanol reactor arrangement can have several individual reactors for methanol synthesis that are connected in parallel in terms of process technology.

[0013] In the proposed process, a residual gas stream containing unreacted carbon oxides is obtained from the methanol reactor arrangement, which is then fed to a recycling compressor to increase the pressure of the residual gas stream. The residual gas stream may also contain unreacted hydrogen or even methane (which has not previously been converted into synthesis gas). The residual gas stream may also contain inert components such as nitrogen or noble gases. If the methanol reactor arrangement has more than one reactor stage (e.g. two reactor stages), this residual gas stream can be obtained after any reactor stage. A residual gas stream can also be present between the first and second reactor stages. An unreacted substance / component orAn unreacted component is understood here and below to be a substance (in the gaseous state) which was fed as a reactant for the methanol synthesis to a reactor stage of the methanol reactor arrangement, in particular the first reactor stage, and then exited the reactor stage without having participated in a reaction to synthesize methanol. An unreacted substance can, so to speak, be a substance fed to the synthesis gas reactor arrangement but not converted there. The recycle compressor serves to circulate the substantial portion of the unreacted residual gas through the methanol reactor arrangement. The process further provides that the pressure-increased residual gas stream is fed to the methanol reactor arrangement for partial conversion into methanol. This therefore involves recirculating the now pressure-increased residual gas stream to the methanol reactor arrangement from which the residual gas stream was obtained.

[0014] In an optional variant, unreacted residual gas from the first and / or second reactor stage can be fed in the form of a recovery stream to a hydrogen recovery arrangement for obtaining an H recycle stream, which H recycle stream comprises unreacted hydrogen from the unreacted residual gas from the first reactor stage and / or from the unreacted residual gas from the second reactor stage, wherein the unreacted hydrogen from the H recycle stream is fed again to the first reactor stage for at least partial conversion into methanol. Typically, only a partial stream of the unreacted residual gas (e.g., from the first and / or second reactor stage) is fed to the hydrogen recovery arrangement as a recovery stream. The recovery stream can be obtained from the unreacted residual gas from the first and / or second reactor stage, for example by branching off.This is because, according to the invention, a partial stream of the recovery stream can be fed to the synthesis gas reactor arrangement as a recycle stream. The H recycle stream comprises unreacted hydrogen from the unreacted residual gas (of the first and / or second reactor stage), which unreacted hydrogen of the H recycle stream is fed again to the first reactor stage for at least partial conversion into methanol. The unreacted hydrogen of the H recycle stream may be only a portion of the total unreacted hydrogen of the first and / or second reactor stage and / or only a portion of the total unreacted hydrogen of the unreacted residual gas. The unreacted hydrogen of the H recycle stream can be fed back to the first reactor stage both directly and indirectly. In the case of indirect feeding, the unreacted hydrogen is therefore first fed to other devices.

[0015] The proposed method is characterized in that a hydrogen stream containing external hydrogen is supplied to one of the streams upstream or downstream of the synthesis gas reactor arrangement, and in that a portion of the residual gas stream and / or the optional recovery stream is diverted and fed to the synthesis gas reactor arrangement as a recycle stream. A preferred embodiment may be one in which the water stream containing external hydrogen is supplied to the synthesis gas stream (downstream of the synthesis gas reactor arrangement). However, the external hydrogen does not necessarily have to be supplied to the synthesis gas stream (i.e., downstream of the synthesis gas reactor arrangement); it may also be provided to feed the external hydrogen into the system before synthesis gas generation.

[0016] By adding external hydrogen, the aforementioned hydrogen recovery system can be reduced in size or even eliminated entirely. Compared to a process without the addition of external hydrogen, a smaller amount of internal hydrogen, or even no internal hydrogen, needs to be generated by a hydrogen recovery system when external hydrogen is added.

[0017] Whether a hydrogen recovery system is completely omitted or the size of the hydrogen recovery system is reduced, purge gas must be removed to prevent excessive accumulation of inert components such as nitrogen and methane. A smaller hydrogen recovery system or the omission of one can result in a larger residual gas flow, in addition to the need to remove purge gas or fuel gas.

[0018] To avoid this, the proposed invention provides for diverting a portion of the residual gas stream, and / or the optional recovery stream, and / or a stream downstream of the hydrogen recovery arrangement and feeding it to the synthesis gas reactor arrangement as a recycle stream. This reduces the residual gas stream fed to the recycle compressor and then again to the methanol reactor arrangement (i.e., less unreacted residual gas circulates in the methanol reactor arrangement). Unreacted residual gas from the first reactor stage and / or unreacted residual gas from the optional second reactor stage is thus fed back to the methanol reactor arrangement (i.e., the reactor stages) in a smaller proportion. The proportion of residual gas remaining or circulating in the methanol reactor arrangement is thus reduced. Those components not converted to synthesis gas during synthesis gas production (e.g.,Methane) that have entered the synthesis gas stream can be recycled back into the synthesis gas reactor arrangement and converted there into synthesis gas. Furthermore, recycling reduces the total amount of fuel gas produced, which – since fuel gas is usually burned off – has a positive effect on the ecological balance of methanol synthesis. For example, the residual gas may contain a certain amount of methane. If this is recycled back into the synthesis gas reactor arrangement as fuel gas instead of being burned off, it can be converted – at least to a certain extent – ​​into synthesis gas and ultimately into methanol.The aforementioned effects can be achieved if only a portion of the residual gas stream is diverted and fed to the synthesis gas reactor arrangement as a recycle stream, but also if only a portion of the recovery stream (this can be provided optionally if a hydrogen recovery arrangement is used) is recirculated. Since both the recovery stream and the residual gas stream contain unreacted residual gas, the aforementioned effects can be achieved with both recycle variants. A combined recycle of a diverted portion of the residual gas stream and a diverted portion of the recovery stream can also be provided and advantageous. A "diversion" does not necessarily mean a piping branch, but can also be understood as a "feed to" or "line to" (e.g., to the synthesis gas reactor arrangement).

[0019] Advantageous embodiments of the invention are described below, including those features of the invention specified in the subclaims. Further embodiments or features of the invention not specified in the subclaims may also be described below. All of the further embodiments or features described in the subclaims and below may specify the invention across category boundaries. Thus, those embodiments or features mentioned in connection with the process proposed by the invention (for the synthesis of methanol) may also readily represent embodiments or features of the plant proposed by the invention (for the synthesis of methanol), and vice versa. The same applies to other claim categories not mentioned here (e.g., a use).

[0020] According to a first embodiment of the invention, it can be provided that the synthesis gas stream is fed to a heat recovery device for recovering heat from the synthesis gas stream and then to the synthesis gas compressor. It is conceivable that the synthesis gas stream is fed to another device or several other devices between the heat recovery device and the synthesis gas compressor. It should also be noted that the heat recovery device usually represents only one stage of a heat recovery arrangement with several heat recovery devices. In other words, it can be that the synthesis gas stream is fed to only one heat recovery device of several interconnected heat recovery devices.

[0021] According to a further embodiment of the proposed process, the unreacted hydrogen of the H recycle stream can be pressure-increased at least partially from the first reactor stage until it is fed back to the first reactor stage by the recycle compressor with the unreacted carbon oxides. In other words, at least a portion of the unreacted hydrogen in the H recycle stream can be pressure-increased by the recycle compressor between the exit of this unreacted hydrogen from the first reactor stage and the refeed of this unreacted hydrogen to the first reactor stage. Since the recycle compressor—as already described—pressure-increases the residual gas stream containing unreacted carbon oxides, the pressure increase of the unreacted hydrogen by the recycle compressor can occur together with the unreacted carbon oxides.The unreacted hydrogen of the H recycle stream can be essentially completely pressurized from the first reactor stage until it is fed back to the first reactor stage by the recycle compressor with the unreacted carbon oxides.

[0022] The synthesis gas reactor arrangement, the synthesis gas compressor, the methanol reactor arrangement, the heat recovery device, the recycle compressor and the hydrogen recovery arrangement can be comprised in a plant for the synthesis of methanol.

[0023] In principle, the residual gas stream fed to the recycle compressor can have any composition, as long as the residual gas stream comprises unreacted carbon oxides in any proportion and optionally unreacted hydrogen from the recovery stream.

[0024] According to a further embodiment of the proposed method, it can be provided that the hydrogen stream, for example from a hydrogen recovery device, is fed to the synthesis gas stream after it exits the heat recovery device. Thus, the feed of the hydrogen stream to the synthesis gas stream does not impair the heat recovery from the synthesis gas stream, which is advantageous for environmental impact reasons (e.g., due to a possible temperature reduction after the feed of the hydrogen stream). It is also advantageous that the hydrogen stream is fed to the synthesis gas stream before it is fed into the synthesis gas compressor. This can ensure that a substoichiometric hydrogen content in the synthesis gas stream can be at least partially compensated before the synthesis gas enters the first reactor stage of the methanol reactor arrangement.The hydrogen stream, as well as the external hydrogen, can in principle be fed into the system at any point, including upstream of the recycle compressor, downstream of the first reactor stage, upstream of the synthesis gas reactor arrangement, etc. According to a further embodiment of the proposed process, unreacted hydrogen from the H recycle stream can be additionally fed to the (external) hydrogen stream. In this case, the hydrogen stream is composed of external hydrogen and hydrogen recycled from the recovery stream in the recovery arrangement. Whether hydrogen recovery is necessary depends largely on the respective plant design and the amount of hydrogen (or hydrogen fraction) present in the synthesis gas stream. Furthermore, the need for hydrogen recovery can depend on the feed gas used and the amount of hydrogen available.By means of appropriate hydrogen recovery, additional hydrogen can be added to the synthesis gas stream in addition to the external hydrogen via the aforementioned hydrogen stream (which can compensate for any hydrogen deficit).

[0025] The hydrogen stream can be pressurized by means of a hydrogen compressor before being fed into the methanol reactor arrangement, in particular into the synthesis gas stream. This is advantageous in order to raise the hydrogen stream to the pressure level of the synthesis gas stream, if necessary, or to set a desired pressure level. Transporting a pressurized hydrogen stream can be advantageous because this can take place in smaller lines than transporting a non-pressurized hydrogen stream. It can be advantageous to compress the pressure of the hydrogen stream (i.e. to increase the pressure) shortly before it is fed to the methanol reactor arrangement or to the synthesis gas stream. This is because, from a plant engineering perspective, transporting hydrogen over short distances is advantageous. The hydrogen compressor can have one or more compressor units.

[0026] According to a further embodiment of a proposed method, the unreacted hydrogen from the H recycle stream can be fed to the hydrogen stream via the hydrogen compressor, in particular, the unreacted hydrogen and the external hydrogen are jointly pressure-increased by means of the hydrogen compressor. A joint pressure increase in the hydrogen compressor can have cost advantages.

[0027] According to a further embodiment of a proposed method, it can be provided that the external hydrogen is supplied to the hydrogen stream from an electrolysis hydrogen stream obtained from an electrolysis arrangement for decomposing water into external hydrogen and oxygen. The electrolysis arrangement can be arranged externally to the proposed plant for synthesizing methanol, but can also be integrated into this plant (i.e., be part of it). The electrolysis hydrogen stream preferably essentially comprises hydrogen. The electrolysis referred to is therefore an electrolysis of water (water electrolysis). In such a water electrolysis, water (H2O) is decomposed into its components hydrogen (H2) and oxygen (O2) using electrical current. It is particularly advantageous if the electrical current used is generated from renewable energy sources (e.g.,Wind, sun, biomass, etc.). The oxygen produced during water electrolysis can be used simultaneously in the reforming reactor (in the case of autothermal reforming) or in the oxidation reactor (in the case of partial oxidation) to produce synthesis gas.

[0028] The methanol reactor arrangement preferably comprises a first methanol separation device for recovering the unreacted residual gas from the first reactor stage and a first crude methanol stream from the first reactor stage. In particular, the first methanol separation device can comprise a first condensation device for recovering the unreacted residual gas from the first reactor stage and the first crude methanol stream from the first reactor stage by condensation. Optionally, the methanol reactor arrangement can comprise a second methanol separation device for recovering the unreacted residual gas from the second reactor stage and a second crude methanol stream from the second reactor stage, wherein in particular the second methanol separation device comprises a second condensation device for recovering the unreacted residual gas from the second reactor stage and the second crude methanol stream from the second reactor stage by condensation.In principle, the first and / or second methanol separation device can be designed in any desired manner. As mentioned, it may be advantageous for the first and / or second methanol separation device to comprise a first or second condensation device, respectively.

[0029] As already stated, it can in principle be provided that the methanol reactor arrangement comprises only a single (first) methanol reactor stage. However, the methanol reactor arrangement can also have a plurality of reactor stages for methanol synthesis connected in series in terms of process technology, for example a first reactor stage and a second reactor stage connected downstream of the first reactor stage. Each individual reactor stage can have one or more reactors. The reactors of a reactor stage can, in particular, be arranged in parallel with one another in terms of process technology. Furthermore, it is possible for a respective unreacted residual gas to be recovered from each of the plurality of reactor stages by means of a methanol separation device. Each reactor stage can be assigned a separate methanol separation device.A common methanol separation device can also be assigned to several or all reactor stages, in which case the reactor stages are connected in parallel. In this case, the term "reactor stage" should not be understood to mean that these are "stages" of reactors connected in series for process engineering purposes, but rather "reactors" connected in parallel.

[0030] The fact that the first and second reactor stages are connected in series in terms of process technology (the second reactor stage is connected downstream of the first reactor stage) means that residual gas from one reactor stage - unless it is the last reactor stage in a series of several reactor stages - is fed directly or indirectly to the reactor stage connected next to it. In the case of a first and second reactor stage, residual gas from the first reactor stage is thus fed directly or indirectly to the second reactor stage. In principle, the above-mentioned recycle compressor can be arranged in any desired manner with regard to the plurality of reactor stages. One variant is that the recycle compressor is arranged between two reactor stages in terms of process technology, for example, in the case of two reactor stages, between the first and second reactor stage.This means that at least part of the unreacted residual gas from a reactor stage is fed to the recycle compressor as a residual gas stream and the pressure-increased residual gas stream is then fed to the reactor stage downstream of this reactor stage.

[0031] In principle, the aforementioned H2 recycle stream can be conducted in any desired manner, as long as at least a portion of its hydrogen is converted into methanol. According to an advantageous embodiment of the process, the H2 recycle stream can be fed to the unreacted residual gas of a reactor stage downstream of the first reactor stage (e.g., the second). If two reactor stages are present, the unreacted hydrogen from the H2 recycle stream can be fed to the unreacted residual gas of the second reactor stage.

[0032] In other words, the unreacted hydrogen of the H recycle stream is treated after feeding together with at least a portion of the unreacted residual gas from a reactor stage other than the first reactor stage. In this way, the H recycle stream "skips" one or more reactor stages after the first reactor stage. The advantage of such an approach is that the pressure loss of the H recycle stream due to hydrogen recovery essentially occurs parallel to the pressure loss of the unreacted residual gas from the downstream (e.g., second) reactor stage in this reactor stage. In other words, the respective pressures of this unreacted residual gas and the H recycle stream are closer to each other, which in turn reduces the pressure loss that occurs when they are combined due to equalization to the lower pressure level. The H recycle stream can be fed to the recycle compressor with the residual gas stream to increase the pressure.

[0033] According to a further embodiment of the method, it can be provided that the residual gas stream is obtained from a reactor stage downstream of the first reactor stage in terms of process technology, in particular the second reactor stage. In other words, the residual gas stream fed to the recycle compressor then does not originate from the first reactor stage - i.e. the reactor stage to which the synthesis gas stream is at least partially fed directly - but from a downstream reactor stage. Furthermore, the recycle compressor can feed the pressurized residual gas stream to the first reactor stage. In principle, however, the pressurized residual gas stream can also be fed to another reactor stage of the plurality of reactor stages. Likewise, the pressurized residual gas stream can be divided and fed to several reactor stages of the plurality of reactor stages.

[0034] According to a further embodiment of the proposed process, the residual gas stream can be obtained from a reactor stage located last in the plurality of reactor stages. In the case of two reactor stages, the second reactor stage represents the last reactor stage. This and the preceding variant also allow for the reduction of pressure losses required for combining streams.

[0035] In principle, the recovery stream can be obtained at any location and from any source within the methanol reactor arrangement. The recovery stream contains unreacted hydrogen from an unreacted residual gas from the first reactor stage and / or the second reactor stage. One variant provides for the recovery stream to be diverted at least partially from the unreacted residual gas from the first reactor stage. According to a further variant, the recovery stream (if two reactor stages are provided) can be diverted from the unreacted residual gas from the second reactor stage. A diversion of the recovery stream from both the unreacted residual gas from the first reactor stage and the unreacted residual gas from the second reactor stage is also conceivable. It is therefore possible that the recovery stream is diverted at least partially upstream of the recycle compressor in terms of process technology.

[0036] In principle, it should be noted that by recovering hydrogen from the recovery stream and at least partially feeding the H2 recycle stream back to the first reactor stage, the hydrogen content in the first reactor stage can be increased, thus improving the stoichiometry for methanol synthesis. The same applies to the addition of external hydrogen to the synthesis gas stream (via the hydrogen stream) and its subsequent addition to the first reactor stage. This also applies to a combination of external hydrogen and recovered hydrogen from the recovery stream.

[0037] The synthesis gas reactor arrangement can comprise a reforming reactor or an oxidation reactor. In particular, an oxygen-containing stream can be supplied to the synthesis gas reactor arrangement to obtain the synthesis gas stream. In particular, it can be provided that the synthesis gas stream is obtained from the carbon-containing energy carrier stream in the synthesis gas reactor arrangement by autothermal reforming in the reforming reactor or partial oxidation in the oxidation reactor. In addition to a reactor for generating the synthesis gas, the synthesis gas reactor arrangement can have further devices.Thus, the synthesis gas reactor arrangement can comprise a device for desulfurizing the carbon-containing energy carrier stream, a saturation stage for saturating the carbon-containing energy carrier stream with water, a pre-reforming reactor (pre-reformer) for pre-reforming the carbon-containing energy carrier stream and / or a device for heating the carbon-containing energy carrier stream, each of which is located upstream of the reactor in terms of process technology.

[0038] In principle, the synthesis gas stream can be obtained from the energy carrier stream in any desired manner. It is preferred that an oxygen-containing stream be fed to the synthesis gas reactor arrangement to obtain the synthesis gas stream. In principle, the oxygen-containing stream can contain other components besides oxygen. For example, the oxygen-containing stream can also be ambient air.

[0039] In principle, the synthesis gas stream can be obtained, for example, through steam reforming (using a steam reformer as the reforming reactor) of the carbon-containing energy source stream. The use of a steam reformer can be useful when adding CO2 or using a CO2-rich carbon-containing energy source stream (such as biogas).

[0040] A further preferred embodiment of the process is characterized in that, in the synthesis gas reactor arrangement, the synthesis gas stream is obtained from the carbon-containing energy carrier stream by autothermal reforming, namely in the aforementioned reforming reactor. In such autothermal reforming (ATR), catalytic partial oxidation provides the heat required for the endothermic reforming reactions. Compared to pure steam reforming, autothermal reforming offers the advantage that the synthesis gas stream can be provided at a higher pressure. Alternatively or additionally, the synthesis gas stream may be obtained from the carbon-containing energy carrier stream by partial oxidation in the synthesis gas reactor arrangement, namely in the aforementioned oxidation reactor. In principle, autothermal reforming can also be operated with ambient air.However, it is preferred that the oxygen comprised in the oxygen-containing stream be obtained from an air separation device for obtaining an oxygen stream from ambient air. The air separation device can also be configured to obtain a nitrogen stream. In particular, the oxygen-containing stream can then essentially comprise oxygen. In this way, the proportion of inert gases in the methanol synthesis is reduced, so that various devices in the plant can be made smaller. The plant for synthesizing methanol preferably comprises the air separation device.

[0041] According to a further embodiment of the proposed process, the oxygen contained in the oxygen-containing stream can be extracted from the electrolysis system. When external hydrogen is generated by water electrolysis, oxygen is also produced due to the chemical reaction underlying this process. Utilizing this oxygen, which is already produced, for synthesis gas production (autothermal reforming or partial oxidation), makes the proposed process particularly efficient and simultaneously improves its environmental footprint. Otherwise, the resulting oxygen would have to be stored for other purposes, forwarded, or discarded.

[0042] According to a further embodiment of the proposed method, the recycle stream can be fed to the synthesis gas reactor arrangement upstream of the reforming reactor or the oxidation reactor. This allows the recycle stream and the constituents it contains to pass through the reforming reactor (e.g., an autothermal reforming reactor or steam reformer) or the oxidation reactor (for partial oxidation) again. The constituents contained in the recycle stream, in particular methane, can then undergo the (chemical) processes taking place in the synthesis gas reactor arrangement again and be converted into synthesis gas. If catalysts are used, this allows the constituents of the recycle stream to come into contact again with the catalysts used to generate synthesis gas.According to a further embodiment of the proposed process, a pre-reformer reactor can be arranged upstream of the reforming reactor, with the recycle stream being fed to the synthesis gas reactor arrangement between the pre-reformer reactor and the reforming reactor. Since the components of the recycle stream have already passed through the pre-reformer reactor in a previous run, a repeat pass through the pre-reformer reactor may be unnecessary. Therefore, further processing in the sense of pre-reforming can be omitted.

[0043] In principle, the H recycle stream can have any composition, provided it contains the unreacted hydrogen from the unreacted residual gas of the first reactor stage. According to a further preferred embodiment of the process, the H recycle stream has a higher molar proportion of hydrogen than the recovery stream. This refers not only to the unreacted hydrogen from the unreacted residual gas of the first reactor stage, but to the hydrogen in the H recycle stream as a whole. In other words, the hydrogen in the H recycle stream is enriched compared to the recovery stream. It is also preferred that the H recycle stream has a higher molar proportion of hydrogen than the purge stream.

[0044] In principle, the hydrogen recovery arrangement can operate according to any desired principle, for example based on a membrane arrangement or a refrigeration device. According to a further embodiment of the process, the hydrogen recovery arrangement can comprise a pressure swing adsorption device (PSA) for obtaining the H recycle stream from the recovery stream. In this way, a high recovery of hydrogen in the H recycle stream can be achieved. Likewise, the pressure losses in such a pressure swing adsorption device are acceptable. Although high hydrogen purity is not fundamentally required in this case, it can nevertheless be achieved. It is therefore possible that the H recycle stream essentially comprises hydrogen.

[0045] According to a further embodiment of the proposed method, it can be provided that the hydrogen recovery arrangement outputs a purge stream, and / or that a purge stream is diverted from the recycle stream, and / or that a purge stream is diverted from the recovery stream, and / or that a purge stream is diverted from the residual gas stream. The purge stream is preferably fed to a combustion unit or directed to a flare.

[0046] According to a further embodiment of the proposed method, a ratio of a first mass flow formed by a sum of carbon-containing compounds present in the purge stream relative to a second mass flow formed by a sum of carbon-containing compounds present in the synthesis gas stream can have a value of 10' 5to 0.4, and preferably assume a value of 0.0001 to 0.3, and more preferably assume a value of 0.0005 to 0.21. The first and / or second mass flow can in particular comprise CO, CO2, CPU and / or methanol as carbon-containing compounds. In particular, the said ratio can assume a value of approximately 0.0005, 0.05 or 0.22, preferably of exactly 0.0005, 0.015 or 0.22. These (low) ratios can embody reduced emissions compared to the prior art. Furthermore, in a process or plant that makes use of the said connections, the recycle stream in the methanol synthesis can be kept low.

[0047] In addition to the described process for the synthesis of methanol, the object underlying the invention is also achieved by a plant for the synthesis of methanol.

[0048] A plant for the synthesis of methanol is proposed, comprising a synthesis gas reactor arrangement for obtaining a synthesis gas stream containing hydrogen and carbon oxides from a carbon-containing energy carrier stream fed to the synthesis gas reactor arrangement, optionally comprising a synthesis gas compressor for increasing the pressure of the synthesis gas stream, a methanol reactor arrangement having a first reactor stage and optionally a second reactor stage, a recycle compressor, and optionally a hydrogen recovery arrangement. Furthermore, the plant comprises a device for at least partially feeding the (optionally pressurized) synthesis gas stream into the first reactor stage for at least partial conversion into methanol. The "device" may be a physical device configured to at least partially feed the (optionally pressurized) synthesis gas stream into the first reactor stage.Such a "device" may, for example, be a line. The "device" may include general valve systems, control and regulation systems.

[0049] The plant may further comprise an optional device for supplying unreacted residual gas from the first reactor stage to the optional second reactor stage for at least partial conversion into methanol. The "device" may be a physical device configured to supply unreacted residual gas from the first reactor stage to the optional second reactor stage. Such a "device" may, for example, be a conduit. The "device" may include general valve systems, pumping systems, and control and regulation systems.

[0050] The plant further comprises a device for recovering a residual gas stream from the methanol reactor assembly containing unreacted carbon oxides. This "device" is understood to mean a physical device designed to recover a residual gas stream from the methanol reactor assembly containing unreacted carbon oxides. For example, this may be a methanol separation device including the associated piping system.

[0051] The system further comprises a device for feeding the residual gas stream into the recycle compressor to increase the pressure of the residual gas stream. The "device" may be a physical device configured to feed the residual gas stream into the recycle compressor. Such a "device" may, for example, be a line. The "device" may include general valve systems, pump systems, and control and regulation systems.

[0052] The system further comprises a device for feeding the pressurized residual gas stream into the methanol reactor arrangement for at least partial conversion into methanol. The "device" may be a physical device configured to feed the pressurized residual gas stream into the methanol reactor arrangement. Such a "device" may, for example, be a conduit. The "device" may include general valve systems, control and regulation systems. Furthermore, the system may optionally comprise a device for feeding a recovery stream comprising unreacted residual gas from the first and / or second reactor stage into the hydrogen recovery arrangement to obtain an H recycle stream, wherein the H recycle stream comprises unreacted hydrogen from the unreacted residual gas from the first reactor stage and / or from the unreacted residual gas from the second reactor stage.The "device" may be a physical device configured to feed a recovery stream comprising unreacted residual gas from the first and / or second reactor stage into the hydrogen recovery arrangement. Such a "device" may, for example, be a conduit. The "device" may include general valve systems, pumping systems, and control and regulation systems. Furthermore, the system may optionally include a device for reintroducing the unreacted hydrogen from the H recycle stream into the first reactor stage for at least partial conversion to methanol. The "device" may be a physical device configured to reintroduce the unreacted hydrogen from the H recycle stream into the first reactor stage. Such a "device" may, for example, be a conduit. The "device" may include general valve systems, control and regulation systems.

[0053] The plant is characterized by a device for supplying a hydrogen stream with external hydrogen to one of the streams upstream or downstream of the synthesis gas reactor arrangement. It may be advantageous to supply the hydrogen stream with external hydrogen into the synthesis gas stream. The "device" may be a physical device configured to supply a hydrogen stream with external hydrogen into the synthesis gas stream. This "device" may, for example, be a line. The "device" may include general valve systems, control and regulation systems. The "device" may also include a hydrogen compressor.

[0054] The plant is further characterized by one or more devices for branching off and feeding a portion of the residual gas stream, and / or the optional recovery stream, and / or a stream downstream of the hydrogen recovery arrangement into the synthesis gas reactor arrangement as a recycle stream. Said "device(s)" may be physical devices configured to branch off and feed a portion of the residual gas stream, and / or the optional recovery stream, and / or a stream downstream of the hydrogen recovery arrangement into the synthesis gas reactor arrangement as a recycle stream. This "device" may, for example, be a conduit. The "device" may include general valve systems, control and regulation systems.

[0055] The features, advantages and properties of the proposed plant correspond to the features, advantages and properties of the proposed process and vice versa.

[0056] Further details, features, objects and advantages of the present invention are explained below with reference to the drawings, which only represent exemplary embodiments. In the drawings,

[0057] Fig. 1 shows a schematic flow diagram of a plant for the synthesis of methanol known from the prior art,

[0058] Fig. 2 shows schematically the flow diagram of the plant for the synthesis of methanol according to Figure 1, but with further specifications known from the prior art,

[0059] Fig. 3 schematically shows the flow diagram of a plant for carrying out the proposed method according to a first embodiment,

[0060] Fig. 4 schematically shows the flow diagram of a plant for carrying out the proposed method according to a second embodiment,

[0061] Fig. 5 schematically shows the flow diagram of a plant for carrying out the proposed method according to a third embodiment,

[0062] Fig. 6 shows a schematic flow diagram of a plant for carrying out the proposed method according to a fourth embodiment, Fig. 7 shows a schematic flow diagram of a plant for carrying out the proposed method according to a fifth embodiment,

[0063] Fig. 8 shows a schematic flow diagram of a plant for carrying out the proposed process, wherein the external hydrogen is produced on the basis of water electrolysis,

[0064] Fig. 9 shows a schematic flow diagram of a plant for carrying out the proposed method according to a further embodiment,

[0065] Fig. 10 schematically shows the flow diagram of a plant for carrying out the proposed method according to a further embodiment.

[0066] The prior art plant shown in Fig. 1 is used for the synthesis of methanol 1. Unless otherwise stated or explained, the components or processes known from this plant can be transferred to the plant or method proposed according to the invention. This also applies to the reference numerals used. Those features known from the prior art or equivalent across the embodiments will be explained only once each to avoid unnecessary repetition.

[0067] Figure 1 shows the supply of an energy carrier stream 11, formed from, for example, natural gas or biogas and thus containing carbon, into a synthesis gas reactor arrangement 13. In the synthesis gas reactor arrangement 13, a synthesis gas stream 2 comprising hydrogen, carbon monoxide, and carbon dioxide is generated from the energy carrier stream 11. The synthesis gas reactor arrangement 13 can have a reforming reactor 30 or an oxidation reactor 31. Assuming the synthesis gas reactor arrangement 13 comprises a reforming reactor 30, an autothermal reforming takes place in the synthesis gas reactor arrangement 13 to obtain the synthesis gas stream 2. For the autothermal reforming, an oxygen-containing stream 22 is supplied, which here was obtained from an air separation device 23 and essentially comprises oxygen.The air separation device 23 is configured to extract an oxygen stream—here, the oxygen-containing stream 22—from the ambient air. The synthesis gas stream 2 is first fed to a heat recovery device 10, in which the synthesis gas stream 2 is cooled, thus recovering a portion of the heat generated during the autothermal reforming. The synthesis gas stream 2 is then fed to a synthesis gas compressor 3 of the plant for further pressure increase.

[0068] Subsequently, the synthesis gas stream 2 from the first reactor stage 21a is fed to a methanol reactor arrangement 4, in which first reactor stage 21a, methanol synthesis takes place and at least a portion of the synthesis gas stream 2 is converted into methanol 1. Subsequently, unreacted residual gas 16a from the first reactor stage 21a is fed to a second reactor stage 21b of the methanol reactor arrangement 4 for at least partial conversion into methanol 1. A residual gas stream 15 containing unreacted carbon oxides is then obtained from the methanol reactor arrangement 4 and fed to a recycle compressor.

[0069] The plant comprises a hydrogen recovery system 5 configured as a pressure swing adsorption system 24—which can also be referred to as a PSA—which recovers an H recycle stream 7 from a recovery stream 6. This H recycle stream 7 essentially comprises hydrogen. True to the plant concept shown in Figure 1, the recovery stream 6 is branched off from unreacted residual gas 16a of the first reactor stage. Likewise, the remaining gas from the hydrogen recovery system 5 is discharged as purge stream 8 and subsequently combusted in a fired heating device of the plant (not shown here). The H recycle stream 7 is fed to the residual gas stream 15.

[0070] As already mentioned, the plant has a recycle compressor 14, which compresses the residual gas stream 15. The residual gas stream 15 comprises unreacted residual gas 16b from the second reactor stage 21b, which in turn essentially comprises those components of the synthesis gas that were not converted into methanol 1 in the methanol reactor arrangement 4. Accordingly, the residual gas stream 15 contains, in particular, unreacted carbon oxides. The thus pressure-increased residual gas stream 15 is fed back to the methanol reactor arrangement 4, namely the first reactor stage.

[0071] The unreacted residual gas 16a, b is obtained from a first methanol separation device 17a and a second methanol separation device 17b of the methanol reactor arrangement 4. Condensation is used in these devices to obtain the unreacted residual gas 16a, b on the one hand and a respective first and second crude methanol stream 19a, b on the other hand. The crude methanol streams 19a, b are then fed to a distillation 20 of the plant, so that methanol 1 can be obtained from the crude methanol streams 19a, b. The first methanol separation device 17a is connected downstream of the first reactor stage 21a. The second methanol separation device 17b is connected downstream of the second reactor stage 21b.

[0072] In the plant shown in Fig. 1, the methanol reactor arrangement 4—as mentioned—comprises two reactor stages 21a, b for methanol synthesis, which are connected in series in terms of process technology. The first reactor stage 21a comprises two isothermal reactors arranged in parallel, and the second reactor stage 21b comprises a single isothermal reactor. The product stream from each of the two methanol separation devices 17a, 17b is fed to a respective reactor stage 21a, b. The reactor stage 21a to which the synthesis gas stream 2 is fed directly is referred to as the first reactor stage 21a. The reactor stage 21b is then downstream of the first reactor stage 21a in the sense that the unreacted residual gas 16a from the first reactor stage 21a is fed to it for conversion into methanol 1.

[0073] In addition to the aforementioned unreacted carbon oxides, the residual gas stream 15 also contains unreacted hydrogen from the first reactor stage 21a. Any unreacted hydrogen from the residual gas 16a of the first reactor stage 21a is fed to the second reactor stage 21b. Since complete reaction of the hydrogen does not occur in the second reactor stage 21b either, the unreacted residual gas 16b of the second reactor stage 21b also contains unreacted hydrogen from the first reactor stage 21a. In the plant according to Fig. 1, a ratio of a first mass flow formed by a sum of carbon-containing compounds present in the purge stream 8 relative to a second mass flow formed by a sum of carbon-containing compounds present in the synthesis gas stream 2 assumes a value of approximately or exactly 0.22.

[0074] The plant shown in Figure 2 comprises all components of the plant already shown in Figure 1. Nevertheless, Figure 2 specifies the type of synthesis gas production based on autothermal reforming in a reforming reactor 30. Prior to entering the reforming reactor 30, the energy carrier stream 11 is passed through a pre-reforming reactor 29. After the addition of steam 33, the pre-reformed energy carrier stream 11 enters the reforming reactor 30. Subsequently, a generated synthesis gas stream 2 enters a heat recovery device 10.

[0075] Figure 3 shows a first embodiment of a plant according to the invention. Synthesis gas is generated in a reforming reactor 30 (cf. the preceding explanations regarding Figure 2). In this example, the reforming reactor 30 thus provides the synthesis gas reactor assembly 13 or a portion of the synthesis gas reactor assembly 13. A hydrogen stream 35 containing external hydrogen is fed to the synthesis gas stream 2 between the heat recovery device 10 and the inlet to the synthesis gas compressor 3. The hydrogen stream 35 is pressurized by a hydrogen compressor 45 before being fed into the synthesis gas stream 2. Furthermore, a portion of the recovery stream 6 (alternatively from the residual gas 16a) is branched off and fed to the synthesis gas reactor assembly 13 as recycle stream 40, namely directly between the pre-reforming reactor 29 and the reforming reactor 30.Alternatively or additionally, a recycle stream 40 can be branched off from a stream 71 downstream of the hydrogen recovery arrangement 5 (here, for example, a pressure swing adsorption device 24), as indicated by dashed lines. The recycle stream 40 is fed to the synthesis gas reactor arrangement 13 as a recycle stream 40, namely directly between the pre-reforming reactor 29 and the reforming reactor 30.

[0076] The second embodiment of the proposed plant, shown in Fig. 4, differs from the embodiment of Fig. 3 in that the recovery stream 6 is branched off from the residual gas stream 15 or the residual gas 16b (downstream of the second reactor stage 21b). As in the embodiment of Fig. 3, the H recycle stream 7 is fed to the residual gas 16b of the second reactor stage 21b, which is downstream of the first reactor stage 21a. Alternatively, the H recycle stream 7 can be fed to the synthesis gas stream upstream of the synthesis gas compressor 3. Specifically, this feed takes place before the pressure increase by the recycle compressor 14.In this way, the hydrogen in the H recycle stream 7, corresponding to the unreacted hydrogen from the residual gas 16a of the first reactor stage 21a in the recovery stream 6, receives a pressure increase from the recycle compressor 14 along with the remaining unreacted residual gas 16b of the second reactor stage 21b, and in particular with unreacted carbon oxides. This pressure increase occurs before this unreacted hydrogen is fed back to the first reactor stage 21a. As already shown in the example according to Figure 3, in this example too—as indicated by dashed lines—a recycle stream 40 can be branched off from a stream 71 downstream of the hydrogen recovery arrangement 5 (here, for example, a pressure swing adsorption device 24). The recycle stream 40 is fed to the synthesis gas reactor arrangement 13 as recycle stream 40, namely directly between the pre-reforming reactor 29 and the reforming reactor 30.As in the example according to Figure 3, a part of the recovery stream 6 can also be branched off and fed to the synthesis gas reactor arrangement 13 as a recycle stream.

[0077] The third embodiment of the proposed plant, shown in Fig. 5, differs from the embodiment of Fig. 4 in that the hydrogen recovery arrangement 5 is a membrane arrangement 25. An H recycle stream 7 obtained in the membrane arrangement 25 is fed to the hydrogen stream 35 via the hydrogen compressor 45 before being fed into the synthesis gas stream 2, where it is pressurized. A portion of the recovery stream 6 (here branched off from the residual gas 16b or residual gas stream 15) is fed to the synthesis gas reactor arrangement 13 as a recycle stream 40 after passing through the membrane arrangement 25. This can also be understood as a "branch-off" from a stream 71 downstream of the hydrogen recovery arrangement 5. A "branch" does not necessarily mean a branch in the pipeline, but can also be understood as a "feed to" or "line to" (e.g. to the synthesis gas reactor arrangement 13).The feed takes place upstream of the reforming reactor 30. A purge stream 8 is branched off from the recycle stream 40 and burned off. In this embodiment, the H recycle stream 7 is not recycled to the residual gas 16b or residual gas stream 15, but is recycled back into the synthesis loop via the hydrogen compressor 45.

[0078] The fourth embodiment of the proposed system, shown in Fig.

[0079] 6, differs from the embodiment according to Fig. 5 in that the purge stream 8 is not branched off from the recycle stream 40 (Fig. 5), but directly from the recovery stream 6. In this example, the stream 71 downstream of the hydrogen recovery arrangement 5 is directly recirculated as recycle stream 40 to the synthesis gas reactor arrangement 13 or upstream of the reforming reactor 30. A "branch" in the piping sense does not occur, but a direct recycle can also be understood as a "branch" in the sense of the terminology used here.

[0080] The fifth embodiment of the proposed system, shown in Fig.

[0081] 7, differs from the preceding exemplary embodiments by omitting a hydrogen recovery arrangement 5 including H recycle stream 7 and recovery stream 6. A recycle stream 40 is branched off from the residual gas stream 15 and fed to the synthesis gas reactor arrangement 13, namely between the pre-reforming reactor 29 and the reforming reactor 30. A purge stream 8 is branched off from the recovery stream 40 and burned off. In the plant according to Fig. 7, a ratio of a first mass flow formed by a sum of carbon-containing compounds present in the purge stream 8 relative to a second mass flow formed by a sum of carbon-containing compounds present in the synthesis gas stream 2 assumes a value of approximately or exactly 0.0008.

[0082] Figure 8 shows a section of a proposed plant in which the oxygen-containing stream 22 supplied to the reforming reactor 30 is not obtained from an air separation device 23, but from an electrolysis arrangement 60. The oxygen-containing stream 22 can be supplemented with oxygen from another source, e.g., an air separation device 23. This is an electrolysis arrangement 60 for water electrolysis. This produces oxygen (O2) and hydrogen (H2), with the oxygen being / can be pressure-increased before the oxygen-containing stream 22 is formed. The hydrogen produced during the electrolysis can also be utilized, namely by supplying an electrolysis hydrogen stream 50 to the synthesis gas stream 2 as hydrogen stream 35 after pressure increase by the hydrogen compressor 45. Accordingly, the external hydrogen supplied to the synthesis gas stream 2 can originate from the electrolysis arrangement 60.For reasons of clarity, the plant components and streams shown in Figures 1 to 7 are bracketed out in Figure 8, namely those components and streams between the first reactor stage 21a and the produced methanol 1. All of the exemplary embodiments, features, and streams shown in Figures 3 to 7 can be combined with the production of external hydrogen by an electrolysis arrangement 60, as illustrated in Figure 8. This also applies to the use of an oxidation reactor 31 instead of a reforming reactor. In particular, the methanol reactor arrangement 4 in this example can have only a single reactor stage, but can also have multiple reactor stages. In this example, too, a residual gas stream 15 can be pressure-increased in a recycle compressor 14. After the pressure increase (but also beforehand), a recycle stream 40 can be branched off from the residual gas stream 15 and recirculated upstream of the reforming reactor 30.A purge stream 8 can also be diverted from the residual gas stream 15 and burned. In the example shown in Fig. 8, the carbon-containing energy carrier stream 11 can be, in particular, biogas or another CO2-rich gas, for example, natural gas mixed with CO2. It should be noted that when biogas is used as the carbon-containing energy carrier stream 11, the pre-reformer 29 can be omitted, since biogas contains hardly any higher hydrocarbons.

[0083] Fig. 9 shows an embodiment of the proposed plant, in which, in contrast to the embodiment according to Fig. 7, a synthesis gas compressor 3 is omitted. After the residual gas stream 15 has been pressure-increased in the recycle compressor 14, a recycle stream 40 is branched off and fed to the synthesis gas reactor arrangement 13, namely between the pre-reforming reactor 29 and the reforming reactor 30. Alternatively, the recycle stream can also be branched off before the pressure increase, compressed in a separate compressor, and fed to the synthesis gas reactor arrangement 13. A purge stream 8 is branched off from the residual gas stream 15 and burned off. In the plant according to Fig.9, a ratio of a first mass flow formed by a sum of carbon-containing compounds present in the purge stream 8 relative to a second mass flow formed by a sum of carbon-containing compounds present in the synthesis gas stream 2 assumes a value of approximately or exactly 0.005.

[0084] Fig. 10 shows a further embodiment of the proposed plant, wherein the reforming reactor 30 is designed as a steam reformer. A carbon-containing energy carrier stream 11 is first fed to a preparation stage 71 and then, with the addition of steam 72 and CO2, fed to the reforming reactor 30 designed as a steam reformer. Only one methanol reactor arrangement 4 with a single reactor stage (the first reactor stage 21a) is provided. Accordingly, only one first methanol separation device 17a downstream of the reactor stage 21 is provided. A recycle stream 40 is branched off from the residual gas stream 15 and recycled upstream of the reforming reactor 30. In this embodiment, the carbon-containing energy carrier stream 11 can be the same energy carrier as in the embodiments according to Figs. 1 to 7, but also biogas. In the plant according to Fig.10, a ratio of a first mass flow formed by a sum of carbon-containing compounds present in the purge stream 8 relative to a second mass flow formed by a sum of carbon-containing compounds present in the synthesis gas stream 2 assumes a value of approximately or exactly 0.015 or even values ​​< 0.015.

Claims

Patent claims 1. A process for the synthesis of methanol (1), wherein a carbon-containing energy carrier stream (11) is fed to a synthesis gas reactor arrangement (13) for obtaining a synthesis gas stream (2) containing hydrogen and carbon oxides, wherein the synthesis gas stream (2) is at least partially fed to a first reactor stage (21a) of a methanol reactor arrangement (4) for at least partial conversion into methanol (1), wherein optionally unreacted residual gas (16a) from the first reactor stage (21a) is subsequently fed to a second reactor stage (21b) of the methanol reactor arrangement (4) for at least partial conversion into methanol (1), wherein a residual gas stream (15) containing unreacted carbon oxides is obtained from the methanol reactor arrangement (4), which residual gas stream (15) is fed to a recycle compressor (14) for increasing the pressure of the residual gas stream (15),wherein the pressure-increased residual gas stream (15) is fed to the methanol reactor arrangement (4) for at least partial conversion into methanol (1), wherein optionally a recovery stream (6) comprising unreacted residual gas (16a, 16b) of the first and / or second reactor stage (21a, 21b) is fed to a hydrogen recovery arrangement (5) for obtaining an H recycle stream (7), which H recycle stream (7) comprises unreacted hydrogen from the unreacted residual gas (16a) of the first reactor stage (21a) and / or from the unreacted residual gas (16b) of the second reactor stage (21b), wherein the unreacted hydrogen of the H recycle stream (7) is fed again to the first reactor stage (21a) for at least partial conversion into methanol (1), characterized in that upstream or downstream of the synthesis gas reactor arrangement, one of the streams (2, 6, 7, 11, 15) a hydrogen stream (35) with external hydrogen is supplied, and that a part of the residual gas stream (15),and / or the optional recovery stream (6), and / or a stream (71) downstream of the hydrogen recovery arrangement (5) and fed to the synthesis gas reactor arrangement (13) as a recycle stream (40).

2. Process according to claim 1, characterized in that the synthesis gas stream (2) is fed to a synthesis gas compressor (3) for pressure increase.

3. The method according to claim 2, characterized in that the synthesis gas stream (2) is fed to a heat recovery device (10) for recovering heat from the synthesis gas stream (2) and then to the synthesis gas compressor (3).

4. The method according to claim 3, characterized in that the hydrogen stream (35) is fed to the synthesis gas stream (2) after it leaves the heat recovery device (10).

5. Method according to one of claims 1 to 4, characterized in that the hydrogen stream (35) is fed to the synthesis gas stream (2) before it is fed into the synthesis gas compressor (3).

6. Process according to one of the preceding claims, characterized in that unreacted hydrogen from the H-ecycle stream (7) is additionally supplied to the hydrogen stream (35).

7. Method according to one of the preceding claims, characterized in that the hydrogen stream (35) is pressurized by means of a hydrogen compressor (45) before being fed into the methanol reactor arrangement (4), in particular into the synthesis gas stream (2).

8. The method according to claim 6 and 7, characterized in that the unreacted hydrogen from the H recycle stream (7) is fed to the hydrogen stream (35) via the hydrogen compressor (45), in particular that the unreacted hydrogen and the external hydrogen are pressure-increased together by means of the hydrogen compressor (45).

9. Process according to one of the preceding claims, characterized in that the unreacted hydrogen from the H-recycle stream (7) is fed to the unreacted residual gas (16b) of the second reactor stage (21b).

10. Experience according to one of the preceding claims, characterized in that the external hydrogen is supplied to the hydrogen stream (35) from an electrolysis hydrogen stream (50) which is obtained from an electrolysis arrangement (60) for decomposing water into the external hydrogen and oxygen.

11. Experience according to one of the preceding claims, characterized in that the methanol reactor arrangement (4) comprises a first methanol separation device (17a) for obtaining the unreacted residual gas (16a) of the first reactor stage (21a) and a first crude methanol stream (19a) of the first reactor stage (21a), in particular that the first methanol separation device (17) comprises a first condensation device (18a) for obtaining the unreacted residual gas (16a) of the first reactor stage (21a) and the first crude methanol stream (19a) of the first reactor stage (21a) by condensation, and optionally further characterized in that the methanol reactor arrangement (4) comprises a second methanol separation device (17b) for obtaining the unreacted residual gas (16b) of the second reactor stage (21b) and a second crude methanol stream (19b) of the second reactor stage (21b) includes, in particular,that the second methanol separation device (17b) comprises a second condensation device (18b) for recovering the unreacted residual gas (16b) of the second reactor stage (21b) and the second crude methanol stream (19b) of the second reactor stage (21b) by condensation., 12. Method according to one of the preceding claims, characterized in that the second reactor stage (21b) is arranged downstream of the first reactor stage (21a) in terms of process technology, wherein the recycle compressor (14) is preferably arranged between the two reactor stages (21a, b) in terms of process technology.

13. Process according to one of the preceding claims, characterized in that the residual gas stream (15) is obtained from the second reactor stage (21b), in particular that the recycle compressor (14) feeds the pressure-increased residual gas stream (15) to the first reactor stage (21a).

14. Experience according to one of the preceding claims, characterized in that the synthesis gas reactor arrangement (13) comprises a reforming reactor (30) or an oxidation reactor (31).

15. The method according to any one of the preceding claims, characterized in that an oxygen-containing stream (22) is fed to the synthesis gas reactor arrangement (13), wherein the oxygen comprised in the oxygen-containing stream (22) is obtained from an air separation device (23) for obtaining oxygen from ambient air, and / or that the oxygen comprised in the oxygen-containing stream (22) is obtained from the electrolysis arrangement (60).

16. The method according to any one of the preceding claims, characterized in that the recycle stream (40) of the synthesis gas reactor arrangement (13) is fed upstream of the reforming reactor (30) or the oxidation reactor (31).

17. The method according to any one of the preceding claims, wherein a pre-reforming reactor (29) is arranged upstream of the reforming reactor (30), wherein the recycle stream (40) is fed to the synthesis gas reactor arrangement (13) between the pre-reforming reactor (29) and the reforming reactor (30).

18. Process according to one of the preceding claims, characterized in that the hydrogen recovery arrangement (5) comprises a pressure swing adsorption device (24) or a membrane arrangement (25) for obtaining the H recycle stream (7) from the recovery stream (6).

19. Method according to one of the preceding claims, characterized in that the hydrogen recovery arrangement (5) outputs a purge stream (8), and / or that a purge stream (8) is branched off from the recycle stream (40), and / or that a purge stream (8) is branched off from the recovery stream (6), and / or that a purge stream (8) is branched off from the residual gas stream (15), wherein the purge stream is preferably fed to a combustion unit or fed to a flare.

20. Experience according to one of the preceding claims, characterized in that a ratio of a molar mass flow of carbon-containing compounds in the purge stream (8) relative to the synthesis gas stream (2) has a value of 10' 5 to 0.4, and preferably takes a value of 0.0001 to 0.3, and more preferably takes a value of 0.0005 to 0.

21.

21. Plant for the synthesis of methanol (1) with a synthesis gas reactor arrangement (13) for obtaining a synthesis gas stream (2) with hydrogen and carbon oxides from a carbon-containing energy carrier stream (11) supplied to the synthesis gas reactor arrangement (13), with a methanol reactor arrangement (4) which has a first reactor stage (21a) and optionally a second reactor stage (21b), with a recycle compressor (14), and optionally with a hydrogen recovery arrangement (5), a device for at least partially feeding the synthesis gas stream (2) into the first reactor stage (21a) for at least partial conversion into methanol (1), an optional device for feeding unreacted residual gas (16a) from the first reactor stage (21a) to the optional second reactor stage (21b) for at least partial conversion into methanol (1), with a device for obtaining a residual gas stream (15) from the methanol reactor arrangement (4) with unreacted carbon oxides,with a device for feeding the residual gas stream (15) into the recycle compressor (14) to increase the pressure of the residual gas stream (15), with a device for feeding the pressure-increased residual gas stream (15) into the methanol reactor arrangement (4) for at least partial conversion into methanol (1), with an optional device for feeding a recovery stream (6) comprising unreacted residual gas (16a, 16b) from the first and / or second reactor stage (21a, 21b) into the hydrogen recovery arrangement (5) to obtain an H recycle stream (7), wherein the H recycle stream (7) comprises unreacted hydrogen from the unreacted residual gas (16a) from the first reactor stage (21a) and / or from the unreacted residual gas (16b) from the second reactor stage (21b), with a device for re-feeding the unreacted hydrogen of the H recycle stream (7) into the first reactor stage (21a) for at least partial conversion into methanol (1),characterized by means for supplying a hydrogen stream (35) with external hydrogen to one of the streams (2, 6, 7, 11, 15) upstream or downstream of the synthesis gas reactor arrangement, one or more devices for branching off and feeding a portion of the residual gas stream (15), and / or the optional recovery stream (6), and / or a stream (71) downstream of the hydrogen recovery arrangement (5) into the synthesis gas reactor arrangement (13) as a recycle stream (40).

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