WO2025003398A1

WO2025003398A1 - Methanol synthesis process

Info

Publication number: WO2025003398A1
Application number: PCT/EP2024/068243
Authority: WO
Inventors: Pietro Moreo; Isabella MUSCIONICO; Riccardo POLETTI
Original assignee: Casale SA
Current assignee: Casale SA
Priority date: 2023-06-28
Filing date: 2024-06-28
Publication date: 2025-01-02
Anticipated expiration: 2025-12-28
Also published as: EP4735411A1; CN121419956A; AU2024309199A1; AR133059A1

Abstract

A process for synthesis of methanol including formation of a crude stream of methanol in a methanol converter and purification of said crude stream, wherein the purification process includes distillation of a methanol-containing stream in a distillation column (2, 28); a gaseous stream (3, 37) containing methanol vapour is withdrawn from said column; a portion of said gaseous stream is compressed in a vapour compressor (19, 38); the compressed gaseous stream (20, 39) is subject to a heat exchange step wherein at least part of the methanol vapour is condensed and heat is transferred to an aqueous stream (15, 31) withdrawn from said column; the heated aqueous stream is reintroduced into said column (2, 28).

Description

Methanol synthesis process

DESCRIPTION

Field of application

The invention is in the field of industrial production of methanol.

Prior art

Methanol is produced industrially by reacting a make-up gas comprising hydrogen (H2) and carbon oxides (CO2 and CO) at elevated temperature and pressure through one or more beds of a suitable methanol synthesis catalyst. The catalytic beds are contained in one or more reactors (methanol converters). The product of the reaction is a methanol-containing gas which is cooled to a temperature below the dew point of methanol so that a stream of crude methanol can be separated. Part of the gaseous fraction separated from the converter effluent is reintroduced in the converter, thus forming a so-called synthesis loop. The circulation in the loop is maintained by a suitable compressor (circulator).

Crude methanol is in a liquid state and contains by-products of the synthesis including ethanol, ketones, higher alcohols, and some dissolved gases including H2, CO, CO2, N2 and CH4. To meet the purity specification required by the market, a purification of the crude methanol is necessary. The purification is typically carried out by distillation.

A distillation process may use one or more distillation column. In a distillation column, an overhead gaseous stream (“light gas”) is withdrawn from top of the column and an aqueous solution is collected from the bottom of the same column. A portion of the bottom solution is heated in a suitable heat exchanger (“bottom reboiler”) and reintroduced into the column to provide the distillation heat. The heat source of the reboiler is typically hot steam. In the distillation of crude methanol, the light gas contains vapours of methanol which can be condensed to obtain a pure methanol product. If required, more than one distillation column may be used. A known configuration includes two distillation columns, namely a preliminary treatment column, known as topping column or pre-run column, followed by a second distillation column known as refining column. The topping column substantially has the purpose of separating the more volatile components contained in the crude methanol. The topping column receives the crude methanol and separates the lighter components (light ends) at the top and an aqueous solution at the bottom. The refining column carries out the actual distillation separating a refined methanol at the top and an aqueous stream at the bottom. Another stream known as "fusel oil" is separated from the second column, typically at intermediate elevation.

The fusel oil contains water, residual methanol (ca. 1-1.5% of the total) and most of the by-products of the synthesis reaction. Fusel oil has a certain heating value and is commonly used as a fuel.

Each column comprises a respective bottom reboiler that heats the bottom of the column and maintains the distillation process. The heat is typically provided by steam, or by a process gas, when available at a suitable thermal level. Moreover, each column may have a top reflux, which means that part of the distilled methanol is condensed and reintroduced in the top of the column. For this purpose, each column is equipped with a respective top condenser which uses air or water as heat sink.

The above two-column layout is simple and achieves a satisfactory purification but has the major drawback of consuming a substantial amount of energy. The energy consumption is due predominantly to the heat supplied to the bottom reboilers and the cooling water and/or electricity (for pumps and/or cooling air fans) required by the top condensers. Another drawback is a relatively large diameter of the distillation columns, in relation to the production capacity, and the consequent high cost.

The order of magnitude of the heat consumption of the two bottom reboilers is in the range of 1.0-1 .5 MWh per ton of refined methanol, depending on raw methanol composition. The amount of heat removed in the condensers is comparable with the amount of heat exchanged in the reboilers.

A known attempt to reduce the heat consumption is the use of three distillation columns at different pressure, as disclosed in US 4 210 495. A preliminary treatment column or topping column is followed by a medium-pressure distillation columns and a final distillation column. The medium-pressure column is operated at about 7-8 bar whilst the topping and final columns a are operated at atmospheric pressure or slightly above, such as 1 .5 bar.

The advantage of this configuration is the possibility to condense the top vapors of the medium-pressure column in the bottom reboiler of the subsequent column with the advantage of recovering heat. However, both the topping column and the intermediate column must be heated, resulting in a high specific heat consumption. Furthermore, the intermediate column requires a heat input at a higher temperature than the other columns at lower pressure. A typical energy consumption of this configuration is around 0.7 - 1.0 MWh per ton of methanol produced, which is still high.

Additionally, an emerging problem is in connection with the use of a make-up gas containing little or no carbon monoxide (CO). This may be the case of a make-up gas obtained from CO2 capture and hydrogen produced by electrolysis of water, which is receiving great interest for environmental reasons. The conversion of CO to methanol releases significantly more heat than conversion of CO2 to methanol. Then, a CO-free make-up gas inherently produces less heat of reaction compared to a conventional CO-containing feedstock. The heat of reaction is removed by producing steam for internal use in the process, including distillation. Consequently, a CO-free make-up gas results in less heat available for distillation.

A methanol plant where part or all of the hydrogen feed comes from a renewable source may also suffer from the fluctuation of the source, as is typically the case of many renewable sources like solar or wind energy. The hydrogen feed fluctuates correspondingly and, in a condition of reduced feed, the heat recoverable from the process may be insufficient for the distillation process.

In all the above cases missing heat may be provided by fired heaters or electric heaters, introducing however the major drawback of consuming electric energy or, in the case of fired heaters, emission of combustion gas. Another drawback of electrically-heated reboilers is they have a limited maximum size, so that multiple units should be installed in case of large duty of the distillation.

In summary, the installation of auxiliary boilers does not solve the above problems and a strong incentive remains in reducing the heat consumption of the distillation process.

Prior art of methanol distillation can be found in: CN 111 995 499; CN 106 075 947; CN 106 957 214; US 3 230 155.

Summary of the invention

The invention aims to overcome the drawbacks of the prior art and to reduce the power consumption of the methanol distillation process.

The aim is reached with a process according to the claims.

The invention is based on the judicious insight that a methanol-containing gaseous stream withdrawn from top of a distillation column, after a suitable compression, can be used to provide at least part of the heat input required by the column to operate. Particularly, the latent heat of the methanol vapors contained in said gaseous stream is transferred to a liquid stream which is withdrawn from the bottom of the column and reintroduced in the column after heating.

The compression step allows to raise the condensation temperature of the methanol vapors to a suitable temperature as required by the distillation process. This step of compressing a vapor stream to increase its condensation temperature for heat recovery purpose is known, as such, as mechanical vapor recompression or MVR.

The invention is further based on the perception that latent heat of the condensation of methanol can be a useful source of heat for the distillation process, despite its low temperature make it appear unsuitable for this use. The compression of the vapour brings the gaseous stream to a proper temperature to heat the column.

It can be noted that the invention requires energy for compression of the gaseous stream. This is more than compensated, however, by the latent heat recovered from said stream. The condensation heat of methanol is significant, being around 800-1000 kJ/kg, therefore the invention allows internal recovering of a substantial amount of heat, which would be otherwise supplied by hot steam or electrically.

The invention may be applied to a distillation process with a single distillation column or more than one column. In embodiments with multiple columns, the heating by MVR may be applied to one or more column(s). A preferred embodiment has two distillation columns.

The compression of the methanol-containing gaseous stream can be performed in one or more stages of compression with inter-cooling if necessary. In embodiments with multiple distillation columns, a separate MVR compressor is preferably provided for each column, wherein the MVR compressor provides heat for the reboiler of the respective distillation column. In preferred embodiments, a portion of the overhead gas from a column, or from each column, is compressed to provide the necessary input to the bottom reboiler of the same column.

An interesting application of the invention is a methanol synthesis process wherein part or all of the make-up gas has a low content of carbon monoxide (CO) or is a substantially CO-free gas. In preferred applications, the content of CO in the make-up gas is not greater than 10%, preferably not greater than 7% and more preferably not greater than 5%. The above percentages are in volume. When using a make-up gas with low or no CO content, the present invention is particularly advantageously because it reduces the energy requirements of the distillation section and compensates for the less heat (lack of steam) recoverable from the synthesis reaction.

In case of lack of steam, the use of mechanical vapor recompression as a tool to recovery and provide heat to the reboiler is more energetically efficient than the use of electrically heated reboilers. Depending on the compressor efficiency and layout, at fixed re-boiling duty, the electrical power of mechanical vapour recompression compared to electric heaters typically ranges from 65 to 85%.

Another advantage of the invention is that a single line of mechanical vapor recompression can provide a significant amount of heat, avoiding the need of installing multiple heaters, with advantages in terms of CAPEX, operability and maintenance.

A further advantage is that the mechanical vapor recompression allows smooth managing of the fluctuating production of hydrogen obtained from renewable sources, so that the distillation process can run without a strict dependence from the heat recovery in the synthesis loop.

Description of the invention

The invention concerns a process for catalytic synthesis of methanol including reaction of a suitable make-up gas in a converter to obtain a so-called crude methanol. The crude methanol is purified to obtain a purified methanol and the purification process includes distillation in one column or more columns.

In the invention, a gaseous stream containing methanol vapour is withdrawn from a first location of a distillation column at a first temperature; said gaseous stream is sent to a vapour compressor where it is compressed obtaining a compressed gaseous stream at a second temperature which is greater than said first temperature; said compressed gaseous stream is subject to a heat exchange step wherein at least part of the methanol vapour contained in the stream is condensed and heat removed from said gaseous stream is transferred to a liquid stream withdrawn from a second location of said column, obtaining a heated stream which is reintroduced into said column.

Said column receives a methanol-containing stream which may be the crude stream as such or after a first or preliminary purification or distillation step. For example, said methanol-containing stream may be the effluent of a topping column.

Said gaseous stream may be a portion of the total amount of overhead gas withdrawn from the column. A remaining portion of gas may be sent to a methanol condenser without compression, obtaining a reflux stream which is then recycled back to the column.

Said liquid stream may be a methanol-containing aqueous stream or a fusel oil withdrawn from the column. Said first location in the column is typically at a greater elevation than the second location. Generally, the first location is at the top of the column and the second location is at or near the bottom of the column.

The heat transferred from the compressed gas to said liquid stream comes predominantly from condensation of methanol vapours. The related heat exchanger can be termed methanol-heated reboiler.

In some embodiments, said liquid stream may be heated in at least one additional heater in parallel to said heat exchange step with the compressed gaseous stream. An additional heat exchanger may be an electrical heater or a conventional steam-heated reboiler. In some embodiments, a liquid stream collected from the column is split into a first stream and a second stream; the first stream is heated by heat exchange with the compressed gas; the second stream is heated separately in a steam-heated reboiler or in an electric heater.

Heating a portion of the liquid stream in an electric heater consumes energy but may be preferred due to flexibility and fast regulation. An electrical heater may be useful also during transients. It can be understood that, thanks to the invention, a large portion of the distillation heat is recovered via MVR of the overhead gas of the column, and the need to use electric energy for this purpose is reduced. Compared to a prior art where a substantial part of the distillation heat is produced electrically, the invention gives a considerable saving.

Compared to electrical heating, MVR heating according to the invention is expected to save 70% to 85% of electric energy, for the same reboiling duty.

The compressed gaseous stream, after heat exchange step and condensation, results in an effluent stream containing condensed methanol. Preferably, said effluent stream is subject to a separation step obtaining a liquid methanol product and a gaseous stream containing methanol vapour; said gaseous stream, or at least a portion thereof, is preferably flashed to the suction pressure of said vapour compressor and sent to said compressor. Accordingly, methanol contained in the gas can be recovered and latent heat of vapour can still be recycled.

The distillation of said methanol-containing stream can be performed in a standalone distillation column or in a plurality of distillation columns including at least a first distillation column and a second distillation column. In a multiple-column embodiment, said methanol containing stream is sent to the first column and an aqueous solution withdrawn from said first column is further processed in the one or more following column(s). A preferred embodiment has two columns. Said columns may be refining columns downstream of a topping column. In some embodiments, MVR is applied to one or more refining columns but not to the topping column. In a multiple-column embodiment, MVR can be applied to any column and to one or more column(s). In a two-column embodiment, MVR can be applied to either the first column, the second column or both columns. When MVR is applied to two or more columns, each column may be connected to a respective vapour compressor and methanol-heated reboiler.

In a preferred embodiment, a first methanol-containing gaseous stream, which is withdrawn from the first distillation column, is sent to a first vapour compressor obtaining a first compressed gaseous stream, a liquid stream is withdrawn from said first column and heated by heat exchange with said first compressed gaseous stream, and reintroduced into said first column after heating, and a second methanol-containing gaseous stream, which is withdrawn from the second distillation column, is sent to a second vapour compressor obtaining a second compressed gaseous stream, a liquid stream is withdrawn from said second column and heated by heat exchange with said second compressed gaseous stream, and reintroduced into said second column after heating.

In a further preferred embodiment, using a first distillation column and a second distillation column, a liquid stream withdrawn from the second column is heated by heat exchange with a non-compressed methanol-containing gaseous stream withdrawn from the first column, and said liquid stream is reintroduced into the second column after heating.

Accordingly, in some embodiments, two liquid streams are withdrawn from the second distillation column; one liquid stream is heated by condensation of methanol in a gas taken from the second column and compressed (MVR); the other liquid stream is separately heated by non-compressed vapour from the first distillation column. The two liquid streams, after heating, may be reintroduced into the second column together or separately.

In an embodiment, a liquid stream withdrawn from a distillation column is heated in a first heat exchanger, which is preferably steam-heated; a portion of the so obtained heated liquid stream is reintroduced directly into the column; a remaining portion is heated by heat exchange with the methanol-containing compressed gaseous stream withdrawn from the same column. Preferably said column is the first column in a multiple-column embodiment.

The heat exchange step between the compressed gas and the solution can be performed in an indirect heat exchanger (vapor condenser/reboiler) having a first side traversed by the gaseous stream where methanol condenses and a second side traversed by the solution. For example, a shell-and-tube heat exchanger or a plate heat exchanger may be used.

The condensation of methanol vapours, after compression, is carried out preferably at a temperature in the range 130 to 170 °C. The pressure after compression is preferably at pressure in the range 7 to 16 bar g. The symbol bar g. denotes bar gauge.

In a preferred application, crude methanol is produced by reacting a CO-free make-up gas. Said CO-free make-up gas may contain CO2 from a CO2 capture process and hydrogen produced from water electrolysis or from a hydrogen production process with no emissions of CO2 (“blue hydrogen”) or from a biogenic source. In an interesting application, for example, some or all of the CO2 for the make-up gas can be recovered from the fumes of an industrial furnace. Water electrolysis for the production of hydrogen is preferably powered by a renewable source, such as solar, wind, biomass. The invention, by recovering the latent heat of methanol vapours, compensates for the inherent lack of steam due to the use of a make-up gas with little or no carbon monoxide, avoid/minimize the import of low-pressure steam, generated by not renewable fuels, and minimize the consumption of electrical power.

An aspect of the invention is also a distillation section adapted to perform the above-described distillation process. In a general embodiment, a distillation section according to the invention includes: a distillation column; a line arranged to withdraw a gaseous stream containing methanol vapour from a first location of said distillation column; a vapour compressor arranged to provide compression of said gaseous stream and to obtain a compressed gaseous stream at a higher temperature than the temperature of extraction from the column; a first heat exchanger arranged to provide condensation of at least part of the methanol vapour contained in said compressed gaseous stream and to transfer heat removed form said gaseous stream to a liquid stream withdrawn from said column, obtaining a heated stream, and a line arranged to reintroduce the so obtained heated stream into the column.

The distillation section may include a second heat exchanger or an electrical heater in parallel to said first heat exchanger, and connection lines arranged so that a first portion of a liquid stream withdrawn from the column is heated in said first heat exchanger and a second portion thereof is heated in the second heat exchanger or in the electrical heater, and both portions are reintroduced in the column after heating.

The distillation section may include a single distillation column or a plurality of distillation columns. The mechanical vapor recompression may be applied to one or more columns in accordance with the embodiments of the purification process described above.

The invention is applicable to new methanol plants and to revamping (modernization) of existing plants. Accordingly, another aspect of the invention is a procedure for revamping a distillation section of a methanol plant, wherein the distillation section is modified to put into practice the process of the invention. Preferred embodiments of a revamping procedure according to the invention are set out in the attached claims.

Description of the figures

Fig. 1 illustrates a process for the synthesis of methanol according to a first embodiment of the invention wherein distillation is performed in a single column.

Fig. 2 illustrates a variant of Fig. 1 including an electric heater for the distillation column.

Figs. 3 to 5 illustrate embodiments with two distillation columns.

Fig. 1 illustrates a process wherein a crude methanol stream 1 is purified using a stand-alone distillation column 2. The crude methanol 1 may be obtained from a topping column (not shown).

The distillation column 2 is connected to a bottom reboiler 11 , a methanol condenser 6, a reflux drum 7, an MVR compressor 19, a methanol-heated reboiler 17.

The distillation column 2 separates a methanol-containing gaseous stream 3 and a bottom aqueous solution 4. The methanol-containing gas 3 (overhead gas) is generally withdrawn from top of the column, whereas the solution 4 is collected at the bottom of the same column.

A first portion of the overhead gas 3 is sent via line 5 to the methanol condenser 6; the condensate stream is sent to the reflux drum 7 and recycled back to the column 2 using a pump 8. A portion of condensed stream can be removed via line 26.

The remaining portion of the overhead gas 3 is sent via line 18 to the MVR compressor 19. The compressed gas 20 delivered by said compressor 19 is sent to one side of the reboiler 17. Here, the condensation of methanol vapours contained in the stream 20 transfers heat to a stream 15 of aqueous solution collected from bottom of the column 2. After heating, said aqueous solution is reintroduced into the column 2 via line 13. Accordingly, latent heat of methanol is recovered from the stream 20 and used to heat the column 2 and to maintain the distillation process.

More in detail, the aqueous solution 4 collected from the bottom of the column 2 is partially passed in the reboiler 11 via line 14 and heated by steam 12. The remaining part of the solution 4 is sent via line 15 to the methanol-heated reboiler 17, where it is heated by the condensation of the stream 20.

The steam 12 is generally produced from process heat recovery, such as cooling of the reaction effluent of the methanol converter or imported from outside the battery limits of the plant.

The methanol-heated reboiler 17 is preferably a shell and tube heat exchanger or a plate heat exchanger.

The condensed stream 21 , effluent from the reboiler 17, is separated in a flash drum 22 into a methanol product 23 and a gas 24. Said gas 24 is flashed and sent to the suction side of the MVR compressor 19 together with the overhead gas in line 18.

Fig. 2 illustrates a variation of the process described in Fig. 1 wherein an electrical heater 25 is arranged in parallel to the reboiler 17, so that the aqueous stream of line 14 is heated in the electrical heater 25 and the aqueous stream of line 15 is heated in the reboiler 17. Compared to Fig. 1 , the embodiment of Fig. 2 uses the electrical heater 25 instead of the steam-heated reboiler 11 .

In further variants, an electrical heater may be in parallel to a steam heated reboiler and to the reboiler 17, or may receive the entire aqueous stream of line 4. When used, an electrical heater provides preferably a minor portion of the heat input of the column, to minimize the consumption of electric power. The use of electric power for the MVR process is thermodynamically more efficient.

Line 32 of Figs. 1 -2 denotes an outlet of refined methanol (heavy product) from the column 2. Fig. 3 illustrates an embodiment with a second distillation column 28. Items corresponding to Fig. 1 are denoted by the same reference numbers. A portion of the aqueous effluent of the column 2 is sent to the second column 28 via line 27 for further processing. In Fig. 3, the MVR is applied to the first column only. The second distillation column 28 produces a methanol-rich gas 29 at the top of the column and a bottom water 30. A fusel oil is extracted at line 35, which contains water, residual methanol and by-products of the methanol synthesis is extracted

Another bottom stream is withdrawn from the column 28 at line 31 and is heated in the first condenser 6 by the non-compressed fraction of the overhead gas taken from the first column 2, in line 5. The so obtained heated stream is recycled back to the second column 28 via line 34, so that heat recovered from the noncompressed overhead gas of the first column 2 is used to provide some distillation heat to the second column 28.

Said stream of line 31 is a liquid stream which may be a bottom water or a fusel oil with a composition depending on the point where it is extracted from the column.

The methanol-rich gas 29 emerging from the second column 28 is condensed in a condenser 36, feed to a reflux drum 35 and at least partly recycled back to the column 28 via a pump 33.

The column 2 operates at higher pressure than the second column 28. The pressure of the bottom effluent is reduced by a pressure regulation valve 43 on line 27. The pressure is regulated so that the top of the first column has a temperature higher than the bottom of the second column 28 and the heat exchanger 6 can heat the stream 31 .

Figs. 4 and 5 illustrate further variants of embodiments with two columns, where corresponding items or flow lines have the same reference numbers as in Fig. 3.

Fig. 4 shows a variant of Fig. 3 where MVR is applied also to the second column 28. A stream 37 of overhead gas from the second column 28 is sent to MVR compressor 38 and the so obtained compressed gas 39 is sent to a methanol- heated reboiler 40 to heat a bottom stream 41 of said column 28.

The so obtained heated stream 42 is reintroduced into the column 28. Said stream 42 may be introduced separately or together with the stream 34 heated in the heat exchanger 6 with the non-compressed gas from the first column 2.

The condensate stream 47 from the reboiler 40 is fed to a flash drum 45 where it is separated into a methanol product 46 and a gaseous fraction 44. Said gaseous fraction 44 is flashed and sent to the suction side of said compressor 38.

A remaining portion of methanol-rich gas from the column 28 is conventionally recycled to the column without compression, via line 29, condenser 36, reflux drum 35 and pump 33.

Fig. 5 illustrates an embodiment which is similar to Fig. 4, wherein the MVR is applied only to the second column 28. Accordingly, the first column 2 in Fig. 5 is not equipped with MVR compressor and related methanol-heated reboiler. The overhead gas 3 removed from the first column 2 is sent entirely to the methanol condenser 6, where it transfers heat to the second column 28 by heating the liquid stream 31 . The purified methanol in this embodiment is obtained at line 46.

Claims

1 ) A process for catalytic synthesis of methanol including formation of a crude stream of methanol and a purification process of said crude stream to obtain a purified methanol stream, wherein the purification process includes: distillation of a methanol-containing stream in a distillation column (2), wherein a gaseous stream (3) containing methanol vapour is withdrawn from a first location of said column, said gaseous stream (3) having a first temperature; said gaseous stream is sent to a vapour compressor (19) where it is compressed obtaining a compressed gaseous stream (20) at a second temperature which is greater than said first temperature; said compressed gaseous stream (20) is subject to a heat exchange step wherein at least part of the methanol vapour contained in the stream is condensed and heat removed from said gaseous stream (20) is transferred to a liquid stream (15) withdrawn from a second location of said column, obtaining a heated stream (13) which is reintroduced into said column (2).

2) Process according to claim 1 , wherein a first liquid stream (15) withdrawn from said second location of said column (4) is heated by said heat exchange step with the compressed gaseous stream (20) and a second liquid stream (14) withdrawn from the column is heated in at least one additional heater (25), preferably including at least one electric heater, in parallel to said heat exchange step with the compressed gaseous stream and before reintroduction into the column.

3) Process according to claim 1 or 2 wherein: said compressed gaseous stream, after said heat exchange step and condensation, results in an effluent stream (21 ) containing condensed methanol; said effluent stream (21 ) is subject to a separation step obtaining a liquid methanol product (23) and a gaseous stream (24) containing methanol vapours, at least part of said gaseous stream is sent to said vapour compressor (19).

4) Process according to any of claims 1 to 3 wherein: distillation of said methanol-containing stream is performed in a plurality of distillation columns including at least a first distillation column (2) and a second distillation column (28), wherein said methanol containing stream (1 ) is sent to the first column (2) and an aqueous solution (27) withdrawn from said first column (2) is further processed in the second column (28).

5) Process according to claim 4 wherein: the gaseous stream sent to said vapour compressor is withdrawn from the first distillation column (2), and the liquid stream which is heated by heat exchange with said compressed gaseous stream is a liquid stream (15) collected from the first column and reintroduced into said first column after heating.

6) Process according to claim 4 wherein: the gaseous stream sent to said vapour compressor is withdrawn from the second distillation column (28), and the liquid stream which is heated by heat exchange with said compressed gaseous stream is a liquid stream (41 ) collected from the second column and reintroduced into said second column after heating.

7) Process according to claim 4 wherein: a first methanol-containing gaseous stream (3), which is withdrawn from the first distillation column (2), is sent to a first vapour compressor (19) obtaining a first compressed gaseous stream, a liquid stream (15) withdrawn from said first column is heated by heat exchange with said first compressed gaseous stream, and reintroduced into said first column after heating, and a second methanol-containing gaseous stream (37), which is withdrawn from the second distillation column (28), is sent to a second vapour compressor (38) obtaining a second compressed gaseous stream (39), a liquid stream (41 ) is withdrawn from said second column, heated by heat exchange with said second compressed gaseous stream and reintroduced into said second column after heating.

8) A process according to any of claims 4 to 7 wherein a liquid stream (31 ) withdrawn from the second column (28) is heated by heat exchange with a non-compressed methanol-containing gaseous stream (5) withdrawn from the first column (2), and said liquid stream is reintroduced into the second column after heating.

9) A process according to any of the previous claims wherein: in at least one distillation column (2), a first portion (14) of a liquid stream (4) withdrawn the column is heated in a heat exchanger (11 ), which is preferably steam-heated, and the so obtained heated stream (16) is reintroduced directly into said column (2); a remaining portion (15) of said liquid stream (4) is heated separately by heat exchange with the methanol-containing compressed gaseous stream (20) withdrawn from the same column, and reintroduced into the column (2) after heating.

10)Process according to any of the previous claims wherein said compression of methanol containing gaseous stream is performed to a pressure of in the range between 7 and 16 bar g.

11 )Process according to any of the previous claims wherein condensation of methanol vapours, after compression, is carried out at a temperature in the range 130 to 170 °C.

12) Process according to any of the previous claims wherein crude methanol is produced by reacting a make-up gas containing not more than 10% CO in volume, preferably not more than 7% and more preferably not more than 5%.

13)Process according to claim 12 wherein some or all of the CO2 contained in the CO-free make-up gas is obtained from a CO2 capture process and/or biogenic CO2, and/or wherein some or all of the hydrogen contained in said CO-free make-up gas is hydrogen produced from water electrolysis, preferably powered by a renewable source of energy, or from a hydrogen production process with no emissions of CO2.

14) A distillation section for the purification of a crude stream of methanol, said distillation section including: a distillation column (2); a line arranged to withdraw a gaseous stream (3) containing methanol vapour from a first location of said distillation column; a vapour compressor (19) arranged to provide compression of said gaseous stream and to obtain a compressed gaseous stream (20) at a higher temperature than the temperature of extraction from the column; a first heat exchanger (17) arranged to provide condensation of at least part of the methanol vapour contained in said compressed gaseous stream (20) and to transfer heat removed form said gaseous stream to a liquid stream (15) withdrawn from said column (2), obtaining a heated stream, and a line arranged to reintroduce the so obtained heated stream into the column.

15) A distillation section according to claim 14 including a second heat exchanger or an electrical heater (25) in parallel to said first heat exchanger (17); a line (15, 13) arranged to heat a first portion of a liquid stream withdrawn from said column in said first heat exchanger and to reintroduce the so obtained heated stream in the column; a line (14, 16) arranged to heat a second portion of said liquid stream in the second heat exchanger to reintroduce the so obtained heated stream in the column.

16) A distillation section according to claim 14 or 15 including: a first distillation column (2) and a second distillation column (28), and a line arranged to send an aqueous solution (27) withdrawn from said first column (2) to the second column (28) for further processing; a first vapour compressor (19) arranged to compress a methanol-containing gaseous stream (3) withdrawn from the first distillation column (2); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said first compressor to a liquid stream (15) withdrawn from said first column, and a line arranged to reintroduce the so obtained heated stream in said first column; a second vapour compressor (36) arranged to compress a methanolcontaining gaseous stream withdrawn from the second distillation column (28); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said second compressor to a liquid stream withdrawn from said second column, and a line arranged to reintroduce the so obtained heated stream in said second column.

17) A distillation section according to claim 16 additionally including a heat exchanger (6) configured to heat a liquid stream (31 ) withdrawn from the second column (28) by heat exchange with a non-compressed methanolcontaining gaseous stream (5) withdrawn from the first column (2), and including a line to reintroduce the so obtained heated liquid stream into the second column.

18)A methanol plant including at least a methanol synthesis section and a distillation section arranged to process a stream of crude methanol obtained after synthesis, for purification of said stream of crude methanol, the distillation section being in accordance with any of claims 14 to 17. )A procedure of revamping a methanol plant, wherein the methanol plant includes at least a methanol synthesis section and a distillation section arranged for purification of a stream of crude methanol obtained after synthesis, wherein the distillation section includes at least one distillation column, wherein the procedure includes modifying the distillation section to include at least: a line arranged to withdraw a gaseous stream (3) containing methanol vapour from a first location of said distillation column; a vapour compressor (19) arranged to provide compression of said gaseous stream and to obtain a compressed gaseous stream (20) at a higher temperature than the temperature of extraction from the column; a first heat exchanger (17) arranged to provide condensation of at least part of the methanol vapour contained in said compressed gaseous stream (20) and to transfer heat removed form said gaseous stream to a liquid stream (15) withdrawn from said column (2), obtaining a heated stream, and a line arranged to reintroduce the so obtained heated stream into the column. )A procedure according to claim 19 wherein the distillation section is modified to include a second heat exchanger or an electrical heater (25) in parallel to said first heat exchanger (17); a line (15, 13) arranged to heat a first portion of a liquid stream withdrawn from said column in said first heat exchanger and to reintroduce the so obtained heated stream in said distillation column; a line (14, 16) arranged to heat a second portion of said liquid stream in the second heat exchanger to reintroduce the so obtained heated stream in said distillation column. )A procedure according to claim 19 or 20, wherein the distillation section includes a second distillation column, or a second distillation column in added to the distillation section, and the distillation section is modified to include: a line arranged to send an aqueous solution (27) withdrawn from said first column (2) to the second column (28) for further processing; a first vapour compressor (19) arranged to compress a methanol-containing gaseous stream (3) withdrawn from the first distillation column (2); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said first compressor to a liquid stream (15) withdrawn from said first column, and a line arranged to reintroduce the so obtained heated stream in said first column; a second vapour compressor (36) arranged to compress a methanolcontaining gaseous stream withdrawn from the second distillation column (28); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said second compressor to a liquid stream withdrawn from said second column, and a line arranged to reintroduce the so obtained heated stream in said second column. )A procedure according to any of claims 19 to 21 , wherein the distillation section is modified to include: a heat exchanger (6) configured to heat a liquid stream (31 ) withdrawn from the second column (28) by heat exchange with a non-compressed methanolcontaining gaseous stream (5) withdrawn from the first column (2); a line to reintroduce the so obtained heated liquid stream into the second column.