A low-steam-consumption methanol recovery system and process based on heat pump integration

Abstract

This invention provides a low-steam-consumption methanol recovery system and process based on heat pump integration, belonging to the field of residual methanol recovery technology in MTBE production lines. It includes a preheating tank, whose tube side is sequentially connected to the tube side of a distillation column, a heat exchanger, a distillation compressor, the shell side of a reboiler, and the shell side of another heat exchanger. A condenser is connected to the shell-side outlet of the heat exchanger. A pipe for methanol reflux is provided between the condenser and the upper part of the distillation column. The reboiler is embedded in the lower part of the distillation column, and a flash tank is connected to the bottom of the distillation column. The top of the flash tank is connected to the lower part of the distillation column via a flash compressor, and the bottom of the flash tank is connected to the lower middle part of the distillation column. This invention utilizes the latent heat of methanol vapor at the top of the distillation column to heat the bottom liquid, and replenishes the heat by compressing and returning the flash vapor. The heat exchanger further improves the heat utilization rate, breaking through the high-energy-consumption mode of traditional distillation that relies on external steam heating, and significantly reducing the steam consumption required for methanol recovery in MTBE production.

Description

Technical Field

[0001] This invention relates to the field of residual methanol recovery technology in MTBE production lines, specifically to a low-steam-consumption methanol recovery system and process based on heat pump integration. Background Technology

[0002] Methyl tert-butyl ether (MTBE), chemical formula C5H 12 Methanol (O3) is a commonly used additive in gasoline. It is mainly produced by the etherification reaction of isobutylene (a C4 component) with methanol in the presence of an acidic catalyst. During MTBE production, unreacted methanol forms an azeotrope with the remaining C4 components. If this azeotrope is directly introduced into the subsequent alkylation process, it may lead to catalyst poisoning, equipment corrosion, and waste of C4 resources. Furthermore, given methanol's volatility, toxicity, and flammability, coupled with its high economic value, effective methanol recovery is typically required during the production process.

[0003] Existing methanol recovery processes in MTBE production typically employ a water extraction + distillation method. This method leverages the miscibility of methanol and water, while C4 hydrocarbons are insoluble in water. Methanol is separated through water washing and extraction, and then the methanol-water mixture is distilled in a distillation column to achieve methanol recovery. This process usually relies on external steam as a heat source to provide the heat required for the reboiler in the distillation column. However, conventional methanol recovery systems suffer from high steam consumption, high energy consumption, and high operating costs. Especially under large-scale continuous production conditions, steam consumption becomes one of the key factors restricting the energy efficiency and economic benefits of the unit.

[0004] To reduce steam consumption and improve energy efficiency, in recent years, technicians in related fields have attempted to introduce energy-saving measures such as thermal integration technology, waste heat recovery systems, and heat pump-assisted distillation. Utility model patent CN222384192U discloses a methanol-water solution heat pump distillation system. This system compresses and heats the distilled methanol vapor before sending it to an evaporator. The evaporator then provides heat to the distillation column bottom through heat exchange, reducing the system's steam consumption. However, the temperature difference between the top and bottom of the methanol distillation column is often too large (around 30-40°C), significantly reducing the heat pump's heating capacity. To meet the system's temperature requirements, the compressor's energy consumption needs to increase significantly.

[0005] Patent application CN111995499A discloses a methanol heat pump distillation method and apparatus. This scheme is applied to methanol production and refining, rather than MTBE methanol recovery, and the processing differs, but the heat pump system has certain reference value. This invention combines refined methanol vapor obtained from the high-pressure distillation section with refined methanol vapor obtained from the low-pressure distillation section and processed by a primary compressor, and then enters a secondary compressor for pressurization and heating, achieving dual-tower heat pump distillation instead of double-effect distillation. Although the invention raises the temperature of the methanol vapor before secondary compression through a dual-tower heat pump, the pressure of the methanol vapor after compression increases significantly. The compressor power consumption is related to the gas temperature and initial pressure; excessively high pressure may still lead to excessively high heat pump power, thus increasing energy consumption. Furthermore, if the system hardware does not meet the high-pressure requirements, it may involve hardware upgrades and modifications, resulting in excessive costs. Summary of the Invention

[0006] The purpose of this invention is to provide a low-steam-consumption methanol recovery system and process based on heat pump integration to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-steam-consumption methanol recovery system based on heat pump integration includes a preheating tank. The tube side of the preheating tank is sequentially connected to the tube side of a distillation column, the tube side of a heat exchanger, a distillation compressor, the shell side of a reboiler, and the shell side of another heat exchanger. The shell side outlet of the heat exchanger is connected to a condenser. A pipe for methanol reflux is provided between the condenser and the upper part of the distillation column. The reboiler is embedded in the lower part of the distillation column. A flash tank is connected to the bottom of the distillation column. The top of the flash tank is connected to the lower part of the distillation column through a flash compressor. The bottom of the flash tank is connected to the lower middle part of the distillation column, forming a circulation reflux channel for the flashed material. The bottom of the distillation column is also connected to the shell side of the preheating tank for feed preheating.

[0009] Preferably, the reboiler includes an upper liquid plate and a lower liquid plate fixedly connected to the inner wall of the distillation column. A plurality of liquid pipes are fixedly installed between the upper liquid plate and the lower liquid plate. The space enclosed by the upper liquid plate, the lower liquid plate, the inner wall of the distillation column, and the outer wall of the liquid pipes constitutes the shell side of the reboiler. A gas pipe is also coaxially fixedly installed inside the liquid pipes through a fixing block. The liquid pipes are used for liquid to flow from the upper liquid plate to the lower liquid plate, and the gas pipes are used for gas to flow from the lower liquid plate to the upper liquid plate. A float valve is provided at the top of the gas pipe to prevent gas-liquid conflict in the reboiler during the operation of the distillation column.

[0010] Preferably, the top of the flash tank is connected to the flash vapor inlet of the distillation column, and the bottom of the flash tank is connected to the flash liquid inlet of the distillation column. The flash vapor inlet is located below the lower liquid plate, and the flash liquid inlet is located above the upper liquid plate.

[0011] Preferably, the bottom of the lower liquid plate is higher than the liquid level of the distillation column reboiler when it is fully loaded.

[0012] Preferably, the float valve has an air hole at the top, a stabilizing rod and a hook are evenly distributed around the bottom outer periphery of the float valve, and a groove that cooperates with the hook is provided at the top of the gas pipeline.

[0013] Specifically, the hook is made of a corrosion-resistant, rigid, and elastic material. During installation, the hook deforms under the action of the inner wall of the gas pipeline. After installation, the hook returns to its original shape and rebounds in the groove to cooperate with the installation.

[0014] This solution also provides a low-steam-consumption methanol recovery process, which uses the aforementioned low-steam-consumption methanol recovery system based on heat pump integration, and includes the following steps:

[0015] Raw material preheating: The extracted methanol mixture is preheated in a preheating tank and then sent to the middle of the distillation column;

[0016] Distillation separation: In the distillation column, mass and heat are transferred through the trays. The generated methanol vapor is discharged from the top outlet and successively passes through the heat exchanger tube side for heating and the distillation compressor for pressurization and heating. Finally, it enters the reboiler shell side and the heat exchanger shell side as a heat source and finally enters the condenser. Part of it is refluxed and the other part is stored and recovered.

[0017] Flash circulation: The liquid at the bottom of the distillation column is divided into two paths. One path enters the flash tank for flashing, and the other path enters the shell side of the preheating tank and / or is discharged. The gas in the flash tank is pressurized and heated by the flash compressor and then sent to the bottom of the distillation column. The remaining unflashed liquid in the flash tank is sent back to the middle and lower part of the distillation column through pipelines.

[0018] Preferably, in the distillation separation, the methanol vapor pressure at the top of the distillation column is 0.11~0.15 MPa, and the pressure boost of the distillation compressor is 0.1~0.2 MPa.

[0019] Preferably, in the distillation separation, the reflux ratio of the condenser to the distillation column is 1.5 to 2.2.

[0020] Preferably, in the flash evaporation cycle, the flow rate of the circulating liquid entering the flash tank is 20-50% of the feed flow rate, the pressure inside the flash tank is reduced to 0.09-0.12 MPa, and the flash compressor is pressurized to 0.20-0.25 MPa.

[0021] The beneficial effects of the above-described technical solution of the present invention are as follows:

[0022] This invention integrates the reboiler into the lower part of the distillation column, employing a nested structure of liquid and gas pipelines. This allows for dual heating of the column bottom liquid by externally compressed methanol vapor and internal gas pipeline vapor, effectively improving heat transfer efficiency and enhancing the heating capacity of the heat pump system. A floating valve device is added to the top of the gas pipeline, enabling it to achieve sealing and flexible opening under different gas velocity conditions. This effectively reduces gas-liquid impact, improves the anti-interference capability of the gas-liquid mass transfer equipment, and ensures the stability and reliability of the system operation.

[0023] This invention compresses methanol vapor from the top of the distillation column and sends it to a reboiler, utilizing its latent heat of condensation to heat the bottom liquid, replacing the traditional steam heating method and significantly reducing external steam consumption. A flash tank is added to flash-evaporate a low-concentration methanol solution under reduced pressure, further removing residual methanol. Simultaneously, the vapor generated by flash evaporation is compressed and sent back to the bottom of the distillation column to replenish heat. The residual liquid at the bottom of the flash tank is used as reflux in the stripping section of the distillation column, achieving effective recovery and reuse of low-grade heat energy.

[0024] This invention sets up a heat exchanger before the distillation compressor to form a thermal energy coupling of preheating before compression and heat release after compression. This allows the methanol vapor to be compressed to be preheated by the waste heat of the reboiler before compression, and the high-temperature and high-pressure steam to release heat after compression to heat the material. This changes the high-energy-consuming operation mode of the traditional distillation process that relies on external steam heating and cooling water condensation. It constructs an internal thermal circulation system with compressed steam as the core, forming a tiered utilization path of high-grade heat, medium-grade heat and low-grade heat, and maximizing the exploitation of the internal thermal energy potential of the system. Attached Figure Description

[0025] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:

[0026] Figure 1 This is a schematic diagram of the production system of the present invention;

[0027] Figure 2 This is a schematic diagram of the reboiler structure of the present invention;

[0028] Figure 3 For the present invention Figure 2 Enlarged view of A in the middle;

[0029] Figure 4 This is a schematic diagram of the float valve structure of the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Preheating tank; 2. Distillation column; 3. Heat exchanger; 4. Distillation compressor; 5. Reboiler; 501. Upper liquid plate; 502. Lower liquid plate; 503. Liquid pipeline; 504. Gas pipeline; 505. Fixing block; 511. Float valve; 512. Gas vent; 513. Stabilizing bar; 514. Hook; 515. Slide rail; 521. Heat source inlet; 522. Heat source outlet; 523. Flash vapor phase inlet; 524. Flash liquid phase inlet; 6. Condenser; 7. Flash tank; 8. Flash compressor. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Those skilled in the art should understand that the embodiments described below are only some, not all, of the embodiments disclosed. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] In MTBE production, methanol recovery systems typically employ distillation to separate unreacted methanol from water and other components, achieving methanol purification and reuse. However, in large-scale continuous production, conventional methanol-water distillation requires external steam heating in the reboiler to vaporize and rise the methanol in the mixture; the overhead steam is then condensed and partially refluxed, with the remainder being collected as product. This process is highly dependent on low- or medium-pressure steam, and steam production itself consumes a large amount of fuel, resulting in high energy consumption for the entire system. In large-scale, long-term continuous operation plants, this steam cost constitutes a significant portion of operating costs.

[0034] To address the issue of excessive steam consumption, the industry has attempted to introduce heat pump distillation technology. The basic principle is to pressurize and heat the low-temperature, low-pressure methanol vapor at the top of the distillation column using a compressor, increasing its calorific value before using it as a heat source for the reboiler. This achieves internal heat recycling, significantly reducing or even replacing external steam input. However, heat pump distillation technology in methanol-water distillation systems often faces an unavoidable problem: the large temperature difference between the top and bottom of the distillation column. This means that achieving the required reboiler temperature necessitates an extremely high compressor compression ratio, potentially leading to a sharp increase in compressor power consumption. While steam is saved, the increased electricity consumption may offset most of the energy savings, resulting in a negligible reduction in overall operating costs, or even a situation where "steam savings do not reduce costs." Furthermore, if the existing system does not meet the high-pressure design requirements of a high compression ratio, introducing high-pressure heat pump steam will necessitate a complete upgrade of the pressure-bearing components in the system. This upgrade involves a series of engineering modifications, including safety assessments, pressure vessel replacement, and upgrades to explosion-proof ratings, resulting in excessive investment costs and a long payback period.

[0035] Based on this, the present invention introduces the methanol vapor from the reboiler 5 into the tube side of the heat exchanger 3 for preheating before it enters the distillation compressor 4, thereby realizing the internal heat energy recycling in the methanol recovery process. Specifically, the methanol vapor discharged from the reboiler 5 is used to preheat the methanol vapor about to enter the distillation compressor 4, increasing its inlet temperature and realizing the cascade utilization of heat energy, effectively reducing the energy consumption of the distillation compressor 4; the vapor generated by the flash evaporation of the liquid in the distillation column 2 is compressed and returned to the column as a supplementary heat source, further improving the energy utilization efficiency of the system; the remaining liquid in the flash tank 7 is sent back to the lower part of the distillation column 2, and the reboiler 5 heats the liquid in the distillation column 2 through flash evaporation circulation. At the same time, the present invention embeds the reboiler 5 inside the distillation column 2, realizing efficient heat transfer; the floating valve 511 structure inside the reboiler 5 effectively avoids the gas-liquid impact problem; the present invention effectively improves the overall efficiency of methanol recovery and reduces operating costs.

[0036] After introducing the basic principles of the present invention, various non-limiting embodiments of the present invention are described in detail below. Any number of elements in the accompanying drawings is for illustrative purposes only and not for limitation, and any naming is for distinction only and has no limiting meaning.

[0037] The principles and spirit of the present invention will be explained in detail below with reference to several representative embodiments. Example 1

[0038] A low-steam-consumption methanol recovery system based on heat pump integration, such as Figure 1-4 As shown, it includes a preheating tank 1, a distillation column 2, a heat exchanger 3, a distillation compressor 4, a reboiler 5, a flash tank 7, a flash compressor 8, and a condenser 6. Among them, the preheating tank 1, the heat exchanger 3, and the reboiler 5 all have tube-side and shell-side structures. The tube side is used for the inflow and outflow of the material to be heated, while the shell side is used for the flow of the heat source to heat the material.

[0039] like Figure 1As shown, the tube-side outlet of preheating tank 1 is connected to the feed inlet in the middle of distillation column 2. Preheating tank 1 is used to preheat the material before distillation column 2. The methanol vapor outlet at the top of distillation column 2 is connected in sequence to the tube side of heat exchanger 3, distillation compressor 4, shell side of reboiler 5, shell side of heat exchanger 3, and condenser 6. The methanol vapor separated from distillation column 2 first exchanges heat with methanol vapor from the shell side of reboiler 5 in heat exchanger 3 to raise its temperature. Then, it is pressurized and heated by distillation compressor 4 and sent to the shell side of reboiler 5 to heat the bottom liquid of distillation column 2 in the tube side of reboiler 5. After heating, the methanol vapor is sent back to the shell side of heat exchanger 3, thus realizing internal circulation and cascade utilization of thermal energy. The methanol vapor that has completed heat exchange in the shell side of heat exchanger 3 then enters condenser 6 for cooling and collection. Condenser 6 is also connected to the reflux port at the top of distillation column 2, which is used to return part of the condensed methanol product as reflux liquid to distillation column 2, further improving the purity and quality of the product.

[0040] The bottom of the distillation column 2 is connected to a flash tank 7. The top of the flash tank 7 is connected to the lower part of the distillation column 2 via a flash compressor 8, which is used to compress the flash gas and send it back to the reboiler of the distillation column 2 for heating. The pressure of the compressed flash gas is the same as the pressure of the reboiler of the distillation column 2. The bottom of the flash tank 7 is connected to the middle and lower part of the distillation column 2, which is used to send the remaining unflashed liquid back to the middle and lower part of the distillation column 2 for reflux. The two together form a circulation reflux channel for the flashed material. The bottom of the distillation column 2 is also connected to the shell side of the preheating tank 1 for feed preheating.

[0041] like Figure 2-4 As shown, in this embodiment, the reboiler 5 is embedded in the lower part of the distillation column 2. Its structure includes an upper liquid plate 501 and a lower liquid plate 502, which are welded and fixed to the inner wall of the distillation column 2. The space formed by the two plates and the distillation column 2 together is the shell side of the reboiler 5. Multiple liquid pipes 503 that penetrate the upper liquid plate 501 and the lower liquid plate 502 are uniformly fixedly installed inside the shell side. A gas pipe 504 is coaxially arranged inside the liquid pipe 503. The gas pipe 504 is fixedly installed inside the liquid pipe 503 by a fixing block 505. The space formed between the outer wall of the gas pipe 504 and the inner wall of the liquid pipe 503 is the tube side of the reboiler 5.

[0042] Liquid pipe 503 is used for liquid to flow from upper liquid plate 501 to lower liquid plate 502, and gas pipe 504 is used for gas to flow from lower liquid plate 502 to upper liquid plate 501. According to the flow rate design of distillation column 2, the bottom of lower liquid plate 502 is higher than the liquid level in the distillation column 2's reboiler under full load conditions to prevent liquid seals from forming in liquid pipe 503 or gas pipe 504 when the liquid in the reboiler of distillation column 2 boils, thus preventing operational malfunctions. A float valve 511 is also provided at the top of gas pipe 504 to prevent gas-liquid conflict during distillation column 2 operation. The top of the float valve 511 is provided with an air hole 512 to prevent damage caused by the rotation of the float valve 511 when it floats. The bottom outer circumference is uniformly fixed with a stabilizing rod 513 and a hook 514. The upper part of the gas pipeline 504 is provided with a sliding groove 515 that cooperates with the hook 514. The hook is made of corrosion-resistant hard elastic material. During installation, the hook deforms under the action of the inner wall of the gas pipeline. After installation, the hook returns to its original shape and rebounds in the sliding groove to cooperate with its installation, effectively preventing the float valve 511 from falling off.

[0043] In addition, the distillation column 2 is equipped with a heat source inlet 521 and a heat source outlet 522 connected to the shell side of the reboiler 5, for introducing and discharging methanol vapor heated by the distillation compressor 4. To make the heat exchange in the reboiler 5 more efficient, a baffle (not shown in the figure) is also provided inside the reboiler 5 to extend the flow path of methanol vapor in the shell side of the reboiler 5. This baffle is a conventional design in the field of heat exchangers 3 and will not be described in detail here.

[0044] To ensure stable system operation, the top of flash tank 7 is connected to the flash vapor inlet 523 of distillation column 2, and the bottom of flash tank 7 is connected to the flash liquid inlet 524 of distillation column 2. Flash vapor inlet 523 is located below the lower liquid plate 502, and flash liquid inlet 524 is located above the upper liquid plate 501. During operation, methanol vapor compressed by distillation compressor 4 enters the shell side of reboiler 5. The flash compressed gas and vapor in the reboiler of distillation column 2 are transported upwards via gas pipe 504, while the feed from preheater 1 and the remaining liquid in flash tank 7 are transported downwards via liquid pipe 503. During liquid transport, the gas and liquid flow in opposite directions. The gas in the shell side of reboiler 5 and the gas pipe 504 provide double-layer heating to the liquid, ensuring more thorough heating of the liquid material.

[0045] Specifically, in this embodiment, the distillation column 2 is designed with 35 layers, the methanol mixture feed position is 18 layers, the reflux position of the condenser 6 is 2 layers, the flash liquid phase inlet 524 is 25 layers, and the flash vapor phase inlet 523 is connected to an aeration plate (not shown in the figure) through a pipe. The aeration plate is located below the liquid level in the distillation column 2, so that the flash compressed gas and the liquid in the distillation column 2 can fully contact and heat each other.

[0046] This invention also provides a low-steam-consumption methanol recovery process, employing the aforementioned low-steam-consumption methanol recovery system, comprising the following steps:

[0047] Raw material preheating: The extracted methanol mixture is preheated in preheating tank 1 and then sent to the middle of distillation column 2;

[0048] Distillation separation: In the distillation column 2, mass and heat are transferred through the trays. The generated methanol vapor is discharged from the top outlet and passes through the tube side of the heat exchanger 3 for heating and the distillation compressor 4 for pressurization and heating. Finally, it enters the shell side of the reboiler 5 and the shell side of the heat exchanger 3 as a heat source. Finally, it enters the condenser 6, where part of it is refluxed and the other part is stored and recovered.

[0049] Flash circulation: The liquid at the bottom of the distillation column 2 is divided into two paths. One path enters the flash tank 7 for flashing, and the other path enters the shell side of the preheating tank 1 and / or is discharged. The gas in the flash tank 7 is pressurized and heated by the flash compressor 8 and then sent to the bottom of the distillation column 2. The remaining unflashed liquid in the flash tank 7 is sent back to the lower part of the distillation column 2 through the pipeline.

[0050] In the distillation separation, the methanol vapor pressure at the top of distillation column 2 is 0.11~0.15 MPa, and the temperature is 65~75℃. The pressure boost of distillation compressor 4 is 0.1~0.2 MPa. The pressure in the bottom of distillation column 2 is 0.18~0.22 MPa, and the temperature is 100~110℃. The reflux ratio of condenser 6 to distillation column 2 is 1.5~2.2. In the flash evaporation cycle, the circulating liquid flow rate entering flash tank 7 is 20~50% of the feed flow rate, and the pressure inside flash tank 7 is reduced to 0.09~0.12 MPa.

[0051] For an MTBE system with an annual production capacity of 100,000 tons, the comparison between this scheme and other processes in the methanol recovery system is as follows:

[0052]

[0053] In summary, this solution utilizes an integrated distillation heat pump and flash heat pump process. Methanol vapor discharged from the reboiler preheats the methanol vapor entering the distillation compressor, increasing its inlet temperature and achieving cascaded utilization of thermal energy, effectively reducing the energy consumption of the distillation compressor. The vapor generated from flash evaporation of the liquid in the distillation column is compressed and returned to the column as a supplementary heat source, simultaneously achieving further flash separation of methanol and improving the system's energy utilization efficiency. The remaining liquid in the flash tank is returned to the lower part of the distillation column, where flash circulation reheats the liquid in the reboiler. Compared to traditional processes, this solution significantly reduces the steam consumption required for methanol recovery, resulting in annual savings of 2.96 million yuan in operating costs. Compared to existing improved processes, although the initial investment is slightly higher and the payback period is slightly longer, this solution still saves 1.56 million yuan in operating costs annually, with cumulative benefits exceeding costs starting from the third year.

[0054] Based on comprehensive calculations, the normal operating life of the equipment after the modification in this scheme is about 10-15 years. Taking 10 years as an example, this scheme can save a total of 29.6 million yuan in operating costs over the entire life cycle, and the net savings after deducting the modification costs is 22.4 million yuan. In contrast, the net savings of the improved process scheme over 10 years is only 11.1 million yuan. From the perspective of long-term economic benefits, the advantages of this scheme are more significant.

[0055] The above-described preferred embodiments of the present invention are provided as examples, but it will be apparent to those skilled in the art that such embodiments are provided merely by way of example. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and intent of the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. The appended claims are intended to define the scope of protection of the invention and therefore cover the modular compositions, equivalents, or alternatives within the scope of these claims.

Claims

1. A low-steam-consumption methanol recovery system based on heat pump integration, characterized in that, The system includes a preheating tank (1), the tube-side outlet of which is connected to the material inlet of a distillation column (2), the top steam outlet of the distillation column (2) being connected to the tube-side inlet of a heat exchanger (3), the tube-side outlet of the heat exchanger (3) being connected to the shell-side inlet of a reboiler (5) via a distillation compressor (4), the shell-side outlet of the reboiler being connected to the shell-side inlet of the heat exchanger (3), and a condenser (6) connected to the shell-side outlet of the heat exchanger (3). The condenser (6) is connected to the distillation column (2). A pipe for methanol reflux is provided between the upper and lower parts; the reboiler (5) is embedded in the lower part of the distillation column (2), and the bottom of the distillation column (2) is connected to the flash tank (7). The top of the flash tank (7) is connected to the lower part of the distillation column (2) through the flash compressor (8), and the bottom of the flash tank (7) is connected to the middle and lower part of the distillation column (2) to form a circulation reflux channel for flash material. The bottom of the distillation column (2) is also connected to the shell side of the preheating tank (1) for feed preheating. The reboiler (5) includes an upper liquid plate (501) and a lower liquid plate (502) fixedly connected to the inner wall of the distillation column (2). Several liquid pipes (503) are fixedly installed between the upper liquid plate (501) and the lower liquid plate (502). The space enclosed by the upper liquid plate (501), the lower liquid plate (502), the inner wall of the distillation column (2), and the outer wall of the liquid pipes (503) is the shell side of the reboiler (5). A gas pipe (504) is also coaxially fixedly installed inside the liquid pipe (503) through a fixing block (505). The liquid pipe (503) is used for liquid... Gas flows from the upper liquid plate (501) to the lower liquid plate (502). Gas pipe (504) is used for gas to flow from the lower liquid plate (502) to the upper liquid plate (501). Gas pipe (504) is provided with a float valve (511) at the top. The float valve (511) is provided with a gas hole (512) at the top. The float valve (511) is provided with a stabilizing rod (513) and a hook (514) evenly distributed on the bottom outer periphery. Gas pipe (504) is provided with a sliding groove (515) that cooperates with the hook (514) at the upper part. The float valve (511) is used to prevent gas-liquid conflict in the reboiler (5) during the operation of the distillation column (2).

2. The low-steam-consumption methanol recovery system based on heat pump integration according to claim 1, characterized in that: The top of the flash tank (7) is connected to the flash vapor phase inlet (523) of the distillation column (2), and the bottom of the flash tank (7) is connected to the flash liquid phase inlet (524) of the distillation column (2). The flash vapor phase inlet (523) is located below the lower liquid plate (502), and the flash liquid phase inlet (524) is located above the upper liquid plate (501).

3. The low-steam-consumption methanol recovery system based on heat pump integration according to claim 1, characterized in that: The bottom of the lower liquid plate (502) is higher than the liquid level of the distillation column (2) when it is fully loaded.

4. A low-steam-consumption methanol recovery process, employing the low-steam-consumption methanol recovery system based on heat pump integration as described in any one of claims 1-3, characterized in that, Includes the following steps: Raw material preheating: The extracted methanol mixture is preheated in a preheating tank (1) and then sent to the middle of the distillation column (2); Distillation separation: In the distillation column (2), mass and heat are transferred through the trays. The generated methanol vapor is discharged from the top outlet and passes through the heat exchanger (3) tube side for heating and the distillation compressor (4) for pressurization and heating. Finally, it enters the reboiler (5) shell side and the heat exchanger (3) shell side as heat sources. Finally, it enters the condenser (6), where part is refluxed and the other part is stored and recovered. Flash circulation: The liquid at the bottom of the distillation column (2) is divided into two paths. One path enters the flash tank (7) for flashing, and the other path enters the shell side of the preheating tank (1) and / or is discharged. The gas in the flash tank (7) is pressurized and heated by the flash compressor (8) and then sent to the bottom of the distillation column (2). The remaining unflashed liquid in the flash tank (7) is sent back to the lower part of the distillation column (2) through the pipeline.

5. The low-steam-consumption methanol recovery process according to claim 4, characterized in that: In the distillation separation, the methanol vapor pressure at the top of the distillation column (2) is 0.11~0.15 MPa, and the pressure boosting range of the distillation compressor (4) is 0.1~0.2 MPa.

6. The low-steam-consumption methanol recovery process according to claim 4, characterized in that: In the distillation separation, the reflux ratio of the condenser (6) to the distillation column (2) is 1.5~2.

2.

7. The low-steam-consumption methanol recovery process according to claim 4, characterized in that: In the flash evaporation cycle, the flow rate of the circulating liquid entering the flash tank (7) is 20-50% of the feed flow rate. The pressure inside the flash tank (7) is reduced to 0.09-0.12 MPa, and the flash compressor (8) is increased to 0.20-0.25 MPa.

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