An apparatus and method for concentrating bioethanol by absorption condensation heat coupled rectification

Abstract

The application provides a device and a method for concentrating bioethanol by absorption condensation coupled rectification, and belongs to the field of chemical engineering technology.The device comprises a vacuum rectification tower (T101), an absorption condensation tower (T102), a regeneration tank (V101), a reboiler (R101) and the like.The vacuum rectification tower (T101) and the absorption condensation tower (T102) implement a heat coupling technology, and a high-cost refrigerant is not used to condense ethanol-water vapor (3) at the top of the vacuum rectification tower (T101).The ethanol-water vapor (3) at the top enters the absorption condensation tower (T102) and is absorbed by circulating absorbent (9).In the absorption process, heat needs to be removed to ensure the absorption effect.The removed heat can be used to further supply heat for the vacuum rectification tower (T101), so that the external heat source input of the vacuum rectification tower (T101) is reduced or even completely replaced.Compared with a traditional vacuum rectification mode, the device reduces the amount of utilities, and reduces the operation cost by more than 30%.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically relating to an apparatus and method for the absorption, condensation, thermal coupling, distillation, and concentration of bioethanol. Background Technology

[0002] Distillation is a commonly used separation method in chemical engineering. When concentrating bioethanol using distillation, the reboiler temperature needs to be controlled below 30°C to avoid damage to yeast cells from the high temperature in the reboiler. At this temperature, the operating pressure at the top of the column is approximately 1 kPa, and the top temperature is approximately 5°C. When the top temperature is low, the circulating water condensation is insufficient, often requiring the use of refrigerant, which significantly increases operating costs. Absorption condensation technology does not use expensive refrigerants and utilizes the heat removed during the absorption process to heat the distillation column. Therefore, by thermally coupling the distillation and absorption processes, the proposed absorption condensation thermally coupled distillation process can significantly reduce operating costs.

[0003] Patent CN106215445 discloses a combined evaporation / stripping absorption module that concentrates alcohol in fermentation broth through three steps: evaporation, absorption, and heat transfer. This module can preferentially remove ethanol from the ethanol-water mixture while simultaneously cooling the mixture. However, this method only uses LiBr brine as the absorbent, and the equipment is relatively complex.

[0004] Patent CN102070401 discloses an energy-saving process for producing anhydrous ethanol from a bioethanol aqueous solution. This process utilizes the heat contained in the material of the preceding distillation column to provide a heat source for the next distillation column, with any shortfall supplemented by an air-source heat pump system. Furthermore, it uses the unused waste heat from the distillation column discharge to preheat the ethanol aqueous solution raw material, forming a thermally coupled network. However, this method results in a relatively high temperature at the bottom of the column, which can easily damage yeast cells.

[0005] Patent CN108046989 discloses an equipment and method for purifying bioethanol, which mainly employs a pre-separation tower, an azeotropic distillation tower, an azeotropic agent recovery tower, a compressor, and a phase separator. Bioethanol-water solution is sequentially separated by three distillation towers to obtain anhydrous ethanol with a mass fraction of 99.9% or higher. However, this process involves high reboiler temperatures and a complex process flow. Summary of the Invention

[0006] One objective of this invention is to propose an absorption-condensation thermal coupling distillation method based on a bioethanol concentration device.

[0007] The present invention relates to an absorption-condensation thermal coupling distillation method based on a bioethanol concentration device, the device comprising: a vacuum distillation column (T101), an absorption-condensation column (T102), a regeneration tank (V101), and a reboiler (R101). Bioethanol (1) is fed from the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is collected from the top of the vacuum distillation column (T101), and aqueous solution (2) is discharged from the bottom of the column. Circulating absorbent (9) is fed from the top of the absorption condenser (T102). Ethanol-water vapor (3) enters the absorption condenser (T102) and is absorbed by the circulating absorbent (9). Ethanol-water-absorbent (4) is collected from the bottom of the absorption condenser (T102) and pressurized by the pump (P101). After being heated by the heat exchanger (E101), it is fed into the regeneration tank (V101) as feed (6). Concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101) and cooled by the heat exchanger (E102). The separated absorbent (8) is collected from the bottom of the regeneration tank (V101) and pressurized by the pump (P102) before entering the top of the absorption condenser (T102) for recycling. In this process, thermal coupling technology is implemented between the vacuum distillation column (T101) and the absorption-condensation column (T102). The heat removed during the absorption process is used to heat the vacuum distillation column (T101). Heat exchange occurs between the heat exchange trays through the column walls or heat exchange plates, reducing or even completely replacing the external heat source input to the vacuum distillation column (T101). The absorption-condensation thermal coupling distillation and concentration equipment for bioethanol of this invention does not use expensive refrigerants, and at the same time utilizes the heat released during the absorption process to heat the distillation column, achieving internal thermal coupling of the system, reducing utility usage, and saving operating costs.

[0008] In addition, the absorption-condensation thermal coupling distillation method based on a bioethanol concentration device according to the above embodiments of the present invention may also have the following additional technical features:

[0009] Furthermore, the vacuum distillation column (T101) has 5 to 30 theoretical plates and an operating pressure of 5.00 × 10⁻⁶. 2 Pa ~ 1.50 × 10 3 Pa, the temperature at the top of the column is 4℃~6℃, the temperature at the bottom of the column is 20℃~30℃, and the feed position of bioethanol (1) is the top of the vacuum distillation column (T101).

[0010] Furthermore, the absorption condenser (T102) has a theoretical plate count of 2 to 10, and an operating pressure of 5.00 × 10⁻⁶. 2 Pa ~ 1.00 × 10 3 Pa, the temperature at the top of the tower is 40℃~50℃, the temperature at the bottom of the tower is 35℃~45℃, and the feed position of the circulating absorbent (9) is the top of the absorption condenser tower (T102).

[0011] Furthermore, the vacuum distillation column (T101) is a plate column or a packed column; the absorption condensation column (T102) is a plate column or a packed column.

[0012] The distillation method includes the following steps:

[0013] Step 1: Bioethanol (1) is fed from the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is collected from the top of the vacuum distillation column (T101), and aqueous solution (2) is discharged from the bottom of the column. The circulating absorbent (9) is fed from the top of the absorption condenser (T102). Ethanol-water vapor (3) enters the bottom of the absorption condenser (T102) and is absorbed by the circulating absorbent (9).

[0014] Step 2: The ethanol-water-absorbent (4) collected from the bottom of the absorption condenser (T102) is pressurized by the pump (P101) and heated by the heat exchanger (E101) and then fed into the regeneration tank (V101) as feed (6). The concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101), cooled by the heat exchanger (E102), and collected. The separated absorbent (8) is collected from the bottom of the regeneration tank (V101), pressurized by the pump (P102), and then recycled to the top of the absorption condenser (T102).

[0015] Furthermore, the circulating absorbent (9) is a saline solution or an ionic liquid.

[0016] Furthermore, the vacuum distillation column (T101) and the absorption condenser column (T102) are thermally coupled. The absorption process requires the removal of heat to ensure the absorption effect. The removed heat is used to heat the vacuum distillation column (T101). Heat exchange is carried out between the heat exchange trays through the column wall or heat exchange plates, reducing or even completely replacing the external heat source input of the vacuum distillation column (T101).

[0017] Furthermore, the negative pressure of the vacuum distillation column (T101) and the absorption condenser column (T102) is provided by the vacuum system (11) to maintain pressure stability.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The attached figure is a process flow diagram of the absorption-condensation thermal coupling distillation method for concentrating bioethanol according to the present invention;

[0020] In the diagram, T101 is a vacuum distillation column, T102 is an absorption condenser, V101 is a regeneration tank, E101 is a heat exchanger, E102 is a heat exchanger, R101 is a reboiler, P101 is a pump, P102 is a pump, 1 is bioethanol, 2 is an aqueous solution, 3 is ethanol-water vapor, 4 is ethanol-water-absorbent, 5 is pressurized ethanol-water-absorbent, 6 is the feed to the regeneration tank, 7 is concentrated ethanol-water vapor, 8 is the separated absorbent, 9 is the circulating absorbent, 10 is cooled ethanol-water vapor, and 11 is the vacuum system. Detailed Implementation

[0021] The following details embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals are consistently used to denote the same or similar elements or elements having the same or similar functions. The following description of the illustrated embodiments is merely illustrative and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] As shown in the attached figures, the equipment used in this invention mainly includes a vacuum distillation column (T101), an absorption condenser column (T102), a regeneration tank (V101), a reboiler (R101), heat exchangers (E101, E102), and pumps (P101, P102).

[0023] Bioethanol (1) is fed from the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is collected from the top of the vacuum distillation column (T101), and aqueous solution (2) is discharged from the bottom of the column. Circulating absorbent (9) is fed from the top of the absorption condenser (T102). Ethanol-water vapor (3) enters the bottom of the absorption condenser (T102) and is absorbed by the circulating absorbent (9).

[0024] The ethanol-water-absorbent (4) collected from the bottom of the absorption condenser (T102) is pressurized by the pump (P101) and heated by the heat exchanger (E101) before being fed into the regeneration tank (V101) as feed (6). The concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101), cooled to 40°C by the heat exchanger (E102), and collected from the bottom of the regeneration tank (V101). The separated absorbent (8) is collected from the bottom of the regeneration tank (V101), pressurized by the pump (P102), and recycled to the top of the absorption condenser (T102).

[0025] The negative pressure of the vacuum distillation column (T101) and the absorption condenser column (T102) of the present invention is provided by the vacuum system (11), and the heat exchange tower plates exchange heat through the tower wall or heat exchange plates.

[0026] In this invention, the vacuum distillation column (T101) and the absorption-condensation column (T102) are plate columns or packed columns. The absorbent is brine or an ionic liquid. In this invention, stream 7 is concentrated ethanol-water vapor with a purity of 30 wt% or higher.

[0027] The present invention can be illustrated by the following implementation examples.

[0028] Example 1

[0029] The specific process of using the equipment and method of the present invention is shown in the attached figures.

[0030] The vacuum distillation column (T101) is a plate column with a theoretical number of 5 plates. Bioethanol with an ethanol content of 5 wt% (1) is fed from the top of the vacuum distillation column (T101) at an operating pressure of 5.00 × 10⁻⁶. 2 Pa, the temperature at the top of the tower is 4℃, the temperature at the bottom of the tower is 20℃, ethanol-water vapor (3) is collected from the top, and aqueous solution (2) is discharged from the bottom of the tower. The absorption condenser (T102) adopts a plate tower with a theoretical number of 2 plates. The circulating absorbent (9) is 55wt% LiBr brine, which enters from the top of the tower. The ethanol-water vapor (3) enters from the bottom of the absorption condenser (T102). The operating pressure is 5.00×10 2 Pa, the top temperature of the column is 40℃ and the bottom temperature of the column is 35℃. The negative pressure of the vacuum distillation column (T101) and the absorption condensation column (T102) is provided by the vacuum system (11). The heat exchange plates are exchanged through the column wall or heat exchange plate. The heat removed in the absorption process is used to heat the vacuum distillation column (T101), thereby replacing the external heat source input of the vacuum distillation column (T101). The calculated logarithmic average heat transfer temperature difference is 24℃, which meets the heat transfer temperature difference requirement for implementing thermal coupling.

[0031] Ethanol-water-absorbent (4) is collected from the bottom of the absorption condenser (T102), and after being pressurized by the pump (P101) and heated by the heat exchanger (E101), it is fed into the regeneration tank (V101) for adiabatic flash evaporation (6). The concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101), and cooled to 40°C by the heat exchanger (E102) before being collected. The temperature of the regeneration tank (V101) is 133°C. The separated absorbent (8) is collected from the bottom, and after being pressurized by the pump (P102), it is recycled to the top of the absorption condenser (T102).

[0032] The flow rates and compositions of bioethanol (1), aqueous solution (2), circulating absorbent (9), and concentrated ethanol-water vapor (7) in Example 1 are shown in Table 1.

[0033] Table 1. Flow rates and composition of logistics items 1, 2, 9, and 7 in Example 1

[0034]

[0035] Example 2

[0036] The specific process using the equipment and technology of this invention is shown in the attached figures.

[0037] The process flow is the same as described in Example 1, except that the absorbent is an ionic liquid 1-butyl-3-methylimidazolium acetate ([bmim][OAc]), the vacuum distillation column (T101) is a packed column with 30 theoretical plates, and bioethanol (1) with an ethanol content of 5wt% is fed from the top of the vacuum distillation column (T101) at an operating pressure of 1.50 × 10⁻⁶. 3 Pa, the temperature at the top of the tower is 6℃, the temperature at the bottom of the tower is 30℃, ethanol-water vapor (3) is collected from the top, and aqueous solution (2) is discharged from the bottom of the tower. The absorption condenser (T102) is a packed tower with 10 theoretical plates. The circulating absorbent (9) is an ionic liquid [bmim][OAc], which enters from the top of the tower. The ethanol-water vapor (3) enters from the bottom of the absorption condenser (T102). The operating pressure is 1.00×10 3 Pa, the top temperature of the column is 50℃, and the bottom temperature of the column is 45℃. The negative pressure of the vacuum distillation column (T101) and the absorption condenser column (T102) is provided by the vacuum system (11). The heat exchange plates are exchanged through the column wall or heat exchange plate. The heat removed in the absorption process is used to heat the vacuum distillation column (T101), thereby replacing the external heat source input of the vacuum distillation column (T101). The calculated logarithmic average heat transfer temperature difference is 27℃, which meets the heat transfer temperature difference requirement for implementing thermal coupling.

[0038] The ethanol-water-absorbent (4) is collected from the bottom of the absorption condenser (T102), and after being pressurized by the pump (P101) and heated by the heat exchanger (E101), it is fed into the regeneration tank (V101) for adiabatic flash evaporation (6). The concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101), and cooled to 40°C by the heat exchanger (E102). The temperature of the regeneration tank (V101) is 145°C. The separated absorbent (8) is collected from the bottom, and after being pressurized by the pump (P102), it is recycled to the top of the absorption condenser (T102).

[0039] The flow rates and compositions of bioethanol (1), aqueous solution (2), ionic liquid (9), and concentrated ethanol-water vapor (7) in Example 2 are shown in Table 2.

[0040] Table 2. Flow rates and composition of logistics items 1, 2, 9, and 7 in Example 2

[0041]

[0042] Example 3

[0043] The process flow is the same as described in Example 1, except that the absorbent used is the ionic liquid 1-butyl-3-methylimidazolium tetrafluoro borate ([bmim][BF4]). The vacuum distillation column (T101) is a plate column with a theoretical number of 17 plates. Bioethanol (1) with an ethanol content of 5 wt% is fed from the top of the vacuum distillation column (T101) at an operating pressure of 1.00 × 10⁻⁶. 3 Pa, the top temperature of the column is 5℃, the bottom temperature of the column is 24℃, ethanol-water vapor (3) is collected from the top, and aqueous solution (2) is discharged from the bottom of the column. The absorption condenser (T102) is a packed column with 5 theoretical plates. The absorbent is an ionic liquid [bmim][BF4], which enters from the top of the column. The ethanol-water vapor (3) collected from the top of the vacuum distillation column (T101) enters from the bottom of the absorption condenser (T102). The operating pressure is 8.00×10 2 Pa, the top temperature of the column is 47℃ and the bottom temperature of the column is 40℃. The negative pressure of the vacuum distillation column (T101) and the absorption condenser column (T102) is provided by the vacuum system (11). The heat exchange plates are exchanged through the column wall or heat exchange plate. The heat removed by the absorption process is used to heat the vacuum distillation column (T101), thereby replacing the external heat source input of the vacuum distillation column (T101). The calculated logarithmic average heat transfer temperature difference is 27℃, which meets the heat transfer temperature difference requirement for implementing thermal coupling.

[0044] The ethanol-water-absorbent (4) is collected from the bottom of the absorption condenser (T102), and after being pressurized by the pump (P101) and heated by the heat exchanger (E101), it is fed into the regeneration tank (V101) for adiabatic flash evaporation (6). The concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101), and cooled to 40°C by the heat exchanger (E102) before being collected. The temperature of the regeneration tank (V101) is 147°C. The separated absorbent (8) is collected from the bottom, and after being pressurized by the pump (P102), it is recycled to the top of the absorption condenser (T102).

[0045] The flow rates and compositions of bioethanol (1), aqueous solution (2), ionic liquid (9), and concentrated ethanol-water vapor (7) in Example 3 are shown in Table 3.

[0046] Table 3. Flow rates and composition of logistics items 1, 2, 9, and 7 in Example 3.

[0047]

[0048] The method for concentrating bioethanol by absorption-condensation thermal coupling distillation of the present invention has the following advantages:

[0049] By thermally coupling the vacuum distillation column (T101) with the absorption condenser (T102), the ethanol-water vapor at the top of the vacuum distillation column (T101) is condensed without the use of expensive refrigerants (3). Simultaneously, the heat removed during the absorption process is used to heat the distillation column, reducing or even completely replacing the external heat source input to the vacuum distillation column (T101). Compared to traditional vacuum distillation methods, this invention can reduce operating costs by more than 30%. With the reduction in utility usage, greenhouse gas emissions are also reduced accordingly, resulting in significant environmental benefits.

[0050] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for absorption-condensation thermal coupling distillation based on a bioethanol concentration device, characterized in that, The equipment includes: a vacuum distillation column (T101), an absorption condenser (T102), a regeneration tank (V101), and a reboiler (R101). The distillation method includes the following steps: Step 1: Bioethanol (1) is fed from the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is collected from the top of the vacuum distillation column (T101), and aqueous solution (2) is discharged from the bottom of the column. The circulating absorbent (9) is fed from the top of the absorption condenser (T102). Ethanol-water vapor (3) enters the bottom of the absorption condenser (T102) and is absorbed by the circulating absorbent (9). Step 2: The ethanol-water-absorbent (4) collected from the bottom of the absorption condenser (T102) is pressurized by the first pump (P101) and heated by the first heat exchanger (E101) and then fed into the regeneration tank (V101) as feed (6). The concentrated ethanol-water vapor (7) is collected from the top of the regeneration tank (V101), cooled by the second heat exchanger (E102), and collected. The separated absorbent (8) is collected from the bottom of the regeneration tank (V101), pressurized by the second pump (P102), and then recycled to the top of the absorption condenser (T102). The vacuum distillation column (T101) has 5 to 30 theoretical plates and operates at a pressure of 5.00 × 10⁻⁶. 2 Pa ~ 1.50 × 10 3 Pa, the temperature at the top of the column is 4℃~6℃, the temperature at the bottom of the column is 20℃~30℃, and the feed position of bioethanol (1) is the top of the vacuum distillation column (T101); The absorption condenser (T102) has a theoretical plate count of 2 to 10, and an operating pressure of 5.00 × 10⁻⁶. 2 Pa ~ 1.00 × 10 3 Pa, the temperature at the top of the tower is 40℃~50℃, the temperature at the bottom of the tower is 35℃~45℃, and the feed position of the circulating absorbent (9) is the top of the absorption condenser tower (T102).

2. The absorption-condensation thermal coupling distillation method based on a bioethanol concentration device according to claim 1, characterized in that, The vacuum distillation column (T101) is a plate column or a packed column; the absorption condensation column (T102) is a plate column or a packed column.

3. The absorption-condensation thermal coupling distillation method based on a bioethanol concentration device according to claim 1, characterized in that, Heat exchange occurs between the heat exchange trays of the vacuum distillation column (T101) and the absorption condenser column (T102) through the column walls or heat exchange plates.

4. The absorption-condensation thermal coupling distillation method based on a bioethanol concentration device according to claim 1, characterized in that, The circulating absorbent (9) is a saline solution or an ionic liquid.

5. The absorption-condensation thermal coupling distillation method based on a bioethanol concentration device according to claim 1, characterized in that, The vacuum distillation column (T101) is thermally coupled with the absorption condenser (T102). The absorption process requires the removal of heat to ensure the absorption effect. The removed heat is used to heat the vacuum distillation column (T101), reducing or even completely replacing the external heat source input of the vacuum distillation column (T101).

6. The absorption-condensation thermal coupling distillation method based on a bioethanol concentration device according to claim 1, characterized in that, The negative pressure of the vacuum distillation column (T101) and the absorption condenser column (T102) is provided by the vacuum system (11) to maintain pressure stability.

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