Plant and method for converting co 2 to methanol

Abstract

The invention relates to a methanol plant, the methanol plant comprising: a CO2-rich fee; a hydrogen-rich feed; a boiler feed water stream; an electrical reverse water gas shift section arranged to output a syngas stream; a heat exchange section; a methanol synthesis loop arranged to receive a syngas stream and to output a raw methanol stream, a purge gas stream, and a flash gas stream; a methanol upgrading section arranged to receive a raw methanol stream and to output an upgraded methanol stream. At least a portion of the purge gas stream is arranged to be recycled to the CO2-rich feed, and / or at least a portion of the flash gas stream is arranged to be recycled to at least one of: the methanol synthesis loop and / or the CO2-rich feed. The invention also relates to a method for converting CO2 to methanol.

Description

[0001] Plant and method for converting CO2to methanol

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a methanol plant and a method for converting CO2to methanol.

[0004] BACKGROUND

[0005] Carbon capture, carbon utilisation, and carbon storage technologies are effective to mitigate the greenhouse effect. Captured CO2can be utilised by converting it to methanol. A standard synthesis route for methanol production from CO2is by direct hydrogenation of CO2. This process is typically dependent on the import of additional heat to close the heat balance of the process.

[0006] There is a need for a plant and method for converting CO2to methanol wherein the plant and method are self-sufficient in steam production and consumption.

[0007] It is an object to provide a plant and method for converting CO2to methanol using renewable energy. Finally, it is an object to provide a plant and method for converting CO2to methanol wherein the plant and method are self-sufficient in steam production and consumption.

[0008] SUMMARY

[0009] The invention relates to a methanol plant and method for converting CO2to methanol, via the generation of CO- and H2-rich syngas in an electrical reverse water gas shift section.

[0010] In a first aspect, the invention relates to a methanol plant, the methanol plant comprising:

[0011] a CO2-rich feed,

[0012] a hydrogen-rich feed,

[0013] a boiler feed water stream,

[0014] an electrical reverse water gas shift (eRWGS) section arranged to receive, preferably in admixture, the CO2-rich feed and the hydrogen-rich feed, to convert at least a portion of the CO2-rich feed and at least a portion of the hydrogen-rich feed to a syngas stream, and to output the syngas stream,a heat exchange section arranged to heat exchange at least a portion of the syngas stream with the boiler feed water stream so as to output a cooled syngas stream and a steam stream,

[0015] a methanol synthesis loop arranged to receive at least a portion of the cooled syngas stream and to output a raw methanol stream, a purge gas stream, and a flash gas stream, and

[0016] a methanol upgrading section arranged to receive at least a portion of the raw methanol stream and to output an upgraded methanol stream and an off-gas stream,

[0017] wherein at least a first portion of the steam stream is arranged to provide heat energy for one or more components of the methanol upgrading section, and

[0018] wherein at least a portion of the purge gas stream is arranged to be recycled to the CO2-rich feed, and / or at least a portion of the flash gas stream is arranged to be recycled to at least one of: the methanol synthesis loop and the CO2-rich feed.

[0019] Also provided is a method for converting CO2to methanol, comprising the steps of:

[0020] a) providing a CO2-rich feed,

[0021] b) providing a hydrogen-rich feed,

[0022] c) providing a boiler feed water stream,

[0023] d) supplying the CO2-rich feed and the hydrogen-rich feed, preferably in admixture, to an electrical reverse water gas shift section (eRWGS),

[0024] e) carrying out syngas synthesis in the eRWGS section, the syngas synthesis comprising the step of:

[0025] reacting at least a portion of the CO2from the CO2-rich feed and at least a portion of the hydrogen from the hydrogen-rich feed to produce a syngas stream,

[0026] f) outletting the syngas stream from the eRWGS section,

[0027] g) heat exchanging at least a portion of the syngas stream with the boiler feed water stream so as to produce a cooled syngas stream and a steam stream, h) providing at least a portion of the cooled syngas stream to a methanol synthesis loop to output a raw methanol stream, a purge gas stream, and a flash gas stream,

[0028] i) upgrading at least a portion of the raw methanol stream in a methanol upgrading section to output an upgraded methanol stream and an off-gas stream, j) using at least a portion of the steam stream to provide heat energy for one or more components of the methanol upgrading section, and

[0029] k) one or more of the following steps:

[0030] - recycling at least a portion of the purge gas stream to the CO2-rich feed, and- recycling at least a portion of the flash gas stream to the methanol synthesis loop and / or to the CO2-rich feed.

[0031] Further details of the invention are provided in the following description and figures.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Fig. 1 shows a layout of the plant and method of the invention.

[0034] Fig. 2 shows a further layout of the plant and method of the invention.

[0035] Fig. 3 shows a further layout of the plant and method of the invention.

[0036] DETAILED DISCLOSURE

[0037] For the purposes of the present application:

[0038] The term 'flash gas' denotes a gas obtained by degassing raw methanol through a reduction in pressure of the raw methanol. The gas contains primarily CO2and other dissolved gases like H2, CO, CH4, Ar and / or N2. The gas may also compromise traces of methanol and other reaction byproducts from the methanol synthesis.

[0039] The term 'synthesis gas', abbreviated as 'syngas', denotes a gas comprising hydrogen, carbon dioxide, and carbon monoxide in various ratios. Optionally, the gas also comprises small amounts of other gasses, such as argon, nitrogen, and / or methane.

[0040] The term 'raw methanol' denotes a fluid containing methanol and water which has not been subject to upgrading, i.e., removal of water and / or byproducts by distillation. Optionally, the fluid also comprises small amounts of byproducts like, but not limited to, ethanol and other higher alcohols, ketones, ethers, esters, and organic acids from the synthesis of methanol. Optionally, the fluid also comprises small amounts of dissolved synthesis gas.

[0041] The term carbon 'efficiency' denotes the total number of moles carbon in the CO2-rich feed divided by the total number of moles carbon in the methanol product.

[0042] The term hydrogen 'efficiency' denotes the total number of moles hydrogen in the hydrogen feed divided by the total number of moles hydrogen in the methanol product.The terms 'at least a portion of' and 'at least (a) part of', in connection with a physical element, such as a feed, a stream, a section, or a unit, mean the entire element or a portion / part (fraction) thereof. Accordingly, the term 'at least partly' in connection with a physical element, such as a feed, a stream, a section, or a unit, means 'a part of' or 'the entirety of'.

[0043] The term 'electrical reverse water gas shift' is abbreviated 'eRWGS'.

[0044] The term 'section' refers normally in the specification to a subset of a plant or system.

[0045] Other definitions are provided throughout the patent application in connection with the recital of one or more embodiments of the invention.

[0046] In general terms, the methanol plant disclosed herein comprises:

[0047] a CO2-rich feed,

[0048] a hydrogen-rich feed,

[0049] a boiler feed water stream,

[0050] an electrical reverse water gas shift (eRWGS) section, comprising one or more electrical reverse water gas shift reactors.

[0051] a heat exchange section,

[0052] a methanol synthesis loop, comprising one or more methanol synthesis reactors and a heat exchange section and separation section.

[0053] a methanol upgrading section.

[0054] Details of the components of the plant are described in the following.

[0055] The CO2-rich feed comprises CO2gas, and preferably comprises at least 70% vol. CO2, more preferably at least 90% vol. CO2, more preferably at least 95% vol. CO2, more preferably at least 98% vol. CO2. The CO2-rich feed may consist essentially of CO2. In one embodiment, the CO2-rich feed comprises captured CO2, such as CO2captured from air, from point source emission, or from a CO2-producing process.

[0056] The hydrogen-rich feed comprises hydrogen gas, and preferably comprises at least 70% vol. H2, more preferably at least 90% vol. H2, more preferably at least 95% vol. H2, more preferably at least 98% vol. H2, more preferably at least 99% vol. H2. The H2-rich feed may consist essentially of H2.

[0057] The eRWGS section is arranged to receive, preferably in admixture, the CO2-rich feed and the hydrogen-rich feed, to convert at least a portion of the CO2-rich feed and at least a portion ofthe hydrogen-rich feed to a syngas stream, and to output the syngas stream. The syngas stream comprises CO2, CO, and H2. Optionally, the syngas stream also comprises small amounts of other gases, such as argon, nitrogen, and / or methane.

[0058] In one embodiment, at least 60% of the CO2in the CO2-rich feed is converted into CO, more preferably at least 70%, more preferably at least 75%.

[0059] In one embodiment, the hydrogen-rich feed is arranged to be obtained from electrolysis of water. The hydrogen-rich feed can be obtained from electrolysis of water using electricity optionally partly or fully from a renewable energy source. For this purpose, in one embodiment, the plant comprises an H2O-electrolysis section and a water feedstock for the H2O-electrolysis section. The electrolysis section is arranged to electrolyse the water feedstock to a hydrogen-rich stream, and to feed at least a portion of the hydrogen-rich stream as at least a portion of the hydrogen-rich feed to the electrical reverse water gas shift section.

[0060] The electrolysis section can be arranged to use one or more electrolysis processes to generate hydrogen, such as Solid-Oxide Electrolysis Cell (SOEC) electrolysis, alkaline electrolysis, and / or polymer electrolyte membrane electrolysis (also called proton exchange membrane electrolysis, abbreviated PEM electrolysis). Accordingly, the electrolysis section may comprise, for example, an alkaline electrolyser, a PEM electrolyser, and / or an SOEC electrolyser. The steam used in the SOEC electrolysis can be steam produced in the plant.

[0061] The eRWGS section can be arranged to receive the CO2-rich feed and the hydrogen-rich feed in admixture or separately. If received separately, the eRWGS section is arranged to mix the CO2-rich feed and the hydrogen-rich feed, e.g. at the inlet thereof.

[0062] In one embodiment, the CO2-rich feed and / or the hydrogen-rich feed are compressed upstream the eRWGS section, either separately or in admixture. For this purpose, in one embodiment, the methanol plant comprises a first feed compression section arranged to compress the CO2-rich feed and a second feed compression section arranged to compress the hydrogen-rich feed. In another embodiment, the methanol plant comprises a feed compression section arranged to compress the mixed CO2-rich and hydrogen-rich feeds.

[0063] In one embodiment, the compressed CO2-rich feed is subjected to one or more cleaning steps to remove impurities, e.g. sulphur species. In one embodiment, the methanol plant comprises a first feed purification section arranged to purify the CO2-rich feed and an optional second feed purification section arranged to purify the hydrogen-rich feed. The first feed purification section is preferably arranged to purify the compressed CO2-rich feed. The secondfeed purification section is preferably arranged to purify the compressed hydrogen-rich feed. In one embodiment, the methanol plant comprises a feed purification section arranged to purify the compressed CO2-rich feed and the hydrogen-rich feed in admixture.

[0064] At least a portion of the CO2in the CO2-rich feed is converted to CO in the eRWGS section, via electrical reverse water gas shift. The eRWGS section comprises one or more eRWGS reactors wherein the electrical reverse gas shift reaction takes place. In one embodiment, the eRWGS section is arranged to heat the CO2-rich feed and the hydrogen-rich feed in admixture. The eRWGS reactor is electrically heated. In one embodiment, the eRWGS reactor uses renewable electrical power. The eRWGS reactor can be, for example, resistance-heated or induction-heated.

[0065] The use of an eRWGS reactor is described in published PCT Application No. WO22079098A1, the contents of which are incorporated herein by reference in their entirety.

[0066] In one embodiment, the eRWGS section suitably comprises:

[0067] a structured catalyst comprising a macroscopic structure of electrically conductive material capable of catalysing reverse water gas shift reaction, the structured catalyst comprising a macroscopic structure of electrically conductive material, the macroscopic structure supporting a ceramic coating, wherein the ceramic coating supports a catalytically active material;

[0068] a pressure shell housing the structured catalyst; the pressure shell comprising an inlet for letting in the CO2-rich and hydrogen-rich feed, preferable in admixture, and an outlet for letting out the syngas product; wherein the inlet is positioned so that the feed enters the structured catalyst in a first end of the structured catalyst and the syngas product exits the structured catalyst from a second end of the structured catalyst;

[0069] a heat insulation layer between the structured catalyst and the pressure shell; and at least two conductors electrically connected to the structured catalyst and to an electrical power supply placed outside the pressure shell, wherein the electrical power supply is dimensioned to heat at least part of the structured catalyst to a temperature of at least 500°C by passing an electrical current through the macroscopic structure of electrically conductive material; wherein the at least two conductors are connected to the structured catalyst at a position on the structured catalyst closer to the first end of the structured catalyst than to the second end of the structured catalyst, and wherein the structured catalyst is constructed to direct an electrical current to run from one conductor substantially to the second end of the structured catalyst and return to a second of the at least two conductors, and wherein the structured catalysthas electrically insulating parts arranged to direct the current from one conductor, which is closer to the first end of the structured catalyst than to the second end, towards the second end of the structured catalyst and back to a second conductor closer to the first end of the structured catalyst than to the second end.

[0070] The RWGS reaction carried out in the eRWGS reactor involves the reduction of CO2from the CO2-rich feed with hydrogen from the hydrogen-rich feed, to produce CO and water:

[0071] CO2+ H2CO + H2O (1).

[0072] The RWGS reaction is endothermic. It is suitably carried out at high temperature to move the reaction equilibrium in the forward direction. The high temperature also increases the reaction rate.

[0073] In one embodiment, the syngas synthesis in the eRWGS reactor occurs at a temperature of between 600°C and 1400°C, preferably between 800°C and 1200°C, more preferably between 850°C and 1100°C.

[0074] In one embodiment, the syngas synthesis in the eRWGS reactor is carried out at a pressure of between 2 and 40 bar g, such as between 4 and 25 bar g, such as between 5 and 20 bar g, such as between 7 and 15 bar g. A low pressure in the eRWGS reactor reduces methane slip from the eRWGS section.

[0075] In one embodiment, the conversion of CO2to CO in the electrical reverse water gas shift section is above 50%, preferably above 60%, preferably above 70%, preferably above 75%.

[0076] The heat exchange section is arranged to heat exchange at least a portion of the syngas stream outputted from the eRWGS section with the boiler feed water stream, so as to produce a cooled syngas stream and a steam stream.

[0077] The cooled syngas stream comprises CO and CO2. In one embodiment, the molar ratio between CO and CO2is the same in the syngas stream outputted from the eRWGS section and the cooled syngas stream.

[0078] In one embodiment, the heat exchange section comprises a cooling train. The cooling train may comprise one or more heat exchangers for recovering heat from at least a portion of the syngas stream. Furthermore, the cooling train may comprise a separator for removing water from the cooled syngas stream.The removal of water from the cooled syngas stream is useful to reduce sintering and deactivation of the catalyst that is used in the production of methanol in the methanol synthesis loop. A lower water content reduces catalyst sintering and deactivation due to hydrothermal effects.

[0079] Excess heat from at least a portion of the syngas stream can be utilised elsewhere in the plant to reduce the dependency of the plant on additional power, and to close the heat balance of the plant. At least a first portion of the steam stream outputted from the heat exchange section can be used in reboilers of the methanol upgrading section. Additionally, or alternatively, at least a second portion of the steam stream can be used for pre-heating the CO2-rich feed and / or the hydrogen-rich feed.

[0080] In one embodiment, the methanol plant comprises a first preheating section arranged to preheat the CO2-rich feed and a second pre-heating section arranged to pre-heat the hydrogenrich feed, wherein one or more components of one or both of the pre-heating sections are arranged to receive heat energy from at least a portion of the steam stream from the heat exchange section.

[0081] In one embodiment, the methanol plant comprises a preheating section arranged to preheat the CO2-rich feed and the hydrogen-rich feed in admixture, wherein one or more components of the pre-heating section are arranged to receive heat energy from at least a portion of the steam stream from the heat exchange section.

[0082] In the situation where the CO2-rich feed and the hydrogen-rich feed are supplied in admixture to the electrical reverse water gas shift (eRWGS) section, the plant may comprise a combined preheating section arranged to pre-heat the combined CO2-rich feed and hydrogen-rich feed, wherein one or more components of the combined pre-heating sections are arranged to receive heat energy from at least a portion of the steam stream from the heat exchange section.

[0083] In one embodiment, the first feed purification section is arranged to receive and to purify the pre-heated CO2-rich feed, and the second feed purification section is arranged to receive and to purify the pre-heated hydrogen-rich feed. In one embodiment, the feed purification section is arranged to receive and to purify the pre-heated CO2-rich feed and hydrogen-rich feed in admixture.

[0084] The methanol synthesis loop is arranged to receive at least a portion of the cooled syngas stream and to output a raw methanol stream, a purge gas stream, and a flash gas stream. The cooled syngas is partly converted into methanol in one or more methanol synthesisreactors whereafter the partly converted syngas is cooled in one or more heat exchangers before it is sent to one or more gas-liquid separators. The gas-liquid separation may comprise both high-pressure and low-pressure separators.

[0085] The methanol synthesis reactors may be selected amongst adiabatic reactors, water-cooled boiling water reactors or gas-cooled reactors or combinations hereof.

[0086] The cooled syngas stream is rich in H2, CO and CO2. In one embodiment, the methanol synthesis loop is arranged to receive at least a portion of the cooled syngas stream, wherein the at least a portion of the cooled syngas stream has a molar module of between

[0087]

[0088] 1.5 and 2.5, such as around 2.0, such as between 2.0 and 2.1, such as 2.01.

[0089] In one embodiment, the methanol synthesis in the one or more methanol synthesis reactors occurs primarily via hydrogenation of CO present in the syngas stream, as opposed to primarily or fully via direct hydrogenation of CO2.

[0090] The production of methanol from CO and hydrogen can be expressed as follows:

[0091]

[0092] A smaller part of the methanol produced in the methanol synthesis loop may be formed by direct hydrogenation of CO2present in the syngas stream. Direct hydrogenation of CO2can be expressed as:

[0093]

[0094] Direct hydrogenation of CO2to methanol produces water. A high water content accelerates sintering and deactivation of the methanol catalyst in the methanol synthesis loop due to hydrothermal effects. Producing methanol via hydrogenation of CO, as opposed to via hydrogenation of CO2, reduces the water content in the methanol synthesis loop, and thus reduces sintering and deactivation of the methanol catalyst.

[0095] The plant and method of the present invention allow for the use of less catalyst in the methanol production in the methanol synthesis loop, and for a smaller methanol synthesis loop and a smaller methanol synthesis reactor, compared to when CO2is converted to methanol primarily or entirely by direct hydrogenation of CO2. This is due to the higher reactivity of CO compared to CO2.The recycling of heat energy between different sections of the plant allows for minimising the power consumption of the plant, and for minimising or avoiding the need for import of external heat.

[0096] In one embodiment, the methanol synthesis loop comprises one or more methanol synthesis reactors, a heat exchanger, a methanol separation unit, and a compressor. The methanol synthesis loop is arranged to receive at least a portion of the cooled syngas stream and to output a raw methanol stream, a purge gas stream, and a flash gas stream.

[0097] In one embodiment, the purge gas stream comprises unreacted syngas. In one embodiment, the major part of the unreacted syngas is recycled to the methanol synthesis reactor.

[0098] At least a portion of the purge gas stream is arranged to be recycled, optionally through a hydrogen recovery unit (HRU), to the CO2-rich feed. Recycling at least a portion of the purge gas stream increases the overall plant hydrogen efficiency. In one embodiment, at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90% of the purge gas stream is arranged to be recycled to the CO2-rich feed. If an HRU is installed, the hydrogen rich stream may be returned directly to the methanol synthesis loop and part of the hydrogen depleted stream optionally recycled to the CO2-rich feed.

[0099] The recycling of purge gas also increases the carbon efficiency of the process as the purge gas contains equilibrium slip of methane from the eRWGS. Recycling part of the purge contains the carbon in the system and increases overall feedstock efficiency. In case a HRU is installed part of the retentate stream can optionally be recycled to increase carbon efficiency. Part of the purge or retentate must be routed out of the process to avoid accumulation of inerts.

[0100] In one embodiment, the flash gas stream is a low-pressure flash gas stream. The flash gas stream is generated by degassing of the liquid methanol stream produced in the loop through pressure reduction from loop pressure to pressure in the low-pressure separator.

[0101] At least a portion of the flash gas stream is arranged to be recycled to at least one of: the methanol synthesis loop and the CO2-rich feed. Recycling of a least a portion of the flash gas increases plant overall C-efficiency. In one embodiment, at least 90% of the flash gas stream is arranged to be recycled to the methanol synthesis loop and / or CO2-rich feed, more preferably at least 95%, more preferably at least 98%, more preferably at least 99%.

[0102] Recycling to the CO2-rich feed is typically preferred for layouts where the pressure of the CO2-rich feed is lower than pressure of the flash gas stream, since this removes the need fora dedicated compressor for compressing the flash gas stream before it is recycled to the CO2-rich feed.

[0103] The methanol upgrading section is arranged to receive at least a portion of the raw methanol stream from the methanol synthesis loop and to output an upgraded methanol stream and an off-gas stream. At least a portion of the steam stream outputted from the heat exchange section is arranged to provide heat energy for one or more components of the methanol upgrading section.

[0104] In one embodiment, the methanol upgrading section comprises one or more methanol distillation columns, wherein at least at portion of the steam stream from the heat exchange section is arranged to provide heat energy for the one or more of the methanol distillation columns. In one or more embodiments at least 90% of the heat energy required for the methanol upgrade section is supplied by providing some of the steam stream from the heat exchange section. In some embodiments all the required heat energy for the methanol upgrade section is supplied by providing at least some of the steam stream from the heat exchange section.

[0105] In one embodiment, the methanol plant is self-sufficient in steam production and consumption. Several other benefits can be achieved with the embodiments disclosed herein, compared to conventional methanol production by direct hydrogenation of CO2. Some of the benefits are e.g. :

[0106] smaller loop and methanol synthesis reactor;

[0107] reduction in the import of steam, up to 100% reduction; and

[0108] minimum waste-water generation.

[0109] The plant provides a cost-effective solution to methanol production and allows for substantially complete CO2utilisation. A CO2-to-methanol carbon efficiency above 95%, such as above 98%, can be achieved. Grade AA methanol can be produced using electricity from renewable energy, electrolytic H2, and captured CO2.

[0110] The present invention also provides a method for converting CO2to methanol, comprising the steps of:

[0111] a) providing a CO2-rich feed,

[0112] b) providing a hydrogen-rich feed,

[0113] c) providing a boiler feed water stream,

[0114] d) supplying the CO2-rich feed and the hydrogen-rich feed, preferably in admixture, to an electrical reverse water gas shift (eRWGS) section,e) carrying out syngas synthesis in the eRWGS section, the syngas synthesis comprising the step of:

[0115] reacting at least a portion of the CO2from the CO2-rich feed and at least a portion of the hydrogen from the hydrogen-rich feed to produce a syngas stream,

[0116] f) outletting the syngas stream from the eRWGS section,

[0117] g) heat exchanging at least a portion of the syngas stream with the boiler feed water stream so as to produce a cooled syngas stream and a steam stream,

[0118] h) providing at least a portion of the cooled syngas stream to a methanol synthesis loop to output a raw methanol stream, a purge gas stream, and a flash gas stream, i) upgrading at least a portion of the raw methanol stream in a methanol upgrading section to output a upgraded methanol stream and an off-gas stream,

[0119] j) using at least a portion of the steam stream to provide heat energy for one or more components of the methanol upgrading section, and

[0120] k) one or more of the following steps:

[0121] - recycling at least a portion of the purge gas stream to the CO2-rich feed, and - recycling at least a portion of the flash gas stream to the methanol synthesis loop and / or to the CO2-rich feed.

[0122] In one embodiment, the method further comprises heating the CO2-rich feed and hydrogenrich feed in admixture.

[0123] In one embodiment, the method uses the methanol plant as disclosed herein.

[0124] In one embodiment, the method further comprises the steps of:

[0125] purifying the CO2-rich feed upstream of the electrical reverse water gas shift section and,

[0126] optionally, purifying the hydrogen-rich feed upstream of the electrical reverse water gas shift section.

[0127] In one embodiment, the hydrogen-rich feed is obtained from electrolysis of water. Thus, method may further comprise the steps of:

[0128] carrying out electrolysis of a water feedstock in an H2O-electrolysis section to generate a hydrogen-rich stream,

[0129] feeding the hydrogen-rich stream as at least a portion of the hydrogen-rich feed to the reverse water gas shift section.

[0130] In one embodiment, at least a portion of the steam stream is used to pre-heat the CO2-rich feed and the hydrogen-rich feed upstream the eRWGS section.In one embodiment, the purge gas stream comprises unreacted synthesis gas. In one embodiment, at least a portion of the purge gas stream is recycled to the CO2-rich feed, optionally through a hydrogen recovery unit (HRU). Recycling at least a portion of the purge gas stream increases the overall plant hydrogen efficiency. In one embodiment, at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90% of the purge gas stream is recycled to the CO2-rich feed.

[0131] In one embodiment, the flash gas stream is a low-pressure flash gas stream. The flash gas stream is generated by degassing of the liquid methanol stream produced in the loop through pressure reduction from loop pressure to pressure in low pressure separator. In one embodiment, at least a portion of the flash gas stream is recycled to the CO2-rich feed. Recycling of a least a portion of the flash gas increases plant overall C-efficiency. In one embodiment, at least 90% of the flash gas is arranged to be recycled to the CO2-rich feed, more preferably at least 95%, more preferably at least 98%, more preferably at least 99%. Optionally, the flash gas is washed before recycled to reduce methanol content in the returned flash gas stream.

[0132] In one embodiment, the H2 / CO2inlet molar ratio in the eRWGS section is between 2.5 and 3.5, such as between 2.8 and 3.2, such as between 2.95 and 3.05.

[0133] In one embodiment, the syngas streams have molar modules M =

[0134]

[0135] of between 1.5 and

[0136]

[0137] 2.5, preferably around 2.0, more preferably 2.01. Converting CO2and H2into syngas with a module of between 1.5 and 2.5, preferably around 2.0, more preferably 2.01 allows for an optimised methanol synthesis.

[0138] In one embodiment, the syngas synthesis in the electrical reverse water gas shift section is carried out at a pressure of between 2 and 40 bar g, such as between 4 and 25 bar g, such as between 5 and 20 bar g, such as between 7 and 15 bar g. Conducting the electrical reverse water gas shift reaction at a low pressure reduces methane slip from the eRWGS section.

[0139] In one embodiment, the syngas synthesis occurs at a temperature of between 600°C and 1400°C, preferably between 800°C and 1200°C, more preferably between 850°C and 1100°C.

[0140] In one embodiment, the conversion of CO2to CO in the electrical reverse water gas shift is above 50%, preferably above 60%, preferably above 70%, preferably above 75%.In one embodiment, the electrical RWGS section is powered with energy from a renewable energy source.

[0141] In one embodiment, all processes, including water electrolysis, the reverse water gas shift reaction, methanol synthesis, and raw methanol purification, are powered using electricity from renewable energy.

[0142] Specific embodiments

[0143] Fig. 1 shows a first embodiment of the methanol plant (100) of the invention, the methanol plant comprising:

[0144] a CO2-rich feed (1),

[0145] a hydrogen-rich feed (2),

[0146] a boiler feed water stream (3),

[0147] an electrical reverse water gas shift section (10),

[0148] a heat exchange section (20),

[0149] a methanol synthesis loop (30), and

[0150] a methanol upgrading section (40).

[0151] The electrical reverse water gas shift (eRWGS) section (10) is arranged to receive the CO2-rich feed (1) and the hydrogen-rich feed (2), preferably in admixture, to convert the CO2-rich feed (1) and the hydrogen-rich feed (2) to a syngas stream (11), and to output the syngas stream (11).

[0152] The heat exchange section (20) is arranged to heat exchange at least a portion of the syngas stream (11) with the boiler feed water stream (3) so as to output a cooled syngas stream (21) and a steam stream (22). The methanol synthesis loop (30), which comprises one or more methanol synthesis reactors, e.g., a boiling water reactor (BWR), an adiabatic reactor, a gas cooled reactor or combinations hereof, is arranged to receive at least a portion of the cooled syngas stream (21) and to output a raw methanol stream (31), a purge gas stream (32), and a flash gas stream (33).

[0153] The methanol upgrading section (40) is arranged to receive at least a portion of the raw methanol stream (31) and to output an upgraded methanol stream (41) and an off-gas stream (42), wherein at least a portion of the steam stream (22) from the heat exchange section (20) is arranged to provide heat energy for one or more components of the methanol upgrading section (40). The portion of the steam stream (22) supplied to the methanolupgrade section (40) may be sufficient to provide all necessary heat energy for the one or more components of the methanol upgrade section (40).

[0154] At least a portion of the purge gas stream (32) is arranged to be recycled to the CO2-rich feed (1), and / or at least a portion of the flash gas stream (33) is arranged to be recycled to at least one of: the methanol synthesis loop (30) and the CO2-rich feed (1).

[0155] When the flash gas stream (33) is recycled to the methanol synthesis loop (30), it is preferably supplied separately to the methanol synthesis loop (30), such that the flash gas stream (33) and the cooled syngas stream (21) enter separately into the methanol synthesis loop (30), as shown in Fig. 1. However, the two streams may also be mixed prior to being fed to the methanol synthesis loop (30).

[0156] As a further development, and as shown in Fig. 2, the methanol plant (100) may comprise a first preheating section (60) arranged to pre-heat the CO2-rich feed (1) and a second preheating section (70) arranged to pre-heat the hydrogen-rich feed (2), wherein one or more components of one or both of the pre-heating sections (60, 70) are arranged to receive heat energy from at least a portion of the steam stream (22). Furthermore, the methanol plant may comprise a first feed purification section (80) arranged to receive the pre-heated CO2-rich feed and to purify the CO2-rich feed (1), and an optional second feed purification section (90) arranged to receive the pre-heated hydrogen-rich stream and to purify the hydrogenrich feed. Fig. 2 shows recycling of flash gas stream (33) only to the CO2-rich feed, not to the methanol synthesis loop (30).

[0157] The layout illustrated in Figure 3 is the same as that of Figure 2, and additionally includes a hydrogen recovery unit (HRU, 110) arranged to receive the purge gas stream (32) and separate it into a hydrogen rich stream (32A) and a hydrogen depleted stream (32B). If an HRU is installed, the hydrogen rich stream (32A) may be returned directly to the methanol synthesis loop (30) and at least part of the hydrogen depleted stream optionally recycled to the CO2-rich feed (1).

[0158] Examples

[0159] Table 1 shows a comparison of methanol production via direct hydrogenation of CO2and methanol production according to the plant and method disclosed herein, based on calculated heat and mass balances for the plant and method. Energy from steam per ton of methanol product has been calculated based on the steam flow and its saturation enthalpy.Table 1

[0160]

[0161] Table 2 shows a comparison of methanol production according to the plant and method disclosed herein with and without the recycle of flash gas and purge gas, based on calculated heat and mass balance for the plant and method.

[0162]

Claims

CLAIMS1. A methanol plant (100), the methanol plant (100) comprising:a CO2-rich feed (1),a hydrogen-rich feed (2),a boiler feed water stream (3),an electrical reverse water gas shift (eRWGS) section (10) arranged to receive, preferably in admixture, the CO2-rich feed (1) and the hydrogen-rich feed (2), to convert at least a portion of the CO2-rich feed (1) and at least a portion of the hydrogen-rich feed (2) to a syngas stream, and to output the syngas stream (11),a heat exchange section (20) arranged to heat exchange at least a portion of the syngas stream (11) with the boiler feed water stream (3) so as to output a cooled syngas stream (21) and a steam stream (22),a methanol synthesis loop (30) arranged to receive at least a portion of the cooled syngas stream (21) and to output a raw methanol stream (31), a purge gas stream (32), and a flash gas stream (33), anda methanol upgrading section (40) arranged to receive at least a portion of the raw methanol stream (31) and to output an upgraded methanol stream (41) and an off-gas stream (42),wherein at least a first portion of the steam stream (22) is arranged to provide heat energy for one or more components of the methanol upgrading section (40), and whereinat least a portion of the purge gas stream (32) is arranged to be recycled to the CO2-rich feed (1), and / orat least a portion of the flash gas stream (33) is arranged to be recycled to at least one of: the methanol synthesis loop (30) and / or the CO2-rich feed (1).

2. The methanol plant (100) according to claim 1, wherein the flash gas stream (33) is a low-pressure flash gas stream.

3. The methanol plant (100) according to any one of the preceding claims, wherein the purge gas stream (32) comprises unreacted syngas.

4. The methanol plant (100) according to any one of the preceding claims, further comprising a first preheating section (60) arranged to pre-heat the CO2-rich feed (1) and a second pre-heating section (70) arranged to pre-heat the hydrogen-rich feed (2), wherein one or more components of one or both of the pre-heating sections (60, 70) are arranged to receive heat energy from at least a portion of the steam stream (22) from the heat exchange section (20).

5. The methanol plant (100) according to any one of claims 1-3, comprising a combined preheating section arranged to pre-heat the combined CO2-rich feed (1) and the hydrogen-rich feed (2), wherein one or more components of the combined pre-heating sections are arranged to receive heat energy from at least a portion of the steam stream (22) from the heat exchange section (20).

6. The methanol plant (100) according to any one of the preceding claims, further comprising a first feed purification section (80) arranged to purify the CO2-rich feed (1) and an optional second feed purification section (90) arranged to purify the hydrogenrich feed (2).

7. The methanol plant (100) according to any one of the preceding claims, wherein the methanol upgrading section (40) comprises one or more methanol distillation columns, wherein at least a portion of the steam stream (22) from the heat exchange section (20) is arranged to provide heat energy for the one or more of the methanol distillation columns.

8. The methanol plant (100) according to any one of the preceding claims, wherein the plant additionally includes a hydrogen recovery unit (110) arranged to receive at least a portion of said purge gas stream (32) and separate it into a hydrogen rich stream (32A) and a hydrogen depleted stream (32B), preferably wherein the hydrogen rich stream (32A) is recycled to the methanol synthesis loop (30) and wherein at least part of the hydrogen depleted stream is optionally recycled to the CO2-rich feed (1).

9. A method for converting CO2to methanol, comprising the steps of:a) providing a CO2-rich feed (1),b) providing a hydrogen-rich feed (2),c) providing a boiler feed water stream (3),d) supplying the CO2-rich feed (1) and the hydrogen-rich feed (2), preferably in admixture, to an electrical reverse water gas shift (eRWGS) section (10), e) carrying out syngas synthesis in the eRWGS section (10), the syngas synthesis comprising the step of:reacting at least a portion of the CO2from the CO2-rich feed (1) and at least a portion of the hydrogen from the hydrogen-rich feed (2) to produce a syngas stream (11),f) outletting the syngas stream (11) from the eRWGS section (10),g) heat exchanging at least a portion of the syngas stream (11) with the boiler feed water stream (3) so as to produce a cooled syngas stream (21) and a steam stream (22),19h) providing at least a portion of the cooled syngas stream (21) to a methanol synthesis loop (30) to output a raw methanol stream (31), a purge gas stream (32), and a flash gas stream (33),i) upgrading at least a portion of the raw methanol stream (31) in a methanol upgrading section (40) to output an upgraded methanol stream (41) and an offgas stream (42),j) using at least a portion of the steam stream (22) to provide heat energy for one or more components of the methanol upgrading section (40), andk) one or more of the following steps:- recycling at least a portion of the purge gas stream (32) to the CO2-rich feed (1), and- recycling at least a portion of the flash gas stream (33) to the methanol synthesis loop (30) and / or to the CO2-rich feed (1).

10. The method according to claim 9, wherein at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90% of the purge gas stream (32) is recycled to the CO2-rich feed (1).

11. The method according to claim 9 or 10, wherein at least 90%, more preferably at least 95%, more preferably at least 98%, more preferably at least 99% of the flash gas stream (33) is recycled to the CO2-rich feed (1).

12. The method according to any one of claims 9-11, wherein the hydrogen-rich feed (2) is obtained from electrolysis of water.

13. The method according to any one of claims 9-12, wherein at least a portion of the steam stream (22) is used to pre-heat the CO2-rich feed (1) and / or the hydrogen-rich feed (2).

14. The method according to any one of claims 9-13, wherein the syngas streams (11, 21) have molar modules M = of between 1.5 and 2.5, preferably around 2.0, morepreferably 2.01.

15. The method according to any one of claims 9-14, wherein the syngas synthesis in the eRWGS section (10) is carried out at a pressure of between 2 and 40 bar g, such as between 4 and 25 bar g, such as between 5 and 20 bar g, such as between 7 and 15 bar g-

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