Rectification method for efficiently producing high-purity methanol by using low-temperature heat

Abstract

The invention discloses a rectification method for efficiently producing high-purity methanol by using low-temperature heat. According to the technology, a pressurized tower and an atmospheric tower are connected in parallel, so that crude methanol from a pre-tower kettle enters the two towers in a split-flow manner, low-temperature heat is used for supplying heat, and steam at the top of the pressurized tower serves as a heat source of a reboiler of the atmospheric tower; a tower section heat exchanger which can be flexibly arranged is arranged in the vacuum tower to utilize low-temperature heat; and thirdly, a recovery tower is changed into a vacuum tower, and low-temperature heat is used as a heat source of a reboiler. The technology can be flexibly implemented partially or completely, and a remarkable energy-saving effect can be achieved. The embodiment shows that the technology can stably produce high-precision methanol with the ethanol content as low as 10 ppm or below, the fresh steam consumption per ton of methanol is reduced to 0.2 ton or below, the productivity of the device can also be improved, and compared with a traditional four-tower double-effect rectification technology (the ethanol content is about 50 ppm, and the fresh steam consumption per ton of methanol is 1.0-1.2 tons), the technology has remarkable advantages in the aspects of product purity reduction and energy consumption reduction. The method effectively solves the problems of difficult production of high-precision methanol, high energy consumption and insufficient utilization of low-temperature heat in the prior art, and has good economic and environment-friendly benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of methanol distillation, and in particular to a distillation technology for efficiently producing high-purity methanol with an ethanol content of less than 10 ppm by optimizing the combination of a pressurization tower, an atmospheric pressure tower, a vacuum tower, and a recovery tower and making full use of low-temperature heat as a heat source. Background Art

[0002] Methanol, a vital basic chemical raw material, is widely used in numerous fields, including chemical engineering, medicine, and agriculture. Currently, industrial methanol production mostly uses synthesis gas as the raw material. Crude methanol is obtained through a synthesis reaction, which undergoes initial flash separation before entering the distillation process. However, crude methanol contains not only impurities such as ethanol, water, dimethyl ether, and acetone, but also dissolved gases such as carbon dioxide, carbon monoxide, methane, argon, and nitrogen.

[0003] The quality standard system for methanol primarily includes the US Federal Grade A and Grade AA standards, as well as my country's GB338-2011 standard. Controlling ethanol content is particularly critical. For example, the Federal Grade AA standard specifies a maximum ethanol content of 10 ppm, while the Federal Grade A standard does not. Although the requirements for ethanol content in methanol have been relaxed to some extent with the continuous advancement of acetic acid catalyst technology, strict control still remains necessary in certain high-end application areas such as electronics and pharmaceuticals.

[0004] Traditional methanol distillation units are typically designed to meet US Federal Class AA standards, but achieving this standard in actual production is difficult due to technical challenges. To reduce energy consumption, the industry has developed energy-saving technologies such as double-effect distillation, triple-effect distillation, quadruple-effect distillation, quintuple-effect distillation, and even hexaplefect distillation, as well as heat pump distillation. While these technologies can reduce steam consumption per ton of methanol produced to a certain extent, they remain difficult to consistently produce high-quality methanol products with an ethanol content below 10 ppm in large-scale industrial practice.

[0005] As a relatively common methanol distillation process, four-tower distillation technology achieves partial cascade utilization of heat through a combination of a pre-distillation tower, a pressurized distillation tower, an atmospheric distillation tower, and a recovery tower, and can produce a higher-purity methanol product. However, with the continuous expansion of industrial production scale and the further improvement of product quality requirements, the four-tower distillation technology is not ideal for separating certain key impurities (such as ethanol, higher alcohols, etc.) when processing crude methanol with high impurity content, and there is still much room for improvement in energy utilization efficiency. In addition, when faced with crude methanol from different sources and different compositions, the flexibility and adaptability of its process are also insufficient.

[0006] Against this backdrop, four-effect methanol distillation technology emerged. Existing four-effect methanol distillation technology typically consists of a pre-rectifier, multiple pressurized distillation towers (e.g., a single pressurized tower, a second pressurized tower, and a third pressurized tower), and an atmospheric distillation tower. In the traditional four-effect methanol distillation process, crude methanol first enters the pre-rectifier, where it is heated to separate low-boiling-point impurities (such as dimethyl ether and methyl formate) and dissolved gases, which are then discharged from the top of the tower. The material from the bottom of the pre-rectifier then enters each pressurized distillation tower in sequence. Each pressurized distillation tower operates at a different pressure, decreasing in pressure and correspondingly reducing the temperature of the overhead steam. The overhead steam from the previous pressurized distillation tower serves as the heat source for the reboiler in the next pressurized distillation tower, achieving multi-stage heat utilization. Finally, the material from the pressurized distillation tower enters the atmospheric distillation tower for further separation at atmospheric pressure. Refined methanol product is obtained from the top of the tower, while wastewater containing small amounts of methanol and other impurities is discharged from the bottom of the tower.

[0007] Although the four-effect methanol distillation technology has improved energy utilization and product purity to a certain extent, there are still some problems that need to be solved. On the one hand, the separation of some trace impurities in crude methanol is not thorough enough, making it difficult to meet the strict requirements of high-end electronics, pharmaceuticals and other industries for high-purity methanol. On the other hand, although multi-effect distillation is adopted, the recovery and utilization of low-temperature heat is still not sufficient. The large amount of low-temperature waste heat generated in the industrial production process has not been efficiently utilized, resulting in high overall energy consumption. In addition, the operating parameters of this process are relatively complex, and the coordinated control between different towers is difficult, which is prone to unstable operation, thus affecting product quality and production efficiency.

[0008] The main problems of the existing technology are as follows:

[0009] 1. High-purity methanol production is difficult: Existing methanol distillation technology struggles to consistently produce high-purity methanol with an ethanol content below 10 ppm. The complex impurity composition and extremely stringent purity requirements of traditional processes significantly increase production technical complexity, making it difficult to achieve the desired purity standards.

[0010] 2. High energy consumption: The traditional methanol distillation process requires large amounts of steam for heating and circulating water for cooling, resulting in high energy consumption. Although some existing energy-saving technologies can reduce steam consumption, energy consumption remains a significant issue in the large-scale production of high-purity methanol.

[0011] 3. Insufficient utilization of low-temperature heat: Existing distillation technology fails to fully and effectively utilize the low-temperature waste heat resources generated in industrial processes, which not only wastes a large amount of low-grade energy, but also increases overall energy consumption and operating costs.

[0012] Therefore, a new technology is urgently needed to solve the above problems in order to achieve stable production of high-purity methanol and significantly reduce energy consumption. Summary of the Invention

[0013] The main purpose of the present invention is to provide a distillation method for efficiently producing high-purity methanol using low-temperature heat, aiming to solve the problems of high-purity methanol production difficulty, high energy consumption and insufficient low-temperature heat utilization in the prior art, thereby achieving stable production of high-purity methanol and significantly reducing energy consumption.

[0014] Technical Solution

[0015] Specific logistics process

[0016] Process 1: Figure 1 As shown:

[0017] Crude methanol split after the pre-tower: The crude methanol in the pre-tower kettle contains 80%-95% (mass fraction) methanol and impurities such as water and ethanol, and enters the parallel T1 atmospheric pressure tower and T2 pressure tower through pipelines 2 and 3 respectively at a ratio of 0.8-1.2:1.

[0018] Atmospheric pressure tower and pressurized tower treatment: The T2 pressurized tower is heated by steam condensate or other low-temperature waste heat. The operating pressure of the pressurized tower is maintained at 0.2-0.4MPaG, and the tower top temperature reaches 90-115℃. Steam is supplied to the T1 atmospheric pressure tower, and the refined methanol (≥99% (mass fraction)) at the top of the tower is condensed by C2 and then produced through pipeline 6.

[0019] The reboiler of the atmospheric tower T1 and the condenser of the pressurized tower T2 are the same device, C2. Heat is provided by the condensed steam from the overhead of the T2 pressurized tower, creating a double-effect distillation process. The operating pressure is 0.01-0.05 MPa (gauge) and the tower top temperature is 65-75°C. The refined methanol (≥99% by mass) produced from the overhead is condensed in C1 and withdrawn via pipeline 4. The remainder enters the subsequent process via pipeline 5.

[0020] Vacuum Tower Treatment: The combined outputs from the T1 and T2 bottoms enter the vacuum tower, operating at a pressure of -0.02 to -0.06 MPaG and a tower top temperature of 40-60°C. A tower section heat exchanger (see Process 2) is installed, with various heat sources, such as C1 condensate. The tower section heat exchanger can be integrated with the tower or installed independently. Finally, high-quality methanol (≥99.9% by mass) is condensed from the tower top via C3 and withdrawn via pipeline 9. The alcohol-containing wastewater from the bottom of the tower is discharged via pipeline 10.

[0021] Recovery tower treatment: The product from the bottom of vacuum tower T3 enters the recovery tower, which also operates at a vacuum pressure of -0.02 to -0.06 MPaG and a tower top temperature of 40-60°C. A side line is set up in the tower to produce fusel oil, which is discharged through pipeline 12.

[0022] Process 2, set up a vacuum tower with a tower section heat exchanger, such as Figure 2 As shown:

[0023] Figure 2 The process of setting up an internal tower section heat exchanger for the T3 vacuum tower is as follows: a tower section heat exchanger is set up inside T3, and the heat source of the tower section heat exchanger comes from the condensed steam of the atmospheric tower or other low-temperature heat.

[0024] Process 3: The tower section heat exchanger is moved out of the vacuum tower, such as Figure 3 As shown:

[0025] Figure 3 The process for removing the heat exchanger from the vacuum tower section of the T3 tower: Liquid material is drawn from the vacuum tower, vaporized in the heat exchanger section, and then returned to the vacuum tower. The heat source for the heat exchanger section is the condensate from the atmospheric tower or other low-temperature heat.

[0026] Comparison of the advantages of this invention and traditional methanol distillation technology

[0027] The distillation technology proposed in the present invention for efficiently producing high-purity methanol using low-temperature heat has significant advantages over traditional methanol distillation technology in many aspects. The specific comparison is as follows:

[0028] Product purity:

[0029] This invention, through the optimized combination of a pressurized tower, an atmospheric tower, a vacuum tower, and a recovery tower, as well as the use of tower section heat exchangers, can stably produce high-quality methanol with an ethanol content below 10 ppm. The methanol content in the final product can reach 99.9% (mass fraction) or higher. High-end applications in electronics and pharmaceuticals require extremely stringent methanol purity. This technology can meet these stringent requirements for controlling impurities, especially ethanol content, and provide high-quality raw materials for these applications.

[0030] Traditional Technology: Traditional methanol distillation units are typically designed to US Federal Class AA standards, but achieving these standards is difficult in practice. For example, the methanol produced by the traditional four-tower double-effect distillation process has an ethanol content of approximately 50 ppm. Traditional three-tower distillation technology is not ideal for separating key impurities such as ethanol when processing crude methanol with high impurity content, making it difficult to meet the high-end industry's demand for high-purity methanol.

[0031] Energy consumption:

[0032] The present invention fully utilizes low-temperature heat as a heat source. By designing a pressure tower and a normal-pressure tower in parallel, the pressure tower can fully utilize the low-temperature heat, reducing its reliance on high-temperature steam. The pressure-reducing tower also utilizes low-temperature waste heat for heating, efficiently recovering and utilizing the low-temperature heat through a tower section heat exchanger. The recovery tower also utilizes low-temperature waste heat for heating. Several energy-saving measures can reduce fresh steam consumption per ton of methanol to below 0.2 tons, far lower than typical methanol distillation units (where the vast majority of steam consumption is around 1.0 tons per ton of methanol, with a very small portion consuming around 0.65 tons per ton of methanol). This significantly reduces energy consumption, improves economic efficiency, and reduces carbon emissions, meeting environmental requirements.

[0033] Conventional Technology: The traditional methanol distillation process consumes large amounts of steam for heating and circulating water for cooling, resulting in high energy consumption. While some energy-saving technologies can reduce steam consumption, energy consumption remains a significant issue in large-scale production of high-quality methanol. For example, the traditional four-tower double-effect distillation process consumes 1.0 to 1.2 tons of fresh steam per ton of methanol, far exceeding the energy consumption of the technology proposed in this paper.

[0034] Low temperature heat utilization:

[0035] This invention innovatively switches the series connection of the pressurized and atmospheric towers to a parallel one, introduces a vacuum tower afterward, utilizes a tower section heat exchanger, and introduces a vacuum recovery tower. This technology allows the use of a variety of low-temperature heat sources as the reboiler heat source, reducing steam consumption. The tower section heat exchanger can be flexibly configured, with its heat source being methanol vapor, steam condensate, or other low-temperature waste heat from the atmospheric tower overhead. This fully recovers and utilizes low-temperature waste heat resources generated during industrial processes, reducing reliance on conventional heat sources such as high-temperature steam, lowering overall operating costs, and improving the system's economic efficiency and stability.

[0036] Traditional technology: Existing distillation technology fails to fully and effectively utilize the low-temperature waste heat resources generated in industrial processes. A large amount of low-grade energy is wasted, which not only increases overall energy consumption but also increases operating costs. There is still much room for improvement in energy utilization efficiency.

[0037] Process flexibility and adaptability:

[0038] The present invention offers flexible operation, allowing for partial or complete implementation of energy-saving measures. The tower section heat exchanger can be integrated with the distillation tower or installed independently. This flexible design enhances the system's flexibility and adaptability, enabling it to better handle crude methanol from different sources and compositions. Adjustments and optimizations can be made based on actual conditions, ensuring stable system operation and product quality.

[0039] Traditional technology: Taking three-tower distillation technology as an example, when faced with crude methanol of different compositions, its process flexibility and adaptability are insufficient, the separation effect of certain key impurities will be affected, and it is difficult to ensure the stability of product quality.

[0040] Traditional technology: The operating parameters of traditional four-effect methanol distillation technology are relatively complex, and the coordinated control between different towers is difficult, which is prone to unstable operation, thus affecting product quality and production efficiency.

[0041] In summary, the distillation technology of the present invention is superior to traditional methanol distillation technology in terms of product purity, energy consumption, low-temperature heat utilization, process flexibility and operational stability, and has broad application prospects and significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the methanol distillation process of this patented technology

[0043] T1—atmospheric pressure tower; T2—pressure tower; T3—vacuum tower; T4—recovery tower

[0044] C1—Atmospheric pressure tower condenser; C2—Pressure tower condenser and atmospheric pressure tower reboiler; C3—Vacuum tower condenser; C4—Recovery tower condenser

[0045] B2—pressure tower reboiler; B3—vacuum tower reboiler; B4—recovery tower reboiler

[0046] 1, 2, 3—crude methanol; 4, 6—refined methanol; 5—extraction from the kettle of the atmospheric pressure tower

[0047] 7—extraction from the pressurized tower kettle; 8—feed to the vacuum tower; 9—high-purity methanol; 10—alcohol-containing wastewater;

[0048] 11—Recovered methanol; 12—Fusel oil; 13—Qualified discharged wastewater

[0049] Figure 2 Schematic diagram of a vacuum tower with a tower section heat exchanger

[0050] Figure 3 Schematic diagram of a vacuum tower with the tower section heat exchanger removed from the tower DETAILED DESCRIPTION

[0051] Example

[0052] This example utilizes some of the energy-saving measures of the present invention to technically transform a four-tower, double-effect methanol distillation unit with an annual output of 500,000 tons. Key points of the transformation are: 1. The connection between the pressure tower and the atmospheric tower is changed from series to parallel; 2. A vacuum tower is added after the atmospheric tower; 3. Low-temperature heat or steam condensate is used as the heat source instead of steam; 4. The vacuum tower uses an ejector to create a vacuum; 5. The process parameters of the pressure tower are adjusted (refer to the parameters provided in this patent). 6. The recovery tower is not modified.

[0053] The original process consisted of four distillation towers: a pre-tower, a pressure tower, an atmospheric tower, and a recovery tower. The pre-tower removed light components, while the bottoms of the tower flowed into the pressure tower, the bottoms of the pressure tower flowed into the atmospheric tower, and the bottoms of the atmospheric tower flowed into the recovery tower. The atmospheric tower had a side stream for producing fusel oil. The top temperature of the pressure tower was approximately 120°C, forming a dual-effect distillation system with the atmospheric tower. Condensation from the top of the pressure tower provided heat for the atmospheric tower's bottom reboiler. The recovery tower recovered methanol from the wastewater.

[0054] The original process produced 460,000 tons of methanol annually, with an ethanol content of approximately 50 ppm, and in most cases around 80 ppm. The pre-column reboiler was heated with condensate steam, while the reboilers in the pressurization and recovery towers were heated with steam. Fresh steam consumption was 1 ton of steam per ton of methanol.

[0055] The transformation achieved the following results: 1. While producing methanol containing 50 ppm ethanol, it also consistently produced methanol containing 10 ppm ethanol; 2. Annual production increased to 600,000 tons, reaching a maximum of 660,000 tons, with over 150,000 tons of high-purity methanol containing 10 ppm ethanol; 3. Fresh steam consumption per ton of methanol was 0.17 to 0.18 tons of steam; and 4. All environmental indicators met standards. These results demonstrate that the distillation technology presented here offers significant advantages in reducing energy consumption and improving product purity, demonstrating its suitability for industrial applications. Key process data are listed in Table 1.

[0056] Table 1 Key data of the embodiment

[0057] project Example Crude methanol feed mass flow ratio (pressure tower: atmospheric pressure tower) 1.2:1 Pressurized tower operating pressure (MPaG) 0.3 Pressure tower top temperature (℃) 104 Atmospheric tower operating pressure (MPaG) Normal pressure Atmospheric tower top temperature (℃) 67 Vacuum tower operating pressure (MPaG) -0.05 Vacuum tower top temperature (℃) 45 Recovery tower operating pressure (MPaG) -0.05 Recovery tower top temperature (℃) 48 Fresh steam consumption per ton of methanol (tons) ～0.18 High-purity methanol and ethanol content (ppm) <10

[0058] In summary, the distillation method for efficiently producing high-purity methanol using low-temperature heat provided by the present invention effectively solves the problems of the prior art through innovative tower structure design and low-temperature heat utilization, and has broad application prospects and significant economic and environmental benefits.

Claims

1. A distillation method for efficiently producing high-purity methanol using low-temperature heat, characterized in that: The following steps are involved: The pressure tower and the atmospheric pressure tower are designed to be in parallel structure, and the crude methanol from the pre-tower kettle enters the pressure tower and the atmospheric pressure tower respectively at a ratio of 0.8-1.2:1; The bottom of the pressure tower is heated by steam condensate or low-temperature waste heat from other devices, and the methanol vapor generated at the top of the tower is used as the heat source of the atmospheric pressure tower; A vacuum tower is arranged after the pressure tower and the atmospheric pressure tower. The bottom of the vacuum tower is heated by steam condensate or other low-temperature waste heat, and the top of the tower is cooled by circulating water or air. A tower section heat exchanger is arranged inside the vacuum tower, and the heat source of the tower section heat exchanger comes from methanol vapor, steam condensate or other low-temperature waste heat at the top of the atmospheric pressure tower.

2. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: A vacuum tower is set after the vacuum tower, which is called a recovery tower. The bottom of the recovery tower is heated by steam condensate or other low-temperature waste heat, and the top of the tower is cooled by circulating water or air. A side line is set inside the recovery tower to produce fusel oil.

3. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: The crude methanol after the pre-tower has a methanol content of 80%-95% (mass fraction) and also contains impurities such as water, ethanol, and fusel alcohol.

4. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: The operating pressure of the pressurized tower is maintained at 0.2-0.4 MPaG (G represents gauge pressure, the same below), and the tower top temperature reaches 90-115°C.

5. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: The atmospheric tower is heated by methanol vapor at the top of the pressure tower, with an operating pressure of 0.01-0.05 MPa (gauge pressure) and a tower top temperature of 65-75°C.

6. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: The operating pressure of the vacuum tower and the recovery tower is -0.02 to -0.06 MPaG, and the tower top temperature is 40-60°C.

7. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: The tower section heat exchanger can be integrated with the vacuum tower or be independently provided.

8. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1 and claim 2, characterized in that: The pressure reduction of the pressure reducing tower and the recovery tower comes from the injection of methanol vapor or low-pressure steam from the top of the pressure tower, without the use of dynamic equipment such as vacuum pumps and induced draft fans.

9. The distillation method for efficiently producing high-purity methanol using low-temperature heat according to claim 1, characterized in that: The condensation at the top of the atmospheric tower can be used as low-temperature heat.

10. An apparatus for implementing the distillation method for efficiently producing high-purity methanol using low-temperature heat as claimed in any one of claims 1 to 9, characterized in that: It includes a pressure tower and a normal pressure tower connected in parallel, a pressure reducing tower arranged after the pressure tower and the normal pressure tower, and a pressure reducing recovery tower arranged behind the pressure reducing tower. A tower section heat exchanger is arranged inside or outside the pressure reducing tower. The pressure tower, the normal pressure tower, the pressure reducing tower and the pressure reducing recovery tower are connected by corresponding pipelines, and each tower is provided with a heating device, a condensing device and a material inlet and outlet.

11. The device according to claim 10, characterized in that The heat exchange area of ​​the tower section heat exchanger can be adjusted according to the actual production scale.

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