Method and apparatus for distillation

Abstract

The present invention relates to an apparatus and process for the distillation of methanol (Figure 1), but can also be used for the distillation of other products, such as ethanol. The present invention is a method aimed at reducing the consumption of energy, cooling water and / or electricity in the distillation process of a crude intermediate product, including a pre-treatment stage known as a stabilization stage to remove volatile components, and a concentration stage comprising one or more columns for distillation.

Description

[Technical Field]

[0001] Application field The present invention relates to a method, an apparatus and a plant for distilling methanol. The method and apparatus can also be used to distill other products such as ethanol. [Background technology]

[0002] Background technology The product of a methanol synthesis plant is generally defined as crude methanol, but is known to be an aqueous methanol solution that contains by-products of the synthesis reaction, including ethanol, ketones, higher alcohols, and several dissolved gases, primarily H2, CO, CO2, N2, and CH4.

[0003] This crude methanol is distilled to meet market-required purity specifications, for example, Grade AA requires a minimum methanol concentration of 99.85% by mass and not more than 10 ppm ethanol.

[0004] Known distillation processes are substantially based on one or more distillation columns, typically at least one column capable of separating lighter products (e.g., gases) recovered at the top of the column from methanol, and at least one column capable of separating heavier products (e.g., aqueous solutions) recovered at the bottom of the column from methanol.

[0005] A particular process widely used for distilling methanol involves two columns operating at or near atmospheric pressure. More specifically, the process employs a pretreatment column known as a stabilization or pre-run column and a second distillation column. The first column, essentially intended to separate the more volatile components contained in the crude methanol, receives the crude methanol and separates lighter components at the top and an aqueous solution at the bottom. The second column, known as a concentrate column, performs the actual distillation, yielding (i) purified methanol at the top, (ii) a primarily aqueous solution ("bottoms water") at the bottom, and (iii) a side stream known as "fusel oil," which contains primarily water, residual methanol (about 1% of the total), and most of the by-products of the synthesis reaction. The fusel oil has a calorific value and is typically used as a fuel or feedstock for synthesis gas production.

[0006] Each column is equipped with a reboiler, which heats the bottom of the column and maintains the heat input to the distillation process. Each column also contains a condenser (at least partially) that condenses the overhead product and recycles it to the column. At an appropriate heat level, heat is supplied to the condensation (or distillation) column by steam or process gas. The cooling medium for the condenser is usually water or air. While the above configuration with two columns is simple from the plant (e.g., a methanol distillation plant) point of view, it has the major drawback of consuming a significant amount of energy, both due to the heat supplied to the bottom reboiler and due to the consumption of cooling water and / or electricity in the overhead condenser. Furthermore, the column diameters are relatively large relative to the production capacity, resulting in high plant costs.

[0007] The heat consumption of the two bottom reboilers is approximately 3.35x10 per ton of purified methanol. 9 The energy consumption required to produce 1 ton of crude methanol is approximately (25.10-33.47x10 9Since the energy consumption of the distillation is 6-8 Gcal, the order of magnitude of the energy consumption of the distillation is estimated to be 10% of the total consumption of the plant. The heat discarded in the condenser is about the same as the heat exchanged in the reboiler. Theoretically, for example, if the heat is removed only by cooling water, the circulating flow rate is about 80 m per ton of methanol. 3 This results in higher costs for pumps etc.

[0008] There are other known distillation plants and methods that attempt to at least partially mitigate these drawbacks.

[0009] US 4,210,495 describes a process using three distillation columns: a pretreatment or stabilization column and two rectification columns, each operating at a medium pressure of approximately 7-8 bar (bars), and a final rectification column. The stabilization and final rectification columns operate at substantially atmospheric pressure or slightly higher (e.g., 1.5 bar). This configuration allows for heat recovery by condensing the top vapor of the medium-pressure column in the bottom reboiler of the final column at atmospheric pressure; this concept is known as a "staggered column" or "cascade column." The staggered column concept can also be used multiple times, for example, with a high-pressure rectification column supplying heat to a rectification column operating at intermediate pressure, which in turn supplies heat to a column operating at lower pressure. However, because both the stabilization column and the rectification column operating at the highest pressure must be heated, specific consumption, while lower, remains high compared to a two-column plant.

[0010] A further development of this idea is disclosed in WO2013110369, which describes a method in which the final distillation column is operated at the highest pressure and the overhead vapor from the final rectifying column is condensed to provide heat to the stabilizing column reboiler. This configuration allows for energy savings compared to the configuration described in US4210495, but this configuration has a significant drawback in that all rectifying columns operate at a higher pressure than the others. Another drawback of this configuration is that the amount of heat required for the stabilizing column is much lower (about 30-70%) than that required for the final rectifying column, resulting in a mismatch between the load of the stabilizing condenser and the load of the final rectifying column reboiler.

[0011] The implication of a mismatch between the stabilizer condenser duty and the final rectifying column reboiler duty is that either part of the final rectifying column condensation duty must be supplied by a separate condenser cooled by air or water (extra cost and energy consumption) or the stabilizer column must be unnecessarily large (diameter).

[0012] The drawbacks of increasing the pressure of the rectifying columns are twofold. First, as the pressure of the rectifying columns increases, the heat source specifications become more stringent, and a heat source that is adequate for heating two staggered rectifying columns may not be adequate for heating the resulting three staggered rectifying columns. Furthermore, the separation efficiency of the rectifying columns decreases as the pressure increases. This leads to increased energy consumption for a given distillation column, as shown in Tables 1 and 2.

[0013] [Table 1]

[0014] [Table 2] [Prior art documents] [Patent documents]

[0015] [Patent Document 1] US4210495 [Patent Document 2] WO2013110369 Summary of the Invention [Problem to be solved by the invention]

[0016] Document WO2013110369 addresses the problem of considerable energy consumption, both due to the heat supplied to the bottom reboiler and the cooling water and / or electricity consumption of the top condenser, but does not provide (or suggest) a solution that efficiently solves this problem and allows comparable energy savings when having more than two concentrating columns for the distillation of methanol.

[0017] According to this document, the use of a substantially high bottom pressure (i.e., in a final distillation column corresponding to column V3 of the present invention) allows for energy savings and optimization of heat flow. By increasing the bottom pressure (in a final distillation column corresponding to column V3 of the present invention) and (corresponding to column P3 of the present invention), the gaseous distilled methanol produced in the bottom stage has a temperature substantially higher than that in the top stage (corresponding to stabilizer column V0 of the present invention), sufficient to allow the distilled methanol stream to be used as a heat source for the preliminary top stage. This document also claims that it is possible to reduce or eliminate the consumption of heat (e.g., from condensed steam) for heating the top stage. It also discloses that the pressure p4 in the bottom stage is substantially higher than the topping pressure p1 so that the temperature of the gaseous methanol distilled in column 400 is substantially higher than the temperature of the liquid at the bottom of column 100. It also discloses that this temperature difference is at least 10°C, i.e., the temperature of the gaseous methanol at the top of column 400 is at least 10°C higher than the temperature of the liquid at the bottom of column 100. This allows at least a portion of the gaseous methanol to be used to heat the topping column 100.

[0018] Furthermore, CN108101748 and other documents mention an energy-saving process and apparatus for methanol purification that uses four columns to produce methanol from crude methanol, and mention a reduction in operating energy consumption, but do not clarify or suggest how this is achieved or what the process conditions should be.

[0019] Description of the Invention The present invention relates to an apparatus and method for the distillation of methanol (FIG. 1), but is also applicable to the distillation of other products such as ethanol.

[0020] The present invention has the object of reducing the consumption of energy and cooling water and / or electricity in the distillation process of a crude intermediate product (e.g., methanol) which includes a pretreatment stage known as a stabilization stage for removing volatile components and a concentration stage comprising one or more columns for distillation. [Means for solving the problem]

[0021] Such an object is achieved in a preferred embodiment of the present invention by a process for the purification or distillation of a stream of crude methanol (A), said process comprising: (i) pretreatment of a crude methanol stream A in a stabilization column V0 at a pressure P0 for the separation of volatile components, from the top of V0 a light gas stream L is obtained and from the bottom of V0 a liquid stream B0 containing methanol is obtained; (ii) B0 is then directed to a rectifying column V1 at a pressure P1; (iii) gas stream T1 withdrawn from the top of V1 is condensed in heat exchanger E2 to provide energy to rectifying column V2; (iv) part of the condensed methanol obtained in step (iii) is sent to product C1, and the remainder of the condensed methanol is added to the top of V1 and used as reflux; (v) A liquid stream B1 comprising methanol is withdrawn from the bottom of V1 and passed through V2 at a pressure P2; (vi) the gas stream T2 withdrawn from the top of V2 is split into two, one stream being condensed in heat exchanger E0 to provide energy to V0, and the other stream being condensed in heat exchanger E3 to provide energy to rectifying column V3; (vii) part of the condensed methanol obtained in step (vi) is sent to product C2, and the remainder of the condensed methanol is added to the top of V2 and used as reflux; (viii) a liquid stream B2 comprising methanol is withdrawn from V2 and passed to V3 at a pressure P3; (ix) The gas stream T3 recovered from the top of V3 is condensed, part of the condensed methanol is sent to product C3, and the rest is added to the top of V3 and used as reflux. (x) one or more side streams H containing higher alcohols and other minor by-products are removed from V3, and a liquid stream B3 is removed from V3; where - columns V1, V2 and V3 operate at decreasing pressures such that P1>P2>P3; -P0>0barg and P3>0barg, - each column V0, V1, V2 and V3 is associated with a corresponding heat exchanger E0, E1, E2 and E3 which is a reboiler for the same column, heat exchangers E0 and E3 are condensers for column V2, heat exchanger E2 is a condenser for column V1, -P3<2barg; and The method is characterized in that the heat exchanger E1 is supplied with energy from an external source.

[0022] The invention also relates to an apparatus for the distillation of methanol, comprising a stabilization column V0 connected in series at a pressure P0 with at least three distillation columns V1, V2 and V3 at corresponding reduced pressures P1, P2 and P3, each column associated with a heat exchanger E0, E1, E2 and E3, said heat exchanger being a reboiler for that column, a) Heat exchangers E0 and E3 are the condensers of column V2. b) Heat exchanger E2 is the condenser of column V1; c) E1 has a heat flow that flows outside the device. d) P3<2barg characterized in that Similarly, there is provided a plant for the distillation of methanol, comprising at least one apparatus according to the invention, in which the amount of steam required for E1 is less than 1.3 kg / kg of produced methanol, and also the use of said apparatus for the distillation of methanol.

[0023] The process of the present invention preferably comprises at least four columns V0, V1, V2 and V3, but may comprise more concentrating columns, i.e. columns V1 to Vn, preferably connected in series, operating at reduced pressure.

[0024] All said concentrating columns are operated in such a way that a portion of the distillation products C1, C2, C3 etc. is withdrawn from the top of each concentrating column, and the remaining liquids B0, B1, B2, B3 etc. are passed on to other columns, for example up to the final concentrating column. In a preferred embodiment of the invention, said column is V3, from which the final fraction of product C3 is withdrawn from the top, a stream B3 containing mainly water is recovered from the bottom, and a mixture often called fusel oil is recovered from a side stream H from the last concentrating column, usually taken off between the feed tray and the bottom of the column.

[0025] The heat exchange is preferably carried out in condensers / reboilers E0, E1, E2 and E3, which may be tube bundle or plate exchangers, in which the distilled methanol condenses on the hot side and the solution evaporates on the cold side.

[0026] Preferably, the pressures in the condensers for the stabilization step and the low-pressure rectification column are both slightly above atmospheric pressure, for example 0.1 to 0.5 bar, so that typically the pressure in the reboiler for the stabilization step is 0.5 to 1.5 bar and the pressure in the condenser for the rectification column providing heat is at least 2 bar. Consequently, the pressure in the reboiler for the column providing heat is in the range 2 to 8 bar, more preferably about 7 bar.

[0027] In some embodiments, including multiple concentrating columns and multiple pressure levels, the column with the next lowest pressure level always provides heat to the stabilization process.

[0028] The described pretreatment (stabilization) and concentration stages can be carried out using a single column or multiple columns in parallel, as desired.

[0029] The final concentration column V3 produces distilled methanol C3, a solution B3 consisting mainly of water, and may also produce a side stream H, represented by the so-called fusel oil, which may optionally also be extracted from an intermediate distillation stage.

[0030] Since the relative volatility of methanol and ethanol is highest at low pressure, it is advantageous to carry out the separation at as low a pressure as possible.

[0031] Each time column 1 receives heat from another column 2, the temperature level of column 1 increases, and therefore the pressure of column 2 must also be higher than that of column 1. This is necessary to obtain the desired driving force in the heat exchangers that function as condensers for the higher-temperature column and reboilers for the lower-temperature column. This temperature difference is preferably 4 to 10°C. Furthermore, the temperature level of the external heat source (typically steam) is preferably 4 to 10°C higher than the temperature level of the bottom of the column with the highest temperature level. Some prior art documents suggest staggering all rectifying columns above the stabilizing column, but these would impose higher requirements on the temperature level of the external heat source than in the present invention, where the final rectifying column operates at the same pressure level, and therefore essentially the same temperature level, as the stabilizing column. [Brief explanation of the drawings]

[0032] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a preferred embodiment of the methanol distillation process according to the present invention, in which three rectifying columns V1, V2 and V3 with decreasing pressures P1>P2>P3 are connected to a stabilizing column V0 at pressure P0, where: a. A: Crude methanol feed b. V0: Stabilization column at pressure P0 c. V1, V2, V3: Rectifying columns at pressures P1>P2>P3 d. B0: Methanol-containing liquid stream recovered from the bottom of stabilization column V0 e. B1, B2, B3: Methanol-containing liquid streams recovered from the bottom of rectifying columns V1, V2, V3 f. C1, C2, C3: Liquid products obtained by distilling methanol g. E0,E1,E2,E3: Heat exchanger h. T0: Gas stream recovered from the top of stabilization column V0 i. T1, T2, T3: Gas streams recovered from the top of rectifying columns V1, V2, and V3 j. L: Light gas flow from V0 k. H: Side stream collected from V3 l. S: Flow division. DETAILED DESCRIPTION OF THE INVENTION

[0033] definition "Atmospheric pressure" means 1.01325 bar, i.e., approximately 1 bar.

[0034] "Concentration column" or "distillation column" or "bottoms," Vn, where n ≠ 0 (e.g., V1, V2, or V3), refers to a column divided into a series of stages. These correspond to a cascade of equilibrium stages. Liquid flows down the column from stage to stage, contacting the vapor flowing upward. Traditionally, most distillation columns are constructed with a collection of "trays" or "plates," and these terms are essentially interchangeable with "stage." Each tray in a distillation column is designed to promote contact between the vapor and liquid on that stage. Distillation can be performed in a packed column (similar to how absorption can be performed in a tray column). Stages may be numbered from top to bottom or bottom to top. The stream recovered from the top of the column is called the overhead product, T, "overhead," or "top product." The distillate, C, may be liquid or vapor (or sometimes both), depending on the type of condenser used. The distillate stream is referred to herein as C, and the product recovered from the bottom of the column is sometimes referred to as the bottom product and is given the symbol B herein. In some circumstances, one or more "side" products H may be removed from the column. The section of the column above the feed tray is called the rectifying section. In this section, vapors are concentrated by contact with reflux liquid. The section of the column below the feed tray is called the stripping section. A liquid portion of the feed serves as reflux for this section. The column's operating pressure Pn (P1, P2, P3, etc.) is usually controlled by adjusting heat removal in heat exchangers. The base of the column is usually used as a reservoir to hold the liquid leaving the bottom tray. A heat exchanger such as a reboiler is used to boil this liquid. The resulting vapor, or "boil-up," is returned to the bottom of the column.

[0035] A "condenser" is required to provide a cooling step to condense the gas or vapor stream collected from the top of the concentrating column. The condensed vapor is partially refluxed back to the top of the column to increase the sharpness of the separation (the higher the reflux ratio, the better the separation). Condensers are classified as total condensers and partial condensers. In total condensers, all of the overhead vapor is condensed to liquid, while in partial condensers, only a portion of the vapor is condensed, the liquid is refluxed back to the column, and the uncondensed vapor is withdrawn for further processing. In this case, the partial condenser can be considered an additional VLE separation, while in total condensers, the product at the top of the column has the same composition as the reflux.

[0036] "Crude (unrefined) methanol" A refers to a solution containing methanol, typically 65-95% methanol, water, and other components. Crude methanol A contains low-boiling and high-boiling components (light and heavy ends). The light ends (L) primarily include dissolved gases (e.g., CO2), dimethyl ether, methyl formate, and acetone. The heavy ends (H) include higher alcohols, long-chain hydrocarbons, higher ketones, and esters of lower alcohols with formic acid, acetic acid, and propionic acid.

[0037] "Distillation" or "fractional distillation" or "fractionation" refers to the process of separating a liquid mixture into two or more vapor or liquid products of differing composition. Distillation is an equilibrium stage operation. In each stage, the vapor phase contacts the liquid phase, and mass transfers from vapor to liquid and from liquid to vapor. Less volatile "heavy" or "high-boiling" components concentrate in the liquid phase, while more volatile "light" components concentrate in the vapor. Separation is achieved through many successive stages, often with recycles. The feed to a distillation column can be liquid, vapor, or a mixture of liquid and vapor. It can be fed from any point within the column. Multiple streams may be fed to the system, and multiple products may be extracted. Vapors leaving the top of the column (e.g., T0, T1, T2, T3) pass through heat exchangers, where they are partially or fully condensed. The resulting liquid is temporarily held in an "accumulator" or reflux drum. A liquid stream is withdrawn from the drum and returned to the trays at the top of the column as reflux, furthering the separation.

[0038] "Equilibrium stage" or "theoretical plate" refers to an imaginary zone or stage in many separation processes, such as distillation, where two phases, such as the liquid and vapor phases of a substance, establish equilibrium with each other. Such equilibrium stages are sometimes called ideal stages or theoretical trays. The performance of many separation processes depends on having a series of equilibrium stages and is improved by providing more such stages. In other words, having more equilibrium stages increases the efficiency of the separation process.

[0039] The "feed" or "column feed" to a distillation column can be liquid, vapor, or a liquid-vapor mixture. It can enter at any point in the column, although the optimum feed tray location must be determined and used. Alternatively, more than one stream may be fed into the system, and more than one product may be extracted. The thermal requirements of the feed determine the internal column flow. If the feed is below its boiling point, heat is required to raise it to a vaporizable point. This heat must be obtained by condensing the vapor rising through the column, so the liquid flow down the column increases by the total amount of the feed and condensate, while the vapor flow up the column decreases.

[0040] The "gas streams" such as T0, T1, T2, or T3 recovered from the top of the stabilization column V0 and the concentrating columns, e.g., V1, V2, or V3, are streams resulting from the distillation process recovered from the upper portions of the columns. These streams consist primarily of methanol with increasingly lower impurity contents until the gas stream, e.g., T3, recovered from the final concentrating column, e.g., V3, has a very low impurity content. The mixed product stream of C1+C2+C3 is required to meet the required product specifications (e.g., grade AA).

[0041] "Heat load" or "load" refers to the amount of heat required to move from a hotter side to a colder side in a unit of time. There are usually two formulas for calculating heat load: a) one that can be used for sensible heat transfer, where the fluid does not undergo a phase change, and b) one that can be used for latent heat transfer, where the fluid does undergo a phase change, e.g., condensation.

[0042] "Heat exchanger" refers to a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing, or they may be in direct contact. In particular, "heat exchanger" refers to a reboiler / condenser, such as E0, E1, E2, or E3, for example, a tube bundle exchanger that evaporates a solution on the shell side and condenses a distillate on the tube side (or vice versa). Plate heat exchangers, in which the heat exchange plates are housed within the shell, can also be used.

[0043] A "partial reboiler" is a reboiler that vaporizes only a portion of the column base liquid. The vapor produced is returned to the column, and the liquid stream is removed as product or as feed to an additional column. The compositions of these three streams are different. A partial reboiler also provides an ideal separation stage. A sidestream reboiler can be used to withdraw liquid from a tray, heat it, and then return the vapor-liquid mixture to the same or a similar tray.

[0044] "Heavy by-products" or "sidestream" H refers to the stream containing higher alcohols and other by-products recovered from the final enrichment column, typically taken between the feed tray and the bottom of the column. This is also called "fusel oil" and contains water, residual methanol (about 1% of the total), and most of the by-products of the synthesis reaction. Fusel oil has a certain calorific value and is typically used as fuel or as feed to the synthesis gas generation section. Optionally, a fusel oil sidestream can also be extracted from an intermediate distillation stage.

[0045] "Intermediate products" refers to the vapor and liquid streams between and leaving the columns of the multi-stage distillation, apart from feed stream A, product streams C1, C2, C3, L, H and B3.

[0046] "Light by-products" or "light gases" or "light end" L means the gas stream obtained from the top of the stabilization column V0, preferably V0, and mainly contains dissolved gases (e.g., CO2), dimethyl ether, methyl formate and acetone.

[0047] "Methanol-containing liquid stream", e.g., B0, B1, B2 or B3, refers to the stream recovered from the bottom of stabilization column V0 and from concentrating columns such as V1, V2 and V3. As the distillation proceeds, the streams contain progressively lower amounts of methanol and higher amounts of water, until the final stream, e.g., B3, recovered from the last concentrating column, e.g., V3, contains mainly water and only residual amounts of methanol, preferably less than 50 ppm.

[0048] "Downstream" or "underflow" means the stream obtained or withdrawn from the bottom of a column such as V0, V1, V2 and V3.

[0049] "Pressure" P stands for gauge pressure and is measured in bar (g). Gauge pressure is a pressure relative to atmospheric pressure, being positive for pressures above atmospheric pressure and negative for pressures below atmospheric pressure. The difference between bar and bar (g) is the difference in the reference being considered. Pressure measurements are always made relative to a reference and correspond to the value obtained with a pressure measuring instrument. If the reference in a pressure measurement is a vacuum, absolute pressure is obtained and is measured only in bar. If the reference pressure is atmospheric pressure, pressure is given in bar (g).

[0050] "Products", e.g., C1, C2, C3, are the distilled methanol liquids recovered from the concentrating columns V1, V2, V3, etc.

[0051] "Reboiler" refers to a heat exchanger typically used to provide heat to the bottom of an industrial distillation column. A reboiler boils liquid from the bottom of the distillation column to generate vapor, which is then returned to the V0, V1, V2, V3, and other columns to drive the distillation separation. The heat provided to the column from the reboiler at the bottom is removed in the condenser at the top of the column. Reboilers are often shell-and-tube heat exchangers, and typically use steam as their heat source. However, other heat transfer media, such as hot synthesis gas, oil, or Dowtherm™, can also be used. Fuel-fired furnaces are also sometimes used as reboilers.

[0052] "Stream splitting" S means the separation of at least one original stream (liquid or gas) into two separate streams or substreams (liquid or gas). In the context of the present invention, S denotes the point where the gas stream T2 recovered from the top of V2 is split into two outlet streams or substreams: one stream or substream is condensed in heat exchanger E0 to provide energy to V0, and the other stream or substream is condensed in heat exchanger E3 to provide energy to rectifying column V3.

[0053] The "stabilization column" or topping column or pre-run column or V0 is used to separate the more volatile components from the heavier components in a crude product such as crude methanol.

[0054] "Volatile component" or "volatile substance" refers to a component or substance that readily vaporizes at low temperatures. Volatility can also refer to the tendency of a vapor to condense into a liquid or solid. Less volatile substances condense from vapors more easily than more volatile substances. Vapor pressure measures how easily a condensed phase forms a vapor at a given temperature. A substance enclosed in a sealed container initially has a vacuum (no air inside), and the vacant space quickly fills with vapor. This vapor pressure can be measured after the system reaches equilibrium and no more vapor is produced. Increasing the temperature increases the amount of vapor produced and therefore the vapor pressure. In a mixture, each substance contributes to the overall vapor pressure of the mixture, with more volatile compounds contributing more. The boiling point is the temperature at which a liquid's vapor pressure equals the ambient pressure and the liquid rapidly evaporates, or boils. It is closely related to vapor pressure but is pressure-dependent. The usual boiling point is the boiling point at atmospheric pressure, but boiling points at higher and lower pressures are sometimes reported.

[0055] "Upstream" or "overhead stream" means the stream obtained or withdrawn from the top of a column such as V0, V1, V2 and V3.

[0056] Preferred Embodiments (1) (i) pretreatment of a crude methanol stream A in a stabilization column V0 at a pressure P0 for the separation of volatile components, obtaining a light gas stream L from the top of V0 and a liquid methanol stream B0 from the bottom of V0, (ii) B0 is then directed to rectifying column V1 at pressure P1; (iii) gas stream T1 withdrawn from the top of V1 is condensed in heat exchanger E2 to provide energy to rectifying column V2; (iv) part of the condensed methanol obtained in step (iii) is sent to product C1, and the remainder of the condensed methanol is added to the top of V1 and used as reflux; (v) A liquid stream B1 comprising methanol is withdrawn from the bottom of V1 and passed through V2 at a pressure P2; (vi) gas stream T2 recovered from the top of V2 is split (S) into two separate streams, one stream being condensed in heat exchanger E0 to provide energy to V0, and the other stream being condensed in heat exchanger E3 to provide energy to rectifying column V3; (vii) part of the condensed methanol obtained in step (vi) is sent to product C2, and the remainder of the condensed methanol is added to the top of V2 and used as reflux; (viii) a liquid stream B2 comprising methanol is withdrawn from V2 and passed to V3 at a pressure P3; (ix) the gas stream T3 withdrawn from the top of V3 is condensed, part of the condensed methanol is sent to product C3, and the rest is added to the top of V3 and used as reflux; (x) one or more side streams H comprising higher alcohols and other minor by-products are withdrawn from V3, and a liquid stream B3 is withdrawn from V3; where columns V1, V2 and V3 operate at decreasing pressures such that P1>P2>P3, -P0>0barg and P3>0barg, - each column V0, V1, V2 and V3 is associated with a corresponding heat exchanger E0, E1, E2 and E3 which is a reboiler for the same column, heat exchangers E0 and E3 are condensers for column V2, heat exchanger E2 is a condenser for column V1, 1. A process for methanol distillation comprising: -P3<2 barg; and The method, characterized in that the heat exchanger E1 is supplied with energy from an external source.

[0057] (2) 2. The method of embodiment 1, wherein the temperature of the coldest portion of V2 is higher than the temperatures of the hottest portions of V3 and V0, and the temperature of the coldest portion of V1 is higher than the temperature of the hottest portion of V2.

[0058] (3) 3. The method of claim 1 or 2, wherein the temperature of the coldest part of V2 is preferably 4°C higher than the temperature of the hottest parts of V3 and V0, and the temperature of the coldest part of V1 is preferably 4°C higher than the hottest part of V2.

[0059] (4) 4. The method according to any one of the preceding embodiments, wherein the difference between P1 and P0 is 7.7 bar or more.

[0060] (5) 5. The method according to any one of the preceding claims, wherein P1 is higher than 9.7 bar(g) and P2 is comprised between 6.9 and 13 bar(g).

[0061] (6) 6. The method according to any one of embodiments 1 to 5, wherein P1 is preferably 17 bar(g), P2 is preferably 9 bar(g), and P3 is preferably 0.98 bar(g).

[0062] (7) 7. The method according to any one of the preceding embodiments, wherein the thermal load of E0 is at least 30% less than the load of E1.

[0063] (8) 8. The method according to any one of the preceding embodiments, wherein B3 is water removed from the circulation stream and recovered from the bottom of V3.

[0064] (9) 9. The method of any one of embodiments 1 to 8, wherein the crude product distilled is ethanol or other suitable product.

[0065] (10) 1. An apparatus for the distillation of methanol, comprising a stabilization column V0 of pressure P0 connected in series with at least three distillation columns V1, V2 and V3 of correspondingly decreasing pressures P1, P2 and P3, wherein each column is associated with a heat exchanger E0, E1, E2 and E3, said heat exchanger being a reboiler for that column, a) Heat exchangers E0 and E3 are the condensers of column V2; b) heat exchanger E2 is the condenser of column V1; c) E1 has a heat flow into the exterior of the device; d) P3<2 barg; The device, characterized in that

[0066] (11) 11. The apparatus of embodiment 10, wherein the external heat flow to E1 is steam or syngas containing sensible heat.

[0067] (12) 12. An apparatus according to embodiments 10 and 11, wherein the crude product to be distilled is ethanol or other suitable product.

[0068] (13) 12. A plant for the distillation of methanol according to any one of embodiments 1 to 9, comprising at least one apparatus according to any one of embodiments 10 to 11, wherein the amount of steam required for E1 is less than 1.3 kg / kg of product methanol.

[0069] (14) Use of the apparatus according to any one of embodiments 10-11 for the distillation of methanol according to any one of embodiments 1-9 in a plant according to embodiment 13.

[0070] (15) Use of the method, apparatus and plant according to embodiments 1 to 13, comprising N concentration columns V1, V2, V3 and up to Vn, connected to a stabilization column V0 at a pressure P0, with the pressures decreasing in the order P1>P2>P3; where: A: crude methanol feed; B0-Bn: methanol-containing liquid streams recovered from the bottom of columns V0-Vn; C1-Cn: products, for example, liquid distilled methanol; E0~En: energy flows, especially heat exchangers; T0-Tn: gas streams recovered from the tops of columns V0-Vn; L: light gas flow from the ballast; H: heavy side stream recovered from final concentrator Vn; S: Split stream Tn-1 into two sub-streams, condense one sub-stream in heat exchanger E0 to supply energy to V0, and condense the other sub-stream in heat exchanger En to supply energy to rectifying column Vn; V0: Stabilization tower; V1~Vn: Concentration tower; where - The columns V1, V2 and Vn operate at decreasing pressures, such that P1>P2 and Pn; -P0>0barg, Pn>0barg, - Each column V0, V1, V2, Vn corresponds to a heat exchanger E0, E1, E2, En, which is the reboiler of the same column, - heat exchanger E0 and En is a condenser for column Vn-1; Heat exchanger E2 is the condenser for column V1. And here, - Pn<2barg; and - Heat exchanger E1 is supplied from an external energy source. The present invention includes the following items. [Item 1] (i) pretreatment of a crude methanol stream A in a stabilization column V0 at a pressure P0 for the separation of volatile components, obtaining a light gas stream L from the top of V0 and a liquid methanol stream B0 from the bottom of V0, (ii) B0 is then directed to rectifying column V1 at pressure P1; (iii) gas stream T1 withdrawn from the top of V1 is condensed in heat exchanger E2 to provide energy to rectifying column V2; (iv) part of the condensed methanol obtained in step (iii) is sent to product C1, and the remainder of the condensed methanol is added to the top of V1 and used as reflux; (v) A liquid stream B1 comprising methanol is withdrawn from the bottom of V1 and passed through V2 at a pressure P2; (vi) gas stream T2 recovered from the top of V2 is split (S) into two separate streams, one stream being condensed in heat exchanger E0 to provide energy to V0, and the other stream being condensed in heat exchanger E3 to provide energy to rectifying column V3; (vii) part of the condensed methanol obtained in step (vi) is sent to product C2, and the remainder of the condensed methanol is added to the top of V2 and used as reflux; (viii) a liquid stream B2 comprising methanol is withdrawn from V2 and passed to V3 at a pressure P3; (ix) the gas stream T3 withdrawn from the top of V3 is condensed, part of the condensed methanol is sent to product C3, and the rest is added to the top of V3 and used as reflux; (x) one or more side streams H comprising higher alcohols and other minor by-products are withdrawn from V3, and a liquid stream B3 is withdrawn from V3; where - columns V1, V2 and V3 operate at decreasing pressures such that P1>P2>P3, - P0>0 barg and P3>0 barg; - each column V0, V1, V2 and V3 is associated with a corresponding heat exchanger E0, E1, E2 and E3 which is a reboiler for the same column, heat exchangers E0 and E3 are condensers for column V2, heat exchanger E2 is a condenser for column V1, 1. A process for methanol distillation comprising: -P3<2 barg; and - the method, characterized in that the heat exchanger E1 is supplied with energy from an external source. [Item 2] Item 1, the method according to item 1, characterized in that the temperature of the coldest part of V2 is higher than the temperatures of the hottest parts of V3 and V0, and the temperature of the coldest part of V1 is higher than the temperature of the hottest part of V2. [Item 3] 3. The method according to item 1 or 2, wherein the temperature of the coldest part of V2 is preferably 4°C higher than the temperature of the hottest parts of V3 and V0, and the temperature of the coldest part of V1 is preferably 4°C higher than the hottest part of V2. [Item 4] 4. The method according to any one of items 1 to 3, wherein the difference between P1 and P0 is 7.7 bar or more. [Item 5] 5. The method according to any one of items 1 to 4, wherein P1 is higher than 9.7 bar(g) and P2 is comprised between 6.9 and 13 bar(g). [Item 6] 6. The method according to any one of items 1 to 5, wherein P1 is preferably 17 bar(g), P2 is preferably 9 bar(g), and P3 is preferably 0.98 bar(g). [Item 7] 7. The method according to any one of items 1 to 6, wherein the thermal load of E0 is at least 30% less than the load of E1. [Item 8] 8. The method according to any one of items 1 to 7, wherein B3 comprises water removed from the circulation stream and is collected from the bottom of V3. [Item 9] 1. An apparatus for the distillation of methanol, comprising a stabilization column V0 of pressure P0 connected in series with at least three distillation columns V1, V2 and V3 of correspondingly decreasing pressures P1, P2 and P3, wherein each column is associated with a heat exchanger E0, E1, E2 and E3, said heat exchanger being a reboiler for that column, a) Heat exchangers E0 and E3 are the condensers of column V2; b) heat exchanger E2 is the condenser of column V1; c) E1 has a heat flow into the exterior of the device; d) P3<2 barg; The device, characterized in that [Item 10] 10. The apparatus of item 9, wherein the external heat flow to E1 is steam or synthesis gas containing sensible heat. [Item 11] 11. A plant for the distillation of methanol according to any one of items 1 to 8, comprising at least one apparatus according to any one of items 9 to 10, wherein the amount of steam required for E1 is less than 1.3 kg / kg of product methanol. [Item 12] Use of the apparatus according to any one of items 9 to 10 in the plant according to item 11 for the distillation of methanol according to any one of items 1 to 8.

Claims

1. (i) pretreating a crude methanol stream A in a stabilization column V0 at a pressure P0 for the separation of volatile components, obtaining a light gas stream L from the top of V0 and a liquid methanol stream B0 from the bottom of V0, (ii) B0 is then directed to rectifying column V1 at pressure P1; (iii) gas stream T1 withdrawn from the top of V1 is condensed in heat exchanger E2 to provide energy to rectifying column V2; (iv) a part of the condensed methanol obtained in step (iii) is sent to product C1, and the rest of the condensed methanol is added to the top of V1 and used as reflux; (v) A liquid stream B1 comprising methanol is withdrawn from the bottom of V1 and passed through V2 at a pressure P2; (vi) gas stream T2 withdrawn from the top of V2 is split (S) into two separate streams, one stream being condensed in heat exchanger E0 to provide energy to V0, and the other stream being condensed in heat exchanger E3 to provide energy to rectifying column V3; (vii) a part of the condensed methanol obtained in step (vi) is sent to product C2, and the rest of the condensed methanol is added to the top of V2 and used as reflux; (viii) a liquid stream B2 comprising methanol is withdrawn from V2 and passed to V3 at pressure P3; (ix) the gas stream T3 recovered from the top of V3 is condensed, part of the condensed methanol is sent to product C3, and the rest is added to the top of V3 and used as reflux; (x) one or more side streams H comprising higher alcohols and other minor by-products are removed from V3, and a liquid stream B3 is removed from V3; where - columns V1, V2 and V3 operate at decreasing pressures such that P1>P2>P3, - P0>0 barg and P3>0 barg, - each column V0, V1, V2 and V3 is associated with a corresponding heat exchanger E0, E1, E2 and E3 which is the reboiler for the same column; heat exchangers E0 and E3 are condensers for column V2, - heat exchanger E2 is the condenser for column V1, 1. A process for methanol distillation comprising: - P3 < 2 barg; and - the process as described above, characterized in that the heat exchanger E1 is supplied with energy from an external source.

2. 2. The method of claim 1, wherein the temperature of the coldest portion of V2 is higher than the temperature of the hottest portions of V3 and V0, and the temperature of the coldest portion of V1 is higher than the temperature of the hottest portion of V2.

3. 3. The method of claim 1 or 2, wherein the temperature of the coldest part of V2 is 4°C higher than the temperature of the hottest parts of V3 and V0, and the temperature of the coldest part of V1 is 4°C higher than the hottest part of V2.

4. 4. The method according to claim 1, wherein the difference between P1 and P0 is 7.7 bar or more.

5. 5. The method according to claim 1, wherein P1 is higher than 9.7 bar (g) and P2 is comprised between 6.9 and 13 bar (g).

6. 6. The method according to claim 1, wherein P1 is 17 bar (g), P2 is 9 bar (g), and P3 is 0.98 bar (g).

7. 7. The method according to claim 1, wherein the thermal load of E0 is at least 30% less than the load of E1.

8. 8. The process of claim 1, wherein B3 comprises water removed from the recycle stream and is recovered from the bottom of V3.

9. 1. An apparatus for the distillation of methanol, comprising a stabilization column V0 of pressure P0 connected in series with at least three distillation columns V1, V2 and V3 of correspondingly decreasing pressures P1, P2 and P3, wherein each column is associated with a heat exchanger E0, E1, E2 and E3, said heat exchanger being a reboiler for that column, a) heat exchangers E0 and E3 are condensers of column V2; b) heat exchanger E2 is the condenser of column V1; c) E1 has a heat flow into the exterior of the device; d) P3<2 barg; The device, characterized in that

10. 10. The apparatus of claim 9, wherein the external heat flow to E1 is steam or syngas containing sensible heat.

11. 11. A plant for the distillation of methanol according to any one of claims 1 to 8, comprising at least one apparatus according to any one of claims 9 to 10, in which the amount of steam required for E1 is less than 1.3 kg / kg of product methanol.

12. Use of the device according to any one of claims 9 to 10 in a plant according to claim 11 for the distillation of methanol according to any one of claims 1 to 8.

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