Energy integration system for acetic acid distillation and methanol distillation processes

Abstract

The present application relates to a kind of energy integration system of acetic acid rectification and methanol rectification process, second reboiler and / or third reboiler are configured to methanol rectification pressurized tower, second reboiler uses the overhead gas of acetic acid rectification drying tower as heat source, third reboiler uses the overhead gas of acetic acid rectification product tower as heat source, whereby the energy collection of methanol rectification process and acetic acid rectification process is realized, the heat of acetic acid rectification drying tower and acetic acid rectification product tower overhead gas is recycled, the use amount of methanol rectification pressurized tower reboiler steam is reduced, the energy consumption level of methanol rectification device is reduced, and the technical effects such as energy saving, water saving, emission reduction are realized.

Description

Technical Field

[0001] This invention relates to the field of energy conservation and environmental protection, specifically to an energy integration system for acetic acid distillation and methanol distillation processes. Background Technology

[0002] Acetic acid is an important chemical raw material, widely used in pesticides, pharmaceuticals, chemicals, light industry, textiles, rubber, photographic chemicals manufacturing, electronics, and food. There are various methods for producing acetic acid, such as the ethanol method, the ethylene acetaldehyde method, and the methanol carbonyl synthesis method. Among these, the methanol carbonyl synthesis method has become a mainstream process for coal chemical enterprises to produce acetic acid due to its high methanol conversion rate.

[0003] When producing acetic acid using the methanol carbonyl synthesis method, the raw material methanol is mainly synthesized from syngas. Enterprises usually set up methanol production units at the same time as acetic acid production units to ensure a continuous supply of raw material methanol.

[0004] Unpurified crude methanol often contains a lot of impurities. In order to improve the purity of methanol and meet the requirements of the acetic acid production process, it is usually necessary to perform distillation on the crude methanol to remove impurities.

[0005] Distillation is a common purification method that utilizes the difference in boiling points of different components to gradually separate impurity components and obtain purified products by repeatedly heating and cooling the liquid mixture.

[0006] Methanol distillation is a high-energy-consuming step in the methanol production process. To reduce energy consumption in methanol distillation, researchers have proposed various methods, including a three-tower double-effect process, a four-tower double-effect process, a four-tower triple-effect process, and a five-tower quadruple-effect process. Among these, the four-tower double-effect process is the most widely used. The four-tower double-effect process consists of four distillation columns: a methanol pre-distillation column, a pressurized methanol distillation column, an atmospheric methanol distillation column, and a methanol recovery column. The methanol pre-distillation column removes light components and operates at atmospheric pressure, with the bottom temperature generally controlled at around 70°C. The pressurized methanol distillation column has a bottom temperature of around 120°C, and the atmospheric methanol distillation column has a bottom temperature of around 100°C. The pressurized and atmospheric methanol distillation columns constitute a double-effect distillation process, meaning the top vapor phase of the pressurized methanol distillation column is methanol distillate. The reboiler in the atmospheric distillation column provides heat and condenses the liquid, part of which is collected as product, and part is returned to the top of the pressurized methanol distillation column as reflux. Methanol is collected from the top of the atmospheric distillation column, while wastewater containing small amounts of methanol and fusel oils from the bottom enters the recovery column. The atmospheric distillation column also often has a side stream in the stripping section to remove most of the fusel oils. The methanol distillation recovery column is essentially a stripping column, recovering alcohols from the wastewater to meet discharge standards. Energy consumption in methanol distillation units is generally evaluated using steam consumption per ton of methanol. Current processes typically consume 0.9-1.3 tons of steam per ton of methanol (of which the pressurized methanol distillation column and its reboiler account for approximately 90% of the total energy consumption of the distillation unit). Although multi-effect distillation reduces energy consumption to some extent, the energy consumption level of the distillation process remains high. Furthermore, multi-effect distillation systems are complex, difficult to operate, and have high production costs. Therefore, exploring new energy-saving pathways for methanol distillation systems remains crucial.

[0007] After the purified raw material methanol is prepared, it is transported together with other components to the acetic acid production unit for the synthesis of acetic acid. Due to the differences in the physicochemical properties of the materials, the process route design, the influence of side reactions, etc., the crude acetic acid product coming out of the acetic acid reactor inevitably contains unreacted raw materials, catalysts, by-products, water and other impurities. The crude acetic acid product also needs to undergo a series of separation processes to obtain purified acetic acid.

[0008] Distillation is also a major purification process for acetic acid. The acetic acid distillation process involves two energy-intensive distillation columns: the acetic acid distillation drying column (or "water separation column," depending on convention) and the acetic acid distillation product column (or "refining column," depending on convention). The acetic acid distillation drying column is mainly used to remove water and other impurities from the material, while the acetic acid distillation product column is mainly used to produce acetic acid products. The temperature of the overhead gas in the acetic acid distillation drying column is around 133℃, and the temperature of the overhead gas in the acetic acid distillation product column is around 135℃. Both columns have high overhead gas temperatures and large latent heat of condensation, comparable in quality to conventional low-pressure steam. However, currently, there is a lack of effective means to recover and utilize this heat. The heat from the overhead gas in both the acetic acid distillation drying column and the acetic acid distillation product column is mainly dissipated through circulating water cooling. This process not only wastes potential energy but also consumes a large amount of circulating water.

[0009] For coal chemical enterprises, it is of great significance to find ways to recover and utilize the heat from the top gas of the acetic acid distillation drying tower and the acetic acid distillation product tower in the acetic acid distillation process, reduce the consumption of circulating water, and reduce the energy consumption of the methanol distillation process.

[0010] However, in production practice, since acetic acid distillation units and methanol distillation units are usually from different suppliers, each supplier designs the acetic acid distillation unit and methanol distillation unit according to its own process characteristics, without considering the opportunity for energy interaction and integration between the two distillation units.

[0011] The inventors discovered that the temperature of the overhead gas in the acetic acid distillation drying tower and the acetic acid distillation product tower is between 133-135℃, and the latent heat of condensation of the overhead gas is very large. In contrast, methanol distillation consumes a lot of heat, and the temperature of the bottom of each tower is lower than the aforementioned overhead gas temperature. Taking a four-tower double-effect process as an example, the bottom temperature of the methanol distillation pre-tower is about 70℃, the bottom temperature of the methanol distillation pressurized tower is about 120℃, and the bottom temperature of the methanol distillation atmospheric tower is about 100℃. Furthermore, the material heating in the reboiler of the methanol distillation pressurized tower is also a vaporization process, mainly using latent heat, with a small temperature variation range. Therefore, there is a feasibility for energy interaction between the overhead gas (133-135℃) of the acetic acid distillation drying tower and the acetic acid distillation product tower and the reboiler of the methanol distillation pressurized tower (bottom temperature of the methanol distillation pressurized tower is about 120℃). Moreover, methanol distillation units and acetic acid distillation units often coexist in coal chemical enterprises, providing the possibility for energy interaction between the two. The goal of this invention is to achieve energy interaction and utilization between the methanol distillation process and the acetic acid distillation process, so as to fully recover and utilize the heat of the top gas of the acetic acid distillation drying tower and the acetic acid distillation product tower in the acetic acid distillation process, while reducing the consumption of circulating water and the energy consumption of the methanol distillation process, thereby achieving energy conservation and emission reduction. Summary of the Invention

[0012] The present invention aims to address the problems of high energy loss and high circulating water consumption in existing acetic acid distillation devices and high energy consumption in methanol distillation devices by providing an energy integration system for the acetic acid distillation and methanol distillation processes.

[0013] To achieve the above-mentioned objectives, according to one embodiment of the present invention, the technical solution provided is as follows:

[0014] An energy integration system for acetic acid distillation and methanol distillation processes includes an acetic acid distillation unit and a methanol distillation unit; the acetic acid distillation unit includes an acetic acid distillation drying tower and an acetic acid distillation product tower; the methanol distillation unit includes a methanol distillation pressurization tower; the methanol distillation pressurization tower is equipped with a first reboiler, which uses steam as a heat source.

[0015] The methanol distillation pressurized column is also equipped with a second reboiler and / or a third reboiler;

[0016] The second reboiler uses the overhead gas from the acetic acid distillation and drying column as a heat source. The methanol distillation and pressurization column is connected to the second reboiler via pipeline, and the second reboiler is connected to the acetic acid distillation and drying column via pipeline.

[0017] The third reboiler uses the overhead gas from the acetic acid distillation product column as its heat source. The methanol distillation pressurization column is connected to the third reboiler via pipeline, and the third reboiler is connected to the acetic acid distillation product column via pipeline.

[0018] Preferably, the methanol solution outlet side of the second reboiler is connected to the methanol solution inlet side of the third reboiler via a pipeline.

[0019] The second and third reboilers described in this invention are selected from high-efficiency heat exchangers commonly used in the art. Preferably, the second and third reboilers are fully welded plate type high-efficiency reboilers. More specifically, for example, the kettle-type reboiler disclosed in prior patent 201520479909.X can be used.

[0020] According to one embodiment of the present invention, a first valve is provided on the connecting pipeline between the methanol distillation pressurization column and the second reboiler, and the first valve controls the connection between the methanol distillation pressurization column and the second reboiler; a second valve is provided on the connecting pipeline between the methanol distillation pressurization column and the third reboiler, and the second valve controls the connection between the methanol distillation pressurization column and the third reboiler; a third valve is provided on the connecting pipeline between the methanol solution outlet side of the second reboiler and the methanol solution inlet side of the third reboiler, and the third valve controls the connection between the second reboiler and the third reboiler.

[0021] In the production process, one operating method is as follows:

[0022] A portion of the methanol solution discharged from the bottom of the methanol distillation pressurization column enters the first reboiler, where it exchanges heat with the steam entering the first reboiler and is partially converted into a gaseous phase. This gaseous phase is then returned to the methanol distillation pressurization column. Simultaneously, the first and third valves are opened, and the second valve is closed. A portion of the methanol solution discharged from the bottom of the methanol distillation pressurization column then enters the second and third reboilers sequentially via pipelines for reboiling operations. Specifically, a portion of the methanol solution discharged from the bottom of the methanol distillation pressurization column enters the second reboiler via pipelines, where it exchanges heat with the overhead gas entering the second reboiler from the top of the acetic acid distillation drying column and is partially converted into a gaseous phase. This gaseous phase is then returned to the methanol distillation pressurization column via pipelines. The unvaporized methanol solution enters the third reboiler via pipelines from the second reboiler, where it exchanges heat with the overhead gas entering the third reboiler from the top of the acetic acid distillation product column and is partially converted into a gaseous phase. This gaseous phase is then returned to the methanol distillation pressurization column via pipelines. The methanol solution that has not been converted into a gaseous phase is transported from the third reboiler to the methanol distillation pressurization column via pipelines.

[0023] In the above operation, the second reboiler uses the overhead gas from the acetic acid distillation drying column as a heat source, and the third reboiler uses the overhead gas from the acetic acid distillation product column as a heat source, so that the methanol solution flows continuously through the second and third reboilers in sequence, ensuring the vaporization effect of the liquid methanol.

[0024] Another operating method during the production process is as follows:

[0025] A portion of the methanol solution discharged from the bottom of the pressurized methanol distillation column enters the first reboiler, where it exchanges heat with the steam entering the first reboiler and is partially converted into a gaseous phase. This gaseous phase is then returned to the pressurized methanol distillation column. Simultaneously, by "opening the first valve, closing the second valve, and closing the third valve" or "opening the second valve, closing the first valve, and closing the third valve," a portion of the methanol solution discharged from the bottom of the pressurized methanol distillation column enters the second or third reboiler via pipeline for reboiling. Specifically, this reboiling process causes the methanol solution discharged from the methanol distillation column to undergo reboiling. A portion of the methanol solution discharged from the bottom of the pressurized distillation column enters the second or third reboiler via pipeline. In the second or third reboiler, it exchanges heat with the overhead gas entering the second reboiler from the acetic acid distillation drying column or the overhead gas entering the third reboiler from the acetic acid distillation product column, and is partially converted into a gaseous phase. The gaseous phase flowing out of the second or third reboiler is returned to the methanol distillation pressurized column via pipeline. The methanol solution that has not been converted into a gaseous phase is returned to the methanol distillation pressurized column via pipeline, respectively, from the second or third reboiler. Optionally, a fourth valve is installed in the methanol solution loop from the second reboiler to the methanol distillation pressurized column; and a fifth valve is installed in the methanol solution loop from the third reboiler to the methanol distillation pressurized column.

[0026] The above operation method controls the opening and closing of the second and / or third reboilers through the first, second, and third valves. In production practice, the opening and closing of the second and / or third reboilers can be flexibly adjusted according to the production load of methanol distillation and acetic acid distillation, or the steam volume required by the first reboiler. When the steam volume required by the first reboiler is large, it is advisable to simultaneously operate the second and third reboilers to fully utilize the overhead heat of the acetic acid distillation drying tower and the acetic acid distillation product tower as energy supplementation.

[0027] According to the technical solution provided by the present invention, the overhead gas from the acetic acid distillation drying tower entering the second reboiler is condensed and cooled in the second reboiler and then transported to the first reflux tank via pipeline; the overhead gas from the acetic acid distillation product tower entering the third reboiler is condensed and cooled in the third reboiler and then transported to the second reflux tank via pipeline.

[0028] Preferably, a first cooler is installed on the connecting pipeline between the second reboiler and the first reflux tank. The overhead gas from the acetic acid distillation drying column entering the second reboiler flows out of the second reboiler and is cooled again by the first cooler before being transported to the first reflux tank. Similarly, a second cooler is installed on the connecting pipeline between the third reboiler and the second reflux tank. The overhead gas from the acetic acid distillation product column entering the third reboiler flows out of the third reboiler and is cooled again by the second cooler before being transported to the second reflux tank. By installing the first and second coolers, sufficient cooling and temperature reduction are ensured after the overhead gas condenses.

[0029] According to the technical solution provided by the present invention, the gas phase flowing out from the second reboiler and / or the third reboiler is sent back to the methanol distillation pressurization tower via pipeline.

[0030] Preferably, the gas phase flowing out of the second and / or third reboiler is further heated by a superheater before being sent back to the methanol distillation pressurization tower via pipeline. The superheater is a heat exchanger commonly used in the field. By setting up the superheater, liquefaction of the gas phase can be prevented before it is sent to the methanol distillation pressurization tower, ensuring the vaporization effect, avoiding the problem of condensation and liquid accumulation, and ensuring smooth transportation.

[0031] The basic principle of this invention:

[0032] Considering that companies typically include methanol production units alongside acetic acid production lines to meet methanol supply demands, and that both acetic acid and methanol production units generally incorporate distillation systems, the overhead gas temperature in the drying and product columns of the acetic acid distillation system is between 133-135°C, with a significant latent heat of condensation. In contrast, the methanol distillation system consumes a large amount of heat, and the temperature of the reboiler in each column is lower than the aforementioned overhead gas temperature. Furthermore, the material heating in the reboiler is also a vaporization process, primarily utilizing latent heat, resulting in a smaller temperature variation range. Therefore, the temperature difference between the overhead gas (133-135°C) of the acetic acid drying and product columns and the reboiler (reboiler of the pressurized column) of the methanol distillation system is significant. At a temperature of around 120℃, there is potential for energy integration and interactive utilization. To recover and utilize the heat from the overhead gases of the drying and product columns in the acetic acid distillation system and effectively reduce the energy consumption of the methanol distillation system, this invention adds a second and / or a third reboiler to the methanol distillation pressurization column. The second reboiler uses the overhead gas from the acetic acid distillation drying column as a heat source, and the third reboiler uses the overhead gas from the acetic acid distillation product column as a heat source. This achieves interactive energy utilization between the methanol distillation process and the acetic acid distillation process, utilizing the heat from the overhead gases of the acetic acid distillation drying and product columns to reduce the steam consumption of the reboiler in the methanol distillation pressurization column and lower the energy consumption level of the methanol distillation system.

[0033] The beneficial effects of this invention are:

[0034] In order to fully recover and utilize the heat from the overhead gas of the drying tower and product tower in the acetic acid distillation system and effectively reduce the energy consumption of the methanol distillation system, this invention adds a second reboiler and / or a third reboiler to the methanol distillation pressurized tower. The second reboiler uses the overhead gas from the acetic acid distillation drying tower as a heat source, and the third reboiler uses the overhead gas from the acetic acid distillation product tower as a heat source. This realizes the energy interaction between the methanol distillation process and the acetic acid distillation process, utilizing the heat from the overhead gas of the acetic acid distillation drying tower and the acetic acid distillation product tower. With appropriate load configuration, the steam consumption of the first reboiler is very small during normal production, or even no steam is used. More steam is used only during start-up or load adjustment, reducing the steam consumption of the reboiler in the methanol distillation pressurized tower and reducing the energy consumption of the methanol distillation system.

[0035] Taking a 500,000-ton / year methanol production line as an example, the general energy consumption level in existing technologies is 0.9-1.3 tons of steam per ton of methanol. Based on this standard, when using steam as the heat source for the methanol distillation system, the annual steam requirement is 450,000-650,000 tons. If the energy integration technology of this invention is adopted, the annual steam requirement is 104,000-204,000 tons. The energy consumption of this invention is only 23%-31% of that of existing technologies. Furthermore, using the technical solution provided by this invention can save approximately 25 million tons of circulating cooling water annually, reduce water consumption by approximately 346,000 tons, save approximately 31,000 tons of standard coal, and reduce CO2 emissions by 79,000 tons.

[0036] Specifically, the technical effects of the technical concept of this invention are as follows:

[0037] 1. By adding a second and / or third reboiler to the methanol distillation pressurized column, the second reboiler uses the overhead gas from the acetic acid distillation drying column as a heat source, and the third reboiler uses the overhead gas from the acetic acid distillation product column as a heat source. This achieves energy interaction between the methanol distillation process and the acetic acid distillation process. By utilizing the heat from the overhead gas of the acetic acid distillation drying column and the acetic acid distillation product column, and with appropriate unit load configuration, the steam consumption of the first reboiler is very small during normal production, or even no steam is used. More steam is used only during start-up or load adjustment, which effectively reduces the steam consumption of the methanol distillation pressurized column reboiler and lowers the energy consumption level of the methanol distillation system. This not only saves energy but also reduces emissions.

[0038] 2. This invention fully recovers and utilizes the heat of the overhead gas from the acetic acid distillation drying tower and the acetic acid distillation product tower in the acetic acid distillation system, while also reducing the amount of cooling water used for the overhead gas circulation, thus reducing water and electricity consumption and lowering the company's operating costs.

[0039] 3. The present invention provides a first valve on the connecting pipeline between the methanol distillation pressurization tower and the second reboiler, a second valve on the connecting pipeline between the methanol distillation pressurization tower and the third reboiler, and a third valve on the connecting pipeline between the methanol solution outlet side of the second reboiler and the methanol solution inlet side of the third reboiler. The opening or closing of the second and / or third reboilers is controlled by the first, second, and third valves. The heat supply and supply-demand relationship of the top gas of the acetic acid distillation drying tower and the acetic acid distillation product tower can be adjusted according to the production load of methanol distillation and acetic acid distillation and the actual needs of the production line.

[0040] 4. By installing a first cooler on the connecting pipeline between the second reboiler and the first reflux tank, and a second cooler on the connecting pipeline between the third reboiler and the second reflux tank, sufficient cooling and temperature reduction of the overhead gas of the acetic acid distillation drying tower and the acetic acid distillation product tower are ensured.

[0041] 5. The gas phase flowing out from the second and / or third reboiler is further heated by the heater, which effectively prevents the gas phase from liquefying before being sent to the methanol distillation pressurization tower, ensuring the vaporization effect, avoiding the problem of condensation and liquid accumulation, and ensuring smooth transportation. Attached Figure Description

[0042] Figure 1 Example 1 of this invention shows a schematic diagram of an energy integration system for acetic acid distillation and methanol distillation processes.

[0043] Figure 2 Example 2 of this invention shows a schematic diagram of an energy integration system for acetic acid distillation and methanol distillation processes.

[0044] Figure 3 Example 3 of this invention shows a schematic diagram of an energy integration system for acetic acid distillation and methanol distillation processes.

[0045] Figure 4 Example 4 of this invention shows a schematic diagram of an energy integration system for acetic acid distillation and methanol distillation processes.

[0046] Explanation of reference numerals in the attached figures:

[0047] Methanol distillation pre-column 1, methanol distillation pressurized column 2, methanol distillation atmospheric column 3, methanol distillation recovery column 4;

[0048] Acetic acid distillation drying tower 5; acetic acid distillation product tower 6;

[0049] First reboiler 7, second reboiler 8, third reboiler 9;

[0050] First valve F1, second valve F2, third valve F3, fourth valve F4, fifth valve F5;

[0051] First reflux tank 10, second reflux tank 11;

[0052] First cooler 12, second cooler 13, superheater 14. Detailed Implementation

[0053] The present invention will now be further described with reference to the accompanying drawings, but the following embodiments do not constitute a limitation of the present invention.

[0054] Example 1

[0055] Figure 1 The diagram shows a schematic of the energy integration system structure for the acetic acid distillation and methanol distillation processes provided by the present invention.

[0056] The energy integration system is equipped with a methanol distillation unit and an acetic acid distillation unit, such as... Figure 1 As shown, the methanol distillation unit includes a methanol distillation pre-tower 1, a methanol distillation pressurized tower 2, a methanol distillation atmospheric tower 3, and a methanol distillation recovery tower 4.

[0057] The acetic acid distillation unit includes an acetic acid distillation drying tower 5 and an acetic acid distillation product tower 6;

[0058] The methanol distillation pressurized column 2 is equipped with a first reboiler 7, which uses steam as a heat source; the methanol distillation pre-column 1, the methanol distillation atmospheric column 3, and the methanol distillation recovery column 4 can also be equipped with reboilers as needed.

[0059] The methanol distillation pressurized column 2 is also equipped with a second reboiler 8 and / or a third reboiler 9; Figure 1 In addition, a second reboiler 8 and a third reboiler 9 are also provided.

[0060] The second reboiler 8 uses the overhead gas from the acetic acid distillation and drying tower 5 as a heat source. The methanol distillation and pressurization tower 2 is connected to the second reboiler 8 via a pipeline, and the second reboiler 8 is connected to the acetic acid distillation and drying tower 5 via a pipeline.

[0061] The third reboiler 9 uses the overhead gas from the acetic acid distillation product column 6 as a heat source. The methanol distillation pressurized column 2 is connected to the third reboiler 9 via pipeline, and the third reboiler 9 is connected to the acetic acid distillation product column 6 via pipeline.

[0062] The methanol solution outlet side of the second reboiler 8 is connected to the methanol solution inlet side of the third reboiler 9 via a pipeline.

[0063] A first valve F1 is installed on the connecting pipeline between the methanol distillation pressurization column 2 and the second reboiler 8, and the connection between the methanol distillation pressurization column 2 and the second reboiler 8 is controlled by the first valve F1; a second valve F2 is installed on the connecting pipeline between the methanol distillation pressurization column 2 and the third reboiler 9, and the connection between the methanol distillation pressurization column 2 and the third reboiler 9 is controlled by the second valve F2; a third valve F3 is installed on the connecting pipeline between the methanol solution outlet side of the second reboiler 8 and the methanol solution inlet side of the third reboiler 9, and the connection between the second reboiler 8 and the third reboiler 9 is controlled by the third valve F3.

[0064] In the production process, one operating method is:

[0065] A portion of the methanol solution discharged from the bottom of the methanol distillation pressurization column 2 enters the first reboiler 7, where it exchanges heat with the steam entering the first reboiler 7 and is partially converted into a gaseous phase. This gaseous phase is then returned to the methanol distillation pressurization column 2. Simultaneously, the first valve F1 and the third valve F3 are opened, while the second valve F2 is closed. A portion of the methanol solution discharged from the bottom of the methanol distillation pressurization column 2 enters the second reboiler 8 via pipeline, where it exchanges heat with the overhead gas entering the second reboiler 8 from the top of the acetic acid distillation drying column 5 and is partially converted into a gaseous phase. This gaseous phase is then returned to the methanol distillation pressurization column 2 via pipeline. The unvaporized methanol solution enters the third reboiler 9 via pipeline from the second reboiler 8, where it exchanges heat with the overhead gas entering the third reboiler 9 from the top of the acetic acid distillation product column 6 and is partially converted into a gaseous phase. This gaseous phase is then returned to the methanol distillation pressurization column 2 via pipeline. The unvaporized methanol solution is also returned to the methanol distillation pressurization column 2 via pipeline.

[0066] The gas phase flowing out from the second reboiler 8 and the third reboiler 9 is sent back to the methanol distillation pressurization tower 2 via pipeline, while the methanol solution that has not been converted into the gas phase is transported from the third reboiler 9 to the methanol distillation pressurization tower 2 via pipeline.

[0067] The overhead gas from the acetic acid distillation drying column 5 enters the second reboiler 8 and is condensed and cooled in the second reboiler 8 before being transported to the first reflux tank 10 via pipeline; the overhead gas from the acetic acid distillation product column 6 enters the third reboiler 9 and is condensed and cooled in the third reboiler 9 before being transported to the second reflux tank 11 via pipeline.

[0068] The above operation method utilizes the second reboiler 8 and the third reboiler 9. The second reboiler 8 uses the overhead gas from the acetic acid distillation drying column 5 as a heat source, and the third reboiler 9 uses the overhead gas from the acetic acid distillation product column 6 as a heat source, so that the methanol solution continuously flows through the second reboiler 8 and the third reboiler 9, ensuring the vaporization effect of the methanol liquid phase.

[0069] Another operating method in the production process is:

[0070] A portion of the methanol solution discharged from the bottom of the methanol distillation pressurization column 2 enters the first reboiler 7, where it exchanges heat with the steam entering the first reboiler 7 and is partially converted into a gas phase, which is then sent back to the methanol distillation pressurization column 2.

[0071] Simultaneously, by "opening the first valve F1, closing the second valve F2, and closing the third valve F3" or "opening the second valve F2, closing the first valve F1, and closing the third valve F3," a portion of the methanol solution delivered from the bottom of the methanol distillation pressurization tower 2 enters the second reboiler 8 or the third reboiler 9 via pipeline. In the second reboiler 8 or the third reboiler 9, the methanol solution undergoes heat exchange with the overhead gas entering the second reboiler 8 from the top of the acetic acid distillation drying tower 5 or the overhead gas entering the third reboiler 9 from the top of the acetic acid distillation product tower 6, and is partially converted into a gaseous phase. The gaseous phase flowing out of the second reboiler 8 or the third reboiler 9 is sent back to the methanol distillation pressurization tower 2 via pipeline. The methanol solution that has not been converted into a gaseous phase is sent back to the methanol distillation pressurization tower 2 via pipeline from the second reboiler 8 or the third reboiler 9, respectively. A fourth valve F4 is installed on the methanol solution loop from the second reboiler 8 to the methanol distillation pressurization tower 2; a fifth valve F5 is installed on the methanol solution loop from the third reboiler 9 to the methanol distillation pressurization tower 2.

[0072] The above operation method, by controlling the first valve F1, the second valve F2, and the third valve F3, allows for the control of the opening or closing of the second reboiler 8 and / or the third reboiler 9 according to the actual needs of the production line. The opening or closing of the second reboiler 8 and / or the third reboiler 9 can be flexibly adjusted based on the production load of methanol distillation and acetic acid distillation, or the steam required by the first reboiler 7. When the first reboiler 7 requires more steam to meet production demands, the second reboiler 8 and the third reboiler 9 can be opened simultaneously to fully utilize the overhead heat from the acetic acid distillation drying tower 5 and the acetic acid distillation product tower 6 as energy supplementation. With appropriate unit load configuration, the steam consumption of the first reboiler 7 is very small during normal production, or even non-existent, with larger steam requirements only during start-up or load adjustments.

[0073] Example 2

[0074] Figure 2 A schematic diagram of an energy integration system for another acetic acid and methanol distillation process provided by the present invention is shown. The difference between this system and Example 1 is as follows:

[0075] A first cooler 12 is installed on the connecting pipeline between the second reboiler 8 and the first reflux tank 10. The overhead gas from the acetic acid distillation drying column 5 enters the second reboiler 8, flows out of the second reboiler 8, and is cooled again by the first cooler 12 before being transported to the first reflux tank 10. A second cooler 13 is installed on the connecting pipeline between the third reboiler 9 and the second reflux tank 11. The overhead gas from the acetic acid distillation product column 6 enters the third reboiler 9, flows out of the third reboiler 9, and is cooled again by the second cooler 13 before being transported to the second reflux tank 11. By installing the first cooler 12 and the second cooler 13, it is ensured that the overhead gas is fully cooled after condensation.

[0076] Example 3

[0077] Figure 3 A schematic diagram of an energy integration system for another acetic acid and methanol distillation process provided by the present invention is shown. The difference between this system and Example 1 is as follows:

[0078] The vapor phase flowing out from the second reboiler 8 and / or the third reboiler 9 is further heated by the superheater 14 before being sent back to the methanol distillation pressurization tower 2 via pipeline. The superheater 14 adopts a common heat exchanger type in the field. By setting the superheater 14, liquefaction of the vapor phase can be prevented before it is sent to the methanol distillation pressurization tower 2, ensuring the vaporization effect, avoiding the problem of condensation and liquid accumulation, and ensuring smooth transportation.

[0079] Example 4

[0080] Figure 4 This diagram illustrates another energy integration system structure for the acetic acid and methanol distillation processes provided by the present invention. The difference between this system and Example 2 is as follows:

[0081] The vapor phase flowing out from the second reboiler 8 and / or the third reboiler 9 is further heated by the superheater 14 before being sent back to the methanol distillation pressurization tower 2 via pipeline. The superheater 14 adopts a common heat exchanger type in the field. By setting the superheater 14, liquefaction of the vapor phase can be prevented before it is sent to the methanol distillation pressurization tower 2, ensuring the vaporization effect, avoiding the problem of condensation and liquid accumulation, and ensuring smooth transportation.

[0082] The present invention has been described in detail above. Specific examples have been used in the specification to illustrate the principles and implementation methods of the present invention. However, the examples are only used to help understand the present invention and should not be construed as limiting the present invention.

Claims

1. An energy integration system for acetic acid distillation and methanol distillation processes, comprising an acetic acid distillation unit and a methanol distillation unit; the acetic acid distillation unit includes an acetic acid distillation drying tower and an acetic acid distillation product tower; the methanol distillation unit includes a methanol distillation pressurization tower, the methanol distillation pressurization tower being equipped with a first reboiler, the first reboiler using steam as a heat source; Its features are: The methanol distillation pressurized column is also equipped with a second reboiler and a third reboiler; The second reboiler uses the overhead gas from the acetic acid distillation and drying column as a heat source. The methanol distillation and pressurization column is connected to the second reboiler via pipeline, and the second reboiler is connected to the acetic acid distillation and drying column via pipeline. The third reboiler uses the overhead gas from the acetic acid distillation product column as a heat source. The methanol distillation pressurization column is connected to the third reboiler via pipeline, and the third reboiler is connected to the acetic acid distillation product column via pipeline. The opening or closing of the second and third reboilers is controlled according to the production load of methanol distillation and acetic acid distillation, or the amount of steam required by the first reboiler. The methanol solution outlet side of the second reboiler is connected to the methanol solution inlet side of the third reboiler via a pipeline; A first valve is installed on the connecting pipeline between the methanol distillation pressurization tower and the second reboiler; a second valve is installed on the connecting pipeline between the methanol distillation pressurization tower and the third reboiler; and a third valve is installed on the connecting pipeline between the second reboiler and the third reboiler.

2. The energy integration system as described in claim 1, characterized in that: During the production process, the first and third valves are opened and the second valve is closed. A portion of the methanol solution delivered from the methanol distillation pressurization tower enters the second and third reboilers sequentially through pipelines to perform reboiling operations.

3. The energy integration system as described in claim 1, characterized in that: During the production process, "open the first valve, close the second valve, close the third valve" or "open the second valve, close the first valve, close the third valve" means that part of the methanol solution delivered from the methanol distillation pressurization tower enters the second or third reboiler through pipelines to perform reboiling operation.

4. The energy integration system as described in claim 1, characterized in that: The vapor phase flowing out from the second and / or third reboiler is sent back to the methanol distillation pressurization tower via pipeline.

5. The energy integration system as described in claim 4, characterized in that: The vapor phase flowing out of the second and / or third reboiler is further heated by a heater before being sent back to the methanol distillation pressurization column.

6. The energy integration system as described in claim 1, characterized in that: The overhead gas from the acetic acid distillation drying column enters the second reboiler, is condensed and cooled in the second reboiler, and then transported to the first reflux tank via pipeline; the overhead gas from the acetic acid distillation product column enters the third reboiler, is condensed and cooled in the third reboiler, and then transported to the second reflux tank via pipeline.

7. The energy integration system as described in claim 6, characterized in that: A first cooler is installed on the connecting pipeline between the second reboiler and the first reflux tank; a second cooler is installed on the connecting pipeline between the third reboiler and the second reflux tank.

8. The energy integration system as described in claim 1, characterized in that: The methanol solution liquid phase flowing out from the second and / or third reboiler is returned to the methanol distillation pressurization tower via pipeline.

9. The energy integration system as described in claim 1, characterized in that: The second and third reboilers are fully welded plate-type high-efficiency reboilers.

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