Equipment and method for concentrating bioethanol through absorption condensation thermal coupling rectification

Abstract

The invention provides equipment and a method for concentrating bioethanol through absorption condensation thermal coupling rectification, and belongs to the technical field of chemical engineering, the equipment comprises a vacuum rectification tower (T101), an absorption condensation tower (T102), a regeneration tank (V101), a reboiler (R101) and the like. The vacuum rectifying tower (T101) and the absorption condensing tower (T102) are subjected to a thermal coupling technology, an expensive refrigerant is not used for condensing ethanol-water vapor (3) at the top of the vacuum rectifying tower (T101), the ethanol-water vapor (3) at the top of the tower enters the absorption condensing tower (T102) and then is absorbed by a circulating absorbent (9), and heat needs to be removed in the absorption process to ensure the absorption effect. The removed heat can be further used for supplying heat to the vacuum rectifying tower (T101), so that the external heat source input of the vacuum rectifying tower (T101) is reduced or even completely replaced. Compared with a traditional vacuum rectification mode, the use amount of public engineering is reduced, and the operation cost is reduced by more than 30%.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and particularly relates to a device and method for concentrating bioethanol by absorption condensation heat-coupled distillation. Background Art

[0002] Distillation is a commonly used separation method in chemical engineering. When concentrating bioethanol using the distillation method, to avoid damaging yeast cells due to the high temperature at the bottom of the tower, the temperature at the bottom of the tower needs to be controlled below 30°C. At this time, the operating pressure at the top of the tower is about 1 kPa, and the temperature at the top of the tower is about 5°C. When the temperature at the top of the tower is relatively low, condensation by circulating water cannot meet the requirements, and refrigerants are often required for condensation, resulting in a significant increase in operating costs. The absorption condensation technology does not use expensive refrigerants and uses the heat removed during the absorption process to supply heat to the distillation column. Therefore, implementing heat coupling between the distillation process and the absorption process and proposing an absorption condensation heat-coupled distillation process can significantly reduce operating costs.

[0003] Patent CN106215445 discloses a combined evaporation / stripping absorption module that concentrates alcohol in the fermentation broth through three steps: evaporation, absorption, and heat transfer. This module can preferentially remove ethanol from the ethanol-water mixture and simultaneously cool the ethanol-water 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 an aqueous solution of bioethanol, using the heat contained in the material of the previous distillation column itself to provide heat for the next distillation column, and the insufficient part is supplemented by an air-source heat pump system. Additionally, the waste heat that has not been utilized in the material discharged from the distillation column is used to preheat the raw material of the aqueous ethanol solution to form a heat-coupled network. However, in this method, only the temperature at the bottom of the tower is relatively high, which is likely to damage yeast cells.

[0005] Patent CN108046989 discloses a device and method for purifying bioethanol, mainly using a pre-separation column, an azeotropic distillation column, an azeotropic agent recovery column, a compressor, a phase separator, etc. After the bioethanol-water solution is separated by three distillation columns in sequence, anhydrous ethanol with a mass fraction of 99.9% or more is obtained. However, the temperature at the bottom of the tower in this process is relatively high, and the process flow is complex. Summary of the Invention

[0006] An object of the present invention is to propose a device for concentrating bioethanol by absorption condensation heat-coupled distillation.

[0007] The equipment for concentrating bio - ethanol by absorption - condensation heat - coupled distillation according to the present invention includes: a vacuum distillation column (T101), an absorption - condensation column (T102), a regeneration tank (V101), and a reboiler (R101). Bio - ethanol (1) is fed into the top of the vacuum distillation column (T101). Ethanol - water vapor (3) is taken out from the top of the vacuum distillation column (T101), and an aqueous solution (2) is discharged from the bottom of the column. The circulating absorbent (9) is fed into the top of the absorption - condensation column (T102). The ethanol - water vapor (3) enters the absorption - condensation column (T102) and is absorbed by the circulating absorbent (9). The ethanol - water - absorbent mixture (4) taken out from the bottom of the absorption - condensation column (T102) is pressurized by a pump (P101) in sequence and then heated by a heat exchanger (E101), and then enters the regeneration tank (V101) as the feed (6). The concentrated ethanol - water vapor (7) is taken out from the top of the regeneration tank (V101) and is taken out after being cooled by the heat exchanger (E102). The separated absorbent (8) is taken out from the bottom of the regeneration tank (V101), pressurized by a pump (P102), and then enters the top of the absorption - condensation column (T102) for recycling. During this process, a heat - coupling technology is implemented for the vacuum distillation column (T101) and the absorption - condensation column (T102). The heat removed during the absorption process is used to supply heat to the vacuum distillation column (T101). Heat exchange is carried out between the heat - exchange trays through the tower wall or heat - exchange plates, reducing or even completely replacing the external heat source input of the vacuum distillation column (T101). The equipment for concentrating bio - ethanol by absorption - condensation heat - coupled distillation according to the present invention does not use expensive refrigerants, and at the same time uses the heat released during the absorption process to supply heat to the distillation column, realizing internal heat coupling of the system, reducing the consumption of utilities, and saving the operating cost.

[0008] In addition, the equipment for concentrating bio - ethanol by absorption - condensation heat - coupled distillation according to the above - mentioned embodiment of the present invention may further have the following additional technical features:

[0009] Further, the number of theoretical plates of the vacuum distillation column (T101) is 5 to 30, the operating pressure is 5.00×10 2 Pa to 1.50×10 3 Pa, the top - tower temperature is 4℃ to 6℃, the bottom - tower temperature is 20℃ to 30℃, and the feeding position of the bio - ethanol (1) is at the top of the vacuum distillation column (T101).

[0010] Further, the number of theoretical plates of the absorption - condensation column (T102) is 2 to 10, the operating pressure is 5.00×10 2 Pa to 1.00×10 3 Pa, the top - tower temperature is 40℃ to 50℃, the bottom - tower temperature is 35℃ to 45℃, and the feeding position of the circulating absorbent (9) is at the top of the absorption - condensation column (T102).

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

[0012] Further, the equipment further includes multiple heat exchangers and multiple pumps.

[0013] Further, there are at least 2 heat exchangers among the multiple heat exchangers, and at least 2 pumps among the multiple pumps.

[0014] Another object of the present invention is to provide a method for concentrating bioethanol by absorption-condensation heat-coupled distillation using the above equipment.

[0015] The method for concentrating bioethanol by absorption-condensation heat-coupled distillation using the above equipment includes the following steps:

[0016] Step 1: Bioethanol (1) is fed into the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is taken out from the top of the vacuum distillation column (T101), and an aqueous solution (2) is discharged from the bottom of the column. The circulating absorbent (9) is fed into the top of the absorption and condensation column (T102), and the ethanol-water vapor (3) enters the bottom of the absorption and condensation column (T102) and is absorbed by the circulating absorbent (9).

[0017] Step 2: The ethanol-water-absorbent (4) taken out from the bottom of the absorption and condensation column (T102) is pressurized by a pump (P101) in sequence, heated by a heat exchanger (E101), and then enters a regeneration tank (V101) as a feed (6). Concentrated ethanol-water vapor (7) is taken out from the top of the regeneration tank (V101), cooled by a heat exchanger (E102) and then taken out. The separated absorbent (8) is taken out from the bottom of the regeneration tank (V101), pressurized by a pump (P102), and then enters the top of the absorption and condensation column (T102) for recycling.

[0018] Further, the circulating absorbent (9) is brine or ionic liquid.

[0019] Further, the vacuum distillation column (T101) and the absorption and condensation column (T102) are heat-coupled. Heat needs to be removed during the absorption process to ensure the absorption effect. The removed heat is used to supply heat to the vacuum distillation column (T101). Heat exchange is carried out between the heat exchange trays through the tower wall or heat exchange plates, reducing or even completely replacing the external heat source input of the vacuum distillation column (T101).

[0020] Further, the negative pressure of the vacuum distillation column (T101) and the absorption and condensation column (T102) is provided by a vacuum system (11) to maintain pressure stability.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0022] The attached drawing is a process flow diagram of the method for concentrating bioethanol by absorption and condensation heat-coupled distillation of the present invention;

[0023] In the figure, T101 - vacuum distillation column, T102 - absorption and condensation column, V101 - regeneration tank, E101 - heat exchanger, E102 - heat exchanger, R101 - reboiler, P101 - pump, P102 - pump, 1 - bioethanol, 2 - aqueous solution, 3 - ethanol-water vapor, 4 - ethanol-water-absorbent, 5 - pressurized ethanol-water-absorbent, 6 - feed to the regeneration tank, 7 - concentrated ethanol-water vapor, 8 - separated absorbent, 9 - recycled absorbent, 10 - cooled ethanol-water vapor, 11 - vacuum system. Detailed implementation manners

[0024] The embodiments of the present invention are described in detail below. The examples of the embodiments are shown in the attached drawings, where the same or similar reference numerals are always used to represent the same or similar elements or elements with the same or similar functions. The following description of the illustrated embodiments is only for illustrative purposes and is intended to explain the present invention, and should not be construed as a limitation of the present invention.

[0025] As shown in the attached drawing, the equipment adopted by the present invention mainly includes a vacuum distillation column (T101), an absorption and condensation column (T102), a regeneration tank (V101), a reboiler (R101), heat exchangers (E101, E102) and pumps (P101, P102).

[0026] Bioethanol (1) is fed into the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is taken out from the top of the vacuum distillation column (T101), and an aqueous solution (2) is discharged from the bottom of the column. The recycled absorbent (9) is fed into the top of the absorption and condensation column (T102), and the ethanol-water vapor (3) enters the bottom of the absorption and condensation column (T102) and is absorbed by the recycled absorbent (9);

[0027] The ethanol-water-absorbent (4) taken out from the bottom of the absorption and condensation column (T102) is pressurized by a pump (P101) in sequence, heated by a heat exchanger (E101), and then enters the regeneration tank (V101) as a feed (6). Concentrated ethanol-water vapor (7) is taken out from the top of the regeneration tank (V101), cooled to 40 °C by a heat exchanger (E102) and then taken out. The separated absorbent (8) is taken out from the bottom of the regeneration tank (V101), pressurized by a pump (P102), and then enters the top of the absorption and condensation column (T102) for recycling.

[0028] The negative pressure of the vacuum distillation column (T101) and the absorption and condensation column (T102) of the present invention is provided by a vacuum system (11), and heat exchange is carried out between the heat exchange trays through the tower wall or the heat exchange plate.

[0029] During the operation of the present invention, the vacuum rectification column (T101) and the absorption and condensation column (T102) are plate columns or packed columns. The absorbent is brine or ionic liquid. In the present invention, the stream 7 is concentrated ethanol-water vapor with a purity of 30 wt% or more.

[0030] The present invention can be illustrated by the following embodiments.

[0031] Embodiment 1

[0032] The equipment and method of the present invention are adopted, and the specific process is as shown in the attached drawings.

[0033] The vacuum rectification column (T101) adopts a plate column with 5 theoretical plates. Bioethanol (1) with an ethanol content of 5 wt% is fed into the top of the vacuum rectification column (T101). The operating pressure is 5.00×10 2 Pa, the top temperature of the column is 4 °C, the bottom temperature of the column is 20 °C, ethanol-water vapor (3) is withdrawn from the top, and the aqueous solution (2) is discharged from the bottom of the column kettle. The absorption and condensation column (T102) adopts a plate column with 2 theoretical plates. The circulating absorbent (9) is 55 wt% LiBr brine, which enters from the top of the column. Ethanol-water vapor (3) enters from the bottom of the absorption and condensation column (T102). The operating pressure is 5.00×10 2 Pa, the top temperature of the column is 40 °C, and the bottom temperature of the column is 35 °C. The negative pressure of the vacuum rectification column (T101) and the absorption and condensation column (T102) is provided by the vacuum system (11). Heat exchange is carried out between the heat exchange trays through the column wall or the heat exchange plate. The heat removed during the absorption process is used to supply heat to the vacuum rectification column (T101), thereby replacing the external heat source input of the vacuum rectification column (T101). The calculated logarithmic mean temperature difference for heat transfer is 24 °C, meeting the heat transfer temperature difference requirements for implementing thermal coupling.

[0034] The ethanol-water-absorbent (4) is withdrawn from the bottom of the absorption and condensation column (T102), pressurized by the pump (P101) and heated by the heat exchanger (E101) in sequence, and then enters the regeneration tank (V101) as the feed (6) for adiabatic flashing. The concentrated ethanol-water vapor (7) is withdrawn from the top of the regeneration tank (V101), cooled to 40 °C by the heat exchanger (E102) and then withdrawn. The temperature of the regeneration tank (V101) is 133 °C, and the separated absorbent (8) is withdrawn from the bottom, pressurized by the pump (P102), and then enters the top of the absorption and condensation column (T102) for recycling.

[0035] In Embodiment 1, the flow rates and compositions of bioethanol (1), aqueous solution (2), circulating absorbent (9), and concentrated ethanol-water vapor (7) are shown in Table 1.

[0036] Table 1 Flow rates and compositions of streams 1, 2, 9, and 7 in Embodiment 1

[0037]

[0038] Example 2

[0039] The equipment and process of the present invention are adopted, and the specific process is as shown in the attached drawings.

[0040] It is the same as the process flow described in Example 1, except that the absorbent is the ionic liquid 1-butyl-3-methylimidazolium acetate ([bmim][OAc]), the vacuum rectification column (T101) is a packed column with 30 theoretical plates. Bioethanol (1) with an ethanol content of 5 wt% is fed from the top of the vacuum rectification column (T101), the operating pressure is 1.50×10 3 Pa, the top temperature of the column is 6 °C, and the bottom temperature is 30 °C. Ethanol-water vapor (3) is withdrawn from the top, and the aqueous solution (2) is discharged from the bottom of the column kettle. The absorption and condensation column (T102) is a packed column with 10 theoretical plates. The circulating absorbent (9) is the ionic liquid [bmim][OAc], which enters from the top, and ethanol-water vapor (3) enters from the bottom of the absorption and condensation column (T102). The operating pressure is 1.00×10 3 Pa, the top temperature of the column is 50 °C, and the bottom temperature is 45 °C. The negative pressure of the vacuum rectification column (T101) and the absorption and condensation column (T102) is provided by the vacuum system (11). Heat exchange is carried out between the heat exchange trays through the column wall or heat exchange plates. The heat removed during the absorption process is used to supply heat to the vacuum rectification column (T101), thereby replacing the external heat source input of the vacuum rectification column (T101). The calculated logarithmic mean temperature difference for heat transfer is 27 °C, meeting the heat transfer temperature difference requirements for implementing thermal coupling.

[0041] The ethanol-water-absorbent (4) is withdrawn from the bottom of the absorption and condensation column (T102), pressurized by the pump (P101) and heated by the heat exchanger (E101) in sequence, and then enters the regeneration tank (V101) as the feed (6) for adiabatic flash evaporation. The concentrated ethanol-water vapor (7) is withdrawn from the top of the regeneration tank (V101), cooled to 40 °C by the heat exchanger (E102) and then withdrawn. The temperature of the regeneration tank (V101) is 145 °C, and the separated absorbent (8) is withdrawn from the bottom, pressurized by the pump (P102), and then enters the top of the absorption and condensation column (T102) for recycling.

[0042] 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.

[0043] Table 2 Flow rates and compositions of streams 1, 2, 9 and 7 in Example 2

[0044]

[0045] Example 3

[0046] The process flow is the same as that described in Example 1, except that the absorbent is the ionic liquid 1-butyl-3-methylimidazolium tetrafluoro borate ([bmim][BF4]). The vacuum rectification column (T101) is a plate column with 17 theoretical plates. Bioethanol (1) with an ethanol content of 5 wt% is fed into the top of the vacuum rectification column (T101), and the operating pressure is 1.00×10 3 Pa, the top temperature of the column is 5 °C, and the bottom temperature is 24 °C. Ethanol-steam (3) is withdrawn from the top of the column, and the aqueous solution (2) is discharged from the bottom of the column kettle. The absorption and condensation column (T102) is a packed column with 5 theoretical plates. The absorbent is the ionic liquid [bmim][BF4], which enters from the top of the column. Ethanol-steam (3) withdrawn from the top of the vacuum rectification column (T101) enters from the bottom of the absorption and condensation column (T102), and the operating pressure is 8.00×10 2 Pa, the top temperature of the column is 47 °C, and the bottom temperature is 40 °C. The negative pressure of the vacuum rectification column (T101) and the absorption and condensation column (T102) is provided by the vacuum system (11). Heat exchange is carried out between the heat exchange trays through the column wall or the heat exchange plate. The heat removed during the absorption process is used to supply heat to the vacuum rectification column (T101), thereby replacing the external heat source input of the vacuum rectification column (T101). The calculated logarithmic mean temperature difference for heat transfer is 27 °C, meeting the heat transfer temperature difference requirements for implementing thermal coupling.

[0047] Ethanol-water-absorbent (4) is withdrawn from the bottom of the absorption and condensation column (T102), pressurized by a pump (P101) and heated by a heat exchanger (E101) in sequence, and then enters the regeneration tank (V101) as the feed (6) for adiabatic flash evaporation. Concentrated ethanol-steam (7) is withdrawn from the top of the regeneration tank (V101), cooled to 40 °C by the heat exchanger (E102) and then withdrawn. The temperature of the regeneration tank (V101) is 147 °C, and the separated absorbent (8) is withdrawn from the bottom, pressurized by a pump (P102), and then enters the top of the absorption and condensation column (T102) for recycling.

[0048] The flow rates and compositions of bioethanol (1), aqueous solution (2), ionic liquid (9), and concentrated ethanol-steam (7) in Example 3 are shown in Table 3.

[0049] Table 3 Flow rates and compositions of streams 1, 2, 9, and 7 in Example 3

[0050]

[0051] The method for concentrating bioethanol by absorption condensation heat-coupled rectification of the present invention has the following advantages:

[0052] Thermally couple the vacuum distillation column (T101) with the absorption and condensation column (T102), without using an expensive refrigerant to condense the ethanol-water vapor (3) at the top of the vacuum distillation column (T101). At the same time, utilize the heat removed during the absorption process to supply heat to the distillation column, reducing or even completely replacing the external heat source input to the vacuum distillation column (T101). Compared with the traditional vacuum distillation method, the present invention can reduce the operating cost by more than 30%. With the reduction of the consumption of public utilities, the emissions of greenhouse gases are also correspondingly reduced, having good environmental benefits.

[0053] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. An absorption and condensation heat-coupled rectification method based on a bioethanol concentration equipment, characterized in that, The equipment includes: a vacuum distillation column (T101), an absorption and condensation column (T102), a regeneration tank (V101), and a reboiler (R101): The distillation method includes the following steps: Step 1: Bioethanol (1) is fed into the top of the vacuum distillation column (T101). Ethanol-water vapor (3) is taken out from the top of the vacuum distillation column (T101), and an aqueous solution (2) is discharged from the bottom of the column. The circulating absorbent (9) is fed into the top of the absorption and condensation column (T102). The ethanol-water vapor (3) enters the bottom of the absorption and condensation column (T102) and is absorbed by the circulating absorbent (9). Step 2: The ethanol-water-absorbent (4) taken out from the bottom of the absorption and condensation column (T102) is pressurized by a pump (P101) in sequence, heated by a heat exchanger (E101), and then enters the regeneration tank (V101) as a feed (6). The concentrated ethanol-water vapor (7) is taken out from the top of the regeneration tank (V101), cooled by a heat exchanger (E102), and then taken out. The separated absorbent (8) is taken out from the bottom of the regeneration tank (V101), pressurized by a pump (P102), and then enters the top of the absorption and condensation column (T102) for recycling. The number of theoretical plates of the vacuum distillation column (T101) is 5 to 30, the operating pressure is 5.00×10 2 Pa to 1.50×10 3 Pa, the top temperature of the column is 4°C to 6°C, the bottom temperature of the column is 20°C to 30°C, and the feeding position of bioethanol (1) is at the top of the vacuum distillation column (T101); The number of theoretical plates of the absorption and condensation tower (T102) is 2 to 10, the operating pressure is 5.00×10 2 Pa to 1.00×10 3 Pa, the top temperature of the tower is 40°C to 50°C, the bottom temperature of the tower is 35°C to 45°C, and the feeding position of the circulating absorbent (9) is at the top of the absorption and condensation tower (T102).

2. The apparatus for concentrating bioethanol by absorption and condensation heat-coupled distillation according to claim 1, characterized in that The vacuum distillation column (T101) is a plate column or a packed column; the absorption and condensation column (T102) is a plate column or a packed column.

3. The apparatus for concentrating bioethanol by absorption and condensation heat-coupled distillation according to claim 1, characterized in that, The equipment further includes multiple heat exchangers and multiple pumps.

4. The apparatus for concentrating bioethanol by absorption and condensation heat-coupled distillation according to claim 3, wherein, At least two of the multiple heat exchangers are included, and at least two of the multiple pumps are included.

5. The apparatus for concentrating bioethanol by absorption and condensation heat-coupled rectification according to claim 1, wherein, Heat exchange is carried out between the heat exchange trays of the vacuum distillation column (T101) and the absorption and condensation column (T102) through the column wall or the heat exchange plate.

6. The method for concentrating bioethanol by absorption and condensation heat-coupled distillation according to claim 1, characterized in that, The circulating absorbent (9) is brine or ionic liquid.

7. The method for concentrating bioethanol by absorption and condensation heat-coupled rectification according to claim 1, characterized in that The vacuum distillation column (T101) and the absorption and condensation column (T102) are thermally coupled. Heat needs to be removed during the absorption process to ensure the absorption effect. The removed heat is used to supply heat to the vacuum distillation column (T101), reducing or even completely replacing the external heat source input of the vacuum distillation column (T101).

8. The method for concentrating bioethanol by absorption and condensation heat-coupled rectification according to claim 1, wherein The negative pressure of the vacuum distillation column (T101) and the absorption and condensation column (T102) is provided by a vacuum system (11) to maintain the pressure stability.

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