A distillation energy-saving system and method for coal-based ethanol separation

Abstract

This invention relates to the field of separation and distillation technology. It discloses an energy-saving distillation system and method for separating coal-based ethanol, comprising an ethanol refining tower and a methanol deesterification tower. Liquid is discharged from the bottom of the ethanol refining tower through a liquid outlet. The discharged liquid undergoes counter-current mass transfer and heating in the low-temperature zone of the counter-current heat exchange unit. Liquid is also discharged from the bottom of the methanol deesterification tower through a liquid outlet. The heated liquid enters the high-temperature zone of the counter-current heat exchange unit for secondary counter-current mass transfer and heating, then enters the methanol deesterification tower through a reflux inlet. Utilizing the gas flow rate and temperature, and reflux flow rate and temperature characteristics of the ethanol refining and methanol deesterification towers, the invention employs top gas pressurization and synergistic heat exchange to overcome the equipment impact caused by large temperature differences. The reverse mass transfer method, connected in series, solves the problems of large liquid volume, small gas volume, and difficulty in heating in the ethanol refining tower, while simultaneously addressing the heat waste caused by large gas volume and small liquid volume in the methanol deesterification tower.

Description

Technical Field

[0001] This invention relates to the field of separation and distillation technology, specifically to an energy-saving distillation system and method for separating coal-based ethanol. Background Technology

[0002] Coal-based ethanol is an ethanol product obtained through processes such as dimethyl ether carbonylation and methyl acetate hydrogenation from coal-to-syngas. In actual production, the crude ethanol product has a complex composition, typically containing methanol, methyl acetate, isopropanol, and other higher alcohols in addition to the target product ethanol. To obtain qualified ethanol, these components must be effectively separated by distillation. In existing coal-based ethanol separation processes, the ethanol refining tower is one of the key pieces of equipment. Its main function is to remove methanol, residual methyl acetate, and other heavy components from the crude ethanol, and to collect qualified ethanol from the side stream at the bottom of the tower. In actual operation, both the ethanol refining tower and the subsequent methanol deesterification tower share the following common problems: Both columns require a large amount of external steam to maintain the heat balance of the distillation process in their bottom reboilers, and steam consumption accounts for a significant proportion of the unit's operating costs. The overhead vapor phase of both columns needs to be condensed in a condenser, and the large amount of latent heat it carries is carried away by the circulating water and cannot be effectively recovered and utilized.

[0003] Adding a heat exchanger allows the reflux liquid at the bottom of the column to exchange heat with the gas. While this can reduce steam usage, the following problems have arisen in practical applications: The output temperature of the gas at the top of the ethanol refining column after compression is about 100°C, and the temperature of the reflux from the heat exchanger to the bottom of the column is above 90°C. This shows that if the ethanol refining column wants to effectively utilize gas-liquid heat exchange, it is necessary to increase the residence time of the liquid and gas in the heat exchanger in order to make the reflux temperature close to 90°C.

[0004] The output temperature of the compressed gas at the top of the methanol deesterification tower is above 130℃, and the reflux liquid temperature is above 115℃. This is because the pressure inside the methanol deesterification tower is high, hence the high temperature requirement.

[0005] In actual operation, the reflux liquid flow rate of the ethanol refining tower is greater than that of the methanol deesterification tower, and the overhead gas output of the ethanol refining tower is less than that of the methanol deesterification tower.

[0006] In methanol deesterification towers, the gas volume is large and the liquid volume is small, resulting in rapid liquid temperature rise and a significant amount of latent heat not being fully utilized. In ethanol refining towers, the gas volume is small and the liquid volume is large, resulting in slow liquid temperature rise and sometimes even failure to reach the required temperature. Summary of the Invention

[0007] The purpose of this invention is to provide an energy-saving distillation system and method for coal-based ethanol separation. The system centrally integrates the heat exchangers for the ethanol refining tower and the methanol deesterification tower, utilizing synergistic heat exchange between the two exchangers to solve the problem of wasted heat due to the large gas volume and small liquid volume in the methanol deesterification tower. Simultaneously, it addresses the issues of slow temperature rise and substandard temperature in the ethanol refining tower caused by the small gas volume and large liquid volume. After coupling, the reflux liquid from the heat exchange is more compliant with standards, further reducing the use of additional heat sources and thus solving the problems mentioned in the background section.

[0008] To achieve the above objectives, the present invention provides the following technical solution: An energy-saving distillation system for coal-based ethanol separation includes an ethanol refining tower and a methanol deesterification tower. The top gas phase outlet of the ethanol refining tower is connected to a compression unit. The gas output from the compression unit enters the hot side of the counter-current heat exchange unit for heat exchange and is then collected in a reflux tank. The gas phase outlet at the top of the ethanol refining tower is connected to the compression unit. The gas output from the compression unit enters the hot side of the reverse heat exchange unit for heat exchange and is then collected in the reflux tank. The liquid is discharged from the bottom of the ethanol refining tower through the liquid phase outlet. The discharged liquid is heated by reverse mass transfer in the low-temperature zone of the reverse heat exchange unit. After being heated, the liquid enters the low-temperature zone of the reverse heat exchange unit for a second temperature increase by reverse mass transfer and then enters the interior of the ethanol refining tower through the reflux inlet. Liquid is discharged from the bottom of the methanol deesterification tower through the liquid phase outlet. The discharged liquid undergoes counter-current mass transfer and heating in the high-temperature zone of the counter-current heat exchange unit. After being heated, the liquid enters the high-temperature zone of the counter-current heat exchange unit for secondary counter-current mass transfer and heating, and then enters the interior of the methanol deesterification tower through the reflux inlet.

[0009] As a further embodiment of the present invention: the reverse heat exchange unit has a high-temperature heat exchange zone and a low-temperature heat exchange zone connected in series on the heat side, the gas output by the compression unit passes through the high-temperature heat exchange zone and the low-temperature heat exchange zone in sequence, and the gas output by the compression unit passes through the high-temperature heat exchange zone and the low-temperature heat exchange zone in sequence.

[0010] As a further embodiment of the present invention: the liquid discharged from the ethanol refining tower through the liquid phase outlet enters through the low-temperature end of the low-temperature heat exchange zone, the liquid heated by heat exchange is output through the high-temperature end of the low-temperature heat exchange zone and transported to the low-temperature end of the low-temperature heat exchange zone, and the liquid is finally output through the high-temperature end of the low-temperature heat exchange zone.

[0011] As a further embodiment of the present invention: the liquid discharged from the methanol deesterification tower through the liquid phase outlet enters through the low-temperature end of the high-temperature heat exchange zone, the liquid heated by heat exchange is output through the high-temperature end of the high-temperature heat exchange zone and transported to the low-temperature end of the high-temperature heat exchange zone, and the liquid is finally output through the high-temperature end of the high-temperature heat exchange zone.

[0012] As a further embodiment of the present invention: the discharge channel of the ethanol refining tower is divided into three paths, one of which enters the reverse heat exchange unit and returns to the bottom of the tower, the second path returns to the bottom of the tower via the reboiler, and the third path is discharged as heavy components.

[0013] As a further embodiment of the present invention: the liquid flowing out of the liquid phase outlet of the methanol deesterification tower is divided into three paths: one path enters the reverse heat exchange unit and returns to the bottom of the tower; the second path returns to the bottom of the tower after being heated by the reboiler; and the third path is discharged as methanol product.

[0014] As a further embodiment of the present invention: a condensate pipeline is provided between the hot side outlet of the compression unit and the reflux tank, and the outlet of the reflux tank is connected to the top reflux inlet of the ethanol refining tower and the feed inlet of the methanol deesterification tower, respectively.

[0015] As a further embodiment of the present invention: a condensate pipeline is provided between the hot side outlet of the reverse heat exchange unit and the reflux tank, and the outlet of the reflux tank is connected to the top reflux inlet of the methanol deesterification tower and the methyl acetate discharge pipeline, respectively.

[0016] As a further aspect of the present invention: the reboiler and the heat source of the reboiler are external steam.

[0017] As a further aspect of the present invention: a method of using a distillation energy-saving system for coal-based ethanol separation, comprising the following steps: S1: The crude ethanol after the removal of methyl acetate is sent to the ethanol purification tower for distillation and separation. S2: The gaseous methanol and methyl acetate at the top of the ethanol refining tower are compressed and heated by the compression unit. The heated gas enters the counter-current heat exchange unit to exchange heat with part of the bottom liquid. After condensation, it enters the reflux tank. Part of the condensate in the reflux tank is returned to the top of the ethanol refining tower, and the other part is sent to the methanol deesterification tower. S3: The heavy component liquid flowing out of the bottom of the ethanol refining tower is divided into three paths: the first path enters the reverse mass transfer and heats up through the cold side of the low-temperature zone of the reverse heat exchange unit. The heated liquid is then transported to the cold side inlet of the low-temperature zone of the reverse heat exchange unit and undergoes a second reverse mass transfer and heats up in the low-temperature zone of the reverse heat exchange unit. The heated liquid is then returned to the interior of the ethanol refining tower. The second path is heated by the reflux tank and then returned to the bottom of the tower. The third path is discharged from the tower as a heavy component. S4: The vapor phase at the top of the methanol deesterification tower is compressed and heated by the compression unit, and then enters the counter-current heat exchange unit to exchange heat with part of the bottom liquid. After condensation, it enters the reflux tank. Part of the condensate in the reflux tank is returned to the top of the methanol deesterification tower, and the other part is discharged as methyl acetate. S5: The methanol liquid flowing out of the bottom of the methanol deesterification tower is divided into three paths: the first path is heated by reverse mass transfer in the high-temperature zone of the reverse heat exchange unit, and the heated liquid enters the high-temperature zone of the reverse heat exchange unit for a second temperature increase by reverse mass transfer. The liquid after the second temperature increase flows back to the ethanol refining tower. The second path is heated by the reboiler and then returned to the bottom of the tower. The third path is discharged as methanol product.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This technical solution utilizes the gas flow rate and temperature, as well as the reflux liquid flow rate and temperature, of the ethanol refining tower and the methanol deesterification tower. It employs top gas pressurization and synergistic heat exchange to overcome the equipment impact caused by large temperature differences. By using a reverse mass transfer method in series, it solves the problems of large liquid volume, small gas volume, and difficulty in heating in the ethanol refining tower, while simultaneously addressing the heat waste caused by large gas volume and small liquid volume in the methanol deesterification tower. With these two components complementing each other, the temperature of the ethanol refining tower more easily approaches the required temperature. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a distillation energy-saving system for coal-based ethanol separation; Figure 2 This is a schematic diagram of one implementation of reverse heat exchange unit A and reverse heat exchange unit B in a distillation energy-saving system for coal-based ethanol separation; In the diagram: 1. Ethanol refining tower; 11. Compression unit A; 12. Countercurrent heat exchange unit A; 121. High-temperature heat exchange zone A; 122. Low-temperature heat exchange zone A; 13. Reflux tank A; 14. Reboiler A; 2. Methanol deesterification tower; 21. Compression unit B; 22. Countercurrent heat exchange unit B; 221. High-temperature heat exchange zone B; 222. Low-temperature heat exchange zone B; 23. Reflux tank B; 24. Reboiler B. Detailed Implementation

[0021] Please see Figures 1-2This embodiment includes an ethanol refining tower 1 and a methanol deesterification tower 2. The top gas phase outlet of the ethanol refining tower 1 is connected to a compression unit A11. The gas output from the compression unit A11 enters the hot side of the counter-current heat exchange unit A12 for heat exchange and is then collected in a reflux tank A13. The top gas phase outlet of the ethanol refining tower 1 is connected to a compression unit B21. The gas output from the compression unit B21 enters the hot side of the counter-current heat exchange unit B22 for heat exchange and is then collected in a reflux tank B23. A condensate pipeline is provided between the hot side outlet of the compression unit A11 and the reflux tank A13. The outlet of the reflux tank A13 is connected to the top reflux inlet of the ethanol refining tower 1 and the feed inlet of the methanol deesterification tower 2, respectively. A condensate pipeline is provided between the hot side outlet of the counter-current heat exchange unit B22 and the reflux tank B23. The outlet of the reflux tank B23 is connected to the top reflux inlet of the methanol deesterification tower 2 and the methyl acetate discharge pipeline, respectively.

[0022] The crude ethanol after methyl acetate removal is fed into ethanol refining column 1 for distillation separation. The vaporous methanol and methyl acetate at the top of ethanol refining column 1 are compressed and heated by compression unit A11. The heated gas enters the counter-current heat exchange unit A12 to exchange heat with part of the bottom liquid. After condensation, it enters reflux tank A13. Part of the condensate in reflux tank A13 is returned to the top of ethanol refining column 1, and the other part is sent to methanol deesterification column 2. The vapor at the top of methanol deesterification column 2 is compressed and heated by compression unit B21. It enters the counter-current heat exchange unit B22 to exchange heat with part of the bottom liquid. After condensation, it enters reflux tank B23. Part of the condensate in reflux tank B23 is returned to the top of methanol deesterification column 2, and the other part is discharged as methyl acetate.

[0023] Furthermore, liquid is discharged from the bottom of ethanol refining tower 1 through the liquid phase outlet. The discharged liquid undergoes reverse mass transfer and heating in the low-temperature zone of reverse heat exchange unit A12. After heating, the liquid enters the low-temperature zone of reverse heat exchange unit B22 for secondary reverse mass transfer and heating, and then enters the interior of ethanol refining tower 1 through the reflux inlet. Liquid is discharged from the bottom of methanol deesterification tower 2 through the liquid phase outlet. The discharged liquid undergoes reverse mass transfer and heating in the high-temperature zone of reverse heat exchange unit A12. After heating, the liquid enters the high-temperature zone of reverse heat exchange unit B22 for secondary reverse mass transfer and heating, and then enters the interior of methanol deesterification tower 2 through the reflux inlet.

[0024] The gas from the top of methanol deesterification column 2 is compressed by compression unit B21 and then enters the countercurrent heat exchange unit B22. The output temperature of compression unit B21 is close to 130℃. The temperature of the gas from the top of ethanol purification column 1 after passing through compression unit A11 is in the range of 100℃-105℃. The gas volume of compression unit B21 is greater than that of compression unit A11. Due to the lower temperature of reverse heat exchange unit A12 compared to reverse heat exchange unit B22, the reflux liquid from compression unit A11 first enters reverse heat exchange unit A12 for preheating. Since the temperature difference between compression unit A11 and reverse heat exchange unit A12 is small and reverse heat transfer is used, controlling the temperature difference improves the service life of the equipment. After being preheated, the liquid enters through the low-temperature zone of reverse heat exchange unit B22. The preheating by reverse heat exchange unit A12 will not affect the service life of reverse heat exchange unit B22. Moreover, the gas delivery volume of reverse heat exchange unit B22 is large, the reflux liquid volume of ethanol refining tower 1 is large, and the gas temperature of reverse heat exchange unit B22 is high. After the two are coupled, the temperature of the reflux liquid in ethanol refining tower 1 is more likely to approach 90℃.

[0025] The bottom liquid of methanol deesterification tower 2 flows into the high-temperature zone of the reverse heat exchange unit A12. The bottom liquid enters the countercurrent mass transfer and heats up through the middle of the reverse heat exchange unit A12. The bottom temperature of methanol deesterification tower 2 is higher than that of ethanol refining tower 1. Therefore, the bottom liquid of methanol deesterification tower 2 can reduce the impact of temperature difference on the equipment by entering through the middle of the reverse heat exchange unit A12. Methanol deesterification tower 2 exits through the high-temperature zone of the reverse heat exchange unit A12 and is close to the hot side inlet of the reverse heat exchange unit A12, and enters the high-temperature zone of the reverse heat exchange unit B22. The flow rate of the bottom liquid discharged from methanol deesterification tower 2 is less than that of ethanol refining tower 1. The high-temperature zones of the reverse heat exchange units A12 and B22 are compatible with the reflux liquid temperature of methanol deesterification tower 2. Therefore, the liquid temperature can still be maintained at a high level.

[0026] This technical solution centrally integrates the heat exchangers for ethanol refining tower 1 and methanol deesterification tower 2, utilizing the synergistic heat exchange of the two heat exchangers to solve the problem of wasted heat caused by the large gas volume and small liquid volume in methanol deesterification tower 2, while simultaneously addressing the issues of slow heating and substandard temperature in ethanol refining tower 1 due to its small gas volume and large liquid volume. After coupling, the reflux liquid from the heat exchange is more compliant with standards, thereby further reducing the use of additional heat sources.

[0027] Furthermore, the reverse heat exchange unit A12 has a high-temperature heat exchange zone A121 and a low-temperature heat exchange zone A122 connected in series on the hot side, and the reverse heat exchange unit B22 has a high-temperature heat exchange zone B221 and a low-temperature heat exchange zone B222 connected in series on the hot side. The gas output from the compression unit A11 passes through the high-temperature heat exchange zone A121 and the low-temperature heat exchange zone A122 in sequence, and the gas output from the compression unit B21 passes through the high-temperature heat exchange zone B221 and the low-temperature heat exchange zone B222 in sequence. The liquid discharged from the ethanol refining tower 1 through the liquid phase outlet passes through... The liquid enters from the low-temperature end of the low-temperature heat exchange zone A122, and after heat exchange and heating, it exits through the high-temperature end of the low-temperature heat exchange zone A122 and is transported to the low-temperature end of the low-temperature heat exchange zone B222. The liquid is finally exited through the high-temperature end of the low-temperature heat exchange zone B222. The liquid discharged from the methanol deesterification tower 2 through the liquid phase outlet enters from the low-temperature end of the high-temperature heat exchange zone A121, and after heat exchange and heating, it exits through the high-temperature end of the high-temperature heat exchange zone A121 and is transported to the low-temperature end of the high-temperature heat exchange zone B221. The liquid is finally exited through the high-temperature end of the high-temperature heat exchange zone B221.

[0028] Plate heat exchangers offer higher heat exchange efficiency, but the flow channels are primarily located within the plate grooves, and the inlet and outlet are mainly at the ends, making it difficult to integrate with this technical solution. To address this issue, the following improvements are made: The reverse heat exchange unit A12 consists of two independent plate heat exchangers: a high-temperature heat exchange zone A121 and a low-temperature heat exchange zone A122. The hot-side pipes of the two heat exchangers are connected in series, while the cold-side pipes are independently connected. Similarly, the reverse heat exchange unit B22 consists of two independent plate heat exchangers: a high-temperature heat exchange zone B221 and a low-temperature heat exchange zone B222. The hot-side pipes of the two heat exchangers are connected in series, while the cold-side pipes are independently connected, thus forming… Figure 2 The cold side of the independent plate heat exchangers is connected in series. The overall structure is simple, the heat exchange is more efficient, and the modification cost is low; ready-made equipment can be purchased and connected in series with pipes.

[0029] The discharge channels of ethanol refining tower 1 are divided into three paths. One path enters the reverse heat exchange unit A12 and returns to the bottom of the tower via the reverse heat exchange unit B22. The second path returns to the bottom of the tower via the reboiler A14. The third path is discharged as heavy components.

[0030] The first stream of the ethanol refining column 1 enters the cold side of the low-temperature zone of the reverse heat exchange unit A12 and undergoes reverse mass transfer heating. The heated liquid is then transported to the cold side inlet of the low-temperature zone of the reverse heat exchange unit B22 and undergoes a second reverse mass transfer heating in the low-temperature zone of the reverse heat exchange unit B22. The heated liquid is then returned to the interior of the ethanol refining column 1. The second stream is heated by the reflux tank A13 and then returned to the bottom of the column. The third stream is discharged from the column as a heavy component.

[0031] The liquid flowing out of the liquid phase outlet of methanol deesterification tower 2 is divided into three paths: one path enters the reverse heat exchange unit A12 and returns to the bottom of the tower through the reverse heat exchange unit B22; the second path returns to the bottom of the tower after being heated by the reboiler B24; and the third path is discharged as methanol product. The heat source for reboilers A14 and B24 is external steam.

[0032] The first path of methanol deesterification tower 2 is heated by reverse mass transfer in the high-temperature zone of reverse heat exchange unit A12. The heated liquid enters the high-temperature zone of reverse heat exchange unit B22 for secondary heating by reverse mass transfer. The heated liquid is then returned to ethanol refining tower 1. The second path is heated by reboiler B24 and then returned to the bottom of the tower. The third path is discharged as methanol product.

[0033] The liquid at the bottom of the tower is divided into three streams, which are heated by the reboiler and heat exchanger respectively before returning. These three streams, when combined, allow for flexible matching of external steam heating and heat pump heating by adjusting the flow ratio of each stream, adapting to different heat demands under various operating conditions. The original steam reboiler is retained as an auxiliary heat source and backup, ensuring normal operation of the unit even during heat pump system maintenance or failure, without affecting production continuity.

[0034] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A distillation energy-saving system for coal-based ethanol separation, comprising an ethanol refining tower (1) and a methanol deesterification tower (2), characterized in that: The top gas phase outlet of the ethanol refining tower (1) is connected to the compression unit A (11). The gas output from the compression unit A (11) enters the reverse heat exchange unit A (12) for heat exchange on the hot side and is then collected in the reflux tank A (13). The top gas phase outlet of the ethanol refining tower (1) is connected to the compression unit B (21). The gas output from the compression unit B (21) enters the reverse heat exchange unit B (22) for heat exchange on the hot side and is then collected in the reflux tank B (23). The bottom of the ethanol refining tower (1) discharges liquid through the liquid phase outlet. The discharged liquid undergoes reverse mass transfer and heating in the low-temperature zone of the reverse heat exchange unit A (12). After heating, the liquid enters the low-temperature zone of the reverse heat exchange unit B (22) for secondary heating through reverse mass transfer and then enters the interior of the ethanol refining tower (1) through the reflux inlet. The methanol deesterification tower (2) discharges liquid through the liquid phase outlet at the bottom. The discharged liquid undergoes reverse mass transfer and heating in the high-temperature zone of the reverse heat exchange unit A (12). After heating, the liquid enters the high-temperature zone of the reverse heat exchange unit B (22) for secondary reverse mass transfer and heating, and then enters the interior of the methanol deesterification tower (2) through the reflux inlet.

2. The distillation energy-saving system for coal-based ethanol separation according to claim 1, characterized in that: The reverse heat exchange unit A (12) has a high-temperature heat exchange zone A (121) and a low-temperature heat exchange zone A (122) connected in series on the hot side. The reverse heat exchange unit B (22) has a high-temperature heat exchange zone B (221) and a low-temperature heat exchange zone B (222) connected in series on the hot side. The gas output from the compression unit A (11) passes through the high-temperature heat exchange zone A (121) and the low-temperature heat exchange zone A (122) in sequence. The gas output from the compression unit B (21) passes through the high-temperature heat exchange zone B (221) and the low-temperature heat exchange zone B (222) in sequence.

3. The distillation energy-saving system for coal-based ethanol separation according to claim 2, characterized in that: The ethanol refining tower (1) discharges liquid through the liquid phase outlet and enters through the low-temperature end of the low-temperature heat exchange zone A (122). After heat exchange and heating, the liquid is output through the high-temperature end of the low-temperature heat exchange zone A (122) and transported to the low-temperature end of the low-temperature heat exchange zone B (222). Finally, the liquid is output through the high-temperature end of the low-temperature heat exchange zone B (222).

4. The distillation energy-saving system for coal-based ethanol separation according to claim 2, characterized in that: The methanol deesterification tower (2) discharges liquid through the liquid phase outlet and enters through the low-temperature end of the high-temperature heat exchange zone A (121). After the liquid is heated by heat exchange, it is output through the high-temperature end of the high-temperature heat exchange zone A (121) and transported to the low-temperature end of the high-temperature heat exchange zone B (221). Finally, the liquid is output through the high-temperature end of the high-temperature heat exchange zone B (221).

5. The distillation energy-saving system for coal-based ethanol separation according to claim 1, characterized in that: The discharge channel of the ethanol refining tower (1) is divided into three paths. One path enters the reverse heat exchange unit A (12) and returns to the bottom of the tower via the reverse heat exchange unit B (22). The second path returns to the bottom of the tower via the reboiler A (14). The third path is discharged as a heavy component.

6. The distillation energy-saving system for coal-based ethanol separation according to claim 5, characterized in that: The liquid flowing out of the liquid phase outlet of the methanol deesterification tower (2) is divided into three paths: one path enters the reverse heat exchange unit A (12) and returns to the bottom of the tower through the reverse heat exchange unit B (22); the second path returns to the bottom of the tower after being heated by the reboiler B (24); and the third path is discharged as methanol product.

7. The distillation energy-saving system for coal-based ethanol separation according to claim 1, characterized in that: A condensate pipeline is provided between the hot side outlet of the compression unit A (11) and the reflux tank A (13). The outlet of the reflux tank A (13) is connected to the top reflux inlet of the ethanol refining tower (1) and the feed inlet of the methanol deesterification tower (2), respectively.

8. The distillation energy-saving system for coal-based ethanol separation according to claim 1, characterized in that: A condensate pipeline is provided between the hot side outlet of the reverse heat exchange unit B (22) and the reflux tank B (23). The outlet of the reflux tank B (23) is connected to the top reflux inlet of the methanol deesterification tower (2) and the methyl acetate discharge pipeline, respectively.

9. A distillation energy-saving system for coal-based ethanol separation according to claim 6, characterized in that: The heat source for reboiler A (14) and reboiler B (24) is external steam.

10. A method of using a distillation energy-saving system for coal-based ethanol separation according to any one of claims 1-9, characterized in that: include: S1: The crude ethanol after the removal of methyl acetate is sent to the ethanol refining tower (1) for distillation separation; S2: The gaseous methanol and methyl acetate at the top of the ethanol refining tower (1) are compressed and heated by the compression unit A (11). The heated gas enters the reverse heat exchange unit A (12) to exchange heat with part of the bottom liquid. After condensation, it enters the reflux tank A (13). Part of the condensate in the reflux tank A (13) is returned to the top of the ethanol refining tower (1), and the other part is sent to the methanol deesterification tower (2). S3: The heavy component liquid flowing out of the bottom of the ethanol refining tower (1) is divided into three paths: the first path enters the reverse mass transfer and heats up through the cold side of the low temperature zone of the reverse heat exchange unit A (12). The heated liquid is transported to the cold side inlet of the low temperature zone of the reverse heat exchange unit B (22) and undergoes a second reverse mass transfer and heats up in the low temperature zone of the reverse heat exchange unit B (22). The heated liquid flows back into the interior of the ethanol refining tower (1). The second path returns to the bottom of the tower after being heated by the reflux tank A (13). The third path is discharged out of the tower as a heavy component. S4: The gas phase at the top of the methanol deesterification tower (2) is compressed and heated by the compression unit B (21), and then enters the reverse heat exchange unit B (22) to exchange heat with part of the bottom liquid. After condensation, it enters the reflux tank B (23). Part of the condensate in the reflux tank B (23) is returned to the top of the methanol deesterification tower (2), and the other part is discharged as methyl acetate. S5: The methanol liquid flowing out of the bottom of the methanol deesterification tower (2) is divided into three paths: the first path is heated by reverse mass transfer in the high-temperature zone of the reverse heat exchange unit A (12), and the heated liquid enters the high-temperature zone of the reverse heat exchange unit B (22) for a second heating by reverse mass transfer. The heated liquid flows back to the ethanol refining tower (1), the second path is heated by reboiler B (24) and then returns to the bottom of the tower, and the third path is discharged as methanol product.

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