Split-flow methanol multi-effect rectification system

Abstract

The disclosed methanol multi-effect rectification system of a split-flow method comprises a split-flow column, a light-removing column communicated with the top of the split-flow column through a pipeline, a medium-pressure column communicated with the bottom of the split-flow column through a pipeline, a medium-pressure column post-cooler and a medium-pressure column reflux tank communicated with the top of the medium-pressure column in turn through a pipeline after being communicated with the bottom of the split-flow column and the bottom of the light-removing column through a heat exchanger, a fine methanol pipeline communicated with the bottom end of the medium-pressure column reflux tank and the bottom end of the light-removing column, the fine methanol pipeline communicated with the medium-pressure column reflux tank communicated to the top of the medium-pressure column through a branch pipeline, and a recovery column communicated with one side of the medium-pressure column through a pipeline and communicated with the bottom of the light-removing column through a pipeline. The disclosed methanol multi-effect rectification system of a split-flow method solves the problem of high energy consumption of the existing methanol rectification device.

Description

Technical Field

[0001] This invention belongs to the field of methanol distillation technology, specifically relating to a multi-effect methanol distillation system using a split-flow method. Background Technology

[0002] The feedstock for the methanol distillation unit is crude methanol, which contains light components, water, and fusel oil, and the feed temperature is 30°C. Currently, the Lurgi process, a four-tower double-effect methanol distillation method, is commonly used in China to produce refined methanol. Its main feature is that the methanol distillation tower is divided into two towers: a pressurized tower (02) and an atmospheric tower (03). Increasing the operating pressure of the pressurized tower allows its overhead gas to heat the bottom of the atmospheric tower. Combined with a pre-distillation tower (01) to remove light components and a recovery tower (04) to recover methanol from wastewater, this forms a four-tower double-effect forward-pressure distillation process. Figure 1 As shown, the process flow is as follows:

[0003] 1) Crude methanol can be preheated to 116℃ via a series of heat exchangers, and then fed into the atmospheric distillation section of pre-distillation column 01 by a feed pump to remove light components. This column operates at atmospheric pressure. A portion of the liquid phase in the bottom of the column enters the reboiler of the pre-distillation column, and the low-pressure vapor is partially vaporized and returned to the bottom of the column. The bottom temperature is 75℃. The bottom material contains a large amount of methanol, a small amount of water, and trace amounts of fusel oil, and enters the lower part of the pressurized column 02. The vapor phase at the top of the pre-distillation column 01 is partially condensed by the top condenser and then completely refluxed. The top gas is then washed with water to recover methanol before returning to the top of the column. The top temperature is controlled at around 45℃ to facilitate condensation with circulating water.

[0004] 2) The operating pressure of pressurized column 02 is increased to 0.8 MPa, raising the top vapor temperature to approximately 128°C, which facilitates heating the material in the bottom of atmospheric column 03. The bottom temperature of this column reaches approximately 135°C, typically heated with 0.4 MPa steam. The top vapor enters the double-effect heat exchanger in the bottom of the atmospheric column to heat atmospheric column 03. After condensation, it enters the pressurized column reflux tank, with a portion returning to the top reflux and the other portion exiting the unit as refined methanol. The remaining methanol and water in the bottom of the column enter the lower part of atmospheric column 03 for further distillation.

[0005] 3) Atmospheric pressure column 03 operates at atmospheric pressure. The liquid phase in the column bottom enters the double-effect heat exchanger and is partially vaporized by the overhead gas from pressurized column 02 before returning to the column bottom. The column bottom temperature is generally around 116℃. Fusel oil collected from the stripping section enters the middle of recovery column 04, and the column bottom wastewater exits the unit. The overhead gas temperature is around 72℃. After condensation, it enters the reflux tank, with a portion sent back to the column top for reflux and the other portion exiting the unit as refined methanol product.

[0006] 4) Recovery tower 04 operates at atmospheric pressure. The liquid in the bottom of the tower enters the reboiler of the recovery tower and is partially vaporized by low-pressure steam, then returned to the bottom. The bottom temperature is generally around 105℃. The wastewater from the bottom of the tower is pumped out of the unit via the recovery tower bottom pump. The overhead gas of recovery tower 04 is around 69℃. After condensation, it enters the reflux tank of the recovery tower. Part of it is pumped back to the top of the tower for total reflux, and the other part is discharged from the unit as refined methanol product. Fusel oil is collected from the side stream of the stripping section of the recovery tower and discharged from the unit.

[0007] Currently, the steam consumption of most factories using similar processes is between 1.1 and 1.3 tons. The above process flow is simulated using the actual feed of a factory with an annual output of 400,000 tons of refined methanol. The calculated steam consumption per ton of refined methanol is 1.1 tons at 0.4 MPa. Although sufficient heat exchange is achieved, the energy consumption is still relatively high. Summary of the Invention

[0008] The purpose of this invention is to provide a multi-effect methanol distillation system using a split-flow method, which solves the problem of high energy consumption in existing methanol distillation devices.

[0009] The technical solution adopted in this invention is: a multi-effect methanol distillation system using a split-flow method, including a split-flow column. The top of the split-flow column is connected to a light-light product removal column via a pipeline. The bottom of the split-flow column is connected to a medium-pressure column via a pipeline. The top of the medium-pressure column is connected to a medium-pressure column aftercooler and a medium-pressure column reflux tank via pipelines to heat exchangers connected to the bottoms of the split-flow column and the light-light product removal column, respectively. The bottoms of the medium-pressure column reflux tank and the light-light product removal column are both connected to refined methanol pipelines. The refined methanol pipeline connected to the medium-pressure column reflux tank is connected to the top of the medium-pressure column via a branch pipeline. A recovery column is connected to one side of the medium-pressure column via a pipeline. The top of the recovery column is connected to the bottom of the light-light product removal column via a pipeline.

[0010] The invention is further characterized in that,

[0011] The top of the distribution tower is connected to the condenser of the distribution tower via a pipe, and then to the top of the reflux tank of the distribution tower. The top of the reflux tank of the distribution tower is then connected to the middle section of the light-duty removal tower via a pipe, and the bottom of the reflux tank of the distribution tower is connected to the top of the distribution tower via a pipe.

[0012] The top of the light-weight waste removal tower is connected to the condenser of the light-weight waste removal tower via a pipeline, and then to the top of the reflux tank of the light-weight waste removal tower. The bottom of the reflux tank of the light-weight waste removal tower is connected to the top of the light-weight waste removal tower via a pipeline. The top of the reflux tank of the light-weight waste removal tower is then connected to the aftercooler of the light-weight waste removal tower via a pipeline, and then to the bottom of the water washing tower. The bottom of the water washing tower is connected to the top of the reflux tank of the distribution tower via a pipeline. A water inlet pipeline is connected to one side of the water washing tower, and a non-condensable gas pipeline is connected to the top of the water washing tower.

[0013] The medium-pressure tower bottom is connected to the medium-pressure tower reboiler II via a pipeline. The inlet end of the medium-pressure tower reboiler II is also connected to the compressor via a pipeline and then to the top of the medium-pressure tower. The outlet end of the medium-pressure tower reboiler II is also connected to the light-light tower aftercooler, light-light tower condenser and diversion tower condenser via a pipeline and then to the middle section of the medium-pressure tower.

[0014] The top of the recovery tower is connected to the condenser of the recovery tower via a pipeline, and then to the top of the recovery tower reflux tank. The top of the recovery tower reflux tank is then connected to the bottom of the light-duty removal tower via a pipeline, and the bottom of the recovery tower reflux tank is connected to the top of the recovery tower via a pipeline.

[0015] The bottom of the medium-pressure tower is connected to the medium-pressure tower reboiler I via a pipeline. The inlet of the medium-pressure tower reboiler I is also connected to a steam pipeline. The outlet of the medium-pressure tower reboiler I is also connected to a vacuum flash tank via a pipeline. The top of the vacuum flash tank is connected to the bottom of the recovery tower via a secondary steam pipeline. The bottom of the recovery tower is connected to the recovery tower reboiler via a pipeline. The inlet of the recovery tower reboiler is also connected to the bottom of the vacuum flash tank via a pipeline. The outlet of the recovery tower reboiler is also connected to a steam condensate pipeline.

[0016] The bottom of the medium-pressure tower and the bottom of the recovery tower are connected to a wastewater pipeline, and the middle section of the recovery tower is connected to a fusel oil pipeline.

[0017] A pressurization tower is connected between the medium-pressure tower and the recovery tower. The bottom of the medium-pressure tower is connected to the middle section of the pressurization tower via a pipeline. The bottom of the medium-pressure tower is connected to a double-effect heat exchanger via a pipeline. The inlet of the double-effect heat exchanger is connected to the top of the pressurization tower via a pipeline. The outlet of the double-effect heat exchanger is connected to the condenser of the pressurization tower via a pipeline and then to the top of the reflux tank of the pressurization tower. The bottom of the reflux tank is connected to a refined methanol pipeline and then to the top of the pressurization tower via a branch pipeline. The middle section of the pressurization tower is connected to the middle section of the recovery tower via a pipeline.

[0018] The pressurized tower bottom is connected to the pressurized tower reboiler via a pipeline. The inlet of the pressurized tower reboiler is also connected to a steam pipeline. The outlet of the pressurized tower reboiler is also connected to a vacuum flash tank via a pipeline. The top of the vacuum flash tank is connected to the bottom of the recovery tower via a secondary steam pipeline. The recovery tower bottom is connected to the recovery tower reboiler via a pipeline. The inlet of the recovery tower reboiler is also connected to the bottom of the vacuum flash tank via a pipeline. The outlet of the recovery tower reboiler is also connected to a steam condensate pipeline.

[0019] The bottom of the pressurization tower and the bottom of the recovery tower are connected to a wastewater pipeline, and the middle section of the recovery tower is connected to a fusel oil pipeline.

[0020] The beneficial effects of this invention are:

[0021] 1) After the crude methanol is split in the splitter, the gas phase at the top of the splitter directly enters the light methanol removal tower, providing a heat source for the light methanol removal tower;

[0022] 2) In the feed to the light component removal tower, since most of the methanol is separated from the bottom of the diversion tower and almost all of the heavy components are carried away, the methanol obtained from the bottom of the light component removal tower is high-purity refined methanol. Moreover, the temperature of the bottom of the light component removal tower is relatively low, and it can be directly heated by the methanol vapor from the top of the medium-pressure tower. In addition, the light component removal tower removes less than half of the methanol in advance, which reduces the load on subsequent equipment and can also reduce the size of subsequent equipment.

[0023] 3) Instead of producing liquid methanol at the top of the recovery tower, the gaseous methanol is directly fed into the light-light product removal tower for heating, which can reduce the heat load of the light product removal tower. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an existing methanol distillation unit;

[0025] Figure 2 This is a schematic diagram of the structure of Example 1 of the methanol multi-effect distillation system using the split-flow method of the present invention;

[0026] Figure 3 This is a schematic diagram of the structure of Example 2 of the methanol multi-effect distillation system using the split-flow method of the present invention;

[0027] Figure 4a This is a partial structural schematic diagram of Example 3 of the methanol multi-effect distillation system using the split-flow method of the present invention;

[0028] Figure 4b (See diagram 3) is another part of the structural schematic diagram of the methanol multi-effect distillation system of the present invention.

[0029] In the diagram, 01 is the pre-distillation column, 02 is the pressurized column, 03 is the atmospheric column, and 04 is the recovery column.

[0030] 1. Diverter, 2. Lightweight gas stripping tower, 3. Medium-pressure tower, 4. Medium-pressure tower aftercooler, 5. Medium-pressure tower reflux tank, 6. Refined methanol pipeline, 7. Recovery tower, 8. Diverter condenser, 9. Diverter reflux tank, 10. Lightweight gas stripping tower condenser, 11. Lightweight gas stripping tower reflux tank, 12. Lightweight gas stripping tower aftercooler, 13. Water washing tower, 14. Inlet water pipeline, 15. Non-condensable gas pipeline, 16. Medium-pressure tower reboiler II, 17. Compressor, 18. Recovery tower condenser, 19. Recovery tower reflux tank, 20. Medium-pressure tower reboiler I, 21. Steam pipeline, 22. Vacuum flash tank, 23. Recovery tower reboiler, 24. Steam condensate pipeline, 2 5. Wastewater pipeline; 26. Fusel oil pipeline; 27. Pressurized tower; 28. Medium-pressure tower double-effect heat exchanger; 29. ​​Pressurized tower condenser; 30. Pressurized tower reflux tank; 31. Pressurized tower reboiler; 32. Diverter tower reflux pump; 33. Diverter tower bottom pump; 34. Diverter tower double-effect heat exchanger; 35. Light oil removal tower double-effect heat exchanger; 36. Medium-pressure tower reflux pump; 37. Light oil removal tower bottom pump; 38. Light oil removal tower reflux pump; 39. Recovery tower reflux pump; 40. Medium-pressure tower wastewater pump; 41. Recovery tower wastewater pump; 42. Medium-pressure tower bottom pump; 43. Pressurized tower reflux pump; 44. Recovery tower bottom pump; 45. Crude methanol feed pipeline. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0032] This invention provides a multi-effect methanol distillation system using a split-flow method, such as... Figure 2As shown, the system includes a splitter tower 1, with a crude methanol feed pipe 45 connected to the middle section of the splitter tower 1. The top of the splitter tower 1 is connected to the splitter tower condenser 8 via a pipe and then to the top of the splitter tower reflux tank 9. The top of the splitter tower reflux tank 9 is then connected to the middle section of the light methanol removal tower 2 via a pipe. The bottom of the splitter tower reflux tank 9 is connected to the splitter tower reflux pump 32 via a pipe and then to the top of the splitter tower 1. The bottom of the diversion tower 1 is connected to the diversion tower bottom pump 33 via a pipeline, and then to the medium-pressure tower 3. The top of the medium-pressure tower 3 is connected to the medium-pressure tower aftercooler 4 and the medium-pressure tower reflux tank 5 via pipelines through the diversion tower double-effect heat exchanger 34 and the light-light removal tower double-effect heat exchanger 35. The bottom of the medium-pressure tower reflux tank 5 and the light-light removal tower 2 are both connected to the refined methanol pipeline 6. The refined methanol pipeline 6 connected to the medium-pressure tower reflux tank 5 is equipped with the medium-pressure tower reflux pump 36 and is connected to the top of the medium-pressure tower 3 via a branch pipeline. The refined methanol pipeline 6 connected to the light-light removal tower 2 is equipped with the light-light removal tower bottom pump 37 to send the refined methanol out of the system. The top of the light-weight waste removal tower 2 is connected to the condenser 10 of the light-weight waste removal tower via a pipeline, and then to the top of the reflux tank 11 of the light-weight waste removal tower. The bottom of the reflux tank 11 is connected to the reflux pump 38 of the light-weight waste removal tower via a pipeline, and then to the top of the light-weight waste removal tower 2. The top of the reflux tank 11 is then connected to the aftercooler 12 of the light-weight waste removal tower via a pipeline, and then to the bottom of the water washing tower 13 via a pipeline. The bottom of the water washing tower 13 is connected to the top of the reflux tank 9 of the distribution tower via a pipeline. A water inlet pipeline 14 is connected to one side of the water washing tower 13, and a non-condensable gas pipeline 15 is connected to the top of the water washing tower 13. A recovery tower 7 is connected to one side of the medium-pressure tower 3 via a pipeline. The top of the recovery tower 7 is connected to the condenser 18 of the recovery tower via a pipeline, and then to the top of the reflux tank 19 of the recovery tower. The top of the reflux tank 19 is then connected to the bottom of the light-weight waste removal tower 2 via a pipeline. The bottom of the reflux tank 19 is connected to the reflux pump 39 of the recovery tower via a pipeline, and then to the top of the recovery tower 7. The bottom end of the medium-pressure tower 3 is connected to the wastewater pipe 25 via the medium-pressure tower wastewater pump 40 and the bottom end of the recovery tower 7 is connected to the recovery tower wastewater pump 41. The middle section of the recovery tower 7 is connected to the fusel oil pipe 26.

[0033] In the above manner, the methanol multi-effect distillation system of the present invention uses a split-flow distillation tower 1 to divert the methanol, with the vapor phase from the top of the tower directly entering the light component removal tower 2, providing a heat source (equivalent to an intermediate reboiler) for the light component removal tower 2. Since most of the methanol is diverted from the bottom of the split-flow distillation tower 1, and almost all the heavy components are carried away, the methanol obtained from the bottom of the light component removal tower 2 is high-purity refined methanol. Furthermore, its temperature is relatively low (72°C), allowing it to be directly heated by the 92.8°C methanol vapor from the top of the medium-pressure tower 3. Additionally, the light component removal tower 2 pre-diverts approximately 30% of the methanol, reducing the load on subsequent equipment and meaning that the size of subsequent equipment can be reduced, saving on equipment investment. The recovery tower 7 does not produce liquid methanol product at the top; instead, it directly feeds vaporized methanol into the light component removal tower 2 for heating, reducing the heat load on the light component removal tower by 7.5%.

[0034] As a further improvement of the present invention, the bottom of the medium-pressure tower 3 is connected to a medium-pressure tower reboiler I 20 via a pipeline. The inlet end of the medium-pressure tower reboiler I 20 is also connected to a steam pipeline 21, and the outlet end of the medium-pressure tower reboiler I 20 is also connected to a vacuum flash tank 22 via a pipeline. The top of the vacuum flash tank 22 is connected to the bottom of the recovery tower 7 via a secondary steam pipeline. The bottom of the recovery tower 7 is connected to a recovery tower reboiler 23 via a pipeline. The inlet end of the recovery tower reboiler 23 is also connected to the bottom end of the vacuum flash tank 22 via a pipeline, and the outlet end of the recovery tower reboiler 23 is also connected to a steam condensate pipeline 24. By performing multi-stage heat exchange on the heating steam condensate of the medium-pressure tower reboiler I 20 and then reducing the pressure and flashing, secondary steam is generated and directly enters the bottom of the recovery tower 7 for heating. The condensate then enters the recovery tower reboiler 23 as a heat source, which can fully meet the heating needs of the recovery tower 7.

[0035] like Figure 3 As shown, the methanol multi-effect distillation system of the present invention has the significant feature of reducing the system pressure through diversion, which provides favorable conditions for the application of heat pump process: the bottom of medium-pressure tower 3 is connected to medium-pressure tower reboiler II 16 through a pipeline, the inlet end of medium-pressure tower reboiler II 16 is also connected to compressor 17 through a pipeline and then connected to the top of medium-pressure tower 3, and the outlet end of medium-pressure tower reboiler II 16 is also connected to light tower aftercooler 12, light tower condenser 10 and diversion tower condenser 8 through a pipeline and then connected to the middle section of medium-pressure tower 3. A portion of the methanol vapor from the top of the medium-pressure column 3 is separated and compressed to about 145°C by compressor 17. It then enters the medium-pressure column reboiler II 16 to heat the wastewater at about 133°C in the bottom of the medium-pressure column 3. The vapor then enters the light-light-removal column aftercooler 12, light-light-removal column condenser 10, and diversion column condenser 8 for depressurization and vaporization. The latent heat of vaporization is used to provide cooling. The vaporized methanol cold vapor is then returned to the rectification section of the medium-pressure column 3 to complete a heat pump cycle. This not only further saves steam but also saves on the amount of circulating cold water at the top of the column.

[0036] like Figure 4a )and Figure 4bAs shown in the figure, the multi-effect methanol distillation system of the present invention can be used not only for the above four-tower double-effect distillation, but also for five-tower triple-effect, six-tower quadruple-effect, and seven-tower five-effect methanol distillation. Taking the five-tower triple-effect methanol distillation as an example: the connection method of the split tower 1 and the light-light removal tower 2 is the same as that of the above four-tower double-effect distillation. The difference is that a pressurization tower 27 is also connected between the medium-pressure tower 3 and the recovery tower 7. The bottom end of the medium-pressure tower 3 is connected to the medium-pressure tower bottom pump 42 through a pipeline and then connected to the middle section of the pressurization tower 27. The bottom of the medium-pressure tower 3 is connected to the medium-pressure tower double-effect heat exchanger 28 through a pipeline. The inlet end of the medium-pressure tower double-effect heat exchanger 28 is also connected to the medium-pressure tower bottom pump 42 through a pipeline. The pipeline connects to the top of the pressurization tower 27. The outlet of the double-effect heat exchanger 28 of the medium-pressure tower is also connected to the pressurization tower condenser 29 via a pipeline and then to the top of the pressurization tower reflux tank 30. The bottom of the pressurization tower reflux tank 30 is connected to the refined methanol pipeline 6. The refined methanol pipeline 6 is equipped with a pressurization tower reflux pump 43 and is connected to the top of the pressurization tower 27 via a branch pipeline. The middle section of the pressurization tower 27 is connected to the middle section of the recovery tower 7 via a pipeline. The bottom of the pressurization tower 27 and the bottom of the recovery tower 7 are connected to the wastewater pipeline 25. The wastewater pipeline 25 is equipped with the recovery tower bottom pump 44. The middle section of the recovery tower 7 is connected to the fusel oil pipeline 26. By adding a pressurized tower 27, the liquid in the bottom of the medium-pressure tower 3 can be further refined. The methanol vapor at the top of the pressurized tower 27 can also be used to heat the bottom of the medium-pressure tower 3 through the double-effect heat exchanger 28 of the medium-pressure tower, so that the material in the tower is kept in a gaseous state as much as possible. This allows the energy-saving effect of this thermal coupling to be maximized, and the steam consumption per ton of refined methanol produced can be directly reduced from 0.94 tons to 0.65 tons, a reduction of about 45%.

[0037] Similarly, heating steam can be added to the five-tower, three-effect methanol distillation process. The reboiler of pressurized tower 27 is connected to a pressurized tower reboiler 31 via a pipeline. The inlet of pressurized tower reboiler 31 is also connected to a steam pipeline 21, and the outlet of pressurized tower reboiler 31 is connected to a vacuum flash tank 22 via a pipeline. The top of vacuum flash tank 22 is connected to the reboiler of recovery tower 7 via a secondary steam pipeline. The reboiler of recovery tower 7 is connected to a recovery tower reboiler 23 via a pipeline. The inlet of recovery tower reboiler 23 is also connected to the bottom of vacuum flash tank 22 via a pipeline, and the outlet of recovery tower reboiler 23 is connected to a steam condensate pipeline 24. By using high-pressure steam in the pressurized tower reboiler 31 of pressurized tower 27, and then through depressurization flash evaporation, the secondary steam is directly supplied to the reboiler of recovery tower 7 for heating. The high-temperature steam condensate then enters the recovery tower reboiler 23 of recovery tower 7 for heating, fully utilizing the heat of the steam.

[0038] Example 1

[0039] The four-tower double-effect methanol distillation process using a split-flow method employs the same feed and product quality requirements as the background technology. The process flow and simulation calculation operating conditions are briefly described below.

[0040] 1) Crude methanol, after undergoing a series of heat exchangers to reach approximately 70°C, is pumped into the middle section of diverter 1 by a feed pump. This diverter operates at atmospheric pressure. The liquid phase at the bottom of the diverter enters the double-effect heat exchanger 34, where it is partially vaporized by the vapor phase at the top of the medium-pressure diverter 3 and returned to the bottom. The bottom temperature is 79.5°C. The bottom material mainly consists of methanol, a small amount of water, and trace amounts of fusel oil, which is pumped into the middle section of the medium-pressure diverter 3 by the diverter bottom pump 33. The vapor phase at the top of the diverter mainly consists of methanol and light components. After partial condensation by the diverter condenser 8, it enters the diverter reflux tank 9 and is pumped back to the top of diverter 1 by the diverter reflux pump 32. The light components in the vapor phase of the diverter reflux tank 9 are then pumped under pressure into the middle section of the light component removal diverter 2. The top temperature of this diverter is 71.6°C.

[0041] 2) Lightweight gas removal tower 2 operates at atmospheric pressure. The liquid phase at the bottom of the tower enters the double-effect heat exchanger 35 of the lightweight gas removal tower. After being partially vaporized by the gas phase at the top of the medium-pressure tower 3, it returns to the bottom of the tower. The bottom temperature is 72°C. The bottom material is high-purity methanol, which can be used to preheat the crude methanol before being sent out of the system via the bottom pump 37 of the lightweight gas removal tower. The gas phase at the top of the tower is 68°C. After being partially condensed in the condenser 10 of the lightweight gas removal tower, it enters the reflux tank 11 of the lightweight gas removal tower. The liquid phase is pumped back to the top of the lightweight gas removal tower 2 for total reflux via the reflux pump 38 of the lightweight gas removal tower. The temperature of the reflux tank 11 of the lightweight gas removal tower is 45°C. The non-condensable gas contains a lot of methanol. After being further condensed and cooled by the aftercooler 12 of the lightweight gas removal tower, it enters the water washing tower 13 to remove methanol by water. The non-condensable gas exits the system through the non-condensable gas pipeline 15. The washing water enters the reflux tank 9 of the diversion tower.

[0042] 3) The operating pressure of medium-pressure tower 3 is 0.3 MPa, and the tower bottom temperature is 133℃. The liquid phase from the tower bottom enters the medium-pressure tower reboiler I 20, where it is partially vaporized by steam and returned to the tower bottom. The tower bottom wastewater is pumped out of the system via the medium-pressure tower wastewater pump 40, or it can be used to preheat the crude methanol before exiting the system. The medium-pressure tower reboiler I 20 is heated by 0.4 MPa steam. The steam condensate is depressurized to 0.2 MPa and enters the vacuum flash tank 22. The secondary steam directly enters the bottom of the recovery tower 7 for heating. The condensate, at 143℃, heats the recovery tower reboiler 23. Additionally, a low-pressure steam stream can be set up for backup in the vacuum flash tank 22. The vapor phase at the top of the intermediate-pressure tower 3 is 92.8℃. Part of it enters the double-effect heat exchanger 34 of the diversion tower and is condensed by the liquid phase at the bottom of diversion tower 1. The other part enters the double-effect heat exchanger 35 of the light-light-removal tower and is condensed by the liquid phase at the bottom of light-light-removal tower 2. These two condensates mix and then enter the intermediate-pressure tower aftercooler 4 for complete condensation before entering the intermediate-pressure tower reflux tank 5. The liquid phase in the intermediate-pressure tower reflux tank 5 is partially returned to the top of intermediate-pressure tower 3 via the intermediate-pressure tower reflux pump 36, and the other part exits the system through the refined methanol pipeline 6. Fusel oil is drawn from the side stream of intermediate-pressure tower 3 and enters the recovery tower 7.

[0043] 4) Recovery tower 7 operates at atmospheric pressure with a bottom temperature of 105℃. Part of the liquid from the bottom enters the reboiler 23 of the recovery tower. The condensate at 143℃ in the vacuum flash tank 22 heats the reboiler 23, causing partial vaporization of the liquid from the bottom of recovery tower 7, which then returns to the bottom. The secondary steam at 143℃ in the vacuum flash tank 22 directly heats the bottom of recovery tower 7. The overhead gas from recovery tower 7 enters the condenser 18 of the recovery tower, where it is partially condensed and then enters the reflux tank 19. The condensate is pumped back to the top of the tower by the reflux pump 39 for total reflux, while the vapor phase enters the bottom of the light alcohol removal tower 2 to provide partial heat, saving approximately 7.5% of the tower's energy consumption. A side stream from the middle section of recovery tower 7 produces fusel oil, and a small amount of wastewater at 105℃ from the bottom is cooled to 40℃ and then pumped out of the system by the wastewater pump 41.

[0044] This embodiment also uses the actual feed of a certain plant with an annual output of 400,000 tons of refined methanol for process simulation calculation. The calculated steam consumption per ton of refined methanol product is 0.94 tons at 0.4 MPa, which saves 15% of steam compared to the currently well-operated Lurgi process.

[0045] Example 2

[0046] Split-flow four-tower double-effect methanol distillation process (including heat pump process)

[0047] The process flow of Example 2 is largely the same as that of Example 1. The difference is that in Example 2, a portion of the methanol vapor from the top of the medium-pressure tower 3 is separated and compressed to about 145°C by compressor 17. It then enters the reboiler II 16 of the medium-pressure tower to heat the wastewater at about 133°C in the bottom of the medium-pressure tower 3. The vapor then enters the aftercooler 12 of the light-light-removal tower, the condenser 10 of the light-light-removal tower, and the condenser 8 of the diversion tower for depressurization and vaporization. The latent heat of vaporization is used to provide cooling. The vaporized methanol cold vapor is then returned to the rectification section of the medium-pressure tower 3 to complete a heat pump cycle. This not only further saves steam but also saves the amount of circulating cold water at the top of the tower.

[0048] Example 3

[0049] The five-tower, triple-effect methanol distillation process using a split-flow method employs the same feedstock and product quality requirements as the background technology. The process flow and simulated operating conditions are briefly described below.

[0050] 1) Diverter 1 operates at atmospheric pressure, with top and bottom temperatures of 71.6℃ and 79.2℃, respectively. Crude methanol is heated to 93.6℃ through a series of heat exchangers and then pumped into the middle section of diverter 1. The liquid phase at the bottom of the diverter enters the double-effect heat exchanger 34, is partially vaporized by the gas phase at the top of the medium-pressure diverter 3, and returns to the bottom. The bottom material consists of residual methanol, a small amount of water, and trace amounts of fusel oil, which is pumped into the middle section of the medium-pressure diverter 3 by the diverter bottom pump 33. The gas at the top of the diverter consists of methanol and light components. After being partially condensed by the diverter condenser 8, it enters the diverter reflux tank 9 and is pumped back to the top of diverter 1 for total reflux by the diverter reflux pump 32. The gas phase in the diverter reflux tank 9 then enters the middle section of the light component removal diverter 2 under its own pressure.

[0051] 2) Light Methanol Removal Tower 2 operates at atmospheric pressure, with top and bottom temperatures of 68℃ and 72℃, respectively. The liquid phase from the bottom enters the double-effect heat exchanger 35 of the light methanol removal tower, is partially vaporized by the top gas from the medium-pressure tower 3, and then returns to the bottom. The vapor phase in the reflux tank 11 of the light methanol removal tower, at 45℃, is further condensed and cooled to 40℃ by the aftercooler 12 before entering the water washing tower 13 to remove methanol. The non-condensable gas exits the system, and the washing water enters the reflux tank 9 of the diversion tower. The bottom of the light methanol removal tower 2 contains high-purity refined methanol, which is sent out of the system via the bottom pump 37. The vapor phase from the top of the tower enters the condenser 10 of the light methanol removal tower, is partially condensed, and then enters the reflux tank 11. The liquid phase is pumped back to the top of the tower for total reflux via the reflux pump 38.

[0052] 3) The operating pressure of medium-pressure tower 3 is 0.33 MPa, and the temperatures at the top and bottom of the tower are 96℃ and 103℃, respectively. The liquid phase at the bottom of the tower enters the double-effect heat exchanger 28 of the medium-pressure tower, is partially vaporized by the gas phase at the top of the pressurized tower 27, and then returns to the bottom of the tower. The material at the bottom of the tower is sent to the middle section of the pressurized tower 27 by the medium-pressure tower bottom pump 42. Part of the 96℃ top gas enters the double-effect heat exchanger 34 of the diversion tower and is condensed by the liquid at the bottom of the diversion tower 1. The other part enters the double-effect heat exchanger 35 of the light-light removal tower and is condensed by the liquid at the bottom of the light-light removal tower 2. The two condensates are mixed and then enter the aftercooler 4 of the medium-pressure tower for full condensation before entering the reflux tank 5 of the medium-pressure tower. Part of the liquid phase in the reflux tank 5 is sent back to the top of the medium-pressure tower 3 as reflux by the reflux pump 36 of the medium-pressure tower, and the other part can be used to preheat the crude methanol before exiting the system.

[0053] 4) The operating pressure of pressurized tower 27 is 0.72 MPa, and the temperatures at the top and bottom of the tower are 123℃ and 166℃, respectively. The liquid in the bottom of the tower enters the reboiler 31 of the pressurized tower, where it is partially vaporized by 1.0 MPa steam and returned to the bottom of the tower. The steam condensate enters the vacuum flash tank 22 after heat exchange to reduce the pressure and flash to 184℃. The material in the bottom of pressurized tower 27 can be used to preheat crude methanol before being sent out of the system by the bottom pump 44 of the recovery tower. The fusel oil collected from the middle section of pressurized tower 27 enters the middle section of recovery tower 7. The top gas of pressurized tower 27, at 123°C, enters the double-effect heat exchanger 28 of the medium-pressure tower. After being condensed by the bottom liquid of the medium-pressure tower 3, it enters the condenser 29 of the pressurized tower, where it is condensed to 103°C. This condensed gas can then be used to preheat the crude methanol. When the temperature drops to 80°C, the crude methanol enters the reflux tank 30 of the pressurized tower. Part of the liquid phase in the reflux tank 30 is sent back to the top of pressurized tower 27 as reflux via the pressurized tower reflux pump 43, while the other part is sent out of the system as refined methanol through the refined methanol outlet pipeline 6.

[0054] 5) Recovery tower 7 operates at atmospheric pressure, with top and bottom temperatures of 69℃ and 105℃, respectively. The bottom liquid is wastewater, a portion of which enters the recovery tower reboiler 23. The 184℃ liquid phase in the vacuum flash tank 22 is first preheated to the feed to the pressurized tower 27, then cooled to 148℃ to heat the recovery tower reboiler 23, causing partial vaporization of the bottom liquid in recovery tower 7, which is then returned to the bottom. The bottom wastewater is pumped out of the system via recovery tower bottom pump 44. The secondary steam in the vacuum flash tank 22 directly enters the bottom of recovery tower 7 for heating. The top gas from recovery tower 7 enters the recovery tower condenser 18, where it is partially condensed and then enters the recovery tower reflux tank 19. It is then pumped back to the top of recovery tower 7 by the recovery tower reflux pump 39 for total reflux. The 69℃ vaporized methanol enters the bottom of the light alcohol removal tower 2 for heating. Fusel oil from the middle section of recovery tower 7 is collected and exits the system via fusel oil pipeline 26.

[0055] This embodiment also uses the actual feed of a certain plant with an annual output of 400,000 tons of refined methanol for process simulation calculation. The calculated steam consumption per ton of refined methanol product is 0.65 tons at 0.4 MPa, which saves 41% of steam compared to the currently well-operating Lurgi process.

Claims

1. A multi-effect methanol distillation system using a split-flow method, characterized in that, The system includes a distribution tower (1), the top of which is connected to a light-light removal tower (2) via a pipe. The top of the distribution tower (1) is connected to the distribution tower condenser (8) via a pipe, and then to the top of the distribution tower return tank (9). The top of the distribution tower return tank (9) is connected to the middle section of the light-light removal tower (2) via a pipe. The bottom of the distribution tower return tank (9) is connected to the top of the distribution tower (1) via a pipe. The top of the light-light removal tower (2) is connected to the light-light removal tower condenser (1) via a pipe. 0) is then connected to the top of the light-light tower reflux tank (11). The bottom of the light-light tower reflux tank (11) is connected to the top of the light-light tower (2) through a pipe. The top of the light-light tower reflux tank (11) is then connected to the light-light tower aftercooler (12) through a pipe, and then connected to the bottom of the water washing tower (13). The bottom of the water washing tower (13) is connected to the top of the diversion tower reflux tank (9) through a pipe. One side of the water washing tower (13) is connected to the inlet pipe (14). The water washing tower (13) The top of the tower is connected to a non-condensable gas pipeline (15). The bottom of the diversion tower (1) is connected to a medium-pressure tower (3) via a pipeline. The top of the medium-pressure tower (3) is connected to a medium-pressure tower aftercooler (4) and a medium-pressure tower reflux tank (5) via pipelines to the bottom of the diversion tower (1) and the light-light removal tower (2). The bottom of the medium-pressure tower reflux tank (5) and the light-light removal tower (2) are both connected to a refined methanol pipeline (6). The pipeline is connected to the medium-pressure tower reflux tank (5). The methanol pipeline (6) is connected to the top of the medium-pressure tower (3) via a branch pipeline. One side of the medium-pressure tower (3) is connected to the recovery tower (7) via a pipeline. The top of the recovery tower (7) is connected to the condenser (18) of the recovery tower via a pipeline and then to the top of the reflux tank (19) of the recovery tower. The top of the reflux tank (19) of the recovery tower is connected to the bottom of the light removal tower (2) via a pipeline. The bottom of the reflux tank (19) of the recovery tower is connected to the top of the recovery tower (7) via a pipeline.

2. The methanol multi-effect distillation system using the split-flow method as described in claim 1, characterized in that, The bottom of the medium-pressure tower (3) is connected to the medium-pressure tower reboiler II (16) via a pipeline. The inlet end of the medium-pressure tower reboiler II (16) is also connected to the compressor (17) via a pipeline and then to the top of the medium-pressure tower (3). The outlet end of the medium-pressure tower reboiler II (16) is also connected to the light-removal tower aftercooler (12), light-removal tower condenser (10) and diversion tower condenser (8) via a pipeline and then to the middle section of the medium-pressure tower (3).

3. The methanol multi-effect distillation system using the split-flow method as described in claim 1, characterized in that, The bottom of the medium-pressure tower (3) is connected to the medium-pressure tower reboiler I (20) via a pipeline. The inlet end of the medium-pressure tower reboiler I (20) is also connected to a steam pipeline (21). The outlet end of the medium-pressure tower reboiler I (20) is also connected to a vacuum flash tank (22) via a pipeline. The top of the vacuum flash tank (22) is connected to the bottom of the recovery tower (7) via a secondary steam pipeline. The bottom of the recovery tower (7) is connected to the recovery tower reboiler (23) via a pipeline. The inlet end of the recovery tower reboiler (23) is also connected to the bottom end of the vacuum flash tank (22) via a pipeline. The outlet end of the recovery tower reboiler (23) is also connected to a steam condensate pipeline (24).

4. The methanol multi-effect distillation system using the split-flow method as described in claim 1, characterized in that, The bottom end of the medium-pressure tower (3) and the bottom end of the recovery tower (7) are connected to a wastewater pipe (25), and the middle section of the recovery tower (7) is connected to a fusel oil pipe (26).

5. The methanol multi-effect distillation system using the split-flow method as described in claim 1 or 2, characterized in that, A pressurization tower (27) is also connected between the medium-pressure tower (3) and the recovery tower (7). The bottom of the medium-pressure tower (3) is connected to the middle section of the pressurization tower (27) through a pipeline. The bottom of the medium-pressure tower (3) is connected to the medium-pressure tower double-effect heat exchanger (28) through a pipeline. The inlet end of the medium-pressure tower double-effect heat exchanger (28) is also connected to the top of the pressurization tower (27) through a pipeline. The outlet end of the medium-pressure tower double-effect heat exchanger (28) is also connected to the pressurization tower condenser (29) through a pipeline and then connected to the top of the pressurization tower reflux tank (30). The bottom end of the pressurization tower reflux tank (30) is connected to the refined methanol pipeline (6) and connected to the top of the pressurization tower (27) through a branch pipeline. The middle section of the pressurization tower (27) is connected to the middle section of the recovery tower (7) through a pipeline.

6. The methanol multi-effect distillation system using the split-flow method as described in claim 5, characterized in that, The pressurized tower (27) is connected to the reboiler (31) via a pipeline. The inlet of the pressurized tower reboiler (31) is also connected to a steam pipeline (21). The outlet of the pressurized tower reboiler (31) is also connected to a vacuum flash tank (22) via a pipeline. The top of the vacuum flash tank (22) is connected to the bottom of the recovery tower (7) via a secondary steam pipeline. The bottom of the recovery tower (7) is connected to the reboiler (23) via a pipeline. The inlet of the recovery tower reboiler (23) is also connected to the bottom of the vacuum flash tank (22) via a pipeline. The outlet of the recovery tower reboiler (23) is also connected to a steam condensate pipeline (24).

7. The methanol multi-effect distillation system using the split-flow method as described in claim 5, characterized in that, The bottom end of the pressurization tower (27) and the bottom end of the recovery tower (7) are connected to a wastewater pipe (25), and the middle section of the recovery tower (7) is connected to a fusel oil pipe (26).

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