A process for the synthesis of methanol

Abstract

A process for the synthesis of methanol in a methanol plant including conversion of a make-up gas by a methanol converter in a synthesis loop and purification of crude methanol by distillation in a distillation section; the distillation process includes a first distillation step performed in a topping column and a second distillation step performed in three refining columns in cascade configuration; a first part of distillation heat is retrieved from the synthesis loop; a second part of distillation heat is provided by one or more additional heat sources.

Description

[0001] A process for the synthesis of methanol

[0002] DESCRIPTION

[0003] Field of application

[0004] The present invention relates to the field of methanol production. The invention relates to a process for the synthesis of methanol in fluctuating and nonfluctuating condition.

[0005] Prior art

[0006] Methanol is manufactured on an industrial scale by reacting a gas mixture containing hydrogen (H2) and carbon oxides (CO2 and CO) at high temperatures and pressures. This reaction takes place in one or more catalytic beds within reactors known as methanol converters. The reaction produces a gas rich in methanol, which is then cooled and condensed to yield a liquid stream of crude methanol. Any unreacted gas is separated from the liquid stream and recirculated back into the converter using a circulation compressor, forming a continuous process loop known as the synthesis loop (synloop).

[0007] The crude methanol, effluent from the converter and cooled by condensation, contains reaction products, methanol, water, liquid byproducts and dissolved gases. To meet various purity specifications required by the market (e.g. A grade, AA grade, fuel grade) or to increase the concentration of methanol compared to water and other non-methanol species, the crude methanol is purified in a distillation section.

[0008] A methanol distillation section includes one or more distillation columns, each comprising a number of separation stages which may be actual vapor-liquid contacting trays, or sections of contactor packings equivalent to trays. Each stage contributes to the overall separation of the methanol by allowing a portion of the more volatile component to transfer to the vapor phase and the less volatile component to the liquid phase.

[0009] In a typical distillation setup, there is a topping column, also known as a pre-run column, used for initial processing to remove volatile components, followed by one or more refining columns used to eliminate higher alcohols and water. The topping column receives the crude methanol and separates lighter components such as methane, hydrogen, carbon dioxide, nitrogen and lighter boiling byproducts of the methanol synthesis reaction from the stream of methanol. The refining columns then performs the main distillation, producing distilled methanol at the top and an aqueous solution at the bottom.

[0010] In each distillation column, a light-boiling stream is produced as an overhead vapor stream, also referred to as “top product”, effluent from the top stage of the distillation column. For the topping columns, said vapor stream is a stream of “light ends”, which are non-condensable gases or stream of gases lighter than the methanol byproducts; while for the refining columns the overhead vapor stream is almost pure methanol. Each distillation column might have a top reflux system, where a portion of the top product is recovered and fed back to the top of the column. If the column is equipped with a partial overhead condenser, the light-boiling stream, which may be either waste light gas (light ends) for the topping column or methanol product distillate for the refining columns, is reintroduced as a liquid stream. If the top column is equipped with a total condenser, a portion of the top product is reintroduced as a liquid stream.

[0011] From the bottom stage of each distillation column, a heavy-boiling stream is produced as a liquid stream, known as "bottom solution", or “liquid bottom product”. A portion of the bottom solution is heated using a heat exchanger, which employs hot steam or process gas. The heated bottom solution is reintroduced into the column to supply the necessary distillation heat. Heat is provided to the column with the aim of enriching the vapor in the light boiling stream and the liquid in the heavy boiling stream. Another stream is separated from the refining column, the "fusel oil", which is a mixture of methanol, water and by-products of the methanol production reaction having an intermediate boiling point heavier than methanol. The fusel oil is provided as an extraction from an intermediate stage or from several intermediate stages of a refining column. Such extraction enables purging of intermediate boiling components like ethanol and higher alcohols, and it prevents that they accumulate in the methanol or water product streams thereby compromising the purity of those streams.

[0012] Typically, the liquid bottom product of a column becomes the feed stream of the following column, however other configurations are possible. The feed stream of each column is provided to one or multiple trays or stages. In an alternative design, the functions of the distillation column may be combined in a single device carrying out the separation of light ends, methanol product, water and intermediate boiling components in one or more separate streams.

[0013] In recent years, the production of hydrogen from renewable energy sources has gained attention as a way to reduce emissions and carbon intensity in e-methanol processes. E-methanol refers generally to methanol produced from renewable energy sources via electrolysis of water and resulting in a methanol product with a low carbon footprint compared to methanol produced from fossil fuels. An example of e-methanol production of relevant interest is based on the reaction of a make-up gas consisting mainly of H2 and CO2, where H2 is produced through water electrolysis using low-carbon or renewable energy, and the CO2 is preferably captured from exhaust fumes or air. Typically, the make-up gas in e- methanol production contains little to no carbon monoxide, making it CO-free, unlike in grey methanol production where the make-up gas is obtained by reforming or gasification of hydrocarbons and is primarily made of H2 and CO.

[0014] The conversion of CO2 to methanol releases significantly less heat compared to the conversion of CO to methanol, as shown in the reaction enthalpy below, carried out at 25°C and 1 bar: 49.8 kJ / mol

[0015] Thus, a CO-free or CO-lean make-up gas inherently generates less reaction heat than a conventional CO-containing feedstock. Consequently, the production of e- methanol releases significantly less heat compared to grey methanol production. This reaction heat is typically used in the distillation process, meaning e-methanol production may suffer from a lack of heat for distillation.

[0016] Moreover, e-methanol synthesis produces a higher concentration of water, as a consequence of the reaction of the make-up gas which is CO2-rich and CO2- lean, compared to conventional grey methanol processes which are known to be based on converting CO-rich make-up gas. The crude methanol in e-methanol synthesis may contain up to 50% mol water, while crude grey methanol typically contains 5-20% mol water. The difference in the water content is related to the fact that the feed to the synthesis loop in grey methanol contains less CO2 with respect to the feed of e-methanol. As per the reaction above, the reaction from CO2 produces water as co-product of methanol. Since water must be separated from the methanol in the distillation step to achieve commercial purity grade of methanol, the increased water content in crude methanol may lead to energy deficit in the distillation process.

[0017] Yet another reason that produces a shortage of heat available for distillation in e- methanol plants compared to grey methanol plants is the absence of fossil-based syngas generation units (like steam reformers, autothermal reformers, combined steam and autothermal reformers, gas heated reformers, gasifiers) which is a known source of heat for the grey methanol distillation plants. Hence, the problem of having shortage of heat for distillation may be present also for e-methanol processes which incorporate reverse water gas shift steps to convert partly the CO2 in CO prior to the synthesis. Another challenge for e-methanol plants, particularly those using hydrogen from renewable energy sources, is the variability of these sources. Renewable energy sources, like solar and wind, are naturally subject to fluctuations, causing the synthesis loop to operate under varying conditions, from 10% to 110% load, wherein 100% load is considered the nominal capacity. Methods to control the synthesis loop at low loads are known from EP3819261A1 , EP4054979B1 , however the distillation section is inherently less flexible than the synthesis loop. A distillation section may have a load flexibility ranging between 40% to 85% of its nominal capacity, with stable operation typically requiring a minimum load of at least 50%. As a result, the distillation section cannot match the lower loads of the synthesis loop. Moreover, the nominal capacity of the distillation section may be different than the nominal capacity of the loop, for example lower if the loop has higher load flexibility.

[0018] The heat generated from the synthesis loop is used to drive the distillation process by heating the column bottom solution. The heat induces boiling of the bottom solution, producing a bottom vapor enriched in the lighter components. If heat produced by the synthesis loop is insufficient to run the distillation section, it is necessary to provide additional heat sources to reach the required heat for the distillation. Adding heat from external sources may cause an increase in the energy consumption and, depending on the carbon footprint associated to the external source, it may increase emissions of CO2 associated to the methanol product. A situation in which the heat produced by the synthesis loop is insufficient is common in plants subjected to fluctuating conditions, but heat deficiency may occur also during non-fluctuating conditions of the synthesis loop. The fluctuating availability of the renewable energy source worsen this issue, for example in periods of low energy availability where less hydrogen is provided to the loop or where the synthesis loop operates at lower load than the distillation. In these cases, the heat generated in the loop and provided to the distillation may be below the minimum required for the distillation. This heat deficiency prevents the proper execution of the distillation process, creating a challenge in maintaining effective heat integration between the synthesis loop and the distillation section across a full range of operating conditions and achievement of the product purity during the full operation range of the loop and distillation.

[0019] Additional prior art is W02020052979A1 , WO2018019875A1 ,

[0020] US20210188747A1 , WO2022136374A1 , WO2022152749A1 , EP3885335A1 , US20220064541A1 , WO2021148262A1 , CN218146429U, EP3935034B1 , WO20231 10479A1 , US2023125966A1 , US20150008116A1 .

[0021] Summary of the invention

[0022] The invention addresses the problem of how to reduce the gap between the heat required for the distillation and heat recovered from synthesis loop in an energy efficient manner, without consuming excess external energy. Therefore, the problem concerns the balance of heat demand and heat recovery between methanol synthesis and methanol distillation. The invention further addresses the problem of how to reduce carbon emissions of the overall synthesis and distillation process.

[0023] These problems are solved with a process for the synthesis of methanol according to the claims.

[0024] The process of the invention reduces the heat demand of distillation with a cascade configuration of refining columns. A first part of the heat input required by the distillation process (distillation heat) is retrieved from the synthesis loop, whereas a second part of the distillation heat is provided by at least one additional source.

[0025] The first part of distillation heat, which is retrieved from the synthesis loop, may include reaction heat removed directly from a methanol converter, such as heat removed from a catalytic bed or removed from the gas during an inter-bed cooling stage in a multi-bed reactor, and / or heat removed from a methanol-containing effluent of the converter, during a cooling step of said effluent. The second part of distillation heat is provided by one or more suitably selected additional source(s). Said second part of distillation heat is transferred to a bottom solution of a topping column and / or to a bottom solution of one or more refining column(s).

[0026] Accordingly, the distillation section can receive enough heat to maintain the distillation process, even when the synthesis loop operates at a low load and / or does not produce enough heat for this purpose.

[0027] The invention is applicable to a methanol process both in a fluctuating condition and steady condition.

[0028] The invention reduces the heat energy consumption of the distillation process and maximizes the use of heat recovered from the methanol synthesis loop. This reduces the overall energy required for production that must be imported from synthesis heat recovery.

[0029] Description of the invention

[0030] The present invention discloses a process for the synthesis of methanol in a methanol plant including conversion of a methanol make-up gas by a methanol converter in a synthesis loop producing a methanol-containing reaction effluent; said reaction effluent is cooled, and optionally pre-treated, resulting in a stream of crude methanol to be purified; purification of said crude methanol is performed by a distillation process in a distillation section producing a stream of distilled methanol.

[0031] The distillation process includes a first distillation step performed in a topping column and a second distillation step performed in a first refining column, a second refining column and a third refining column arranged in cascade configuration; wherein a heat input is provided to the distillation process to obtain said distilled methanol. The topping column and each refining column may be defined as distillation columns. Each of said first refining column, second refining column and third refining column is equipped with a top condenser arranged for condensing an overhead vapor stream effluent from the respective refining column. At least part of heat removed from the overhead vapor stream of at least one of said columns, during condensation of said vapor stream, is transferred to a bottom solution of a subsequent refining column of the cascade. Preferably, the condensation heat of the overhead vapor of a column is transferred to the next column, for example by heating a stream of a bottom solution.

[0032] Preferably, at least part of heat removed from the overhead vapor stream of the first column and second column is transferred to a bottom solution of a subsequent refining column of the cascade. Typically, heat from condensation of the overhead vapor of the first column is transferred to a bottom solution of the second column of the cascade and heat from condensation of the overhead vapor of the second column is transferred to a bottom solution of the third column.

[0033] The distillation process requires a heat input, which is provided partially from the synthesis loop and partially from one or more additional sources. A first part of said heat input for the distillation process is retrieved from the synthesis loop by removing reaction heat from the methanol converter and / or by cooling of the reaction effluent from the methanol converter; a second part of said heat input for the distillation process is provided by one or more of the following sources according to options a) to e) listed below: a) at least one electrical heater; b) at least one electrical heated steam boiler; c) combustion of a purge gas withdrawn from the synthesis loop in at least one fired equipment of the distillation section; d) combustion of a stream of fusel oil withdrawn from the distillation section in at least one fired equipment of the distillation section; e) combustion of a hydrogen stream in at least one fired equipment of the distillation section.

[0034] Said second part of heat input for the distillation process provides at least in part heat to a stream of a bottom solution of the topping column and / or to a stream of a bottom solution of one or more of the refining columns.

[0035] Said hydrogen stream of option e) may be retrieved from one or more of the following sources: a hydrogen storage, which is preferably a buffer storage between a hydrogen source and said methanol converter; a water splitting process, preferably by electrolysis performed in an electrolysis unit; hydrogen taken from a stream of methanol make-up gas.

[0036] In an embodiment, methanol is produced from H2 and CO2 as starting materials. Hydrogen and carbon dioxide may be fed separately to the methanol synthesis process, as a H2 input stream and CO2 input stream. Each of the hydrogen input stream and CO2 input stream may be provided by any suitable source. Said input streams may be reacted directly in a methanol converter or may be subject to preliminary steps including reverse water-gas shift, according to embodiments of the invention. A preferred source of hydrogen is splitting of water, such as electrolysis of water. Suitable sources of CO2 may include capture of CO2 from air (direct air capture) or the use of a CO2 stream separated in the context of another process, e.g. from combustion fumes or from a process stream.

[0037] In another interesting embodiment, a hydrogen feed for the methanol synthesis process is produced by SOEC technology.

[0038] The second part of the distillation heat, coming from one or more of the above- mentioned sources a) to e), may be provided when the heat transferred from the synthesis loop to the distillation section is insufficient for the distillation process.

[0039] Preferably, distilled methanol is retrieved from the overhead vapour stream condensed by each top condenser of the respective refining column. Preferably, the third refining column is the last refining column of the distillation section.

[0040] Methanol synthesis is an exothermic reaction and produces heat; in the present invention the heat of reaction is used for providing the first part of the distillation heat. The heat transferred from the synthesis loop to the distillation section includes heat recovered by cooling the reaction in the methanol converter and / or heat recovered by cooling the reaction effluent from the methanol converter. A preferred configuration includes that distillation heat is recovered from both the converter and the reaction effluent because of their different temperature levels: heat recovered in the converter is suitable to heat up the bottom solution of the topping column, which is colder; heat recovered from the reaction effluent is suitable to heat up the bottom solution of the first refining column, which is hotter. This configuration is preferable because heat is supplied to the distillation section more efficiently if the temperature level of the bottom of the topping column and of the bottom of the refining column match with the temperature levels of the recovered heat. Another advantage of using heat from both the converter and the reaction effluent is that more heat is recovered from the loop, hence the gap of the distillation heat demand is less.

[0041] Each distillation column may comprise a respective bottom reboiler that heats the bottom of the distillation column and maintains the distillation process. The heat retrieved from the synthesis loop may be transferred to the distillation section using steam or a process gas stream as a heat transfer medium; if steam is used, the steam can be used in steam-heated reboilers or can be added to the bottom solution of the column, while a process gas stream, after heating, can be sent to a heat exchanger or a reboiler to heat up the bottom solution. The advantage of using steam reboilers instead of adding steam to the bottom solution is that it does not dilute the methanol in the column. Direct steam generation occurs typically in the methanol converter. In a preferred embodiment, steam generated in the methanol converter supplies heat to the bottom solution of the first refining column by means of a first reboiler and the reaction effluent from the converter supplies heat to the bottom solution of the topping column by means of a second reboiler. To make the heat transfer possible, the pressure of the topping column is preferably at least 5 bar lower than the pressure of the methanol converter, to achieve appropriate temperature approach for the use of heat from the reaction effluent. The temperature approach denotes here the temperature difference (delta-T) between the condensing vapor in the top condenser and the boiling liquid in the reboiler at the bottom of the column. The advantage of this configuration is that by generating steam in the methanol converter and recovering heat from the reaction effluent, at low temperatures heat can be supplied to the topping column by using the recovered heat from the reaction effluent, and to the first refining column by using the steam generated in the converter, reducing the need to import external heat by a factor of 20% to 80%.

[0042] The distillation process in accordance with the present invention is performed in at least three refining columns in cascade configuration. In the cascade configuration, the first refining column works typically at high-pressure (HP), the second refining column works typically at medium-pressure (MP) and the third refining column works typically at Low-Pressure (LP), and the columns are heat integrated to exploit the multiple heat effect.

[0043] In a preferred embodiment, the distillation in the first refining column is performed at a first pressure P1 , distillation in the second refining column is performed at a second pressure P2, distillation in the third refining column is performed at the third pressure P3, being P1 greater than P2, and P2 greater than P3. Preferably, said first pressure P1 is in the range 15 to 30 bar, said second pressure P2 is in the range 7 to 15 bar, said third pressure P3 is in the range 1 to 5 bar.

[0044] From the top of each refining column, an overhead vapor stream is withdrawn, which primarily consists of distilled methanol with a low content of impurities. Each of these overhead vapor streams of distilled methanol is processed by the respective top condenser and provide condensing heat to the subsequent refining column. According to an embodiment, wherein each top condenser coupled with each refining column generates condensing heat, the process includes the step of providing condensing heat from the first refining column (HP) to the second refining column (MP) and providing condensing heat from the second refining column (MP) to the third refining column (LP). The condensing heat of LP refining column is discharged to air or cooling water or to a cold utility.

[0045] The condensing heat of higher-pressure refining column is used as reboiling heat for the following lower-pressure refining column. At least part of the distillation heat required by each distillation column is provided by the condensing heat to the bottom solution of each distillation column through a respective heat exchanger or reboiler.

[0046] The use of condensing heat to provide at least part of heat for the distillation is possible thanks to the decreasing pressure levels of the refining columns. This configuration provides the benefit of reducing the distillation heat requirement. In a preferred embodiment, all the heat for MP and LP refining columns comes from the top condensers of HP and MP refining columns respectively.

[0047] After being heated, the bottom solution is reintroduced in the bottom of the same column, thereby heating the column itself. This process is applicable to any additional refining column placed downstream. Optionally, the bottom solution of the topping column and / or the bottom solution of one or more of the refining column(s) is heated by at least one electrical heater according to the above- mentioned option a) before or after being heated by the top condenser.

[0048] The overhead vapor stream effluent from the top of each refining column is condensed during the heat exchange with the bottom solution of the following column, resulting in a liquid stream of distilled methanol. This arrangement and process flow allows for efficient energy utilization and heat recovery within the distillation system, enhancing the overall efficiency of the methanol production process. This advantageous effect is confirmed by analysis of the specific heat consumption of the distillation section: in a conventional two-column design the heat consumption is typically around 1 .9 ton of steam per ton of methanol, while the specific heat consumption of a distillation section with three refining columns in cascade configuration according to the invention is about 1.1 ton of steam per ton of methanol.

[0049] Generally, a high grade-heat must be supplied to the HP refining column to keep the pressure of the HP column at a suitable level, for example in the range 15-30 bar. In the methanol distillation process, heat may be supplied to the HP refining column as steam from the loop. When heat is provided to the refining column by means of steam, the steam pressure must be high enough so that, upon condensation of steam in the reboiler, a suitable temperature difference is kept to drive the heat transfer. For example, the temperature of the fluid used to heat up the bottom of the HP refining column should be preferably at least 5°C warmer than the temperature of the bottom of HP refining column.

[0050] The optimal temperature range for the operation of the methanol converter is 220- 270 °C. Operating the HP refining column at 15-30 bar allows the bottom of the HP refining column to maintain a temperature in the range of 180-230 °C. The advantage of having the bottom of the HP refining column at a temperature close to the temperature of the methanol converter is the possibility to make a full use of the available heat from the reaction, enabling a direct reboiler for the HP refining column coupled with the converter's heat. In specific embodiments, this may require the presence of two different reboilers for the HP refining column: one for the initial portion of heat recovered from the synthesis loop and another with the second portion of heat from an additional external heat source.

[0051] The pressure of the HP refining column may be selected in the lower portion or the upper portion of the preferred range of 15 to 30 bar, according to different embodiments.

[0052] Operating the HP refining column at a pressure in the lower part of the range, such as a pressure of 15-20 bar, provides the advantage of maintaining a small temperature approach for the reboilers paired to the columns in the cascade configuration, typically within the range of 10-15 °C. Maintaining reasonable values of temperature approach is highly advantageous for the efficient coupling of condensers and reboilers in distillation columns operating at different pressure levels because it ensures effective heat transfer between the distillation stages. If the approach is too small, the heat transfer rate decreases, requiring larger heat exchange surfaces to achieve the same amount of heat transfer, which increases the capital costs and carbon footprint of the equipment. Maintaining a temperature approach within a reasonable range provides optimal design and operation of distillation columns in a cascade configuration, where different pressure levels are used to maximize energy recovery and minimize operational costs. With a lower pressure range, the temperature required from the methanol converter and from the external heat source is lower.

[0053] On the other hand, operating the HP refining column at a pressure in the upper part of the range, such as 25-30 bar, results in a greater temperature approach, typically greater than 15 °C. This allows for the design of smaller heat exchangers / reboilers and top condensers, which have a positive impact on the capital expenditure. At this pressure level, the temperature required at the bottom of the HP refining column is close to the maximum of the optimal range for the converter, and the temperature required from the external heat source is higher.

[0054] Selecting a pressure above 30 bar can lead to reduced heat recovery from the reactor, or may require the methanol converter to depart from the optimal temperature range of operation, to provide the necessary heat at the higher temperature.

[0055] With the three cascaded refining columns combined with loop heat recovery configured as the inventive process, the applicant has found that minimal additional heat input, such as less than 20% of the total heat demand of distillation, is required by the distillation section in a methanol process at full load, i.e. with the same production rate of the synthesis loop and the distillation section. Therefore, the second part of the heat input needed by the distillation when the three refining columns are used and the load of distillation and loop is the same, can be minimized to less than 20% by the specific configuration of the distillation. This finding has been confirmed by simulation for the case of production AA grade methanol, and also for the cases of production of lower grade methanol.

[0056] If heat recovered in the converter is provided to the refining column and heat recovered by the reaction effluent from the converter is provided to the topping column, the heat gap is further minimized to less than 10%. When the loop is operated at a lower rate than the distillation, the heat gap increases to more than 10%. In this case, the inventive process includes the provision of additional second part of the heat input according to any of the options a) to e).

[0057] The cascade arrangement of three refining columns is advantageous due to the heat transfer from the HP to MP refining columns and from the MP to LP refining columns by means of condensers and reboilers that reduce the energy consumption for the distillation of methanol. Moreover, the range of pressure of the first refining column corresponds to a bottom reboiling temperature of 180- 230 °C. This temperature range is similar and slightly lower than the optimal operating temperature of the methanol converter, which is about 220-270 °C. A configuration with two refining columns would result in a bottom temperature for the HP refining column lower than the temperature range the methanol converter could provide. This configuration would consume more heat, hence resulting in larger heat gap. On the contrary, four refining columns would result in a higher bottom temperature for the HP than the temperature range the converter could provide.

[0058] In a preferred embodiment of the invention, the at least one electrical heated steam boiler of option b) provides steam to the bottom solution of one or more of the refining columns and / or to the bottom solution of the topping column by means of one or more steam reboiler(s). A specific advantage of this configuration is the benefit given by the high steam utilization efficiency of the three cascaded refining columns combined with the load flexibility of the electric heated steam boiler. Electric heated steam boilers are known to operate in the range 0-100% of load with a high energy efficiency at any loads. Hence, this configuration ensures that the minimum amount of energy is consumed at all loads to fill up the heat gap of the distillation.

[0059] Heat can be transferred from the loop to the distillation section with the aid of a suitable medium, preferably water (steam). In a preferred configuration of the invention, the methanol converter is a pseudo-isothermal steam generation methanol converter producing steam; the process includes the step of providing distillation heat by means of said steam produced in the pseudo-isothermal steam generation methanol converter. A pseudo-isothermal converter denotes a converter with a heat exchanger immersed in the catalyst arranged to remove reaction heat so that the temperature of the reactor is nearly constant or maintained within a target range.

[0060] According to an embodiment, pressure and temperature of steam effluent from the methanol converter meet pressure and temperature of steam of a reboiler coupled with the first refining column, or the process includes the step of regulating pressure and temperature of steam effluent from the methanol converter by means of a valve to meet pressure and temperature of steam of a reboiler coupled with the first refining column.

[0061] In a preferred configuration, the coolant of the pseudo-isothermal methanol converter is boiling water supplied as a heat transfer fluid to transfer a first part of heat input to the distillation section. The pressure of the steam generated in the methanol converter by cooling the reaction is preferably about 25-45 bar, more preferably 30-35 bar. A range of 30-35 bar is preferable because the corresponding temperature is optimal for the methanol synthesis.

[0062] In any case, the pressure of the steam generated in the converter should not be lower than the pressure that ensures appropriate temperature approach at the bottom of the HP refining column (typically at least 10-15 °C). This pressure coincides with the minimum pressure at which the electrical heated steam boiler must be operated. For example, if the HP refining column is operated at 20 bar to ensure a 15 °C approach, the steam boiler is preferably operated in order to provide a steam delivery pressure of at least 20 bar. The advantage of having the steam generated in the converter and the steam generated by the steam boiler at the same pressure is that it allows the use of the same steam reboiler for both heat sources.

[0063] In specific cases the steam generated in the converter can be at a higher pressure than that required at the bottom of the HP refining column and thus generated by the electrical heated steam boiler to ensure an optimal temperature range for the methanol converter. The steam generated in the methanol converter may be at a pressure up to 45 bar to maintain an optimal temperature in the converter. In this scenario, a valve can be installed downstream of the steam drum of the converter to regulate the pressure of the steam sent to the distillation section, maintaining it at the same pressure as the steam generated by the steam boiler.

[0064] In an embodiment, the bottom solution of the topping column and / or the bottom solution of one or more of the refining columns is heated up by means of at least one fired equipment of the distillation section, wherein said fired equipment is a fired heater or a heating boiler. Said fired heater provides heat to the bottom of the distillation column burning flue gases, while the heating boiler provides heat using steam as a heating medium for the steam reboilers. The advantage of using steam is that the same steam reboilers can be used also with steam from synthesis loop. In a preferred embodiment of the invention, said fired heater provides heat to the distillation section by burning hydrogen and at least one of the following fuels: purge gas withdrawn from the synthesis loop; light ends withdrawn from the top condenser of the topping column; fusel oil withdrawn from the distillation section. An advantage of this embodiment is the steam consumption efficiency of the three refining columns combined with the utilization of energy from the combustion of the purge and light ends streams to produce missing steam. This configuration enables the recovery of combustion heat of purge gas and light ends, which otherwise would be flared or vented, and it provides the additional advantage to solve the disposal of waste. This is advantageous specifically for e- methanol plants without a fossil-fueled frontend which is conventionally used to combust these streams in grey methanol plants. This embodiment avoids the disposal of light ends and waste gas, which are used to supply additional heat to distillation and to enhance the overall carbon efficiency.

[0065] In an embodiment, the process includes the step of collecting purge gas in a purge storage and / or the step of collecting a hydrogen stream effluent from an electrolysis unit and / or taken from the make-up gas of the synthesis loop in a hydrogen storage. The connection to the hydrogen storage as extra fuel is useful also to provide a control in the fuel flow rate, e.g. when the loop is operated at low load and the purge gas is low. This embodiment enables to exploit the heat content of the purge gas enhancing the overall process efficiency and the use of available hydrogen for heat generation therefore reducing import of extra electric energy to heat up the system.

[0066] In an embodiment, said fired equipment includes an engine or a gas turbine fired with fusel oil. Preferably, the process includes the step of collecting fusel oil and / or crude methanol in a collecting storage and feeding said engine and / or said gas turbine with a stream withdrawn from said collecting storage. This enables to avoid dedicate disposal of liquid by-products which is an additional expensive cost in methanol plants. Preferably said engine and / or said gas turbine produce electric energy powering at least in part the methanol plant; additionally, heat recovered from the engine and / or gas turbine can be supplied to the distillation section. The advantage is that the flow of the stream withdrawn from the collecting storage is controllable, allowing to bum only the desired quantity of effluent when necessary, producing the required quantity of energy. Moreover, additional heat is retrieved from the flue gas or from the cooling of the engine which can be used for the distillation process. The advantage of this embodiment is the possibility to produce both electricity and heat. Optionally, with this configuration, also light ends and purge gas are burnt, producing additional heat and avoiding the disposal of waste gases.

[0067] In an embodiment, at least one electrical trim heater is used in addition to any of the heat inputs of options a) to e) to provide trim heating to the bottom of the topping column and / or to the bottom of one or more refining column(s). The term trim heating denotes the heat regulation provided to a distillation column to fill the heat gap required to run a stable distillation. Trim heaters do not provide the whole heat required by the distillation column, but they provide heat in addition to other heat sources. The advantage of this embodiment is that trim heaters have a rapid response, thus minimizing transient conditions.

[0068] In an embodiment, the process includes the use of an intermediate crude methanol storage tank collecting the crude methanol effluent from the synthesis loop, decoupling the flow rate of methanol in the synthesis loop and the flow rate of methanol in the distillation section.

[0069] Preferably, the process includes the step of separation of carbon dioxide from a stream of flue gas of at least one heating boiler of the distillation section, said carbon dioxide separated from the flue gas is collected in a recovery unit and / or recycled as a feed stream for the methanol synthesis loop. This configuration avoids accumulation of inert gases like a nitrogen bleed stream, improving the overall carbon efficiency of the process and avoiding emissions of carbon dioxide. In an embodiment, the process includes the step of using a distillation storage between two subsequent distillation columns collecting at least part of a bottom solution from a distillation column and feeding a subsequent distillation column with a methanol stream withdrawn from said distillation storage. Said distillation storage can be used to smooth disturbances on the flow of the product stream effluent from the first column and directed to the second column.

[0070] Optionally, the bottom solution collected in the distillation storage and / or the intermediate crude methanol storage tank is / are heated by means of at least one electrical heater according to the above option a). This enables to decouple different distillation units and to avoid propagation of disturbances in fluctuating operations.

[0071] In an embodiment, at least part of the heat input for the distillation process is provided by recovered waste heat of an electrolysis unit, wherein preferably the waste heat is transferred to a heat exchange medium and said heat exchange medium transfers heat to the steam used for the distillation. This embodiment advantageously uses a source of heat produced from the electrolysis unit to heat up the distillation section, enhancing the overall energy efficiency and requiring less extra electricity. This embodiment is beneficial especially when the distillation section works with a low load.

[0072] The invention outlines how heat recovered from burning of fusel oil may be used in the distillation section and / or for pre-heating or heat boost of the methanol reactor. The invention further provides a way to cool down the fusel oil burner with crude methanol and / or with fusel oil during steady-state operation of methanol synthesis and / or independently from its operating point.

[0073] As explained above, the extra heat required by the distillation section may be provided by any of the heat sources outlined in this description; however, the preferred configurations are with an electrical heated steam boiler and with the combustion of purge gas and / or hydrogen. The electrical heated boiler has several advantages compared to the fired heater, as outlined below:

[0074] - it does not produce emissions of NOx since there is no combustion;

[0075] - it has fast load ramps, going from 0% to 100% in minutes, which is crucial to adapt to sudden load changes, especially in e-methanol processes;

[0076] - it can be put in warm standby when the load is zero, with minor parasitic consumption, differently from the fired heated boiler which has a minimum turndown of about 20% and associated fuel consumption at minimum load;

[0077] - it is more flexible, energy efficient and clean than the fired heated boiler;

[0078] - it is less energy consuming than a hydrogen fired boiler.

[0079] A hydrogen boiler uses hydrogen for combustion, which is typically produced by electrolysis. The electrolysis units are powered by electricity and have an energy efficiency typically in the range of 60%-80%, consequently, the electrical consumption associated with using a hydrogen boiler is 60% to 80% higher compared to the electrical consumption associated with using an electric steam boiler.

[0080] However, also the burning of purge gas and hydrogen in a fired boiler has specific advantages. One advantage is that burning the purge stream, instead of flaring it, prevents inert accumulation in the loop and it increases the energy efficiency of the plant recovering the combustion heat of purge. This solution is particularly advantageous for relatively large capacity of the methanol synthesis loop and of the plant because the hydrogen / purge gas boiler can be built as a single unit even for capacities of several thousands of tons of methanol per day. Whereas the electrical steam boiler has less scalability and would require the installation of parallel units, with higher capital expenditure.

[0081] The present invention is of great advantage for methanol process plants, particularly for e-methanol process plants wherein methanol is produced from hydrogen and carbon dioxide, both in fluctuating and non-fluctuating conditions. This invention is also applicable to e-methanol process plants with integrated reverse water gas shift and / or with integrated solid oxide electrolyzer cell (SOEC), for different feedstock productions.

[0082] This invention is particularly advantageous when methanol is produced starting from CO2 because the higher content of water in the product and the consequently the higher duty required for distillation is balanced by the additional heat sources described by the above embodiments. This invention is also advantageous when the scope is producing methanol with higher specification (A, AA), because the distillation section requires higher duty and therefore more needing for heat provision.

[0083] Another advantage of the invention is the reduction of energy consumption of the distillation section of an e-methanol process with a cascaded configuration of the distillation columns. The minimization of the additional energy required for the distillation section is enhanced by means of an intermediate storage of crude methanol which decouples the synthesis loop and the distillation section. Also the introduction of other storages such as the distillation storage collecting bottom solution between two subsequent distillation columns, the storage for purge gas, the storage for hydrogen and the storage for fusel oil are useful to improve the recycle of heat generated throughout the process and to reduce the addition of energy from external sources. The need of extra heat for the distillation section is satisfied with the production of energy via engines and / or heating boilers burning the synthesis loop purge and / or hydrogen stream and / or fusel oil that are integrated in the methanol process plant.

[0084] The minimization of additional heat to the distillation section is particularly relevant for e-methanol synthesis process, in which the plant is operated in fluctuating mode. The invention offers a more energy-efficient and environmentally friendly method for producing methanol, especially in scenarios with varying energy inputs and the need for a sustainable energy balance. Detailed description

[0085] Fig. 1 and 2 illustrate a methanol distillation section according to two embodiments of the invention.

[0086] Fig. 3 shows the recovery of heat from the methanol converter to the distillation section.

[0087] Figs. 4a, 4b, 5a, 5b, 6a, 6b and 7 are plots of various parameters useful to show the advantages of the invention.

[0088] Fig. 1 illustrates a simplified diagram of a methanol distillation process of a stream of crude methanol 30, including a topping column 2 and three refining columns in cascade configuration: a first refining column 3 working at high pressure (HP), with a pressure P1 , a second refining column 4 working at medium pressure (MP), with a pressure P2, a third refining column 5 working at low pressure (LP), with a pressure P3; wherein P1 is greater than P2, and P2 is greater than P3.

[0089] The topping column 2 is equipped with a reflux condenser 6, a heat exchanger 10 and an electrical heater 12; the first refining column 3 is connected to a top condenser 7, a bottom heat exchanger 11 and an electrical heater 13; the second refining column 4 is connected to a top condenser 8 and an electrical heater 14; the third refining column 5 is connected to a top condenser 9 and an electrical heater 15.

[0090] The crude methanol 30 is produced in a synthesis section, not shown. The distillation section further comprises a crude methanol storage 1 , to which the feed line of the crude methanol 30 is connected. The crude methanol is fed to the topping column 2 from the storage 1 , via a pump 19 and line 31.

[0091] The topping column 2 produces a stream of volatile components 32 effluent from the top of the topping column and processed by the reflux condenser 6. Said condenser 6 generates a stream of light ends 33 and a reflux flow 34. The light ends stream 33 is at least in part recycled via line 70, the remainder being removed from the process. The reflux flow 34 is reintroduced in the topping column.

[0092] A bottom solution 35 is withdrawn from the bottom of the topping column 2. A first part of said bottom solution 35 is sent to the electrical heater 12 via line 71 , a second part of the solution 35 is sent the heat exchanger 10 via line 36 and a remaining part of the solution is sent to the first refining column 3 via line 38 for further purification.

[0093] The bottom solution heated in the heat exchanger 10 is reintroduced in the topping column 2 as a heated solution 37, and the stream of bottom solution heated by the electrical heater 12 is reintroduced in the topping column 2 as a heated solution 72. In the heat exchanger 10, the bottom solution is heated by a suitable hot fluid 39 used as a heating medium, for example steam produced in the methanol synthesis section (e.g. from cooling of hot reaction effluent).

[0094] The stream 38 of bottom solution is fed to the refining column 3 through a pump 20, a let-down valve 22 and input line 40.

[0095] Typically, a refining column produces two main streams: an overhead vapour stream effluent from the top of the refining column and a bottom solution effluent from the bottom of the refining column. In the example shown in figure, the overhead vapour stream 41 of the first refining column 3 is processed by the top condenser 7. The condensation of the vapour stream 41 releases heat which is used by the heat exchanger 27 to heat the bottom solution 77 of the second refining column 4. The condensation of the vapor stream 41 results in a liquid stream of distilled methanol 42.

[0096] The bottom solution 43 of the column 3 is partly sent to the electrical heater 13 via line 73 and partly sent to the heat exchanger 11 via line 44. The stream of bottom solution heated by the heat exchanger 11 is reintroduced in the refining column 3 as a heated solution 45, and the stream of bottom solution heated by the electrical heater 13 is reintroduced in the refining column 3 as a heated solution 74. The heat exchanger 11 receives hot steam 47 from an external source 48 (e.g. process steam) and / or from a fired heating boiler 16.

[0097] Said fired heating boiler 16 produces steam from feed water 49. The fuel for the heating boiler 16 may include one or more of: a purge gas 50 from the synthesis loop; a stream of flash gases 75 effluent from the synthesis loop; a stream of hydrogen 51 from a hydrogen storage and / or an electrolysis unit (not shown in figure); a fusel oil stream 80 effluent from the last refining column 5 of the distillation section; a stream of light ends effluent from the topping column 2, such as light ends in the line 70 from the reflux condenser 6; a stream of vent methanol 81 retrieved from the crude methanol storage 1 .

[0098] A stream of flue gases is removed from the fired boiler 16 through line 29. The steam 47 releases heat to the heat exchanger 11 and the cooled steam is released through line 52. A part of the bottom solution 43 is sent to the second refining column 4 via line 46 and a let-down valve 23 to regulate its pressure.

[0099] The overhead vapour stream 53 of the second refining column 4 is processed by the top condenser 8. The heat released by the vapour stream 53 subjected to the condensation process is collected by the heat exchanger 28 and supplied to the third refining column 5 via line 61 . The vapor stream 53 condensed during the heat exchange results in a liquid stream of distilled methanol 54.

[0100] A part of the bottom solution 76 of the second refining column 4 is sent via line 55 to an electrical heater 14 obtaining a heated solution 56 which is reintroduced in the refining column 4. A part of the bottom solution 77 of the refining column 4, is sent to the heat exchanger 27 coupled with the first refining column 3. The heat retrieved by the heat exchanger 27 from the condensation of the vapor stream 41 , heats up the bottom solution 77 and the heated stream is reintroduced in the second refining column 4 via line 60. The remaining part of the bottom solution is fed to the third refining column 5 via line 57 and let-down valve 24.

[0101] The overhead vapor stream 58 effluent from the top of the third refining column 5 is processed by the top condenser 9 forming a stream of distilled methanol 59. A part of the bottom solution 62 is sent to the heat exchanger 28 coupled with the second refining column 4. The bottom solution 62 is heated by means the heat retrieved by the heat exchanger 28 from the overhead vapor stream 53 of the second refining column 4. The heated stream of bottom solution is reintroduced in the third refining column 5 through line 61 . A part of the bottom solution 63 is sent to an electrical heater 15 and after heating it is reintroduced in the third refining column 5 via line 78.

[0102] Residual water is withdrawn through line 66 from the bottom of the third refining column 5. A stream of by-products of the distillation, named fusel oil 67, is sent to a fusel oil accumulator 17. Part of the fusel oil stream can be sent to the heating boiler 16 through line 80 to provide additional fuel for the combustion.

[0103] The distilled methanol can be withdrawn from the process through line 64, which collects all the streams of distilled methanol, 42, 54, 59, effluent from the top condensers 7, 8, 9. In case the distilled methanol does not meet the quality specification required by the market, it is sent to a storage tank 18 passing through a control valve 25. A stream of distilled methanol of poor quality 65 is withdrawn from the storage tank 18 and sent to the storage of crude methanol 1 for a further distillation process, in order to improve the quality of methanol. The stream 65 is sent upstream the distillation section passing through a pump 21 and a control valve 26.

[0104] Fig. 2 is based on the same distillation configuration illustrated in Fig. 1 , with differences in the heat input sources. According to this embodiment, the fired heating boiler 16 is replaced with an electrical heated steam boiler 89, which is fed with water 49 and electricity 88. Steam from external source 48 is added to the steam 47 effluent from the electrical steam boiler 89. The electrical heaters 12, 13, 14, 15 of Fig. 1 are replaced with steam reboilers 82, 83, 84, 85, which are fed with steam 47 from the electrical steam boiler 89 and additional steam 48 (e.g. process steam). In a preferred embodiment, the steam reboilers 82, 83, 84, 85 are in parallel to the heat exchangers 10, 11 of the respective distillation columns.

[0105] The bottom solution 35 effluent from the topping column 2 is heated partly by the heat exchanger 10 and partly by the steam reboiler 82. A part of the steam 47 is directed to the steam reboiler 82 through line 90. The steam 90 passing through the steam reboiler 82 releases heat to the bottom solution 71 . The heated bottom solution is fed back to the bottom off the topping column 2 through line 72, while the steam cooled down by the steam reboiler 82 is withdrawn in liquid form through line 95.

[0106] A part of the steam 47 is directed to the heat exchanger 11 through line 91 and a part is directed to the steam reboiler 83 through line 92. The bottom solution 43 effluent from the first refining column 3 is partly heated by the steam reboiler 83. The steam reboiler 83 heats up the bottom solution 73 which is then fed back to the refining column 3 through line 74. The steam cooled down by the steam reboiler 83 is withdrawn in liquid form through line 96.

[0107] The steam 47 is partly directed to the steam reboiler 84 through line 93 and to the steam reboiler 85 through line 94, which are coupled with the second and third refining columns 4, 5 respectively. A part of the bottom solution 55 effluent from the second refining column 4 is heated by the steam reboiler 84, the heated bottom solution is reintroduced in the refining column 4 through line 56. The steam 93 releases heat through the steam reboiler 84 and is withdrawn in liquid form through line 97. Similarly, a part of the bottom solution 68 effluent from the third refining column 5 is heated by the steam reboiler 85, the heated bottom solution is reintroduced in the refining column 5 through line 78. The steam 94 releases heat through the steam reboiler 94 and is withdrawn in liquid form through line 98. The fusel oil 67 effluent from the last refining column 5 is collected in a fusel oil accumulator 17. Part of the fusel oil stream 80 may be withdrawn from the process or sent to other units.

[0108] Fig. 3 shows the heat recovery from the methanol converter to provide heat for the distillation section. The heat is recovered removing reaction heat from the converter and cooling the reaction effluent. The heat recovery illustrated in Fig. 3 is suitable for any embodiment of the invention.

[0109] The methanol converter 100 is fed with make-up gas 107 and steam 108 producing a reaction effluent 106 comprising methanol and reaction byproducts. The reaction effluent 106 is directed to a heat recovery section 101 where heat is recovered from the effluent 106. The line 113 denotes the transfer of heat from section 101 to the distillation section. In Fig. 3, the heat recovered in section 101 is supplied to the bottom of the topping column 2 by means of a reboiler 104.

[0110] The reaction effluent 106 withdrawn from heat recovery section 101 is then sent through line 110 to a cooler 102 which cools down the effluent. The cooled effluent is directed to a crude methanol separator 103 via line 111. The crude methanol separator 103 produces a crude methanol stream 30 which is directed to the crude methanol storage tank 1 and subsequently to the distillation section. The separator 103 produces also a stream of light components 112 which are separated from the crude methanol and are removed from the process.

[0111] The steam 109 generated from the reaction in the methanol converter 100 is used to supply heat to the bottom of the first refining column 3. The pressure of the steam generated in the converter ensures an appropriate temperature difference, preferably of at least 10-15°C, at the bottom of the first refining column 3. In some cases, the steam 109 is at a high pressure, up to 45 bar, to maintain optimal temperatures in the methanol converter 100. The pressure of the steam 109 produced in the converter 100 may be greater than the pressure in the line 47; in such case, a pressure regulation valve 114 downstream of the steam drum of the converter 100 matches the pressure of the steam from the converter (line 48 of expanded steam) with the pressure of the steam from the electrical boiler 89, facilitating the use of a single reboiler 105 at the bottom of the first refining column 3. The steam 47 releases heat to the bottom solution 44 through the reboiler 105 and the cooled steam exits from the reboiler in liquid form through line 115.

[0112] The following examples illustrate the operation of the invention.

[0113] Example 1

[0114] Fig. 4a and Fig. 4b relate to the production of e-methanol in a synthesis loop and distillation section, assuming 50 MTPD (metric tons per day) peak production with photovoltaic energy. The synthesis loop operates in a range 20% - 110% of nominal load, whereas the distillation section operates at a stable load of 70% with feed from intermediate crude methanol storage tank. The distillation steam requirement is 1 .13 t / h (tons per hours) of medium pressure steam, and the steam produced in the synthesis loop varies between 0.21 - 1.18 t / h. The additional heat required to run a stable distillation process is shown in Fig. 4b and is provided by the one or more additional sources, for example the electrical heaters 12, 13, 14, 15 of Fig. 1. In case of electric heating, an additional specific consumption of 219 kWh / t is required on average daily production, and the peak power required for electric heating is 745 kW.

[0115] Example 2

[0116] Figs. 5a and 5b illustrate an example wherein the synthesis loop operates as in Figs. 4a and 4b, whereas the distillation section operates with a variable load in the range 60% - 80%, following the load of the loop, instead of a constant load of 70%. This situation leads to a steam required in the distillation section between 0.97 - 1 .30 t / h as shown in Fig. 5b. In this case the additional source needed to run distillation is decreased to 214 kWh / t and the maximum required additional heating power is 614 kW. Example 3

[0117] This example is a variation of example 2, wherein the distillation section is run with a wider variable load between 50% and 85%, as shown in Fig. 6a, leading to steam required in the distillation section of 0.81 - 1 .38 t / h, as shown in Fig. 6b. In this situation the additional heating source needed for the distillation is still 214 kWh / t as in example 2, however the peak power consumption is decreased to 530 kW.

[0118] Example 4

[0119] This example has the same working conditions of example 3, therefore Fig. 6a describes the loop and distillation load condition for this example. The difference in this case with respect to example 3 is the use of purge combustion to increase the steam production necessary for the distillation section. Purge combustion generates 1 .2 t / h of steam at 50 MTPD loop production, as shown in Fig. 7. Considering the same ranges of load described in example 3, using purge combustion at variable load as per the synthesis loop, the additional heating source needed for the distillation is reduced to 42 kWh / t, with a peak electric power consumption of 288 kW. Composition and flow of the purge can vary depending on the cases, resulting in more or less additional steam. The use of the purge gas may be increased if the distillation section requires more heat, with the advantage to lower the concentration of inerts in the loop. In a preferred embodiment, the flow of purge gas is kept to a steady value to avoid operational bums in the loop that would be a consequence to a continuous flow rate change of purge.

[0120] Example 5

[0121] If e-methanol is operated at stable conditions, with the synthesis loop and the distillation section both operating at 100%, 20% of the duty required for the distillation is provided by burning the purge gas effluent from the distillation section, the remaining 80% is retrieved from the synthesis loop.

[0122] Example 6

[0123] If e-methanol is operating in fluctuating conditions, with the synthesis loop and the distillation section operating at their minimum load, which is 10% and 50% respectively, the burning of purge gas provides more than 50% of the duty of the distillation.

[0124] Example 7

[0125] The table below shows how the heat retrieved from the distillation section for the distillation process changes depending on the number of refining columns. In all the following cascade configurations outlined, the overhead vapor stream of a refining column is cooled in a top condenser and the heat retrieved from the condenser is used to heat the bottom solution of a following refining column.

[0126] Table 1

[0127] The table shows that three refining columns is the optimal number of columns to carry out the distillation process in e-methanol production. With this configuration the synthesis loop provides enough steam to the distillation section to carry out an optimal distillation process, and the steam provided is at a level of pressure which is the optimal working pressure in a methanol converter. A configuration with four refining columns would require a steam pressure greater than 35 bar, which is higher than the optimal pressure at which the converter works. The addition of a fourth column of refining would entail a higher operating temperature of the converter, and lower conversion per pass in the converter. Hence the introduction of a fourth refining column would not be useful to reduce the heat gap between the loop and the distillation, making this solution less desirable.

[0128] The configuration with three refining columns at full load provides enough heat to the distillation section to avoid the use of any additional heat source. While, if the distillation section comprises two columns in cascade configuration, the additional heat required from external sources is more than double that provided from the synthesis loop. In case of low load with three cascade configuration, external heat input is necessary, but the percentage of heat required is lower than the one required with two refining columns configuration.

Claims

1.CLAIMS1 ) A process for the synthesis of methanol in a methanol plant including: conversion of a methanol make-up gas by a methanol converter in a synthesis loop producing a reaction effluent; said reaction effluent being cooled, and optionally pre-treated, resulting in a stream of crude methanol to be purified; purification of said crude methanol by a distillation process in a distillation section producing a stream of distilled methanol; wherein the distillation process includes a first distillation step performed in a topping column (2) and a second distillation step performed in a first refining column (3), a second refining column (4) and a third refining column (5) arranged in cascade configuration; wherein a heat input is provided to the distillation process to obtain said distilled methanol; each of said first refining column, second refining column and third refining column (2, 3, 4) is equipped with a top condenser (7, 8, 9) condensing an overhead vapor stream (41 , 53, 58) effluent from the respective refining column, and at least part of heat removed from the overhead vapor stream of at least one of said columns, during condensation of the vapor stream, is transferred to a bottom solution of a subsequent refining column of the cascade; a first part of said heat input for the distillation process is retrieved from the synthesis loop by removing reaction heat from the methanol converter and / or by cooling of said reaction effluent; a second part of said heat input for the distillation process is provided by one or more of the following sources: a) at least one electrical heater (12, 13, 14, 15); b) at least one electrical heated steam boiler (89);c) combustion of a purge gas (50) withdrawn from the synthesis loop in at least one fired equipment (16) of the distillation section; d) combustion of a stream of fusel oil (80) withdrawn from the distillation section in at least one fired equipment (16) of the distillation section; e) combustion of a hydrogen stream (51 ) in at least one fired equipment (16) of the distillation section; wherein said second part of heat input for the distillation process provides heat to a stream of a bottom solution of the topping column and / or to a stream of a bottom solution of one or more of the refining column(s).2) A process according to claim 1 , wherein said hydrogen stream (51 ) of option e) is retrieved from one or more of the following sources: a hydrogen storage, which is preferably a buffer storage between a hydrogen source and said methanol converter; a water splitting process, preferably by electrolysis performed in an electrolysis unit; hydrogen taken from a stream of methanol make-up gas.3) A process according to claim 1 or 2, wherein methanol is produced from hydrogen and carbon dioxide as starting materials.4) A process according to any of the previous claims, wherein the second part of the distillation heat from one or more of the heat input(s) of options a) to e) is provided when the heat transferred from the synthesis loop to the distillation section is insufficient for the distillation process.5) A process according to any of the previous claims, wherein steam generated in the methanol converter supplies heat to the bottom solution of the first refining column (3) by means of a first reboiler and the reactioneffluent from the methanol converter supplies heat to the bottom solution of the topping column (2) by means of a second reboiler.6) A process according to any of the previous claims, wherein the distillation in the first refining column is performed at a first pressure P1 , distillation in the second refining column is performed at a second pressure P2, distillation in the third refining column is performed at the third pressure P3, being P1 greater than P2, and P2 greater than P3; wherein said first pressure P1 is in the range 15 to 30 bar, said second pressure P2 is in the range 7 to 15 bar, said third pressure P3 is in the range 1 to 5 bar.7) A process according to any of the previous claims, wherein each top condenser coupled with each refining column generates condensing heat, the process includes the step of providing condensing heat from the first refining column to the second refining column and providing condensing heat from the second refining column to the third refining column.8) A process according to any of the previous claims, wherein the bottom solution of the topping column and / or the bottom solution of one or more of the refining column(s) is heated by the at least one electrical heater of option a) before or after being heated by a top condenser.9) A process according to any of the previous claims, wherein the at least one electrical heated steam boiler of option b) provides steam to the bottom solution of one or more of the refining columns and / or to the bottom solution of the topping column by means of one or more steam reboiler(s) (82, 83, 84, 85).10)A process according to any of the previous claims, wherein the methanol converter is a pseudo-isothermal steam generation methanol converter producing steam; the process includes the step of providing distillation heat by means of said steam produced in the pseudo-isothermal steamgeneration methanol converter.11 )A process according to any of the previous claims, wherein pressure and temperature of steam (109) effluent from the methanol converter meet pressure and temperature of steam of a reboiler coupled with the first refining column, or the process includes the step of regulating pressure and temperature of steam (109) effluent from the methanol converter by means of a valve (114) to meet pressure and temperature of steam of a reboiler coupled with the first refining column (105).12)A process according to any of the previous claims, wherein the bottom solution of the topping column and / or the bottom solution of one or more of the refining columns is heated by means of at least one fired equipment of the distillation section, wherein said fired equipment is a fired heater or a heating boiler.13)A process according to claim 12, wherein said fired heater provides heat to the distillation section by burning a hydrogen stream (51 ) according to option e) and at least one of the following fuels: purge gas withdrawn from the synthesis loop; light ends withdrawn from the top condenser of the topping column; fusel oil withdrawn from the distillation section.14)A process according to any of the previous claims, wherein the process includes the step of collecting purge gas in a purge storage and / or the step of collecting a hydrogen stream effluent from an electrolysis unit and / or taken from the make-up gas of the synthesis loop in a hydrogen storage.15)A process according to any of the previous claims, wherein the fired equipment includes an engine or a gas turbine fired with fusel oil.16)A process according to claim 15, wherein the process includes the step ofcollecting fusel oil and / or crude methanol in a collecting storage and feeding said engine and / or said gas turbine with a stream withdrawn from said collecting storage.17)A process according to claims 15 or 16, wherein said engine and / or said gas turbine produce electric energy powering at least in part the methanol plant and heat recovered from the engine and / or gas turbine is supplied to the distillation section.18)A process according to any of the previous claims, wherein at least one electrical trim heater is used in addition to any of the heat inputs a) to e) to provide trim heating to the bottom of the topping column and / or to the bottom of one or more of the refining column(s).19)A process according to any of the previous claims, wherein the process includes the use of an intermediate crude methanol storage tank (1 ) collecting the crude methanol effluent from the synthesis loop.20)A process according to any of the previous claims, wherein the topping column and the refining column are defined as distillation columns, the process includes the step of using a distillation storage between two subsequent distillation columns collecting at least part of a bottom solution from a distillation column and feeding a subsequent distillation column with a methanol stream withdrawn from said distillation storage.21 )A process according to claims 19 or 20, wherein the bottom solution collected in the distillation storage and / or the intermediate crude methanol storage tank is / are heated by means of said at least one electrical heater according to option a).22)A process according to any of the previous claims, wherein at least part of the heat input for the distillation process is provided by recovered waste heat of an electrolysis unit.

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