Energy-saving five-tower methanol rectification method based on multi-effect heat coupling

Abstract

This invention discloses an energy-saving five-tower methanol distillation method based on multi-effect thermal coupling. Crude methanol is fed to a pre-tower for distillation; the bottom product of the pre-tower is fed to an atmospheric distillation tower, the bottom product of the atmospheric distillation tower is fed to a negative pressure distillation tower, and the bottom product of the negative pressure distillation tower is fed to a pressurized distillation tower; the bottom product of the pressurized distillation tower is fed to a secondary pressure distillation tower; refined methanol is collected from the tops of the pressurized distillation tower, the atmospheric distillation tower, the negative pressure distillation tower, and the secondary pressure distillation tower; the top product of the pressurized distillation tower heats the reboiler of the secondary pressure distillation tower, and the top product of the secondary pressure distillation tower heats both the reboilers of the pre-tower and the atmospheric distillation tower; the top products of the pre-tower and the atmospheric distillation tower heat the reboiler of the negative pressure distillation tower. This process improves the heat recovery efficiency within the system, significantly reduces the condensation load of the top vapor, lowers the overall energy consumption of the distillation process, and achieves efficient multi-stage heat recovery and utilization within the system, reducing the ethanol content in the refined methanol product and improving methanol recovery efficiency.

Description

Technical Field

[0001] This invention relates to the field of methanol distillation technology, and in particular to an energy-saving five-tower methanol distillation method based on multi-effect thermal coupling. Background Technology

[0002] Methanol is a widely used and important basic organic chemical raw material and new energy fuel, applied in many fields such as fine chemicals, polymers, pesticides, pharmaceuticals, energy, and fuel cells. It holds an extremely important position in the international chemical market. Methanol distillation is one of the most energy-intensive steps in methanol production. Crude methanol distillation purification is a key step in methanol production. The distillation purification process can remove volatile components such as dimethyl ether, as well as non-volatile components such as ethanol, higher alcohols, and water, to obtain refined methanol that meets product requirements. Traditional distillation processes typically use a three- or four-tower process, with each tower independently using steam to heat the reboiler and circulating water to cool the top of the tower. This results in low energy efficiency, with large steam consumption and circulating cooling water usage. Typically, the steam consumption per ton of refined methanol produced is between 1.0 and 1.2 tons, leading to high production costs.

[0003] To reduce energy consumption, the industry has developed multi-effect distillation technology, which utilizes the latent heat of condensation of the steam at the top of the high-pressure column as a heat source for the reboiler in the low-pressure column. While some existing four- or five-column double-effect or triple-effect processes can reduce energy consumption to some extent, current technologies typically employ a combination of multiple pressurized columns connected in series after the pre-column or a negative-pressure column connected after the pre-column. In this case, when a pressurized column is installed after the pre-column, the relative volatility of methanol and impurities such as ethanol and water is reduced by 15%–20% under pressurized conditions compared to atmospheric pressure. To meet product purity requirements, it is necessary to increase the number of theoretical plates or the reflux ratio (usually 10%–15% higher than atmospheric pressure operation), directly increasing steam consumption and equipment investment. Furthermore, crude methanol contains organic acid impurities such as formic acid and acetic acid, which, under the high-temperature environment of the pressurized column, may accelerate the thermal polymerization of certain trace heavy components or impurities, increasing the corrosion rate by 2–3 times compared to atmospheric pressure conditions. This leads to scaling in the reboiler or column bottom, shortening equipment lifespan, increasing maintenance costs, and affecting long-term operation. If a negative pressure column is directly connected after the pre-column, its operating temperature will be further reduced, making it difficult to form an effective temperature difference between the two columns to drive thermal coupling, thus failing to achieve the core energy-saving advantage of multi-effect distillation. Simultaneously, the negative pressure environment may cause trace light components that were not completely removed in the pre-column to volatilize more rapidly in subsequent columns, increasing the difficulty of product impurity control. Furthermore, the entire system requires additional vacuum equipment and other devices, increasing energy consumption and investment, resulting in limited overall energy efficiency improvement. Therefore, under the above conditions, energy-saving efficiency is limited, the number of thermal coupling stages is small, the cascade utilization of heat is not fully realized, and the reduction in steam consumption is not significant, typically remaining above 0.6-0.8 t steam / t refined alcohol.

[0004] To achieve more efficient heat coupling, additional towers or complex heat exchange networks are required, leading to increased equipment investment and greater difficulty in system control. In some integrated heat solutions, maintaining the heat source temperature may sacrifice the tower's operational flexibility, affecting the control of impurity removal such as ethanol, resulting in excessive ethanol content in the refined alcohol (typically required to be below 50 ppm) or a decrease in product yield. Furthermore, in the series connection of the aforementioned towers, most of the overhead vapors require independent condensation, resulting in high cooling water consumption.

[0005] In view of the above problems, there is an urgent need to develop a new methanol distillation process and system that, after removing light components in a pre-distillation column, achieves high-purity separation and can maximize the rational distribution and utilization of heat from the gaseous material in the distillation column, while ensuring high product yield and quality (especially low ethanol content), and rationally distributes and utilizes external steam heat. This will effectively reduce energy consumption and operational complexity of the methanol distillation system, while simultaneously improving methanol recovery. This new process and system will achieve deeper heat recovery and further reduce steam and cooling water consumption. It can then be applied to large-scale methanol production plants in coal chemical and natural gas chemical industries to refine the synthesized crude methanol into high-purity fuel-grade or AA-grade refined methanol. Summary of the Invention

[0006] This invention addresses the problems of high energy consumption, insufficient thermal energy utilization, high cooling load, low refined methanol yield, and high ethanol content in refined methanol in existing technologies. It discloses an energy-saving five-tower methanol distillation method based on multi-effect thermal coupling. This method employs a multi-effect thermal coupling network with a combined integrated design of five towers. Innovatively, it connects the pre-tower, atmospheric pressure tower, negative pressure tower, pressurized tower, and secondary pressure tower in series according to the pipeline connection sequence for distillation. It sets up heat transport pipelines with multi-dimensional and rational heat distribution, fully realizing thermal coupling and achieving multi-dimensional distribution and cascade utilization of external heat steam and the thermal energy of the gaseous material at the top of the towers. This method significantly improves the heat recovery efficiency within the system while greatly reducing the condensation load of the top steam, effectively reducing the overall energy consumption of the distillation process, achieving efficient multi-stage heat recovery and utilization within the system, and simultaneously reducing the ethanol content in the refined methanol product, thus improving methanol recovery efficiency.

[0007] This invention is achieved through the following technical solution: This invention provides an energy-saving five-tower methanol distillation method based on multi-effect thermal coupling, the method comprising the following steps: Crude methanol is fed to a pre-distillation column for rectification; the bottom product of the pre-distillation column is fed to an atmospheric distillation column for rectification; the bottom product of the atmospheric distillation column is fed to a negative pressure distillation column for rectification; the bottom product of the negative pressure distillation column is fed to a pressurized distillation column for rectification; the bottom product of the pressurized distillation column is fed to a secondary pressure distillation column for rectification; refined methanol is collected from the top of the pressurized distillation column, the atmospheric distillation column, the negative pressure distillation column, and the secondary pressure distillation column. The material drawn from the top of the pressurized tower is used to heat the reboiler of the secondary pressure tower. The material drawn from the top of the secondary pressure tower is used to heat the reboiler of the pre-tower and the reboiler of the atmospheric pressure tower. The material drawn from the top of the pre-tower and the reboiler of the atmospheric pressure tower are used to heat the reboiler of the negative pressure tower.

[0008] This invention addresses the technical problems inherent in existing technologies that typically involve directly connecting a pressurized or negative-pressure tower in series after the pre-tower. It innovatively develops a highly efficient methanol distillation process capable of achieving four-stage thermal coupling and energy cascade utilization. Through a unique thermal coupling network, this process utilizes the thermal energy of the steam at the top of the pressurized tower four times in succession, reducing steam consumption to 0.42 t / t of refined methanol and condensate consumption to 21 t / t of refined methanol, achieving a breakthrough energy saving of over 50% compared to traditional processes. While achieving significant energy savings, it also enables precise control of impurities (especially ethanol), maintaining the product ethanol content consistently below 10 ppm and achieving a total methanol yield of 99.5%. The distillation process significantly reduces the number of heat exchangers such as condensers; only two towers (the pre-tower and the negative-pressure tower) require condensers, greatly reducing the number of heat exchangers, floor space, and condensate consumption. Under the above design, the process is ingeniously designed, but the total number of equipment does not increase significantly, the investment cost is controllable, and the investment payback period is short. In addition, the system is environmentally friendly and efficient, and the methanol content in the wastewater at the bottom of the tower is extremely low. This process demonstrates excellent comprehensive performance.

[0009] As a further embodiment, the method also includes a steam heat source, which is divided into two streams in parallel through a steam heat source pipeline for primary heat utilization. One stream supplies heat to at least one pressurized tower steam reboiler and at least one pressurized tower feed preheater, while the other stream supplies heat to at least one pre-tower reboiler. The two streams are then combined to supply heat to the pre-tower preheater for secondary heat utilization before exiting the boundary.

[0010] As a further embodiment, the crude methanol is preheated in two stages before entering a pre-distillation column for distillation. The bottom product of the pre-distillation column is sent to an atmospheric distillation column for rectification, the bottom product of the atmospheric distillation column is sent to a negative pressure distillation column for rectification, the bottom product of the negative pressure distillation column is preheated in two stages before being sent to a pressurized distillation column for rectification, and the bottom product of the pressurized distillation column is sent to a secondary pressure distillation column for rectification.

[0011] As a further embodiment, the crude methanol is first heated by a primary preheater for the pre-tower feed, and then supplemented by a secondary preheater for the pre-tower feed before entering the pre-tower for distillation. The primary preheater for the pre-tower feed is provided by a steam heat source, specifically the secondary heat source of the steam heat source. The secondary preheater for the pre-tower feed is provided by the material from the top of the pressurized tower.

[0012] This invention incorporates a two-stage preheating process in the crude methanol feed pipeline, utilizing a heat source from the top material of the pressurized tower for the secondary preheating of the feed. This approach fully leverages the heat source at the top of the pressurized tower as a supplementary heat source, while also recovering secondary heat from the steam heat source. Furthermore, it fully utilizes the remaining heat source after the primary heating by the steam heat source as the primary preheating heat for the crude methanol. This approach maximizes the utilization of the steam heat source while reducing its consumption, achieving a rational allocation and full utilization of the heat source, and simultaneously reducing the condensation load of the top heat source.

[0013] As a further embodiment, the material collected from the bottom of the negative pressure tower is first preheated by the primary preheater of the pressurized tower feed, and then preheated by the secondary preheater of the pressurized tower feed as a supplementary heat source before entering the pressurized tower for rectification; the material collected from the bottom of the pressurized tower is heated by the primary preheater of the pressurized tower feed before entering the secondary pressure tower for rectification; the secondary preheater of the pressurized tower feed is heated by the primary heat source provided by one of the steam heat sources.

[0014] This invention employs a two-stage preheating system in the pressurized tower feed pipeline. First, the material at the bottom of the pressurized tower is used for initial preheating, while a secondary preheating is performed using one of the steam heat sources. This further maximizes the utilization of the heat source at the bottom of the pressurized tower, providing initial preheating. The secondary preheating is then supplemented by one of the primary steam heat sources, further reducing steam consumption.

[0015] As a further embodiment, the steam heat source is divided into two parallel streams via steam heat source pipelines. One stream supplies heat to the reboiler of the pressurized tower and the secondary preheater of the pressurized tower feed in sequence, while the other stream supplies heat to the first reboiler of the preheater. The two streams are then combined to supply heat to the primary preheater of the preheater feed and then exit as condensate.

[0016] This invention further achieves a rational allocation of steam heat sources. One heat source first supplies heat to the reboiler of the pressurized tower, and after prioritizing the heating of the pressurized tower, its remaining heat can be used for the secondary feed preheating of the pressurized tower. The other heat source supplies heat to the first reboiler of the preheating tower. This rational allocation of heat sources is achieved. At this time, the remaining secondary heat after the two heat sources are combined can also be used for the feed preheating of the preheating tower. Based on the above, the full utilization of heat is achieved.

[0017] As a further embodiment, the material collected from the top of the pressurized tower is heated by the reboiler of the secondary pressure tower, with one stream flowing back to the top of the pressurized tower and the other stream being heated by the secondary preheater of the pre-tower feed to produce refined methanol; the material collected from the top of the secondary pressure tower is heated in parallel by the second reboiler of the pre-tower and the reboiler of the atmospheric pressure tower, with one stream flowing back to the top of the secondary pressure tower and the other stream producing refined methanol; the material collected from the top of the pre-tower is heated by the second reboiler of the negative pressure tower and then refluxed to the top of the pre-tower through secondary condensation; the material collected from the top of the atmospheric pressure tower is heated by the first reboiler of the negative pressure tower, with one stream flowing back to the top of the atmospheric pressure tower and the other stream producing refined methanol; the material collected from the top of the negative pressure tower is refluxed by secondary condensation, with one stream flowing back to the top of the negative pressure tower and the other stream producing refined methanol.

[0018] Through the above-mentioned thermal coupling method and reasonable allocation of heat source, the present invention only requires condensers to be configured in the pre-tower and negative pressure tower, which greatly reduces the number of heat exchange equipment, floor space and condensate consumption.

[0019] As a further preferred embodiment, the material collected from the top of the secondary pressure tower is heated in parallel to the second reboiler of the pre-tower and the reboiler of the atmospheric pressure tower, with one stream flowing back to the top of the secondary pressure tower and the other stream being collected as refined methanol; wherein the material collected from the top of the secondary pressure tower is used to heat the reboiler of the atmospheric pressure tower while the remaining material is used to heat the second reboiler of the pre-tower.

[0020] This invention further optimizes the distribution of heat from the top of the secondary pressure tower as a heat source for the pre-tower and atmospheric pressure tower. By rationally allocating the heat source from the top of the secondary pressure tower, the heat supply to the atmospheric pressure tower is fully met, while the remaining heat source is also supplied to the pre-tower. This achieves a reasonable distribution of heat from the top of the secondary pressure tower. At the same time, while fully meeting the heat supply needs of the atmospheric pressure tower, the heating load of the first reboiler in the pre-tower is also reduced, thereby reducing the consumption of steam heat source.

[0021] As a further embodiment, the bottom material of the negative pressure tower is heated by the first reboiler and the second reboiler of the negative pressure tower in parallel and then refluxed back to the bottom of the negative pressure tower at a temperature of 53~58℃.

[0022] As a further embodiment, the temperature of the crude methanol after being heated by the primary preheater of the pre-tower feed is 65~70℃, and the temperature of the crude methanol after being heated by the secondary preheater of the pre-tower feed is 73~77℃.

[0023] As a further embodiment, the temperature of the material extracted from the bottom of the negative pressure tower after being heated by the primary preheater of the pressurized tower feed is 92~98℃, and the temperature of the material extracted from the bottom of the negative pressure tower after being heated by the secondary preheater of the pressurized tower feed is 133~137℃.

[0024] As a further embodiment, the top temperature of the pre-pressure tower is 73~77℃ and the top pressure is 115~125 kPaA; the top temperature of the atmospheric pressure tower is 65~69℃ and the top pressure is 105~115 kPaA; the top temperature of the negative pressure tower is 46~50℃ and the top pressure is 45~55 kPaA; the top temperature of the pressurized tower is 133~137℃ and the top pressure is 945~955 kPaA; and the top temperature of the secondary pressure tower is 82~86℃ and the top pressure is 200~215 kPaA.

[0025] As a further embodiment, the reflux ratio of the pre-pressure tower is 0.35~0.45, the reflux ratio of the atmospheric pressure tower is 1.35~1.45, the reflux ratio of the negative pressure tower is 1.15~1.25, the reflux ratio of the pressurized tower is 2.35~2.45, and the reflux ratio of the secondary pressure tower is 1.85~1.95.

[0026] The reflux ratio refers to the ratio of the reflux liquid flow rate at the top of each column to the feed flow rate of each column.

[0027] As a further embodiment, the material collected from the top of the pressurized tower is heated by the reboiler of the secondary pressurized tower, then transported to the pressurized tower reflux tank, and split into two streams. One stream flows through the pressurized tower reflux pump and returns to the top of the pressurized tower, while the other stream is collected as refined methanol after being heated by the secondary preheater of the pre-tower feed.

[0028] As a further embodiment, the material drawn from the top of the secondary pressure tower is heated in parallel to the second reboiler of the pre-tower and the reboiler of the atmospheric pressure tower, and then transported to the secondary pressure tower reflux tank. After passing through the secondary pressure tower reflux pump, it is divided into two streams, one of which flows back to the top of the secondary pressure tower, and the other is drawn out as refined methanol.

[0029] As a further option, wastewater and fusel oil are extracted from the bottom of the secondary pressure tower.

[0030] As a further embodiment, the material drawn from the top of the pre-tower is heated by the second reboiler of the negative pressure tower, condensed by the first-stage condenser and the second-stage condenser of the pre-tower, and then transported to the pre-tower reflux tank, and returned to the top of the pre-tower by the pre-tower reflux pump.

[0031] As a further embodiment, the material collected from the top of the atmospheric pressure tower is heated by the first reboiler of the negative pressure tower and then transported to the atmospheric pressure tower reflux tank. Through the atmospheric pressure tower reflux pump, it is divided into two streams: one stream flows back to the top of the atmospheric pressure tower, and the other stream is collected as refined methanol.

[0032] As a further embodiment, the material collected from the top of the negative pressure tower is condensed by the primary and secondary condensers of the negative pressure tower and then transported to the negative pressure tower reflux tank. The material is then divided into two streams by the negative pressure tower reflux pump, one of which flows back to the top of the negative pressure tower and the other is collected as refined methanol.

[0033] As a further embodiment, the pre-tower secondary condenser is also connected to a purge gas scrubbing tank for purge gas discharge, and the purge gas scrubbing tank is connected to an extraction tank for extraction, with some of the extraction products discharged in the form of fusel oil.

[0034] As a further embodiment, the material collected from the top of the pre-tower is heated by the second reboiler of the negative pressure tower, then condensed in the first-stage condenser of the pre-tower. In parallel, one stream is directly fed to the pre-tower reflux tank; the other stream is fed to the second-stage condenser of the pre-tower. A portion of the material condensed in the second-stage condenser enters the extraction tank for extraction, while the other portion exits through a purge gas scrubbing tank. The liquid from the purge gas scrubbing tank enters the extraction tank for extraction. A portion of the extracted material is collected as fusel oil, and the other portion is fed to the pre-tower reflux tank and then refluxed back to the top of the pre-tower via a pre-tower reflux pump.

[0035] As a further embodiment, the negative pressure tower secondary condenser is also connected to a vacuum buffer tank, which is connected to a vacuum pump and then to the pre-tower secondary condenser for condensation.

[0036] As a further embodiment, the negative pressure tower reflux tank is also connected to the negative pressure tower secondary condenser. Part of the liquid flows back to the negative pressure tower reflux tank, and the other part is connected to the vacuum buffer tank. The liquid in the vacuum buffer tank flows back to the negative pressure tower reflux tank, and the condensed gas in the vacuum buffer tank is connected to the pre-tower secondary condenser for condensation through a vacuum pump.

[0037] As a further embodiment, the mass percentage of methanol in the crude methanol is ≤96%.

[0038] As a further option, the total cooling water consumption of the pre-tower primary condenser, pre-tower secondary condenser, negative pressure tower primary condenser, and negative pressure tower secondary condenser is 21 t / t of refined methanol.

[0039] As a further option, the methanol content in the wastewater extracted from the bottom of the secondary pressure tower is ≤100ppm.

[0040] As a further embodiment, the ethanol content in the refined methanol is ≤10 ppm, and the total yield of the refined methanol is ≥99.5%.

[0041] This invention, under the background of deep energy saving, achieves precise control of impurities (especially ethanol) by optimizing the operating temperature, pressure, and reflux ratio of each tower. The ethanol content in the refined methanol product can be stably kept below 10 ppm, which is far superior to the national standard for superior grade products, and the total yield of refined methanol is as high as 99.5%.

[0042] As a further embodiment, the methanol content in the fusel oil collected from the bottom of the secondary pressure tower via a side stream is <27%.

[0043] In this invention, the fusel oil collected from the bottom of the secondary pressure tower has a high methanol concentration, which facilitates subsequent recovery and utilization.

[0044] As a further embodiment, the steam consumption of the energy-saving five-tower methanol distillation process based on multi-effect thermal coupling is ≤0.42 t / t of refined methanol.

[0045] This invention employs a four-stage thermal coupling, utilizing the thermal energy of the pressurized tower steam four times in stages. Simultaneously, it rationally distributes and fully utilizes the steam heat source and the top steam, achieving heating for each tower and the feed, significantly reducing the consumption of external steam and cooling water. The synergistic effect of parameters such as temperature, pressure, and reflux ratio enables the entire system to achieve the stringent quality requirements of ultra-low ethanol content (<10 ppm) and high yield (99.5%) while reducing external steam consumption to an extremely low 0.42 t / t of refined alcohol. This represents an energy saving of over 50% compared to traditional processes and over 30% more than ordinary multi-effect processes. Furthermore, since most of the heat from the top steam is utilized internally in stages, only the pre-tower and negative pressure tower require external cooling, reducing circulating water consumption to less than 35% of the traditional process's approximately 60 t / t of refined alcohol.

[0046] The features and beneficial effects of this invention are as follows: (1) The present invention innovatively performs distillation by connecting the pre-tower, atmospheric pressure tower, negative pressure tower, pressurized tower and secondary pressure tower in series according to the pipeline, which overcomes the problem faced by directly connecting the pressurized tower or negative pressure tower after the pre-tower.

[0047] (2) In the entire unit, only the top of the pre-pressurization tower and the top of the negative pressure tower need to be equipped with independent condensers. The top vapors of the pressurization tower, the secondary pressure tower and the atmospheric pressure tower are fully utilized through a thermal coupling network, without the need for independent condensers.

[0048] (3) This invention constructs a more efficient multi-effect thermal coupling process, reducing steam consumption to below 0.42 t / t of refined methanol; while achieving deep energy saving, it precisely controls the separation efficiency of each tower, maximizing the rational distribution and utilization of heat from the gaseous material at the top of the pressurized distillation tower, effectively reducing the energy consumption of the methanol distillation system. It ensures that the ethanol content in the refined methanol product is below 10 ppm and the total yield is not less than 99.5%, reduces the number of condensers at the top of the tower, and the condensate consumption is below 21 t / t of refined methanol, thus reducing the overall operating cost. It solves the problems of high energy consumption, insufficient thermal energy utilization, and large cooling water consumption in existing methanol distillation technologies. Attached Figure Description

[0049] 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.

[0050] Figure 1 This is an energy-saving five-tower methanol distillation device based on multi-effect thermal coupling used in Embodiment 1 of the present invention.

[0051] Where T1: pre-pressure tower, T2: atmospheric pressure tower, T3: negative pressure tower, T4: pressurized tower, T5: secondary pressure tower; Q101: Primary preheater for pre-tower feed; Q102: Secondary preheater for pre-tower feed; Q103: First reboiler for pre-tower; Q104: Second reboiler for pre-tower; Q105: Boiler pump for pre-tower; Q106: Primary condenser for pre-tower; Q107: Secondary condenser for pre-tower; Q108: Purge gas scrubber; Q109: Extraction tank; Q110: Pre-tower reflux tank; Q111: Pre-tower reflux pump. Q201: Atmospheric pressure column reflux tank; Q202: Atmospheric pressure column reflux pump; Q203: Atmospheric pressure column reboiler; Q204: Atmospheric pressure column bottom pump; Q205: Atmospheric pressure column refined methanol cooler; Q301: Reflux tank of negative pressure tower; Q302: Reflux pump of negative pressure tower; Q303: First stage condenser of negative pressure tower; Q304: Second stage condenser of negative pressure tower; Q305: Vacuum buffer tank; Q306: Vacuum pump; Q307: First reboiler of negative pressure tower; Q308: Second reboiler of negative pressure tower; Q309: Boiler pump of negative pressure tower. Q401: Pressurized tower reflux tank, Q402: Pressurized tower reflux pump, Q403: Pressurized tower reboiler, Q404: Pressurized tower feed primary preheater, Q405: Pressurized tower feed secondary preheater, Q406: Pressurized tower refined methanol cooler; Q501: Secondary pressure tower reflux tank, Q502: Secondary pressure tower reflux pump, Q503: Secondary pressure tower reboiler, Q504: Secondary pressure tower refined methanol cooler, Q505: Fusel alcohol discharge cooler, Q506: Wastewater cooler, Q507: Wastewater discharge pump. K1: Pre-tower feed inlet, K2: Atmospheric pressure tower feed inlet, K3: Negative pressure tower feed inlet, K4: Pressurized tower feed inlet, K5: Secondary pressure tower feed inlet, K6: Pre-tower outlet, K7: Atmospheric pressure tower outlet, K8: Negative pressure tower outlet, K9: Pressurized tower outlet, K10: Secondary pressure tower outlet; X1: Steam heat source pipeline, X2: First branch pipeline of steam heat source, X3: Second branch pipeline of steam heat source, X4: Pre-tower feed pipeline, X5: Pressurized tower feed pipeline. Detailed Implementation

[0052] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0053] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0054] The chemical raw materials used in the following examples and comparative examples are all prior art and commercially available. The experimental apparatus and testing equipment used in the following examples and comparative examples are all conventional equipment in the art, and there are no special requirements or limitations.

[0055] As a specific example of the implementation of this invention, detailed cases are provided below: The crude methanol distillation capacity designed in this embodiment is greater than 180,000 tons / year of refined methanol.

[0056] The energy-saving five-tower methanol distillation unit based on multi-effect thermal coupling includes a pre-tower T1, an atmospheric pressure tower T2, a negative pressure tower T3, a pressurized tower T4, and a secondary pressure tower T5.

[0057] The crude methanol consists of 95.8% methanol by mass, 3.4% water by mass, and 800 ppm ethanol by mass. The feed flow rate of the crude methanol is 23,600 kg / h.

[0058] The crude methanol is preheated by the primary preheater Q101 on the pre-tower feed pipeline X4, with a temperature of 68°C. Then, it undergoes secondary preheating by the secondary preheater Q102, bringing the temperature to 75°C. Finally, it enters the pre-tower T1 for distillation through the pre-tower feed inlet K1. The primary preheater Q101 is powered by a steam heat source, specifically secondary heat from the steam heat source. The secondary preheater Q102 is powered by the material from the top of the pressurized tower T4.

[0059] By setting up a secondary preheating stage on the crude methanol feed pipeline and using the heat source from the top material of the pressurized tower T4 as the secondary preheating stage for the feed of the preheating tower T1, the heat source at the top of the pressurized tower T4 is fully utilized as a supplementary heat source. On the other hand, the secondary heat in the steam heat source can be further recovered. At this time, the remaining heat source after the primary heat source of the steam heat source is fully utilized as the primary preheating heat for crude methanol. On this basis, the steam heat source can be fully utilized and the consumption of the steam heat source can be reduced, so as to achieve reasonable distribution and full utilization of the heat source, while reducing the condensation load of the top heat source.

[0060] The material collected from the bottom of the pre-tower T1 is transported to the atmospheric distillation tower T2 through the pre-tower outlet K6 via the pre-tower bottom pump Q105 and the atmospheric distillation tower inlet K2. The feed temperature into the atmospheric distillation tower T2 is 74℃.

[0061] The material collected from the bottom of atmospheric pressure column T2 is transported to negative pressure column T3 for distillation through atmospheric pressure column outlet K7 and atmospheric pressure column bottom pump Q204 via negative pressure column inlet K3. The feed temperature into negative pressure column T3 is 72℃.

[0062] The material collected from the bottom of the negative pressure tower T3 passes through the negative pressure tower outlet K8 and the negative pressure tower bottom pump Q309. It is first preheated by the first-stage preheater Q404 on the pressurized tower feed pipeline X5, and the temperature of the preheated material is 94℃. Then it is preheated by the second-stage preheater Q405 as a supplementary heat source, and the temperature of the preheated material is 135℃. That is, the feed temperature entering the pressurized tower T4 is 135℃. It enters the pressurized tower T4 through the pressurized tower inlet K4 for rectification. The second-stage preheater Q405 is provided with heat by a primary heat source from the steam heat source, and the first-stage preheater Q404 is provided with heat by the material at the bottom of the pressurized tower T4.

[0063] Specifically: the material collected from the bottom of the pressurized tower T4 is heated by the pressurized tower outlet K9 to supply heat to the primary preheater Q404 of the pressurized tower feed, and then enters the secondary pressure tower T5 for rectification through the secondary pressure tower inlet K5; the feed temperature into the secondary pressure tower T5 is 90℃, and wastewater is discharged through the secondary pressure tower outlet K10 at the bottom of the secondary pressure tower T5, with a methanol content of ≤100ppm.

[0064] By setting up a two-stage preheating system on the feed pipeline X5 of the pressurized tower, the bottom material of pressurized tower T4 is used for priority preheating, and a portion of the steam heat source is used for secondary preheating of the feed to pressurized tower T4. This further utilizes the bottom heat source of pressurized tower T4, which serves as the initial preheating source. The steam heat source, acting as a supplementary heat source, then provides a second stage of preheating for the feed to pressurized tower T4. This approach further reduces the consumption of steam heat source.

[0065] Low-pressure steam of 0.5 MPaG is used as the initial heat source. It flows through the steam heat source pipeline X1 in parallel and is divided into two streams for primary heat utilization. One stream is transported through the first branch pipeline X2 to the pressurized tower reboiler Q403 and the pressurized tower feed secondary preheater Q405, respectively, to provide secondary heat for the bottom of pressurized tower T4 and the feed of pressurized tower T4. The other stream is transported through the second branch pipeline X3 to the pre-tower first reboiler Q103 to provide heat for pre-tower T1. The two streams are then merged and jointly transported to the pre-tower feed primary preheater Q101 to preheat the feed of pre-tower T1 for secondary heat utilization, and the liquid is discharged as condensate.

[0066] By rationally allocating the steam heat source, one heat source first supplies heat to the reboiler Q403 of the pressurized tower, and then prioritizes the heat supply to the pressurized tower T4. The remaining heat can also be used for the secondary feed preheating of the pressurized tower T4. The other heat source supplies heat to the first reboiler Q103 of the pre-tower. This achieves a rational allocation of heat sources. At this time, the remaining secondary heat after the two sources are combined can also be used for the feed preheating of the pre-tower T1. Based on the above, the full utilization of heat is achieved.

[0067] The material collected from the top of the pressurized column T4 is fed to the reboiler Q503 of the secondary pressurized column to provide heat, thus supplying the heat required for distillation in the secondary pressurized column T5. After condensation, the material collected from the top of the pressurized column T4 is fed to the pressurized column reflux tank Q401. One stream flows back to the top of the pressurized column T4 via the pressurized column reflux pump Q402, while the other stream is heated by the secondary preheater Q102 of the pre-column feed. The remaining material then passes through the pressurized column methanol cooler Q406 to produce refined methanol. The refined methanol output from the pressurized column T4 is 5750 kg / h. The ethanol content in the refined methanol is only 9 ppm.

[0068] The material collected from the top of the secondary pressure tower T5 is divided into two streams. One stream heats the second reboiler Q104 of the pre-pressure tower, providing heat for the pre-pressure tower T1, with the condensate returning to the secondary pressure tower reflux tank Q501. The other stream heats the reboiler Q203 of the atmospheric pressure tower, providing heat for the atmospheric pressure tower T2, with the condensate also returning to the secondary pressure tower reflux tank Q501. The material collected from the top of the secondary pressure tower T5 is only sufficient to supply heat to the atmospheric pressure tower reboiler Q203; the remaining material is used to heat the second reboiler Q104 of the pre-pressure tower. The material returning to the secondary pressure tower reflux tank Q501 is pumped back to the top of the secondary pressure tower T5 via the secondary pressure tower reflux pump Q502, while the remaining portion passes through the secondary pressure tower refined methanol cooler Q504 to be collected as refined methanol. The refined methanol production rate is 5970 kg / h. The ethanol content in the refined methanol is only 9 ppm.

[0069] The bottom of the secondary pressure tower T5 is discharged through the fusel alcohol discharge cooler Q505, and the methanol content in the fusel alcohol is <27%.

[0070] The secondary pressure tower T5 is connected to the wastewater cooler Q506 and the wastewater extraction pump Q507 in sequence through the secondary pressure tower outlet K10 to extract wastewater.

[0071] The material collected from the top of pre-tower T1 is heated by the second reboiler Q308 of the negative pressure tower and then condensed in the first-stage condenser Q106. In parallel, one stream is directly fed to the pre-tower reflux tank Q110, and the other is fed to the second-stage condenser Q107. A portion of the condensed material from the second-stage condenser Q107 enters the extraction tank Q109 for extraction. The extraction tank Q109 is equipped with a pipeline for the entry of extraction water. The remaining material enters the purge gas scrubbing tank Q108. The purge gas exits through a pipeline in the purge gas scrubbing tank Q108. The liquid in the purge gas scrubbing tank Q108 enters the extraction tank Q109 for extraction. A portion of the extracted material is collected as fusel oil, and the remaining portion is sent to the pre-tower reflux tank Q110. The material in the pre-tower reflux tank Q110 is refluxed back to the top of pre-tower T1 via the pre-tower reflux pump Q111.

[0072] The material collected from the top of atmospheric distillation column T2 heats the first reboiler Q307 of the negative pressure column, providing heat for negative pressure column T3. Afterward, it is transported to the atmospheric distillation column reflux tank Q201, and then pumped back to the top of atmospheric distillation column T2 via atmospheric distillation column reflux pump Q202. The other half flows to the atmospheric distillation column refined methanol cooler Q205 for refined methanol production. The refined methanol production rate is 4040 kg / h. The ethanol content in the refined methanol is only 9 ppm.

[0073] The steam outlet at the top of negative pressure tower T3 is connected to the first-stage condenser Q303, and then flows back to the negative pressure tower reflux tank Q301. After passing through the negative pressure tower reflux pump Q302, one stream flows back to the top of negative pressure tower T3, and the other stream is used to collect refined methanol. The refined methanol collection rate of negative pressure tower T3 is 6740 kg / h. The ethanol content in the refined methanol is only 4 ppm. The negative pressure tower reflux tank Q301 is also connected to the second-stage condenser Q304. Part of the liquid flows back to the negative pressure tower reflux tank Q301, and the other part flows to the vacuum buffer tank Q305. The liquid in the vacuum buffer tank Q305 flows back to the negative pressure tower reflux tank Q301, and the condensed gas in the vacuum buffer tank Q305 is connected to the second-stage condenser Q107 of the pre-tower for condensation via vacuum pump Q306.

[0074] The bottom material of negative pressure tower T3 is refluxed to the bottom of negative pressure tower T3 in parallel through the first reboiler Q307 and the second reboiler Q308. The temperature at which the material refluxes to the bottom of negative pressure tower T3 is 56℃.

[0075] The top temperature of pre-pressure tower T1 is 75℃ and the top pressure is 120 kPaA; the top temperature of atmospheric pressure tower T2 is 67℃ and the top pressure is 110 kPaA; the top temperature of negative pressure tower T3 is 48℃ and the top pressure is 50 kPaA; the top temperature of pressurized tower T4 is 135℃ and the top pressure is 950 kPaA; and the top temperature of secondary pressure tower T5 is 84℃ and the top pressure is 210 kPaA.

[0076] The reflux ratio of the pre-pressure tower T1 is 0.4, the reflux ratio of the atmospheric pressure tower T2 is 1.4, the reflux ratio of the negative pressure tower T3 is 1.2, the reflux ratio of the pressurized tower T4 is 2.4, and the reflux ratio of the secondary pressure tower T5 is 1.9.

[0077] The reflux ratio refers to the ratio of the reflux liquid flow rate at the top of each column to the feed flow rate of each column.

[0078] The pressure drop of the pre-pressure tower T1, atmospheric pressure tower T2, negative pressure tower T3 and pressurized tower T4 is ≤8 kPa, and the pressure drop of the secondary pressure tower T5 is ≤20 kPa.

[0079] The bottom temperature of the pre-pressure tower T1 is 74℃, the bottom temperature of the atmospheric pressure tower T2 is 72℃, the bottom temperature of the negative pressure tower T3 is 56℃, the bottom temperature of the pressurized tower T4 is 144℃, and the bottom temperature of the secondary pressure tower T5 is 124℃.

[0080] The pre-pressurization tower T1, atmospheric tower T2, negative pressure tower T3, and pressurization tower T4 all use high-efficiency structured metal packing. The secondary pressure tower T5 uses combined internals: the rectification section uses structured packing, and the stripping section uses quincunx solid valve trays.

[0081] The operating results show that the system consumes only 0.418 tons of steam to produce one ton of refined methanol, the ethanol content in the refined methanol is stable at 10 ppm, the total refined methanol yield reaches 99.5%, and the cooling water consumption of the first-stage condenser Q106, the second-stage condenser Q107, the first-stage condenser Q303, and the second-stage condenser Q304 of the negative pressure tower is 472.5 t / h. All indicators have met or exceeded the design targets.

[0082] This invention solves the problems of high energy consumption and insufficient thermal energy utilization in existing methanol distillation technologies. Through the aforementioned four-effect thermal energy cascade utilization process of "steam → pressurized tower T4 → secondary pressure tower T5 → (pre-tower T1 + atmospheric pressure tower T2) → negative pressure tower T3", energy utilization is greatly improved. This scheme constructs a more efficient multi-effect thermal coupling process, reducing steam consumption to 0.418 t / t of refined methanol and achieving a total steam consumption of 9.4 t / h. Cooling water consumption is reduced to 21 t / t of refined methanol. While achieving deep energy savings, the separation efficiency of each tower is precisely controlled, ensuring that the purity of total refined methanol in the refined methanol product reaches 99.99%, the ethanol content is below 10 ppm, and the total yield of refined methanol reaches 99.5%. The system pressure configuration and internal component selection are optimized, reducing the number of tower top condensers and lowering overall operating costs. Under the above-mentioned device, a total refined methanol production capacity of 225,000 tons / h can be achieved. The ethanol content in the obtained refined methanol is 8 ppm (simulated value).

[0083] Comparative Example 1: Referring to patent CN121202673A, crude methanol was distilled, with a steam consumption of 0.55 t / t of refined methanol and a cooling water consumption of 30 t / t of refined methanol. Although a five-tower distillation was used, the separation accuracy was limited due to the two pressurized towers connected in series and the lack of a negative pressure tower, requiring a larger reflux ratio for compensation, resulting in higher energy consumption. The absence of negative pressure operation limited the overall temperature difference drive of the system. To achieve sufficient coupling depth, some heat exchange stages had to handle smaller temperature differences, leading to large sizes of heat exchange equipment such as reboilers, resulting in high investment and floor space costs. Furthermore, the lack of a negative pressure tower weakened the removal capacity of key impurities such as ethanol. To meet the stringent requirement of ≤10 ppm ethanol content in the product, the reflux ratio in the pressurized towers needed to be significantly increased or the number of trays increased. This not only further increased steam consumption but also led to increased reboiler temperature, increasing the risk of polymerization and scaling of heavy components. Meanwhile, its heat utilization method requires that some of the top steam still needs to be condensed independently, requiring three sets of condensing equipment—pre-distillation column condenser, atmospheric pressure column condenser, and pressurized column condenser—to meet the condensation load of Comparative Example 1. Cooling water consumption is maintained at a high level, and ultimately its overall energy consumption and product quality control capabilities are significantly inferior to those of this application.

[0084] Therefore, a comparison between Example 1 and Comparative Example 1 shows that this invention, by introducing and optimizing a negative pressure column and finely optimizing the arrangement sequence and heat coupling method of the distillation columns, effectively reduces the required reflux ratio under the same or even higher separation accuracy requirements, thereby fundamentally reducing the energy consumption of the distillation process. Simultaneously, the reasonable pressure and temperature difference planning avoids the drawbacks of small temperature difference heat exchange. Based on the above, while reducing steam consumption and cooling water usage, it improves the purity, yield, and production capacity of refined methanol.

[0085] Comparative Example 2: Referring to Example 3 of patent CN119185992A, crude methanol was distilled with a steam consumption of 0.54 t / t of refined methanol and a cooling water consumption of 29 t / t of refined methanol. Although a five-tower distillation was used, the series sequence of the distillation towers was: pre-tower, negative pressure tower, pressurized tower, secondary pressure tower, and atmospheric pressure tower. While the high-grade heat energy at the top of the pressurized tower could provide heat to the secondary pressure tower and the atmospheric pressure tower, this parallel thermal coupling method had structural limitations in heat matching. Specifically, the heat transfer path was as follows: the pressurized tower (first effect) simultaneously supplied heat to the secondary pressure tower and the atmospheric pressure tower (second effect), forming a parallel distribution. However, the atmospheric pressure tower had a lower operating pressure, and its top temperature was lower than that of the secondary pressure tower. Although it was technically feasible for the high-grade heat energy of the pressurized tower to simultaneously heat two towers with significantly different temperature requirements, there was a phenomenon of "high-quality, low-use" in terms of heat energy grade—that is, using high-grade heat energy to meet low-grade heating requirements, resulting in a loss of usable energy. The residual heat source of the atmospheric pressure tower may still exist after the negative pressure tower provides heat. On this basis, generating more residual heat requires more cooling water for condensation.

[0086] Referring to Example 4 of patent CN119185992A, crude methanol was distilled with a steam consumption of 0.4 t / t of refined methanol and a cooling water consumption of 19 t / t of refined methanol. A six-tower distillation process was used. Due to the two parallel negative-pressure towers after the pre-tower, the material and energy distribution were complex. Both negative-pressure towers required condensation equipment for cooling, placing extremely high demands on the control system and resulting in poor operational stability. The complex thermal coupling network presented significant challenges in engineering design and commissioning, posing challenges to system reliability and maintainability.

[0087] As can be seen from the comparison between Example 1 and Comparative Example 2, the present invention adopts a more stable and easier-to-control series / integrated tower system layout, replacing the complex parallel negative pressure tower structure. While maintaining the advantage of low energy consumption, it significantly simplifies the process, reduces the complexity of operation and control, and improves the stability and operability of the device. In contrast, the present invention sets the sequence of each distillation tower based on the processing temperature and pressure characteristics of each distillation tower, and adopts a specific step-by-step series and parallel heat cascade utilization method: pressurized tower → secondary pressure tower → (atmospheric pressure tower + pre-tower) → negative pressure tower. This structure and heat coupling method ensure more complete cascade utilization of heat energy and avoid the waste of high-grade heat energy. At the same time, the present invention rationally distributes and utilizes the steam heat source in stages, and couples the condensation at the top of the pre-tower and the negative pressure tower, thereby significantly reducing steam consumption and cooling water usage. With five-tower distillation and separate condensers only at the top of the pre-tower and the top of the negative pressure tower, the technical effect can be comparable to that of Example 4 of Patent CN119185992A, which has six towers and three distillation towers equipped with cooling equipment. This significantly reduces the number of towers and the complexity of the system during methanol distillation, and achieves a level comparable to that of six towers with fewer towers and lower system complexity.

[0088] Comparative Example 3: Referring to patent CN112961033B, crude methanol was distilled. The steam consumption was 0.85 t / t of refined methanol, and the cooling water consumption was 40 t / t of refined methanol. Due to insufficient thermal coupling, the pre-column, atmospheric pressure column, and recovery column tops were directly water-cooled, resulting in a significant waste of low-grade heat energy, which is the key reason for high energy consumption. Furthermore, each column (the first pressurized column) was heated by multiple columns, making optimal heat load matching difficult and hindering further improvement in overall energy efficiency.

[0089] As can be seen from the comparison between Example 1 and Comparative Example 3, the present invention designs a deep and sufficient thermal coupling network (four-effect coupling) to maximize the recovery and utilization of the latent heat of the steam at the top of the tower, and realizes the cascade and efficient utilization of thermal energy.

[0090] In summary, this invention innovatively employs a series of columns in the form of "pre-column → atmospheric column → negative pressure column → pressurized column → secondary pressure column" and a deep four-stage thermal coupling network. The atmospheric column is directly connected after the pre-column, and the negative pressure column is placed after the atmospheric column and before the pressurized column. The secondary pressure column is introduced as an additional thermal coupling hub, thereby constructing a distillation system with a more reasonable pressure and temperature gradient and efficient utilization of thermal energy in four stages. This unique architecture not only achieves groundbreaking energy savings, reducing steam consumption to less than 0.42 t / t of refined methanol while lowering cooling water consumption to 21 t / t of refined methanol, but also ensures superior quality by achieving an ethanol content of less than 10 ppm and a total yield of not less than 99.5% in the refined methanol product through optimized pressure environment and precise reflux control. This invention is significantly superior to traditional and some improved processes in terms of energy consumption, and far surpasses technical solutions with more additional equipment and parallel negative pressure towers in terms of system complexity and operational stability. It successfully achieves a balance between high energy efficiency, high product purity, high yield, and high operational reliability, providing a practical and advanced solution for the green, low-carbon, and low-cost operation of large-scale methanol plants.

[0091] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. An energy-saving five-tower methanol distillation method based on multi-effect thermal coupling, characterized in that, The method includes the following steps: Crude methanol is fed to a pre-distillation tower (T1) for rectification; the bottom product of the pre-distillation tower (T1) is fed to an atmospheric distillation tower (T2) for rectification; the bottom product of the atmospheric distillation tower (T2) is fed to a negative pressure distillation tower (T3) for rectification; the bottom product of the negative pressure distillation tower (T3) is fed to a pressurized distillation tower (T4) for rectification; the bottom product of the pressurized distillation tower (T4) is fed to a secondary pressure distillation tower (T5) for rectification; refined methanol is collected from the tops of the pressurized distillation tower (T4), the atmospheric distillation tower (T2), the negative pressure distillation tower (T3), and the secondary pressure distillation tower (T5). The material drawn from the top of the pressurized tower (T4) is used to heat the reboiler (Q503) of the secondary pressure tower. The material drawn from the top of the secondary pressure tower (T5) is used to heat the reboiler of the pre-tower and the reboiler (Q203) of the atmospheric pressure tower. The material drawn from the top of the pre-tower (T1) and the material drawn from the top of the atmospheric pressure tower (T2) are used to heat the reboiler of the negative pressure tower.

2. The method according to claim 1, characterized in that, The method also includes a steam heat source, which is divided into two streams in parallel through a steam heat source pipeline (X1) for primary heat utilization. One stream supplies heat to at least one pressurized tower steam reboiler and at least one pressurized tower feed preheater, and the other stream supplies heat to at least one pre-tower reboiler. The two streams are then combined to supply heat to the pre-tower feed preheater for secondary heat utilization before exiting the boundary.

3. The method according to claim 1, characterized in that, The crude methanol is preheated in two stages before entering the pre-distillation column (T1) for distillation; the bottom product of the pre-distillation column (T1) is sent to the atmospheric distillation column (T2) for rectification; the bottom product of the atmospheric distillation column (T2) is sent to the negative pressure distillation column (T3) for rectification; the bottom product of the negative pressure distillation column (T3) is preheated in two stages before being sent to the pressurized distillation column (T4) for rectification; the bottom product of the pressurized distillation column (T4) is sent to the secondary pressure distillation column (T5) for rectification. Preferably, the crude methanol is first heated by a primary preheater (Q101) for pre-tower feed, and then supplemented by a secondary preheater (Q102) for pre-tower feed before entering the pre-tower (T1) for distillation; wherein the primary preheater (Q101) for pre-tower feed is heated by a steam heat source, specifically the secondary heat source of the steam heat source; and the secondary preheater (Q102) for pre-tower feed is heated by the material at the top of the pressurized tower (T4). Preferably, the material collected from the bottom of the negative pressure tower (T3) is first preheated by the primary preheater (Q404) of the pressurized tower feed, and then preheated by the secondary preheater (Q405) of the pressurized tower feed as a supplementary heat source before entering the pressurized tower (T4) for rectification; the material collected from the bottom of the pressurized tower (T4) is heated by the primary preheater (Q404) of the pressurized tower feed before entering the secondary pressure tower (T5) for rectification; the secondary preheater (Q405) of the pressurized tower feed is heated by the primary heat source provided by one of the steam heat sources.

4. The method according to claim 1, characterized in that, The steam heat source is divided into two parallel streams via a steam heat source pipeline (X1). One stream supplies heat to the pressurized tower reboiler (Q403) and the pressurized tower feed secondary preheater (Q405) in sequence, while the other stream supplies heat to the preheater tower first reboiler (Q103). The two streams are combined to supply heat to the preheater tower feed primary preheater (Q101) and then exit as condensate.

5. The method according to claim 1, characterized in that, The material collected from the top of the pressurized tower (T4) is heated by the reboiler (Q503) of the secondary pressure tower, with one stream flowing back to the top of the pressurized tower (T4) and the other stream being heated by the secondary preheater (Q102) of the pre-tower feed to produce refined methanol; the material collected from the top of the secondary pressure tower (T5) is heated in parallel by the second reboiler (Q104) of the pre-tower and the reboiler (Q203) of the atmospheric pressure tower, with one stream flowing back to the top of the secondary pressure tower (T5) and the other stream being produced as refined methanol. The material collected from the top of the pre-column (T1) is heated by the second reboiler (Q308) of the negative pressure column and then refluxed back to the top of the pre-column (T1) through a two-stage condenser. The material collected from the top of the atmospheric column (T2) is heated by the first reboiler (Q307) of the negative pressure column, with one stream refluxed back to the top of the atmospheric column (T2) and the other stream being purified methanol. The material collected from the top of the negative pressure column (T3) is refluxed back to the top of the negative pressure column (T3) through a two-stage condenser and the other stream being purified methanol.

6. The method according to claim 1, characterized in that, The material collected from the top of the secondary pressure tower (T5) is used in parallel to heat the second reboiler of the pre-pressure tower (Q104) and the reboiler of the atmospheric pressure tower (Q203). One stream is returned to the top of the secondary pressure tower (T5), and the other stream is used to collect refined methanol. The material collected from the top of the secondary pressure tower (T5) must be sufficient to heat the reboiler of the atmospheric pressure tower (Q203), and the remaining material is used to heat the second reboiler of the pre-pressure tower (Q104). Preferably, the bottom material of the negative pressure tower (T3) is heated by the first reboiler (Q307) and the second reboiler (Q308) of the negative pressure tower in parallel and then refluxed to the bottom of the negative pressure tower (T3), and the temperature of the material refluxed to the bottom of the negative pressure tower (T3) is 53~58℃. Preferably, the temperature of the crude methanol after being heated by the first-stage preheater (Q101) of the pre-tower feed is 65~70℃, and the temperature of the crude methanol after being heated by the second-stage preheater (Q102) of the pre-tower feed is 73~77℃. Preferably, the temperature of the material extracted from the bottom of the negative pressure tower (T3) after being heated by the primary preheater (Q404) of the pressurized tower feed is 92~98℃, and the temperature of the material extracted from the bottom of the negative pressure tower (T3) after being heated by the secondary preheater (Q405) of the pressurized tower feed is 133~137℃.

7. The method according to claim 1, characterized in that, The top temperature of the pre-pressure tower (T1) is 73~77℃ and the top pressure is 115~125 kPaA; the top temperature of the atmospheric pressure tower (T2) is 65~69℃ and the top pressure is 105~115 kPaA; the top temperature of the negative pressure tower (T3) is 46~50℃ and the top pressure is 45~55 kPaA; the top temperature of the pressurized tower (T4) is 133~137℃ and the top pressure is 945~955 kPaA; and the top temperature of the secondary pressure tower (T5) is 82~86℃ and the top pressure is 200~215 kPaA. Preferably, the reflux ratio of the pre-pressure tower (T1) is 0.35~0.45, the reflux ratio of the atmospheric pressure tower (T2) is 1.35~1.45, the reflux ratio of the negative pressure tower (T3) is 1.15~1.25, the reflux ratio of the pressurized tower (T4) is 2.35~2.45, and the reflux ratio of the secondary pressure tower (T5) is 1.85~1.

95.

8. The method according to claim 1, characterized in that, The material collected from the top of the pressurized tower (T4) is heated by the reboiler of the secondary pressurized tower (Q503), then transported to the pressurized tower reflux tank (Q401), and split into two streams. One stream flows through the pressurized tower reflux pump (Q402) and then flows back to the top of the pressurized tower (T4). The other stream is heated by the secondary preheater (Q102) of the pre-tower feed and then collected as refined methanol. Preferably, the material collected from the top of the secondary pressure tower (T5) is heated in parallel to the second reboiler of the pre-tower (Q102) and the reboiler of the atmospheric pressure tower (Q203), and then transported to the secondary pressure tower reflux tank (Q501). After passing through the secondary pressure tower reflux pump (Q502), it is divided into two streams: one stream flows back to the top of the secondary pressure tower (T5), and the other stream is collected as refined methanol. Preferably, wastewater and fusel oil are collected from the bottom of the secondary pressure tower (T5); Preferably, the material drawn from the top of the pre-tower (T1) is heated by the second reboiler (Q308) of the negative pressure tower, condensed by the first-stage condenser (Q106) and the second-stage condenser (Q107) of the pre-tower, and then transported to the pre-tower reflux tank (Q110), and then returned to the top of the pre-tower (T1) by the pre-tower reflux pump (Q111); Preferably, the material collected from the top of the atmospheric pressure tower (T2) is heated by the first reboiler (Q307) of the negative pressure tower and then transported to the atmospheric pressure tower reflux tank (Q201). Through the atmospheric pressure tower reflux pump (Q202), it is divided into two streams: one stream flows back to the top of the atmospheric pressure tower (T2), and the other stream is collected as refined methanol. Preferably, the material collected from the top of the negative pressure tower (T3) is condensed by the first-stage condenser (Q303) and the second-stage condenser (Q304) of the negative pressure tower, and then transported to the negative pressure tower reflux tank (Q301). Through the negative pressure tower reflux pump (Q302), it is divided into two streams, one of which flows back to the top of the negative pressure tower (T3), and the other is collected as refined methanol.

9. The method according to claim 8, characterized in that, The pre-tower secondary condenser (Q107) is also connected to a purge gas scrubbing tank (Q108) for purge gas discharge. The purge gas scrubbing tank (Q108) is connected to an extraction tank (Q109) for extraction, and some of the extraction products are discharged in the form of fusel oil. Preferably, the negative pressure tower secondary condenser (Q304) is also connected to a vacuum buffer tank (Q305), which is connected to a vacuum pump (Q306) and then to a pre-tower secondary condenser (Q107) for condensation.

10. The method according to claim 1, characterized in that, The total cooling water consumption of the pre-tower primary condenser (Q106), pre-tower secondary condenser (Q107), negative pressure tower primary condenser (Q303), and negative pressure tower secondary condenser (Q304) is 21t / t of refined methanol. Preferably, the ethanol content in the refined methanol is ≤10 ppm, and the total yield of the refined methanol is ≥99.5%. Preferably, the methanol content in the fusel oil collected from the bottom of the secondary pressure tower (T5) via a side stream is <27%; Preferably, the methanol content in the wastewater drawn from the bottom of the secondary pressure tower (T5) is ≤100ppm; Preferably, the steam consumption of the energy-saving five-tower methanol distillation process based on multi-effect thermal coupling is ≤0.42 t / t of refined methanol.

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