Waste heat deep utilization type crude methanol three-tower multi-effect rectification device and rectification process thereof

Abstract

The invention provides a waste heat deep utilization type crude methanol three-tower multi-effect rectification device and a rectification process thereof.The device comprises a pre-rectification tower, a negative pressure rectification tower and a pressurization rectification tower, the top of the pre-rectification tower is connected with a second negative pressure tower reboiler through a pre-tower top pipeline, and the top of the negative pressure rectification tower is connected with a negative pressure tower refined methanol extraction device; the negative pressure tower adopts a multi-reboiler mode, external low-temperature waste heat is preferentially introduced except tower top heat of an internal pre-rectifying tower, the top of the pressurized rectifying tower is connected with a pre-tower reboiler II through a pressurized tower top pipeline, and the output end of the pre-tower reboiler II is connected with a pressurized tower refined methanol extraction device; on the basis of an original pre-rectifying tower, a pressurizing tower and an atmospheric tower, the operation pressure and thermal coupling sequence of the rectifying towers is changed, a three-tower series thermal coupling process is adopted, heat outside the device is introduced, a new heat exchange network is formed, the energy-saving space is increased, and the steam unit consumption can be reduced to 0.22-0.26 t steam / t refined alcohol.

Description

Technical Field

[0001] This application relates to the field of methanol distillation technology, specifically to a waste heat deep utilization type crude methanol three-tower multi-effect distillation device and its distillation process. Background Technology

[0002] Methanol is an important chemical raw material widely used in chemical, energy, and fuel cell industries. In methanol production, distillation is a crucial separation operation used to purify the methanol product. Existing methanol distillation units typically employ a three-tower system: a pre-distillation tower, a pressurized tower, and an atmospheric distillation tower. The pressurized tower's overhead steam is used to heat the atmospheric distillation tower, achieving energy savings. However, the use of circulating water for cooling the tops of the atmospheric and pre-distillation towers leads to significant heat waste, resulting in high steam consumption for the entire system, approximately 1.2 t of steam per t of refined methanol. Given the increasingly stringent national carbon emission standards, a new technology is needed to recover heat from the existing system to achieve energy conservation and emission reduction goals.

[0003] In-depth analysis reveals that a significant portion of the low-temperature waste heat within the methanol plant, ranging from 80℃ to 150℃, is not being utilized in a cascade manner, directly leading to high overall energy consumption. For instance, the high temperature of the syngas at the synthesis tower outlet often results in this heat being released into the atmosphere through air cooling, water cooling, or evaporative cooling, without being fully utilized. However, integrating the reaction heat into the distillation system would yield greater energy-saving and carbon-reduction benefits. Although the industry and our team have developed a series of energy-saving technologies, these typically involve configurations of four, five, or six towers, resulting in a large number of towers and a large footprint. Furthermore, in processes employing heat pumps, the large number of heat pumps can lead to safety and fire protection limitations, failing to meet the requirements of new construction or technical upgrades. There remains room for improvement in specific application scenarios.

[0004] This application proposes to use a low-temperature waste heat cascade utilization technology. For heat sources that can be directly utilized, negative pressure distillation is introduced. For the gas phase with low grade but large latent heat, the pressure and temperature of the heat medium are gradually increased to convert the low-grade waste heat into high-grade heat energy, which is then added to the negative pressure tower heat coupling reboiler to achieve its efficient recovery. After a detailed search, no relevant existing technologies were found.

[0005] Therefore, a new technical solution is needed to solve the above-mentioned technical problems. Summary of the Invention

[0006] This application provides a waste heat deep utilization type crude methanol three-tower multi-effect distillation device, including a pre-distillation tower, a negative pressure distillation tower, and a pressurized distillation tower connected in sequence. A feed pipeline is connected to one side of the pre-distillation tower. A pre-tower reboiler I and a pre-tower reboiler II are provided at the bottom of the pre-distillation tower. A negative pressure reboiler I and a negative pressure reboiler II are provided at the bottom of the negative pressure distillation tower. A pressurized reboiler is provided at the bottom of the pressurized distillation tower. The top of the pre-distillation tower is connected to the negative pressure reboiler II through a pre-tower top pipeline. A negative pressure distillation tower refined methanol collection device is connected to the top of the negative pressure distillation tower. The top of the pressurized distillation tower is connected to the pre-tower reboiler II through a pressurized tower top pipeline. The output end of the pre-tower reboiler II is connected to the pressurized tower refined methanol collection device.

[0007] As a preferred embodiment, the input end of the first negative pressure tower reboiler is connected to an external waste heat pipeline, and the output end of the first negative pressure tower reboiler is connected to a circulation pipeline; the external waste heat pipeline is used to connect to the heat source for the vaporization of methanol working fluid, and the methanol working fluid is vaporized by low-temperature waste heat.

[0008] As a preferred embodiment, the external waste heat pipeline is connected to one input end of the reboiler, the other input end of the reboiler is connected to the methanol material input pipeline, one output end of the reboiler is connected to one input end of the negative pressure tower reboiler, and the other output end of the reboiler is connected to the reboiler output pipeline.

[0009] As a preferred embodiment, the circulation pipeline is connected to the methanol feed line.

[0010] As a preferred option, the low-temperature waste heat includes at least one of conversion gas, shift gas, and syngas.

[0011] As a preferred embodiment, the top of the pressurized distillation column is also connected to the reboiler of the negative pressure column via a pressurized column top pipeline, and the reboiler of the negative pressure column is connected to the feed pipeline of the pressurized column reflux tank via a reboiler of the negative pressure column output pipeline.

[0012] As a preferred embodiment, the top pressure of the pre-distillation column is 90 kPa-180 kPa (A), the top pressure of the negative pressure distillation column is 35 kPa-70 kPa (A), and the top pressure of the pressurized distillation column is 170 kPa-480 kPa (A).

[0013] As a preferred embodiment, the output end of the second negative pressure tower reboiler is connected to the pre-tower condenser via the feed pipeline of the extraction tank.

[0014] As a preferred embodiment, the pre-column condenser includes an extraction tank connected to the feed pipeline of the extraction tank. The feed pipeline of the extraction tank is equipped with a first-stage condenser and a second-stage condenser of the pre-column. A non-condensable gas collection pipeline is provided at the top of the extraction tank. An extraction water inlet pipeline is provided on one side of the extraction tank. The bottom of the extraction tank is connected to the pre-column reflux tank through a column bottom pipeline. The bottom of the pre-column reflux tank is connected to the upper middle part of the pre-distillation column through a pre-column reflux pipeline.

[0015] As a preferred embodiment, a pre-tower reflux pump is installed on the pre-tower reflux pipeline.

[0016] As a preferred embodiment, the negative pressure tower refined methanol extraction device includes a negative pressure tower reflux tank. The negative pressure tower reflux tank is connected to the top of the negative pressure distillation tower via a negative pressure tower top pipeline. A negative pressure tower condenser is installed on the negative pressure tower top pipeline. The top of the negative pressure tower reflux tank is connected to a gas-liquid separator via a reflux tank top pipeline. A reflux tank top condenser is installed on the reflux tank top pipeline. A gas phase extraction pipeline is installed at the top of the gas-liquid separator. The bottom of the gas-liquid separator is connected to the negative pressure tower reflux tank via a gas-liquid separator bottom pipeline. A negative pressure tower refined methanol extraction pipeline is connected to the bottom of the negative pressure tower reflux tank. A negative pressure tower extraction pump and a negative pressure tower methanol cooler are installed on the negative pressure tower refined methanol extraction pipeline. A negative pressure tower reflux pipeline is also connected to the negative pressure tower refined methanol extraction pipeline.

[0017] As a preferred embodiment, the methanol extraction pipeline from the negative pressure tower is connected to the methanol tank.

[0018] As a preferred embodiment, the pressurized tower refined methanol extraction device includes a pressurized tower reflux tank, the bottom of which is connected to a pressurized tower refined methanol extraction pipeline, which is connected to the pressurized tower reflux pipeline.

[0019] As a preferred embodiment, the pressurized tower's outflow pipeline is connected to the refined methanol tank.

[0020] As a preferred embodiment, the input ends of the pre-tower reboiler and the pressurized tower reboiler are respectively connected to the steam pipeline, and the output ends of the pre-tower reboiler and the pressurized tower reboiler are respectively connected to the steam condensate pipeline.

[0021] As a preferred embodiment, a feed preheater is provided on the feed pipeline, and the steam condensate pipeline passes through the feed preheater.

[0022] As a preferred embodiment, the bottom of the negative pressure distillation column is connected to the pressurized distillation column via a pressurized column feed line, and a pressurized column preheater is installed on the pressurized column feed line.

[0023] As a preferred embodiment, the reboiler of the pressurized distillation column is equipped with a wastewater discharge pipeline, which passes through the pressurized column preheater. A wastewater discharge pump is installed on the wastewater discharge pipeline in front of the pressurized column preheater, and a wastewater cooler is installed on the wastewater discharge pipeline behind the pressurized column preheater.

[0024] This application provides a waste heat-intensive three-tower multi-effect distillation process for crude methanol, as follows: Crude methanol enters the pre-distillation column for distillation. The vapor phase collected from the top of the pre-distillation column goes to the second reboiler in the negative pressure column to provide the heat required for distillation in the negative pressure distillation column. The pre-distillation column is provided with the heat required for distillation through indirect heating by the first and second reboilers. The heat source for the first reboiler is steam, and the heat source for the second reboiler is the vapor phase at the top of the pressurized distillation column. The liquid phase collected from the bottom of the pre-distillation column enters the negative pressure distillation column for distillation, and refined methanol is collected from the top of the negative pressure distillation column. The negative pressure distillation column is provided with the heat required for distillation by indirect heating through negative pressure reboiler one and negative pressure reboiler two. The heat source of negative pressure reboiler one is external low-temperature waste heat or heat from the top of the pressurized distillation column. Fusel alcohol is collected from one side of the pressurized distillation column, wastewater is collected from the bottom of the pressurized distillation column, and the vapor phase collected from the top of the pressurized distillation column goes to the second pre-distillation column reboiler to provide the heat required for distillation in the pre-distillation column; or the vapor phase collected from the top of the pressurized distillation column goes to the second pre-distillation column reboiler and the first negative pressure column reboiler to provide the heat required for distillation in the pre-distillation column and the negative pressure distillation column, respectively; the pressurized distillation column provides the heat required for distillation in the pressurized distillation column through indirect heating via the pressurized column reboiler, and the heat source of the pressurized column reboiler is steam.

[0025] As a preferred embodiment, the vapor phase from the top of the pre-distillation column is taken to the second reboiler of the negative pressure column, then condensed in the first-stage condenser of the pre-distillation column. The condensed liquid phase enters the pre-distillation column reflux tank, while the vapor phase enters the second-stage condenser of the pre-distillation column. The condensed liquid phase from the second-stage condenser of the pre-distillation column enters the extraction tank, through which extraction water is introduced. The liquid phase in the extraction tank returns to the pre-distillation column reflux tank, while the non-condensable vapor goes to the tail gas emission system. The liquid phase in the pre-distillation column refluxes back to the pre-distillation column.

[0026] As a preferred option, the gas phase collected from the top of the negative pressure distillation column is condensed by the negative pressure column condenser and then enters the negative pressure column reflux tank. The liquid phase in the negative pressure column reflux tank is divided into two streams, one of which flows back to the negative pressure distillation column, and the other is collected as refined methanol.

[0027] As a preferred option, the vapor phase collected from the top of the pressurized distillation column goes to the second reboiler of the pre-distillation column and then enters the pressurized column reflux tank. Part of the methanol liquid in the pressurized column reflux tank is refluxed, and part of it is cooled by the pressurized column methanol cooler and then collected as refined methanol.

[0028] As a preferred option, the vapor phase collected from the top of the pressurized distillation column is sent to the reboiler of the negative pressure column and then enters the pressurized column reflux tank. Part of the methanol liquid in the pressurized column reflux tank is refluxed, and part of it is cooled by the pressurized column methanol cooler and then collected as refined methanol.

[0029] As a preferred option, crude methanol is preheated by a feed preheater before entering the pre-distillation column, and the heat source for the feed preheater is steam.

[0030] As a preferred option, the material in the bottom of the negative pressure distillation column is preheated by the pressure tower preheater before entering the pressure distillation column. The waste heat of the wastewater is used to heat the material that needs to enter the pressure distillation column through the pressure tower preheater.

[0031] This application, based on the existing pre-distillation column, pressurized column, and atmospheric column, changes the order of operating pressure and heat coupling of the distillation columns, adopting a three-column series heat coupling process. The negative pressure column adopts a multi-reboiler mode. In addition to the heat from the top of the internal pre-distillation column, external waste heat is preferentially introduced to form a new heat exchange network, improving energy-saving potential. It can reduce steam consumption to 0.22-0.26 t steam / t refined alcohol, and can extract methanol with a concentration >99.99% and an ethanol content of 10~100ppm. Preferably, the external waste heat is the low-temperature waste heat generated by the methanol synthesis-conversion section, methanol synthesis-reaction section, and methanol synthesis-conversion section to meet the heat requirements of the methanol distillation process, significantly reducing operating costs, significantly reducing carbon emissions, and improving enterprise competitiveness. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of Embodiment 2 of this application; Figure 2 This is a structural schematic diagram of Embodiment Seven of this application; Figure 3 This is a schematic diagram of the heating structure of the negative pressure tower reboiler of this application; 1. Pre-distillation column; 2. Feed line; 3. Feed preheater; 4. Pre-column reboiler line; 5. Negative pressure distillation column; 6. Pre-column reboiler pump; 7. Pressurized column feed line; 8. Pressurized distillation column; 9. Pressurized column preheater; 10. Fusel alcohol collection line; 11. Fusel alcohol cooler; 12. Wastewater collection line; 13. Wastewater collection pump; 14. Wastewater cooler; 15. Pre-column reboiler one; 16. Pre-column reboiler two; 17. Negative pressure 18. Reboiler 1 of the tower; 19. Reboiler 2 of the negative pressure tower; 20. Reboiler of the pressurized tower; 21. Top pipeline of the pre-tower; 22. Top pipeline of the pressurized tower; 23. Steam pipeline; 24. Steam condensate pipeline; 25. External waste heat pipeline; 26. Circulation pipeline; 27. Feed pipeline of the extraction tank; 28. Extraction tank; 29. ​​First-stage condenser of the pre-tower; 30. Second-stage condenser of the pre-tower; 31. Non-condensable gas extraction pipeline; 32. Extraction water inlet pipeline; 32. Bottom pipe of the tower; 33. Pre-tower reflux tank; 34. Pre-tower reflux pipeline; 35. Pre-tower reflux pump; 36. Negative pressure tower reflux tank; 37. Negative pressure tower top pipeline; 38. Negative pressure tower condenser; 39. Top pipeline of reflux tank; 40. Gas-liquid separator; 41. Reflux tank top condenser; 42. Gas phase extraction pipeline; 43. Bottom pipeline of gas-liquid separator; 44. Negative pressure tower refined methanol extraction pipeline; 45. Negative pressure tower extraction pump; 46. ​​Negative pressure tower methanol cooler; 47. Negative pressure tower reflux pipeline; 48. Refined methanol tank; 49. Pressurized tower reflux tank; 50. Pressurized tower refined methanol outlet pipeline; 51. Pressurized tower outlet pump; 52. Pressurized tower methanol cooler; 53. Pressurized tower reflux pipeline; 54. Negative pressure tower reboiler output pipeline; 55. Methanol material input pipeline; 56. Pressurized tower reflux tank feed pipeline; 57. Reboiler; 58. Reboiler output pipeline. Detailed Implementation

[0033] The following is in conjunction with the appendix Figure 1 To be continued Figure 3 The specific embodiments of the present invention will be described in detail below. It should be noted that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention. Example 1

[0034] This application provides a waste heat-intensive three-tower multi-effect distillation process for crude methanol, as follows: Crude methanol enters pre-distillation column 1 after being preheated by feed preheater 3. The heat source for feed preheater 3 is steam. Crude methanol enters pre-distillation column 1 for distillation. The vapor phase collected from the top of pre-distillation column 1 goes to reboiler 18 of the negative pressure column to provide the heat required for distillation in negative pressure distillation column 5. After passing through reboiler 18, the vapor phase from the top of pre-distillation column 1 is condensed in the first-stage condenser 28. The condensed liquid phase enters the pre-distillation column reflux tank 33, and the vapor phase enters the second-stage condenser 29. The condensed liquid phase from the second-stage condenser 29 enters the extraction tank 27. Extraction water is introduced into extraction tank 27, and the liquid phase in extraction tank 27 is returned to pre-column reflux tank 33, while the non-condensable vapor is sent to the tail gas emission system; the liquid phase in pre-column reflux tank 33 is returned to pre-distillation column 1; pre-distillation column 1 is provided with the heat required for distillation by pre-column reboiler 15 and pre-column reboiler 26 through indirect heating, wherein the heat source of pre-column reboiler 15 is steam, and the heat source of pre-column reboiler 216 is the gas phase at the top of pressurized distillation column 8; The liquid phase collected from the bottom of pre-distillation column 1 enters the negative pressure distillation column 5 for distillation, and refined methanol is collected from the top of the negative pressure distillation column 5. More specifically, the gas phase collected from the top of the negative pressure distillation column 5 is condensed by the negative pressure column condenser 38 and then enters the negative pressure column reflux tank 36. The gas phase in the negative pressure column reflux tank 36 is condensed by the condenser 41 at the top of the reflux tank and then enters the gas-liquid separator 40. The gas phase in the gas-liquid separator 40 is collected, and the liquid phase in the gas-liquid separator 40 enters the negative pressure column reflux tank 36. The liquid phase in the negative pressure column reflux tank 36 is divided into two streams, one of which is refluxed. The other stream is collected as refined methanol in the negative pressure distillation column 5. The negative pressure distillation column 5 is indirectly heated by the negative pressure column reboiler 17 and the negative pressure column reboiler 28. The heat source of the negative pressure column reboiler 1 is the heat source for the vaporization of methanol working medium or the heat from the top of the pressurized distillation column 8. The methanol working medium is vaporized by external low-temperature waste heat. External waste heat is preferred. When there is no available external waste heat, the heat from the top of the pressurized distillation column 8 is used to regulate the distribution of the output from the negative pressure distillation column 5 and the pressurized distillation column 8. External waste heat utilizes low-temperature waste heat, which includes at least one of converted gas, shift gas, and synthesis gas. Converted gas refers to the high-temperature process gas produced in the methanol synthesis-conversion section after raw materials such as natural gas and coal gas undergo deep conversion reactions in a conversion furnace or reformer. In other words, converted gas, after conversion or reforming steps, provides the necessary active components (CO, CO2, CO2, CO2) for methanol synthesis. , The feed gas is the gas used in methanol synthesis; it serves as a bridge connecting the upstream gasification and downstream methanol synthesis. Its temperature can reach 1300°C-1600°C, and its pressure range is approximately 2.5 MPag-3 MPag. Typically, it is generated from steam in a waste heat boiler, and the low-temperature waste heat ranges from approximately 200°C-220°C and 1.5 MPag-2 MPag. Synthesis gas refers to the gas exiting the methanol synthesis tower after passing through the feed gas preheater in the methanol synthesis-reaction section. Its temperature range is approximately 80°C-150°C, and its pressure range is approximately 5 MPag-9 MPag. Shift gas refers to the carbon monoxide (CO)-rich conversion gas or feed gas in the methanol synthesis-shift section, which reacts with water vapor (CO) under the action of a catalyst. The gas obtained after the water-gas shift reaction still has high recovery value for low-grade waste heat, and the temperature of low-grade waste heat is below 200°C; at least one of the conversion gas, shift gas, and synthesis gas is used to vaporize the methanol circulating working medium, and the vaporized methanol circulating working medium is used as a heat source to heat the reboiler-17 of the negative pressure tower.

[0035] Fusel alcohol is collected from one side of pressurized distillation column 8, and wastewater is collected from the bottom of pressurized distillation column 8. The vapor phase collected from the top of pressurized distillation column 8 goes to the reboiler 16 of the pre-distillation column to provide the heat required for distillation in pre-distillation column 1. After going to the reboiler 16 of the pre-distillation column 8, the vapor phase collected from the top of pressurized distillation column 8 enters the pressurized column reflux tank 49. Part of the methanol liquid in the pressurized column reflux tank 49 is refluxed, and part is cooled by the pressurized column methanol cooler 52 and collected as refined methanol; or the vapor phase collected from the top of pressurized distillation column 8 goes to the reboiler 16 of the pre-distillation column. The reboiler 17 and the negative pressure distillation column provide the heat required for distillation to the pre-distillation column 1 and the negative pressure distillation column 5, respectively. The vapor phase collected from the top of the pressurized distillation column 8 goes to the reboiler 17 and then enters the pressurized column reflux tank 49. Part of the methanol liquid in the pressurized column reflux tank 49 is refluxed, and part of it is cooled by the pressurized column methanol cooler 52 and collected as refined methanol. The pressurized distillation column 8 is provided with the heat required for distillation by indirect heating through the pressurized column reboiler 19, and the heat source of the pressurized column reboiler 19 is steam.

[0036] Preferably, the material in the bottom of the negative pressure distillation column 5 is preheated by the pressure column preheater 9 and then enters the pressure distillation column 8. The waste heat of the wastewater is used to heat the material that needs to enter the pressure distillation column 8 through the pressure column preheater 9. Example 2

[0037] This embodiment provides a waste heat deep utilization type crude methanol three-tower multi-effect distillation device, including a pre-distillation tower 1, a feed line 2 connected to one side of the pre-distillation tower 1, a feed preheater 3 installed on the feed line 2, and a top pressure of 90 kPa-180 kPa (A) for the pre-distillation tower 1. The pre-distillation tower 1 is connected to a negative pressure distillation tower 5 via a pre-tower reboiler line 4, and a pre-tower reboiler pump 6 is installed on the pre-tower reboiler line 4. The top pressure of the negative pressure distillation tower 5 is 35 kPa-70 kPa (A), and the reboiler of the negative pressure distillation tower 5 is connected to a pressurized distillation tower 8 via a pressurized tower feed line 7, and a pressurized tower preheater 6 is installed on the pressurized tower feed line 7. The pressurized distillation column 8 has a top pressure of 170 kPa-480 kPa (A). A fusel oil collection pipeline 10 is provided on one side of the pressurized distillation column 8. A fusel oil cooler 11 is provided on the fusel oil collection pipeline 10. The fusel oil collected from the fusel oil collection pipeline 10 enters the recovery system for further recovery of valuable methanol, ethanol, etc. A wastewater collection pipeline 12 is provided at the bottom of the pressurized distillation column 8. Preferably, the wastewater collection pipeline 12 passes through the pressurized column preheater 9. A wastewater collection pump 13 is provided on the wastewater collection pipeline 12 before the pressurized column preheater 9, and a wastewater cooler 14 is provided on the wastewater collection pipeline 12 after the pressurized column preheater 9.

[0038] The lower part of the pre-distillation column 1 is equipped with a first pre-column reboiler 15 and a second pre-column reboiler 16. The lower part of the negative pressure distillation column 5 is equipped with a first negative pressure reboiler 17 and a second negative pressure reboiler 18. The lower part of the pressurized distillation column 8 is equipped with a pressurized reboiler 19. The top of the pre-distillation column 1 is connected to the second negative pressure reboiler 18 via a top pre-column pipeline 20. The methanol vapor at the top of the pre-distillation column 1 heats the second negative pressure reboiler 18, achieving thermal coupling. The top of the negative pressure distillation column 5 is connected to a negative pressure column refined methanol collection device to collect refined methanol. The top of the pressurized distillation column 8 is connected to the second pre-column reboiler 16 via a top pressurized column pipeline 21. The output end of the second pre-column reboiler 16 is connected to a pressurized column refined methanol collection device. The vapor at the top of the pressurized distillation column 8 heats the second pre-column reboiler 16, achieving thermal coupling.

[0039] The input ends of the pre-reboiler 15 and the pressurized reboiler 19 are respectively connected to the steam pipeline 22, and the output ends of the pre-reboiler 15 and the pressurized reboiler 19 are respectively connected to the steam condensate pipeline 23. The pre-reboiler 15 and the pressurized reboiler 19 are heated by 0.5 MPa Ag steam. Preferably, in order to improve the utilization of heat, the steam condensate pipeline 23 passes through the feed preheater 3, that is, the steam condensate pipeline 23 is connected to the input end and the output end of the feed preheater 3 respectively, to provide heat to the feed preheater 3. The pre-reboiler 15 only uses steam heating during the start-up phase, and only the pressurized reboiler 19 uses steam heating during normal operation.

[0040] One input end of the negative pressure tower reboiler-17 is connected to an external waste heat pipeline 24, which is used to introduce a heat source for the vaporization of methanol working fluid. The methanol working fluid is vaporized by the external low-temperature waste heat, which heats the negative pressure tower reboiler-17. One output end of the negative pressure tower reboiler-17 is connected to a circulation pipeline 25. The external waste heat includes low-temperature waste heat, which is at least one of conversion gas, shift gas, and synthesis gas. More specifically, the external waste heat pipeline 24 is connected to one input end of the reboiler 57, and the other input end of the reboiler 57 is connected to the methanol material input pipeline 55. The methanol material input pipeline 55 introduces liquid methanol or a low-concentration methanol mixture. One output end of the reboiler 57 is connected to one input end of the negative pressure tower reboiler-17, and the other output end of the reboiler 57 is connected to the reboiler output pipeline 58. Preferably, the circulation pipeline 25 is connected to the methanol material input pipeline 55, and the methanol solution circulates to the reboiler 57.

[0041] In this context, "converted gas" refers to the high-temperature process gas produced in the methanol synthesis-conversion section after raw materials such as natural gas and coal gas undergo deep conversion reactions in a reformer or converter. Essentially, converted gas provides the necessary active components (CO, CO2, CO2, CO2, CO2) for methanol synthesis after the conversion or reforming process. , The feed gas is the bridge connecting the front-end gasification and the back-end methanol synthesis. Its temperature can reach 1300°C-1600°C and the pressure range is about 2.5Mpag-3Mpag. Usually, after steam is generated by waste heat boiler, the temperature range of its low-temperature waste heat is about 200°C-220°C and the pressure range is 1.5Mpag-2Mpag. Synthesis gas refers to the gas exiting the methanol synthesis tower after passing through the feed gas preheater in the methanol synthesis-reaction section. The temperature of the methanol synthesis tower outlet gas is generally 270℃-280℃, and after preheating the feed gas, the outlet gas temperature is 80℃-150℃, with a pressure range of approximately 5MPaG-9MPaG.

[0042] Shift gas refers to the converted gas or feed gas rich in carbon monoxide (CO) in the methanol synthesis-shift process, which reacts with water vapor (CO) under the action of a catalyst. The gas obtained after the water-gas shift reaction still has high recovery value for low-grade waste heat, which is below 200°C.

[0043] At least one of the above-mentioned conversion gas, shift gas, and synthesis gas is used to vaporize the methanol working medium. The vaporized gas is then used in the methanol distillation section to provide heat for the reboiler-17 of the negative pressure tower.

[0044] The heating method of this negative pressure tower reboiler-17 can recover and utilize a large amount of low-temperature waste heat in the methanol plant, with a temperature range of 80℃-150℃, such as the low-temperature waste heat generated in the methanol synthesis-conversion section, methanol synthesis-reaction section, and methanol synthesis-conversion section; it can also recover and utilize other low-temperature waste heat in the plant to transform traditional processes and achieve a significant reduction in energy consumption. Example 3

[0045] In this embodiment, the output end of the reboiler 2 18 of the negative pressure tower is connected to the pre-tower condenser through the feed line 26 of the extraction tank. The pre-tower condenser includes an extraction tank 27 connected to the feed line 26 of the extraction tank. The feed line 26 of the extraction tank is equipped with a first-stage condenser 28 and a second-stage condenser 29 of the pre-tower. The top of the extraction tank 27 is equipped with a non-condensable gas outlet line 30. The side of the extraction tank 27 is equipped with an extraction water inlet line 31. The bottom of the extraction tank 27 is connected to the pre-tower reflux tank 33 through the bottom line 32 of the tower. The bottom of the pre-tower reflux tank 33 is connected to the upper middle part of the pre-distillation tower 1 through the pre-tower reflux line 34. The pre-tower reflux pump 35 is equipped on the pre-tower reflux line 34.

[0046] The steam from the top of the pre-distillation column 1 goes to the reboiler 2 18 of the negative pressure column for heat exchange, and then to the first-stage condenser 28 of the pre-distillation column. Most of the steam is condensed, and the condensed liquid phase enters the pre-distillation column reflux tank 33. The gas phase enters the second-stage condenser 29 of the pre-distillation column, and the condensed liquid phase enters the extraction tank 27. Extraction water is simultaneously introduced into the extraction tank 27. The liquid phase of the extraction tank 27 returns to the pre-distillation column reflux tank 33, and the non-condensable vapor goes to the tail gas emission system. Example 4

[0047] This embodiment provides a detailed description of the negative pressure tower refined methanol extraction device and the pressurized tower refined methanol extraction device, specifically: The negative pressure tower methanol extraction device includes a negative pressure tower reflux tank 36, which is connected to the top of the negative pressure distillation tower 5 via a negative pressure tower top pipeline 37. A negative pressure tower condenser 38 is installed on the negative pressure tower top pipeline 37. The top of the negative pressure tower reflux tank 36 is connected to a gas-liquid separator 40 via a reflux tank top pipeline 39, which is equipped with a reflux tank top condenser 41. A gas phase extraction pipeline 42 is installed at the top of the gas-liquid separator 40, and the bottom of the gas-liquid separator 40 is connected to the negative pressure tower reflux tank 36 via a gas-liquid separator bottom pipeline 43. The bottom of tank 36 is connected to a negative pressure tower refined methanol collection pipeline 44, which is equipped with a negative pressure tower collection pump 45 and a negative pressure tower methanol cooler 46. A negative pressure tower reflux pipeline 47 is connected to the negative pressure tower refined methanol collection pipeline 44, and the negative pressure tower reflux pipeline 47 is connected to the upper middle part of the negative pressure distillation tower 5. Preferably, the negative pressure tower refined methanol collection pipeline 44 is connected to a refined methanol tank 48. Methanol vapor condensate is sent into the negative pressure tower reflux tank 36, and part of the reflux liquid is returned and part is collected. The collected stream enters the negative pressure tower methanol cooler 46, and the cooled refined methanol is sent to the refined methanol tank 48.

[0048] The pressurized tower refined methanol extraction device includes a pressurized tower reflux tank 49. The output end of the pre-tower reboiler 16 is connected to the pressurized tower reflux tank 49 via a pressurized tower reflux tank feed line 56. A pressurized tower refined methanol extraction line 50 is connected to the bottom of the pressurized tower reflux tank 49. A pressurized tower extraction pump 51 and a pressurized tower methanol cooler 52 are installed on the pressurized tower refined methanol extraction line 50. The pressurized tower refined methanol extraction line 50 is connected to the pressurized tower reflux line 53. Preferably, the pressurized tower refined methanol extraction line 50 is connected to a refined methanol tank 48. Methanol vapor from the top of pressurized distillation column 8 is fed into the pre-reboiler 2 16. The condensed methanol vapor enters the pressurized column reflux tank 49, where part is refluxed and part is collected and sent to the pressurized column methanol cooler 52. The cooled refined methanol is sent out of the boundary area to the refined methanol tank 48.

[0049] The specific working principle of this embodiment is as follows: Crude methanol from the synthesis section first exchanges heat with low-pressure saturated steam condensate, then enters pre-distillation column 1. The top steam of pre-distillation column 1 exchanges heat with reboiler 2 (18) in the negative pressure column, and then goes to the first-stage condenser 28. Most of the steam is condensed by the first-stage condenser 28. The condensed liquid phase enters the pre-distillation column reflux tank 33, and the gas phase enters the second-stage condenser 29. The condensed liquid phase from the second-stage condenser 29 enters the extraction tank 27. Extraction water is simultaneously introduced into the extraction tank 27. The liquid phase from the extraction tank 27 returns to the pre-distillation column reflux tank 33, and the non-condensable vapor goes to the tail gas emission system. A regulating valve is installed on the non-condensable gas extraction pipeline 30. The pressure of pre-distillation column 1 is stabilized by operating the regulating valve. When pre-distillation column reboiler 1 (15) is started, steam is used as a heat source. Pre-distillation column reboiler 2 (16) uses part of the top steam of pressurized distillation column 8 as a heat source. The material from the bottom of the pre-distillation column 1 is fed into the lower part of the negative pressure distillation column 5 by the pre-distillation column bottom pump 6. The methanol vapor from the top of the negative pressure distillation column 5 directly enters the negative pressure column condenser 38 for condensation and then enters the negative pressure column reflux tank 36. Part of the methanol in the negative pressure column reflux tank 36 is refluxed, and part is collected. The collected stream enters the negative pressure column methanol cooler 46 for cooling. The cooled refined methanol is sent to the refined methanol tank 48. The gas phase in the negative pressure column reflux tank 36 is condensed by the reflux tank top condenser 41 and then enters the gas-liquid separator 40. The gas phase in the gas-liquid separator 40 goes to the vacuum pump, and the liquid phase in the gas-liquid separator 40 enters the negative pressure column reflux tank 36. The negative pressure column reboiler 17 uses external waste heat as a heat source, and the negative pressure column reboiler 2 18 uses methanol vapor from the top of the pre-distillation column 1 as a heat source. The bottom liquid of the negative pressure distillation column 5 is sent to the lower part of the pressurized distillation column 8 by the negative pressure column bottom pump 54. The methanol vapor at the top of the pressurized distillation column 8 is sent to the pre-column reboiler 16. The methanol vapor condensate enters the pressurized column reflux tank 49. Part of the methanol in the pressurized column reflux tank 49 is refluxed, and part is collected and sent to the pressurized column methanol cooler 52 for cooling. The cooled refined methanol is sent to the refined methanol tank 48. The fusel oil collection pipeline 10 on the side of the pressurized distillation column 8 collects fusel oil. After being cooled by the fusel oil cooler 11, the fusel oil enters the fusel oil intermediate tank. The wastewater collected from the bottom of the pressurized distillation column 8 is first preheated for the pressurized column feed, and then cooled by the wastewater cooler 14 before being sent to the wastewater treatment device. The pressurized column reboiler 19 uses low-pressure saturated steam as a heat source. Example 5

[0050] This embodiment provides a specific application scenario: At a methanol plant, a new crude methanol refining and recovery unit with an annual output of 500,000 tons was installed. The feed rate is 74,696.1 kg / h. The pressurized reboiler 19 uses steam as a heat source. The methanol vapor at the top of the pressurized distillation column 8 provides heat to the pre-reboiler 16. The heat of the treated synthesis gas from the outlet of the methanol synthesis column is used to vaporize the methanol working medium and serve as the heat source for the negative pressure reboiler 17. The synthesis gas feed temperature is 127.7℃, the conversion gas feed pressure is 8270 kPaA, and the conversion gas flow rate is 367,518.33 kg / h.

[0051] The methanol vapor at the top of pre-distillation column 1 provides heat to the reboiler 2 (18) in the negative pressure column. When the process parameters are optimized to the best, the steam energy consumption of refined methanol is about 0.23 tons of steam / refined methanol, with methanol purity reaching over 99.99%, methanol recovery rate ≥99.5%, and ethanol content <100ppm, reducing steam consumption by 60%-80%. For the market of upgrading traditional three-tower systems, the investment is small and the operation is highly feasible. By optimizing heat recovery and thermal distillation through the above-mentioned heat exchange network, the steam consumption is greatly reduced.

[0052] In this embodiment, the crude methanol feedstock contains 96% methanol, 3% water, and approximately 500 ppm ethanol. The crude methanol is preheated to 70°C by the feed preheater 3 and then enters the pre-distillation column 1. The operating parameters of each column are shown in Table 1 below, the composition parameters of the syngas are shown in Table 2 below, and the process parameters for syngas heat recovery are shown in Table 3 below. Table 1:

[0053] Table 2:

[0054] Table 3: . Example 6

[0055] This embodiment provides another specific application scenario: At a methanol plant, a new crude methanol refining and recovery unit with an annual production capacity of 200,000 tons was installed. The feed rate is 31,166.11 kg / h. The pressurized reboiler 19 uses steam as a heat source. Methanol vapor from the top of the pressurized distillation column 8 provides heat to the pre-reboiler 16. Converted gas is used as the heat source for the negative pressure reboiler 17. The converted gas feed temperature is 202℃, the converted gas feed pressure is 1682 kPa, and the converted gas flow rate is 57,485 kg / h. The top of the pre-distillation column 1... Methanol steam provides heat to the reboiler 218 of the negative pressure tower. When the process parameters are optimized to the best, the energy consumption is about 0.255t of steam per ton of refined methanol. The methanol purity can reach over 99.99%, the methanol recovery rate is ≥99.5%, and the ethanol content is <100ppm, reducing steam consumption by 60%-80%. For the transformation of the traditional three-tower market, the investment is small and the operation is highly feasible. By adopting energy-saving measures such as heat recovery optimization of heat exchange network and thermal distillation, steam consumption is greatly reduced.

[0056] In this embodiment, the crude methanol feedstock contains 84.92% methanol, 14.89% water, and approximately 1000 ppm ethanol. The crude methanol is preheated to 70°C by the feed preheater 3 before entering the pre-distillation column 1. The operating parameters of each column are shown in Table 4 below, the composition parameters of the converted gas are shown in Table 5 below, and the process parameters for the heat recovery of the converted gas are shown in Table 6 below. Table 4:

[0057] Table 5:

[0058] Table 6: . Example 7

[0059] In this embodiment, the top of the pressurized distillation column 8 is also connected to the reboiler 17 of the negative pressure column through the top pipeline 21 of the pressurized column, and the reboiler 17 of the negative pressure column is connected to the feed pipeline 56 of the reflux tank of the pressurized column through the output pipeline 54 of the reboiler 17 of the negative pressure column.

[0060] When there is no available residual heat from the outside, the steam from the negative pressure distillation column 5 and the pressurized distillation column 8 is adjusted and distributed. The reboiler 17 of the negative pressure column is heated by the steam from the top of the pressurized distillation column 8. At this time, the steam consumption is 0.65-0.68.

[0061] Specifically, in a methanol plant, a new crude methanol refining and recovery unit with an annual output of 120,000 tons was installed, with a feed rate of 16,276.6 kg / h. The pressurized reboiler 19 uses steam as a heat source. The methanol steam from the top of the pressurized distillation column 8 provides heat to the pre-reboiler 16 and the negative pressure reboiler 17, respectively. The methanol steam from the top of the pre-distillation column 1 provides heat to the negative pressure reboiler 18. When the process parameters are optimized to the best, the energy consumption per ton of refined methanol is approximately 0.67 tons of steam. The methanol purity can reach over 99.99%, the methanol recovery rate is ≥99.5%, and the ethanol content is <50 ppm. For the transformation of the traditional three-tower market, the investment is small, the operation is highly feasible, and the use of heat exchange network optimization, heat recovery, and thermal distillation and other energy-saving measures greatly reduces steam consumption.

[0062] In this embodiment, the crude methanol feedstock contains 92.6% methanol, 5.85% water, and approximately 997 ppm ethanol. The crude methanol is preheated to 65°C by the feed preheater 3 before entering the pre-distillation column 1. The operating parameters of each column are shown in Table 7 below: Table 7:

[0063] Using the above technical solution, when there is no external heat source available in the plant area and the process parameters are optimized to the best, the energy consumption per ton of refined methanol is approximately 0.67 tons of steam.

[0064] In summary, by adopting the above-mentioned technical solutions, this application, based on the original pre-distillation tower, pressurized tower, and atmospheric tower, changes the order of operating pressure and heat coupling of the distillation towers, adopts a three-tower heat coupling process, introduces heat from outside the unit, forms a new heat exchange network, and improves energy-saving potential. Compared with the traditional methanol process, it can reduce steam consumption to 0.22-0.26 t steam / t refined alcohol, and can produce methanol with a concentration >99.99% and an ethanol content of 10-100 ppm. Preferably, the low-temperature waste heat generated by the methanol synthesis-conversion section, methanol synthesis-reaction section, and methanol synthesis-conversion section is used to meet the heat requirements of the methanol distillation process, significantly reducing operating costs, significantly reducing carbon emissions, and improving the competitiveness of enterprises.

[0065] The preferred embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this application, various simple modifications can be made to the technical solution of this application, and these simple modifications all fall within the protection scope of this application.

[0066] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the various possible combinations in this application will not be described separately.

[0067] Furthermore, various different implementations of this application can be combined in any way, as long as they do not violate the spirit of this application, and such combinations should also be regarded as the content disclosed in this application.

Claims

1. A waste heat deep utilization type three-tower multi-effect distillation unit for crude methanol, characterized in that, The system includes a pre-distillation column (1), a negative pressure distillation column (5), and a pressurized distillation column (8) connected in sequence. A feed line (2) is connected to one side of the pre-distillation column (1). A first pre-distillation column reboiler (15) and a second pre-distillation column reboiler (16) are installed at the bottom of the pre-distillation column (1). A first negative pressure distillation column reboiler (17) and a second negative pressure distillation column reboiler (18) are installed at the bottom of the negative pressure distillation column (5). The pressurized distillation column (8) is equipped with... A pressurized reboiler (19) is provided. The top of the pre-distillation column (1) is connected to the second negative pressure column reboiler (18) via the top pipeline (20) of the pre-distillation column. The top of the negative pressure column (5) is connected to a negative pressure column methanol extraction device. The top of the pressurized distillation column (8) is connected to the second pre-distillation column reboiler (16) via the top pipeline (21) of the pressurized column. The output end of the second pre-distillation column reboiler (16) is connected to a pressurized column methanol extraction device.

2. The waste heat deep utilization type crude methanol three-tower multi-effect distillation unit according to claim 1, characterized in that, The input end of the negative pressure tower reboiler (17) is connected to the external waste heat pipeline (24), and the output end of the negative pressure tower reboiler (17) is connected to the circulation pipeline (25). The external waste heat pipeline (24) is used to connect to the heat source for the vaporization of methanol working medium, and the methanol working medium is vaporized by low temperature waste heat. The external waste heat pipeline (24) is connected to one input end of the reboiler (57), the other input end of the reboiler (57) is connected to the methanol material input pipeline (55), one output end of the reboiler (57) is connected to one input end of the negative pressure tower reboiler (17), and the other output end of the reboiler (57) is connected to the reboiler output pipeline (58).

3. The waste heat deep utilization type crude methanol three-tower multi-effect distillation unit according to claim 2, characterized in that, The circulation pipeline (25) is connected to the methanol material input pipeline (55).

4. The waste heat deep utilization type crude methanol three-tower multi-effect distillation device according to claim 1, characterized in that, The top of the pressurized distillation column (8) is also connected to the reboiler of the negative pressure column (17) via the top pipeline (21) of the pressurized column. The reboiler of the negative pressure column (17) is connected to the feed pipeline (56) of the reflux tank of the pressurized column via the output pipeline (54) of the reboiler of the negative pressure column.

5. The waste heat deep utilization type crude methanol three-tower multi-effect distillation unit according to claim 1, characterized in that, The bottom of the negative pressure distillation column (5) is connected to the pressure distillation column (8) through the pressure column feed line (7), and the pressure column feed line (7) is equipped with a pressure column preheater (9).

6. The waste heat deep utilization type crude methanol three-tower multi-effect distillation unit according to claim 5, characterized in that, The pressurized distillation column (8) is equipped with a wastewater outlet pipeline (12), which passes through the pressurized column preheater (9). A wastewater outlet pump (13) is installed on the wastewater outlet pipeline (12) in front of the pressurized column preheater (9), and a wastewater cooler (14) is installed on the wastewater outlet pipeline (12) behind the pressurized column preheater (9).

7. A waste heat deep utilization type crude methanol three-tower multi-effect distillation process, employing the waste heat deep utilization type crude methanol three-tower multi-effect distillation device as described in any one of claims 1 to 6, characterized in that, Including the following processes: Crude methanol enters the pre-distillation column (1) for distillation. The vapor phase collected from the top of the pre-distillation column (1) goes to the second reboiler of the negative pressure column (18) to provide the heat required for distillation in the negative pressure distillation column (5). The pre-distillation column (1) provides the heat required for distillation in the pre-distillation column (1) through indirect heating via the first reboiler (15) and the second reboiler (16). The heat source of the first reboiler (15) is steam, and the heat source of the second reboiler (16) is the vapor phase at the top of the pressurized distillation column (8). The liquid phase collected from the bottom of the pre-distillation column (1) enters the negative pressure distillation column (5) for distillation, and refined methanol is collected from the top of the negative pressure distillation column (5). The negative pressure distillation column (5) is provided with the heat required for distillation by indirect heating through the negative pressure column reboiler one (17) and the negative pressure column reboiler two (18). The heat source of the negative pressure column reboiler one (17) is the heat source for the vaporization of methanol working medium or the heat from the top of the pressurized distillation column (8). The methanol working medium is vaporized by external low-temperature waste heat. Fusel alcohol is collected from one side of the pressurized distillation column (8), wastewater is collected from the bottom of the pressurized distillation column (8), and the vapor phase collected from the top of the pressurized distillation column (8) goes to the second pre-distillation column reboiler (16) to provide the heat required for distillation of the pre-distillation column (1); or the vapor phase collected from the top of the pressurized distillation column (8) goes to the second pre-distillation column reboiler (16) and the first negative pressure column reboiler (17) to provide the heat required for distillation of the pre-distillation column (1) and the negative pressure distillation column (5) respectively; the pressurized distillation column (8) provides the heat required for distillation of the pressurized distillation column (8) through indirect heating via the pressurized column reboiler (19), and the heat source of the pressurized column reboiler (19) is steam.

8. The waste heat deep utilization type crude methanol three-tower multi-effect distillation process according to claim 7, characterized in that, The gas phase taken from the top of the negative pressure distillation column (5) is condensed by the negative pressure column condenser (38) and then enters the negative pressure column reflux tank (36). The liquid phase in the negative pressure column reflux tank (36) is divided into two streams, one of which flows back to the negative pressure distillation column (5) and the other is taken out as refined methanol.

9. The waste heat deep utilization type crude methanol three-tower multi-effect distillation process according to claim 7, characterized in that, Crude methanol is preheated by the feed preheater (3) and then enters the pre-distillation column (1). The heat source of the feed preheater (3) is steam.

10. The waste heat deep utilization type crude methanol three-tower multi-effect distillation process according to claim 7, characterized in that, The material in the bottom of the negative pressure distillation column (2) is preheated by the pressure tower preheater (9) and then enters the pressure distillation column (8). The waste heat of the wastewater is used to heat the material entering the pressure distillation column (9) that needs to be heated.

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