METHOD AND SYSTEM FOR RECYCLING DISTILLATION ENERGY IN PLANTS WITH CO2 IMPORT FROM CARBON CAPTURE

Abstract

The present invention relates to a method, a system, and a plant for reducing energy consumption, preferably a green methanol plant. The present invention provides a reduced overall energy consumption of the green plant—through the reuse of distillation energy in the stabilizer column and the CO2 reboiler in the carbon capture unit—and consequently, reduced electricity import for the heater / boiler or reduced fuel consumption for steam generation.

Description

The present invention relates to a method, a system, and a plant for reducing energy consumption, preferably a green methanol plant. Background of the Invention The product of plant-based methanol synthesis, commonly defined as crude methanol, is known to be an aqueous solution of methanol containing byproducts of the synthesis reaction, including ethanol, ketones, higher alcohols, and some dissolved gases, mainly including H2, CO, CO2, N2, and CH4. Known distillation processes are substantially based on one or more distillation columns, where typically at least one column is capable of separating light products (e.g., gas) recovered at the top of the methanol column, and at least one column is capable of separating the heavier product (e.g., aqueous solution) recovered at the bottom of the methanol column. One specific method, widely used for methanol distillation, comprises two columns operating at or near atmospheric pressure. More specifically, the method uses a pretreatment column, known as a stabilization column or pre-run column, and a second distillation column. The first column is designed to substantially separate the more volatile components of the crude methanol. It receives the crude methanol and separates the lighter components at the top, leaving an aqueous solution at the bottom.The second column, known as the concentration column, carries out the actual distillation to obtain (i) refined methanol at the top, (ii) a predominantly aqueous stream at the bottom (bottom water), and (iii) a secondary stream known as fusel oil, which contains mainly water, residual methanol (approximately 1% of the total), and most of the byproducts of the synthesis reaction. Fusel oil has some calorific value and is typically used as fuel or feedstock for synthesis gas generation. Each column comprises a reboiler that heats the bottom of the column and maintains the heat input for the distillation process. Each column also comprises a condenser, which condenses the top product and recycles it (at least partially) back to the column. Heat is supplied to the concentration (or distillation) column by steam, or by a process gas—when available—of the appropriate temperature. The cooling medium for the condenser is normally water or air. The two-column configuration is simple in terms of a plant (e.g., a methanol distillation plant), but has the major disadvantage of consuming a substantial amount of energy, both due to the heat supplied to the bottom reboilers and the cooling water and / or electricity consumption of the top condensers.On the other hand, the columns have a relatively large diameter in relation to the production capacity and the cost of the plant is consequently high. The standard solution shown in Figure 1 is based on a low-pressure concentrating column, and the generated methanol vapor is condensed by a water cooler. For larger plants, the concentrating column is divided into two or three distillation columns with gradually increasing pressure levels to reuse the overhead distillate yield as the reboiler yield in the next column. Typically, the heat required for methanol distillation and CO2 removal is supplied primarily or entirely by steam. However, there is a need to find more sustainable ways to work in methanol production, which provide for reuse and / or energy savings. The burning of fossil fuels generates more than 13 billion tons (13 gigatons) of CO2 annually. Concern about the effects of CO2 on climate change and ocean acidification has led governments and industries to investigate the feasibility of technologies that capture the CO2 entering the carbon cycle. However, existing power plants require post-combustion separation of CO2 from the exhaust gas using a scrubber. In this system, fossil fuels are burned with air, and the CO2 is selectively removed from a gas mixture that also contains N2, H2O, O2, and trace impurities of sulfur, nitrogen, and metals. While the exact separation conditions depend on the fuel and technology, CO2 is generally present in low concentrations (4–15% v / v) in gas mixtures near atmospheric pressure and at temperatures of approximately -60°C.Carbon capture sorbents are regenerated by means of temperature, pressure or vacuum, so that CO2 can be collected for sequestration or utilization and the sorbent can be reused. The most significant impediment to carbon capture is the large amount of electricity required. Without policies or tax incentives, the electricity produced by these plants is not competitive with other energy sources. The largest operating cost for carbon capture power plants is the reduction in the amount of electricity produced,[6] because energy in the form of steam is diverted from turbine power generation to regenerate the sorbent. Thus, minimizing the amount of energy required for sorbent regeneration is the primary objective behind much of the research on carbon capture. The present invention (Figure 2) follows a similar principle to the standard solution mentioned above, but operates the concentration column at a higher pressure, preferably between approximately 200 and 1000 kPa (gauge pressure) (2 to 10 barg), for the purpose of reusing the overhead distillate yield. Operating the column at a higher pressure increases the boiling point of the liquids at various locations in the column. A higher boiling point temperature, between approximately 110 and 190 degrees Celsius, is targeted. A higher temperature is required in the heat exchanger D, such as the reboiler (for imported steam), but the condensation temperature in the overhead distillate heat exchanger C, such as a reboiler, is also increased, allowing the heat to be used elsewhere, such as for CO2 reboiler output or district heating. Since green distillation plants are small, there is typically only one concentration column in this type of plant, and the yield cannot be reused in a second concentration column. Instead, the overhead distillate yield is at least partially reused in the CO2 reboiler to recycle this energy and minimize waste. Brief Description of the Figures Figure 1 shows the standard solution for methanol production in a green methanol plant, with CO2 scrubbing. Figure 2 shows a preferred embodiment of the present invention for the production of methanol in a green methanol plant, with CO2 scrubbing. Reference Numbers: (1) - hot head distillate stream comprising methanol vapor (2) - heat supplied from heat exchanger C to CO2 scrubbing unit A (3) - vapor stream Definitions Atmospheric pressure means 101.325 kPa (1.01325 bar), that is approximately 100 kPa (1 bar). Carbon capture refers to the method of capturing carbon dioxide from a stream, typically exhaust gas, but also pressurized process gas. The method involves an absorption device where a liquid sorbent is in contact with the gas and selectively absorbs the CO2. The CO2-laden sorbent is then sent to a scrubber where the CO2 is purified by the use of heat so that the CO2 exits the scrubber in a concentrated form. Carbon dioxide sorbent means a sorbent agent that is capable of absorbing CO2. A carbon dioxide sorbent can be physical, such as a porous material, or chemical, such as aqueous amine solutions that form a chemical bond. A carbon dioxide scrubbing unit is a unit for the desorption of captured CO2. Typically, it is a column where the loaded CO2 solution is boiled to remove the captured CO2. Chemical sorbent means a sorbent agent that absorbs CO2 and forms a chemical bond with the active component and CO2. A concentration column, distillation column, or bottoms column refers to a column divided into a series of stages. These correspond to a cascade of equilibrium stages. The liquid flows down the column from stage to stage and comes into contact with the upward-flowing vapor. Traditionally, most columns have been constructed from a set of different trays or plates, so these terms have become essentially interchangeable with "stages." Each tray in a distillation column is designed to promote vapor-liquid contact within that stage. Distillation can be conducted in a packed column (just as absorption can be performed in a tray column). The column's operating pressure is typically controlled by adjusting the heat removal in the heat exchanger. The base of the column is typically used as a reservoir to hold the liquid exiting the bottom tray.A heat exchanger, such as a reboiler, is used to boil this liquid. The resulting vapor, the product that is boiled, is returned to the bottom of the column. Crude methanol is distilled to meet market-required purity specifications. Crude methanol is a solution comprising methanol, typically 65 to 95% methanol, water, and other components. Crude methanol contains both 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, acetic, and propionic acids. For example, the Grade A1 specification requires a minimum methanol concentration of 99.85% by weight, where the ethanol content must not exceed 10 ppm by weight.Distillation is a method for separating liquid mixtures into two or more vapor or liquid products with different compositions. Distillation is an equilibrium-stage operation. In each stage, a vapor phase is brought into contact with a liquid phase, and the flow is from vapor to liquid and from liquid to vapor. The less volatile, heavier, or high-melting-point components concentrate in the liquid phase; the more volatile, lighter components concentrate in the vapor. Separation can be achieved by using multiple stages in series with recirculation. The feed to a distillation column can be a liquid, a vapor, or a liquid-vapor mixture. It can enter at any point in the column. More than one stream can be fed to the system, and more than one product can be extracted.Distillation in the concentration column typically takes place at the lowest possible pressure, but in the present invention the pressure is increased to recover heat. A green methanol plant means a plant that uses renewable H2 as fuel. Heat efficiency, or efficiency, means the amount of heat required for transfer from a hot side to a cold side during a unit of time. The equation for calculating heat efficiency is normally written in two ways: a) one that can be used for sensible heat transfer, meaning the fluid does not undergo a phase change; b) the other that can be used for latent heat transfer, meaning the fluid undergoes a phase change, i.e., condenses. A heat exchanger is 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, a heat exchanger means a reboiler / condenser, such as a tube bundle heat exchanger, for example, with evaporation of the solution on the jacket side and condensation of the distillate on the tube side (or vice versa). It is also possible to use a plate heat exchanger with heat exchange plates housed within a jacket. Heavy by-products or secondary streams H refers to a stream comprising higher alcohols and other minor byproducts recovered from the last concentration column—typically taken between the feed tray and the bottom of the column. Also known as fusel product, it comprises water, residual methanol (approximately 1% of the total), and most of the synthesis reaction byproducts. Fusel oil has a certain calorific value and is normally used as a fuel or feedstock for a synthesis gas generation section. Secondary fusel oil streams can also be extracted, if suitable, from intermediate distillation stages. High-pressure distillation refers to a distillation method that operates above normal operating pressure. Typically, methanol distillation is operated at low pressures to facilitate component separation, but high-pressure distillation operates at elevated pressures, such as above 200 kPa (gauge pressure) (2 barg). Loaded carbon dioxide sorbent means a solution comprising captured CO2. Methanol synthesis gas (MeOH) means synthetic gas containing components for the synthesis of MeOH, a mixture of H2, CO and CO2 (alternatively just H2 and CO2). Overhead distillate yield means the heat transferred that is achieved by condensing the methanol vapor at the top of the column, for example, a concentration column. A partial reboiler is a reboiler where only a portion of the liquid at the bottom of the column is evaporated. The vapor produced is returned to the column, and the liquid stream is removed as product or used as feed to an additional column. The compositions of these three streams are different. Partial reboilers also provide an ideal separation stage. Side-stream reboilers can be used, which draw liquid from a tray, heat it, and then return the vapor-liquid mixture to the same or similar trays. Physical sorbent means a sorbent that absorbs CO2 without forming a chemical bond with the active component and CO2. Pressure, P, stands for gauge pressure and is measured in kPa (gauge pressure) (bar(g)). Gauge pressure is the pressure relative to atmospheric pressure and is positive for pressures above atmospheric pressure and negative for pressures below it. The difference between kPa (bar) and kPa (gauge pressure) (bar(g)) is the difference in the reference pressure. Pressure measurements are always taken against a reference pressure and correspond to the value obtained from a pressure measuring instrument. If the reference pressure is a vacuum, the result is absolute pressure, measured in kPa (bar). If the reference pressure is atmospheric pressure, then the pressure is quoted in kPa (gauge pressure) (bar(g)). Crude methanol product means a liquid product directly from the synthesis in step (d) in the method of the present invention, mainly methanol, but also water, by-products, and dissolved gases. A reboiler is a heat exchanger typically used to provide heat to the bottom of industrial distillation columns. Reboilers boil the liquid at the bottom of a distillation column to generate vapors, which are then returned to the column to further the distillation process. The heat supplied to the column by the reboiler at the bottom is removed by the condenser at the top. Most reboilers are of the jacketed-tube type, and steam is normally used as the heat source. However, other heat transfer fluids such as hot synthesis gas, oil, or Dowtherm™ can be used. In some cases, fuel-fired furnaces can also be used as reboilers. The stabilization column, or stacking column, or pre-run column is for separating the more volatile components from the heavier components, both contained in the crude product, such as crude methanol. Volatile components or volatile substances are those that readily evaporate at low temperatures. Volatility can also describe the tendency of a vapor to condense into a liquid or solid: less volatile substances will condense more readily from a vapor than highly volatile substances. Vapor pressure is a measure of how readily a condensed phase forms a vapor at a given temperature. A substance enclosed in a sealed container initially under vacuum (with no air inside) will quickly fill any empty space with vapor. After the system reaches equilibrium and no more vapor forms, this vapor pressure can be measured. Increasing the temperature increases the amount of vapor formed and thus the vapor pressure. In a mixture, each substance contributes to the overall vapor pressure of the mixture, with more volatile compounds making a larger contribution.The boiling point is the temperature at which the vapor pressure of a liquid equals the surrounding pressure, causing the liquid to evaporate rapidly, or boil. It is closely related to vapor pressure but is pressure-dependent. The normal boiling point is the boiling point at atmospheric pressure, but it can also be reported at higher and lower pressures. Top current or highest current means a current obtained or recovered from the top section of a column. Description of the Invention The present invention provides a reduced total energy consumption of the green plant (reuse of distillation energy in the stabilizing column and CO2 reboiler in the carbon capture unit) and consequently a reduced electrical import for the heater / boiler (or reduced fuel consumption in steam generation). The present invention uses one or more columns for distillation, wherein the column at the highest pressure is connected to at least one CO2 scrubbing unit. One or more of the columns comprise a stabilization column V0, at pressure P0, connected in series with at least one distillation column VI, at pressure Pl, wherein each column is associated with a heat exchanger E0 and El, the heat exchanger being a reboiler for that column, characterized in that, a) El has an incoming heat stream external to the apparatus; d) Pl > 200 kPa (gauge pressure) (2 barg). One purpose of the present invention is to reduce the energy input for green methanol plants. A standard design has been developed where the plant consists of an electrolyzer, carbon capture unit, methanol synthesis unit, and methanol distillation unit. Both traditional carbon capture and methanol distillation units require heat to drive CO2 scrubbing (e.g., in a carbon capture unit) and crude methanol distillation. Normally, this heat is supplied by steam, and since excess steam is not readily available in a typical green methanol plant, this steam must be generated by electricity (if CO2 emissions are to be minimized) or, alternatively, by burning fuel to generate the steam.By switching to a high-pressure distillation step, the overhead distillate yield obtained from the overhead distillate stream (1) in the concentration column can be used as reboiler yield in the CO2 scrubbing process (in a carbon capture unit) and alternatively also in the stabilizing column within the methanol distillation or can be supplied for district heating. Preferably, the operating pressure in the concentration column is higher than or approximately 200 kPa (gauge pressure) (2 barg). The main advantage of the present invention is the reduced total energy consumption, i.e., approximately the same amount of heat sent to the concentration column can be reused in the CO2 reboiler. Examples Example 1 Energy consumption in the CO2 scrubber and methanol distillation Table 1. Comparison of energy consumption in the CO2 scrubber and methanol distillation for a traditional design versus the new invention with energy reuse of the MeOH vapor from the overhead distillate of the concentration column. Total steam import is reduced to 61% of the standard solution. In this case, the heat reuse is directed to the CO2 scrubber reboiler; alternatively, it could also replace the steam in the stabilizer reboiler or be used for district heating. Heating Source Unit Standard Solution Invention CO2 Scrubber (Steam) Efficiency Steam MW 8.7 0.6 CO2 Scrubber (MeOH) Efficiency MeOH MW 0.0 8.1 Stabilizer Reboiler Efficiency Steam MW 1.2 1.2 Concentrator Column Efficiency Steam MW 6.9 8.5 Total Steam Consumption MW 16.8 10.3 Total Steam Consumption % 100 61 By using the method, system and plant of the present invention, the total steam consumption is therefore significantly reduced, in this particular case by approximately 39%, in relation to the standard solution.

Claims

1. A method for preparing methanol, comprising the steps of: (a) capturing carbon dioxide by means of a carbon dioxide sorbent and forming a loaded carbon dioxide sorbent; (b) passing the loaded carbon dioxide sorbent to a carbon dioxide purification unit A; (c) providing a methanol synthesis gas comprising hydrogen and carbon dioxide; (d) passing the methanol synthesis gas from step (c) to a methanol synthesis unit and forming a crude methanol product; (e) purifying the crude methanol product in a distillation unit B comprising at least one distillation column, obtaining a hot-head distillate stream (1) from at least the distillation column, characterized in that the hot-head distillate stream (1) provides heat for heating the heat exchanger C and at least part of the heat (2) is supplied to at least oneCarbon dioxide scrubbing unit A is used to scrub carbon dioxide from the loaded carbon dioxide sorbent, thereby condensing stream (1) into liquid methanol. The entire overhead distillate stream (1) will preferably be reused. Either 100% will be used in scrubbing unit A, or less than 100%, with the remainder being reused elsewhere (e.g., either as stabilizer reboiler yield or for district heating). It is also possible for 100% of the heat or yield from the overhead distillate (1) to be used in the CO2 scrubbing unit, but this would require additional steam.

2. A method according to modality 1, wherein the methanol synthesis gas in step (c) comprises hydrogen obtained partially or totally from electrolysis.

3. A method according to modality 1, wherein the methanol synthesis gas in step c) comprises hydrogen obtained from sources other than electrolysis.

4. A method according to modality 1, wherein the heat (2) supplied to at least one carbon dioxide scrubbing unit A is approximately between 20 and 100%, preferably between 45% and up to 100% of the energy requirements in the scrubbing unit.

5. A method according to modality 1, wherein the heat (2) supplied to the carbon dioxide scrubbing unit A is additionally supplied by steam (3). The stream (1) required for the CO2 scrubber is fixed. While stream (1) nftzonn / cznz / B / viAi is supplied from the distillation, the required imported steam is reduced accordingly.

6. A method according to modality 1, wherein the carbon dioxide sorbent in step (a) is a physical or chemical sorbent.

7. A method according to modality 1, wherein the methanol synthesis gas further comprises carbon monoxide.

8. A method according to modality 1, wherein the carbon dioxide in step (a) originates from exhaust gas and / or synthesis gas.

9. A method according to modality 1, wherein part or all of the hot-head distillate stream (1) is supplied for district heating.

10. A method according to modality 1 or 9, wherein part of the hot-head distillate stream (1) is supplied to the stabilization reboiler.

11. A system for the preparation of methanol according to any of embodiments 1 to 10, comprising at least one CO2 purification unit A, at least one methanol distillation unit B,at least one overhead distillate heat exchanger unit C fluidly connected to at least one heat exchanger unit D, units A, B, C, and D being arranged such that a crude methanol product is purified in a distillation unit B comprising at least one distillation column, a hot overhead distillate stream (1) is obtained from at least the distillation column, wherein the hot overhead distillate stream (1) supplies heat to heat exchanger C and at least part of the heat (2) is supplied to at least one carbon dioxide scrubbing unit A to scrub carbon dioxide from the loaded carbon dioxide sorbent, thereby condensing the stream (1) into liquid methanol.

12. A system according to embodiment 11, wherein units A, B,C and D are arranged such that a portion or all of the hot-head distillate stream (1) is supplied for district heating.

13. A system according to any embodiment 11 or 12 wherein units A, B, C, and D are arranged such that a portion of the hot-head distillate stream (1) is supplied to the stabilization reboiler.

14. A plant with CO2 import from carbon capture comprising a system according to any of embodiments 11 to 13 for the preparation of methanol according to any of embodiments 1 to 10. nftzonn / cznz / B / viAi CLAIMS 1. A method for the preparation of methanol,characterized in that it comprises the steps of: (a) capturing carbon dioxide by means of a carbon dioxide sorbent and forming a charged carbon dioxide sorbent; (b) passing the charged carbon dioxide sorbent to a carbon dioxide purification unit A; (c) providing a methanol synthesis gas comprising hydrogen and carbon dioxide; (d) passing the methanol synthesis gas from step (c) to a methanol synthesis unit and forming a crude methanol product; (e) purifying the crude methanol product in a distillation unit B comprising at least one distillation column, obtaining a hot-head distillate stream (1) from at least the distillation column, characterized in that the hot-head distillate stream (1) provides heat for heating the heat exchanger C and at least part of the heat (2) is supplied to at least oneA carbon dioxide scrubbing unit A for scrubbing carbon dioxide from the loaded carbon dioxide sorbent, thereby condensing the stream (1) into liquid methanol.

2. A method according to claim 1, characterized in that the methanol synthesis gas in step (c) comprises hydrogen obtained partially or wholly from electrolysis.

3. A method according to claim 1, characterized in that the methanol synthesis gas in step (c) comprises hydrogen obtained from sources other than electrolysis.

4. A method according to claim 1, characterized in that the heat (2) supplied to at least one carbon dioxide scrubbing unit A is approximately between 20% and 100%, preferably between 45% and up to 100%, of the energy requirements in the scrubbing unit.

5. A method according to claim 1,characterized in that the heat (2) supplied to the carbon dioxide scrubbing unit A is additionally supplied by steam (3).

6. A method according to claim 1, characterized in that the carbon dioxide sorbent in step (a) is a physical or chemical sorbent.

7. A method according to claim 1, characterized in that the methanol synthesis gas further comprises carbon monoxide.

8. A method according to claim 1, characterized in that the carbon dioxide in step (a) originates from the exhaust gas and / or synthesis gas / b / v.

9. A method according to claim 1, characterized in that part or all of the hot head distillate stream (1) is supplied for district heating.

10. A method according to claim 1 or 9, characterized in that part of the hot head distillate stream (1) is supplied to the stabilization reboiler.

11. A system for the preparation of methanol according to any one of claims 1 to 10, characterized in that it comprises at least one CO2 scrubbing unit A, at least one methanol distillation unit B, at least one overhead distillate heat exchanger unit C fluidly connected to at least one heat exchanger unit D, units A, B, C and D being arranged such that a crude methanol product is purified in a distillation unit B comprising at least one distillation column, a hot overhead distillate stream (1) is obtained from at least the distillation column, wherein the hot overhead distillate stream (1) supplies heat to the heat exchanger C and at least part of the heat (2) is supplied to at least one carbon dioxide scrubbing unit A for scrubbing carbon dioxide from the loaded carbon dioxide sorbent,which consequently condenses stream (1) into liquid methanol.

12. A system according to claim 11, characterized in that units A, B, C and D are arranged in such a way that part or all of the hot head distillate stream (1) is supplied for district heating.

13. A system according to any of claims 11 or 12, characterized in that units A, B, C and D are arranged in such a way that a portion of the hot head distillate stream (1) is supplied to the stabilization reboiler.

14. A plant with CO2 import from carbon capture, characterized in that it comprises a system according to any of claims 11 to 13 for the preparation of methanol according to any of claims 1 to 10.