Five-tower reverse triple-effect heat pump assisted methanol rectification energy-saving device and process method

Abstract

The invention relates to a five-tower reverse triple-effect heat pump assisted methanol rectification energy-saving device and process method, a tower top steam recompression type heat pump is adopted by a normal pressure rectification tower, and a tower bottom liquid phase flash evaporation type heat pump is adopted by a high pressure rectification tower; part of the gas phase at the top of the normal-pressure rectifying tower is compressed and heated by a compressor at the top of the normal-pressure rectifying tower and then supplies heat to a reboiler I of the high-pressure rectifying tower to heat reduced-pressure wastewater at the bottom of the high-pressure rectifying tower to increase the gasification amount. The process is coupled with the heat pump assisted rectification and multi-effect rectification technology, the comprehensive COP value of a heat pump reaches 3.348, the unit production consumption of refined methanol is 0.25 steam unit consumption and 95kW power consumption, remarkable energy conservation of methanol rectification is realized, and the method is suitable for energy-saving transformation of the existing five-tower reverse double-hot-trap process.

Description

Technical Field

[0001] The present invention relates to the technical field of distillation, and in particular to a five-tower reverse triple-effect heat pump-assisted methanol distillation energy-saving device and a process method. Background Art

[0002] Global warming is already occurring, and increasing global temperature rise will lead to multiple and complex hazards. Deep, rapid, and sustained emissions reductions can significantly reduce climate warming within about 20 years and significantly change the composition of the atmosphere within a few years.

[0003] Methanol plays multiple roles in the modern chemical industry. It serves as both a vital clean energy carrier and a key precursor for the synthesis of bulk chemicals such as formaldehyde and acetic acid. Industry statistics show that its global consumption ranks fourth among basic organic raw materials, behind only ethylene, propylene, and benzene. my country holds significant advantages in this field, possessing not only the world's largest cluster of production facilities but also the largest consumer market. Notably, annual carbon emissions from the entire industry chain have reached 200 million tons. Separation and purification, as energy-intensive processes, account for approximately 25% of the total energy consumption. While the currently widely used co-current three-tower distillation process ensures product purity, it suffers from inherent thermodynamic inefficiencies, making it difficult to meet the demands of modern green manufacturing. This necessitates the development of new, more energy-efficient separation technologies. Summary of the Invention

[0004] In order to solve the technical problems in the background technology, the present invention proposes a five-tower reverse triple-effect heat pump assisted methanol distillation energy-saving device and process method.

[0005] The first technical solution of the present invention is a five-tower reverse triple-effect heat pump-assisted methanol distillation energy-saving device, comprising a pre-distillation tower, an atmospheric distillation tower, a medium-pressure distillation tower, a high-pressure distillation tower, and a methanol recovery tower connected in sequence, wherein the lower portion of the pre-distillation tower is connected to a pre-distillation tower reboiler 1 and a pre-distillation tower reboiler 2, the lower portion of the atmospheric distillation tower is connected to an atmospheric distillation tower reboiler, the lower portion of the medium-pressure distillation tower is connected to a medium-pressure distillation tower reboiler, the lower portion of the high-pressure distillation tower is connected to a high-pressure distillation tower reboiler 1 and a high-pressure distillation tower reboiler 2, and the lower portion of the methanol recovery tower is connected to a methanol recovery tower reboiler. The first gas phase branch at the top of the medium-pressure distillation tower supplies heat to the pre-distillation tower reboiler 2, and the second gas phase branch at the top of the medium-pressure distillation tower supplies heat to the atmospheric distillation tower reboiler. The high-pressure distillation tower's overhead gas phase provides heat to the medium-pressure distillation tower's reboiler, while high-temperature wastewater extracted from the high-pressure distillation tower's bottoms provides heat to the methanol recovery tower's reboiler. The atmospheric distillation tower utilizes an overhead vapor recompression heat pump, while the high-pressure distillation tower utilizes a bottom liquid flash heat pump. A portion of the atmospheric distillation tower's overhead gas phase is compressed and heated by the atmospheric distillation tower's overhead compressor, then used to heat the high-pressure distillation tower's reboiler.

[0006] As a preferred solution, the high-pressure distillation tower T4 produces high-temperature wastewater.

[0007] As a preferred solution, fuel alcohol is produced at the bottom of the methanol recovery tower T5.

[0008] As a preferred solution, the temperature of the high-temperature wastewater produced from the bottom of the high-pressure distillation tower T4 is about 140°C, and the temperature of the fuel alcohol produced from the bottom of the methanol recovery tower T5 is 75-80°C.

[0009] As a preferred solution, refined methanol is extracted from the tops of the vacuum distillation tower T2, the medium-pressure distillation tower T3, the high-pressure distillation tower T4 and the methanol recovery tower T6.

[0010] As a preferred solution, the process is suitable for energy-saving transformation of the existing five-tower reverse double heat sink process.

[0011] As a preferred solution, the atmospheric distillation tower T2 adopts a top vapor recompression heat pump, and the high-pressure distillation tower T4 adopts a bottom liquid phase flash heat pump. Part of the gas phase at the top of the atmospheric distillation tower T2 is compressed by the heat pump to increase the temperature and grade to heat the bottom stream wastewater of the high-pressure distillation tower T4 that has been reduced in pressure and cooled. The heated and vaporized bottom stream of the high-pressure distillation tower T4 is compressed by the compressor and returned to the bottom of the high-pressure distillation tower T4. The comprehensive COP value of the heat pump reaches 3.348.

[0012] As a preferred solution, the residual load at the bottom of the high-pressure distillation tower T4 is heated by 0.5 MPa (G) steam.

[0013] As a preferred solution, the compression ratios of the atmospheric distillation tower top compressor C1 and the high-pressure distillation tower bottom compressor C2 are both less than 6, thereby avoiding excessively high compression ratios.

[0014] As a preferred solution, the process coupling relationship is relatively complex and requires a carefully designed control solution.

[0015] The second technical solution of the present invention is a process method for a five-tower reverse triple-effect heat pump-assisted methanol distillation energy-saving device, comprising the following steps:

[0016] S1: The raw material crude methanol flows into the pre-distillation tower T1, and the overhead vapor is partially condensed to separate the light component non-condensable gas; part of the stream at the bottom of the pre-distillation tower T1 flows into the pre-distillation tower reboiler R1A for steam heating, and another part of the stream flows into the pre-distillation tower reboiler R1B for heating through the first gas phase branch at the top of the medium-pressure distillation tower T3. After heating and vaporization, it flows into the pre-distillation tower T1, and the remaining stream flows into the middle and lower part of the atmospheric distillation tower T2 for separation;

[0017] S2: Part of the gas phase at the top of the atmospheric distillation tower T2 is compressed and heated by the atmospheric distillation tower top compressor C1 to provide heat to the reboiler 1 of the high-pressure distillation tower. The remaining gas phase at the top of the atmospheric distillation tower T2 is fully condensed in the atmospheric distillation tower condenser CX1 and partially refluxed, and part of it flows out of the boundary area as the refined methanol product; the bottom stream of the atmospheric distillation tower T2 flows into the atmospheric distillation tower reboiler R2, and is heated by the second gas phase branch at the top of the medium-pressure distillation tower T3. After heating and vaporization, it flows into the atmospheric distillation tower T2, and the remaining stream flows into the middle and lower part of the medium-pressure distillation tower T3 for separation;

[0018] S3: The first gas phase branch at the top of the medium-pressure distillation tower T3 supplies heat to the reboiler 1 of the pre-distillation tower, and the second gas phase branch supplies heat to the reboiler of the atmospheric distillation tower. After supplying heat, it flows back to the condenser CX2 of the medium-pressure distillation tower, is fully condensed, and part of it is refluxed, and part of it flows out of the boundary area as the refined methanol product; the bottom stream of the medium-pressure distillation tower T3 flows into the medium-pressure distillation tower reboiler R3, and is heated by part of the steam at the top of the high-pressure distillation tower. After heating and vaporization, it flows into the medium-pressure distillation tower T3, and the remaining stream flows into the middle and lower part of the high-pressure distillation tower T4 for separation;

[0019] S4: The steam from the top of the high-pressure distillation tower T4 provides heat to the reboiler R3 of the medium-pressure distillation tower; part of the bottom stream of the high-pressure distillation tower T4 flows into the high-pressure distillation tower reboiler R4A after reduced pressure flash evaporation through the pressure reducing valve V1, and is heated by the compressed gas phase at the top of the atmospheric distillation tower T2. After heating, it is compressed by the high-pressure distillation tower bottom compressor C2 and enters the bottom of the high-pressure distillation tower T4. The other part of the stream flows into the high-pressure distillation tower reboiler R4B, where it is heated by steam, heated and vaporized, and then flows into the high-pressure distillation tower T4. The high-temperature wastewater produced at the bottom of the tower provides heat to the methanol recovery tower reboiler R5 and then flows out of the boundary area;

[0020] S5: The steam from the top of methanol recovery tower T5 is partially refluxed after full condensation, and part of it flows out of the boundary area as refined methanol product, and the bottom flow flows out of the boundary area as fuel alcohol product.

[0021] Furthermore, the operating pressure of the pre-distillation tower T1 is 150±10 kPa; the operating pressure of the atmospheric distillation tower T2 is 100±10 kPa, and the reflux ratio is 1.5; the operating pressure of the medium-pressure distillation tower T3 is 320±10 kPa, and the reflux ratio is 2.

[0022] Furthermore, the operating pressure of the high-pressure distillation tower T4 is 600±10 kPa, and the reflux ratio is 2; the operating pressure of the methanol recovery tower T5 is 100±10 kPa, and the reflux ratio is 3.5.

[0023] Furthermore, the temperature of the wastewater taken out from the bottom of the high-pressure distillation tower T4 is 140±10°C, and the methanol content is less than 50ppm; the temperature of the fuel alcohol taken out from the bottom of the methanol recovery tower T5 is 78.6±5°C.

[0024] In order to reduce energy consumption, the present invention proposes for the first time an innovative five-tower reverse three-effect heat pump-assisted methanol distillation energy-saving device. The process couples heat pump-assisted distillation technology with multi-effect distillation technology, including a pre-distillation tower, an atmospheric distillation tower, a medium-pressure distillation tower, a high-pressure distillation tower and a methanol recovery tower. The atmospheric distillation tower adopts a top vapor recompression heat pump, and the high-pressure distillation tower adopts a bottom liquid-phase flash heat pump, realizing the two-way running of the two heat pump technical solutions and introducing a new structure and operation mode for the methanol distillation process. In the present invention, the comprehensive COP value of the heat pump reaches 3.348, and the unit refined methanol production has a steam consumption of only 0.25 and an electricity consumption of 95kW, achieving significant energy saving in methanol distillation, and is suitable for energy-saving transformation of the existing five-tower reverse double heat sink process.

[0025] This application has the following advantages:

[0026] 1. In this process, the atmospheric distillation tower, the medium-pressure distillation tower and the high-pressure distillation tower form a reverse three-effect, and the pre-distillation tower and the methanol recovery tower serve as heat sinks. The first gas phase branch at the bottom of the medium-pressure distillation tower supplies heat to the second reboiler of the pre-distillation tower, and the high-temperature wastewater produced from the bottom of the high-pressure distillation tower supplies heat to the reboiler of the methanol recovery tower. On this basis, the process adopts heat pump-assisted distillation technology. The atmospheric distillation tower adopts a top vapor recompression heat pump, and the high-pressure distillation tower adopts a bottom liquid flash heat pump. Part of the gas phase at the top of the atmospheric distillation tower is compressed by the heat pump to increase the temperature and grade to heat the wastewater at the bottom of the high-pressure distillation tower that has been reduced in pressure and cooled, thereby increasing the gasification amount.

[0027] 2. The production capacity of refined methanol is dispersed, with refined methanol products extracted from the top of the atmospheric distillation tower, medium-pressure distillation tower, high-pressure distillation tower and methanol recovery tower. The yield is high and the tower equipment is small in size, which is easy to manufacture, transport and install.

[0028] 3. The compression ratios of the atmospheric distillation tower top compressor and the high-pressure distillation tower bottom compressor are both less than 6, avoiding excessively high compression ratios.

[0029] 4. The process couples heat pump-assisted distillation technology with multi-effect distillation technology, making full use of waste heat. The comprehensive COP value of the heat pump reaches 3.348, and the unit of refined methanol production only consumes 0.25 steam and 95kW of electricity, achieving the goal of energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flowchart of this application;

[0031] T1 pre-distillation tower, T2 atmospheric distillation tower, T3 medium-pressure distillation tower, T4 high-pressure distillation tower, T5 methanol recovery tower, R1A pre-distillation tower reboiler one, R1B pre-distillation tower reboiler two, R2 atmospheric distillation tower reboiler, R3 medium-pressure distillation tower reboiler, R4A high-pressure distillation tower reboiler one, R4B high-pressure distillation tower reboiler two, R5 methanol recovery tower reboiler, CX1 atmospheric distillation tower condenser, CX2 medium-pressure distillation tower condenser, CX3 high-pressure distillation tower condenser, CX4 methanol recovery tower condenser, D1 pre-distillation tower reflux tank, C1 atmospheric distillation tower top compressor, C2 high-pressure distillation tower bottom compressor, V1 pressure reducing valve. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1 The specific embodiments of the present invention are described in detail. It should be noted that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0033] Example 1:

[0034] like Figure 1 As shown, this embodiment provides a five-tower reverse triple-effect heat pump-assisted methanol distillation energy-saving device, comprising a pre-distillation tower T1, an atmospheric distillation tower T2, a medium-pressure distillation tower T3, a high-pressure distillation tower T4, and a methanol recovery tower T5, which are connected in sequence. Through a carefully designed process, the present invention achieves bidirectional coupling between the overhead vapor recompression heat pump and the bottom liquid flash heat pump, and combines multiple-effect distillation technology to further improve energy efficiency. The process includes the following steps:

[0035] 1) The crude methanol feedstock flows into the pre-distillation tower T1, and the overhead vapor is partially condensed to separate the light component non-condensable gas; part of the stream at the bottom of the pre-distillation tower T1 flows into the pre-distillation tower reboiler R1A to be heated by steam, while another part of the stream flows into the pre-distillation tower reboiler R1B to be heated by the first gas phase branch at the top of the medium-pressure distillation tower T3. After heating and vaporization, it flows into the pre-distillation tower T1, and the remaining stream flows into the middle and lower part of the atmospheric distillation tower T2 for separation.

[0036] 2) Part of the gas phase at the top of the atmospheric distillation tower T2 is compressed and heated by the atmospheric distillation tower top compressor C1 to provide heat to the reboiler 1 of the high-pressure distillation tower. The remaining gas phase at the top of the atmospheric distillation tower T2 is fully condensed in the atmospheric distillation tower condenser CX1 and partially refluxed, and part of it flows out of the boundary area as the refined methanol product; the bottom stream of the atmospheric distillation tower T2 flows into the atmospheric distillation tower reboiler R2, and is heated by the second gas phase branch at the top of the medium-pressure distillation tower T3. After being heated and vaporized, it flows into the atmospheric distillation tower T2, and the remaining stream flows into the middle and lower part of the medium-pressure distillation tower T3 for separation.

[0037] 3) The first gas phase branch from the top of the medium-pressure distillation tower T3 supplies heat to the reboiler 1 of the pre-distillation tower, and the second gas phase branch supplies heat to the reboiler of the atmospheric distillation tower. After supplying heat, it flows back to the condenser CX2 of the medium-pressure distillation tower, is fully condensed, and part of it is refluxed, and part of it flows out of the boundary area as the refined methanol product; the bottom stream of the medium-pressure distillation tower T3 flows into the medium-pressure distillation tower reboiler R3, is heated by part of the steam from the top of the high-pressure distillation tower, is heated and vaporized, and flows into the medium-pressure distillation tower T3. The remaining stream flows into the middle and lower part of the high-pressure distillation tower T4 for separation.

[0038] 4) The steam from the top of the high-pressure distillation tower T4 provides heat to the reboiler R3 of the medium-pressure distillation tower; part of the bottom stream of the high-pressure distillation tower T4 flows through the pressure reducing valve V1 and flash evaporation, then flows into the high-pressure distillation tower reboiler R4A, the top compressed gas phase of the atmospheric distillation tower T2, and then is heated by the high-pressure distillation tower bottom compressor C2, and then flows into the bottom of the high-pressure distillation tower T4. Another part of the stream flows into the high-pressure distillation tower reboiler R4B, where it is heated by steam, heated and vaporized, and then flows into the high-pressure distillation tower T4. The high-temperature wastewater produced from the bottom of the tower provides heat to the reboiler R5 of the methanol recovery tower, and then flows out of the boundary area.

[0039] 5) After full condensation, part of the steam from the top of methanol recovery tower T5 is refluxed, part of it flows out of the boundary area as refined methanol product, and the bottom flow flows out of the boundary area as fuel alcohol product.

[0040] The operating pressure of the pre-distillation tower T1 is 150±10kPa; the operating pressure of the atmospheric distillation tower T2 is 100±10kPa, and the reflux ratio is 1.5; the operating pressure of the medium-pressure distillation tower T3 is 320±10kPa, and the reflux ratio is 2; the operating pressure of the high-pressure distillation tower T4 is 600±10kPa, and the reflux ratio is 2; the operating pressure of the methanol recovery tower T5 is 100±10kPa, and the reflux ratio is 3.5.

[0041] The temperature of the wastewater taken out from the bottom of the high-pressure distillation tower T4 is 140±10°C, and the methanol content is less than 50ppm; the temperature of the fuel alcohol taken out from the bottom of the methanol recovery tower T5 is 78.6±5°C.

[0042] The water content of the crude methanol raw material is about 4%.

[0043] Compared with the existing industrial process, the unit consumption of refined methanol production in this solution is only 0.25 steam unit consumption and 95kW electricity consumption, with a yield of 99.99% and a purity of refined methanol as high as 99.99%.

[0044] The preferred embodiment of the present application is described in detail above in conjunction with the accompanying drawings. However, the present application is not limited to the specific details in the above-mentioned embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the scope of protection of the present application.

[0045] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner unless there is any contradiction. In order to avoid unnecessary repetition, the various possible combinations of this application will not be described separately.

[0046] In addition, the various implementation methods of the present application can be arbitrarily combined, as long as they do not violate the concept of the present application, and they should also be regarded as the contents disclosed in the present application.

Claims

1. A five-tower reverse triple-effect heat pump assisted methanol distillation energy-saving device, characterized in that: It includes a pre-distillation tower T1, an atmospheric distillation tower T2, a medium-pressure distillation tower T3, a high-pressure distillation tower T4, and a methanol recovery tower T5 connected in sequence; The atmospheric distillation tower T2 adopts a tower top vapor recompression heat pump. The gas phase at the top of the atmospheric distillation tower T2 is compressed and heated by the atmospheric distillation tower top compressor C1 to provide heat to the high-pressure distillation tower reboiler R4A. The high-pressure distillation tower T4 uses a bottom liquid-phase flash heat pump. The decompression wastewater at the bottom of the high-pressure distillation tower T4 is heated and vaporized, and then returns to the bottom of the tower through the high-pressure distillation tower bottom compressor C2; The lower part of the pre-distillation tower T1 is connected to a pre-distillation tower reboiler R1A and a pre-distillation tower reboiler R1B, the lower part of the atmospheric distillation tower T2 is connected to an atmospheric distillation tower reboiler R2, the lower part of the medium-pressure distillation tower T3 is connected to a medium-pressure distillation tower reboiler R3, the lower part of the high-pressure distillation tower T4 is connected to a high-pressure distillation tower reboiler R4A and a high-pressure distillation tower reboiler R4B, and the lower part of the methanol recovery tower T5 is connected to a methanol recovery tower reboiler R5; The first gas phase branch at the top of the medium-pressure distillation tower T3 supplies heat to the second reboiler R1B of the pre-distillation tower, and the second gas phase branch at the top of the medium-pressure distillation tower T3 supplies heat to the reboiler R2 of the atmospheric distillation tower; the gas phase at the top of the high-pressure distillation tower T4 supplies heat to the reboiler R3 of the medium-pressure distillation tower, and the high-temperature wastewater produced at the bottom of the high-pressure distillation tower T4 supplies heat to the reboiler R5 of the methanol recovery tower; the tops of the atmospheric distillation tower T2, the medium-pressure distillation tower T3, the high-pressure distillation tower T4 and the methanol recovery tower T5 all produce refined methanol; High-temperature wastewater is produced at the bottom of the high-pressure distillation tower T4.

2. The five-tower reverse triple-effect heat pump-assisted methanol distillation energy-saving device according to claim 1 is characterized in that: Fuel alcohol is produced at the bottom of the methanol recovery tower T5.

3. A five-tower reverse triple-effect heat pump assisted methanol distillation energy-saving device according to claim 1, characterized in that: The atmospheric distillation tower T2 adopts a top vapor recompression heat pump, and the high-pressure distillation tower T4 adopts a bottom liquid flash heat pump. The gas phase at the top of the atmospheric distillation tower T2 is compressed by the heat pump to increase the temperature and grade to heat the wastewater at the bottom of the high-pressure distillation tower T4 that has been decompressed and cooled. The heated and vaporized bottom stream of the high-pressure distillation tower T4 is compressed by the compressor and returned to the bottom of the high-pressure distillation tower T4. The comprehensive COP value of the heat pump reaches 3.

348.

4. A process method for a five-tower reverse triple-effect heat pump-assisted methanol distillation energy-saving device according to any one of claims 1 to 3, characterized in that: The steps include: S1: The raw material crude methanol flows into the pre-distillation tower T1, and the overhead vapor is partially condensed to separate the light component non-condensable gas; part of the stream at the bottom of the pre-distillation tower T1 flows into the pre-distillation tower reboiler R1A for steam heating, and another part of the stream flows into the pre-distillation tower reboiler R1B for heating through the first gas phase branch at the top of the medium-pressure distillation tower T3. After heating and vaporization, it flows into the pre-distillation tower T1, and the remaining stream flows into the middle and lower part of the atmospheric distillation tower T2 for separation; S2: Part of the gas phase at the top of the atmospheric distillation tower T2 is compressed and heated by the atmospheric distillation tower top compressor C1 to provide heat to the reboiler 1 of the high-pressure distillation tower. The remaining gas phase at the top of the atmospheric distillation tower T2 is fully condensed in the atmospheric distillation tower condenser CX1 and partially refluxed, and part of it flows out of the boundary area as the refined methanol product; the bottom stream of the atmospheric distillation tower T2 flows into the atmospheric distillation tower reboiler R2, and is heated by the second gas phase branch at the top of the medium-pressure distillation tower T3. After heating and vaporization, it flows into the atmospheric distillation tower T2, and the remaining stream flows into the middle and lower part of the medium-pressure distillation tower T3 for separation; S3: The first gas phase branch at the top of the medium-pressure distillation tower T3 supplies heat to the reboiler 1 of the pre-distillation tower, and the second gas phase branch supplies heat to the reboiler of the atmospheric distillation tower. After supplying heat, it flows back to the condenser CX2 of the medium-pressure distillation tower, is fully condensed, and part of it is refluxed, and part of it flows out of the boundary area as the refined methanol product; the bottom stream of the medium-pressure distillation tower T3 flows into the medium-pressure distillation tower reboiler R3, and is heated by part of the steam at the top of the high-pressure distillation tower. After heating and vaporization, it flows into the medium-pressure distillation tower T3, and the remaining stream flows into the middle and lower part of the high-pressure distillation tower T4 for separation; S4: The steam from the top of the high-pressure distillation tower T4 provides heat to the reboiler R3 of the medium-pressure distillation tower; part of the bottom stream of the high-pressure distillation tower T4 flows into the high-pressure distillation tower reboiler R4A after reduced pressure flash evaporation through the pressure reducing valve V1, and is heated by the compressed gas phase at the top of the atmospheric distillation tower T2. After heating, it is compressed by the high-pressure distillation tower bottom compressor C2 and enters the bottom of the high-pressure distillation tower T4. The other part of the stream flows into the high-pressure distillation tower reboiler R4B, where it is heated by steam, heated and vaporized, and then flows into the high-pressure distillation tower T4. The high-temperature wastewater produced at the bottom of the tower provides heat to the methanol recovery tower reboiler R5 and then flows out of the boundary area; S5: The steam from the top of methanol recovery tower T5 is partially refluxed after full condensation, and part of it flows out of the boundary area as refined methanol product, and the bottom flow flows out of the boundary area as fuel alcohol product.

5. The method according to claim 4, characterized in that The operating pressure of the pre-distillation tower T1 is 150±10 kPa; the operating pressure of the atmospheric distillation tower T2 is 100±10 kPa, and the reflux ratio is 1.

5.

6. The method according to claim 4, characterized in that The operating pressure of the medium-pressure distillation tower T3 is 320±10 kPa, and the reflux ratio is 2.

7. The method according to claim 4, characterized in that The operating pressure of the high-pressure distillation tower T4 is 600±10 kPa, and the reflux ratio is 2.

8. The method according to claim 4, characterized in that The operating pressure of the methanol recovery tower T5 is 100±10 kPa, and the reflux ratio is 3.

5.

9. The method according to claim 4, characterized in that The temperature of the wastewater taken out from the bottom of the high-pressure distillation tower T4 is 140±10° C., and the methanol content is less than 50 ppm.

10. The method according to claim 4, characterized in that The temperature of the fuel alcohol recovered from the bottom of the methanol recovery tower T5 is 78.6±5°C.

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